UNIVERSIDAD COMPLUTENSE DE MADRID FACULTAD DE CIENCIAS GEOLÓGICAS TESIS DOCTORAL Evolución tectono-sedimentaria de la cuenca de San Pedro (República Dominicana) y su potencial de hidrocarburos Tectono-sedimentary evolution of the San Pedro basin (Dominican Republic) and its hydrocarbon potential MEMORIA PARA OPTAR AL GRADO DE DOCTOR PRESENTADA POR José Miguel Gorosabel Araus Directores José Luis Granja Bruña Andrés Carbó Gorosabel José Ramón Mas Mayoral Madrid © José Miguel Gorosabel Araus, 2020 UNIVERSIDAD COMPLUTENSE DE MADRID FACULTAD DE CIENCIAS GEOLÓGICAS TESIS DOCTORAL EVOLUCIÓN TECTONO-SEDIMENTARIA DE LA CUENCA DE SAN PEDRO (REPÚBLICA DOMINICANA) Y SU POTENCIAL DE HIDROCARBUROS TECTONO-SEDIMENTARY EVOLUTION OF THE SAN PEDRO BASIN (DOMINICAN REPUBLIC) AND ITS HYDROCARBON POTENTIAL MEMORIA PARA OPTAR AL GRADO DE DOCTOR PRESENTADA POR José Miguel Gorosabel Araus DIRECTORES José Luis Granja Bruña Andrés Carbó Gorosabel José Ramón Mas Mayoral Madrid, 2020 Agradecimientos / acknowledgements En primer lugar, me gustaría dar las gracias a mis tutores y directores de Tesis. A José Luis, por todo lo me has enseñado y por aprender a moldear mis planteamientos pese a mi cabezonería. Por los buenos ratos en mitad de la jungla y por los malos en los que supiste hacer que siguiera ade- lante. A Ramón Mas, por tu siempre predisposición a revisar mi trabajo. Y a Andrés, qué puedo decir, sin ti ni siquiera hubiera descubierto mi verdadera pasión, mil gracias. Aunque no esté en la lista oficial de tutores por un mero formalismo, debo reconocer la inmensa labor de Antonio Gallego, sin la cual esta Tesis Doctoral no habría alcanzado los objetivos de la forma que lo ha hecho. Muchas gracias por las infinitas pero productivas discusiones, por tu enorme paciencia y por la absoluta dedicación que has mostrado desde el minuto 1. Y por su puesto a CEPSA, y en especial a Jorge Navarro, por confiar en mí y poner los recursos necesarios a mi alcance, gracias. A Álvaro por los miles de cafés en forestales, verdadero carburante de la Tesis, y por las siempre interesantes conversaciones en las que acabábamos resolviendo los problemas geológicos más complejos o solucionando el mundo. A la tripulación del Sarmiento de Gamboa y a los miembros de la Unidad de Tecnología Marina UTM que hicieron del proyecto NORCARIBE una aventura inolvidable de la cual obtuvimos los datos que han terminado siendo el punto de partida de este trabajo. Debo agradecer la especial implicación del Servicio Geológico Nacional de la República Domi- nicana, y en especial de su director el Ing. Santiago José Muñoz Tapia, por toda la ayuda recibida a lo largo de nuestra andadura conjunta. Sin olvidarme de nuestros compañeros de campo, el Ing. Ricardo Reinosa, Wilson y Johny, ni de Gregorio y Tatys que entre todos nos habéis hecho todo más fácil. Un especial recuerdo para María Calzadilla, de cuyo esfuerzo surgió la fructífera rela- ción entre el SGN y la UCM. Así mismo debo agradecer la implicación del resto de miembros del equipo investigador del pro- yecto SISPETRO-DO, Marisa, Sol, Mª Eugenia y José. Muchas gracias por vuestro esfuerzo y apoyo. Desde aquí agradecer también a Schlumberger, Oasis y dGB por las licencias académicas que han facilitado a la Universidad Complutense de Madrid y sin las cuales trabajos como éste no serías posibles. A mis amigos, por las interminables conversaciones de esas que hacen que los de al lado nos miren raro, por la vidilla que dan. Por último, y solamente por motivos protocolarios, no por relevancia, a mi familia. A mis abuelos haber estado toda mi vida ahí, aunque no se les viera. A Pepe por haber forjado en mí el espíritu crítico y todo lo necesario para estar ahora presentando mi Tesis Doctoral. A Tinu y Carmen por haberme cuidado siempre. A todos mis primos y tíos, por todos los buenos ratos en familia, por las sobremesas, los vermús, las cenas, las barbacoas y la cercanía que hacen de este mundo un sitio mejor. Y un especial recuerdo para los que ya no están. A Aurora, por estar siempre ahí, en lo bueno y en lo malo. Gracias por haber sido el apoyo nece- sario para que siguiera adelante. Por aguantarme y por no tirarme por la ventana durante el con- finamiento. Llegarán tiempos mejores y espero que estés ahí para vivirlos conmigo. Y finalmente a mi madre. Tanto que agradecer. Verdadera financiadora de este proyecto. Gracias por seguir siempre creyendo en mí. Porque si soy la persona que soy es sólo por ti. Por educarme, soportarme y darlo todo siempre, sin preguntas ni dudas. ¡Gracias! Funding This work was partially funded by the Spanish Science Program (Projects: REN2003-08520, CTM2006-13666 and CGL2010-17715) and by the Dominican Project, Modelización Tecto-se- dimentaria de las Cuencas Mesozoicas y Cenozoicas del Sur-Sureste de la República Dominica: Aplicación a Identificación y Caracterización de los Elementos del Sistema Petrolífero”, of the “Ministerio de Educación Superior, Ciencia y Tecnología” (MESCYT). Content Resumen .................................................................................................................................... 15 Abstract ...................................................................................................................................... 17 Chapter 1: Introduction .............................................................................................................. 19 1.1 Introduction and objectives .............................................................................................. 21 1.2 Organization of this volume ............................................................................................. 23 Chapter 2: Geological setting .................................................................................................... 27 2.1 Tectonic overview for the Caribbean Region .................................................................... 29 2.2 Crustal structure (and composition) of the interior? CARIB ............................................. 31 2.2.1 Nicaraguan Rise and Jamaica .................................................................................... 32 2.2.2 Colombian Basin ........................................................................................................ 32 2.2.3 Beata Ridge ................................................................................................................ 32 2.2.4 Venezuelan Basin ...................................................................................................... 33 2.3 Tectonic evolutionary models for the Caribbean Region .................................................. 35 2.3.1 The Pacific Model ...................................................................................................... 35 2.3.2 The In-Situ Model ....................................................................................................... 37 2.4 The border region between the CARIB and the NOAM .................................................... 39 2.4.1 Tectonic evolution of the northern CARIB ................................................................. 41 2.5 Hispaniola Island ............................................................................................................... 43 2.5.1 Physiography of Hispaniola Island and the offshore nearby ..................................... 43 2.5.2 Geology of Hispaniola ................................................................................................ 48 2.6 The San Pedro Basin .......................................................................................................... 53 2.6.1 Structure of the basin ................................................................................................ 55 Chapter 3: Data and methods ................................................................................................... 59 3.1 Preliminary research ......................................................................................................... 63 3.1.1 Compilation and review of scientific literature .......................................................... 63 3.1.2 Elaboration of the database ....................................................................................... 63 3.1.3 Geo-referencing and digitalization of information in a GIS ....................................... 64 3.2 Integrated geological model ............................................................................................. 68 3.2.1 Definition of lithostratigraphic units .......................................................................... 68 3.2.2 Well-seismic tie ......................................................................................................... 75 3.2.3 Basement identification and characterization .......................................................... 94 3.2.4 Basin structural model ............................................................................................ 110 3.3 Elements of the petroleum system ................................................................................ 118 3.3.1 Post-mortem analysis ............................................................................................... 118 3.3.2 Evaluation of elements ............................................................................................ 121 3.4 Basin modelling ............................................................................................................... 131 3.4.1 Geothermal gradient determination ....................................................................... 131 3.4.2 Hydrocarbon windows determination ..................................................................... 132 Chapter 4: Basin Modelling ..................................................................................................... 135 4.1 Tectono-Stratigraphic Domains ....................................................................................... 137 4.2 Fore arc - collisional domain ........................................................................................... 143 4.2.1 Lithostratigraphic units description ......................................................................... 144 4.2.2 Wells correlation ...................................................................................................... 172 4.2.3 Structure of the fore arc / collisional domain ......................................................... 177 4.2.4 Partial discussion for the fore-arc / collisional domain ........................................... 182 4.3 Island Arc Domain ........................................................................................................... 185 4.3.1 Structure of the island arc domain .......................................................................... 193 4.3.2 Partial discussion for the island arc domain ............................................................ 197 4.4 Cretaceous to Eocene Basin Domain............................................................................... 201 4.4.1 Lithostratigraphic units description ......................................................................... 202 4.4.2 The San Cristóbal region, onshore extension of the San Pedro Basin ..................... 213 4.4.3 Structure and evolution of the Cretaceous to Eocene Basin Domain ..................... 220 4.4.4 Partial discussion of the Cretaceous to Eocene Basin Domain ................................ 224 4.5 Oceanic Caribbean Domain ............................................................................................. 227 4.5.1 Lithostratigraphic units description ......................................................................... 227 4.5.2 Wells correlation ...................................................................................................... 250 4.5.3 Oceanic Caribbean Domain Structure ...................................................................... 253 4.5.4 Partial discussion for the Oceanic Caribbean Domain ............................................. 256 4.6 General Discussion .......................................................................................................... 259 4.6.1 The tectono-stratigraphic domains division ............................................................ 259 4.6.2 Regional constrains .................................................................................................. 263 4.6.3 Evolution model of the study area ........................................................................... 266 4.7 Interpretation of the San Pedro Basin............................................................................. 269 4.7.1 Identification of main unconformities ..................................................................... 270 4.7.2 Seismic facies analysis and units correlation ........................................................... 276 4.7.3 Structure of the basin .............................................................................................. 287 4.7.4 The Oligocene to middle Miocene sequence ........................................................... 300 4.7.5 Integrated discussion and main conclusions for the San Pedro Basin evolution .... 307 Chapter 5: Petroleum system for the San Pedro Basin ........................................................... 313 5.1 Exploration background .................................................................................................. 315 5.2 Available exploration data .............................................................................................. 320 5.2.1 Surface geology ....................................................................................................... 320 5.2.2 Geochemical data .................................................................................................... 321 5.2.3 Seismic data ............................................................................................................. 321 5.2.4 Gravity and magnetic data ...................................................................................... 323 5.3 Wells post-mortem analyses .......................................................................................... 325 5.3.1 Villa Isabel #1 (VI-1): post-mortem analysis ............................................................ 328 5.3.2 Licey #1 (LIC-1): post-mortem analysis ................................................................... 333 5.3.3 San Francisco Reef #1 (SFR-1): post-mortem analysis ............................................ 337 5.3.4 Caño Azul #1 (CA-1): post-mortem analysis ............................................................ 343 5.3.5 San Pedro #1 (SP-1): post-mortem analysis ............................................................ 349 5.3.6 Punta Salinas #1 (PS-1): post-mortem analysis ....................................................... 353 5.3.7 Maleno DT-1 (MDT-1): post-mortem analysis ........................................................ 357 5.3.8 Candelon #1 (CAN-1): post-mortem analysis .......................................................... 364 5.3.9 Charco Largo #1 (CHL-1): post-mortem analysis ..................................................... 370 5.3.10 Post-mortem conclusions ...................................................................................... 378 5.3.11 Lessons learned for the San Pedro Basin .............................................................. 383 5.4 Source rock ..................................................................................................................... 386 5.4.1 Cretaceous Source Rock ........................................................................................... 388 5.4.2 Eocene Source Rock ................................................................................................. 392 5.4.3 Oligocene Source Rock ............................................................................................. 394 5.4.4 Miocene Source Rock .............................................................................................. 397 5.4.5 Maturation ............................................................................................................... 398 5.5 Reservoir ......................................................................................................................... 407 5.5.1 Unit E1 ...................................................................................................................... 408 5.5.2 Unit O2 ..................................................................................................................... 410 5.5.3 Unit N1.1 .................................................................................................................. 412 5.5.4 Unit N1.2 .................................................................................................................. 412 5.5.5 Unit N1.3 .................................................................................................................. 413 5.5.6 Sub-unit N5 .............................................................................................................. 415 5.5.7 Reservoir summary .................................................................................................. 417 5.6 Seal ................................................................................................................................. 418 5.7 Trap ................................................................................................................................. 419 5.7.1 Structural traps associated to compression ............................................................. 420 5.7.2 Structural traps associated to shearing ................................................................... 423 5.7.3 Structural traps associated to accommodation of deformation.............................. 425 5.7.4 Stratigraphic traps .................................................................................................... 426 5.8 Timing and preservation ................................................................................................. 428 5.9 Summary ......................................................................................................................... 430 5.10 Conclusions and forward look of exploration activities ................................................ 433 Chapter 6: Summary and conclusions ..................................................................................... 435 6.1 The tectono-stratigraphic domains division ................................................................... 437 6.2 The structure of the SPB ................................................................................................. 439 6.3 The evolutionary model of the SPB ................................................................................ 440 6.4 Conclusions ...................................................................................................................... 441 Chapter 7: Forward look ........................................................................................................... 443 7.1 Forward look ................................................................................................................... 445 References ............................................................................................................................... 449 Appendices ............................................................................................................................... 471 List of acronyms .................................................................................................................... 473 Supplementary material ....................................................................................................... 475 15 Resumen EVOLUCIÓN TECTONOSEDIMENTARIA DE LA CUENCA SAN PEDRO (REPÚBLICA DOMINICANA) Y SU POTENCIAL DE HIDROCARBUROS La Cuenca de San Pedro (CSP) se define como una depresión batimétrica con tendencia E-O y una extensión aproximada de 6000 km2, situada en el margen sureste de la isla de La Española (República Dominicana y Haití). Estructuralmente, el SPB está ubicada en la parte trasera del Cinturón Deformado de los Muertos (CDM). Considerada tradicionalmente como una cuenca de edad Mioceno medio, cuyo relleno ha sido depositado en el espacio de configuración generado por la progresiva deformación del CDM. El área de estudio pertenece al límite norte entre las Placas Norteamericana y Caribe, habiendo registrado la compleja interacción entre ambas. Aun- que la CSP se encuentra próxima a un sistema petrolero confirmado (los descubrimientos de Ma- leno e Higuerito en la región de Azua recuperaron 50,000 brls de petróleo), podría considerarse como poco explorada y los diferentes intentos de correlaciones estructurales y estratigráficas con la región de San Cristóbal (tradicionalmente considerada como la extensión en tierra de la CSP) y la cuenca de Azua han puesto de manifiesto importantes discrepancias. En consecuencia, tanto la evolución de la CSP como su potencial de hidrocarburos siguen sin estar claramente definidos. La presente Tesis Doctoral se centra en la evolución geológica del margen sureste de la isla de La Española, y en particular de la CSP, cuyos resultados se aplicarán a la revisión del potencial de hidrocarbonado de la cuenca. Para llegar a este objetivo, se han integrado diferentes datos y me- todologías, entre los que se incluyen: una revisión detallada de la cartografía geológica de los programas SYSMIN I y II acompañada de las observaciones y el muestreo de afloramientos, que se han combinado con la integración de un gran volumen de datos geofísicos y geológicos de subsuelo. Dicha integración se basa en el análisis de hasta 60 pozos exploratorios proporcionado por el Banco Nacional de Datos de Hidrocarburos (BNDH) de la República Dominicana, el pro- cesamiento de nuevos datos de sísmica 2D multicanal del Proyecto NORCARIBE, el reprocesa- miento de campañas sísmicas previas, y la interpretación de los datos magnéticos y gravimétricos. Tras el análisis de datos, el registro geológico se clasificó en unidades lito-estratigráficas con el fin de correlacionar las diferentes formaciones presentes en tierra. Posteriormente, la isla fue di- vidida en cuatro dominios tectono-estratigráficos, teniendo en cuenta tanto las relaciones estruc- turales como la composición del basamento. Esta metodología ha llevado a proponer los princi- pales eventos tectónicos que afectaron a cada dominio y las secuencias deposicionales que los caracterizan. Estos resultados fueron proyectados a la CSP mediante la interpretación de anoma- lías magnéticas y gravimétricas. Como principal resultado de este trabajo, se ha propuesto un nuevo modelo de evolución tectono- sedimentaria para la CSP. Bajo este modelo, el basamento de la cuenca estaría compuesto por rocas sedimentarias y volcánicas de edad Cretácica, pertenecientes a ambientes de arco isla y de trasera de arco. Un cambio en el régimen de esfuerzos durante el Campaniense propició la inver- sión parcial de las unidades del basamento, favoreciendo la deposición de dos secuencias durante los periodos Campaniense-Maastrichtiense y Paleoceno?-Eoceno en un contexto de cuenca sub- marina de antepaís. Debido a la colisión entre los Bancos de las Bahamas y La Española en el Eoceno medio, los esfuerzos de compresivos se trasladaron hacia el sur, invirtiendo los sedimen- tos cretácicos y paleógenos, e iniciando la configuración actual del sistema SPB-CDM desde el Eoceno-Oligoceno hasta la actualidad. El nuevo modelo evolutivo permite revisar el potencial de hidrocarburos de la CSP gracias a la identificación de los principales elementos del sistema petrolero, incluyendo: rocas madre madu- ras del Cretácico Superior y el Oligoceno junto con reservorios carbonáticos y clásticos del Oli- goceno-Mioceno intercalados con lutitas y margas que actúan como los sellos del sistema. Las 16 principales trampas son estructurales y estratigráficas, y su formación parece coetánea a la gene- ración principal de petróleo durante el periodo Oligoceno-Mioceno. Si bien los principales ele- mentos del sistema petrolero parecen estar presentes en la cuenca, el timing representa el mayor riesgo que debe ser evaluado ante cualquier exploración futura de la cuenca. 17 Abstract TECTONO-SEDIMENTARY EVOLUTION OF THE SAN PEDRO BASIN (DOMINICAN REPUBLIC) AND ITS HYDROCARBON POTENTIAL The San Pedro Basin (SPB) consists of an E-W bathymetric depression with an extension of 6000 km2, located in the south-eastern margin of Hispaniola Island (Dominican Republic and Haiti). Structurally, the SPB is situated at the rear zone of the Muertos Thrust Belt (MTB). The basin has been dated as middle Miocene in the bibliography, with the infill deposited in the configuration space generated by the progressive deformation of the MTB. The study area belongs to the north- ern limit of the Caribbean Plate, having recorded the complex interaction with the North Ameri- can Plate. Although the SPB is located close to a confirmed petroleum system (the discoveries of Maleno and Higuerito in the Azua region recovered 50,000 brls of oil), it remains almost unex- plored and the different attempts of onshore-offshore structural and stratigraphic correlations with the nearby San Cristóbal (traditionally considered as the onshore extension of SPB) and Azua Basins have shown strong discrepancies. Therefore, the SPB evolution and its hydrocarbon po- tential remains unclear. This Ph.D. Thesis is focussed in the geological evolution of the south-eastern margin of Hispan- iola Island, and in particular of the SPB, which will be applied to review the hydrocarbon potential of the basin. To achieve the objective of the Thesis, different data and methodologies have been integrated: a detailed review and synthesis of the onshore systematic geological mapping (the SYSMIN I and II programmes) combined with outcrop observations and sampling and the inte- gration of a large volume of subsurface geophysical and geological data. This includes the anal- ysis of 60 exploration wells provided by “Banco Nacional de Datos de Hidrocarburos” (BNDH) of the Dominican Republic, the processing of new 2D multi-channel seismic data from the Span- ish Research Project NORCARIBE, the reprocessing of legacy seismic profiles, and the interpre- tation of gravity and magnetic data. The geological record was classified into lithostratigraphic units in order to correlate the different formations present in the onshore. After this, the Hispaniola Island was divided into four tectono- stratigraphic domains, considering the structural relationships and the basement composition. This methodology has led to propose the main tectonic events that affected each domain and the depositional sequences that characterized them. The results could be applied to the interpretation of the basin by the prolongation of the domains based on gravity and magnetic anomalies. As a result, a new tectono-sedimentary evolution model for the SPB has been proposed. Under this model, the basement of the basin would be composed of Cretaceous sedimentary and volcanic rocks of intra- and back-arc settings. A change in the stress regime in the Campanian led to a partial inversion of the basement units, favouring the deposition of two main sequences of Cam- panian–Maastrichtian and Paleocene?–Eocene age in a submarine foreland setting. Due to colli- sion between the Carbonate Bahamas Province and Hispaniola in the middle Eocene, compres- sional stresses were transferred to the south where Cretaceous and Paleogene sediments were deformed, forming the current configuration of the MTB and generating a new accommodation space where the SPB has developed since the late Eocene–Oligocene until Present. This new model has allowed the review of the hydrocarbon potential of the SPB by the identifi- cation of the main elements of the petroleum system present in the SPB: mature Upper Cretaceous and Oligocene source rocks; and Oligocene–Miocene carbonate and clastic reservoirs interbedded with sealing shales and marls. Main traps are structural and stratigraphic, being of Oligocene– Miocene age and their formation seems to be synchronous to the main oil generation window. While the main elements of the petroleum system seem to be present in the basin, timing is a key issue that must be addressed and assessed in any future exploration in the basin. 18 19 Chapter 1: Introduction 20 21 Section 1.1: Introduction and objectives The Caribbean and its surrounding area, between 60 and 90º W and 10 to 20º N, make up one of the regions with the most complex geology in the world, reduced to a limited extension of only 3.6 million km2, which represents 0.7% of the Earth’s surface. In this area, five main tectonic plates interact, North-American (NOAM), South-American (SOAM), Caribbean (CARIB), Co- cos, and Nazca plates (figure 1.1), characterised by an independent geodynamic evolution and the consequent development of great tectonic units associated with each of them. Considering the CARIB as the central element of the system, the GPS-derived information indi- cates differences on the relative movement between the four remaining plates and the CARIB, including:  The northern convergence between the NOAM and the CARIB with a direction of 70ºN and a velocity of 18 – 20 mm/yr (Mann et al., 2002).  The southern convergence between the SOAM and the CARIB, with a direction of 90ºS and a velocity of 20 mm/yr.  The western convergence of the Cocos and Nazca Plates and the CARIB, with an esti- mated velocity of 59 – 74 mm/yr (DeMets et al., 2000). The resulting distribution of forces has led to different tectonic configurations at the border re- gions which includes the subduction of the NOAM to the east and north-east, the subduction of the CARIB to the south, the subduction of the Cocos and Nazca plates to the west, and the trans- pressional forces and strike-slip displacement to the north and north-west, along the Cayman Trough. After getting my degree, I had the opportunity to join the research team at the Complutense Uni- versity of Madrid which had been studying the Caribbean region since the 90s. Specifically, I was incorporated into the Spanish National Research Project NORCARIBE (Ref: CGL2010-17715), focused on the study of the northern limit between the CARIB and the NOAM. This project had two main objectives. Firstly, the study of active tectonics developed through the collision zone between the Bahamas Banks and Hispaniola Island (Dominican Republic and Haiti). This zone is key to understand the geodynamics of the northern Caribbean as it represents the transition from the active subduction of the NOAM at the Puerto Rican trench and the strike-slip regime of south- ern Cuba. The second objective was the study of the crustal variations of southern Hispaniola, including the Venezuelan Basin, the Beata Ridge and the Colombian Basin. The experience acquired during this project led me to focus my research activities on the analysis of the San Pedro Basin (figure 1.1), whose sedimentary history explains the succession of geo- logical events that affected the region, interpreted by the analysis of seismic lines. The preliminary results were included in the Master’s Thesis “Analysis of the sedimentary infill of the San Pedro Basin (Dominican Repiblic offshore margin) based on reflection seismic data” (Análisis del rel- leno sedimentario de la Cuenca de San Pedro, offshore de la República Dominicana, en base a datos de sísmica de reflexión), presented at the Faculty of Geology at the Complutense University of Madrid in July 2015. The conclusions of this work led to tentatively propose a new interpreta- tion of the tectono-sedimentary evolution of the basin, discussing the evolutionary model ac- cepted at that time in scientific literature. This initial research was the starting point of the Ph.D. Thesis presented amidst this work. The study area, identified by the acronym AOI (Area of Interest), is limited by the geographic coordi- nates 17º - 19º N and 69º - 71º W. This area is located at the south-eastern margin of Hispaniola Island, belonging to the Greater Antilles of the Caribbean, and divided into the countries of The Dominican Republic (2/3) and Haiti (1/3). Although the great part of the AOI is included in the 22 offshore, the current configuration of the San Pedro Basin and the Muertos Thrust Belt, it also comprises their onshore prolongation, the San Cristóbal region (SC), the Llanura Oriental (LLO) and the Trois Rivieres – Peralta Belt (TRPB). Fig. 1.1 Digital elevation model of the study area or area of interest (AOI) and surroundings. The San Pedro Basin is one of the largest offshore basins of Hispaniola. Key to acronyms: AOI, Area of Interest; TRPB, Trois Rivieres – Peralta Belt; SC, San Cristóbal; MTB, Muertos Thrust Belt; LLO, Llanura Oriental; NOAM, North-American Plate; SOAM, South-American Plate; CARIB, Caribbean Plate; CU, Cuba; CT, Cayman Trough; BB, Bahamas Banks; PRT, Puerto Rican Trench; BR, Beata Ridge; CO, Cocos Plate; NA, Nazca Plate; CB, Colombian Basin; VB, Vene- zuelan Basin. The aim of this work is to understand the geological evolution of the south-eastern margin of Hispaniola Island, considering both the submerged areas and their emerged extension. This on- shore – offshore integration should lead to propose the main tectonic events and depositional sequences of the zone, contributing with new constrains to the understanding of the complex evo- lution of the northern Caribbean. At the same time, the implications in the hydrocarbon potential of the San Pedro Basin will be analysed. To achieve the main objectives, different data and methodologies have been integrated: the review of geological maps and the bibliography, the analysis of previous exploration activities, including well logs and reports, and the interpretation of geophysical data, which comprise of seismic, grav- ity and magnetic data. The results provided by this integration have led to propose the main tec- tonic events and depositional sequences of the basin that could be applied as new constrains to understand the evolution of the northern Caribbean region. To achieve the aim of this thesis, the following specific objectives are proposed: 23  Determination of the main onshore regional unconformities that could be applied on the seismic interpretation of the basin.  Correlation of different formations reached in exploration wells or studied in outcrops that could be grouped into different units based on age, lithology, and depositional envi- ronment.  Determination of the main regional potential elements of the petroleum system.  Determination of the current geothermal gradient of the island based on bottom hole tem- peratures of exploration wells.  Seismic interpretation of the main structures and unconformities of the San Pedro Basin and their onshore correlation.  Seismic facies analysis and their correlation with onshore units.  Identification of the main elements of the petroleum system in the basin based on the interpreted units.  Basing modelling and timing analysis that include the elaboration of maturity maps for different periods of time.  Determination of the hydrocarbon potential of the basin based on the available data. Section 1.2: Organization of this volume This work has been divided into seven chapters (table 1.1) in order to achieve the above objectives and to present the results in a clear structure. Each of these parts is subdivided in sections, which are focused on a different and specific topic as follows. Chapter 1 (Introduction of the Thesis), divided into two sections, provides a general overview of this work, where the general motivation of the thesis is presented together with the main and specific objectives and the structure of the volume. Geology setting is introduced within Chapter 2 (Regional Setting), giving the first approach to the Caribbean geology and mentioning the main works carried out in the study area. During Chapter 3 (Data and Methods) the different methodologies and workflows followed along the research are explained in detail, making a record of the available data. The main results are presented during Chapters 4 and 5. Chapter 4 is focussed on the basin mod- elling carried out for the San Pedro Basin. Hispaniola Island has been divided into 4 main tectonic domains (presented in section 4.1) which are detailed studies from Sections 4.2 to 4.5, with gen- eral conclusions presented in Section 4.6. Throughout these chapters, the geology of every domain is analysed by the review of the well’s registers and outcrops from the geology mapping and the bibliography. This led to propose the main unconformities and lithostratigraphic units of the is- land that were applied in Section 4.7 to interpret the San Pedro Basin, proposing an evolution model of the region. The interpretation of the basin resulted from Chapter 4 is combined in Chapter 5 with the review of previous exploration activities (Sections 5.1 to 5.3) to determine the hydrocarbon potential of the basin (Sections 5.4 to 5.10). Finally, the main conclusions of this Thesis are summarized in Chapter 6 and, the forward look of this research is presented in Chapter 7. 24 Chapter 1 Introduction of the Thesis Section 1.1: Introduction Section 1.2: Organization of this volume Chapter 2 Regional Setting Section 2.1: Tectonic overview for the Caribbean Region Section 2.2: Crustal structure of the interior CARIB Section 2.3: Tectonic evolutionary models for the Caribbean Region Section 2.4: The border region between the CARIB and the NOAM Section 2.5: Hispaniola Island Section 2.6: The San Pedro Basin Chapter 3 Data and Methods Section 3.1: Preliminary Research Section 3.2: Integrated geological model Section 3.3: Elements of the petroleum system Section 3.4: Basin modelling Chapter 4 Basin Modelling Section 4.1: Tectonic Domains Section 4.2: Fore Arc / Collisional Domain Section 4.3: Island Arc Domain Section 4.4: Cretaceous to Eocene Basin Domain Section 4.5: Oceanic Caribbean Domain Section 4.6: General Discussion Section 4.7: Interpretation of the San Pedro Basin Chapter 5 Hydrocarbon Potential of the San Pedro Basin Section 5.1: Exploration Background Section 5.2: Available exploration data Section 5.3: Wells post-mortem Section 5.4: Source rock Section 5.5: Reservoir Section 5.6: Seal Section 5.7: Trap Section 5.8: Timing Section 5.9: Summary Section 5.10 Conclusions and forward look of exploration activities Chapter 6 Summary and conclusions Chapter 7 Forward look References Appendices Table 1.1 Organization of the volume. 25 26 27 Chapter 2: Geological setting 28 29 Section 2.1: Tectonic overview for the Caribbean Region The San Pedro Basin (SPB) is located along the central segment of the Greater Antilles, which are comprised of Cuba, Jamaica, Hispaniola and Puerto Rico. More specifically, the basin is lo- cated in the upper slope region of the south-eastern margin of The Dominican Republic (figure 2.1). Both the Greater and the Lesser Antilles are part of the Circum-Caribbean Arc or Great Arc of the Caribbean (Mann, 1999), which is a first order tectonic and physiographic feature of the Caribbean plate (CARIB). To describe the tectonic setting of our studied area this chapter will first address the CARIB as a whole with its main features; continue with the principal provinces or structural elements, followed by the analysis of the northern border of the CARIB to finish with the description of Hispaniola and the SPB. The CARIB is located between longitudes 60ºW and 90ºW and latitudes of 10ºN and 20ºN (figure 2.1). Within the group of large lithospheric plates present in the region, the CARIB is one of the smallest (4*10^6 km2; e.g., Bird, 2003). It has an approximately rectangular shape and extends from Central America on its western border, to the Lesser Antilles on its eastern boundary, and from the south of Cuba to the northern border of South America (figure 2.1). The Caribbean region displays a wide variety of plate boundary interactions including subduction in Central America and the Lesser Antilles, strike-slip motions on the northern and southern boundaries and a sea floor spreading in the Cayman Though (Sommer 2009, and references therein). Following the classification of Dolan and Mann (1998), the main limits of the CARIB can be divided into:  Transcurrent boundaries in the northern CARIB border, consisting mainly of left-lateral strike-slip structures (e.g., Septentrional Fault Zone in Hispaniola, figure 2.1), conjugated with restraining and releasing zones (e.g., Jamaica Island and Cayman trough respec- tively) along the northern border and right lateral structures together with transpressive zones along the southern CARIB limit. These structures are located in continental do- mains (in Central America, the Motagua-Polochic Fault Zone, figure 2.1), on the island of arcs (Hispaniola and Jamaica) and in the oceanic crust (region of the Cayman trough).  Convergent limits are mainly defined by the subduction processes of the oceanic Atlantic lithosphere which is consumed along the eastern boundary of the CARIB (along the Lesser Antilles subduction zone) and the oceanic lithosphere of the Cocos plate and a smaller portion of the Nazca plate consumed throughout the western border of the CARIB (along the Central American Subduction zone). In this classification, the N-NE sector of La Española would enter, producing a high oblique convergence that has resulted into an oblique collision (Dolan et al., 1998, Pérez-Estaún et al., 2007)  Divergent limits: very localized and smaller entity, associated mainly with the extensional zone in the Cayman Trough, and Mona and Anegada Passages (to the east and west of Puerto Rico; Rosencrantz et al., 1988, ten Brink et al., 2002). The CARIB interacts with four large rigid plates: The North American Plate (NOAM) to the North and North-East, the South-American Plate (SOAM) to the south and south-east, the Cocos Plate in the western limit and the Nazca plate in the south-west (figure 2.1 A). The geological, geophysical and geodetic data indicate that the CARIB is moving mainly towards the E in relation to the plates of NOAM and SOAM (figure 2.1). Global Positioning System (GPS) velocities indicate the CARIB moves in respect to the NOAM with a velocity of 18-20 mm / year and an azimuth of 070º (Mann et al., 2002). Regarding the SOAM, it moves with an average speed of 20 mm / year while the azimuth range is from 090º to 068º (Weber et al., 2001). The movement rates predicted by the NUVEL-1A geodetic model for the Cocos and Nazca plates with respect to the CARIB are between 59-74 mm / year in the NE- 30 E direction (DeMets, 2000). A higher concentration of the seismicity in the external border of the plate together with the almost absence of the intraplate indicate that the differential movement between the plates is accommodated mainly on the edge areas of the plate with a "rigid" central region (figure 2.1 B). Fig. 2.1. A, Regional Tectonic setting in a plate tectonic framework. 2.1 B, Regional distribution of seismicity for earthquakes of 4.5 and greater magnitude. White arrows point the plate move- ment relative to the North-American Plate (based on Mann et al., 2002; Weber et al., 2001; De- Mets, 2000). Black insert highlights the position of the study area or Area of Interest (AOI), lo- cated on the southern margin of Hispaniola Island. Key to Acronyms: CU, Cuba; CT, Cayman Trough; MPFZ, Motagua-Polochic Fault Zone; JA, Jamaica; CB, Colombian Basin; BR, Beata Ridge; VB, Venezuelan Basin; SFZ, Septentrional Fault Zone; PR, Puerto Rico. 31 Section 2.2: Crustal structure (and composition) of the interior CARIB The crustal types in the Caribbean includes pre-Mesozoic continental blocks, accretionary crust formed during the Mesozoic and Cenozoic, Jurassic – Early Cretaceous oceanic crust and which has been interpreted as a Mid-Cretaceous Oceanic Plateau comprising major parts of the Central Caribbean (Sommer, 2009, Escuder-Viruete et al., 2007 a, 2014, 2016). According to scientific bibliography, the main part of the interior of the CARIB is essentially oceanic in origin, whereas vast areas have an increased thickness of 10-15 km and a smother upper reflector (B’’) than typical oceanic crust (e.g. Burke et al., 1978; Diebold et al., 1981; Holcombe et al., 1990, Donnelly, 1994; Maufret and Leroy, 1997). From geophysical character and the Deep-Sea Drilling Project results (DSDP), it was concluded that these areas represent the Caribbean Large Igneous Province (CLIP). Extensive basaltic mag- matism was apparently active at circa 90 Ma (Sinton et al 1998) although some biostratigraphic indications and some K-Ar data yield a range of magmatic activity from as early as Aptian-Albian to as young as Santonian and even Campanian (Donnelly et al., 1990; Donnelly, 1994; Weidmann, 1978; Diebold et al., 1999). Several ridges subdivide the interior of the CARIB into different basins (figures 2.1 and 2.2). From west to east, the interior of the CARIB comprises, the Nicaraguan Rise, the Colombian Basin, the Beata Ridge and the Venezuelan Basin, among others, which will be presented for their proximity with Hispaniola Island and the AOI. Fig. 2.2 Regional cross-sections of the CARIB as proposed in the Bibliography. A-B section taken modified from Granja-Bruña (2008) and references therein. 32 2.2.1 Nicaraguan Rise and Jamaica The Nicaraguan Rise (figures 2.1 and 2.2), located between the Cayman Trough and the Colom- bian basin, has a northeast-southwest trend and lies to the southwest of Jamaica. It consists of a northeast-southwest trending bathymetric high, usually divided into the Upper (or northern) and Lower (or southern) Nicaraguan Rise (Sánchez et al., 2019 and references therein). Draper (1986), Pindell and Barret (1990) and Meschede and Frisch (1998) consider the Nicaraguan Rise to be an extinct island arc section. However, they also note that no forearc or accretionary prism material has been found, and therefore, the Nicaraguan Rise-Jamaica arc could have been part of the Chor- tis block. Based on onshore geological studies in Central America and Jamaica and the analysis of samples from offshore wells, recent studies point out the Upper Nicaraguan Rise is underlain by both continental (which has a presumed Precambrian / Paleozoic basement) to island-arc type crust, with a crustal thickness of approximately 20-25 km. On the other hand, the southern Nicaraguan Rise is underlain by an oceanic plateau basement with a crustal thickness of approximately 15– 20 km (Sommer, 2009; Sánchez et al., 2019 and references therein). From west to east the crust of the upper Nicaraguan Rise thins and becomes more magmatic arc in character, as exposed on Jamaica (Sommer, 2009). The boundary zones between the plausibly continental and the Creta- ceous – Paleogene volcanic arc portions of the Nicaragua Rise are still enigmatic. The basement of Jamaica is composed of Lower Cretaceous to Paleocene arc-related volcanic and metamorphic formations, with a composition similar to the Northern Nicaraguan Rise. Jamaica, formed as a restraining bend between the Wagwater and Blue Mountain transpressional faults, was uplifted since late Miocene and can be regarded as an exposed portion of the North Nicara- guan rise (e.g., Boschman et al., 2014). 2.2.2 Colombian Basin The Colombian Basin (figure 2.1) is delimited by the Nicaraguan Rise to the northwest, the Beata Ridge to the northeast and the deformed belt of the Caribbean of Panamá and Costa Rica. It is underlain by the CLIP (Burke et al., 1978; Burke, 1988; Boschman et al., 2014) with a crustal thickness between approximately 10 and 18 km (Carvajal and Mann, 2018). The area of crustal thinning in the central part of the Colombian Basin is interpreted as a localized zone of normal oceanic crust (Bowland and Rosencrantz, 1988). Seismic refraction results show that the entire crustal section is thicker in the Colombian Basin than in the Venezuelan Basin, but instead of a very smooth reflector (horizon-B"), the top of the crust reveals regional ridges and basins. However, at least the western Colombian Basin seems to be underlain by a large oceanic plateau related to Late Cretaceous Caribbean basalt flows (Som- mer, 2009 and references therein). By the integration of potential field data, the seismic interpre- tation and regional data, Olaiz and Swank (2018) interpreted the development of the CLIP as a multi-stage volcanic and magmatic episodes derived from the action of a mantle plume, with the topography of the basement related to the differences in crustal affinity. 2.2.3 Beata Ridge The Beta Ridge (figures 2.1 and 2.2) consists of a structural high (2000 m deep), accentuated by horst and graben structures, that separates the Colombian and Venezuelan Basins southwards 33 Hispaniola Island (Leroy and Mauffret, 1996; Müller et al., 1999, Sommer, 2009). Following the definition given by Granja-Bruña et al., (2014), “The Beata ridge is a thickened aseismic block of pre-Cenozoic oceanic crust that forms a NNE–SSW-trending bathymetric high located in the interior of the Caribbean Large Igneous Province”. The thickness is estimated from 8-10 km in the south to 20 km in the north (Granja-Bruña et al., 2014; Núñez et al., 2016 and references therein). The western Venezuelan basin has the same crustal thickness as the southern section of the Beata Ridge (10 km) while the crust of the Colombian basin in lower than 10 km (Leroy and Mauffret, 1996). The interpretation of seismic profiles led to propose that the Beata Ridge was formed after horizon B’’ time interpreted in the Caribbean, that consists of the emplacement of Upper Cretaceous flood basalt complex of the CLIP (Sommer, 2009). Geological and petrological studies based on sam- ples and deep drilling suggest that the Beata ridge is composed mainly of intrusive rocks (e.g., gabbros and dolerites) resulting in an imbricate sill/ dike complex (Granja-Bruña et al., 2014). After the revision of the bibliography, Granja-Bruña et al (2014) explain a three-stage defor- mation evolution for the Beata ridge based on the works of Diebold and Driscoll (1999), Diebold et al. (1999) and Diebold (2009):  A poorly documented E–W compression phase occurred in the Middle Cretaceous coin- cident with the emplacement of the uppermost and most voluminous volcanic extrusive elements of the igneous province.  A phase of E–W extensional unloading yielded by underplating and causing the uplifting of the Beata ridge as a result of lithospheric flexure in the Upper Cretaceous.  A recent stage of transpressive tectonics (Miocene-Present) related to the convergence between the CARIB's interior and Hispaniola. Uplifted and accreted section of the Beata Ridge crops out in southern Hispaniola, along the Mas- sif de la Hotte and the Chaîne de la Serre in Haiti, and in Sierra de Bahoruco in the Dominican Republic (Escuder-Viruete at el., 2016). This is the result of the oblique component of conver- gence between the island arc and the CARIB's interior. “This indentation has altered the pre- existing E–W trending, intra-oceanic island arc structure of southern Hispaniola. The main con- sequences of the impingement are the termination of the Muertos thrust belt and the uplift and accretion of a part of the oceanic igneous crust of the Beata ridge to form the Bahoruco and Southern peninsulas in southern Hispaniola” (Granja-Bruña et al., 2014). 2.2.4 Venezuelan Basin Located between the Beata Ridge and the Aves Ridge, the Venezuelan Basin is the largest basin of the Caribbean’s interior (figures 2.1 and 2.2). The top of the igneous basement is a smooth surface marked by the seismic reflector B’’ at the north-western section of the basin, while the south-eastern part of the basin exhibits an irregular surface (Sommer, 2009; Granja-Bruña et al., 2010 and references therein). This reflector marks an increase of seismic velocities, because rocks underlying this horizon have velocities > 5 km/s, but the structure and composition of this igneous basement is not well constrained. Different seismic surveys have studied the sedimentary cover of the basin overlying the reflector B’’, correlating the stratigraphy with the data derived from the Deep-Sea Drilling Project (Granja-Bruña et al., 2010 and references therein). Depths increase towards the northern and southern limits, against the island arc and continental margins, respectively. Evidences of young subduction beneath the adjacent plates have been sug- gested for both margins (Sommer, 2009 and references therein). Nevertheless, the subduction of the Caribbean along the Muertos trough is controversial and recent works question the north- dipping subduction of the CARIB beneath island arc terrains. Wide-angle and gravity modelling suggest there is not a Caribbean slab sinking into the upper mantle (Granja-Bruña et al., 2010). 34 Gravity models also led Granja-Bruña et al. (2010) to propose a “new tectonic model for the Muertos Margin in agreement with the deformational features of the upper crust, the results of the sandbox kinematic modeling, the deep seismic sounding modeling and the focal mechanism so- lutions. The new tectonic model for the Muertos Margin in the south of eastern Hispaniola is defined as a retroarc thrusting where a gentle dipping basal detachment yields at least 30 km of N–S horizontal shortening in the upper crust. This shortening has to be accommodated in the lower crust with a single or a more or less complex plate interface”. 35 Section 2.3: Tectonic evolutionary models for the Caribbean Region The tectonic evolution for the Caribbean region has been controversial since the beginning of the tectonic plates framework. Along time, several models have tried to explain the origin and devel- opment of the CARIB. All these models can be divided into two fundamental groups: those which consider the CARIB as an allochthonous body with a Pacific origin which is widely accepted on the scientific literature and, on the other hand, whose consider the CARIB as autochthonous ter- rains of continental crust between the Americas plates. In this chapter they will be named as the Pacific and In-Situ (or inter-American) models, respectively, offering the strengths and weak- nesses according to the bibliography of both points of views. The only consensus between both models is that the history of the CARIB began with the breakup of Pangea and the separation of North and South American Plates in Jurassic times (Mantilla, 2007). Although the results of this work are directly derived from the constrains inferred from the onshore geology and are not de- pendent of this subject, applying one model or the other could have implications at the time of addressing specific topic like the hydrocarbon potential of the basin. In this sense, considering the Pacific model would prognose only the presence of Upper Cretaceous and younger source rocks for the Caribbean Plate while the In-Situ model would open the door to older source intervals, such as the Jurassic source rock that produces hydrocarbons in Cuba or the Gulf of Mexico. 2.3.1 The Pacific Model According to the Pacific model, CARIB was formed during Late Jurassic to Early Cretaceous to the west of the NOAM and SOAM, consisting of an oceanic crust (Wilson 1966, Pindell 1985, 1994; Pindell et al., 1998, 2005, 2006; Pindell and Kennan 2009). Authors of this model consider that the unusual thickness of CARIB (15-20 km) is due to a large basaltic flooding event that formed a basaltic Plateau named the CLIP in Late Cretaceous, between 91 and 88 Ma (Pindell and Kennan, 2009; Boschman et al., 2014 and references therein). According to this model (figure 2.3), the tectonic framework for insertion of the CARIB between both Americas is explained as follows (Pindell and Kennan, 2009; Boschman et al., 2014 and references therein):  First the breakup of Pangea in Late Jurassic started the opening of the Gulf of Mexico and an open basin intra Americas usually named “Proto-Caribbean”  Because of the arrival of the CARIB to the subduction zone of Farallon a reversal of the subduction polarity occurred, initializing the later SW subduction of the Proto-Caribbean. The regional discordance encountered in Caribbean region in Aptian-Albian together with the change in vulcanism to a more calc-alkaline composition is assumed as indica- tors of this event.  The Proto-Caribbean was consumed while the CARIB occupied progressively their cur- rent position since Lower Cretaceous to middle Eocene when part of the Circum-Carib- bean arc collided diachronously with the Bahamas platform. While the Cuban sector was trapped and incorporated to the NOAM, the oblique collision of Hispaniola led to a trans- pressive regime and the formation of great fault systems (such as the Septentrional or Enriquillo – Plantain Garden fault zones).  Since that moment, the CARIB escaped to the East to its current position with an average velocity of 18-20 mm/yr with respect to the NOAM (DeMets et al., 2000). 36 At the same time this model explains the interactions in the border of the CARIB with the adjacent plates, as the rotation of the Chortis block and the collision with the arc or the interaction with the SOAM during the migration to the east. Under the Pacific model, the Yucatan basin and the Cay- man through are products of that escape (figure 2.3) while the Cuban segment and Hispaniola are blocked against the Bahamas platform. In this sense, the Lesser Antilles and the Aves ridge would represent the continuous subduction of the Atlantic - Proto-Caribbean since Cretaceous to present. Fig. 2.3 Tectonic evolution of the CARIB according to the Pacific Model, modified from Bosch- man et al (2014). Red insert indicates the theorical position of the San Pedro Basin. - Strengths of the Pacific Model:  This model manages to explain with details every interaction of the CARIB with the sur- roundings tectonic elements. At the norther border, the authors defending the Pacific Model illustrate the change from subduction to underthrust and finally collision of Cuba and Hispaniola which seems to be in agreement with outcrops in both islands (Pindell and Kennan, 2009; Boschmann et al., 2014 and references therein).  Current GPS displacements and Caribbean configuration seem to point to a continuous derive from the west (DeMets et al., 2000; Calais et al., 2016). Seismicity maps reveal that most part of the plate is aseismic while the great part of earthquakes are located at the limit regions which could imply a lack of heritage structures in the Caribbean. - Problems associated with the Pacific Model  Nevertheless, the quantification of plate movement has led to complex geometries in an attempt of unify everyone. James (2006) exposes the geometric impossibility of entry of the Mesozoic island arc into the Caribbean area and the CARIB between the Americas. The former is related to the lengthiness of the arc, around 3000 km, and the original space between Americas, even more if we fix the position of the Chortis Block. The latter is 37 related to the Caribbean rotation after the collision of the Greater Antilles with the Baha- mas Platform. James (2006) point out that this rotation should have caused a greater de- formation event in the Caribbean Place, southwards the collision zone.  On the other hand, the internal structure of the CARIB represents another controversial point for this model. Seismic profiles inside the Venezuelan Basin, Beata Ridge or the Nicaraguan Rise could be interpreted as extended continental crust instead of a Plateau (James, 2007). 2.3.2 The In-Situ Model As a contraposition, the inter-American or in situ model propose an autochthonous origin for the plate (figure 2.4) being its geodynamic evolution the result of a sinistral transtension between North and South America which begun with the Pangea brake-up (James 2002, 2006, 2009). The geological evolution of the area begun with the Triassic – early Jurassic rifting which reac- tivated former Palaeozoic continental sutures as rifts, accommodating red beds and basalts (James, 2009). Therefore, the early Caribbean was formed at the same time and by the same tec- tonic framework than the Gulf of Mexico. Other structures such us the Nicaraguan Rise or the Cayman Through have a similar origin (James 2002, 2006, 2009). Fig. 2.4 Middle America crustal types/distribution from James (2009), under the in-situ model Key to accronyms: SCA, southern Central America; NLA, Greater Antilles–northern Lesser An- tilles; LNR, Lower Nicaragua Rise; EYB, eastern Yucatán Basin; CP, Caribbean ‘Plateau’; WCB, west Colombia Basin. James 2009 support that major N60ºE trending features was formed as the extensional strain within the regional N60ºW sinistral system of offset between North and South America. The re- sultant new basins accommodated salt deposition. Since salt diapirs and ultramafic rocks are seen along northern Honduras and since serpentinites occur in the Motagua Fault Zone (figure 2.5 B) 38 in the Cretaceous, this paper suggests that the early Cayman Trough extended between Maya and Chortis as a Salt basin at this time. Late Jurassic – Early Cretaceous spreading in the central Atlantic resulted in WNW drift of North America from Gondwana and great extension in Middle America. Thanks to a continuous move- ment of the SOAM relative to NOAM resulted in the continued subduction in the Lesser Antilles (James, 2009). - Strengths of the In-Situ Model:  The presence of continental blocks along the western borders of the CARIB, like Yucatan or Chortis Blocks, could be interpreted as a prove of the continental extension of Mid- Americas. In the same direction, the internal structure of the Nicaraguan Rise and Beata Ridge are considered as the continuation of that extension (James, 2009).  The simplicity of the model, being possible to find analogues from other regions of the world, like Scotia and Banda areas (James 2006). - Problems associated with the In-Situ Model:  Do not explain the structural complexity and the block rotations which have been regis- tered in the CARIB limits. Northern margins of Cuba and Hispaniola show the compres- sion and consequent accretion of basinal terrains between the Greater Arc and Florida and Bahamas. Outcrops from Hispaniola reflect a post compression rotation, which per- fectly would fit with the subduction, collision and transpression scenario (Sommer, 2009).  As it occurs in Gulf of Mexico, it would be expected to find accumulations of salt in the Caribbean owing to the initial stages of extensional regimes. Nevertheless, until present there is no clear probe of diapirism or any other indicator inside the Plate. 39 Section 2.4: The border region between the CARIB and the NOAM Hispaniola Island and the AOI are located at the border region between the CARIB and the NOAM plates. This region consists of a seismogenic band between 100 and 250 km wide, where the deformation is mainly associated to transpressive and transtensive zones which extends around 2000 km along the northern limit of the CARIB (figure 2.5). Recent studies consider the northern Caribbean as an example of an along-strike segmented plate boundary, passing from strike-slip south of Cuba along the Cayman Trough, into a collision/understhrusting along His- paniola, to an oblique subduction in Puerto Rico and finally to a frontal subduction at the Lesser Antilles. This transition is conditioned by the entering into the trench of a thickened crust corre- sponding to the Bahamas Banks (Rodríguez-Zurrunero et al., 2020). The Cayman Trough is a left-lateral strike-slip zone that extends from the Gulf of Honduras to the Windward Passage (figure 2.6), that comprises a floor of thin oceanic crust bounded by steep walls towards continental / magmatic arc crust of the Cayman Ridge to the north and the Nicara- guan Rise to the south (Sommer, 2009 and references therein). Pindell and Barret (1990) define the Cayman Trough as a Cenozoic pull-apart basin, estimating a total sinistral offset of ~1000 km related to the Cayman Trough, accounting to additional extension of arc-related or continental crust at the western and eastern ends of the trough (Corbeau et al., 2016 and references therein). Fig. 2.5 Schematic tectonic map of the northern limit of the CARIB from Mann et al. (1998). A, M>4.5 seismicity for the period 1963-1992 from the International Seismic Comission. B, Tectonic of the northern Caribbean showing microplates and the main transpressive zones between the CARIB and the NOAM. 40 Fig. 2.6 Schematic tectonic setting of the CARIB modified from Rodríguez-Zurrunero et al. (2020). Plate boundaries are represented by the tectonic features marked with red lines. Red insert indicates the AOI for this work. Key to acronyms: H, Haiti; DR, Dominican Republic; PR, Puerto Rico; J, Jamaica; SOFZ, Septentrional Oriente Fault Zone; NHDB, North Hispaniola Deformed Belt; BFZ, Bunce Fault Zone; EPGFZ, Enriquillo-Plantain-Garden Fault Zone. The combined study of the bathymetry and the heat flow together with the gravity and magnetic anomalies led to an overall rate of opening of about 1.5 cm/yr since 26 Ma and 3.0 cm/yr prior to 26 Ma is established (Rosencrantz et al., 1988; ten Brink et al., 2002). From these results it is further argued that the trough opened at least since the early Eocene (45–50 Ma, Rosencrantz et al. 1988; 49 Ma, Leroy et al. 2000 in Sommer, 2009). To the east of the Cayman Trough, the plate boundary comprises a zone of 250 km wide repre- sented by two seismic bands, to the north and south, respectively (Dolan and Mann, 1998). The northern zone is located along the trace of the Septentrional – Oriente Fault Zone, passing along the north of Hispaniola and the south of Cuba (figure 2.6). Marine studies have demonstrated that this zone does not extend to the east of the Mona Passage, but it is replaced by another left-lateral shearing system, at the forearc of the Puerto Rican Trench, such as the Bunce Fault Zone (ten Brink et al., 2004). The southern zone corresponds to the Enriquillo – Plantain Garden Fault Zone, passing through the south of Hispaniola and Jamaica. In summary, the current northern boundary between the CARIB and the NOAM is controlled by a left-lateral strike-slip regime which accommodates the displacement to the east of the CARIB in relation to the NOAM. 41 2.4.1 Tectonic evolution of the northern CARIB As for any other border region, the tectonic evolution of the northern limit of the CARIB is the result of the complex interaction of both plates. This evolution comprises the formation of the Great Arc of the Caribbean, which includes the terrains of Cuba, Hispaniola and Puerto Rico, due to the subduction of the Proto-Caribbean during the Cretaceous. In their work, Dolan and Mann (1998) presented constrains on the norther CARIB that have to be considered to understand the Current configuration of microplate tectonics for the N edge of the Caribbean plate (figure 2.7). Fig. 2.7 Tectonic evolution of the CARIB from the Maastrichtian to the Holocene from Dolan and Mann (1998). According to this model, during the Maastrichtian there is a collision between the CARIB, formed in the Pacific region, and the NOAM and the SOAM consequence of the north-eastward move- ment of the CARIB, colliding with the Yucatan Peninsula (figure 2.7 A). During the latest Paleocene to the early Eocene, this movement continued, resulting in the colli- sion of the Great Arc with the passive margins of the NOAM, represented by the Bahamas Banks (figure 2.7 B). By the end of the early Eocene, the collision evolved from the western region of Cuba to the centre, leading to the clockwise rotation of the collisional margin, and interrupting the NE movement of the arc due to the arriving of the Bahamas Banks to the subduction zone (figure 2.7 C). As a result, the Yucatan Basin pass from being part of the CARIB to being con- sidered as belonged to the NOAM. Between the middle Eocene and the middle Miocene, the Cayman Trough started its activity due to the collision with the Bahamas Banks, the clockwise rotation of the CARIB and its progressive tectonic scape to the east (figure 2.7 D). After the middle Eocene, the oblique collision between 42 the CARIB and the Bahamas Banks generated the tectonic transpression and the uplift of Hispan- iola Island (figure 2.7 E), which led to the development of the Enriquillo – Plantain Garden Fault Zone (figure 2.7 F). According to this model, the tectonic pulses related to the collision were diachronous along the arc, established in the late Paleocene to early Eocene in western Cuba, early to middle Eocene in central Cuba, Eocene to Present in Hispaniola and late Eocene to early Oligocene for the region of Puerto Rico and the Virgin Islands (Dolan y Mann, 1998). 43 Section 2.5: Hispaniola Island This work is focused on the study of the tectono-stratigraphic evolution of the San Pedro Basin, located at the south-eastern margin of Hispaniola Island. As a previous introduction to the basin, this section addresses the physiography of Hispaniola Island and the offshore nearby, followed by a description of the onshore geology. 2.5.1 Physiography of Hispaniola Island and the offshore nearby The topography and the bathymetry of the region reveal the presence of high gradients, where the dips corresponding to the arc alternates with flat and depressed areas, exposing the complexity of the region (figure 2.8). The deepest point is reached at the Puerto Rican Trench, with a maximum depth of -8340 m, while the highest peak of Hispaniola (the Duarte Peak) is 3087 m height. This contrast implies a difference of 11000 m in a distance of 200 km. Figure 2.8 summarises the topographic features of the region, described in this section, which will be referred in this work. They include sedimentary basins such as the Cibao, Azua or Enriquillo Basins; the Septentrional, Central and Oriental Cordilleras or the Sierra de Neiba and Bahoruco massifs; and the system Muertos Thrust Belt – Muertos Trench. The SPB will be addressed in Section 2.6. Fig. 2.8 Digital elevation model of the region with the main topographic features. Key to Acronyms: CS, Cordillera Septentrional; CB, Cibao Basin; CC, Cordillera Central; SJB, San Juan Basin; AB, Azua Basin; SN, Sierra de Neiba; EB, Enriquillo Basin; SB, Sierra de Bahoruco; CB, Colombian Basin; VB, Venezuelan Basin; MTB, Muertos Thrust Belt; MT, Muertos Trough; CO, Cordillera Oriental; YB, Yuma Basin; PRT, Puerto Rican Trench; AOI, Area of Interest. 44 Cordillera Septentrional and the Cibao Basin The Cordillera Septentrional constitutes an elongate, east-northeast trending mountain range that extends at the northern region of Hispaniola, with a maximum elevation of 1249 m. This mountain chain is bounded by seismogenic strike-slip and reverse faults. The oblique convergence between the CARIB and the NOAM is accommodated offshore by the Northern Hispaniola Deformed Belt (figure 2.9), which consists of a north-verging fold and thrust system (Dillon et al., 1996; Dolan et al., 1998). Onshore, the active strike-slip Septentrional Fault Zone accommodates 10-12 mm/year of deformation along E-W direction (Prentice et al., 2003; Manaker et al., 2008; Calais et al., 2010). Thus, the accommodation of the shortening component by the Northern Hispaniola Deformed Belt and the strike-slip component by the Septentrional Fault Zone is associated to a strain partitioning model consequence of the oblique convergence (Mann et al., 1995; Calais et al., 2002; Mann et al., 2004; ten Brink and Lin, 2004). At the same time, Rodriguez-Zurrunero et al. (2020) distinguish two different tectonic domains, the oblique underthrusting and the oblique collision domains. De Zoeten and Mann (1999) proposed a 3-phases tectono-stratigraphic evolution of the zone, including:  The early Eocene folding and uplift event related to the initial subduction of the Bahamas Platform beneath Hispaniola.  The late Eocene to early Miocene deposition of deep marine sediments into two elongated basins juxtaposed by strike-slip faulting. This sedimentation finished by a folding and uplift event associated to transpressional faulting related to the CARIB – NOAM motion.  The late Miocene to early Pliocene deposition of shallow marine limestones which ter- minated by a folding and uplift event. In this context, the Cibao Basin occupied the space between the Cordillera Septentrional and the Cordillera Central. At the Present, this basin is defined as an elongated plain with an approximate length of 230 km and a width between 20 and 10 km. Fig. 2.9 Digital elevation model of the northern margin of Hispaniola showing the division into morphostructural provinces from Rodríguez-Zurrunero et al. (2020). Key to acronyms: NHDF, Northern Hispaniola Deformed Belt; SFZ, Septentrional Fault Zone. Location in figure 2.8. 45 Cordillera Central The Cordillera Central consists on an abrupt mountain range that crosses Hispaniola from the NW to the SE. The great part of the chain is composed of the oceanic and island arc basement, which have been generated and amalgamated during the interval Upper Jurassic – Eocene (Hernaiz- Huerta, 2006). The inversion is consequence of the oblique convergence/collision between the CARIB and the NOAM. By the study of the back-arc sedimentary sequences, Heubeck et al. (1991) determines a 3-stages inversion and uplift of the region that occupies the Cordillera Central under a transpressional regime. This study is based on the analysis of four Upper Cretaceous to Pleistocene marine sequences that crop out along the southern flank of the chain, corresponding to the 320 km long Trois Rivieres – Peralta Belt. The first stage corresponds to the latest Cretaceous – late Eocene closure of the Upper Cretaceous back-arc basin. This episode was followed by the Eocene – early Miocene closure of the Upper Cretaceous back-arc basin and the overlying Paleocene – Eocene basin. Finally, since middle Miocene, all the previous sequences were inverted during the uplift of central Hispaniola. The San Juan – Azua Basin Between the Cordillera Central and the Sierra de Neiba, the San Juan Basin is located at the fore- land region of the Trois Rivieres – Peralta Belt. The zone corresponding with the south-east ex- treme, this basin is named the Azua Basin (figure 2.10). In cross-section, this basin resembles “ramp valleys in which mountain blocks overthrust or "ramp" upward along both sides of the basin floor” (Mann et al., 1991 a) having accumulated as much as 4000 m of sediments and rep- resenting the most completed Neogene marine record of the northern Caribbean (Mann et al., 1991 b). Fig. 2.10 Plate tectonic setting of Hispaniola with the Neogene basins shown in grey from Mann et al. (1991 a), and schematic cross section showing the ramp valley configuration of the basins. 46 Sierra de Neiba The Sierra de Neiba is a mountain range that forms part of the terrain of Presqu'ile du Nord-Ouest – Neiba, defined in Mann et al. (1991 b), which original description includes the Enriquillo Basin (Hernaiz-Huerta, 2006). This chain is characterised by direction changes from WNW-ESE to NW-SE and to W-E, determined by the succession of wide folds, relatively discontinuous. Lith- ologically, the Sierra de Neiba is represented by the Eocene – lower Miocene limestones of the Neiba Formation and the Miocene marls of the Sombrerito Formation (Hernaiz-Huerta, 2006). Enriquillo Basin The Enriquillo Basin corresponds to an elongated depression that extends between the Sierra de Neiba and Sierra de Bahoruco (figure 2.10) with a WNW-ESE direction. In the same way than for the San Juan – Azua Basin, the Enriquillo has been defined as a ramp basin, with a great sedimentary thickness, almost 5000 m of Cenozoic sedimentary rocks reached at the well Charco Largo #1 (Mann et al., 1991 a). One of the unique features of this zone is the presence of evapo- rites, deposited in a restricted ambient, which has not been identified in other basins of Hispaniola (Mann et al., 1991 a; Hernaiz-Huerta, 2006). Sierra de Bahoruco The Sierra de Bahoruco belongs to the terrains of the Hotte-Selle-Bahoruco, which includes the prolongation of the chain into Haiti (Mann et al., 1991 a) with a WNW-ESE direction. The most representative formation of this chain is the Dumisseau Formation, consisting of Cretaceous bas- alts that has been directly correlated with the Caribbean Large Igneous Province (CLIP; Escuder- Viruete et al., 2016 a and references therein). Cordillera Oriental The Cordillera Oriental is a mildly deformed area located at the eastern region of Hispaniola (figure 2.8). This chain is the result of the oblique convergence between the CARIB and the NOAM and the collision with the Bahamas Banks (Pérez-Estaún et al., 2007). The resulted ge- ometry together with the cinematic and the temporal relationships between structures suggest a 2-stages deformation model (figure 2.11; García-Senz et al., 2007 a) consisting of:  A homogeneous contractional deformation in the Late Cretaceous, forming a coherent antiformal structure cored by Lower Cretaceous island-arc rocks which were covered by an Upper Cretaceous fore-arc sedimentation.  A change to partitioned transpression in the Paleocene, which cut the antiform generating a positive flower structure. The superposition of structures to the previous antiformal folding produce dome and basin interference patterns. This change from a homogeneous contraction to a partitioned transpression is correlated with a diminution in the convergence angle between the CARIB and the NOAM (García-Senz et al., 2007 a). 47 Fig. 2.11 Schematic cross-section of the Cordillera Oriental from García-Senz et al. (2007). Lo- cation in figure 2.8. Muertos Thrust Belt – Muertos Trough System The Muertos Thrust Belt – Muertos Trough system is located in the south-eastern margin of His- paniola Island (figure 2.8). The active Muertos Thrust Belt (MTB) consists of a south-verging imbricate thrust system developed in a thin-skin tectonic style over the Venezuelan Basin (figure 2.12; ten Brink et al., 2009; Granja-Bruña et al., 2009, 2014 and references therein). Long-lived active folding and thrusting have led in a stepped slope, where northward steeply-dipping reflec- tors are interpreted as a highly deformed materials that configure the fold and thrust belt. The surface expression is characterized by the alternation of asymmetric elongated troughs and anti- clines ridges, consequence of the underlain northward-dipping fault-propagation folds. The de- tachment extended up to 25 km northwards at the eastern section of the belt in the Hispaniola sector, decreasing progressively westward until it disappears at the westernmost segment (Granja- Bruña et al., 2014). The development of the MTB is essential to understand the tectonic evolution of the San Pedro Basin, as this belt controls the configuration space of the basin. On the other hand, the Muertos Trough correspond with an elongated bathymetric depression located along the base of the insular slope of the Muertos Margin. Active sedimentary and tectonic processes control the bathymetric expression of the trough, leading to along-strike variations (Granja-Bruña et al., 2014). Fig. 2.12 Suggested tectonic model for the Muertos Margin in eastern Hispaniola from Granja- Bruña et al. (2010). Location in figure 2.8. 48 2.5.2 Geology of Hispaniola As any other plate border region in the world, the island has suffered multiple deformational processes derived from the interactions of both plates along time, including the high oblique con- vergence between them from Eocene. The different processes that affected the region have been registered on the island, leading to the most complete geological record of the Greater Antilles (figure 2.13), from the Upper Jurassic to the Present (Pérez-Estaún et al., 2007). Hispaniola is constituted by several geo-structural domains separated by first order fault zones which are in intimate relation with the mountainous systems and basins of the island. These do- mains are constituted by igneous, metamorphic and sedimentary rocks of the Jurassic-Cretaceous period formed in what has been interpreted as an intra-oceanic and island-arc context (Escuder- Viruete et al., 2007 a; Pérez-Estaún et al., 2007). These rocks are covered by mainly sedimentary rocks from the Eocene to Present period, which post-date the volcanic activity of the island arc and record a period of oblique collision (transpressive). Specifically, the Dominican Republic contains island-arc, fore-arc and back-arc rocks, along with ophiolites and high-pressure meta- morphic rocks and other collision units. The high-pressure complexes with eclogites, blue and green schists outcrop in the northern part of the island and are part of the extrusive collision wedge formed between the NOAM and CARIB plates (Pérez-Estaún et al., 2007; Escuder-Viruete and Castillo-Carrión, 2016 and references therein). Mann et al., (1991) divided Hispaniola into 12 tectonic terranes (figure 2.14). From those, 11 correspond to the island arc and another to the oceanic plateau, interpreted in the literature as a part of the Caribbean Large Igneous Province (CLIP), being the Southern-Bahoruco peninsula an onshore expression of the Plateau. The stratigraphic and structural correlations (figure 2.15) of the 11 island arc terrains led to propose eight main tectonic phases for the island arc terrains and other four that affected to the oceanic plateau terrain of southern Hispaniola. Fig. 2.13 Geological map of Hispaniola as resulting from the geological mapping of the SYSMIN I and II Programs (modified from Pérez-Estaún et al., 2007). Numbers refer to locations men- tioned in the text. 49 Mann et al. (1991 b) propose that there were 8 main tectonic phases and events that affected the island arc terrains: 1- Lower Cretaceous to pre-Aptian island arc growth. 2- Pre-Aptian uplift and erosion of the island arc. 3- Post- Albian to pre-Campanian island arc growth. 4- Campanian deformation and metamorphism. 5- Post-Campanian to middle-Eocene island arc growth. 6- Middle to early Upper Eocene island arc collision phase. 7- Upper Eocene to Lower Miocene strike-slip phase. 8- Lower Miocene to Present transpression. Fig. 2.14 Above, tectonic terrenes of Hispaniola stablished by Mann et al. (1991 b). The island is divided into 10 island arc terrains and 1 oceanic plateau terrain. Below, stratigraphic corre- lations for the main oceanic plateau and island arc terrains in Hispaniola (from Mann et al., 1991 b). 50 At the same time, four tectonic phases and events are described for the oceanic plateau terrane of southern Hispaniola (Mann et al., 1991 b): 1- Late Cretaceous oceanic plateau growth. 2- Upper Cretaceous deformation and erosion. 3- Paleocene and to Lower Miocene subsidence and strike-slip faulting. 4- Lower Miocene to Present transpression. Fig. 2.15 Structural cross sections of the Hispaniola island (Mann et al., 1991 b). Stratigraphic and tectonic correlations of them led to postulate 8 main tectonic phases for the island arc ter- rains and 3 for the oceanic Plateau terrain. The systematic geological mapping carried out during the SYSMIN I (1994-2001) and SYSMIN II (2007-2010) Programmes contributed significantly to the understanding of the geology and evolution of the island, constraining the main tectonic events and characterizing the vulcanism and metamorphism of the island. According to these new insights into the Hispaniola geology, the oldest formations identified in the island belong to the Upper Jurassic – Lower Cretaceous (location 1 in figure 2.13), like the Loma La Monja and Duarte complexes (Escuder-Viruete et al., 2007 a). In the Early Cretaceous, diverse CLIP igneous units (e.g., Duarte Complex) were constructed onto a proto-Caribbean oceanic crust (Loma la Monja Assemble) and located in a SW position of the NE facing Primitive Island Arc (Escuder-Viruete et al., 2009 and references therein). The initial stage of the island arc (Tholeiitic or Primitive Island Arc or PIA) took place during the Lower Cretaceous. The Los Ranchos Formation, that crops out at Cordillera Oriental (location 2 51 in figure 2.13), is a good exponent of the PIA. Metamorphic units like the Amina – Maimon schists are connected with this initial vulcanism due to their geochemical composition (Kesler, 1991; Escuder-Viruete et al., 2007 a and references therein). The origin of the metamorphism is related with the subduction of part of the fore-arc region during the formation stages of the PIA. The deformation must be posterior to the Aptian-Albian (~112 Ma) limit and prior to the for- mation of the Hispaniola Fault Zone (figure 2.13) that cut the main foliation and the syn-tectonic Eocene to Oligocene deposits. Initially, this event was correlated with a reversal of the subduction polarity for the period Aptian – Albian (Draper et al., 1996; Lewis et al., 2002). However, this change in subduction polarity is controversial and not totally accepted in the bibliography (Som- mer, 2009). In Cordillera Central, the Tireo Group represents the volcanic activity from Aptian to Turonian (location 3 in figure 2.13). It is divided into the lower and the upper volcanic sequences. The lower volcanic sequence (or Constanza Formation) is dominated by Aptian to Turonian monoto- nous submarine vitric – lithic tuffs and volcanic breccias of andesite to basaltic andesite, with minor interbedded flows of basalts and andesites (Pérez-Estaún et al., 2007; Escuder-Viruete et al., 2007 a). On the other hand, The upper volcanic sequence (or Restauración Formation) is characterized by a spatial and temporal association of Turonian – Coniacian to lower Campanian adakites, high-Mg andesites and Nb-enriched basalts, which collectively define a shift in compo- sition of the subduction-related erupted lavas (Escuder-Viruete et al., 2007 a and references therein). The geochemical change has been explained by an oblique ridge subduction at ~90 Ma and a subsequent slab window formation (Escuder-Viruete et al., 2007 a). Since Campanian, subduction-related island-arc vulcanism is substituted by the Pelona – Pico Duarte basalts that intruded into and extruded onto Turonian – lower Campanian island arc vol- canic, while they are overlain by Maastrichtian platform carbonates (Escuder-Viruete et al., 2011 and references therein). The dating gives a middle Campanian to Maastrichtian age ,79-68 Ma. Geochemical values are characteristic of transitional and alkalic ocean – island basalts (Escuder- Viruete et al., 2011). They are interpreted as partial melts of plume-related, deep-enriched source, which has not been contaminated by active subduction (Escuder-Viruete et al., 2011). Upper Cretaceous sedimentation is well exposed at Cordillera Oriental (location 4 in figure 2.13). García-Senz et al. (2007) divided it into three depositional episodes interpreted as deposited in a forearc context:  Cenomanian-Santonian (Las Guayabas Fm.) sequence is composed of an association of volcanogenic greywackes, pyroclastic rocks, lava flows, silicified lime and pelagic lime- stones, indicating the proximity of the arc.  A Santonian episode composed of thin beds of radiolarian chert (Arroyo La Yabana Fm.) pointing to the cease of the clastic input from the slope.  Santonian-Maastrichtian sedimentary rocks are composed of calcilutites and coarse-re- deposited limestones (Río Chavón Fm. and Las Auyamas Mb.) and, only in the Maas- trichtian, coastal calcarenites and rudist patch reefs lying on serpentinite seamounts (Loma de Anglada Fm). The back-arc region is represented by the Campanian-Maastrichtian Trois Rivieres (in Haiti and western Dominican Republic, location 5 in figure 2.13) and Las Palmas (San Cristóbal and Cor- dillera Central, location 6 in figure 2.13) formations that crop out southwards the San José Res- tauración Fault Zone (figure 2.13). The Trois Rivieres Formation, defined by Boisson (1987) in Haiti, constitutes of predominantly fine materials with intercalated sandstone layers and carbonate shales (Bernárdez-Rodríguez et al., 2004). A complete series of the Trois Rivieres Formation gives an estimated thickness of 1500 m (Ardèvol, 2004). There, the lower part is mainly composed of shales with minor siltstones and very fine sandstones with lenticular and wavy stratification. To the middle part, there are intercalations of fine to medium grain sandstones layers, passing into pebble conglomerates and cobble breccias at the upper section. 52 The Las Palmas Formation is composed of a basal member that consists of Campanian breccias and an upper member integrated by Maastrichtian marls with turbidite sandstones intercalated (Pérez-Varela et al., 2010 a). Below the Las Palmas Formation, there is also a grey limestone formation with minor sandstones and fine levels, yet due to the high grade of deformation and the deficient access to outcrops, it has been englobed into the Tireo Group and is not well studied. The next main event has been constrained to the middle Eocene, when the collision between the island arc and the North American continental crust, represented by the Bahamas Banks, started (Pérez-Estaún et al., 2007 and references therein). At this moment the current transpressional regime started to work in the area with the development of great fault zones as the Hispaniola Fault Zone (Pérez-Estaún et al., 2007; Escuder-Viruete et al., 2007 a and references therein). As a consequence, the late Eocene to Oligocene interval is marked by the deposit of conglomerates, breccias and olistoliths along the island. In the northern sector of Hispaniola, two main events have been proposed at the Cibao Basin for the early and middle Miocene (Calais et al., 1992) that were recorded by the deposition of con- glomerates at Cordillera Septentrional (location 7 in figure 2.13). They could corelate to the grow- ing and development of the Septentrional Fault Zone. In a regional framework, the development of great transpressional fault zones could be assumed as an interference between the collision with the North American Plate and the escape of the CARIB to the East (Pindell and Kenan, 2009; Boschman et al., 2014 and references therein). To the south, the deformation dynamics is mainly controlled by the oblique collision compressive stress transferred across the island arc from middle Eocene and the Beata Ridge indentation since the Miocene (Hernaiz-Huerta and Pérez-Estaún, 2002; Granja-Bruña et al., 2014), causing the uplift of the Sierra de Neiba (location 8 in figure 2.13) and the Sierra de Bahoruco. In Haiti, angular unconformities of early Miocene age are locally observed in the southwestern and eastern areas of the Southern Peninsula (location 10 in figure 2.13; Wessels et al., 2019 and references therein). This is followed by “a widespread homogenization of pelagic sedimentation marks a phase of tectonic quiescence during the middle to late Miocene” (Wessels et al., 2019 and references therein) while the final stage of uplift of the peninsula took place during the late Miocene. To the north (location 9 in figure 2.13), there is a middle Miocene diachronous evolution of the Chaîne des Matheux (Wessels, 2018 and references therein). The development of the Hai- tian fold-and-thrust belt (HFTB) started in western Hispaniola from early Miocene onwards. “The HFTB consists of a series of stacked NW – SE trending southwest-verging thrust sheets with piggy-back basins on their north-eastern flanks” (Wessels, 2018). 53 Section 2.6: The San Pedro Basin The San Pedro Basin (SPB) is defined as “an E-W trending bathymetric depression located at the top of the insular slope, with maximum depths of ≈ 1600m (figure 2.16). The depression is mainly bordered by structural highs and collects most of the southward drainage of eastern Dominican Republic, from Saona Island to Punta Palenque, resulting in a significant accumulation of sedi- ments with a thickness of at least 3.4 s of two-way travel time (TWT)” (Granja-Bruña et al., 2014). The SPB bounds to the south with the Muertos Thrust Belt (MTB), an imbricate system that has been correlated by different authors (Biju-Duval et al., 1982; Heubeck et al., 1991; Her- naiz-Huerta, 2006; Granja-Bruña, 2008) with the onshore Peralta Thrust and Folds Belt (figure 2.17). Fig. 2.16 Regional morphotectonic interpretation in map-view (from Granja-Bruña et al. 2014). Although different studies have been carried out in the vicinity of the SPB in an attempt of corre- lating the infill of the basin with outcrops (figure 2.17), some discrepancies still remain in the scientific community (Gorosabel-Araus et al., 2020). Based on the interpretation of seismic pro- files acquired by the University of Texas in 1977, Ladd et al. (1981) proposed the first interpre- tation of SPB. This work identified four main unconformities and correlated them with onshore geological mapping carried out by Bowin (1966). They correlated the basal unconformity that corresponded to the top of the seismic basement to the Upper Jurassic – Lower Cretaceous Duarte complex. Dip sections revealed the presence of mound-shaped bodies that were interpreted as remnants of the Upper Cretaceous volcanic sequences of the Tireo Group. Under their interpreta- tion, the Cenozoic sedimentary infill of the basin was limited to the low-deformed section (figure 2.18), not including the highly deformed Muertos Thrust Belt. 54 Biju-Duval et al. (1982) considered the San Cristobal Basin to be the onshore extension of the SPB after field observations and proposed the first evolutionary model (figure 2.17) to include two main tectonic events (middle to late Eocene followed by the uplift and erosion of Cordillera Central and Pliocene to recent uplift). It is considered that the sedimentary rocks now observed in the Peralta Thrust Belt “correspond to the off-scraping of pelagic sediments, initially accumu- lated in a relatively deep environment, and the over-thrusting of slope and outer-shelf sediments tectonically incorporated and mixed with accreted oceanic deposits into an accretionary prism” (Biju-Duval et al., 1982). Furthermore, the stratigraphic and paleontological analysis together the estimation of sedimentation rates, led to proposed an “Eocene widening and deepening of the fore-arc basin; followed by Oligocene slope accumulation linked with deformation and migration of the axis of subsidence in Miocene times, with partial infilling in late Neogene” (Biju-Duval et al., 1982). Fig. 2.17 Tectonic evolution of the San Pedro Basin as proposed in Biju-Duval et al (1982), in- cluding the onshore-offshore correlation. According to these authors, the SPB would have been developed as a fore-arc basin at the rear of the Muertos Thrust Belt, considered as an accretion- ary prism. Heubeck et al. (1991) completed the study of Biju-Duval et al. (1982) proposing a three-stage deformation model for the onshore section of the basin. The model included the initial formation of a back-arc basin by Coniacian – Danian, derived from the back-arc rifting that would have been filled by volcanoclastic sedimentary rocks and turbidite marine rocks derived from the arc. The deformation model would include:  Uppermost Cretaceous to early late Eocene closure of the Upper Cretaceous back-arc basin.  Upper Eocene to early Miocene closure of the Cretaceous back-arc basin and overlying Paleocene - Eocene basin. 55  Middle Miocene to Recent closure of the back-arc basin and overlying Paleocene to early Miocene sedimentary basins. This onshore model was extended into the offshore SPB, with the infill of the basin’s low-de- formed section (~3.5 sTWT) seen as middle Miocene to Present (figure 2.18). Fig. 2.18 Example of onshore-offshore correlation carried out for the system San Pedro Basin – Muertos Thrust Belt (modified from Heubeck et al., 1991). The low-deformed section of the basin is highlighted in blue. 2.6.1 Structure of the basin The last structural interpretation of the basin is given by Granja-Bruña et al. (2014). According to the authors, some of the blind thrusts that composed an imbricate structure may be still active and form propagation folds that deformed the seafloor at the rear zone of the MTB. The growth of the MTB and the landward migration of compression is inferred from the progressively folding and northward tilting of the sub-horizontal sedimentary record of the basin (figure 2.19). The variable balance of the sedimentary supply and the growth of the belt results in a complex stratal relationship between the sediment beds and the northward-tilted sedimentary sequences underly- ing the Punta Palenque ridge. The morphology of this ridge reveals the presence of sub-parallel scarps with steps of tens of meters, which are controlled by active “bending-moment normal fault- ing arranged in echelon” (Granja-Bruña et al., 2014). These normal faults are considered the re- sponse to the active growth of the MTB, balancing its critical taper angle by a local shallow ex- tensional regime. 56 Fig. 2.19 Schematic cross-section from Granja-Bruña et al. (2014), based on 2D seismic profiles and bathymetric profiles extracted from multibeam data gridded at 150 m intervals. 57 58 59 Chapter 3: Data and methods 60 61 Chapter 3: Introduction As mentioned in Chapter 1, the main purpose of this work is the elaboration of a geolog- ical model that leads to the evaluation of the petroleum potential of the San Pedro Basin (SPB). However, the limited exploration and scientific data of the basin has implied to undertake more ambitious goals. Primarily the understanding of the main geological pro- cesses that affected the region resulted mandatory when it comes to propose an evolu- tionary model of the basin. Secondly, in order to evaluate the potential of the SPB as rigorously as possible, it was necessary to identify the main regional elements of the pe- troleum system, recognising those that could be present in the basin according to the ge- ological model. To present the methodology, this chapter has been subdivided into sec- tions which follow the workflow established for this research, as represented in figure 3.1. The first stage comprises of the preliminary research necessary to start the work (see Section 3.1). This section includes the compilation and review of scientific and technical literature, which was accompanied by the elaboration of a database and the geo-referenc- ing of data to conform to the basis of the research. The main body of this work is developed in the second stage, designed to elaborate an integrated geological model (see Section 3.2). For that purpose, the stratigraphic record was analysed by the definition and correlation of lithostratigraphic units, including in this process the well-to-outcrop correlation. The seismic data was integrated by the well-seis- mic tie, providing a good approach to the subsurface structure of the Hispaniola Island in general and the SPB in particular. This process was completed with the characterization of the basement throughout the study of potential fields (grav-mag) to carry out the inter- pretation of the basin. The main conclusions of this thesis are inferred from this section, which include the elaboration of a structural model of the basin and the proposition of an evolution model of the San Pedro Basin. Both models not only represent the principal objectives of this work but also feed stages 3 and 4 to determine the hydrocarbon potential of the basin. The evaluation of the petroleum system of the basin makes up the determination of the elements of the system, the basin modelling, the basin analysis and finally, the evaluation and associated exploration risk. The determination of the different potential elements of the petroleum system (see Section 3.3) was first performed by a post-mortem analysis, which identifies the regional elements, and by the evaluation of each element. On the other hand, the basin modelling includes the geothermal gradient and the hydrocarbon windows determination (see Section 3.4). Both stages were integrated into the basin anal- ysis (see Section 3.5). Finally, the evaluation of the basin and the risk determination (see Section 3.5) led to the secondary objective of the thesis, the hydrocarbon potential of the SPB. Throughout this chapter, each research stage will be explained, including the data and the methodology followed to accomplish the aim of this work. 62 Fig. 3.1 Workflow followed during the development of this work to obtain the hydrocarbon po- tential of the basin. 63 Section 3.1: Preliminary research The preliminary research is the starting point for any scientific study, providing a general over- view of the state of the art and laying out the basis of the work. At the same time, this step is fundamental at the time of having all the information organized and disposed in the specific da- tabases and software. 3.1.1 Compilation and review of scientific literature In order to obtain an accurate vision of the geology of the Hispaniola Island, the most relevant works were gathered and organized from regional to local or specific contributions. This process included studies about the internal structure of the Caribbean Plate (e.g. Maufret and Leroy, 1997) or the tectonic evolution of the Caribbean (e.g. Pindell and Kennan, 2009; James, 2009) as well as the geological history of Hispaniola (e.g. Pérez-Estaún et al., 2007) or the analysis of specific basins of the island (Heubeck and Mann, 1991). These works were completed with the infor- mation coming from the geological mapping of the Dominican Republic resulted from the SYS- MIN I and II Programmes. Beyond the geological information, scientific contributions related to the methodologies followed in this work were also gathered and reviewed. 3.1.2 Elaboration of the database The research presented in this work has implied a broad type of data which had to be organized in different databases. The geological maps together with the altimetry and bathymetry data were loaded in a Geographic Information System (GIS) project (see Section 3.1.3) and completed with the locations of the seismic profiles and exploration wells. Seismic and well data were loaded on the geology interpretation software Petrel and OpendTect (under academic licenses). Finally, gravity and magnetic data was loaded and organized on Oasis Montaj (under academic license). The resulting maps from these methods were exported to have the information integrated in the different softwares. Fig. 3.2 Different databases created for this work which are feedback between them. 64 3.1.3 Geo-referencing and digitalization of information in a GIS All locations were geo-referencing and included in a GIS project to combine this information with the topography and the geology, making possible the integration of the results of this work. These locations comprise the position of explorations wells, seismic profiles, geological cross sections and outcrops of interest. The onshore topography was obtained from the 30 m-resolution SRTM data (Shuttle Radar To- pography Mission, SRTM, NASA JPL, 2013), which provides the enough resolution to identify structures and tectonic features (figure 3.3). In order to create digital elevation models, the topography was integrated with the bathymetry data acquired during the GEOPRICO-DO (2005) and CARIBENORTE (2009) cruises aboard the Spanish R/V Hespérides and the NORCARIBE (2013) cruise aboard the Spanish R/V Sarmiento de Gamboa. These surveys covered an area of ≈ 40,000 km2, between water depths of −500 m and −5550 m. Swath bathymetry data was interpolated into 25-50 meter-resolution grids for areas with water depths <1000 m and 150-200 m for depths <5000 m. Although the interpolated data preserve artefacts, especially for the overlap zones of different surveys owing to the specific sound velocity, these artefacts are recognisable and do not interfere with the geological interpretation (figure 3.4). The gaps between the topography and the bathymetry and within the bathymetry are completed with the 30 arc second-resolution with the GEBCO Digital Atlas with a 30 arc-second of resolution (Weatherall et al., 2015). The resulting digital elevation model of the region is shown in figure 3.2. Offshore, the study and interpretation of the bathymetry allows to determine the presence of active processes in the basin as well as different stratigraphic and tectonic features (figure 3.4). A com- bination of the bathymetry and seismic profiles led, for instance, to the identification of sediment waves at the Dominican sub-basin (which forms part of the Venezuelan Basin), channels or es- carpments. Fig. 3.3 Example of geo-referenced data for the Azua region and the westernmost limit of the San Pedro Basin (SPB). Topography corresponds with the 30-m resolution SRTM data. Locations of seismic lines and exploration wells are included in the GIS project together with other features of interest such as hydrocarbon seeps. 65 Fig. 3.4 A, Regional digital elevation model composed. Topography is composed of the 30-me- ters-resolution SRTM data and Bathymetry integrated the data acquired at the GEOPRICO-DO (2005), CARIBENORTE (2009) and NORCARIBE (2013) projects and the 30-arc-seconds reso- lution GEBCO data. See text for references. B, zoom to the San Pedro Basin area. High-resolution bathymetry results useful in the identification of active processes as well as tectonic and strati- graphic features with surface expression like channels, scars, or escarpments. 66 Once the different locations were geo-referenced and the digital elevation models generated, the next step was the digitalization of the geological maps resulted from the SYSMIN Programme. The projects SYSMIN I (1994-2001) and SYSMIN II (2007-2010) were founded by the European Union and leaded by the Dominican General Mining Direction (DGM; Dirección General de Minería) and the Dominican Geological Survey (SGN; Sevicio Geológico Nacional) respectively, in collaboration with the Spanish Geological Survey (IGME; Instituto Geológico y Minero de España), the French Bureau de Reserches Géologiques et Minières (BRGM) and the companies PROINTEC and INYPSA. The final product of these programmes was the systematic geological cartography of the Dominican Republic to 1:50,000 scale. The information resulting from the geological mapping and dedicated reports, as well as the academic bibliography derived from there, have improved the geological knowledge of the island leading to a better understand of the onshore geology of Hispaniola. The systematic mapping covered almost the totality of the Dominican Republic territory with the exceptions of the San Juan (5972) and San Cristóbal (6171) quadrants (figure 3.5), that were not finalised, having been substituted here with the 1:100.000 maps. All the geological maps of the Dominican Republic and dedicated reports used in this work have been provided by the Domini- can Geology Survey (Servicio Geológico Nacional, SGN). After the review of the information, each map was incorporated to the database and the GIS project. The images corresponding to the geological maps were cut, removing the frames and, in case of the coastal maps, the offshore sections. They were geo-referenced into the GIS project thanks to the UTM coordinates includes therein and a transparent filter was applied to integrate the topography into the final image (figure 3.6). Fig. 3.5 Distribution of the 1:50.000 geological sheets for the projects SYSMIN I and II, modified from SGN (2007). Red insets show the quadrants of San Juan (5972) and San Cristóbal (6171) not finalised in these projects and completed with the information coming from the 1:100.000 67 Fig. 3.6 Example of integration of geological maps. In this case, the geological map of Sabana Buey (6070-I), obtained from the Dominican Geology Survey (Servicio Geológico Nacional), was cut, geo-referenced and included into the GIS project. Some degree of transparency was applied to get an integrated image with the digital elevation model of the region. Location in figure 3.4. 68 Section 3.2: Integrated geological model In order to obtain an integrated geological model a wide group of methodologies have been com- bined, including the analysis and correlation of outcrops and exploration wells, the processing and interpretation of seismic data and the characterization of the basement by the study of poten- tial fields (grav-mag). The resulting integration of all these techniques has allowed to propose a basin structural model which led to the evolution model of the San Pedro Basin. In the first place, the well-to-outcrop correlation was established through the definition of lithostratigraphic units (Section 3.2.1). After that, seismic data were integrated with exploration wells by the well seismic tie (Section 3.2.2). This integration, together with the basement identi- fication and characterization (Section 3.2.3) has led to the basin structural model (Section 3.2.4). 3.2.1 Definition of lithostratigraphic units The well-to-well and the well-to-outcrop correlations have been carried out by the definition of informal lithostratigraphic units in an attempt to simplify the geological record of the island. For that purpose, after the digitalization and geo-referencing of the geological maps, the first step was the review and regional integration of geological data in order to obtain an overview of the geol- ogy of the island. This analysis was followed by the detailed study of exploration wells, where the lithostratigraphic units were defined by the designation of stratotypes or type sections. The stratotypes consist of an interval that represents the lithological features of the unit. Then, the well-to-outcrop correlations were established by the identification of the lithological properties of the stratotypes in the geological mapping. Each dedicated report associated to the geological maps was examined, paying special attention to the stratigraphic columns and relationships that could be stablished with the nearby quadrants. At the same time, the most representative columns were gathered to created stratigraphic correla- tion charts for different regions of the territory (figure 3.7). After the stratigraphy correlations, the next step was to understand the structure of the island. For that, the cross-sections from the geological mapping were gathered, scaled and integrated into different composed cross-sections to regional scale (figure 3.8). Thanks to the integration of the stratigraphy correlations, the analysis of regional cross-sections and the topography (30 meter- resolution SRTM data), the main structures of the island proposed in the scientific bibliography (e.g. Mann et al., 1991 b; Pérez-Estaún et al., 2007) were analysed (figure 3.8). The joint analysis of the geology of Hispaniola led to the determination of new constrains in the geodynamic evolution of the island through time that combined with other exploration methods, like the evaluation of exploration wells or the interpretation of geophysical data, provide the ge- ological framework deployed into this work. 69 Fig. 3.7 Example of stratigraphy correlations charts established for the regions of Peralta, Neiba and Bahoruco (above) and for the Cordillera Central (Below). 70 Fig. 3.8 Above, Geological map of Hispaniola showing the main structures of the island, inferred from the stratigraphic correlations, structural analysis and the topography (30 meter-resolution SRTM data). Below, Example of regional composed cross-sections from the different geological sheets of the SYSMIN geological mapping. Every section was scaled and integrated into regional cross-sections. (See Appendices for large-sized images). Red insert highlights the cross section corresponding to the geological maps of Constanza, Sabana Queliz and Yayas de Viajama. Key to acronyms: SFZ, Septentrional Fault Zone; EPGFZ, Enriquillo – Platain Garden Fault Zone; SJRFZ, San José – Restauración Fault Zone; SJLPFZ, San Juan – Los Pozos Fault Zone; BFZ, Bonao Fault Zone; HFZ, Hispaniola Fault Zone; RYFZ, Río Yabón Fault Zone. 71 Review and regional integration of exploration wells The information related to exploration wells has been obtained from the Dominican Hydrocarbon Database (“Base Nacional de Datos de Hidrocarburos”, or BNDH), stablished in 2015 in order to gather all the exploration data acquired in the Dominican Republic, including 1491 maps, 805 seismic profiles (that represents a length of 18300 km of 2D seismic data), 212 well records, 321 reports. In the Dominican Republic, up to 71 onshore exploration wells have been drilled since 1904. Nevertheless, most of them were perforated before 1965 with total depth that in most cases are lower than 2000 m. Moreover, the available information for many wells is limited to well reports, without any well log, or even to total depths and reached lithologies (see Chapter 5.1 for more information). Only 19 wells were used for this work and loaded on Petrel (under academic license for the Complutense University of Madrid), and from those, 9 were selected for a deeper analysis (post-mortem) and correlations based on their total depths, lithologies, quality of the logs and auxiliary information (figure 3.9). Fig. 3.9 Above: Left, time distribution of drilling activities in the Dominican Republic since 1904 to present; Right, total depth distribution of exploration wells. Below: Available wells in the Do- minican Republic. Named wells represent those studied in this work (19) while red inserts high- light wells selected for a post-mortem analysis (9). 72 - Quality control and time-to-depth conversion of well-logs All the reports and well logs related to the 19 wells studied in this work were detailed examined to catalogue the available information and carry out a quality control of the data. For instance, significant irregularities on the positions provided by the BNDH of up to three wells (Río Guiza #1, Pimentel Reef #1 and Caño Azul #1) were detected and corrected (figure 3.10 and table 3.1) by the location of correct coordinates on well reports. These irregularities were detected after the integration of wells with the 2D seismic profiles after the well-seismic tie (see Section 3.2.2) and comparing with the expected position of the well provided by the specific reports. Fig. 3.10 Example of quality control of the well Pimentel Reef #1. A, location of the well over seismic line ONCE-2 as exposed in the well report (ONCE ONCE, 1994). B, Location corrections of the wells Río Guiza #1 (RG1), Pimentel Reef #1 (PR1) and Caño Azul #1 (CA1). C, Seismic line ONCE-2 with the position of Pimentel Reef #1 at the position provided at BNDH (right) and corrected based on coordinates found at well reports (left). 73 Well BNDH Coordinates (m) Corrected Coordinates (m) Pimentel Reef #1 372786 372473 Rio Guiza #1 371373 372181 Caño Azul #1 409144 408076 Table 3.1 Coordinates correction (WGS84, UTM 19N) for the wells Pimentel Reef #1, Río Guiza #1 and Caño Azul #1. 19 wells were imported into a geology interpretation software project (Petrel and OpendTect un- der academic licenses of Complutense University of Madrid) and represent them both in depth and time domain (see Section 3.2.2 for the time conversion). Well logs represented in depth do- main were carefully studied to identify the presence of anomalous and out-of-range data, which was filtered and removed. Limits for the different curves were defined as follows (table 3.2): Log Units Limits Gamma Ray API 0 – 150 Spontaneous Potential mV -80 – 20 Calliper INCH 0 – 20 Sonic µs/ft 140 – 40 Resistivities OHM*M 0.2 – 2000 (Logarithmic) Density g/cm3 1.95 – 2.95 Neutron Porosity (V/V) 0.45 – 0.15 Table 3.2 Units and limits used in this work for the main well logs: Gamma Ray, Spontaneous Potential, Calliper, Sonic, Resistivities, Density and Neutron Porosity. Well-to-well and well-to-outcrop correlations During the elaboration of this work, well logs were studied and correlated using the software Petrel and OpendTect (under academic licenses). For that, the stratigraphic record of exploration wells was divided into the lithostratigraphic units proposed in this work, leading to the correlation of wells regionally. The well-to-outcrop correlation of units has been carried out by the identifi- cation of the lithological properties of the stratotypes in the geological mapping based on the assigned age, simplifying the stratigraphic correlations. At the same time, the development of stratigraphic models was critical to understand the lateral and vertical distribution and variations of reservoirs, source rocks and seals. As an example, the Figure 3.11 shows the well-to-well correlation proposed for the Cibao Basin together with the stratigraphic model based on the study of the Licey, San Francisco Reef and Caño Azul wells, supported by the outcrops correlation and the descriptions given in the bibliography and the geo- logical mapping for that units. 74 Fig. 3.11 Example of well-to-well correlation for the norther section of Hispaniola, including Llanura Oriental and the Cibao basin together with the stratigraphic model proposed for the Cibao Basin. Positions of wells are represented in the Upper map. Wells acronyms: VI, Villa Isabel #1; LIC, Licey #1; SFR, San Francisco Reef #1; CA, Caño Azul #1; SP, San Pedro #1. 75 3.2.2 Well-seismic tie 2D seismic reflection data used in this work consist of the data recently acquired at the NOR- CARIBE 2013 survey in the San Pedro Basin, together with the legacy information stored in the BNDH database, composed of up to 805 seismic profiles which represent a total coverage of 18300 km of 2D seismic data. New seismic data was full processed using the processing software GLOBE Claritas, while for the legacy data the software selected was PROMAX 2D (both under academic licenses). The seismic data was interpreted on a suitable software (Petrel, under aca- demic license) by the identification of the main reflectors of interest, normally unconformities and changes of lithology in the sedimentary infill of the basin. As a secondary result, different maps were elaborated for the basin, such as isopaches, structural or source rock maturity maps. . Fig. 3.12 Seismic profiles available for the San Pedro Basin that have been used for this work. Different surveys are differentiated by colours, indicating the acquisition year and the number of profiles used. Wells acronyms: MAL-DT1, Maleno DT1; HIG #2, Higuerito #1; PS #1, Punta Salinas #1; SP #1, San Pedro #1. Processing of new seismic data During the NORCARIBE (2013) cruise, onboard the Spanish Research Vessel “Sarmiento de Gamboa” up to 8 new seismic profiles were acquired in Dominican waters, 5 at the northern margin and other 3 at the south-eastern margin, in the San Pedro Basin, which have been pro- cessed and interpreted for this work (position in figure 3.12). These lines were acquired with a 6 km-long streamer using a 1750 ci airgun array (see figure 3.13 for a complete list of acquisition parameters). Onboard, the quality control and data assessment (or QA) included the checking of parameters such as the delta Q/C (or delay for every airgun of the array in relation to the Aim Point), misfires, wrong depths or pressure of the source, depth of the streamer (control by the birds) or the real-time revision of the shot gathers (figure 3.13). 76 Fig. 3.13 Main acquisition parameters for the seismic lines acquired during the NORCARIBE 2013 cruise onboard the Spanish Research Vessel “Sarmiento de Gamboa” and example of onboard quality control and data assessment during the seismic acquisition. 77 - Onboard processing After the QA, seismic data was transferred to the workstations for a fast-onboard processing in order to evaluate the quality of the final product, following the workflow showed in figure 3.14. This kind of processing results useful to determine the validity of new data in the field and to evaluate the necessity to repeat a section or to re-evaluate the acquisition program in terms of what is being found on the new profiles. Explanations of the different processing processes will be expanded in the next section (Final processing). Fig. 3.14 Fast onboard processing (during NORCARIBE 2013 cruise) carried out to evaluate the quality of the seismic data recently acquired. 78 - Final processing After the finalization of the NORCARIBE 2013 cruise, the seismic data was processed again in the lab to obtain the final version of the profiles. The workflow (in time domain), designed to increase the signal-to-noise ratio, was divided into six stages: pre-processing, deconvolution, mul- tiple attenuation, Dip Move Out (DMO) correction, final stack and post-stack time migration (fig- ure 3.15). Fig. 3.15 Final processing workflow for the seismic data acquired during the NORCARIBE 2013 cruise, modified from Gómez de la Peña, (2017). 79 Pre-processing The first stage of the processing flow is the quality control, where the data is checked and prepared for the following steps. At this point, checks are carried out routinely by hand for missing and corrupted trace identification and bad or noisy shots. Then, an anti-aliasing filter was applied with corner-frequencies 1-3-100-120 Hz. In this case, it consisted of a Butterworth filter that in addi- tion eliminates different noises like sea swells or those with a human activity origin. During the minimum phase conversion, it is necessary to determine the source wavelet by the autocorrelation of 100 seismic traces with a windows length of approximately 5 times the length of the signal (~500 ms). Once the wavelet is determined, it is converted into minimum phase and a new filter is designed to convert all seismic traces into minimum phase (whose frequency spec- tra will be identical and only the phase changes). Finally, after setting up the geometry information in the seg-y file headers, a spherical divergence amplitude correction based on a geological ve- locity layers model was applied, to recover amplitude decay with depth (Gómez de la Peña, 2017). The first results are shown in figure 3.16 A. Deconvolution The deconvolution improves the vertical resolution by compressing the wavelet while suppressing reverberations. “Ideally, deconvolution should compress the wavelet components and eliminate multiples, leaving only the earth’s reflectivity in the seismic trace. Wavelet compression can be done using an inverse filter as a de-convolution operator. An inverse filter, when convolved with the seismic wavelet, converts it to a spike. When applied to a seismogram, the inverse filter should yield the earth’s impulse response. An accurate inverse filter design is achieved using the least- squares method” (Yilmaz, 2001). For this processing, two pre-stack deconvolutions were applied to the data: A Wiener Predictive deconvolution in Tau-P domain and a surface Consistent Decon- volution. The Wiener Predictive deconvolution is used to compress the seismic wavelet, increasing the vertical resolution. It was carried out with a spatial variant filter, designed in the shots. The design of the filter followed the procedure explain in Gómez de la Peña (2017) with a “variable filter length that corresponded to the water point at each point of the seismic section. The gap length was the same as the time of the bubble. The chosen designed window was from 100 ms below the seafloor till 7000 ms, because this window contains a representative section of the data and do not introduce noise in the deconvolution process. White noise percentage was 0.1%. The decon- volution has been applied in a single window over the whole trace, in the shot sorted data”. Surface consistent deconvolution looks for “variations in wavelet shape affected by near-source and near-receiver conditions and source receiver separation. Decomposition is followed by in- verse filtering to recover the earth’s impulse response. The assumption of surface-consistency implies that the basic wavelet shape depends only on the source and receiver locations, and not on the details of the ray path from source to reflector to receiver” (Yilmaz, 1987). The design and application window were the same than for the Wiener Predictive deconvolution. The result is shown in figure 3.16 B. Multiple attenuation Multiple refers to the seismic event where acoustic energy has been reflected more than once. The presence of water bottom multiples is a common issue in marine seismic acquisition, due to the high acoustic impedance contrast between the water and the seafloor. The presence of multiples might lead to misinterpret seismic sections due to create not-existing events in the final sub-sur- face image. Because of that, their attenuation is a key stage during processing in order to obtain a profile as accurate as possible to the real geology. 80 Surface Related Multiple Elimination (SRME) process is data driven and no additional infor- mation to the seismic record is needed, working on a multiple prediction model. To attenuate the multiple, the multiple prediction model is constructed trace by trace, being subtracted from the original dataset into three steps, with two different methods applied. In the first place, a subtrac- tion based on the publication of Y. Wang (2003) was carried out. This part of the processing is comparatively highly effective attenuating the multiple´s energy in complex seafloor geometries, where steep dips and diffractions are present. Secondly, two more subtractions were performed based on the adaptive trace-by-trace subtractions proposed in Monk (1993), which results useful in shallow waters and horizontal sedimentary layers, where dipping structures or diffraction are not present. The resulted data is shown in figure 3.16 C After the SRME and before the next stage of the workflow, the first velocity model of the section was built. This is required for the Normal Move Out (NMO) correction, which removes the move out effect of the travel times of oblique travel paths common in the multichannel seismic acqui- sition. Once we have applied this correction, it is possible to sum up every trace of the CMP gathers (Common Mid-Point) (Yilmaz, 1987). The common mid-point is defined as “the point on the surface halfway between the source and receiver that is shared by numerous source-receiver pairs while the common depth point (CDP) is the halfway point in the travel of a wave from a source to a flat-lying reflector to a receiver” (Schlumberger oilfield glossary, glossary.oil- field.slb.com). The NMO effect is corrected by applying the NMO velocity, which is equivalent to the velocity of the medium above the target reflection or root medium square velocity (RMS). Dip Move Out (DMO) correction By definition, a particular CMP only meets the CDP when the reflection surface has no dip. In other cases, their position will differ, and an additional processing step is needed. In order to preserve the conflicting dips, the Dip Move Out (DMO) correction is applied to the NMO cor- rected pre-stack data, which assume a constant dip (Yilmaz, 1987; Liner, 1999). The DMO pro- cess corrects the dip effect in the NMO velocities, resulting an efficient alternative to pre-stack migration. By the combining of the NMO and DMO corrections, the offset and the dip effects of the pre-stack data are removed, preserving dips and obtaining a dataset ready for the post-stack migration (Yilmaz, 1987; Liner, 1999). Final Stack The final stack started with a more accurate second velocity analysis which refine the results by a systematic semblance analysis. To remove the stretching deformation, external mutes were ap- plied, picked in the NMO corrected CMPs (Gómez de la Peña, 2017 and references therein). A Zero Phase Conversion was carried out by designing a filter on the basis of the autocorrelation of 1000 stacked traces, similar to the Minimum Phase Conversion. The quality factor amplitude correction was applied to reduce the effect of energy loss due to absorption and dispersion during the traveling of energy. It was determined experimentally, trying different values until getting the best result. Finally, a time and space variant band-pass filter was designed following geological criteria, ap- plying a layer model through the different horizons that define the interpreted geology of the basin. 81 (A) Pre-deconvolution (B) Post-deconvolution (C) SRME multiple attenuation 82 (D) DMO correction (E) Final stack (F) Post-stack migration 83 (G) Velocity Model Fig. 3.16 Evolution of processing of seismic line LSP-1 (acquired during the NORCARIBE 2013 cruise) after: A, pre-processing; B, Deconvolution; C, Multiple attenuation; D, Dip Move Out (DMO) correction; E, Final stack; and F, Post-stack time migration (finite difference). G repre- sents the final velocity model. Arrows highlight zones where it is possible to identify the main improvements of every step. Post-stack migration By the migration process, dipping reflections are moved to their true subsurface positions, col- lapsing diffractions and, therefore, increasing the spatial resolution yielding a seismic image of the subsurface. The goal of migration is to make the stacked section appear similar to the geologic cross-section in depth along a seismic traverse (Yilmaz, 2001). The last stage of the processing workflow included two different post-stack time migration: finite difference and Kirchhoff time domain migrations. The reason of applying two different methods was that the first method ap- plied did not collapse all the diffractions, especially for the section of the line where a series of low-amplitude reflectors appear, possibly due to their irregular shape. “In Kirchhoff migration, the diffraction hyperbola is collapsed by summing the amplitudes, then placing them at the apex. The alternative approach (finite differences)” … “is to use the hyperbola recorded a distance away to construct the hyperbola that would be recorded at another distance closer to the source of the diffraction hyperbola. The process is stopped when the hyperbola col- lapses to its apex” (Yilmaz, 2001). The main input parameters for the finite differences migration are a smooth interval velocity model, a window for the time slices of 20 ms and a dip filter factor equal to the cosine of 0.65 degrees. The algorithm is supposed to be based on a X-T domain implicit 45-degree migration, but it offers reasonable results up to 60 degrees of dipping (Gómez de la Peña, 2017). On the other hand, the Kirchhoff migration requires the a smooth rms (root mean square) veloci- ties, the CDP interval (6.25 m), the maximum frequency to migrate (100 Hz), the migration aper- ture (default value) and the maximum dip to migrate (45). The results are shown in figure 3.17. Most of the diffractions remain after the finite differences migration, especially for the limits between a series of mound-shaped bodies of low-amplitude reflectors and the plane-parallel and medium-to-high amplitude reflectors. However, they were collapsed by the application of the Kirchhoff migration, which leave a clear and diffraction-free section for the interpretation of the line. 84 (A) Finite differences migration (B) Kirchhoff migration Fig. 3.17 Results of seismic section LSP-1 after a time domain finite differences (A) and Kirchhoff (B) post-stack migration. Note the prevalence of diffractions (red arrows) after the finite differ- ence migration, specially at the borders of a series of low-amplitude reflectors and mound-shaped bodies, and how it is solved by applying the Kirchhoff migration. 85 Processing of legacy seismic data In general terms, legacy data could be classified as poor to fair, considering fair data as those that allows the identification and mapping of main sedimentary sequences (and unconformities) and the acoustic basement. Because of that, it was essential to re-process them to improve as much as possible the subsurface image. As no field data is available at the public database (BNDH), only stacked data, the only approach was to carry out a post-stack re-processing. - Pre-processing The first step of the processing workflow (figure 3.18) was the quality control of the data, check- ing the quality, selecting those lines of which improved quality could contribute to the interpre- tation, and paying special attention to geometries and position by the integration of them with the bathymetry and topography in a geological interpretation software (Petrel and OpendTect under academic licenses). This methodology revealed the presence of two groups of poor-quality data: lines with wrong coordinates which do not fit with other verified lines or the bathymetry/topog- raphy, and another group with no assigned geometry on the headers. The first group was fixed by a trial-and-error or heuristic approach to fit the position with the bathymetry/topography due to database does not provides correct coordinates. For instance, in the case of seismic lines IG1503_2, IG1503_3 and IG1503_4 (figure 3.19), wrong coordinates were already used unconsciously in scientific literature (e.g., Ladd et al., 1977), which could imply an acquisition failure and not a geo-referencing mistake at the time of digitalize the lines. Fig. 3.18 Optimized post-stack processing workflow carried out to improve the subsurface image of the legacy data. 86 Fig. 3.19 Example of position correction of seismic profiles. Above, locations provided by the BNDH database. Below, corrected locations. In this case, the integration of lines IG1503_2, IG1503_3 and IG1503_4 with the bathymetry lead to the identification of a position issue. It was corrected by a heuristic approach. The other coordinates issue was related with the lack of information about position on headers. This is the case for some lines of the survey WGC-82, acquire by the Western Geophysical Com- pany in 1982: WGC_07, WGC_08, WGC_09, WGC_10 and WGC_11. For these lines, bytes 73- 76 (source X coordinate) and 77-80 (source Y coordinate) of the trace headers were empty or with random coordinates out of the study area. This issue was fixed by the digitalization and geo- referencing of different maps which contain information regarding to seismic position into the GIS project and assigning corrected coordinates to the seg-y file headers (figure 3.20). In addition, information regarding to the acquisition parameters of the different surveys (table 3.3) and to the seismic velocities (provided on the scanned files from the originals) were gathered during the quality control. This information is essential for a post-stack re-processing due to are demanded by different processes like the Kirchhoff migration or the data enhancement. Seismic velocities were integrated into a database to create velocity models for every line. 87 Fig. 3.20 Assignation of coordinates to the trace headers of seismic lines belonged to the seismic surveys WGC-82 and IG1503. A, location map of legacy data at the SPB. B, original coordinates provided by the BNDH for the lines WGC-08. C, corrected coordinates. Survey RN RI RD S-to-Ch SN SI SV SD SD-77 24 95 8 190 4 70 6000 ci 10 WGC-82 96 25 10 250.5 10 25 745 ci * 5 SP-78 24 100 onshore - - 200 - onshore Table 3.3 Acquisition parameters of the main surveys re-processed for this work: SD-77, Santo Domingo 1979 acquired by the University of Houston (offshore data); WGC-82, acquired by Western Geophysical Company in 1982 (offshore data); and SP-78, acquired by Sociedad Pe- trolera Las Mercedes in 1978 (onshore data). Key to acronyms: RN, Receiver Number; RI, Re- ceiver Interval; RD, Receiver Depth; S-to-Ch, Source-to-near Channel offset; SN, Source Num- ber; SI, Source Interval; SV, Source Volume, *volume per gun; SD, Source Depth. 88 Another issue detected during the quality control is related to the digitalization of seismic lines of which the only original record was preserved in paper. From those, the original seismic lines belonged the survey acquired by Petrolera Las Mercedes in 1978 (SP-78), and provided by the BNDH, had the interpretation painted on them. This interpretation was incorporated to the final digital file (seg-y) as new reflectors. As the frequency content of these lines is low (below 25 Hz), this effect was removed by applying a Butterworth pass-band filter for frequencies greater than 30 Hz (1-3-27-30 Hz), without affecting the true reflector (figure 3.21). Fig. 3.21 As some of the digitalized sections preserved the line-drawn interpretation of the orig- inals paper records, a Butterworth filter was designed to remove these fake reflectors, preserving the original data. This example shows the original file, the seg-y provided by the BNDH database and the final result after applying a pass-band filter (1-3-27-30 Hz) of the onshore seismic profile SP3, acquired by Petrolera Las Mercedes in 1978. 89 - Migration The second step in the workflow was to carry out a post-stack time migration of the data in order to reduce and collapse the diffraction hyperbolas of the data. With the velocity data gathered in the pre-processing stage, different velocity models were established for every line as the primary input of the migration. Two different processes were tested to determine the most effective: the Stolt and the Kirchhoff time migration. The first one was applied for lines of the survey SD-78 in Granja-Bruña (2008), with satisfactory results. However, when the results were compared with those where a Kirchhoff migration was applied, it was observed that, although using the same velocity model, the Stolt migration is less time-consuming processing but displace certain reflectors, especially at highly deformed areas (figure 3.22). Because of that, the Stolt migration was discarded. The parameters used for the migration were basically the same than for the processing of the new lines acquired in the NORCARIBE cruise (2013), varying only the velocity model established for every line and the CDP interval in terms of the different surveys (CDP interval of 47.5 m for the SD-77, 12.5 m for the WGC-82 and 50 m for the SP-78). Fig. 3.22 Different results for the seismic line SD-5 after applying the Stolt (left) and Kirchhoff (right) migration to the original data (above). Note the displacement of the reflectors indicated by the red arrow for the Stolt migration. In both cases the image corresponds to the final product of the workflow, including the data enhancement process which remove the incoherent noise. 90 - Data enhancement The purpose of this step is no other than improve the image of the section by increasing the signal- to-noise ratio (S/N) and lateral coherence. The first step in the workflow was to apply a blending process. This tool takes the output from another processing tool and combines it with the input data at a specific ratio. Blend process makes a copy of each input trace, performs the next pro- cesses in the flow on that trace, and then blends the processed output with the copy of the original, using a selected ratio (ProMAX 2D User Manual). In this case, the input data comes from the Kirchhoff migration that was combined with the output of the F-X deconvolution and the Dynamic S/N filtering in order to reduce some of the effects of the process. The ratio for this process, selected experimentally after the examination of the results, was 3:1. The F-X deconvolution applies a Fourier transform to each trace of an input ensemble or stacked data. It applies a complex, Wiener, unit prediction filter in distance for each frequency in a spec- ified range, and then inverse transforms each resulting frequency trace back to the time domain. This process produce output with less random noise than the input data. When the data is trans- formed from time and distance to frequency and distance, a time slice is converted to a frequency slice. Each sample in the transformed data has both real and imaginary components. Events with similar dips appear as a sinusoidally complex signal along a given frequency slice. That is, they can be described in the form: cos (wt) + i*sin wt. Therefore, this signal is predictable. In the F-X deconvolution process, a complex prediction filter is used to predict the signal one trace ahead, across the frequency slice. Any difference between the predicted waveform and the actual one can be classified as noise and removed (ProMax Help Manual). The parameters required by the F-X deconvolution are the type of filter (Wiener Levinson), the percentage of white noise (0), the horizontal window length (50 traces), the number of filter samples (5), the time window length (1000 ms) and overlap (100 ms), the start (8 Hz) and end (60 Hz) frequencies and the number of times to apply F-X filter to each trace (4). The Dynamic S/N filtering enhances the lateral coherency of data by weighting each frequency by a function derived from the local signal to noise ratio (S/N). The filter is derived from sur- rounding traces, but is apply to each trace as a simple, amplitude only, convolutional filter (Pro- MAX Help Manual). The parameters required by this method are: the horizontal window length (set in 20 traces), the time window length (1000 ms) for prediction windows, the time window overlap (100 ms) to prevent edge effects and the F-X filter start (8 Hz) and end (50 Hz) frequen- cies. The final output of the workflow was exported in a new segy file, with the coordinates corrected (if needed) and imported in Petrel for their interpretation. The differences between the original and the final product are significative. First of all, the Kirchhoff migration, as for the new data, resulted effective for the diffraction collapse and to restore reflectors to a more accurate position. Note as different folds (anticlines and synclines) reduce their wavelengths after the migration process (figure 3.23). This effect has been proved as a more realistic representation of actual geology (Yilmaz, 2001 and references therein) than non-migrated data. The implications of this in exploration are fundamental, due to totally change the volume of a potential structural play. Note also, how synclines look like anticlines in the unmigrated data of figure 3.22 due to the bow tie effect. The data enhancement flow removed most of incoherent noise from the seismic profiles, given an improve imaging of the subsurface with a better signal to noise ratio. This effect is more notorious for deeper events (figure 3.23) or for zones with a high-grade of deformation (figure 3.22). The improvement allows the interpretation of features that before could not be identify. 91 This process resulted essential for the seismic facies analysis that will be explained in the next section. As a final consideration, applying the Kirchhoff migration before the data enhancement provides better results than the opposite, possibly due to the migration by itself improved the seismic image by the removing of all the hyperbolas. Fig. 3.23 Original data and final product of the processing applied to the seismic section WGC- 08. Note how the migration process corrects the geometry of the folds, dipping reflectors and the bow tie effect, recovering the syncline structure collapsing all the diffraction hyperbolas. The data enhancement process removed most of incoherent noise of the section, providing a clearer image of the subsurface geology. This is even more notorious for deeper events, allowing to rec- ognize new seismic features. 92 - Well-seismic tie Tying seismic data to exploration wells is a critical step for the correct geological interpretation. For that purpose, well depths, in meters or feet, must be converted into time depths making use of a velocity model. There are different methodologies to obtain a velocity model such us those derived from the use of check-shots or sonic logs. For this work, there was no check-shots survey at the BNDH database, and sonic logs were not available for all of the selected wells. In the case of not having any sonic record, other registers had to be used to obtain the velocity model, like the porosity log. In essence, a sonic tool “consists of a transmitter that emits a sound-pulse and a receiver that picks up and records the pulse as it passes the receiver” (Schlumberger, 1989). The value registered on a sonic log is known as the interval transit time (Δt), which represents the reciprocal of the veloc- ity. “The interval transit time for a given formation depends upon its lithology and porosity. This dependence upon porosity, when the lithology is known, makes the sonic log very useful as a porosity log. Integrated sonic transit times are also helpful in interpreting seismic records” (Schlumberger, 1989). Sonic log, in LAS format, were imported and filtered to exclude wrong and out of range data. Transit times were converted into interval velocities that were used to calculate the Depth (ft) – TWT (s) correlation, which configures the velocity model (figure 3.24). For those wells without any sonic log available, the velocity model was obtained by the synthetic generation, making use of the tools provided by PETREL (under academic license). In the case of the well Caño Azul #1, the porosity log was selected to tie the well with the seismic line PET- 7 (figure 3.25). Fig. 3.24 Example of velocity model obtained for the well Charco Largo #1 with the geological interpretation software PETREL (under academic license). 93 Fig. 3.25 Above, example of well-seismic-tie carried out by the synthetic generation of the well Caño Azul #1 with the geological interpretation software PETREL (under academic license). Be- low, the well tied to the seismic line PET-7. 94 3.2.3 Basement identification and characterization The analysis and study of gravity and magnetic data are the oldest geophysical data acquired for the mineral and oil & gas exploration and have been extensively used to carry out tectonic studies and to determine the structure and depth of causative sources that in most cases are related to the geologic basement. They are the richest data types in applied geophysics, a huge amount of data with the largest area coverage have been acquired worldwide (Li and Krahenbuhl, 2015). The methodology is based on the study of gravity and magnetic anomalies, defined as the differ- ence, positive or negative, between the value of the field measured and the theorical value calcu- lated for the same coordinates. During this section, the different theorical basis will be present together with the available data for this work, the processing and the interpretation given for the gravity and magnetic anomaly maps. Gravity - Theorical basis Mass produces gravity attraction (g) and leads to the variations of gravity field in spatial locations, where the anomalous gravity field is produced by an anomalous mass distribution in the subsur- face owing to density variations, or in other words by a density contrast to a background density distribution (Li and Krahenbuhl, 2015). Therefore, gravity anomalies are defined as the difference between the real g (measured experimentally) and a theorical gravity calculated for an ellipsoidal shaped Earth in revolution and without lateral density increments. The analysis and interpretation of the gravity anomalies, constrained with geological and geophysical data, allows to determine the structure in depth in a realistic way (e.g., Blakely, 1995). Gravity varies on surface in terms of the latitude due to the distance to the mass centre of the Earth reaches a maximum at the Equator, where in consequence the value of g is minimum, while at the poles, closer to the mass centre, the value of g is maximum. In addition, it is necessary to add the rotational effect of the Earth and the centrifugal force, which is maximum at the Equator and zero for the poles. There are several formulas to determine the theorical value of gravity (gth(ϕ)), selecting for this work the Geodetic Reference System of 1967 (GRS 67). It defines the value of the theorical gravity for any latitude at the surface of the ellipsoid that describes the theorical shape of the earth as: 𝑔𝑔𝑡𝑡ℎ(ϕ) = 𝑔𝑔𝑒𝑒 (1 + 𝛽𝛽1 𝑠𝑠𝑠𝑠𝑠𝑠2𝜙𝜙 + 𝛽𝛽2 𝑠𝑠𝑠𝑠𝑠𝑠4𝜙𝜙) Where ϕ is the latitude, ge = 978031.846 mGal, β1 = 5.3024 10-3, β2 = -8.87 10-6 and the result is expressed in mGal. Any variation between the gravity value measured (g) and the theorical value (gth(ϕ)) is the gravity anomaly resulted of a density distribution variation from that establishes by the theorical model. Different corrections can be applied to the experimental data such as the Free air, Bouguer or the terrain corrections. The Free Air anomaly consist of discounting the effect of the gravity field gradient of the Earth between the reference ellipsoid and the measure height, without considering any kind of material between both points. It is well accepted that the average value of the gradient is 0.3086 mGal/m for medium latitudes, therefore the Free Air Correction (FAC) would be: 𝐹𝐹𝐹𝐹𝐹𝐹 = 0.3086 ∗ ℎ Where h represents the height where the measure is taken. The Free Air Anomaly would is cal- culated by the formula: 95 𝐹𝐹𝐹𝐹𝐹𝐹 = 𝑔𝑔 − (𝑔𝑔𝜙𝜙 − 𝐹𝐹𝐹𝐹𝐹𝐹) Free air anomalies express density variations below the observation points. Nevertheless, bathy- metric variations and the high-density change between the water and the seabed materials, make that bathymetry effects domain the Free Air Anomaly (Blakely, 1995). As the FAC only accounts for the difference in height between the instrument and the datum level, when a gravity station is located on topography above or below the survey datum, is located over a layer of rock that increases the measured value of gravity for the former or decrease for the latter. This effect is compensated by the Bouguer Correction (BOU), which assumes that the Earth is flat, and the rock layer is a flat slab of uniform density extending to infinity in all directions. It is given by: BOU = 2𝜋𝜋𝜋𝜋𝜋𝜋ℎ Where BOU is expressed in mGal, G is the universal gravitational constant (~6.67 10-8 cm3/gs2) and ρ is the Bouguer density (expressed in g/cm3). Therefore, the Bouguer anomaly (BA) is de- fined by: 𝐵𝐵𝐹𝐹 = 𝑔𝑔 − (𝑔𝑔𝜙𝜙 − 𝐹𝐹𝐹𝐹𝐹𝐹 + 𝐵𝐵𝐵𝐵𝐵𝐵) Depending on where a value is measured, it will be used a Bouguer density of 2.67 g/cm3 for the onshore, while for the offshore the FAC is zero and it is used the difference between the medium Bouguer density and the density of the seawater (1.03 g/cm3): 𝜋𝜋 = 2.67 − 1.03 = 1.64 (𝑔𝑔/𝑐𝑐𝑐𝑐3) Nevertheless, BA takes into account a homogeneous flat slab when actually, it is morphologically irregular. To correct the gravity effect resulted from the terrain variations around measures points the Terrain Correction is carried out following the methodologies proposed in Naggy (1966), for onshore data, and in Carbó et al. (2003), for offshore data. The Complete Bouguer Anomaly (CBA) is defined by: 𝐹𝐹𝐵𝐵𝐹𝐹 = 𝑔𝑔 − (𝑔𝑔𝜙𝜙 − 𝐹𝐹𝐹𝐹𝐹𝐹 + 𝐵𝐵𝐵𝐵𝐵𝐵 + 𝑇𝑇𝐹𝐹) Onshore, Terrain Corrections (TC) correspond to topographic variations around the point to cor- rect, with a positive effect to gravity. Nevertheless, for offshore data, this term is connected with the relative bathymetric variations below the point to correct on the sea surface. In this case, the result is the summation of positive and negative effects, depending on whether there is a valley or a ridge around the measure point, and the final value can be positive or negative (e.g., Druet- Vélez, 2015). - Available data and processing Regional data come from the global marine gravity model of Sandwell et al. (2014), which was carried out combining radar altimeter measurements from satellites CryoSat-2 and Jason-1 with existing data. Satellite gravimetry is based on the detection of little undulations of the sea surface, result of density heterogeneities that affect the theorical geoid (Druet- Vélez, 2015). The final product has a spatial resolution of 1 arc-minute (1852 m). In order to improve the onshore resolution, gravity data provided by the American National Ge- ospatial-Intelligence Agency (NGA) were collected and processed with the software Oasis Mon- taj™ (figure 3.26). These data were processed to obtain free air and Bouguer anomaly maps (fig- ure 3.27). For the integration of both datasets, a mask was applied to the NGA Bouguer anomaly map to delate offshore data (figure 3.28) and joined to the Sandwell grid by a Boolean operation (figure 3.29). 96 Fig. 3.26 Above, measure points of the National Geospatial-Intelligence Agency (NGA) dataset used to generate onshore gravity maps. Below, observed gravity map. Grid resolution: 2000 m. 97 Fig. 3.27 Resulted anomaly maps for the NGA dataset. Above, Free air anomaly map. Below, Bouguer anomaly map. Grid resolution: 2000 m. 98 Fig. 3.28 Final Bouguer anomaly maps for the NGA (above) and Sandwell (below) datasets. Grid resolution: 2000 m. 99 Fig. 3.29 Final Bouguer anomaly maps from the NGA (onshore) and Sandwell (offshore) da- tasets. Grid resolution: 2000 m. - Elaboration of maps and identification of main structures Once gravity data were processed to obtain a final bouguer anomaly grid, different tools helped with the interpretation of main structures such as the edge recognition techniques. Different meth- ods have been developed along time to determine the edge of structures from gravity and magnetic anomalies. Initially, horizontal and vertical derivatives were used to delineate the boundaries of geological discontinuities. However, this approach is limited as the edges determined by these methods are somewhat shifted from the true position, even for vertical-sided sources (Chen et al., 2014), providing non-accurate results. Instead, Tilt Angle (TA) derivative (Miller and Singh, 1994) has been selected to determine the main structures present in the basin. The TA is “based on the ratio of the vertical gradient of the field to the absolute horizontal gradient of the field. Studies of tilt angle and its horizontal derivative have demonstrated that they are highly suitable for mapping shallow basement structures” (Chen et al., 2014 and references therein). Miller and Singh (1994) define the TA as: 𝑇𝑇𝐹𝐹 = arctan (𝜕𝜕𝜕𝜕 𝜕𝜕𝜕𝜕� ) (𝜕𝜕𝜕𝜕 𝜕𝜕ℎ� ) 𝜕𝜕𝜕𝜕 𝜕𝜕ℎ� = �(𝜕𝜕𝜕𝜕 𝜕𝜕𝜕𝜕� )2 + (𝜕𝜕𝜕𝜕 𝜕𝜕𝜕𝜕� )2 Where 𝜕𝜕𝜕𝜕 𝜕𝜕𝜕𝜕� is the first vertical derivate of the potential field, and 𝜕𝜕𝜕𝜕 𝜕𝜕ℎ� the horizontal gradient. The resulting maps are shown in figure 3.30. 100 Fig. 3.30 Regional (above) and local (below) tilt angle maps created from the Bouguer Anomaly maps. Grid resolution: 2000 m. 101 In addition, a spectral analysis of the Bouguer anomalies was carried out to determine crustal structures. For that propose, the grid obtained for the Bouguer anomaly was transformed into the frequency domain by the application of the Fourier Transform, necessary step to obtain the radial frequency spectrum (figure 3.31). This spectrum is used to select frequencies cut-offs that sepa- rates the anomalies into groups that can be correlated to different kind of sources (Karner and Watts, 1983). Fig. 3.31 Above, radial spectrum obtained for the NGA dataset. For the determination of deeper sources, a filter was applied between 0.004 < K < 0.015 (in red). Below, Bouguer anomaly map resulted after filtering. 102 - 2D gravity modelling In addition to the study of anomaly maps and to validate geological models, different gravity models were carried out for the SPB. At the time of create gravity models, different approaches can be selected in terms on the objective of the study. 2D models consist of a number of tabular prisms, of constant section and density in the cross-sectional dimension of the model, which is assumed to be infinite. On the other hand, 2+3/4D models allows the truncation of prisms in the cross direction, so they represent a more accurate approximation (figure 3.32; Druet-Vélez, 2015). Nevertheless, as the modelling approach is regional, considering basement blocks with a great lateral continuation, the method followed was a direct 2D modelling performed by an iterative process of adjusting of the models. Fig. 3.32 Example of 2D (A) and 2+3/4D (B) models from Druet (2016) modified from GMSYS User’s Guide, V4.10. The starting point is the creation of geo-structural models of density distribution that integrate the available geological information and the previous seismic data with the new gravimetric data. For that, the interpreted horizons were depth converted (see Section 3.2.3) and exported from Petrel to Oasis (under academic licenses). The gravimetric response of the starting models is calculated and, by the comparison with the actual gravity data, the model is adjusted. Gravimetric models do not provide unique solutions since the same gravimetric anomaly could result from different geological models. Nevertheless, this method allows to discard those models that do not fit with the gravity data. The calculation of the gravimetric response is based on the methods proposed in Talwani et al. (1959) and Talwani and Heirtzler (1964) and the algorithms of Won and Bevis (1987). The mod- els presented in this work were created by the application GMSYS integrated in Oasis (under academic license). In addition to the seismic data, other constrains were included into the models. The thickness of the Caribbean Crust was obtained from previous works (Granja-Bruña et al., 2010, Núñez et al., 2016, and references therein) while densities for the island arc basement were obtained from Gar- cía-Lobón and Ayala (2007). The conversion from velocities to densities were carries out with the relationships given in Brocher (2005). The workflow followed during the adjustment of mod- els consisted of the assignation of the crustal thickness based on previous works and meeting the greater wavelengths of the profile. Secondly, the rest of the elements of the model were modelled until getting an adjustment as fit as possible between the observed and the calculated Bouguer anomaly (figure 3.33). By this process, different models were validated (figure 3.33 A and B) while others were discarded as the adjustment was not possible (figure 3.33 C). 103 Fig. 3.33 Examples of gravity models created for the SPB to assess geological models. These models were constrained with seismic data and the scientific literature. A, gravity model of the SPB-MTB system adjusted to observed data. B, zoom into the basin. C, discarded model of the basin. In this case, the subduction of the Caribbean Plate produces a mass excess that cannot be compensated by the adjustment of the geometry of block limits or densities. 104 Magnetic Like the gravity case, magnetic anomalies are superimposed on the background field, which is the Earth’s main magnetic field (Li and Krahenbuhl, 2015). These variations are a consequence of a heterogenic distribution of the magnetic susceptibility in the materials that constitute the crust, inferring on the subsurface structure and composition. Formally, magnetic anomalies (MA) are defined by the difference, positive or negative, between the observed force (Fobs), measured at a station with known coordinates, and the theorical force (FIGRF), calculated for that specific coordinates. Therefore, the magnetic anomaly is defined as (Blakely, 1995): 𝑀𝑀𝐹𝐹 = 𝐹𝐹𝑜𝑜𝑜𝑜𝑜𝑜 − 𝐹𝐹𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼 The theorical force is calculated by the definition of the International Geomagnetic Reference Field (IGRF; Blakely, 1995; Dentith and Mudge, 2014 and references therein): 𝐹𝐹𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼(𝑟𝑟,𝜙𝜙,𝜃𝜃, 𝑡𝑡) = 𝑎𝑎� � � 𝑎𝑎 𝑟𝑟 � 𝜄𝜄+1𝜄𝜄 𝑚𝑚=0 𝐿𝐿 𝜄𝜄=1 (𝑔𝑔𝜄𝜄𝑚𝑚(𝑡𝑡) cos𝑐𝑐𝜙𝜙 + ℎ𝜄𝜄𝑚𝑚(𝑡𝑡) sen𝑐𝑐𝜙𝜙) 𝑃𝑃𝜄𝜄𝑚𝑚(𝑐𝑐𝑐𝑐𝑠𝑠 𝜃𝜃) Where 𝑟𝑟 is the radial distance from the centre of the Earth, L is the maximum grade of expansion, 𝜙𝜙 is the longitude, 𝜃𝜃 is the co-latitude, 𝑎𝑎 is the radius of the Earth, 𝑔𝑔𝜄𝜄𝑚𝑚 and ℎ𝜄𝜄𝑚𝑚 are the Gauss’ coefficients and 𝑃𝑃𝜄𝜄𝑚𝑚 are the Legendre functions of grade l and order m. However, the original measured data must be corrected before any calculations to avoid short- period variations caused by external sources, such as electric currents in the ionosphere such as the daily or diurnal variations (Blakely, 1995). The diurnal variation (DV) is calculated by the difference between the nocturnal data at a base close to the measure point (𝐹𝐹𝑜𝑜𝑏𝑏𝑜𝑜𝑒𝑒) and the average nocturnal data of the base (𝐹𝐹𝑜𝑜𝑏𝑏𝑜𝑜𝑒𝑒_𝑏𝑏𝑎𝑎𝑎𝑎): 𝐷𝐷𝐷𝐷 = 𝐹𝐹𝑜𝑜𝑏𝑏𝑜𝑜𝑒𝑒 − 𝐹𝐹𝑜𝑜𝑏𝑏𝑜𝑜𝑒𝑒_𝑏𝑏𝑎𝑎𝑎𝑎 Therefore, the corrected observed force would be the subtraction of the DV to the Fobs: 𝐹𝐹𝑜𝑜𝑜𝑜𝑜𝑜_𝐷𝐷𝐷𝐷 = 𝐹𝐹𝑜𝑜𝑜𝑜𝑜𝑜 − 𝐷𝐷𝐷𝐷 Leading to a final corrected magnetic anomaly (MAC) of: 𝑀𝑀𝐹𝐹𝐹𝐹 = 𝐹𝐹𝑜𝑜𝑜𝑜𝑜𝑜_𝐷𝐷𝐷𝐷 − 𝐹𝐹𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼 The main goal of the study of magnetic anomalies is the determination of the depth that corre- sponds to the top of magnetic causative sources. For the hydrocarbon exploration, this represents to determining the thickness of the sedimentary section. On the other hand, for mineral explora- tion, depth estimations are used to determine the depth of ore bodies which contain magnetic minerals (Thompson, 1982). Nevertheless, magnetic anomalies can be also used to map structures when materials that con- formed them have a magnetic footprint. In this case, the inclination of the magnetic field over the area of interest should be corrected due to it produces anomalies which are asymmetric and dis- placed from the edges of the causative bodies (McDonald et al., 1992; Blakely, 1995). To avoid this effect, reduction to pole (RTP) is a standard data processing method when interpreting large- scale structures (LUO et al., 2010). Following the theorical approach given in Blakely (1995), the reduction-to-pole operator is defined by the transformed anomaly in the Fourier domain: ℱ[𝑀𝑀𝐹𝐹𝐹𝐹𝑟𝑟] = ℱ[𝜓𝜓𝑟𝑟]ℱ[𝑀𝑀𝐹𝐹𝐹𝐹] 105 𝑤𝑤ℎ𝑒𝑒𝑟𝑟𝑒𝑒 ℱ[𝜓𝜓𝑟𝑟] = 1 Θ𝑚𝑚Θ𝑓𝑓 𝑑𝑑𝑒𝑒𝜕𝜕𝑠𝑠𝑠𝑠𝑒𝑒𝑑𝑑 𝑡𝑡ℎ𝑒𝑒 𝑟𝑟𝑒𝑒𝑑𝑑𝑟𝑟𝑐𝑐𝑡𝑡𝑠𝑠𝑐𝑐𝑠𝑠 𝑡𝑡𝑐𝑐 𝑝𝑝𝑐𝑐𝑝𝑝𝑒𝑒 𝑐𝑐𝑝𝑝𝑒𝑒𝑟𝑟𝑎𝑎𝑡𝑡𝑐𝑐𝑟𝑟. In this case, ℱ[𝑀𝑀𝐹𝐹𝐹𝐹𝑟𝑟] is the magnetic anomaly that “would be measured at the north magnetic pole, where induced magnetization and ambient field both would be directed vertically down” (Blakely, 1995). These operations have been carried out by the tools incorporated in Oasis (under academic license). In the case of Dominican, the RTP parameters comprise a geomagnetic incli- nation of 45º, a geomagnetic declination of -10º and an amplitude correction inclination of 20º. The resulting reduced to pole data are shown in figure 3.34. Fig. 3.34 Comparison between the magnetic anomaly map (left) and the reduced to pole anomaly map (right) generated with Oasis. - Available data and processing Magnetic data used for the elaboration of this work come from the onshore aeromagnetic survey acquired by CGG in 1996 for the SYSMIN I Program (figure 3.35) and provided by the Domini- can Geological Survey (Servicio Geológico Nacional) that was integrated with the magnetic data gathered during the Spanish Research Projects GeoPRICO 2005 and Caribe Norte 2009 (figure 3.35) and the public database EMAG2 (Meyer et al., 2017). Different grids were created with a spatial resolution of 100 meters and knitted by the software Oasis (under academic license; figure 3.36). In order to avoid artefacts resulted from the lack of information for some areas, another grid was elaborated with a spatial resolution of 1,000 m (figure 3.36). 106 Figure 3.35 Available magnetic data. Above, onshore aeromagnetic anomaly map. Below, mag- netic anomalies from data acquired during the Caribe Norte 2009 Project. 107 Figure 3.36 Final magnetic anomaly grid knitted from the available data. Above, anomaly map with a spatial resolution of 100 m. Below, same grid with a spatial resolution of 1,000 m. 108 - Elaboration of maps and identification of main structures Edge detection methods applied to magnetic data follow the same procedures and methodologies than for the gravity data. The techniques consisted on the elaboration of Tilt Angle anomaly maps (figure 3.37) from the RTP data to determine tendencies and the continuity of structures. In a similar way that for gravity anomalies, these techniques were used to determine onshore- offshore correlation of structures. Fig. 3.37 Tilt Angle magnetic anomaly map of the study area used for the edge detection of the main structures. - Integration of data All the information resulted from these methods (edge detection and spectral analysis for gravity and magnetic data) were integrated with the main structures already mapped onshore in order to extend the interpretation to the offshore (figure 3.38). This joint interpretation has resulted espe- cially useful to delimit the main fault systems that separate tectonic domains, like the Hispaniola or Bonao Fault Zones whose components have a high response on magnetic anomaly maps (figure 3.38). On the other hand, gravity anomalies resulted useful on the interpretation of the main tec- tonic domains. A good example is the basement of the island arc and the metamorphic suites that are represented by maximum values, being possible to follow this anomaly into the offshore (fig- ure 3.38). 109 Figure 3.38 Onshore – offshore joint structural correlation based magnetic and gravity anoma- lies of the basin, including the Bouguer and RTP anomaly maps (above), and the tilt angle maps (below). Key to acronyms: HFZ, Hispaniola Fault Zone; BFZ, Bonao Fault Zone. 110 3.2.4 Basin structural model The structural model of the SPB has been obtained by the integration of the onshore geology with the seismic interpretation (figure 3.39). The main products of this process are the elaboration of depth and isopach maps of the basin and the mentioned structural model. However, secondary results are directly derived from the different steps of the workflow, such as the elaboration of horizons and surfaces, the onshore-to-offshore correlations, the creation of structural maps and the determination of an evolution model of the basin. The seismic interpretation was carried out in a 3-steps flow, consisting of the identification of main unconformities, the seismic facies anal- ysis and the structural interpretation. Fig. 3.39 Schematic workflow followed in this work during the interpretation of the SPB. Identification of main unconformities The first step at the time of interpreting seismic data was the identification of unconformities, carried out by the integration of well tops (figure 3.40) and the recognition of onlaps, downlaps and toplaps on the seismic profiles (figure 3.41). Fig. 3.40 Onshore – Offshore composite section of the San Pedro Basin. The well San Pedro #1 (SP#1) provides three stratigraphic tops that could be interpreted into the basin. 111 Fig. 3.41 Example of onlaps that leads to the identification of two additional unconformities on a seismic section of the San Pedro Basin. Each unconformity was interpreted as independent horizons that could be interpolated to create surfaces in Petrel, using a convergence interpolation algorithm with a regular grid size of 1000 m. However, due to the nature of the algorithm, it extrapolates the data following the detected tendency which makes them to cross-cut the surrounded horizon surfaces. To recreate the strati- graphic relations between the selected horizons, the maps were truncated using the available tools in the software (figure 3.42). This operation allows surfaces to be extrapolated and merged with other surfaces, making possible to recreate onlaps or erosional truncations. Once the final surfaces were generated, it is possible to calculate isochron maps to calculate the TWT thickness of a certain sequence. In addition, these surfaces were used to build a velocity model to be able to convert seismic surfaces from time to depth domain. For that, average interval velocities were calculated for each sequence using when available the vrms derived from the seis- mic processing or/and interval velocities derived from exploration wells for the equivalent se- quences (table 3.4). Table 3.4 Velocity model built for the San Pedro Basin (m/s). Intervals are calculated thanks to vrms velocities from seismic processing and interval velocities from exploration wells for the interpreted sequences. Hispaniola_dem represents the bathymetry of the basin. 112 Fig. 3.42 Creation of surfaces for two of the unconformities interpreted in the basin: Top Creta- ceous and Top middle Eocene with the Bathymetry. Above, Top middle Eocene as it is generated by the automatic making surface process. Note how this new surface cut the interpreted Top Cre- taceous below and the bathymetry above. Below, final product of the same surfaces that have been truncated to avoid that effect. Seismic facies analysis The second step of the interpretation workflow was the seismic facies analysis of the basin. This is based on the different expression that groups of reflectors show in terms of their acoustic im- pedance. In this sense, features such as their amplitude, morphology and lateral continuation were studied and interpreted, associating their seismic facies with diverse depositional systems and finally, correlating with the lithostratigraphic units defined onshore. An example of seismic facies analysis is shown in figure 3.43. Low-amplitude reflectors into mound-shaped bodies are interpreted as a shallow-water carbonate ramp system. The lateral change of facies into high amplitude reflectors interpreted as the pass into the deeper deposition in the basin (figure 3.43). There, high-amplitude, planar-parallel and lateral-continuous reflectors are interpreted as deep-water deposits. They are divided into two groups. Group 1 represents a low energy deposition while group 2, with hummocky reflectors, as a more energy deposition with the presence of channels. The development of platforms, represented by low-amplitude re- flectors is correlated to Unit N1, while the deeper deposits are associated to Units N2 and N5. 113 Fig. 3.43 Example of the seismic facies analysis carried out for the San Pedro Basin. A, low- amplitude and mound-shaped reflectors are interpreted as a shallow water carbonate ramp sys- tem. On the other hand, high-amplitude and lateral continuous reflectors are interpreted as deep- water basin deposits (B). They are divided into low energy (1) and high energy (2) deposits. 114 Structural interpretation Finally, the last step was the structural interpretation of the basin. For those lines which do not allow a good visualization of the tectonic features, especially at the most deformed regions, seis- mic attributes where calculated in other to help in the interpretation. These attributes, such as the structural smoothing, the edge enhancement (figure 3.44 A) or the first and second derivatives (figure 3.44 B), were obtained by the tools integrated in Petrel (under academic license). Fig. 3.44 Example of the seismic attributes carried out in order to improve the image and facili- tate the structural interpretation. A, 3D edge enhancement. B, first derivative. The structural analysis of tectonic features (i.e., folds, normal faults, reverse faults, and thrusts) consists first of the characterization of the structures followed by the analysis of their evolution 115 in time. The characterization involves the determination of the structural style and classification together with the measurement of structures (figure 3.45). Fig. 3.45 Example of the structural interpretation given for the profile SD-5. Key to acronyms: SJRFZ, San José – Restauración Fault Zone; SJLPFZ, San Juan – Los Pozos Fault Zone. The timing of deformation was studied by the flattening of the seismic profiles to certain key horizons (figure 3.46). This process reconstructs the architecture of the basin for a specific period of time, assuming that the horizon selected for this purpose was deposited horizontally, providing the structure of the basin and allowing to determine the presence or absence of deformation at that time. Fig. 3.46 Flattening to Top Middle Miocene horizon, reconstructing the structure of the basin for this period of time. This technique was used to determine the timing of deformation. In this case the SAFZ (Saona Fault Zone) was already active at the late Miocene as the onlap of sediments points out. 116 Finally, the seismic interpretation was integrated with the gravity and magnetic anomaly maps in order to correlate with the onshore structures and to elaborate structural maps and structural models of the basin (figure 3.47). Fig. 3.47 Above, structural map of the SPB and the onshore nearby over the RTP anomaly map. Below, structural model proposed for the SPB. Key to acronyms: BFZ, Bonao Fault Zone; HFZ, Hispaniola Fault Zone;RYFZ, Rio Yabon Fault Zone; SJRFZ, San Juan - Restauración Fault Zone; SJLPFZ, San Juan – Los Pozos Fault Zone; SAFZ, Saona Fault Zone. Depth conversion and isopach maps Thanks to this simplified velocity model, it is possible to calculate isopach maps of the different sequences (figure 3.47), which provides the basis to interpret the basin evolution like the depo- centers location through time or the amount of sediments accumulated at a specific period of time. Furthermore, this was used to create maturation maps of the basin for certain potential intervals by the elaboration of a geothermal gradient of the island that allowed to establish a relationship between depth and maturation (or a vitrinite reflectance equivalent). This process is explained in Section 3.4. 117 Figure 3.47 Isopach map for the Cenozoic interval (Top Cretaceous - Seabed) generated with the surfaces converted into depth domain thanks to the velocity model of table 3.5. 118 Section 3.3: Elements of the petroleum system The determination of the hydrocarbon potential of the basin lies in two main blocks, the identifi- cation and evaluation of the elements of the petroleum system and the basin modelling. Both blocks are based on the results of the integrated geological model which provides the geological constrains needed for the evaluation. The identification of the elements of the petroleum system was carried out by the determination of regional elements resulted from a post-mortem analysis of 9 wells and the subsequent correlation with the seismic interpretation. On the other hand, the basin modelling prognosed the main kitchens of the basin thanks to the determination of geother- mal gradient integrated with the geological model of the basin. 3.3.1 Post-mortem analysis After the quality control of the well records and the examination of parameters such us the total depth, lithologies reached and the quality of the logs, 9 wells were selected for a post-mortem analysis (figure 3.48). This kind of evaluation studies the play (source rock, reservoir and seal) and prospect (which includes the trap) prognosed for a certain well, understanding the lithologies penetrated together with other elements of the petroleum system like the timing or migration. The final purpose of the post-mortem analysis is to determine what worked and what failed at the time of drilling and exploration well, extracting the main lessons that one can learn for a future suc- cessful exploration program in the region. Figure 3.48 Map of exploration wells drilled in Hispaniola Island. Red inserts highlight the po- sition of the wells selected for a post-mortem analysis. 119 For every well, the target, (play and trap) were determined by the examination of all the docu- mentation available at the BNDH database. At some wells, the objective was subdivided into primary and secondary targets following the information provided in the well reports. Traps were identified on seismic profiles when possible, in order to understand the prospect of the well. How- ever, the lack of 3D seismic data in Hispaniola, do not allow to determine the real 3D closure of traps and in some cases, they are only conceptual based on very sparse 2D seismic lines, when available. Secondly, the lithostratigraphic units were defined based on the electric logs, mud-logs and well reports (see Section 3.2.1) and the chrono-stratigraphic tops penetrated by wells identified. There- fore, the well records were subdivided into these lithostratigraphic units based on the age, lithol- ogy, sample descriptions and electro-facies, instead of the different formation names that classi- cally had been attributed, in an attempt of simplifying the geology, facilitating the well-to-outcrop and the well-to-well correlations. For each well. these units were correlated with outcrops by the identification of same lithologies in the memories of the geological mapping and the scientific bibliography (figure 3.49). The new division used in this study contributed to a deeper and comprehensive understanding of the regional geology. In this sense, it has avoided confusion in the literature because classically similar lithologies and facies have been classified into different formations for the same period on time, depending only on the area where they were studied. At the same time, they have been used for determining the age of a particular section when dating was not available, paying atten- tion on the electro-facies, lithology descriptions and relationship with other intervals of the well. This is, for instance, the case of the Licey #1 and Villa Isabel #1 wells, where the upper section is well constrained in the Miocene period, yet the lack of biomarkers did not allow to attribute any age for the lower section of the well. In this sense, the electric records and the lithologies of samples (from the mud logging reports) were examined, finding close similarities with the Oli- gocene to lower Miocene Units O2 and N1. This was used to proposed new correlations with this units, providing at least a feasible tentative dating for that sections. Identification of regional elements During the post-mortem analysis, all the information concerning the elements of the petroleum system was written down such as the results of Drilling Stem Tests (DST), geochemical analysis of potential source rocks or hydrocarbons shows (figure 3.49). The gathering of this kind of in- formation for the selected wells allowed the identification of regional elements of the petroleum system, determining potential intervals of interest in terms of source rock richness, reservoir qual- ity and seal capacity together with the identification of traps systems for a certain region or the effectiveness of the timing/migration processes. 120 Figure 3.49 Example of post-mortem analysis, showing the results for the well San Francisco Reef #1 together with the well-to-outcrop correlation of Unit O2 (photos from the geological sheet of La Vega (Hernaiz-Huerta et al., 2010). 121 3.3.2 Evaluation of elements Along this section, the different methods carried out for the evaluation of the elements of the petroleum system are presented individually. Source rock evaluation At the beginning of exploration, the origin of oil and gas was a controversial matter and the con- cept of source rock was basic and often empirical (Brooks et al., 1987). One of the first scientific contribution for the term was summarised by Snider in 1934 (in Brooks et al., 1987): ‘there seems to be a very nearly universal agreement that these organic materials are buried principally in ar- gillaceous mud and to a less extent in calcareous mud and marls and in sand muds. Coarse sands and gravels and very pure calcareous deposits are generally without any notable content of organic material. Consequently, shales and bituminous limestones consolidated from muds and marls are generally regarded as source rocks for petroleum and natural gas’. With time, thanks to the de- velopment of geochemistry techniques, the study and evaluation of source rock have become one of the fundamental mainstays of exploration. In an updated definition, source rock could be considered as a volume of rock that has generated or is generating and expelling hydrocarbons in sufficient quantities to form commercial oil and gas accumulations. The contained sedimentary organic matter must meet minimum criteria of organic richness, kerogen type and organic maturity (Brooks et al., 1987). While a potential source rock would be a volume of rock that has the capability to generate hydrocarbons in suffi- cient quantities to form commercial oil and gas accumulations but has not yet reached the state of minimum hydrocarbon generation because of insufficient organic maturation. Additionally, the term kerogen that will be used in this section corresponds with the organic matter in rocks which is insoluble in non-oxidizing mineral acids, aque- ous alkaline and organic solvents (Brooks et al., 1987). Source rocks are classified in terms of their kerogen type (figure 3.50). Tissot et al. (1974) and Tissot and Welte (1984) classified the three types of recognized kerogens as follows: • Type I: kerogen with high initial H/C and low O/C atomic ratios. This includes organic rich sediments made up mostly of algae, particu- larly those derived from lacustrine environ- ments that produces mainly waxy oil (Dem- bicki, 2009). • Type II: kerogen with moderately high H/C and moderate O/C atomic ratios related to marine sediments where an autochthonous organic matter has been deposited in a reducing envi- ronment that produce mainly naphthenic oil (Dembicki, 2009). • Type III: kerogen with relatively low initial H/C and high initial O/C atomic ratios derived essential from continental plants and contains identifiable vegetal debris that produces mainly gas. Fig. 3.50, Van Krevelen diagram from McCarthy et al. (2011). Kerogen types are determined in terms of their Hydrogen and Oxygen indexes. 122 Also, there is a residual type of kerogen with a very low H/C ratio and a relatively high O/C ratio that cannot generate any hydrocarbon (Type IV). When evaluating a potential source rock, there are three questions that a geoscientist must ask: What’s the Total Organic Carbon (TOC)? What kerogen type does Rock-Eval indicate? And, what maturity level does the vitrinite reflectance data point to? (Dembicki, 2009). Formally, source rock evaluation is defined as assessing the hydrocarbon-generating potential of sediments by looking at their capacity for hydrocarbon generation, the type of organic matter present and what hydrocarbons might be generated, and the thermal maturity of the sediments and how it has influenced generation (Dembicki, 2009; 2017). For this purpose, the analytical methods most frequently used are the Total Organic Carbon (TOC) content analysis, Rock-Eval pyrolysis and vitrinite reflectance analysis. The TOC content is an indicator of the total amount of organic matter present in the sediments (Ronov, 1958 in Dembicki, 2009) and is expressed as a weight percent. From Peters (1986) sam- ples from outcrops, cuttings, cores, and sidewalk cores are classified in terms of their source rich- ness (table 3.5): Richness TOC (Wt. %) Poor 0.0 – 0.5 Fair 0.5 – 1.0 Good 1.0 – 2.0 Very good > 2.0 Table 3.5, Classification of source rocks richness in terms of the TOC content. This technique is the first on source rocks assessments due to its importance but induces to one of the most common mistakes related to sources rocks. TOC content expresses the total amount of organic carbon but not its quality or genetic potential. To assure the potential of a sample it is necessary to carry out a Rock-Eval pyrolysis and vitrinite reflectance analysis. Rock Eval pyrolysis is based on the selective detection of hydrocarbon compounds and of one of the principal oxygenated compound (CO2) produced by pyrolysis under normalized conditions (in an inert atmosphere and with programmed temperature) of organic matter contained in sedi- ments (Espitalie et al., 1977). The measurements are recorded on a chart known as a pyrogram (figure 3.51). Espitalie et al. (1977) defined the main peaks and indexes as: • Peak P1 corresponds to the free hydrocarbons present in the rock and which are volati- lized at a temperature below 300°C. Its area S1 gives the quantity of free hydrocarbons (oil + gas) contained in the rock expressed in mg Hydrocarbons per gram of rock. • Peak P2 corresponds to hydrocarbon type compounds produced by the cracking of the kerogen up to 550°C. Its area S2 gives the residual petroleum potential of the rock, ex- pressed in mg of hydrocarbons per gram of rock. The ratio S2 (mg Hydrocarbon) / TOC of the rock, is called the "Hydrogen Index". • Peak P3 corresponds to the CO2 produced by the pyrolysis of the organic matter in the rock. Its area S3 gives the quantity of CO2 expressed in mg per gram of rock. The ratio S3 (mg Co2)/TOC of the rock is called the "oxygen index". • Temperature Tmax corresponds to the maximum hydrocarbon type products produced by the cracking of kerogen during pyrolysis. This temperature is characteristic of the evolu- tion level of the organic matter. • The Production Index is given by the ratio S1/(S1 + S2). It characterizes the evolution level of the organic matter and makes possible the detection of oil shows. • Genetic Potential = (S1 + S2) kg Hydrocarbons / metric ton of rock. 123 Hydrogen Index (HI) and Oxygen index (OI) are roughly equivalent to the H/C and O/C atomic ratios (Espitalie et al., 1977; Peters, 1986; Baskin, 1997) are plotted in a modified Van Krevelen diagram (Figure 3.50) to determine the type of kerogen. Fig. 3.51, Example of pyrolysis plot from McCarthy et al. (2011). Vitrinite is a type of kerogen particle formed from humic gels thought to be derived from the lignin-cellulose cell walls of higher plants. It is a common component of coals and the reflectance of vitrinite particles was observed to increase with time and temperature in a predictable manner in coals (Teichmüller, 1982 in Dembicki 2009). Vitrinite reflectance is measured for populations of randomly oriented particles and expressed as a percentage reflectance in oil immersion (%Ro). Dow (1977) and Senftle and Landis (1991) stablished the correlation between vitrinite reflectance and hydrocarbon generation (Table 3.8). Oil-Prone Generation Gas-Prone Generation Generation stage Ro (%) Generation stage Ro (%) Immature < 0.6 Immature < 0.8 Early oil 0.6 – 0.8 Early gas 0.8 – 1.2 Peak oil 0.8 – 1.0 Peak gas 1.2 – 2.0 Late oil 1.0 – 1.35 Late gas > 2.0 Wet gas 1.35 – 2.0 Dry gas > 2.0 Table 3.8, Source rock maturation in terms of the vitrinite reflectance. 124 Sampling of potential source rocks During November 2019, potential source rocks were sampled in Cordillera Central and Cordillera Oriental as a part of the Project funding by the Dominican Educational Ministry (Ministerio de Educación Superior Ciencia y Tecnología, MESCYT) and led by the Dominican Geological Sur- vey and the Complutense University of Madrid: “Modelización Tecto-Sedimentaria de las Cuen- cas Mesozoicas y Cenozoicas del Sur - Sureste de la República Dominicana: Aplicación a Iden- tificación y Caracterización de los Elementos del Sistema Petrolífero”. Field work was divided into two sectors (western and eastern) in order to cover as much area as possible. Final GPS tracks of this project is represented in figure 3.52. Based on the definitions given in the previous sections for source rock types and quality, all the information related to source rocks coming from exploration wells and the bibliography were gathered in order to identify the main potential intervals on the island that could be present in the San Pedro Basin. Based on TOC content and rock-eval results, three potential source rock inter- vals were identified:  Upper Cretaceous: Reached at the well San Pedro #1, consisted of type III with a TOC up to 0.55 %Wt.  Oligocene: Identified in exploration wells (Caño Azul with a TOC content as high as 1.05 %Wt) and outcrops (type III and TOC up to 4.18 %Wt).  Miocene: reached at the well Cul de Sac in Haiti, consisted of type II with a TOC of 2 %. With this information, the geology mapping of the terrains close to the SPB was examined looking for outcrops of the three potential intervals. This comprises the areas of San Cristóbal, Cordillera Central and Oriental. This research was completed with the satellite images provided by the plat- form Google Earth in order to determine the accessibility for sampling (figure 3.53). As a com- plement of the field work, samples that could represent other potential elements of the petroleum system of the basin were collected. Figure 3.52, Location of samples recollected during November 2019 in the Dominican Republic over geological map. Key to acronyms: SPB, San Pedro Basin; CC, Cordillera Central; SC, San Cristóbal; CO, Cordillera Oriental. 125 Fig. 3.53, Above, Geological map of the Valdesia Dam area (at San Cristóbal, onshore extension of the San Pedro Basin) over digital elevation model. Below, satellite images for the same loca- tion. Pins represent the position for sampling. During this project, samples were collected for different purposes: source rock evaluation, pale- ontology and petrology, following the criteria established for each discipline referring to the gath- ering technique, quantity, and preservation of the samples (figure 3.54). Source rock samples were sent to the CAI laboratory (Centro de Apoyo a la Investigación) of the Complutense University of Madrid for source rock evaluation. Nevertheless, at the time of this work and due to COVID-19 crisis, the final analyses are not completed and only preliminary results are included in this work. 126 Fig. 3.54, Left, Collecting of samples for paleontology analysis in Cretaceous shales of Cordillera Central. Right, samples for source rock evaluation preserved in aluminium foil to avoid contam- ination in Cretaceous black shales of Cordillera Central. 127 Reservoir petrophysics The available data was integrated into a Geographic Information System (GIS) project where the onshore topography, 30 m-resolution SRTM data (Shuttle Radar Topography Mission, SRTM, There are different definitions for reservoir depending on disciplines. For explorationists, reser- voirs imply a porous and permeable rock, without a reference to the fluid content. On the other hand, reservoir engineers apply reservoir to a rock that contains hydrocarbons (Hartmann and Beaumont, 1999). This work follows the definition of reservoir given in Hartmann and Beaumont (1999):  A reservoir is a porous and permeable rock saturated with oil or gas in buoyancy pressure equilibrium with a free water level (zero buoyancy pressure). It has one or more contain- ers and is located below a seal.  A transition zone is the interval of rock separating the reservoir from the aquifer; it is less than 100% saturated with water.  An aquifer is a porous and permeable rock 100% saturated with water. It has one or more containers that may or may not be shared with a reservoir. The study of the reservoir properties of the potential reservoirs on the island was carried out by the analysis of the exploration well logs. The initial stage was the identification of the formations where Drilling Stem Tests or DSTs have been positive, producing water and, in consequence, pointing out the reservoir potential of the section. Petrophysical calculations have been performed for these units. Volume of shale and porosities have been calculated through Gamma-ray and density logs, respectively following the procedures given in Rider and Kennedy (2011). Porosity cut-off was 8 % and the volume of shale to 40% to identify reservoir intervals (Satter and Iqbal, 2016). Permeability data was not available therefore, spontaneous potential and calliper logs has been used as a permeability indicator, constraining the results to the intervals where fair to good permeabilities were suggested (figure 3.55). As a result, the reservoir intervals were determined and represented together with the well logs. These calculations allow to carry out the net pay determinations:  Gross thickness: The measured thickness from the top of the Unit to the base, including intervening non-reservoir lithologies.  Net thickness: The measured thickness of limestones or sandstones with reservoir prop- erties (gross thickness minus thickness of shale and other intervening lithologies). May also indicate total thickness of porous sandstones of limestones, in which case, a cut-off porosity must be given.  Net/Gross: Net thickness divided by the gross thickness, expressed as a decimal. As a result, thanks to petrophysical calculations, the reservoir quality of a certain formations is given, only with the examination of well logs. This provide a good first approach to the reservoir properties of the formation, allowing the identification of the main potential reservoir formations on the island that can be extrapolated to the SPB by the units’ interpretation. In this sense, we can predict the presence of potential reservoir with seismic data. Nevertheless, it should be noted here that the information is limited, and further investigations must be carried out. 128 Figure 3.55, Example of petrophysical results for a section of the well Caño Azul #1. Reservoir intervals are calculated considering a porosity cut-off of 8% and a volume of shale of 40%. Key to acronyms: GR, Gamma Ray; SP, Spontaneous Potential; DPHI, Density Porosity; NPHI, Neu- tron Porosity; GRI, Gamma Ray Index; VSH, Volume of shale. 129 Seal capacity The seal capacity of a certain interval was determined in the post-mortem analysis by indirect methods on account of the limited available data. For that, the following cases were considered as indicators of the seal capacity of an interval:  Pressures differentials.  Compositional variations in the formation fluids.  The presence of hydrocarbons accumulations. Nevertheless, further studies must deepen into this subject in order to address the micro and macro characteristics of the potential seals. Traps classification Traps have been classified following the definitions given by Vincelette et al. (1999) in Beaumont and Foster (1999) into:  Structural Traps: Post- or syn-depositional deformation or displacement of reservoir and/or sealing units.  Stratigraphic Traps: Depositional, erosional, or diagenetic configuration of reservoir and/or sealing units. The proposed classification scheme places traps into four ranked levels, from general to specific: 1, System; 2, Regime; 3, Class (Superclass if necessary); 3.a, Subclass; 3.b, Style (if necessary); 4, Family (Superfamily if necessary); 4.a, Subfamily; 4.b, Variety (if necessary). As an example, the following definition is given for a group of traps present in the SPB: Formal classification of Compressional Group 1: Structural; Regime: fold; Class: local anticline; Superfamily: Tectonic; Family: Compressional; Subfamily: Thrust-belt fold. Age: Upper Eocene – Miocene. To characterise a trap, it is necessary to identify the trap closure. Vincelette et al., 1999 defines it as “a measure of the potential storage capacity or size of the trap defined by the trap boundaries. Vertical closure is a measure of the maximum potential hydrocarbon column of the trap. Areal closure is a measure of the maximum area of the potential hydrocarbon accumulation within the trap boundaries. Volumetric closure integrates vertical and areal closure with pay thickness, po- rosity, and hydrocarbon saturation to provide the volume of the potential hydrocarbon accumula- tion within the trap boundaries”. However, the delineation of traps for this work is only conceptual as the available seismic data do not allow closure to be inferred in most cases. Timing evaluation The timing was evaluated by the determination of the critical point of the petroleum system by the elaboration of critical events charts (figure 3.56). This kind of charts includes information regarding the deposition of the main elements of the petroleum system and the timing of the main structural and stratigraphic traps formation. The critical moment is defined as “the time that best depicts the most significant aspect of the generation, migration, and accumulation of hydrocar- bons in a petroleum system. This is usually the initiation of expulsion/migration and is often es- timated from basin model results” (Dembicki, 2017). 130 Fig. 3.56, Example of critical events chart determined for the San Pedro Basin. 131 Section 3.4: Basin modelling 3.4.1 Geothermal gradient determination BHT and Ro data gathering and the geothermal gradient determination In an attempt to determine the main hydrocarbon kitchens of the basin, a relationship between thermal maturity and depth was carried out. The first step was gathering vitrinite reflectance values and Bottom Hole Temperatures (BHT) from explorations wells. These temperatures were corrected to avoid the cooling effect produced by drilling mud, fol- lowing an empirical correction (Dowdle and Cobb, 1975). By representing the corrected BHT and vitrinite reflectance data in terms of depth, it is possible to determine the current geothermal gradient of the island (figure 3.57). Fig. 3.57, Corrected Bottom Hole Temperatures (left) and vitrinite reflectance values (right) gathered from exploration wells of Hispaniola and used to determine the current geothermal gra- dient of the island and the main hydrocarbon generation windows. 132 3.4.2 Hydrocarbon windows determination As any other thermal data are available, the main hydrocarbon windows (oil generation, expulsion, and the wet /dry gas limit) were calculated by applying the current geothermal gradient of the island. This method must be considered cautiously as it assumed that the heat flow has be constant in time and has not changed. At the same time, vitrinite reflec- tances indicate the maximum temperature reached by a certain interval, independently of the current depth. Nevertheless, due to both plots, BHT and vitrinite reflectances, meet the same tendency, this method was applied. The results indicate a necessary burial of ~3,000 m depth to reach the oil generation that would take place from a temperature of 100 ºC and correspond to a vitrinite reflectance of 0.55 % Ro (figure 3.57). The oil expulsion is determined at ~4,000 m, where a tem- perature of 120 ºC is reached and correspond to a maturity of 0.80 % Ro. Finally, the limit wet / dry gas (150 ºC) is prognosed, according to the geothermal gradient, at ~5,500 m and would be equivalent to a vitrinite reflectance of 2 % Ro. Elaboration of maturation maps and determination of main kitchens Based on the correlation of lithostratigraphic units determined by the seismic interpreta- tion of the basin, different maturity maps were elaborated for different periods, assuming a constant heat flow through time and the depth/maturity relationship previously ex- plained (figure 3.58). Burials were determined by the thickness of the main sequences (see Section 3.2.3). Fig. 3.58, Example of maturity map generated for a potential cretaceous source rock at middle Miocene. Green zones represented the areas where the level has entered the oil generation win- dow. 133 134 135 Chapter 4: Basin Modelling 136 137 Section 4.1: Tectono-Stratigraphic Domains The offshore San Pedro Basin (SPB) is an almost unexplored area located in the south-eastern margin of The Dominican Republic, between the coast and the rear part of the Muertos Thrust Belt (MTB) (figure 4.1.1). Although there have been previous studies that proposed alternatives for the SPB geological evolution and sedimentary infill (e.g. Heubeck et al., 1991), the full un- derstanding and integration with the evolution of other areas on the Hispaniola Island has not been properly addressed. It is assumed that the current configuration started at the middle Eocene with the inversion of the former back-arc basin (Biju-Duval et al., 1982; Heubeck et al., 1991; White, 1993). Previous stages and materials remained unsolved as well as their implications on the geological processes that have affected the region. Thus, the aim of Chapter 4 being to elabo- rate an integrated geological model for the SPB, a deep understanding of the regional geology resulted mandatory. In order to complete the objectives of this chapter, the workflow included the well-to-outcrop correlation and the well-to-seismic tie, the basement characterization and finally the interpretation of the basin (see Sections 3.1 and 3.2). For the well-to-outcrop correlation, the first step was the review and the regional integration of geological data. Most of the information was gathered from the reports elaborated after the geo- logical mapping of the SYSMIN I and II Programmes (figure 4.1.1; Pérez-Estaún et al., 2007), which was completed with the scientific literature (e.g. Mann et al., 1991 b) when needed. As a result, a preliminary stratigraphic correlation panel was built (figure 4.1.2), obtaining the first regional overview of the island. Following that, the well-data obtained from the BNDH (Domin- ican Hydrocarbons Database or “Base Nacional de Datos de Hidrocarburos”) was analysed and 9 wells were selected on account of the quality of data, their total depth, the lithologies reached at the well (with special attention paid to the most representative lithologies in the area) and the age of the lithologies, in order to obtaina well record that was as completed as possible. Fig. 4.1.1, Synthetic geological map of Hispaniola modified from Pérez-Estaún et al. (2007). Numbers refer to stratigraphic columns of figure 4.1.2, white inserts indicate the location of the exploration wells represented in figure 4.1.3 and section A-A’ gives the location of figure 4.14. Key to acronyms: SFZ, Septentrional Fault Zone; HFZ, Hispaniola Fault Zone; BFZ, Bonao Fault Zone; SJRFZ, San Juan – Restauración Fault Zone; SJLPFZ, San Juan – Los Pozos Fault Zone. 138 Fig. 4.1.2, Synthetic stratigraphic correlation panel of Hispaniola from data of the geological mapping and the scientific literature. Location of columns in figure 4.1.2. 139 For the well-to-well correlation (figure 4.1.3) and the well-to-outcrop correlation, and in order to simplify the nomenclature and the stratigraphic relationships, the geological record has been di- vided into lithostratigraphic units. These units group different formations of the island “on the basis of its observable and distinctive lithologic properties or combination of lithologic properties and its stratigraphic relations” (Salvador, 2013). According to the formal definition of a lithostrat- igraphic unit, the geographic extent is based on the extent of its diagnostic lithologic feature, which leads to consider a series of laterally discontinuous rock bodies which have the same lith- ologic properties and stratigraphic position as a single lithostratigraphic unit. However, the defi- nitions given in this work are essentially informal and should be only thought for correlation purposes and not as a substitution of the formations that have been formally established. The definition of the lithostratigraphic units is based on the designation of a stratotype or type section, which represents the lithological features of the unit, also providing a well type where the units have been defined. The naming has followed a composite criterion, designating a letter which represents the age and a number to organize them. At the same time, some units have been subdivided into sub-units on account of lithological variations. For instance, Unit N1, which would represent Neogene carbonates, is divided into sub-unit N1.1 for the reef facies, N1.2 for ramp limestones and N1.3 for re-worked carbonates. The well-to-outcrop correlation of units has been carried out by the identification of lithological properties of stratotypes in geological mapping based on assigned age and simplifying strati- graphic correlations. Note that different formations with the same age, defined in the cartography, could have the same lithological properties, and their existing nomenclature is based on the loca- tion and not integrated in a single unit. These correlations were verified by the elaboration of schematic cross-sections, composed from the geological maps, and completed with the infor- mation provided by seismic profiles thanks to the well-seismic tie (figure 4.1.4). The integration of the lithostratigraphic units with the correlations and cross sections, from geo- logical mapping, led to propose a division of the island into four tectono-stratigraphic domains. For this classification, not only were the structural relationships of each domain considered but also the basement composition and the main lithostratigraphic units that belong to them. The lim- its of these domains are defined as follows (figure 4.1.4):  A Forearc – Collisional Domain (FACD) delimited by the Hispaniola Fault Zone to the south and the Northern Hispaniola Deformed Belt to the north. The basement is composed mainly of Mesozoic metamorphic complexes, overlaid by Cenozoic sedimentary se- quences.  The Island-arc Domain (IAD) is limited by the Hispaniola Fault Zone to the north and the San José – Restauración Fault Zone to the south. It is composed of Cretaceous to Paleogene volcanic and volcaniclastic suites and Mesozoic metamorphic materials.  The Cretaceous – Eocene Basin Domain (CEBD) would be delimited by the San José – Restauración Fault Zone to the north and the San Juan – Los Pozos Fault Zone to the south. The thrust and folds belt, known as the Trois Rivieres – Peralta Belt, it is inter- preted in this work as an inverted back-foreland basin that developed between the Island arc and Oceanic Caribbean Domain from the Late Cretaceous (possibly Campanian) to the middle Eocene.  The Oceanic – Caribbean Domain (OCD) would make up the region southwards, the San Juan – Los Pozos Fault Zone, whose basement would be related to the Caribbean Plate. These domains specific comprise of lithostratigraphic units which could be used to predict base- ment composition and stratigraphic relationship on account of their position in relation to the development of the island arc. In this matter, understanding which precise domains the SPB be- longs to, can help with basement and lithostratigraphic units predictions. The extension of the domains into the basin (figure 4.1.5) lies on the identification of the gravimetry and magnetic anomalies produced by the structures that defined the limits of the Domains (e.g. the Hispaniola or the San José Restauración Fault Zones). 140 Fig. 4.1.3 Correlation stablished in this work for the nine most representative wells of the Do- minican Republic, with the main lithostratigraphic units represented. Key to acronyms: VI-1, Villa Isabel; LIC-1, Licey; SFR-1, San Francisco Reef; CA-1, Caño Azul; SP-1, San Pedro; PS, Punta Salinas; MDT, Maleno DT1; CAN, Candelon; CHL, Charco Largo. 141 Fig. 4.1.4 Schematic regional cross-sections reconstructed from the geological mapping of the the SYSMIN I and II Programs and the integration of seismic profiles. Key to acronyms: SFZ, Septentrional Fault Zone; HFZ, Hispaniola Fault Zone; BFZ, Bonao Fault Zone; SJRFZ, San José – Restauración Fault Zone; SJLPFZ, San Juan – Los Pozos Fault Zone. 142 During Sections 4.2 to 4.5 each domain will be addressed separately, providing the definitions of the lithostratigraphic units and their stratigraphic relationships together with an analysis of struc- ture. The main conclusions are discussed in Section 4.6, proposing an evolution model for the SPB that will be applied in the interpretation of the basin, Section 4.7. As an introduction, a gen- eral overview of the domains division is presented in the following lines. The FACD is considered as the same domain in this study for having the same deformational style, with common basement composed of metamorphic materials. Although metamorphism ex- tends southwards the Hispaniola Fault Zone (figure 4.1.5), this structure separates forearc-derived metamorphic rocks to the north (e.g. the Amina-Maimon schists; Escuder-Viruete et al., 2007 b), from other metamorphic suites, to the south, which could represent an older Plateau that config- ures the basement of the volcanic arc (e.g. the Loma La Monja and the Duarte Complexes; Es- cuder-Viruete et al., 2009). Between the Hispaniola and the San José – Restauración Fault Zones, the basement is mainly conformed of island arc materials, having been inverted through north- and south- verging thrusts in a thick-skin system. To the south of the IAD, the CEBD has been established for having a different structural style than the IAD (thin- versus thick-skin tectonic) and a different sedimentation during the period this basin was active in comparison with the OCD. At the CEBD, sedimentation consisted of clastic turbidites derived from the island arc and depos- ited in a deep-water environment (Ardèvol, 2004), while carbonates dominated the deposition in the OCD. This zonation is limited by the San Juan – Los Pozos Fault zone, which represents the frontal thrust of the Trois Rivieres – Peralta Belt. Finally, southwards the San Juan – Los Pozos Fault Zone, the structural style changes progressively into steep north-verging reverse faults or thrusts, which are the dominant structural features identified in the area. Fig. 4.1.5 Geological maps of Hispaniola and Cuba over the digital elevation model of the region. Main structures have been superimposed. The limits of the island arc domain are represented by the red lines. White insert indicated the location of the study area or Area of Interest (AOI). Key to acronyms: FACD, Forearc – Collisional Domain; IAD, Island Arc Domain; CEBD, Creta- ceous – Eocene Basin Domain; OCD, Oceanic – Caribbean Domain. Structures and morphology features: SPB, San Pedro Basin; MTB, Muertos Thrust Belt; SC, San Cristóbal; SFZ, Septentri- onal Fault Zone; CS, Cordillera Septentrional; HFZ, Hispaniola Fault Zone; RYFZ, Río Yabón Fault Zone; CO, Cordillera Oriental; BFZ, Bonao Fault Zone; CC, Cordillera Central; SJRFZ, San José – Restauración Fault Zone; SJLPFZ, San Juan – Los Pozos Fault Zone; EPGFZ, En- riquillo – Platain Garden Fault Zone. 143 Section 4.2: Fore arc - collisional domain The Forearc - Collisional Domain (FACD) is limited by the Northern Hispaniola Deformed Belt and the Hispaniola Fault Zone (HFZ), including the topographic terrains, from north to south, of the Cordillera Septentrional, the Cibao Basin, the Cordillera Oriental and Llanura Oriental (figure 4.2.1). In addition to the HFZ, this domain is also affected by the Septentrional Fault Zone (SFZ; De Zoeten and Mann, 1999) and the Río Yabón Fault Zone (RYFZ; García-Senz et al., 2007 a), which influenced the deformation style of this region. Along this section, the stratigraphic record will be analysed by the definition of lithostratigraphic units and their correlation, followed by the well-to-well correlation and ending with the analysis of the structure. Fig. 4.2.1, Above, Geological maps over the digital elevation model of the region. Below, cross section from the Guayabito (A-A’) and Fantino (B-B’ and C-C’) geological sheets. Numbers refer to locations mentioned in the text. Key to acronyms: VI-1, Villa Isabel #1; LIC-1, Licey #1; SFR- 1, San Francisco Reef #1, CA-1, Caño Azul #1, SP-1, San Pedro #1, CS, Cordillera Septentrional; SFZ, Septentrional Fault Zone; CC, Cordillera Central; HFZ, Hispaniola Fault Zone; CO, Cor- dillera Oriental; RYFZ, Río Yabón Fault Zone. 144 4.2.1 Lithostratigraphic units description The lithostratigraphic units defined in the FACD have been established by the descriptions pro- vided by exploration wells (figure 4.2.2). From those wells selected for the stratigraphic analysis and correlations, 4 correspond to this domain: Villa Isabel #1 (VI-1), Licey #1 (LIC-1), San Fran- cisco Reef #1 (SFR-1), Caño Azul #1 (CA-1) and San Pedro #1 (SP-1). Nevertheless, as none of them reached the sedimentary sequences that comprise the Paleocene and the Eocene, this interval has been described independently, not establishing any lithostratigraphic unit. The basement was only reached at the wells SFR-1 and CA-1 (figure 4.2.3), being composed of a series of quartzites, which correspond to Unit A1, and diorites, which has been designed to Unit A2 (Caño Azul #1 mud logging report, 2000; San Francisco Reef #1 mud logging report, 1995). Although samples from these units were not dated, having been designated with a generic A, the descriptions of outcrops from the geological mapping could point out an Upper Cretaceous age. The oldest preserved sedimentary rocks were reached at the well SP-1 (figures 4.2.2 and 4.2.3), consisting of an alternation of black shales, sandstones and marls of Late Cretaceous age (Units K1 and K2). After the hiatus from Late Cretaceous to Oligocene registered on wells, Units O1 and O2 are composed of Oligocene conglomerates, sandstones and limestones that give the way to the Neogene sequences. The Miocene is characterized by the development of a carbonate plat- form (Unit N1) and the deposition of basinal deposits such as the shaly interval of Unit N2, the sandstones of Unit N5 or the alternation of mudstones, siltstones and sandstones of Units N6 and N7. Finally, the Pliocene and Pleistocene are well represented by the carbonates reached at the well SP-1. Fig. 4.2.2, Schematic stratigraphic correlation chart for the northern segment of Hispaniola, in- cluding columns from the Cibao Basin, the Cordilleras Septentrional, Central and Oriental. 145 Fig. 4.2.3, Units interpreted at the selected wells for the forearc domain. Locations in figure 4.2.1. Not to scale. 146 Unit A1 Definition: Unit A1 is defined at the well San Francisco Reef #1 (SFR-1). At the type locality, this unit comprises quartzites and laminations of dark-green and grey siltites with traces of graph- ite, biotite and pyrite (San Francisco Reef #1 mud logging report, 1995). This interval is not dated. Unit A1 is reached at the wells CA-1, SFR-1 and Pimentel Reef #1 (figure 4.2.3), situated less than 10 km to the southeast of SFR-1, representing the first unit of the basement. At the type well, this unit is overlapped unconformably by Oligocene sediments. At the well SFR-1, a section of almost 200 m of this unit were drilled (figure 4.2.4). This unit is characterised by a low calliper (~ 8-9 inches) and moderately high densities (between 2.6 and 2.7 g/cm3). Resistivities behaviour divided this unit into an upper and lower sections owing to a higher deep resistivity curve for the lower section, where Drilling Stem Test (DST) #1 was carried out, registering gas to surface in 30 min and producing a 2 – 3 ft (0.6 – 0.91 m) flare. However, Spontaneous Potential (SP) remains high (values > -50 mV), which might imply a low permea- bility. From total depth (TD) to 1798 m, Gamma Ray (GR) remains relatively low (between 40 and 70 API), increasing to high values (between 70 and 90 API) from 1798 to 1765 m. The upper section is represented by a low SP (between -90 and -50 mV) and a high GR (between 70 and 90 API) that progressively passes into medium SP values (> -50 mV) and a low GR (< 70 API). Samples of this section are composed of dark green to grey recrystalized quartzites (altered with glauconite and pyrite) and thinly laminated and silicified mudstones with kaolinite and brittle fractures. There is no dating available on well reports for these quartzites. At the well CA-1, Unit A1 cuttings are described as quartzite fragments, dark green to grey, re- crystalized, altered with glauconite, pyrite and traces of graphite and biotite; and minor mudstones with kaolinite, silicified, thinly laminated with brittle fractures (Caño Azul #1 mud logging report, 2000). At Pimentel Reef #1, mud logging reveals the presence of quartzites with silica cement, cherty in part, with traces of milky quartz with pyrite, serpentinite, red rhyolite, dunite and green igneous fragments (Pimentel Reef #1 well logging report, 1995). In the scientific literature there is not any suggested correlation between this unit and outcrops. However, as metamorphic complexes have been described at both sides of the Cibao Basin with similar properties, it could be reasonable assumed that this metasedimentary unit correlates with the metasedimentary sequences of Amina – Maimón Schists at the southern flank of the Cibao Basin (7 and sections B-B’ and C-C’ of figure 4.2.1), or with the El Guineal and Puerca Gorda schists at the northern flank (4 and section A-A’ of figure 4.2.1). The presence of ophiolitic me- langes in northern Caribbean has been attributed to the consumption of an intermediate proto- Caribbean oceanic basin, by a southwest dipping subduction during convergence, and the later exhumation after the collision (Escuder-Viruete et al., 2014, 2011; Draper and Nagle, 1991; Lewis et al., 2006; Pindell and Kennan, 2009; Saumur et al., 2010). The Amina-Maimon schists consist of metavolcanic materials and minor metasediments (carbo- naceous shales, marbles and iron formations) that are correlated with the Tholeiitic Island Arc (TIA or Primitive Island Arc of the Caribbean, PIA; Kesler et al., 1991; Escuder-Viruete et al., 2007 b and references therein). The origin of the metamorphism is related with the subduction of a part of the fore-arc region during the formation stages of the PIA (Escuder-Viruete et al., 2007 b and references therein). The deformation must be posterior to the Aptian-Albian limit (~112 Ma) and prior to the formation of the Hispaniola Fault Zone, that cut the main foliation, and the syn-tectonic Eocene to Oligocene deposits (Escuder-Viruete et al., 2007 b). The Amina – Maimón schists crop out among other metamorphic suites like the Loma La Monja Formation (LLM), the Loma Caribe serpentinized peridotites (LCP) and the Duarte complex (DC). LLM has been inter- preted as an Upper Jurassic section of the Proto-Caribbean. Together with the Lower Cretaceous basalts of the DC, they represent the substrate of the PIA (Pérez-Estaún et al., 2007; Escuder- Viruete et al., 2009). The PIA is well exposed at the volcanic suites of the Los Ranchos Formation at Cordillera Oriental (position 8 of figure 4.2.1). 147 Fig. 4.2.4, Units A1 as seen on San Francisco Reef #1 well logs. Unit A1 is divided into two sections in terms of their resistivity curves. DST-1 was carried for the lower sections, recovering non-commercial amounts of gas that produced a flare of almost 1 m. The Río San Juan (RSJC) and Puerto Plata (PPC) Complexes crop out at the northern side of the Cibao basin. The RSJC (section A-A’ in figure 4.2.1) exposes a segment of a high-P accretionary prism, built during the Late Cretaceous subduction below the intra-oceanic Caribbean Island Arc or CIA (Escuder-Viruete et al., 2016 a and references therein). The metamorphic path followed by this complex is studied in Escuder-Viruete et al (2016). This study suggests a > 100 Ma old (pre-Upper Cretaceous) stage of arc magmatism, a prograde deformative event to high-P meta- morphic conditions for the interval 110 – 95 Ma (Albian - Cenomanian), when the arc-derived igneous rocks were transformed into amphibolites, eclogites and metagabbros, a thermal peak 148 conditions at 92 – 89 Ma (Turonian), ductile exhumation and cooling to T < 550 ºC at 88 – 84 Ma (Coniacian - Santonian) and slow cooling at low P for the period 82 – 70 Ma (Campanian). These authors also relate the subduction of part of the arc with the arriving to the subduction channel of an ocean dorsal or ridge. Similar processes are interpreted for the PPC (position 2 in figure 4.2.1). It represents a series of accreted ophiolites, ophiolites melanges, intra-oceanic volcanic arcs and fragments of the south- ern margin of the North America continent (Escuder-Viruete et al., 2014 and references therein). The metamorphic path studied proposed by Escuder-Viruete et al (2014) included: a pre-126 Ma (pre-Aptian) early phase of PIA magmatism, a high-T deformative event, a post-126 Ma (post- Aptian) late phase of subduction, the intrusion of hornblende tonalites at ~90 Ma (Turonian) and the exhumation of the complex to T < 450 ºC at 90 – 82 Ma (Coniacian) and to T < 150 ºC at 35.8 Ma (upper Eocene). The study of the metamorphism at both sides of the Cibao Basin provides us the main regional events that can be applied to the evolution model of the SPB. The proposed subduction of part of the arc at Aptian - Albian times fits well with the exhumation of the Lower Cretaceous PIA that led to the erosion, recorded by the deposition of conglomerates at the Pueblo Viejo member and the Bayaguana Formation (Martin et al., 1999, Kesler et al., 1991; Kesler et al., 2005; Monthel et al., 2004 a). The PIA and these sedimentary formations were covered by the Albian Hatillo limestones (Kesler et al., 1991; Martín et al., 1999; Myczynksi and Iturralde-Vinent, 2005), rep- resenting the first regional unconformity to consider. A tentative interpretation locates the initial stages of the exhumation of the metamorphic assem- bles in a period of time between the Turonian and Santonian. As no ultramafic, metamorphic or serpentinite clasts are described in the bibliography prior to the latest Cretaceous – Paleocene, the final emplacement would have been registered by high energy formations like: the Upper Creta- ceous? - Paleocene Don Juan conglomerates at Cordillera Oriental (7 and 8 in figure 4.2.1); the basaltic breccias and conglomerates of the La Magua Formation (6 in figure 4.2.1) at Cordillera Central (Tavera Group in Palmer, 1979); and the Paleocene – lower Eocene conglomerates and serpentinite-rich Olistoliths of the Imbert Formation (2 in figure 4.2.1) (Bowin, 1966; Palmer, 1979; Boisseau, 1987; Dolan et al., 1991; Draper et al., 1996; Martin et al., 1999; Hernáiz-Huerta et al., 2004; Joubert et al., 2010 a; Escuder-Viruete et al., 2014). According to the interpretation given in this work, these processes could be related with the subsidence curves carried out for the Cretaceous – Paleogene forearc basin at Cordillera Oriental (figure 4.2.5). There are two inversion of the basin at Aptian – Albian and Campanian that finalised with the exhumation at the Maas- trichtian (Gracía-Senz et al., 2007). These constraints will be applied for the tectonic evolution model of the SPB. Unit A2 Definition: Unit A2 is defined at the well Caño Azul #1 (CA-1; figure 4.2.3). At the type locality (CA-1), this unit comprises igneous bodies composed of diorites reached from 859 m to TD (1060 m; Caño Azul #1 mud logging report, 2000). This interval is nor dated. At the type well, Unit A2 is bounded by the quartzites of Unit A1. This unit is characterized by a low SP (< -60 mV) and high conductivities (between 100 – 1000 Ω−1m−1; figure 4.2.2). Although porosities remain low in general (< 0.10), Density porosity curve points out the presence of poor to fair porosities (between 0.08 and 0.15), and that could be the reason to carry out a DST at this basement unit (Caño Azul #1 well summary, 2000). No correlation has been stablished or suggested between this unit and outcrops in the scientific literature. However, it is possible that it would correlate with the Upper Cretaceous to Paleogene tonalites intrusions that crop out along Cordillera Oriental. They consisted of tonalites and micro- diorites exposed at the geological maps of Sabana Grande de Boya and Cevicos (Monthel et al., 149 2004 b). Although the age of these tonalites is not precise, the emplacement must have taken place after the deposition of the Lower Cretaceous Los Ranchos Formation and prior to the Paleocene - Eocene Don Juan Formation (Monthel et al., 2004 b). The paleosoil generated by weathering of these bodies is appreciable and can reach a thickness up to 10 m. This could be considered as a modern analogous of the Unit O2, described at the well CA-1, above this unit (Monthel et al., 2004 b). Fig. 4.2.5, Subsidence curves for Cordillera Oriental modified from García-Senz et al. (2007 b). Two inversion are prognosed for the Albian and Campanian to Maastrichtian periods which led to the exposition of the Lower Cretaceous island arc and the Upper Cretaceous sedimentary se- quences respectively. 150 Units K1 and K2 Definition: Units K1 and K2 are defined at the well San Pedro #1 (SP-1; figure 4.2.3) at the Llanura Oriental area, next to Santo Domingo, coinciding with the northern limit of the SPB. The stratotype corresponds to an alternation of sandstones and grey-to-black shales, with minor lime- stones, marls and lignite beds, that have suffered a low grade of metamorphism (San Pedro #1 mud logging report, 1979; Munthe, 1996). The difference between Unit K1 and K2 lies in the transition from non-calcareous to calcareous sandstones in Unit K2, accompanied by an increase in limy intervals. The minimum thickness of both units is 946 m, where Unit K1 is defined from total depth (2040 m) to 1800 m and Unit K2 from 1800 to 1094 m. At the type well (SP-1), Unit K2 is overlain by middle Miocene sediments, representing the top of the formation an unconform- ity in this region of the basin. The low grade of metamorphism seems to have had an impact on the electric records, taking place a step in sonic, electric and density logs from the overlying layers (figure 4.2.6). Resistivities, for instance, pass from tens to hundreds of Ω·m while density increases from 2.2 g/cm3 for the for- mation above to 2.6 – 2.7 g/cm3 for Unit K2. Although there is a limited decrease in SP in Unite K2, the division between Units K2 and K1 is marked by the decrease in resistivities (from hundreds to tens Ω·m), accompanied by the separa- tion of the shallow and the deep curves, from 1800 to 1094 m (figure 4.2.6). This change corre- sponds with the lithologic change from the calcareous sandstones that defined Unit K2. Density also decreases slightly for Unit K1, with values between 2.5 and 2.6 g/cm3. Nevertheless, no po- rosity analysis in cores, that could have tested an increase in porosity, is available for these Cre- taceous sandstones. Shales of Unit K1 are described as grey to black, hard, dense, non-calcareous to calcareous, carbonaceous with traces of pyrite while sandstones are grey, fine to very fine, silty, slightly calcareous, moderate to well cemented (San Pedro #1 mud logging report, 1979). For this unit K2, there is an increase in limestones intervals together with a change from non- calcareous to calcareous sandstones in comparison with Unit K1 (San Pedro #1 mud logging re- port, 1979). Shales are dark grey to black and black, dense with traces of pyrite. Rock eval analysis reveal a Total Organic Carbon up to 0.52 %Wt with a kerogen that lie into the Type III on a Van Krevelen diagram (Munthe, 1996), see Chapter 5.4. Sandstones are grey, very fine to fine grain, moderate to well cemented, angular to subangular, calcareous, with traces of pyrite. Finally, lime- stones are described as hard, crystalline with veins of calcite. No correlation has been stablished or suggested between this unit and outcrops in the scientific literature or well reports. However, due to the description of cuttings and their position on the island, northwards the Hispaniola Fault Zone (HFZ), there could be a relationship between Units K1 and K2 and the Upper Cretaceous series at Cordillera Oriental, especially with the Cenoma- nian to Santonian Las Guayabas Formation and the Campanian to Maastrichtian Río Chavón For- mation. Under this assumption, both formations were studied during the field work carried out in November 2019 (see Section 3.2.1). The Las Guayabas Formation is composed of a monotonous succession of sandstones and feldespatic sandstones and shales disposed in regular centimetric to metric plane-parallel layers that crop out at Cordillera Oriental (García-Senz et al., 2007 b and references therein), around 20 km northwards San Pedro #1. This formation finalizes with a 200 m thickness radiolarian chert layer (Bourdon, 1985; Lebron and Mann, 1991; García-Senz et al., 2007 b) dated as Santonian (Van Andel, 1975). 151 Fig. 4.2.6, Units K1 and K2 as seen on San Pedro #1 well logs. Unit K1 consists of an alternation of fine grain sandstones and grey to black shales, with minor limestones, marls and lignite beds. Unit K2 has a similar composition although sandstones pass from non-calcareous to calcareous (in comparison with Unit K1) and there is an increase in limestone intervals. This might be re- flected on well logs. Resistivities for both units differ, with deep and shallow curves separated for unit K1. There is a step on resistivity and density logs at the top of these units which could be associated to a low grade of metamorphism. However, outcrops do not show any evidence of this process, revealing only a well-developed silicification. 152 During the field work, the best observations of the Las Guayabas Formation were taken at the “La Isabela” mine, where the cut has exposed a ~50 m section of this formation. The record was divided into a lower and an upper section (figure 4.2.7). Dark/grey to black shales dominate the lower sequence. Imbedded into the shales, there are centimetric layers of light-grey carbonate sandstones, with fine to very fine grains which includes fragments of globigerina. Depositional structures (sharp bases, flute casts and ripple cross-lamination among others) suggest this se- quence was deposited in a deep environment, being interpreted as thinned turbidites (figure 4.2.7). The proportion of the limy sandstones slightly increases upwards, finalising the sequence with a submetric layer, interpreted on the field as a more proximal deposit. On thin sections, sandstones reveal a high-content in plagioclase, olivine, chert and carbonate crystals. The matrix contains chlorite with a greenish tone. Above this submetric deposit, the upper section consists of and alternation of brown marls and fine grain sandstones, which dominate the sequence. No evidence of structural unconformity was found in the field (figure 4.2.7), and the change from the lower to the upper section is interpreted as a shallowing sequence of the formation, passing from a deep and shaly section, where the black tonality might be related to an anoxic deposition, to a sandier and shallower sequence under non- anoxic conditions. On the other hand, another candidate is the Campanian to Maastrichtian the Río Chavón For- mation (planktonic foraminifera stablish a late Santonian – Maastrichtian age, García-Senz et al., 2007 a), which is divided into the Las Auyamas shales member and the Río Chavón limestones. At top, the Río Chavón Formation gives way to the Maastrichtian Loma de Anglada reef For- mation (García-Senz et al., 2007 a). Las Auyamas member consists of an alternation of laminated shales and fine grain sandstones that progressively pass into the first carbonate sandstones of the Río Chavón Formation. This last consists of an alternation of calcareous sandstones; black shales with pyrite and some fragments of limestones and minor marls (García-Senz et al., 2007 1). These observations were verified at different places of the Llanura and Cordillera Oriental (figure 4.2.8). On thin sections, sandstones and calcareous sandstones of the Río Chavón Formation present parallel lamination with a high content of iron. Carbonate samples constitute levels with a great lateral continuity, corresponding to laminated limestones that alternate textures of mudstone, wackstone and packstone of globigerina. On the other hand, sandstones are organised into plane- parallel levels of very fine clasts that alternates with carbonate layers. The main components iden- tified consist of plagioclase, chert, green minerals, and in some cases chert and chlorite in the matrix. Diagenetic processes such as the formation of phyllosilicates cements and kaolinite among others have been identified. The presence of a high content of organic matter (clasts) is common in this formation. Although the presence of organic matter into the shaly sections has been also described in the geological mapping of Cordillera Oriental (Monthel et al., 2010 a), no rock-eval analysis is available for the Las Guayabas and the Río Chavón formations. Our results are presented in Section 5.4, where the source rock potential of these units is evaluated. The absence of the radiolarian chert layer (studied at top of the Las Guayabas Formation) at SP- 1, points out the Río Chavón Formation as a better candidate for Units K1 and K2. It is also possible, due to the high grade of deformation presented in the Upper Cretaceous sediments at Cordillera Oriental, that all the Río Chavón Formation and the radiolarian chert were totally eroded, and the San Pedro #1 reached the Las Guayabas Formation. However, following the de- scription given on the mud logging reports of San Pedro #1 and the geological mapping of Cor- dillera Oriental, verified during the field work, The Río Chavón Formation fits better with Units K1 and K2. In this sense, non-calcareous sandstones and shales of Unit K1 would be correlated with Las Auyamas member that progressively passes into calcareous sandstones and black shales of the Río Chavón limestones, that would be represented by Unit K2. 153 Fig. 4.2.7, Examples of outcrops from the Las Guayabas Formation taken at the La Isabela min- ing during the field work carried out in November 2019. A, General view of the outcrop, which has been divided into the lower and the upper section. B and C, details of the lower section. Sharp bases shown by red arrows and ripple cross lamination by yellow arrows. D, geological map of the central and eastern sectors of Hispaniola. SP indicates the position of the well San Pedro #1 and LI of the La Isabela mine. Other acronyms: HFZ, Hispaniola Fault Zone; SFZ, Septentrional Fault Zone; RYFZ, Río Yabón Fault Zone. E, Structural relationship between the upper and the lower sections. No unconformity was identified in the field. 154 Fig. 4.2.8, Examples of outcrops from the Río Chavón Formation taken at the trace of the Río Yabón Fault Zone (RYFZ) (A-C) during the field work carried out in November 2019 and at Cor- dillera Oriental (E, from Monthel et al., 2010 a). A, General view of the outcrop, which consisted of the northern flank and the hinge of an anticline. B detail of the northern limb, when Z structures were identified. C, Detail of the dark-grey to black shales and the shaly limestones. D, geological map of the central and eastern sectors of Hispaniola. Key to acronyms: HFZ, Hispaniola Fault Zone; SFZ, Septentrional Fault Zone. E, Outcrops at Cordillera Oriental show the same strati- graphic style, with the alternation of dark-grey to black shales and light-grey to white shaly lime- stones. 155 The progressive compositional change from the Las Guayabas to the Río Chavón formations is correlated here with the inversion of the forearc region since Campanian times (figure 4.2.5). As a result, the Maastrichtian platform was finally exposed and eroded. Signs of weathering were detected at the top of Unit K2 at the well Santo Domingo #1, next to San Pedro #1 (Santo Do- mingo #1 well report, 1979). This would explain the absence of the Loma the Anglada carbonates, that were eroded at that position. The composition of the Upper Cretaceous sandstones has been studied at Cordillera Oriental. Most of the grains are derived from an immature island, therefore the quartz content is low, figure 4.2.9 (García Senz et al., 2007), and similar composition should be expected for the SPB. Figure 4.2.9, QFL triangular diagrams from samples of Llanura Oriental. Modified from García- Senz et al., 2007 b. Upper Cretaceous formations in the area have suffered two deformation episodes related to main tectonic events. The first compressional event took place during the Late Cretaceous, folding the sedimentary beds. This event was subsequentially replace by a transpressional regime that de- formed and cut the pre-existing structures, since Paleogene – Eocene (García-Senz et al., 2007 2). These new constraints will be extrapolated to the evolution model of the SPB. One explanation for the metamorphism documented at SP-1 could be the proximity of the well to the HFZ. Although, it has not a surface expression at the vicinities of San Pedro #1, it is possible to follow the magnetic anomaly produced by serpentinized peridotites that crop out at the trace of the HFZ (figure 4.2.10). This anomaly extends from the northern flank of cordillera central, passes close to San Pedro #1 and enters into the San Pedro Basin in the proximities of Santo Domingo. Close to the trace of the Río Yabón Fault Zone (RYFZ), folds that affected the Río Chavón For- mation present z- and m- structures (figure 4.2.8), more common in ductile conditions. However, samples collected during the field work from the Las Guayabas and Río Chavón formations do not show any indicator of metamorphism. What could be corroborated was a highly developed process of silicification for most samples that could be the responsible of the hardness of these rocks. Therefore, although only silicification was encountered in field samples, a certain grade of metamorphism should not be discharged for Upper Cretaceous units close to the main magnetic anomalies in the SPB The Llanura Oriental is also cross-cut by RYFZ to the east, where other serpentinized materials have been identified in outcrops, as it is reported in the Rincón Chavón and Miches geological maps (Díaz de Neira et al., 2004 a; García-Senz et al., 2004). They have been possibly exhumed by the action of this transpressive fault systems. On the Reduce to Pole (RTP) maps (figure 156 4.2.10), other high amplitude anomalies parallel to the traces of HFZ and RYFZ are observed and interpreted in this work as metamorphic material that could be accreted between the two fault zones. This material would constitute the basement of a part of the Llanura Oriental, in a similar way that in the Cibao Basin, and can be extended to the northern limit of the SPB. Fig. 4.2.10, Reduced-to-pole magnetic anomaly map for the eastern area of Hispaniola (modified from Gorosabel et al., 2020). Purple doted lines separate the fore arc / collisional (FACD), the island arc (IAD), the Cretaceous to Eocene Basin (CEBD) and the Oceanic / Caribbean (OCD) Domains. The main structures are interpreted combining geological maps, digital elevation mod- els, gravity and magnetic anomalies. Anomalies parallel to HFZ and RYFZ (yellow arrows) are interpreted as accreted metamorphic materials that would constitute part of the basement of the FACD. Paleocene to Eocene sedimentary rocks According to well reports, no Paleocene nor Eocene sedimentary rock has been penetrated at the exploration wells drilled at this domain. Nevertheless, they crop out along the boundaries of the Cibao Basin and the southern flank of Cordillera Oriental, and their study provides new constrains and information about regional unconformities and tectonic events. At Cordillera Septentrional (location 2 in figure 4.2.1), and next to metamorphic complexes (Puerto Plata and Río San Juan Complexes), Paleocene to Eocene outcrops consist of serpentinite rich conglomerates and olistoliths (Nagle 1966; 1979; Pindell and Draper, 1991; Draper and Nagle, 1991). This material was transported by gravitational processes to a deep section of the Paleocene / Eocene basin, where grey to blue shales were being deposited (Hernaiz-Huerta et al., 2010; Monthel et al., 2010 b). Figure 4.2.11 shows a good example of the San Marcos Formation at Puerto Plata (Monthel et al., 2010 b). The deposition of serpentinite rich and other metamorphic materials gives us a good constrain about the final exhumation phase of the metamorphic material. In addition, Pindell and Draper (1991) propose a diapiric emplacement for this Paleogene for- mation, which gives information about the potential plastic behaviour of the Paleocene – Eocene shaly formations under pressure conditions. 157 Fig. 4.2.11, Example of the San Marcos Formation at the surroundings of Puerto Plata. It consists of blue / grey shales with conglomerates, breccias and olistoliths embedded. Note the size of some of these olistoliths. Located at position 2 in figure 4.2.1. To the southern side of the Cibao Valley, at the northern flank of Cordillera Central (6 in figure 4.2.1), Paleocene to Eocene outcrops consists of a series of reddish conglomerates (Palmer, 1979; Joubert et al., 2010 a). The clasts are well rounded, mainly between 10 and 30 cm, although their size can reach 1 m. Their composition is variable including basic igneous rocks, granitoids, cherts, limestones, among others (Joubert et al., 2010 a). The red tone is derived to a subaerial deposition (Palmer, 1979; Dolan et al., 1991), which provides a good paleogeographic control, the central segment of Hispaniola was exposed at this period of time. Similar conglomeratic deposits crop out at Llanura Oriental next to the southern flank of Cordil- lera Oriental (8 in figure 4.2.1), consisting also of reddish conglomerates, mainly composed of volcanic clasts, but tuffs, limestones and shales are observed too (Martín et al., 1999). They cor- respond with the Don Juan Formation that was formally proposed by Bowin, 1966. Similar con- glomerates have been identified at the 1:50000 geological maps of Sabana Grande de Boyá, Monte Plata, Antón Sánchez, Bayaguana, Hato Mayor del Rey and Miches (García-Senz et al., 2004). The conglomerate section passes into sandstones and shales and vertically into limestones, where globigerinas and radiolarians are dated as lower to middle Paleocene (Boisseau, 1987). Clasts of serpentinites have been observed embedded into this formation, giving us another con- straint about their exhumation age. Next sequences are represented by middle – upper Eocene siltstones and sandstones that pass vertically into micritic (wackstones) and fossiliferous limestones (packstones-rudstones, mainly composed of red algae and micro-foraminifera), corresponding to the La Luisa Formation at the geological map of Monte Plata (Hernaiz-Huerta et al., 2004 a). The relationship with the con- glomerates has not been observed. Although the correlation has not been studied in the scientific literature, these Eocene limestones could be related with the Paleocene – Eocene limestones of the Bejucal Formation at the eastern-most part of Llanura Oriental (García-Senz et al., 2004). This last consisted of micritic limestones (wackstones) that are followed by red algae and reefal limestones that also overlie the conglomerates belonged to the Don Juan Formation. These Paleo- cene – Eocene limestones were eroded together with part of the Upper Cretaceous sedimentary sequences and redeposited in a series of calcareous sandstones and calcirudites with an age of middle Eocene (Lebron and Mann, 1991; García-Senz et al., 2004). This is interpreted here as a new middle – upper Eocene unconformity after the deposition of shallow marine limestones in the region during a calmer episode at early to middle Eocene, that must be addressed in a regional evolution model. 158 Unit O2 Definition: Unit O2 is defined at the well Caño Azul #1 (CA-1) from 748 to 853 m. The stratotype corresponds to of an alternation of unconsolidated sandstones, conglomerates, earthy limestones, dolomites and shales with lignite beds of Oligocene age. The age is well constrained to the Oli- gocene by foraminifera and micro-fossils (Guerra and Percival, 2000). Unit O2 is also interpreted in this work at the wells SFR-1, LIC-1 and VI-1 (figure 4.2.3). This interpretation is based on the position of the section in the well records, lithological similarities and the seismic interpretation. The description of this unit is limited to mud logging reports and well summaries (Caño Azul #1 mud logging report, 2000; Caño Azul #1 well summary, 2000). From cuttings description, limestones are defined as white to tan, chalky in part with a sucrosic texture. The proportion of sandstones increases downhole, dominating the section from 800 m to TD (figure 4.2.12). In general terms, sandstones are defined as clear to grey and unconsolidated levels composed of fine to very fine grains. Clasts of quartz, hornblende and biotite indicate that they can be derived from Units A1 and A2. Together with the presence of earthy limestones and unconsolidated sands, another main feature is the occurrence of lignite beds. Deep lignite beds near a high-pressure sulfur water zone, tested total organic carbon (TOC) values as high as 14% (Caño Azul #1 well summary, 2000). This unit is characterised by the chaotic character of the calliper curve (figure 4.2.12), which implies an alternation of good and bad hole conditions, possibly due to the alternation of litholo- gies, with unconsolidated materials falling down-hole. This influences the measurement of the density porosity log and to lesser extent for the neutron porosity, observing the same chaotic behaviour for their curves. GR remains generally low (between 20 and 60 API) although it should be noted here that GR is not compensated for borehole conditions and mud weight. SP (non- compensated neither) alternates from high values for the top and the centre of the unit (> -22 mV) to low at the base (< -22 mV), possibly connected with the dominant lithology, limestones or sandstones. Similar lithologies are described on mud logging reports for sections at the wells SFR-1, LIC-1 and VI-1, especially those considered in this work as indicators of this units as the presence of lignite beds together with earthy limestones and unconsolidated sandstones.  At SFR-1, the interpreted Oligocene record is dominated by limestones (from 1576 to 1676 m), in a similar way than at CA-1. Cuttings are described as yellow to grey, mi- cro/crypto-crystalline, silty, bulky, micritic and hard limestones; grey to black, firm to hard siltstones in argillaceous matrix with carbonaceous materials; and minor grey, clean, microconglomeratic together with well cemented sandstones. For the lower section (from 1600 to 1731 m), sandstones progressively dominate the record, composed of grey, fine to medium grains, unconsolidated sandstones; grey to orange, micro/crypto-crystalline, laminal, hard limestones with traces of corals; and grey to black, soft to firm, siltstones with pyrite, glauconite and carbonaceous materials (San Francisco Reef mud logging re- port, 1995).  At LIC-1, the upper part of the interpreted Oligocene section (from 3100 to 3300 m) comprise tan and hard together with white, chalky, soft and earthy limestones; calcareous shales; and grey, consolidated to poorly consolidated, silty sandstones. An intermediate zone (from 3500 m to 3500 m) is dominated by lite grey, fine grain, calcareous, poor consolidated sandstones; and grey/dark grey, calcareous shales with minor carbonaceous intervals and white/tan, hard to earthy limestones. Finally, from 3500 m to TD (3666 m) the proportion of limestones increases again consisted of white, very soft and earthy/sandy limestones accompanied by grey, very fine and poorly consolidated sand- stones and shales.  At VI-1, from 2498 to 2740 m, the section is dominated by very hard, tan/grey and white/milky, chalky and soft limestones with lignite intervals and grey to black shales. An intermediate zone (from 2740 to 2930 m) the section comprises dark grey, calcareous 159 shales; tan/buff chalky, soft to sandy limestones and the appearance of grey fine grain, coarse and consolidated sandstones. To the bottom (from 2930 to 3318 m), the section consists of white/tan, soft, earthy/sandy with minor white, hard limestones; and black/blu- ish, hard and calcareous shales. The wells CA-1 and SFR-1 were tied to seismic which allow the stratigraphic interpretation of the different lines. On seismic line PET-ONCE-07, Oligocene sequence (determine by the CA-1 dating) lie directly over the basement unconformity represented by high amplitude reflectors while is covered by a lower Miocene platform (figure 4.2.13). The onlap of this sequence on the basement reflects a retrogradation of the system in an Oligocene transgression. Although the seis- mic quality is limited at the position of SFR-1 (profile ONCE-05), the interpreted Oligocene se- quence lies over the basement in a similar way, observing the same transgression. The only dif- ference is that in the case of SFR-1, the Oligocene interval is covered by a distal section of the Miocene platform as this well was drilled basinwards. Fig. 4.2.12, Units O1 and O2 as seen on Caño Azul #1 well logs. Note the chaotic behaviour of the calliper, implying an alternation of good and bad hole conditions, possibly due to the presence of unconsolidated sections. 160 Fig. 4.2.13, Above: Caño Azul #1 over seismic section Pet-ONCE-07. Below: San Francisco Reef #1 over seismic section ONCE-05. Well-logs, to the right gamma ray (black) and spontaneous potential; to the left, resistivities. Note the transgression of this level to the south determined by the onlap over the basement and marked by the white arrows. This kind of transgressions are relevant for this study because landwards onlaps might create stratigraphic traps, as it is revealed by the high-pressure sulphurous water and gas that was reached at a depth of 822 m at CA-1. Blow-out preventers had to be used while drilling and the upcoming fluids invaded the porous formations above (Caño Azul well summary. 2000). Unit O2 has not been correlated with outcrops neither the scientific literature nor well reports. Nevertheless, due to their similarities, Unit O2 could be reasonably represented by the Oligocene alternation of sandstones, conglomerates, shales and limestones (figure 4.2.14) that crop out at 161 the 1:50000 geological maps of La Vega and Jánico (Escuder-Viruete et al., 2010; Joubert et al., 2010 a), at the southern limit of the Cibao basin (location 6 of figure 4.2.1). The transgression identified on seismic profiles could be explain by Oligocene outcrops like those from the Los Velazquitos Formation. From bottom to top, it is composed of a basal section of conglomerates and breccias, that intercalates metric layers of sandstones and sandy siltstones. They pass upwards into a decametric section of calcarenites with concentrations of benthic macro- foraminifera, red algae and shallow fauna (bivalves and corals), organized in decimetric accumu- lations of bio-clasts. Finally, at top, this formation passes into an alternation of sandstones, shales and marls with minor calcareous shales and subordinated calcarenites (Joubert et al., 2010 a and references in there). So, there is a deepening of facies, from conglomerates and shallow limestones to an alteration of sandstones, shales and marls. Sands from Unit O2 are interpreted here as syn-tectonic deposits. As the presence of grains of quartz, hornblende and biotite suggest (present in Units A1 and A2), while basement and meta- morphic rocks were exposed, they were eroded and deposited in the nearby area. In this sense, unconsolidated sands could represent a fossilized regolith, consequence of the exhumation of Units A1 and A2. Fig. 4.2.14, Oligocene samples at the northern flank of Cordillera Central (position 6 of figure 4.2.1). Above: Alternation of consolidated and unconsolidated layers of the Jánico Formation at the geological maps of La Vega (Escuder-Viruete et al., 2010). Below: Left, matrix supported conglomerates of the Represa Formation; right, bioclastic limestones of the Velazquitos For- mation (Joubert et al., 2010 a). Unit O1 Definition: Unit O1 is defined at the well Caño Azul #1 (CA-1) located above Unit O2, from 731 to 748 m (figure 4.2.3): The stratotype corresponds to an almost 20 m package of Oligocene black shales. 162 The information regarding to this level is limited to the well summary (Caño Azul #1 well sum- mary, 2000), where this layer is defined as a 55-foot thick (~20 m) bed of organic-rich shales with TOC values ranging from 0.32 to 1.05 %Wt. This level yielded the only oil cut observed of all the samples tested in the well. The results of the analysis concluded that this bitumen was not formed in place but resulted from migrated oils (Caño Azul #1 well summary, 2000). On well logs, it is represented by a local maximum of gamma ray and a high spontaneous potential (figure 4.2.12). Similar packages of black shales are not described at the wells San Francisco Reef #1 and Licey #1. However, at the well Villa Isabel #1, there is an interval that could correlate to Unit O1. This section consists of dark grey to blue, hard, brittle and black, hard, very calcareous shales repre- sented by high spontaneous potential and low resistivities. This would imply that the distribution of Unit O1 is not homogeneous at the Cibao Basin and its deposition would be associated with structural lows or local isolated basins. However, the limited seismic quality and coverage do not allow to solve this issue and further investigations must address this topic. Unit O1 has not been correlated with outcrops at any available technical or scientific report. In this work, it is interpreted that it could correspond with the shaly layers of the Oligocene Altamira and La Toca formations (figure 4.2.15, above and below respectively) at Cordillera Septentrional (locations 1 and 2 in figure 4.2.1). Unfortunately, descriptions of Oligocene shales at Cordillera Septentrional are limited and their source quality for hydrocarbons is poorly understood. Fig. 4.2.15, Oligocene outcrops from Cordillera Septentrional at the Cibao Basin. Above, Alta- mira Formation from Pérez-Varela and Abad (2010) at location 1 of figure 4.2.1. Below, La Toca Formation from Monthel et al. (2010 b) at location 2 of figure 4.2.1. 163 Unit N1 Definition: Unit N1 is defined at the well Caño Azul #1 (CA-1) from 154 to 732 m (figure 4.2.3). The stratotype correspond to an alternation of Miocene limestones, reefs and chalks (Caño Azul #1 well summary, 2000). Foraminifera and micro-fossils determine that these limestones are lower to middle Miocene (Guerra and Percival, 2000). Although the descriptions of lithologies are limited, Unit N1 has been divided into the sub-units N1.1, N1.2 and N1.3, in terms of a clear change in lithologies and logfacies (from Caño Azul #1 mud logging report, 2000; Caño Azul #1 well summary, 2000):  Sub-unit N1.2 consists mainly of chalky limestones (white to cream, bulky, with traces of calcite) with minor reef facies. At 224 m, an 18 m Miocene reef exhibited vuggy po- rosity and took over 1,000 barrels of drilling fluid during a loss of circulation. This sub- unit is characterized by medium resistivities (between 100 and 300  Ω·m, figure 4.2.16), while SP remains high (20 – 30 mV) and GR exhibits low values (18 – 30 API) alternated with small intervals of high values (up to 85 API).  Sub-unit N1.1 is represented by a massive lower to middle Miocene reef which consists of white/tan/pink, hard, bulky and firm limestones with intervals of vuggy porosity. The electro facies of this section is represented by a medium SP (-20 mV, figure 4.2.16) that decreases to low values (up to -50 mV) combined with an alternating GR, generally low (between 20 – 30 API). However, the most representative feature of this sub-unit is a low resistivity, that reaches the minimum (~ 3 – 5 Ω·m for the deep induction logging resis- tivity or RILD) at the central interval (between 420 and 600 m), where medium (RILM) and deep (RILD) resistivity curves are clearly separated. The reduction in resistivity is interpreted here to be related to the presence of formation fluids in a well-developed vuggy porosity, as density porosity curve suggests. Reservoir properties were also tested by 3 DSTs, although they only confirm the presence of non-commercial gas accumula- tions.  Sub-unit N1.3 consists of an alternation of lower Miocene limestones and shales. Resis- tivity ranges from low to medium values (3 – 20 Ω·m) where low values also fit with high porosities in the density porosity curve (figure 4.2.16). SP increases to high values (between -10 and -3 mV) while GR alternates depending on the lithology, from low val- ues for limestones (20 – 30 API) to local highs for shales (40 – 50 API). From the top of this unit to the base of Unit O2 the calliper register became chaotic (figure 4.2.16) which is correlated with the abruptly changes in Neutron logs and may represent the alternation of consolidated and unconsolidated layers in the borehole. Drill Stem Tests (DST) were carried out for sub-units N1.1 and N1.3. They produced saltwater and non-commercial quantities of gas. Petrophysics reveals good porosity intervals for both units with a Net/Gross ratio of 0.88, 0.35 and 0.53 for sub-units N1.1, N1.2 and N1.3 respectively. This information is analysed in more detail in Section 5.3 (Wells post-mortem) and 5.5 (Reservoir). No correlation has been established or suggested between this unit and outcrops in the scientific literature or well reports. Nevertheless, although no lower to middle Miocene reef is described in the bibliography for the terrains that composed this domain, some outcrops at Cordillera Septen- trional could have registered the distal deposits of the carbonate system and are interpreted here as the distal record of Unit N1. For instance, next to the abandoned locality of Jina Clara (position 5 of figure 4.2.1), outcrops corresponding to coral-rich fragments and bio-clasts, embedded into shales, are described at the geological map of Villa Riva (6273-IV, Monthel et al., 2010 c). They could have registered the presence of a lower to middle Miocene platform in the nearby, being in this case, the distal facies of unit N1. Another example of distal facies could correspond to limestones of the La Angostura Formation, described at the Pimentel geological map, that consists of calcarenites and massive limestones (Pérez-Varela et al., 2010 b). 164 Fig. 4.2.16, Unit N1 as seen on Caño Azul #1 well logs. It consists of lower to middle Miocene carbonates that have been divided into three sub-units. Sub-unit N1.1 is represented by a massive reef, differentiated by a lower SP and high resistivities, with deep and shallow curves clearly separated (note that resistivity curves are inverted as only conductivities were available at the database). Sub-unit N1.2 is represented by chalky limestones with a medium to high SP. Sub-unit N1.3 consists of lower Miocene limestones and shales with a medium SP and high resistivities (deep and shallow curves non separated). 165 Distal to intermediate facies could correspond with the limestone sections reached at SFR-1 (fig- ure 4.2.17). At this well, Unit N1 (sub-unit N1.2) is formed of orange/yellow to grey, crypto to micro-crystalline, slight silty, massy and hard limestones; and grey to black, slight sandy, firm to soft siltstones with traces of coral fragments (San Francisco Reef #1 mud logging report, 2000). They are defined by an alternation of low and high GR values together with a high SP and low resistivities. A high SP combined with a low resistivity might indicate the shaly character of the interval, while low GR values fit with an increase in limestones. All together are interpreted here as an indicator of ramp deposits from a relatively close platform. Fig. 4.2.17, Lower to middle Miocene bio-clasts rich shales and limy sandstones at Cordillera Septentrional, next to the abandoned locality of Jina Clara, from the geological map of Villa Riva, (Monthel et al., 2010 c). Position 5 of figure 4.5. Unit N2 Definition: Unit N2 is defined at the well Licey #1 (LIC-1). The stratotype corresponds to an alternation of Miocene shales and sandstones, where fine materials dominate the sequence. Unit N2 is also reached at the well VI-1 (figure 4.2.3). For the intervals where sandstones dominate the record, this unit has been classified as sub-unit N5. At the type well, samples from this unit consist of grey to dark grey, soft and black, hard, calcareous shales; with minor well consolidated sandstones (Licey #1 mud logging report, 1958; Villa Isabel #1 mud logging report, 1958). The main features on electric logs are a high and flat SP (~4 mV) and low resistivities (~4 Ω·m at SFR-1 and 10 at VI-1). SP decreases slightly for the minor sandstone intervals (figure 4.2.18). In terms of correlation, Unit N2 is interpreted in this work as the most distal facies, deposited in the basial part of the basin, of the carbonate system represented by Unit N1. In this case, Unit N1.2 at San Francisco Reef #1 would be an intermediate region between the reef facies and the shaly section here described. There are good examples of lower to middle Miocene shales that have been exposed and crop out along the trace of the Septentrional Fault Zone and could be correlated with Unit N2. The La Toca Formation, described on the geological map of Santiago (6074-II Urien et al., 2010, at location 3 of figure 4.2.1), is composed of grey marls with minor fine grain sandstones and siltstones which are covered by a layer of conglomerates and debris flows, figure 4.2.19. 166 Fig. 4.2.18, Unit N2 and sub-units N5 as seen on San Francisco Reef #1 well logs. Sub-unit N5 consists of lower and middle Miocene sandstones, differentiated by the presence of carbonaceous material and lignite beds. Two intervals are better recognised by a decrease in SP, while the increase in resistivities is only slight. Unit N2 consists of grey to black, hard, calcareous shales with minor well-consolidated sandstones. This unit is represented by a high spontaneous potential together with low resistivities that can alternate medium to low GR values. 167 Similar layers are described at the geological map of Pimentel (6173-I, location 5 of figure 4.2.1), like the La Jagüita unit, consisted of dark shales and calcareous sandstones together with levels of conglomerates and breccias. This unit starts with a metric layer of bio-clastic sandstones that passes upwards into an alternation of grey shales and laminated sandstones with carbonaceous vegetal content (Pérez-Varela et al., 2010 b). The layers of sandstones hardly reach a thickness of 50 cm. There are also levels of breccias, derived from a carbonate platform, and conglomerates embedded in a shaly matrix. Similar lithologies have been described at the geological map of Villa Riva (6273-IV) for the the Arroyón – Los Cafés unit (figure 4.2.19). Sandstones involved in these formations, composed of fine grains, including carbonaceous mate- rials (Monthel et al., 2010 c; Pérez-Varela et al., 2010 b) could correspond with the deeper section of Unit N5 at the wells of San Francisco Reef #1, Licey #1 and Villa Isabel #1 (figure 4.2.3), that will be described next. Calais et al., 1992 interpreted two tectonic phases for the Neogene at the westernmost segment of Cordillera Septentrional, one for the Aquitanian – Burdigalian and another for the Langhian – Serravallian. Then the presence of conglomerates, breccias and debris flows (figure 4.2.19) could be attributed to the early Miocene (Aquitanian – Burdigalian) unconformity. Fig. 4.2.19, Left, lower to middle Miocene debris flow example above grey marls from the geo- logical map of Santiago. Right, bioclasts identified on shaly intervals (Urien et al., 2010 a). - Sub-unit N5 Definition: Belonged to Unit N2, the sub-unit N5 is defined at the well San Francisco Reef #1 (SFR-1) for the intervals where sandstones dominate the record over shales. The stratotype cor- responds to an alternation of fine to medium grain sandstones and siltstones with beds of lignite (San Francisco Reef #1 mud logging report, 1995). At the FACD, sub-unit N5 is reached at the wells SFR-1, LIC-1 and VI-1 (figure 4.2.3). The main feature that differentiates from other younger sandstones is the presence of carbonaceous material and lignite beds. 168 There are two intervals of sub-unit N5 separated by a layer of shales from the Unit N2 (figure 4.2.18). Interval 1 is described at the well SFR-1 from 1189 to 1341 m as a succession of grey, fine to medium grain, sandstones with trace of calcite cement; and grey to yellow/brown, soft to firm siltstones in argillaceous matrix (San Francisco Reef #1 mud logging report, 1995). At top, resistivities increase slightly although remains relatively low and come to low values to the lower half of the interval. Descriptions of samples at LIC-1 and VI-1 consist of an alternation of grey, poor to well consolidated, silty sandstones; and grey / grey to black, sandy to silty, hard shales; with a limestone section at top (Licey #1 mud logging reports, 1958; Villa Isabel #1 mud logging reports, 1958). Interval 2, reached from 540 to 975 m at San Francisco Reef #1, consists of sandstones, siltstones and occasionally limestones that included layers of coal. Sandstones are grey, fine grain, well cemented, hard and with crystalline veins of quartz (San Francisco Reef #1 mud logging report, 1995). From 792 to 853 m sandstones are described as grey, microconglomeratic, with silt, lithic clasts and coal (hard beds of black and subbituminous coal with brittle fractures). Electro-facies of this section consist of a low SP combined with low resistivities (although higher than for the shaly Unit N2), and the presence of coal beds would be represented by higher values on SP com- bined with a medium GR. These intervals are recognised by a decrease in the SP-1 (from -2 / -10 mV for Unit N2 to -30 / - 50 mV for sub-unit N5, at SFR-1) and calliper curves (~13 inches for Unit N2 and ~8 inches for sub-unit N5, at SFR-1), accompanied by a slight increase in resistivities (from 2 Ω·m for Unit N2 up to 15 Ω·m for sub-unit N5). Petrophysics of this unit is analysed in Section 5.5. As it was previously exposed, sub-unit N5 could be correlated with the lower to middle Miocene fine-grain and laminated sandstones of the La Toca Formation and the Jagüita, Arroyón – Los Cafés units, at the eastern area of the Cibao Basin (location 5 in figure 4.2.1), and with the La Jaiba unit to the west (location 1 in figure 4.2.1). This last consists of middle Miocene conglom- erates and sandstones with rests of vegetal carbonaceous material. Middle Miocene conglomer- ates have been described also for the La Trina Formation at the geological map of Santiago (6074- II Urien et al., 2010; location 3 in figure 4.2.1) and the La Piragua Formation at the geological map of Pimentel (6173-I Pérez-Varela et al., 2010 b). They could represent the second uncon- formity (Langhian – Serravallian; Calais et al., 1992), constraining the age of Unit N5 to the interval early Miocene for the lower part and to middle Miocene for the upper. Ternary plots of quartz, feldspar, and lithic fragments (QFL) illustrates a change in composition with time from an undissected magmatic arc to a dissected arc (De Zoeten and Mann, 1999). However, the quartz content can remain low even for Miocene samples (figure 4.2.20) with a great proportion of lithics which would imply bad reservoir properties. Figure 4.2.20, QFL triangular diagrams from samples of the Cibao Basin. Modified from De Zoeten and Mann. 1999. 169 Unit N6 and N7 Definition: Unit N6 is defined at the well San Francisco Reef #1 (SFR-1). The stratotype corre- sponds to an alternation of mudstones, siltstones and minor sandstones. Unit N6 is also reached at the wells CA-1, LIC-1 and VI-1 (figure 4.2.3). At the type well, this unit consisted of a series of Miocene greenish to dark grey and yel- low/brown, soft to firm mudstones and shales; dark grey, firm to hard siltstones in an argillaceous matrix and minor sandstones (San Francisco Reef #1 mud logging report, 1995; Licey #1 mud logging reports, 1958; Villa Isabel #1 mud logging reports, 1958). This unit is defined by a low resistivity (< 10 Ω·m) together with a high SP (~-10 mV). Definition: Unit N7 is defined at the well Licey #1 (LIC-1; figure 4.2.3). The stratotype corre- spond to Miocene grey, well-consolidated sandstones; grey, soft to firm and silty shales; and limestones (Licey #1 mud logging reports, 1958). None of the other wells at the FACD reached Unit N7. This unit is characterized by a high to medium SP at top (~-10 mV) that changes into low values at base (~-20 mV), where sandstones and limestones dominate the section over shales. Resistivi- ties are generally low, decreasing slightly for the lower half of the unit, but always lower than 5 Ω·m. Units N6 and N7 could correlate well with the upper Miocene – lower Pliocene the Castillo For- mation, described at the geological maps of Pimentel (6173-I, Pérez-Varela et al., 2010 b) and Villa Riva (6273-IV, Monthel et al., 2010 c; location 5 in figure 4.2.1). It was defined by Gug- lielmo, 1986, and studied also in Gugliemo et al., 1986; Nadai, 1987; Nadai and Winslow, 1988; and Guglielmo and Winslow, 1988. The Castillo Formation has been divided into three sub-divi- sion following a lithological criterion. The lower member is composed of marls and shales. The intermediate zone is composed of an alternation of marls and fine-grained calcarenites that pass into the upper zone to decimetric layers of calcarenites separated by thin layers of marl (figure 4.2.21). The lower zone could fit well with Unit N6. In this case the intermediate zone would be a transition section to Unit N7, represented by the upper zone. Fig. 4.2.21, Examples of the Castillo Formation from Monthel et al., 2010 c. Left, marls and shales from the lower zone. Right, calcarenites from the upper zone. Position 5 of figure 4.5. 170 Unit N4 Definition: Unit N4 is defined at the well San Pedro #1 (SP-1; figure 4.2.3) from 674 to 908 m. The stratotype corresponds to middle – upper Miocene limestones at top that alternate with sand- stones and shales at base (San Pedro #1 mud logging report, 1979). A higher presence of lime- stones differentiates the base of Unite N4 from the top of Unit N2. Despite of the lack of samples for a great proportion of this units, the upper limit is given by a change in sonic and resistivity logs (figure 4.2.22). As for the units above, the absence of samples might be caused by the presence of caverns in the carbonate sections. Although this unit was separated due to a higher carbonate content than for Unit N2, the lack of complete descriptions does not allow a proper correlation. However, it is possible that it could be related to Units N6 and N7, owing to its estimated age (middle – late Miocene according to Munthe, 1996) and the Pliocene carbonate sequence defined uphole. Units P2 and P3 Unit P3 has been defined from 0 to 518 m at the well San Pedro #1 and consists of Pliocene – Pleistocene carbonates with low resistivities (figure 4.2.22). Sonic log alternates from low to me- dium velocities, increasing towards the base, where there is a clear change in resistivity logs that leads to Unit P2, from 518 to 674 m. Sample gaps are supposed to be produced by caverns, causing circulation lost, possibly located at zones with abnormally low sonic velocities (figure 4.2.22). Regional geology describes the presence of an intense karstification in Pliocene – Pleistocene limestones (Braga et al., 2012) that could correspond with Units P2 and P3. These formations studied in the nearby comprise the Pliocene to lower Pleistocene Yanigua Formation, the Pliocene to lower Pleistocene Los Haitises Formation and the Pleistocene La Isabela Formation. The Yanigua Formation is composed of a monotonous succession of marls interpreted as depos- ited in the lagoon area of the carbonate platform. It could intercalate detritic and calcareous layers, passing into the Los Haitises Formation progressively (Braga et al., 2012 and references therein). The Los Haitises Formation constitute a 3 – 4 km band of reef facies located to the south of the Yanigua Formation. It has been weathered and karstified. The Pleistocene La Isabela formation was deposited in a lower step to the south than the Los Haitises Formation. It is composed of reefal limestones that register a relative sea level falling. This falling state since the Pleistocene might have caused the weathering of the previous Los Haitises Formation. 171 Fig. 4.2.22, Units N4, P2 and P3 as seen on San Pedro #1 well logs. Unit N2, composed of shales and minor sandstones, is represented by a low GR combined with low resistivities. As in other wells, Unit N2 can include low SP values. An increase in the carbonate proportion leads to Unit P4. Despite of the lack of samples, Unit P2 is determined by its higher resistivities. The absence of cuttings is assumed to be caused by the presence of caverns in the carbonates of Units P2 and P3. Pliocene – Pleistocene limestones in the area reveal the presence of an intense karstification that could be connected with these caverns and the loss of circulation at the San Pedro well. Abnormally low sonic velocities are indicated by yellow arrows. 172 4.2.2 Wells correlation As it has been previously explained, the selection of wells for a deeper study and correlation was based on their lithologies, total depths and quality of the logs. A total of nine wells of the island were chosen and from those, five belong to the fore-arc / collisional domain figure 4.2.23: San Pedro #1 (SP-1), Caño Azul #1 (CA-1), San Francisco Reef #1 (SFR-1), Licey #1 (LIC-1) and Villa Isabel #1 (VI-1). The different units presented through section 4.2.1 (defined in terms of lithology, age and electric logs) have been used for the well correlation. At the same time, the integration of wells and 2D seismic lines helps with the correlation of units, like the Unit O2, interpreted between the basement unconformity and the posterior infill of the basin (see figure 4.2.12). Fig. 4.2.23, Position of the wells selected for the stratigraphy analysis and correlation given on figure 4.2.25. The basement is only reached at the wells CA-1 and SFR-1 consisting of metamorphic (quartzites of Unit A1) and intrusive (Unit A2) formations. The low grade of metamorphism identified for Units K1 and K2 at the well SP-1 might be local, associated to the activity of the main fault zones (like the HFZ), as no indicator of this process is observed in outcrops (only a high grade of silic- ification). Based on seismic interpretations and the presence of key lithologies that agree qith Oligocene outcrops (like unconsolidated sands, earthy limestones and lignite beds), Unit O2 is interpreted at the well SFR-1. However, this interpretation can be extended to the wells LIC-1 and VI-1 thanks to their well logs. The interpreted Oligocene sequence has been divided into 4 intervals in terms of their electro-facies (figure 4.2.24). Interval 1 is represented by high resistivities, especially at the well VI-1 where is connected with a greater carbonate content and, in consequence a lower SP. It should be note here that the distance between wells can infer on lithologies. Electro-facies of interval 2 consist of flat resistivities ac- companied by a high SP. The only presence of the upper part of this interval at CA-1 together with the absence of interval 1 at the well SFR-1 are interpreted as a southwards onlap of the Oligocene sequence against the basement, in consonance with the retrogradation observed on seismic lines. Intervals 3 and 4 exhibits similar resistivities and their division is based on a lower SP for interval 4, consequence of a higher limestone proportion. Although SP remains low for the 173 well SFR-1, resistivity curves are in agreement with the rest of wells and this can be related with a different position in the basin and the arriving of sandier facies. Although these four intervals are grouped as Oligocene, an older age for the lowermost intervals should not be totally discharged as no seismic or paleontological data are available for the wells VI-1 and SFR-1, from which the presence of an extra unconformity could be inferred. A similar workflow was followed to correlate Neogene formations. Shallower facies, including lower to middle Miocene reefs (Unit N1), were deposited at the position of CA-1, which possibly represents a paleo-structural high where pre-Oligocene section was totally eroded or not-depos- ited, reaching intrusive bodies. Distal facies (Unit N2) are interpreted for the wells LIC-1 and VI- 1, while the SFR-1 might be located at an intermediate position. The presence of lignite beds in sub-unit N5, especially at the upper sandstones, has been used to correlate sandy levels with a low SP (figure 4.2.25). Outcrops reveal the presence of lignite beds for the middle Miocene sand- stones of Cordillera Septentrional, as it is reported in the geological mapping of the region. The well correlation, figure 4.2.26, reveals the presence of the Neogene depocenter at the middle segment of the Cibao Basin with a minimum thickness of 3000 m, coinciding with the position of Licey #1. Miocene sedimentary sequences wedge and pinch-out to the south, possibly onlapping Paleogene and basement sections. As we move northwards, to the trace of the SFZ, the register exhibits a greater inversion, having exposed and eroded part of the upper Miocene sediments at Villa Isabel #1. The development of carbonate systems is restricted to the areas close to the main cordilleras (Cor- dillera Oriental and Central), exposing that they represent structural highs at least since the Oli- gocene – early Miocene. Conforming we move to the north, proximal facies (Caño Azul #1) pass into intermediate (San Francisco #1) and distal (Licey#1 and Villa Isabel #1). 174 Fig. 4.2.24, Correlation of the Oligocene sequence for the wells CA-1, SFR-1, LIC-1 and VI-1, flattened to the Top Oligocene. 175 Fig. 4.2.25, Correlation of Neogene sequences for the wells SFR-1 and LIC-1, flattened to the top of Unit N5. 176 Fig. 4.2.26, Well correlation panel for the wells selected. Position of the wells in figure 4.2.20. 177 4.2.3 Structure of the fore arc / collisional domain Structurally, this domain is represented by a transpressional left-lateral deformation (Escuder- Viruete et al., 2007). The main tectonic features present from north to south are the Cordillera Septentrional (CS), the Septentrional fault zone (SFZ), the Cordillera Oriental (CO), the Río Yabón fault zone (RYFZ) and the Hispaniola Fault Zone (HFZ), figure 4.2.27. In order to clarify the explanations, this section has been sub-divided into two parts that correspond to two geo- graphical areas: the Cibao Basin, that includes the SFZ, CS, and a the northern segment of the HFZ; and the Cordillera Oriental, that includes CO, RYFZ, the Llanura Oriental and the southern segment of the HFZ (figure 4.2.27). Cordillera Septentrional and the Cibao Basin The CS is formed by a mountain chain with a width between 15 and 40 km and an elevation that can reach 1000 m at its central segment. The direction is WNW – ESE, parallel to the coast from Montecristi to Nagua, with a total onshore length of 200 km (Monthel et al., 2010 b; Pérez-Varela et al., 2010 b). It is a key area for studies of post-middle Eocene island-arc tectonics in Hispaniola because the area includes the Septentrional fault zone, which is presently the main strike-slip fault zone separating the North America and Caribbean plates (Mann et al., 1991 b, 1998). Its origin is related to a transpressive setting, still active at Present, represented by the SFZ (Rosencrantz et al., 1988; Mann et al., 1991 b, Grindlay et al., 1997; Dolan et al., 1998; Mann et al., 2002). The trace of the active fault system does not meet with the frontal part of CS for the whole chain (Mann et al., 1998), passing through the interior of the Cibao basin, semi-buried by the Quater- nary deposits and with a poorly defined path. The western part of SFZ is segmented into different branches that seem more active to the south. The current configuration of the Cibao Basin is delimited by the SFZ to the north and by the HFZ and CO to the south (figure 4.2.27). The integration of the different cross sections from the geo- logical mapping (Section 3.2) together with the seismic profiles and exploration wells give us the necessary inputs to define the structure and the stratigraphy of the basin (figure 4.2.28). Fig. 4.2.27, Main structures of the northern segment of Hispaniola Island over the geological maps: CS, Cordillera Septentrional; SFZ, Septentrional Fault Zone; HFZ, Hispaniola Fault Zone; CC, Cordillera Central; CO, Cordillera Oriental; RYFZ, Río Yabón Fault Zone. Sections I-I’ and II-II’ are given in figures 4.2.25 and 4.2.27, respectively. 178 The SFZ is a regional left-lateral strike-slip system which activity is constrained from middle Eocene onwards. Widespread conglomerates have registered the main tectonic pulses, constrain- ing the timing of at least three unconformities in the late Eocene – Oligocene, early Miocene and middle Miocene (De Zoeten and Mann, 1999). The SFZ also generates secondary structures like the Camú fault or the San Francisco Ridge or push-up (figure 4.2.28), a positive flower structure resulted from the left-lateral transpressive regime that affected the northern part of Hispaniola (Pérez-Varela et al., 2010 b and references therein), favouring the exhumation of part of the sed- imentary record of the Cibao Basin. The HFZ outlines the limit between the fore-arc / collisional and the island arc domains (see Section 4.1). It crosses the island with a NW – SE direction, from the region of Montecristi to the vicinities of Santo Domingo. Geological cross sections, combined with cinematic studies, define the HFZ as a positive flower structure with a sinistral component (Pérez-Estaún et al., 2007 and references therein). At its western sector (figure 4.2.27), this fault zone affects to the Eocene to middle Oligocene sedimentary sequences, being fossilised by upper Oligocene sediments (Con- treras et al., 2004). After that, minor activity has been identified, especially for the eastern section of the fault (Pérez-Estaún et al., 2007 and references therein). Fig. 4.2.28, Interpreted sections from the integration of cross sections, seismic profiles and wells. Above, schematic cross section for the Cibao Basin. Below, stratigraphic model proposed for the infill of the basin. The position is given in figure 4.2.25. 179 Seismic profiles and well correlation of the Cibao basin point out the presence of a thick Neogene sequence, of at least 3 km based on the registers of Licey #1, with the depocenter located at the centre segment of the valley. The sedimentary model proposed for the region (figure 4.2.28) prog- noses the presence of proximal facies to the south of the basin, possibly deposited over paleo- structural-highs. In this sense, unconsolidated sandstones of Units O2 are tentatively interpreted as syn-tectonic deposits, possibly a regolith consequence of the basement exposition. Bio-facies analysis for the well CA-1 suggests an Oligocene – middle Miocene transgression, passing from inner – middle neritic to middle – outer neritic and finally bathyal deposits (figure 4.2.29 based on data from Guerra and Percival, 2000). This hypothesis is backed by seismic pro- files, where a back-stepping architecture is identified for this Oligocene – middle Miocene se- quence. According to the interpretation of seismic line PET-7, there is a posterior progradation which might indicate a middle Miocene regression (figure 4.2.29). This cycle could have exposed the lower Miocene platform, allowing the development of exposure and karstification processes. Although the seismic resolution is limited, a frequency loss identified at the top of Unit N1.1 (reef facies) could be interpreted as a potential karstification of the platform. Fig. 4.2.29, Well Caño Azul #1 over interpreted 2D seismic line PET-7 (from Gorosabel et al., 2020). A transgression of the system and a later regression is interpreted for the early – middle Miocene interval. Red arrows indicate the gas shows registered in the well. Key to acronyms: GR, Gamma Ray; SP-1, Spontaneous Potential; RHOB, density log; LSF, Lowstand Fan. The properties of this kind of carbonate transgressive systems have been studied in the industry due to their potential to create hydrocarbons traps. This is the case of the Perla gas filed in northern Venezuela. There, “the approximately 300-m (984.2 ft)-thick Oligo–Miocene carbonates of the Perla field consist of an overall deepening-upward sequence predominantly composed of larger benthic foraminifera and red algae (oligophotic production) with a minor contribution from 180 shallow-water (euphotic) carbonate components (green algae and corals)” (Pomar et al., 2015). They were deposited “in a context of tectonic subsidence, the building blocks progressively onlapped with backstepping configuration onto a paleo-island” (Pomar et al., 2015). This archi- tecture favours that the distal facies of the system cover previous deposits, creating stratigraphic traps (figure 4.2.30). Stratigraphic traps might have been created also at the Cibao Basin as the well CA-1 indicates. During the perforation, overpressures were detected while drilling Unit O2, and the blow-out preventer had to be used. The drilling mud was ejected causing damages in the up-hole for- mations. The overpressure zone consisted of a little cap of gas, that generated a flat spot on seismic profiles being the primary objective of the well, with sulphurous water (Caño Azul well summary, 2000). This together with the non-commercial gas accumulations registered in Unit N1.1, are interpreted as stratigraphic traps. Fig. 4.2.30, Three-steps deposition model for the Perla Carbonates in northern Venezuela from Pomar et al., 2015. Note how distal facies of every new step cover previous deposits favouring the formation of stratigraphic traps. Cordillera Oriental The Cordillera Oriental (CO) is a moderate deformed area located at the eastern area of Hispaniola Island. It consists of a coherent antiformal structure cored by Lower Cretaceous island-arc rocks and covered by Upper Cretaceous fore-arc sediments (figure 4.2.31). The cordillera is cut by the Río Yabón Fault Zone (RYFZ, figure 4.2.27), a NW-SE sinistral strike-slip fault system that con- figures a positive flower structure (García-Senz et al., 2007). Up to three deformation events have been documented at the Cordillera Oriental. The first event was registered in the Aptian sedimentary record. The whole sequence started with Aptian breccias and conglomerates (composed of material derived from the exposed Primitive Island Arc, PIA), followed by sandstones that pass into the carbonaceous shales (Kesler et al., 1991). They are covered unconformably by the Albian Hatillo limestones, composed of clastic deposits that pass into massive, biogenic limestones, including rudist assembles (Myczynski and Iturralde-Vinent, 2005), constraining a pre-albian deformation event. As opposed to the Amina-Maimon schists, that have experienced a metamorphism related to an obduction process, the Lower Cretaceous volcanic suites and sedimentary sequences have suf- fered only from hydrothermal metamorphism (Torró et al., 2017 and references therein) and pos- terior deformation processes. Hydrothermalism affected only to the PIA and pre-Albian sedimen- tary formations (Torró et al., 2017 and references therein) and could be related with the PIA activity. Although, good TOC carbonaceous layers (up to 2.44 %Wt) have been identified at the localities of Pueblo Viejo and Bayaguana, they have suffered also from the same hydrothermalism, causing 181 a sulfidation of the organic matter associated with the gold mineralization (Kettler et al., 1990) and discarding them as potential source rocks. After the pre-Aptian event, a two-stages deformation model have been proposed for the Cordillera Oriental and the Llanura Oriental regions since the Upper Cretaceous. The first stage took place from the Campanian to the Thanetian (Paleocene) with the development of an antiform that oc- cupied the core of the mountain chain. This folding took place by a homogeneous contractional deformation, forming a coherent antiformal structure cored by Lower Cretaceous island-arc rocks which were covered by an Upper Cretaceous fore-arc sedimentation. A 025º N convergence di- rection between the island arc and the North American plate has been inferred from this folding stage (García-Senz et al., 2007 and references therein). The second stage would extend from the late Paleocene onwards and suppose the formation of oblique structures superimpose to the previous folding (García-Senz et al., 2007 and references therein). This change, from compression to partitioned transpression in the Paleocene, cut the antiform generating a positive flower structure. A comparison between the partitioned transpres- sive model of Sanderson and Marchini (1984) with the transpressive experiments of Tikoff and Peterson (1998) led to propose a convergence vector between the plates during the Cenozoic close to the current vector 070º N (García-Senz et al., 2007). This vector has been determined from GPS measures (DeMets et al., 2000; Mann et al., 2002). A schematic cross-section for the area is shown in figure 4.2.31. The shear bands adjacent to the RYFZ have recorded a progressive rota- tion of the previous folding towards the fault. The superposition of these folds to the previous antiformal folding produce dome and basin interference patterns (García-Senz et al., 2007). This change from a homogeneous contraction to a partitioned transpression is correlated with a diminution in the convergence angle between the CARIB and the NOAM. Regionally, this dimi- nution agrees with a decrease in the arc activity in Hispaniola Island and the initiation of the first structures formed in the Caiman trough (García-Senz et al., 2007 a and references therein). In the nearby of RYFZ, ultra-basic and serpentinites rocks have been described intruding low deformed Upper Cretaceous to Eocene (Oligocene?) sandstones and limestones at the geological maps of Miches, El Seibo and Rincón Chavón (García-Senz et al., 2004; García-Senz et al 2007 a; Díaz de Neira et al., 2004 a; Monthel et al., 2004 c, and references therein). The serpentinites are derived from the hydrothermal alteration of an ultrabasic protolith, alienated parallel to the RYFZ. They have suffered a high-deformation processes, with blocks and ultrabasic elements embedded into a schist matrix. In a same way, a peridotite serpentinite band has been mapped along the trace of the HFZ. Fig. 4.2.31, Schematic cross section for the eastern area of Hispaniola. It has been composed from the geology cross sections of the geological mapping SYSMIN I – II projects. The position is shown in figure 4.49. 182 4.2.4 Partial discussion for the fore-arc / collisional domain Important constrains for the evolution of Hispaniola Island are directly derived from the study of the stratigraphy and the structure of this domain, providing fundamental information about the main tectonic events that have generated regional unconformities, leading to the emplacement of metamorphic materials, and the deformation styles that predominate in the area. Aptian – Albian event As it has been exposed, the first tectonic event took place for the period Aptian – Albian. At this moment, the vulcanism associated with the PIA stopped, and materials geochemically related with the island arc, interpreted as part of the fore-arc region, subducted below the arc. These would be the future Amina – Maimon schists. The mechanism that triggered this process is not clear. However, it is possible that a seamount or ridge, belonged to the Proto-Caribbean, arrived at the subduction channel of the incipient island arc, or any other change in the subduction setting. This event could have been registered by the exposure of the PIA, leading to the deposition of Aptian breccias and conglomerates at the top of the Los Ranchos Formation. These syn-tectonic deposits were covered by the Albian Hatillo limestones. This exposition of the PIA is inferred in the subsidence curves of the forearc region (figure 4.2.5). Initially, this event was correlated with a reversal of the subduction polarity for the period Aptian – Albian (Draper et al; 1996; Lewis et al., 2002), based on the metamorphism of the Amina – Maimon schists and the Los Ranchos Formation. This proposed mid-Cretaceous orogenic event would have resulted in the obduction of peridotites onto the Lower Cretaceous PIA (Draper et al., 1996). In this sense, the metamorphism of the Maimon schists would have been the result of the northward thrust emplacement of the peridotites (figure 4.2.32). As The penetrative foliation decreases progressively to the north-east, from the Maimon to the Los Ranchos formations, and it is not present at the Albian Hatillo limestones, the obduction was restrained to Aptian – Albian time. On the other hand, as this event was synchronous with a change in the magmatism of the Greater Antilles, these authors associated this with a change in the subduction polarity (Draper et al., 1996). Fig. 4.2.32, Geological map of the Hatillo region and schematic cross-section of the Hatillo Thrust from Torró et al., 2016. Note that the contact between the Maimon schists and the Hatillo limestones is mechanic. 183 Nevertheless, recent studies conclude that the emplacement of the peridotites is not enough to reach the green and blue schist facies of the Maimon schists (Torró et al., 2016 and references there in). Furthermore, Amina – Maimon schists have similar signatures than the schists from the Puerto Plata (PPC) and Río San Juan (RSJC) metamorphic complexes, where geochemical studies suggest the subduction of the forearc region for the same period of time (Escuder-Viruete et al., 2014; Escuder-Viruete et al., 2016 b and references therein). From a regional point of view, a unique mechanism for the subduction and exhumation of both metamorphic suites seems more consistent. If we consider so, an Aptian -Albian event would be the responsible of the subduction of part of the fore-arc, the penetrative foliation of the PIA complexes, the interruption in magma- tism and the exposition of the PIA that culminate with the deposition of the Albian reefal Hatillo limestones. Deformation and metamorphic constrains for the Amina Formation, RSJC and PPC include:  Post Aptian – Albian limit (~112 Ma) and pre-Eocene metamorphism processes, for the Amina Formation (Escuder-Viruete et al., 2007 and references therein)  A prograde deformative event to high-P metamorphic conditions at 110 – 95 Ma, a ther- mal peak condition at 92 – 89 Ma (Turonian), ductile exhumation and cooling to T < 550ºC at 88 – 84 Ma (Coniacian - Santonian) and slow cooling at low P at 82 – 70 Ma (Campanian), for the RSJC (Escuder-Viruete et al., 2016 b and references therein).  The exhumation of the complex to T < 450ºC at 90 – 82 Ma (Turonian - Campanian) and to T < 150ºC at 35.8 Ma (late Eocene), for the PPC (Escuder-Viruete et al., 2014 and references therein). These constrains fit well with a subduction during the Aptian – Albian and an exhumation during the Paleocene – Eocene, when the first metamorphic and serpentinites clasts have been reported in conglomerates formations of Hispaniola. Campanian event An inversion since the Campanian is proposed at the subsidence curves for the Cordillera Oriental (García-Senz et al., 2007). This could be related with the start of the exhumation for the RSJC and PPC as it is inferred from cooling of this formation. If we compare with the Cuban Geology, a Campanian event is also proposed, correlated in this case with the arrival of the North American paleo-margin to the subduction zone (García-Casco et al., 2008). In this case, as a preliminary hypothesis, it is possible that the Campanian inversion studied at the Cordillera Oriental would have a common origin. The arrival of a thicker crust might cause the first deformation stage, in a pure compressional regime, described at the previous section (4.2.2), developing antiforms with a 025º N convergence direction. That compression might have caused a sedimentation change, passing from siliciclastic materials to calcareous series at this time (see Units K1 and K2 descriptions). The decrease in magmatism is also noticeable since the Campanian at the island arc domain and its replacement from alkaline to basaltic magmas (Escuder-Viruete et al., 2007 and references therein). This will be described on the island Arc domain section. 184 Paleocene – middle Eocene event During the Paleocene to the middle Eocene, there is a period of high energy sedimentation, marked by the presence of thick conglomerates layers, like the Don Juan Formation (Martín et al., 1999) at the southern part of the domain or the San Marcos Formation to the north (Monthel et al., 2010 b; Hernaiz-Huerta et al., 2010). These formations contain fragments of serpentinites and other metamorphic suites, constraining their final exhumation. In the same framework than for the Campanian event, they could represent the initial stages of the collision between the island arc and the North American Plate that would finalize at the late Eocene. Along this collisional process, there were calm periods during the middle Eocene, expressed by the deposition of limestones like the reefal La Luisa (Hernaiz-Huerta et al., 2004 a) and El Bejucal (García-Senz et al., 2004) formations at Llanura Oriental and the micritic Los Hidalgos for- mations at Cordillera Septentrional (Monthel et al., 2010 b). Upper Eocene – Oligocene event The climax of the collision is well-accepted that took place in the late Eocene – Oligocene, bring- ing to an end of island arc magmatic activity (Pérez-Estaún et al., 2007 and references therein). At this moment the current transpressional regime started to work in the area with the develop- ment of great fault zones as the Hispaniola or the Septentrional Fault Zones (Pérez-Estaún et al., 2007; Escuder-Viruete et al., 2007 and references therein). This period is marked by the deposi- tion of conglomerates, breccias and olistoliths along the domain. Under this collisional event, a new configuration for the Cibao basin was settled as it is shown with the onlap of Neogene series over the previous Oligocene materials and the development of the Neogene depocenter. This collisional model would fit with the two-stages model proposed for Cuba for the Campanian – Paleocene and late Paleocene – late Eocene periods (Iturralde-Vinent, 1998 and references therein) Miocene to present events Two main events have been proposed at the Cibao Basin at the early and middle Miocene (Calais et al., 1992) that are recorded by the deposition of conglomerates at Cordillera Septentrional. They could relate to the growing and development of the Septentrional Fault Zone. In a regional framework, the development of great transpressional fault zones could be assumed as an interference between the collision with the North American Plate and the escape of the Caribbean Plate to the East (Pindell and Kenan, 2009; Boschmann et al., 2014). 185 Section 4.3: Island Arc Domain The Island Arc domain consists mainly of volcanic, volcanoclastic and metamorphic materials with only sparse accumulations of Upper Cretaceous sediments. As proposed in this work, this domain is limited by the Hispaniola Fault Zone (HFZ) to the north and the San José - Restauración Fault Zone (SJRFZ) to the south. The main topographic terrain is the Cordillera Central, that crosses the Island with a NW – SE direction (figure 4.2.1), uplifted by a bivergent thick-skin system. No exploration well has been drilled at the terrains of this domain, and the volcanic se- quences have not been penetrated by any exploration well of the island. Although no well-to- outcrop correlation has been performed at this domain, the timing and kind of materials that com- posed this region contribute to constrain the main tectonic events of the island. In addition, the analysis of these formations is key to understand the basement of the SPB. The main formations that composed the Cordillera Central include remnants of (figure 4.3.2; Pé- rez-Estaún et al., 2007; Bowin, 1975; Mann et al.., 1991; Lewis y Draper, 1990; Draper y Lewis, 1991; Lapierre et al.., 1997, 1999; Lewis et al.., 2002; Escuder-Viruete et al.., 2004, 2007): the Upper Jurassic Proto-Caribbean crust and mantle (the Loma la Monja peridotites and El Aguacate chert); the Lower Cretaceous oceanic plateau (the Duarte Complex); the Lower to Upper Creta- ceous igneous sequences related with the island arc (the Tireo Group), which includes Upper Cretaceous sedimentary sequences; and the Upper Cretaceous intraplate basalts (Peña-Blanca and Pelona – Pico Duarte formations). During the field work carried out for this work, sedimentary sequences of the Tireo Group were studied and sampled in order to determine their composition, stratigraphic structure, depositional ambient and source rock potential. Although the dense vegetation and relief of this area difficult to make regional observations and the access to outcrops is not always possible, at least a 30 meters continuous stratigraphic section was found and analysed. Fig. 4.3.1, Main structures of the central segment of Hispaniola Island over the geological maps: HFZ, Hispaniola Fault Zone; BFZ, Bonao Fault Zone; SJRFZ, San José – Restauración Fault Zone; CC, Cordillera Central. Numbers refer to positions mentioned in the text. Red insert indi- cates the position of figure 4.3.2. I-I’ section indicates the position of the schematic cross sections of figure 4.3.6. 186 No lithostratigraphic unit has been defined for this domain. Nevertheless, the study of the volcanic and sedimentary sequences that composed the Cordillera Central results essential to understand the development of the island arc. In addition, important geodynamic constrains could derive from the main unconformities and geochemical changes that affected these materials. Fig. 4.3.2, Schematic stratigraphic chart carried out for the Island Arc Domain based on the information gathered from the geological mapping (Pérez-Estaún et al., 2007). Loma la Monja Assemble The Loma la Monja volcano-plutonic assemble and the Aguacate chert (location 1 in figure 4.3.1) belong to the pre-arc phase of Hispaniola, representing a dismembered fragment of the Proto- Caribbean oceanic crust (Escuder-Viruete et al., 2009; Joubert et al., 2010 a and references therein). Together with the Loma Caribe peridotite and the Duarte Complex, it follows the defi- nition of ophiolite, conforming a Penrose type pseudo-stratigraphy (Wakabayashi and Dylek, 2003), although incomplete (Joubert et al., 2010 a). The composition of this assemble represents the crystallization products of a typical low-P tholeiitic fractionation of mid-ocean ridge basalts parental magmas, ranging from N-MORB (normal mid-ocean ridge basalts) to E-MORB (en- hanced mid-ocean ridge basalts; incompatible trace element enriched - such as K, Ba, La, Rb), formed in a plume-influenced spreading ridge (Escuder-Viruete et al., 2007 a and references therein). 187 The El Aguacate chert consist of pelagic and siliceous sedimentary sequence with an average hickness of 150 m. Variably recrystallized, it forms 3 to 5 cm regular layers of red, green and clear colours, containing Oxfordian to Tithonian radiolarian microfauna (Montgomery et al., 1994). Locally, cherts intercalate with thin pelagic limestones and are intruded by sills of the Duarte complex (Joubert et al., 2010 a). Textures have been lost due to the ductile deformation associated to the HFZ, the metamorphic recrystallization and the brecciation of the formation (Joubert et al., 2010 a). Duarte Complex The Upper Jurassic - Lower Cretaceous Duarte complex (locations 1 and 2 of figure 4.3.1) was defined by Bowin (1960) and Palmer (1963) to include a series of basic volcanic and ultrabasic rocks, that crop out intruded by the island arc batholiths at Cordillera Central. The porphiridic picrites with the olivine, clinopyroxene and Mg-rich basalts represents an oceanic plateau, subse- quently modified by the Upper Cretaceous to Eocene magmatism (Donnelly et al.., 1990; Draper and Lewis, 1991; Lewis and Jiménez, 1991; Lewis et al.., 2002). It is dated thanks to radiolarian cherts intercalated at the base of the complex (Montgomery et al.., 1994). The Loma la Monja Assemble and the overlying Duarte Complex igneous rocks differ in terms of incompatible elements and Nd isotopic ratios. This geochemical gap suggests an origin from two different plumes separated by the Upper Jurassic El Aguacate Chert (Escuder-Viruete et al., 2009). Spatial clusters of Large Igneous Provinces (LIP) in time have been linked with supercon- tinent fragmentation (Storey, 1995; Li et al., 2003). In the Early Cretaceous, diverse CLIP (Car- ibbean LIP) igneous units (Duarte Complex) were constructed onto this proto-Caribbean oceanic crust (Loma la Monja Assemble) and located in a SW location of the NE facing PIA (Escuder- Viruete et al., 2009). Tireo Group The Lower to Upper Cretaceous Tireo Group (location 3 of figure 4.3.1) represents the vulcanism associated with the island arc at Cordillera Central. Geochemical analysis reveals the presence of a major change of the magma sources that made possible to divide the group into two main vol- canic sequences (Escuder-Viruete et al., 2009 and references therein). The lower volcanic sequence (or Constanza Formation) is dominated by Aptian to Turonian mo- notonous submarine vitric – lithic tuffs and volcanic breccias of andesite to basaltic andesite, with minor interbedded flows of basalts and andesites (Pérez-Estaún et al., 2007; Escuder-Viruete et al., 2007 a). These rocks constitute an island arc tholeiitic suite, derived from melting by fluxing of a mantle wedge with subduction related hydrous fluids (Escuder-Viruete et al., 2007 a). The upper volcanic sequence (or Restauración Formation) is characterized by a spatial and tem- poral association of Turonian – Conician to lower Campanian adakites, high-Mg andesites and Nb-enriched basalts, which collectively define a shift in composition of the subduction-related erupted lavas (Escuder-Viruete et al., 2007 a and references therein). A dacitic to rhyolitic explo- sive vulcanism with subaerial and episodic aerial eruptions and subvolcanic emplacement of domes have been also described in the geological mapping of the area (Escuder-Viruete et al., 2007 a; Gómez et al., 1999). The geochemical change has been explained by an oblique ridge subduction at ~90 Ma and a subsequent slab window formation (Escuder-Viruete et al., 2007 a). Four sedimentary intervals have been described at Cordillera Central: the Constanza - Río Blanco formation, the El Convento shales and the Tireo undifferentiated sedimentary sequences (figure 4.3.3). 188 Fig. 4.3.3, Geological maps over digital elevation model of the Constanza and Bonao region with the main formations mentioned in the text. Location in figure 4.3.1. Key to acronyms: SJRFZ, San José - Restauración Fault Zone; HFZ, Hispaniola Fault Zone. The Constanza limestones consisted of recrystallized, massive and bedded limestones that appear to form a cap to the underlying volcanic rocks and could form a remnant of more extensive Upper Cretaceous platform which supplied carbonate detritus to this area (Lewis et al., 1991). They are interpreted as deposited in an hemipelagic ambient. The age of these limestones is Turonian (Vila et al., 1982 in Lewis et al., 1991). Gómez et al. (1999) correlates the Constanza limestones with the Río Blanco Formation, which is composed of a series of limestones, marls, shales, sandstones and turbiditic tuffs. The Río Blanco Formation was studied during the field work carried out for this work. The best outcrops were localized along the trace of the Blanco River, especially at the Blanco dam, where a 30 meters section of sedimentary rocks was found (figure 4.3.4). This outcrop consists of an alternation of metric layers of dark grey to black mudstones and sandstones. Shaly intervals reveal a non-calcareous composition with TOC values ranging from 0.78 to 3.6 %Wt. The main component of this outcrop is a bed configuration with thin-bedded fine to very fine- grained sandstones and medium- to thick-bedded mudstones. In this facies association, mudstones beds (Mst facies in figure 4.3.3) are in a strong dominance and take up more than 80% of the total thickness of the outcrop. The average thickness of sandstones facies (Sst) is less than 5 cm. This association of facies together with sole marks identified in the field led to interpret this succession as distal turbidite lobes. The estimated thickness of the outcrops is about 30 m. Nevertheless, the presence of faults could cause the repetition of the series, therefore this number should be taken cautiously. In addition, the entire section is strongly deformed. Owing to the dense vegetation of the area, the contact with the volcanic Tireo Group could not be observed and their relationship remains unclear. However, due to its emplacement in a valley predominantly represented by the volcanic association of the Tireo Group, the deposition must have occurred during a minor vol- canic activity period, in a deep environment close to the Upper Cretaceous arc. On thin sections, Sst facies are well laminated classified as silicified grainstones. There is a high chemical com- paction with marked stylolites and fractures filled with organic matter. 189 Fig. 4.3.4, Examples of the Río Blanco Formation taking during the field work at the Banco dam. A, general overview of the outcrop. B, the section consists of an alternation of metric levels of dark-grey / black mudstones (Mst) and centimetric sandstones (Sst). The series might be repeated by the action of faults. C, Facies association and sole marks (red arrows) indicate a turbiditic deposition. D, position of the section. E, Detail of one of the centimetric sandstones. 190 In a higher position of the valley, a limited outcrop was identified in the road to the Blanco dam (figure 4.3.5). It consisted of black, hard limestones (brown-tan by alteration) that emitted a strong fetid odour when cut. Nevertheless, only a few meters of rocks were exposed, and the relief and dense vegetation did not allow to identify their continuation, the relationship with other for- mations or even to discern if they had been remobilised. These limestones are defined, on thin sections, as wackstone that contains globigerina, rests of algae and foraminifera (Turadmina?) in an apparently silicified greenish matrix. Fig. 4.3.5, Picture from a limited outcrop identified on the road to the Blanco dam. The relation- ship between these black limestones and other formations remains unsolved due to the dense vegetation of the area. Other sedimentary formations that crop out at Cordillera Central are the El Convento shales and chert member. The El Convento shales, belonged to the Tireo group, consisting of a series of dark brown to black shales and marls with levels of limestones that culminate with an alternation of tuffs and black limestones (Gómez et al., 1999). The description of these shales is limited to the information already given. It has been reported the presence of fossils interpreted as gastropods, whose moulds reach the size of a geologist hammer (figure 4.3.6). However, there is no reference to species or any other specific data that allows to describe them precisely. Field observations stablish an age of Conician – Santonian in base of their position above the Constanza limestones and below the El Convento – Valle Nuevo riolites – dacites (Gómez et al., 1999). Upwards, the El Convento shales pass into a layer of chert that has been mapped independently. “It consists of a 600 m thick of well-bedded to laminated varicoloured cherts, that crop out along the Constanza to El Convento road. The dominant colours are yellowish to greenish, yellow and reddish. Recrystallization and weathering have destroyed the details of the structure of radiolari- ans in these rocks. It is convenient to refer to this marker horizon as the El Convento Chert Mem- ber” (Lewis et al., 1991). They are supposed to be Conician – Santonian (Gómez et al., 1999). 191 Fig. 4.3.6, Examples of the El Convento shales. The photographs come from the description of the Interesting Geology Spot (“Lugar de Interés Geológico”) of the geological map of Constanza (6072 – I, Gómez et al., 1999). They are Conician to Santonian in Age. The fossils are interpreted as gastropods moulds (Gómez et al., 1999). In base of dating and lithological similarities, as a tentative correlation, the El Convento shales and cherts could fit with the Las Guayabas Formation, described in section 4.2.1 - Unit K1, that crops out at Cordillera Oriental. There, this formation is composed of a monotonous succession of sandstones and shales disposed in regular centimetric to metric plane-parallel layers (García- Senz et al., 2007 b and references in there). It finalizes with a 200 m thickness radiolarian chert layer (Bourdon, 1985; Lebron and Mann, 1991; García-Senz et al., 2007 b) dated as Santonian (Van Andel, 1975). Therefore, there is a similar succession of Cenomanian – Santonian dark-grey to black mudstones and sandstones that culminates with a level of radiolarian cherts. This implies that the deposition is not local but regional, and similar lithologies can be expected for regions where the geology record is unknown. This possible correlation, non-proposed until now in the scientific literature, will be incorporated to the regional model and applied to the stratigraphic evolution of the SPB. Finally, there is a poor studied Campanian to Maastrichtian sequence that crops out at different points of Cordillera Central. The more detailed description is given in Lewis et al. (1991) for the sections between the Yuma river and the Bonao Fault Zone (figure 4.26). There Lewis et al. de- scribe the outcrops near the Bonao Fault Zone: “The dominant rocks in this area seem to be vol- caniclastic and sedimentary types. Major flows and/or centres of acidic rocks appear to be absent, although keratophyres are present. The volcaniclastic rocks include coarse breccias, interpreted as debris flow deposits in the U.S. Geological Survey report, and coarse well-bedded sandstones and shales present as turbidites of volcanic origin. Bioturbated fossiliferous mudstone and pyritic laminated black mudstone constitute the dominant lithology in the upper reaches of the Rio Blanco. Thin-bedded limestones, chert—commonly interbedded with limestones, and red pisolite rock with calcite cement are exposed along the trace of the Bonao Fault. The main limestone, exposed at the mouth of the Rio Blanco, apparently overlies the debris flow units, and therefore should give an upper limit to the age of the Tireo in this area. The limestone exposed in the sequence in the Rio Yuma along the Bonao fault, as well as the limestone near the mouth of the Rio Blanco, both yield Maastrichtian ages, the youngest dates recorded in Tireo rocks.” 192 Micropaleontology analysis of samples at Yuma river (Lewis et al., 1991) reveals the presence of microforaminifera from middle Campanian to Masstrichtian. Tentatively, this section could cor- relate with the Río Chavón Formation at Cordillera Oriental and the Units K1/K2 at San Pedro #1. The presence of pyritic laminated black mudstone could be related with the black shales with pyrite of Units K1/K2, and the carbonates described along the Bonao Fault Zone with the Río Chavón limestones. Nevertheless, new field works that provide more data are required to study the hypothetical cor- relation of these formation as well as the potential source rock characteristic of them. Peña-Blanca and Pelona – Pico Duarte formations These basalts intruded into and extruded onto Turonian – lower Campanian island arc volcanic, related intrusions of gabros and tonalites and sedimentary sequences, while they are overlain by Maastrichtian platform carbonates (Escuder-Viruete et al., 2011 and references therein). The da- ting gives a middle Campanian to Maastrichtian age ,79-68 Ma. Geochemical values are charac- teristic of transitional and alkalic ocean – island basalts (Escuder-Viruete et al., 2011). They are interpreted as partial melts of plume-related, deep-enriched source, which has not been contami- nated by active subduction (Escuder-Viruete et al., 2011). Therefore, mantle wedge-derived Car- ibbean arc magmatism was replaced by non-arc-like magmatism during the latest Late Cretaceous in Central Hispaniola. According to Escuder-Viruete et al. (2011), that change in magmatism was induced by Caribbean arc-rifting, extension and eventually back-arc basin development that allowed the emplacement of CLIP related basalts. This point will be discussed in next section, 4.3.1. 193 4.3.1 Structure of the island arc domain Structurally, this domain is dominated by the up-lift of Cordillera Central and the transpressional deformation associated with the first order faults. The main tectonic features present from north to south are the Hispaniola Fault Zone (HFZ), that represents the northern limit of the domain, the Bonao – La Guácara Fault Zone (BFZ) and the San José - Restauración Fault Zone (SJRFZ), that represents the southern limit of the domain, figure 4.3.7. Fig. 4.3.7, Schematic cross-section for the central segment of the island arc domain. Location in figure 4.3.1 and 4.3.8. Key to abbreviations of structures: HFZ, Hispaniola Fault Zone; BFZ, Bonao – La Guácara Fault Zone; SJFR, San José Restauración Fault Zone. The structure of Cordillera Central is characterized by an imbricate bi-vergent thrust system to- gether with a superimposed left-lateral shear component (figure 4.3.7). The frontal thrusts are represented by the BFZ to the north and the SJRFZ to the south (Gómez et al., 1999). There is a change in direction (figure 4.3.8) from an E-W thrust trend at the geological map of Constanza passing to N-S and NNW-SSE to the east and south (geological maps of Bonao, Arroyo Cana, Sabana Quéliz and San José de Ocoa). It affects also to the frontal thrust and it is interpreted to the turn suffered by a thrust sheet when adapting to a lateral ramp in the footwall block. The presence of normal faults over-imposed to the thrust-traces would be, in this case, drop-faults in the hanging wall block to accommodate the deformation excess (Gómez et al., 1999; Hernaiz- Huerta and Pérez Estaún, 2002). This deformation model related with the interference of the Beata Ridge (Hernaiz-Huerta and Pérez Estaún, 2002). The trace of the thrusts at the southern flank of Cordillera Central denotes high dips, generally greater than 45º. Overall, the thrust sheets seem to correspond with am imbricated wedge, where the sheet structurally higher have progressively greater dips (Hernaiz-Huerta and Pérez Estaún, 2002; Gómez et al., 1999; Hernaiz-Huerta, 2006 and references therein). The associated defor- mation is brittle, and it is usually combined with fault gouge mostly composed of foliated cata- clasites (Hernaiz-Huerta, 2006). The folding is syngenetic to the development of the thrust and classified as fault-bend folds (Gómez et al., 1999). The contact between the Tireo Group and the Paleogene sequences take place throughout a frontal thrust (SJRFZ) which plane is slightly lower (30 – 45º) (Hernaiz-Huerta and Pérez Estaún, 2002; Hernaiz-Huerta, 2006). The trace of the fault is lost at the geological maps of Padre Las Casas and Gajo del Monte, where the contact between the basement and the sedimentary cover is solved by an unconformity. It is interpreted the presence of a tear fault which superficial expression is not well defined (Gómez et al., 1999; Hernaiz-Huerta et al., 2006). 194 Fig. 4.3.8, Direction changes of the main structures that conform this domain. Heubeck et al. (1991) propose a three-stages deformation model for Cordillera Central in base of the depositional and deformational styles of the Upper Cretaceous to Miocene sedimentary se- quences deposited to the south of the island arc. In the context of this work, it can be applied for the Island Arc and the Cretaceous to Eocene domains. There, it is proposed that in a previous stage “the back-arc basin was formed by Coniacian-Danian back-arc rifting of the "Great Arc of the Caribbean" and was initially filled by primary volcaniclastic sedimentary rocks derived from active arc volcanism and turbiditic marine rocks (Boisson, 1987)”. After this initial phase, the three-stages would include:  A latest Cretaceous – early late Eocene closure of the Upper Cretaceous back-arc basin.  An Eocene – early Miocene closure of the Upper Cretaceous back-arc basin and overlying Paleocene- Eocene basin.  And a middle Miocene to Recent closure of the back-arc basin and overlying Paleocene to early Miocene sedimentary basins. On the other hand, Escuder-Viruete et al. (2006) identified three contemporaneous Late Creta- ceous strain fields at Cordillera Central (figure 4.3.9):  A northern and southern domain produced by < 95 Ma arc-perpendicular NE – SW ver- gent folding and thrusting.  An arc-parallel sinistral strike-slip shearing along La Meseta shear zone, active during the 88-74 Ma interval (Conician – Campanian).  The adjacent syn-kinematic emplacement of the Loma Cabrera Batholith at 90-74 (Tu- ronian – Campanian) Ma during sinistral transpressional shearing. This work concludes a shortening across the southern domain that had taken place concurrently with sinistral strike-slip movement along the crustal scale BFZ. In addition, faults were re-acti- vated during the late Eocene – Oligocene thrusting and Miocene to Present Uplift of Cordillera Central (Escuder-Viruete et al., 2006 and references therein). 195 Fig. 4.3.9, Schematic crustal block diagram shows the general model for transpressional shear- ing and strike-slip partitioning during Late Cretaceous deformation in the NW Cordillera Cen- tral. Modified from Escuder-Viruete et al. (2006). García-Lobón and Ayala (2007) provides density and magnetic susceptibilities from Hispaniola, classifying samples into two main petrophysical groups in terms of magnetic character:  Magnetic markers of the area: andesites, basalts, tonalites, serpentinites, some gabros, ultrabasic rocks and acid volcanic rocks.  Paramagnetic set: metasedimentary and granitic rocks. Due to the magnetic properties of the materials that composed Cordillera Central, the main struc- tures described in this chapter are recognisable on the magnetic anomaly maps (figure 4.3.10). This identification will be used to extend structures into the SPB and to identify limit of the do- mains in order to infer basement properties and lithostratigraphic units in the basin. Fig. 4.3.10, Reduced-to-pole magnetic anomaly map used to identify structures and materials. Key to numbers: 1, Duarte Complex; 2, Serpentinites; 3, Gabros; 4, Tireo Group; 5, Foliated tonalites; 6, Tonalites; 7, Foliated tonalites; 8, Paleogene sediments; 9, Quaternary vulcanism. 196 The northern limit of the Island Arc Domain is well constrained by the magnetic response of the serpentinite peridotites that crop out at the trace of the fault (figures 4.3.10 and 4.3.11). Never- theless, potential field anomalies point out a change in the southern limit of the domain when entering into the basin. Onshore, and specially at the centre and the western sector of the island, the southern limit is defined by the SJRFZ. However, the bouguer anomaly map reveals a mini- mum (white arrow, figure 4.3.11) for the prolongation of the fault zone in the SPB. There, the limit of the basement is interpreted along the BFZ. This relay would be related to the compression associated to the indentation of the Beata ridge (red arrow, figure 4.3.11), which acts as a trans- form limit. Fig. 4.3.11, Above, Reduced-to-pole magnetic anomaly map of the south-eastern sector of His- paniola with the main structures superimposed. Below, Bouguer anomaly map of the same region. Arrows refer to features described in the text. See Appendix 1 for acronyms. 197 4.3.2 Partial discussion for the island arc domain The main goal of Section 4.3 is to obtain the regional constraints that could be applied to the evolution model of the SPB. To achieve this objective, the different geodynamic models proposed for this domain must be addressed and compared with those from the northern segment of the island (forearc / collisional domain here) and with regional models for the Northern Caribbean. All of them must fit in and be integrated, as same processes must be involved since the island arc and the forearc form part of the same system. In the first place, two opposite tectonic and deformation models have been proposed for this do- main:  A back-arc rifting for the period Conician – Danian (Heubeck et al., 1991).  And a transpressional regime that inverted the southern part or the arc for the Conician – Campanian (Escuder-Viruete et al., 2006). Regarding to the magmatism, two main sequence have been described for the Tireo Group:  A lower volcanic sequence (or Constanza Formation) defined by an Aptian to Turonian island arc tholeiitic suite, derived from melting by fluxing of a mantle wedge with sub- duction related hydrous fluids (Escuder-Viruete et al., 2007 a).  An upper volcanic sequence (or Restauración Formation) characterized by Turonian – Conician to lower Campanian adakites, high-Mg andesites and Nb-enriched basalts, which collectively define a shift in composition of the subduction-related erupted lavas (Escuder-Viruete et al., 2007 a and references therein). Furthermore, another change could involve the middle Campanian to Maastrichtian (79-68 Ma) basalts of the Pelona – Pico Duarte formations, composed of transitional and alkalic ocean – island basalts (Escuder-Viruete et al., 2011). From a regional point of view of the Northern Caribbean, similar changes have been studied for the arc-related vulcanism in Cuba where the alkaline vulcanism took place for the period Albian – middle Campanian (Ducloz y Vuagnat, 1962; Knipper y Cabrera, 1974; Cobiella, 1978; Itur- ralde-Vinent, 1981, Iturralde-Vinent ed., 1996). Volcanic samples from Cuba and Hispaniola re- veal geochemical similarities (figure 4.3.12) that point out a common origin and evolution. This vulcanism was interrupted in Campanian times due to the arriving to the subduction zone of a thicker crust belonging to the North American Plate, initiating a two-stages collisional process for the Campanian – Maastrichtian and from Paleocene? to late Eocene (Draper y Barros, 1994; Iturralde-Vinent, 1998; García-Casco, 2001 and references therein). In addition, at the same period of time, as it was presented for the fore arc / collisional domain, the following constrains are derived from the study of high-P accretionary complexes and sedi- mentary rocks:  A prograde deformative event to high-P metamorphic conditions at 110 – 95 Ma, a ther- mal peak condition at 92 – 89 Ma (Turonian), ductile exhumation and cooling to T < 550ºC at 88 – 84 Ma (Conician - Santonian) and slow cooling at low P at 82 – 70 Ma (Campanian), for the RSJC (Escuder-Viruete et al., 2016 b and references therein).  The exhumation of the complex to T < 450ºC at 90 – 82 Ma (Turonian - Campanian) and to T < 150ºC at 35.8 Ma (late Eocene), for the PPC (Escuder-Viruete et al., 2014 and references therein).  Change in sedimentary sequences from clastic to calcareous at Campanian times (Rincón Chavón Formation). 198 Fig. 4.3.12, Comparison between volcanic suites of Hispaniola and Cuba: Zr/TiO2 vs Nb/Y dia- grams for Hispaniola (above) and Cuba (centre) from Cabrera et al. (2018). Data comes from available values gathered from the bibliography. Comparison of Caribbean serpentinites: Deu- terium diagram from Lewis et al., 2006. 199 The exhumation of Cuban serpentinites, that have a similar geochemical composition than the Hispaniola samples (figure 4.3.11), is constrained to the Maastrichtian – late Eocene (Lewis et al.., 2006 and references therein). This corelates with the emplacement age (Paleocene – late Eo- cene, determined by the deposition of serpentine and metamorphic clasts into the conglomerates and olistoliths of that time) of the Hispaniola metamorphic suites, exposed along the Section 4.2. Keeping in mind these arguments, a regional compressional phase that started in the Campanian is considered here as the most reasonable option to integrate all the processes. Considering that the subducting Proto-Caribbean has an origin in the rifting process, resulted from the breakup of Pangea (Pindell and Kennan, 2009), it could be assumed that the Campanian events registered in both islands would be related with the arriving of a progressively thicker crust to the subduction zone (figure 4.3.13). This process might have triggered the reversal path for the metamorphic units and the initiation of the inversion of the arc. Fig. 4.3.13, N – S schematic regional cross sections for the Albian – Turonian (above) and the Campanian (below) under the geodynamic interpretation given in this work (Not to scale). Acro- nyms: NOAM, North American Plate; CARIB, Caribbean Plate. At the back-arc, this early collisional stage could have caused the initial thrusting of the basement units (the Tireo Group) to the south, considering here a back-foreland basin model that would have generated the accommodation space for the Upper Cretaceous and the Paleocene – Eocene sediments in the back-arc region. While it is not clear if the assumption of a Conician to Danian back-arc rifting is based on field observation or only proposed in base of an island-arc model where a back-arc spreading is hoped to happen. New observation at Cordillera Oriental that constrain the contact between the back-arc sediments and the arc are required to validate any basin model proposed. This will be expanded on the next section, 4.4. 200 At the same time, it should be considered that the convergence between the North American Plate and the island arc was oblique. This fact, together with the Caribbean Plate tectonic scape to the east, might have propitiated shared forces that deformed some areas under a transpres- sional/transtensional regime. This could have an important role in the emplacement of the Cam- panian – Maastrichtian Pelona – Pico Duarte basalts, after the interruption of the alkaline vulcan- ism. Regarding the sedimentation, the stratigraphic observations taken in the field and the thin sections (wackstone with abundant globigerina and radiolarian fossils; figure 4.3.14) indicate a relatively deep-water environment. This agrees with the subaquatic vulcanism proposed specially for a great part of the Constanza Formation (Escuder-Viruete et al., 2007 a; 2010) and should be considered for paleogeographic reconstructions of the Cretaceous island arc. Fig. 4.3.14, Thin section of the sample KRB1 showing rests of radiolaria and globigerina. The lower margin of the photomicrograph is equal to 2 mm. 201 Section 4.4: Cretaceous to Eocene Basin Domain The Cretaceous to Eocene Basin Domain was established for this work to englobe the deep-water sedimentary rocks that were accumulated at the back-arc zone during the Late Cretaceous through Eocene (Ardèvol. 2004; Hernáiz-Huerta, 2006; Pérez-Varela et al., 2010 a). These deposits con- trast with the volcanic deposits of the Island Arc Domain and the carbonate sedimentation of the Oceanic Caribbean Domain (Hernaiz-Huerta, 2006). Structurally, this domain is represented by a series of thin skin thrusts and folds that affect these sedimentary sequences, constituting the south- ernmost slope of Cordillera Central (Mann et al.., 1991). The domain is delimited by the San José – Restauración Fault Zone (SJRFZ) to the north and the San Juan – Los Pozos Fault Zone (SJLPFZ) to the south (figure 4.4.1). The SJRFZ put in contact materials from the island arc with the sedimentary sequences of this domain (see section 4.3.1). This belt, named in the bibliography the Trois Rivieres – Peralta Belt (TRPB) (Dolan et al., 1991), has a NW-SE trend that crosses the island from the north of Haiti to the southern margin of the Dominican Republic. On the other hand, the SJLPFZ represents the thrusting of these sequences to the south. Only data from one well has been preserved in this domain, Punta Salinas #1 (PS; Punta Salinas #1 well report, 1996), reaching middle Eocene sedimentary rocks with a total depth of 1575 m (PS, figure 4.4.1). However, this domain also includes Upper Cretaceous (at locations 1 and 5 of figure 4.4.1), upper Eocene to Oligocene (at locations 3, 4 and 5 of figure 4.4.1), and Neogene to Present (at location 6 of figure 4.4.1) sedimentary sequences. Formally, Neogene to Present out- crops should not been included into this domain as they are emplaced northwards the SJRFZ. Nevertheless, these formations represent the continuation of the sedimentation to the north during this period, as the deformation continues, overlapping the island arc materials, and has been in- cluded here to analyse the evolution in sedimentation in this part of the island as a whole. Fig. 4.4.1, Main structures of the central segment of Hispaniola Island, that represent the Creta- ceous – Eocene Basin Domain, over the geological map: CC, Cordillera Central; SJRFZ, San José – Restauración Fault Zone; SJLPFZ, San Juan – Los Pozos Fault Zone; BFZ, Bonao Fault Zone; SPB, San Pedro Basin. Punta Salinas #1, drilled by Mobil in 1991, is represented by its acronym PS. Numbers refer to positions mentioned in the text. A-A’, location of cross section of figure 4.4.12. 202 4.4.1 Lithostratigraphic units description Based on the current boundaries defined for the basin in this work, it would include three intervals separated by unconformities: Upper Cretaceous (Campanian to Maastrichtian), lower to middle Eocene and upper Eocene to Oligocene sequences (figure 4.4.2). However, the upper Eocene to Oligocene sequence goes beyond the SJRFZ at the San Cristóbal region (location 5 of figure 4.4.1), overlapping the island arc domain, accompanied by the Neogene sequences. From an evo- lutionary point of view, the Upper Cretaceous and the lower to middle Eocene sequence would have been deposited in a deep basin southwards the island arc, having been inverted due to the collision with the Bahamas Banks in the middle Eocene (Heubeck et al., 1991; Hernaiz-Huerta, 2006) as a consequence of an effective transmission of compressional forces to the south (Granja- Bruña, 2008). After this inversion, the south-eastern region of the island acquired a new configu- ration, where upper Eocene to Neogene sediments were deposited against the Upper Cretaceous to middle Eocene sequence to the south and the island arc domain to the north. This subsequent infill has been separated and studied in section 4.4.2. In this section only the Upper Cretaceous and the lower to middle Eocene sequence are analysed, as their formations are considered in this work as deposited in a back-foreland basin in a different context, giving name to the domain (Cretaceous to Eocene Basin). Fig. 4.4.2, Schematic stratigraphic chart carried out for the Cretaceous – Eocene Basin Domain based on the information gathered from the geological mapping (Pérez-Estaún et al., 2007). 203 The Campanian to Maastrichtian Trois Rivieres Formation Upper Cretaceous sediments crop out at two regions of the domain, at the so-called Trois Rivieres Belt, which extends from the north of Haiti to the centre of the Dominican Republic (location 1 of figure 4.4.1), and a second close to the trace of the SJRFZ (location 5 of figure 4.4.1). It should be noted here that the lack of studies that englobe and correlate both and address the relationships with Paleogene formations has led to spurious correlations and misunderstandings between ma- terials that correspond to different periods of time (Bernárdez-Rodriguez et al., 2004). In first place, the Trois Riviere Formation, which gives the name to the Trois Rivieres Belt, was first studied in Woodring et al. (1924) that attributed an Early to middle Cretaceous age. After- wards, Butterlin (1960) stablished its final aging for the Campanian – Maastrichtian (Bernárdez- Rodríguez et al., 2004). Dolan (1988) joined the Trois Rivieres and the Peralta Belts into the Peralta Basin, assuming that the Cretaceous Fauna was redeposited and suggesting an Eocene age for the whole belt (Bernárdez-Rodríguez et al., 2004). Nevertheless, recent field works have con- firmed a Campanian - Maastrichtian age for the Trois Rivieres Formation (Bernárdez-Rodríguez et al., 2004; Ardèvol, 2004), configuring an independent thrust sheet of the system from the Paleo- gene Peralta Belt (Hernáiz-Huerta et al., 2002). The Trois Rivieres Formation is divided into the Aguamite (Campanian) and the Bois de Laurence (Campanian – Maastrichtian) units. The Aguamite unit is constituted of predominantly fine ma- terials with intercalated sandstone layers and carbonate shales (Bernárdez-Rodríguez et al., 2004). The shales/sandstones ratio varies along the formation, although shales dominate the sequence. In outcrops, shales present a high-grade of alteration with ochre/brown colours, being dark grey in fresh cuts (figure 4.4.3). The composition of sandstones is essentially quartz and feldspars (50 – 75%). Although quartz can dominate the relation in some cases, the percentage of feldspars reach a proportion as high as 48% of samples. Volcanic fragments are generally lower, up to 11%. Argillaceous matrix represents percentages of 20 – 25% and carbonate cements vary from 10 to 20% (Bernárdez-Rodríguez et al., 2004). This system is interpreted as a sandstones-poor turbidite system with thin-bedded turbidites (Ardèvol, 2004). Nevertheless, other depositional environ- ments have been documented locally, like the Arroyo San Pedro series. Outcrops are divided into three intervals. The lower part is mainly composed of shales with minor siltstones and very fine sandstones with lenticular and wavy stratification interpreted as contourites. The central interval consists of an alternation of fine to medium grain sandstones layers that pass vertically into pebble conglomerates and cobble breccias at the upper section, and are interpreted as a submarine canyon (Ardèvol, 2004). Outcrops compose of carbonate breccias have also been observed into the Trois Rivieres Belt, that consist of sharp-angled clasts of micritic and bioclastic limestones in a sandy matrix. In ad- dition, and correlated with these levels, similar breccias have been identified unconformably over the Tireo Group at other locations out of the belt (Bernárdez-Rodriguez et al., 2004). The presence of Campanian breccias is relevant for this study because they could be consequence of a tectonic pulse connected with other Campanian tectonism studied in sections 4.2 and 4.3. The contact between the Trois Rivieres Formation and the volcanic Tireo Group is mainly faulted or represents an unconformity, although at some places is stratigraphically conformable (Lewis et al., 1991 and references therein). The Aguamite Unit passes vertically into the Bois de Laurence Unit, which consists of marls and purple-red calcareous mudstones and minor grey limestones. This unit is well dated by planktonic foraminifera in the middle Campanian – Maastrichtian interval (Bernárdez-Rodríguez et al., 2004), which constraints the Aguamite Unit to the early – middle Campanian. 204 In thin sections, the Bois de Laurence limestones are defined as wackstone-packstone in the Du- ham classification, presenting frequently planktonic foraminifera and radiolarians. At the base of the unit, the presence of volcanic breccias is usual, and at some locations a layer of black radio- larian chert has been identified (Lewis et al., 1991; Bernárdez-Rodríguez et al., 2004 and refer- ences therein). Fig. 4.4.3, Examples of outcrops from the Campanian to Maastrichtian Trois Rivieres Formation. Above, shales from the formation section in Haiti (Goulet-Lessard, 2012). Below, lower section of the Arroyo San Pedro series in the Dominican Republic (Ardèvol, 2004). The Campanian – Maastrichtian Las Palmas Formation The Las Palmas Formation crops out close to the trace of the SJRFZ in the San Cristóbal region (location 5 of figure 4.4.1). This formation shares stratigraphic and sedimentologic characteristics with the Trois Rivieres Formation, being interpreted as belonged to a basin formed after the cease of the volcanic activity of the Tireo Group (Pérez-Varela et al., 2010 a and references therein). It is composed of a basal member that consists of Campanian breccias and an upper member inte- grated by Maastrichtian marls with turbidite sandstones intercalated (Pérez-Varela et al., 2010 a). Below the Las Palmas Formation, there is also a grey limestone formation with minor sandstones and fine levels, yet due to the high grade of deformation and the deficient access to outcrops, it has been englobed into the Tireo Group and is not well defined. These limestones are not dated due to the dolomitization has not preserved the fossils content. However, in base of the strati- graphic position below the Campanian breccias, their age should be assigned to the interval San- tonian – early Campanian (Pérez-Varela et al., 2010 a). 205 The breccias member are composed of polymictic, heterometric, angular clasts of volcanic and plutonic material, volcaniclastics and sedimentary rocks with sporadic limestones (that include coral fragments and algae) and intercalate metric layers of shales (Abad et al., 2010 a). The rela- tionship with the Tireo Group represents an erosive and angular unconformity (Pérez-Varela et al., 2010 a). The upper member comprises shales, marls and brown sandstones, in a quick transition from the previous member, with a minimum thickness of 500 meters (Pérez-Varela et al., 2010 a; Abad et al., 2010 a). Sandstones are interpreted as turbidites, being observed Bouma sequences, with an erosive base composed of soft clasts, followed by cross and parallel laminations. The thickness of every sequence goes from centimetric to metric (Pérez-Varela et al., 2010 a). The fossils asso- ciations: Globotruncana sp., Globotruncana (Rosita) fornicata Plummer, Marssonella? sp., give a Campanian – middle Maastrichtian age. Similar than the Trois Rivieres Formation, the Las Palmas Formation rests unconformably over the Tireo group through an angular and erosive unconformity. This indicates the presence of a tectonic phase between both (Pérez-Varela et al., 2010 a and references therein). This correlation would confer a regional character for the Campanian – Maastrichtian formation of this domain and, in this case, these properties could be extended to the SPB. These similarities were verified during the field work carried out for this work in the Cordillera Central (figures 4.4.4 and 4.4.5) for the Campanian to Maastrichtian interval. The series of out- crops start with a limited interval of sandstones, highly brecciated and fractured (note the prox- imity to the SJRFZ) with carbonate veins and a high content of plagioclase. Above it, there is a level of black silicified limestones, corresponding to a radiolarian chert (figures 4.4.4 and 4.4.5 E). This level passes vertically into a series of laminated limestones that vary from mudstone or wackstone to packstone of globigerinas. Carbonates can alternate with thin levels of feldespatic sandstones, especially to the bottom. In addition to globigerinas, other fossils have been identified on thin sections like echinoderms, ostracods, brachiopods, spicules, hyaline foraminifera and other skeletal clasts. Fig. 4.4.4, Thin section of the sample KC-3 corresponding to a packstone of globigerina. The lower margin of the photomicrograph is equal to 2 mm. 206 Fig. 4.4.5, Examples of outcrops from the Campanian to Maastrichtian interval of Cordillera Central, taken during the fieldwork. A, Compressional structures. B, Alternation of mudstones, wackstones and packstones. C, Appearance of brecciated and fracture outcrops close to the main faults. D, Location of samples (KC) in comparison with other Campanian – Maastrichtian for- mations like the Trois Rivieres (TR) or the Las Palmas (LP) Formations. E, Example of black radiolarian chert. 207 Unit E1 Definition: Unit E1 is defined from 745 to 1575 m at the well Punta Salinas #1 (PS-1, figure 4.4.1), drilled by Mobil in 1995. The stratotype corresponds to middle Eocene limestones, occa- sionally siliceous mudstones, and silty siliceous mudstones. While the upper part of the unit is mainly composed of white/grey to brown limestones with minor claystones, at base (from 1400 m to TD) sandstones, volcanic fragments (blue-green medium-grain lithic clasts) and chert ap- peared in cuttings (Punta Salinas #1 well report, 1996). At the well type, Unit E1 is overlapped by the upper Eocene Unit E3. This unit is represented by a low non-corrected GR (~10-20 API) that only increases for the shaly intervals (~30-40 API). This behaviour is followed by the sonic log, that reveals high velocities for limestones (< 70 µs/ft), decreasing for the shaly intervals (> 70 µs/ft). Sonic porosity revealed intervals with a poor to fair porosity (3% to 7 %), while the higher values resulting from shale interference (figure 4.4.6). On the other hand, SP is relatively high (> -20 mV), and only decreases for some limestone intervals at bottom (< -20 mV), possibly indicating a lack of permeability for most of the unit. Resistivity curves have low – medium values (10 – 60 Ω·m) increasing to high (290 Ω·m) for the intervals with the lowest SP. In general terms, lithologies and wireline logs indicate that this unit is constitute by hemipelagic limestones. No hydrocarbon show was detected while drilling this unit. Nevertheless, the presence of black coats and bitumen (specially for the lower interval) and a small gas show (at top of the unit) were included in the mud logging report (Punta Salinas #1 mud logging report, 1995). Unit E3 Definition: Unit E3 is defined from 305 to 745 m at the well Punta Salinas #1 (PS-1, figure 4.4.1). The stratotype corresponds to an alternation of upper Eocene grey siliceous mudstones and silt- stones (Punta Salinas #1 well report, 1996). At the type well, this unit is overlapped by the upper Eocene Unit E4. Well logs are characterized by a high SP (> -8 mV), combined with almost flat resistivity curves, empathises the shaly character of the unit, which is interpreted that interferes in the sonic porosity curve (figure 4.4.6). Only a limited interval (from 500 to 540 m) reveals fair porosities keeping a low GR, possibly due to the presence of sandstone levels. Unit E4 Definition: Unit E4 is defined from 87 to 305 m at the well Punta Salinas #1 (PS-1, figure 4.4.1) The stratotype corresponds to an alternation of upper Eocene sandstones and siltstones. At the type well, this unit is overlapped by quaternary sand dunes in an unconformably contact. Only GR is available, showing a coarsening uphole of the unit (figure 4.4.6). Units E1, E3 and E4 have been correlated with the middle Eocene sediments that crop out 8 km northwards PS-1, at Sierra el Número (Punta Salinas #1 well report, 1996). They constitute the southernmost segment of the Peralta Belt (position 2 of figure 4.4.1), defined as the Peralta Group (Dolan, 1988; Heubeck, 1988; Heubeck et al., 1991). 208 Fig. 4.4.6, Units E1, E3 and E4 as seen on Punta Salinas #1 well logs. Limestones of Unit E1 are represented by an increase of sonic velocities accompanied by a diminution of GR. Shaly Unit E3 is characterised by almost flat resistivities and a low SP. Porosities, calculated from sonic log, remain generally low (< 10%), good intervals are affected by a greater proportion of shales. 209 The Peralta Group is subdivided into three formations: the Ventura, Jura and El Número For- mations (Dolan, 1989).  The Ventura Formation consists of a succession dominated by sandstones that crop out together with shales and marls with an estimated thickness of at least 1000 m. Sandstone deposits have been interpreted as turbiditic lobes of a submarine fan system, due to the presence of traction carpet at base, parallel lamination, load structures and ripples at top (figure 4.4.7). Sandstones are well cemented presenting mosaic and syntaxial sparitic ce- ments (Pérez-Varela et al., 2010 c). Sections formed of amalgamed sandstones with tab- ular architecture are frequent, containing conglomerates layers at base. Shales have a var- iable carbonate content, being considered as marls at some sections. They range from grey to greenish and reddish. The last 50 m constitutes a transition to the Jura Formation with centimetric sandstones and shaly marls (Hernaiz-Huerta et al., 2002; Hernaiz- Huerta, 2006 and references therein). The fossil content content stablishes an early to middle Eocene age (Dolan et al., 1991), although its extension to the Paleocene is not discarded (Hernaiz-Huerta et al. 2006). Paleo-currents indicate ESE and SE predominant fluxes, in what it is thought a NW – SE deep trench (Heubeck et al., 1991; Hernaiz- Huerta, 2006). Fig. 4.4.7, Example of outcrop from the Ventura Formation taken at the road from Baní to Azua.  The Jura Formation is composed, in general terms, of a monotonous succession of lime- stones (grey in fresh cuts and white by alteration) with intercalated marls. It is subdivided into 3 members: - J1 (or lower member): This member starts with polymictic breccias, mainly vol- canic clasts and minor carbonate fragments of a shallow platform, in a carbonate matrix. This level passes into micritic limestones and marls, well stratified, that 210 represent the main feature of the Jura Formation. The presence of chert is com- mon in this section, forming nodules and layers (Hernaiz-Huerta, 2006 and ref- erences therein). - J2 (or intermediate member): The change from J1 to J2 is gradual with the pres- ence of breccias similar to those at the base of J1 that pass into volcanic sand- stones, calcarenites and greenish shales (Hernaiz-Huerta, 2006; Pérez-Varela et al., 2010 c). - J3 (or upper member): To the top of J2, outcrops reflect the deepening of the basin with the progressive disappearance of the breccias and the deposition of pelagic limestones of J3. They include radiolarian and planktonic foraminifera, consisting of wackstones and minor packstones and grainstones (Hernaiz-Huerta, 2006; Pérez-Varela et al., 2010 c). The transition from J3 to the overlying El Número Formation takes place throughout the Jura red layers (or “Capas Rojas del Jura” as it is defined in Hernaiz-Huerta et al., 2000; and Hernaiz-Huerta, 2006). It is composed of an alternation between red and grey siltstones and white limestones with a thickness between 50 and 100 m, although at some places it is reduced to a couple or meters, where are included into the Jura Formation. It is interpreted as a condensed layer, in an intermediate stage between the distal fa- cies of a carbonate platform of the Jura Formation and the pelagic sedimentation of the overlying the El Número Formation. The red tonality is a consequence of the accumulation of ferruginous materials and oxidized metallic sulphurs (Her- naiz-Huerta et al., 2000; Hernaiz-Huerta, 2006).  The El Número Formation embodies a shaly to marly interval with only decimetric si- liciclastic, and minor calcareous, sandstones. The transition from the Jura Formation is gradual with a diminution in the carbonate content (Hernaiz-Huerta et al., 2000). Based on lithologic similarities sandstones and volcanic clasts of the lower interval of Unit E1, that contains sandstones, volcanic fragments, and chert, could correspond with the J2 member of the Jura Formation. Following this tentative interpretation, the carbonate interval above fits with the J3 member. In outcrops, this member is followed by the shaly El Número Formation, which is in agreement with progression from the carbonates of Unit E1 to the mudstones and siltstones of Units E3 and E4. An almost 500 m interval of the El Número Formation was studied and sampled during the field work (figure 4.4.8), to the north of the village of Las Charcas. The entire section that comprises the outcrop is subdivided into two intervals, ENFA1 and ENFA2 (El Número Formation A1 and A2), in terms of facies associations. The main component of ENFA1 is bed configuration with thin bedded fine to very fine-grained carbonate sandstones, and medium- to thick-bedded mud- stones (figure 4.4.8 A). In this facies association, dark grey to black mudstone beds (figure 4.4.8 B) are in a strong dominance and often take up 80% of the total thickness of ENFA1. The average thickness of sandstone facies within ENFA1 is centimetric (figure 4.4.8 C), although at top, layers can reach a total thickness of 40 cm. The composition varies from bottom to top, passing vertically form a variety of foraminifera (uniseriate and biseriate forams, and globorotalia) and peloids to packstones of globigerina which could indicate a deepening of the section (Canales, personal communication). This hypothetical deepening agrees with an increment of TOC in mudstone sam- ples, from 0.41 %Wt at base to 0.98 %Wt at top. Other skeletal rests include calcispheres, echi- noderms, ostracods, and red algae. The identification of Bouma sequences, sole marks and cross laminations leads to consider ENFA1 as thin-bedded turbidite deposits and, considering the grain size and the relative thick mudstone intervals support the interpretation of ENFA1 as lobe distal fringe with the deposition of dilute low concentration turbidity currents or basin plain with hem- ipelagic deposition. 211 Fig. 4.4.8, Examples of outcrops from the middle – upper Eocene El Número Formation, at the southern flank of Cordillera Central, studied during the fieldwork. A, Example of facies associa- tion ENFA1. B, Detail of dark grey to black mudstones of ENFA1. C, Detail of the interpreted thin bedded turbidites. D, Location of samples (EN) and the well Punta Salinas #1 (PS). E, Ex- ample of facies association ENFA2. Note the angular and erosive unconformity identified in this interval. 212 The main component of ENFA2 is rhythmic thin bedded sequence with sandstone and mudstone beds, brown to grey in this case, that are generally range in thickness from several cm to tens cm (figure 4.4.8 E). Beds have a good lateral continuity. A regularly thin bedded, rhythmic with a high proportion of mudstone, supported the interpretation of ENFA2 as lobe fringe deposits. The shallowing of the El Número Formation is also interpreted in Hernaiz-Huerta (2006), where the culmination of the formation into a shallower platform at top is described. An angular and erosive unconformity was found in the upper interval (ENFA2; figure 4.4.8 E), which might imply some degree of deformation at the time of the deposition of this facies asso- ciation. Further investigations must address if the shallowing of the sequence is related or not with an early stage of deformation of the basin. Paleo-currents of the Peralta Group indicate an ESE and SE predominant fluxes. This inferred direction, parallel to the island arc domain, together with the facies association described for the Units E1, E3 and E4 and their correlated outcrops, led to propose the deposition during the Eocene along a NW – SE deep trench parallel to the arc (Heubeck et al., 1991; Hernaiz-Huerta, 2006). Therefore, considering the inversion of the island arc basement described in Sections 4.2 and 4.3, it is reasonable to assume that this trench could be the result of this process that started since the Campanian. Under this interpretation, the basal breccias of the Trois Rivieres and Las Palmas formations might represent this inversion. As a result, the Cretaceous – Eocene Basin, located at the back-arc zone, could be considered as a back-foreland basin since the Late Cretaceous. 213 4.4.2 The San Cristóbal region, onshore extension of the San Pedro Basin Although this region extends over the limits of the domain, overlying materials that belong to the island arc, it has been included into this section on account of they are the vertical continuation of the Peralta Group since the late Eocene (Biju-Duval et al., 1982). The accommodation for the upper Eocene to Present sequences was generated by the inversion of the Cretaceous – Eocene basin (section A-C’ of figure 4.4.8; Biju-Duval et al., 1982; Heubeck et al., 1991; Heubeck and Mann, 1991). This sedimentation comprises the Río Ocoa Group (upper Eocene to Oligocene), the Majagual Formation (lower Miocene), the Río Nizao Formation (middle to upper Miocene) and the Ingenio Caei Formation (upper Miocene – Pliocene; figure 4.4.9). Therefore, together with the Las Palmas Formation and the Peralta Group (described in Section 4.4.1), this region presents a complete sedimentary record since the Late Cretaceous. The understanding of this zone is crucial for the interpretation of the SPB owing to it is considered the onshore and exhumed extension of the basin (Biju-Duval et al., 1982; Heubeck et al., 1991). The Peralta Belt extends into the offshore along the Muertos Thrust Belt, as a south-westward- verging thrust belt produced by the Eocene inversion after the collision of Hispaniola with the Bahamas Banks (Biju-Duval et al., 1982; Heubeck and Mann, 1991; Hernaiz-Huerta, 2006). Fig. 4.4.9, A: Schematic geological map of the region modified from Pérez-Varela et al. (2010 a) and Abad et al. (2010). B: Cross section of the area, modified from Pérez-Varela et al. (2010 a). Numbers refer to formations: 1, Las Palmas Formation (Campanian to Maastrichtian); 2, Peralta Group (lower to upper Eocene); 3, El Limonal Formation (upper Eocene to Oligocene, Río Ocoa Group); 4, Ocoa Formation (upper Eocene to Oligocene); 5, Majagual Formation (lower Mio- cene); 6, Río Nizao Formation (middle to upper Miocene); 7, Ingenio Caei Formation (upper Miocene - Pliocene). Key to acronyms: SJRFZ, San José – Restauración Fault Zone; SJLPFZ, San Juan – Los Pozos Fault Zone; PS, Punta Salinas #1; LS/LDF: Limonal Syncline / Loma Desecho Fault. 214 The upper Eocene to lower Miocene sedimentary sequences (The Río Ocoa Group) The Río Ocoa Group (locations 4 and 5 of figure 4.4.1 and numbers 3 to 5 of figure 4.4.9), origi- nally defined in Heubeck et al. (1991), “consists of Eocene to early Miocene folded and thrusted conglomerate, sandstone, shale, and olistostromes. The apparent thickness of the sequence is com- monly 2 to 4 km, but locally ranges to as much as 8.2 km. The Rio Ocoa Group appears to be partially overthrust over the Peralta Group along a poorly exposed, fault-modified unconformity. Ages of microfauna from the Rio Ocoa Group range from middle Eocene to early Miocene”. This group is divided into the Ocoa (upper Eocene), El Limonal (Oligocene), and Majagual Formations (lower Miocene) (Heubeck and Mann, 1991 and references therein). This group unconformably overlies the Upper Cretaceous Tireo Group (Heubeck and Mann, 1991). The upper Eocene sediments (Ocoa Formation) are structurally emplaced in the superior level of the Peralta Belt, unconformably overlying the middle Eocene sequences and the basement, con- stituted by the Tireo Group. The Ocoa Formation consists of a thick sequence (3500 to 4000 m estimated at the Geological map of Baní 6170-IV; Pérez-Varela et al., 2010 a and references therein) of marls and shales with intercalations of siliciclastic sandstones and minor calcarenites, conglomerates and olistoliths blocks (Hernaiz-Huerta, 2006; Pérez-Varela et al., 2010 a and ref- erences therein). These conglomerates and olistoliths seem to be related with the active border of the basin, the San José Restauración Fault Zone (Heubeck and Mann, 1991; Heubeck 1992; Pérez- Varela et al., 2010 a). Olistoliths size logarithmically decreases with distance from this suspected basin margin (Heubeck, 1992). Paleo-currents of this formations show a clear NW-SE predomi- nant direction (Heubeck et al., 1991). Apart from the Olistoliths and conglomerates, this formation is dominated by thickening upward sequences of grey to greenish sandy marls and centimetric to decimetric sandstones. Sandstones present normal grading, parallel and cross lamination conforming incomplete Bouma sequences. Finding rests of organic matter accumulated at top of sandstone bodies is usual (Pérez-Varela et al., 2010 a). The upper Eocene? / Oligocene sequence (the El Limonal Formation) consists of a series of con- glomerates and sandstones at base that pass into a rhythmic succession of marls and turbidite sandstones with intercalations of calcarenites and conglomerates with olistoliths (Pérez-Varela et al., 2010 a and references therein). However, “in contrast to the blocks within the Rio Ocoa For- mation, the olistoliths of the E1 Limonal Formation are much smaller and composed of shallow- water, high-energy carbonate facies” (Heubeck et al., 1991). The estimated thickness is 2000 – 4000 m (Heubeck et al., 1991). Biju-Duval et al. (1982) divided this sequence into a basal and an upper interval. The basal inter- val consists of “several hundred meters of polymictic coarse conglomerates. Boulders and pebbles of metamorphic rocks and Eocene limestones accumulated rapidly”. They are overlain by the upper interval of “clastic sequences ranging from shallow-water bioclastic limestones to fine- grained, marly siltstones. Most facies are fine-grained and terrigenous with lenses of conglomer- ates. Graded bedding, channelling, large foreset systems and debris flows indicate deposition along a slope or an unstable area. Conglomeratic, bioclastic, and algal limestones with reworked corals and large forams appear locally. These sediments are interpreted as being deposited as part of an upper slope apron”. This section overly folded Cretaceous to Eocene sediments in angular unconformity (Biju-Duval et al., 1982). However, after the study of this formation during the fieldwork at the nearby of the Valdesia Dam (or “Presa Valdesia”), a division into four main facies association was preferred due to their lith- ological properties. PVFA1 (figure 4.4.10); which would correspond with the basal interval 215 defined in Biju-Duval et al. (1982), consists mainly of polymictic conglomerates of centimetric, rounded, poor-sorted volcanic, metamorphic, and sedimentary clasts. Sub-metric blocks of vol- canic origin were locally observed. Fig. 4.4.10, Example of conglomerates from the PVFA1, consisted of volcanic, metamorphic and sedimentary clasts. These conglomerates pass vertically into PVFA2, constituted by an alternation of mudstones, mi- croconglomerates, and coarse grain sandstones. The contact is conformable, having been ob- served at the road to the Valdesia Dam, where a 20 m thick outcrop was studied. In the PVFA2, grey/dark grey mudstones take up more than 70% of the total thickness. The presence of organic matter, consisting of carbonaceous materials, is usual in mudstones (figure 4.4.11 and 4.4.12 B), which have revealed a TOC up to 0.95 %Wt. Poorly sorted polymictic conglomerates and coarse sandstones are dominated by pieces of coral/algal/larger foraminiferal limestone, volcanic and metamorphic clasts. At top of this association a level of metric blocks was observed although due to bad-access conditions, it could not be studied in detail. Fig. 4.4.11, Examples of Oligocene organic-rich level of the PVFA2 at the San Cristóbal – Baní region. Carbonaceous materials have been identified in mudstones intervals. 216 Fig. 4.4.12, Examples of Oligocene outcrops studied along the Valdesia Dam section in the San Cristóbal Region. A, General overview of the PVFA2 facies association. B, Detail of the alterna- tion of mudstones, microconglomerates and coarse sandstones. The presence of organic matter in mudstone is common, in the form of carbonaceous materials. C, Example of the PVFA3 facies association which alternates layers of marls and sandstones. D, Position of the Presa Valdesia (PV) outcrops. E, Example of the poorly consolidated PVFA4 association, which includes car- bonate clasts and is considered as deposited in the limit Oligocene – Miocene. 217 On thin-sections, microconglomerates, and coarse sandstones of PVFA2 present a greenish tone derived from the presence of a chlorite matrix. Among extra-basinal components stand out vol- canic rock fragments, plagioclase, and chert, while intra-basinal components are represented by globigerina, red algae, coral fragments, molluscs, echinoderms, ostracods, and foraminifera like miliolida or Miogypsina. This last foraminifer dates the deposition in the Oligocene – early Mio- cene interval. Although the contact could not be identified in outcrops, based on the structure, dips of the for- mations and proximity of both associations, the transition from PVFA2 to PVFA3 is assumed as the most likely. PVFA3 consists of an alternation of tan / brownish marls and fine grain sandstones (figure 4.4.12 C). Marls, which dominate this sequence in an approximate proportion of 80:20, have a violaceous alteration patina. On the other hand, sandstones are organized in ~ 10 cm banks. The total thickness of this association could not be estimated based on outcrops. PVFA3 passes vertically into the association PVFA4 (note here that although the contact was not identified in outcrops, this transition is assumed in a similar way than the previous one, consider- ing structural configuration of the region and position of outcrops). PVFA4 is composed of an alternation of poorly consolidated lite brown / tan marls, sandstones, and conglomerates (figure 4.4.12 E). Clasts have mainly a carbonate origin including coral and fossil fragments, although metamorphic and volcanic clasts are also present. This facies association might correlate with the intervals of Oligocene calcirudites and calcarenites, which correspond to a succession of decimet- ric to metric levels with a great accumulation of benthic forams, Lepidocyclina sp. type, together with detritic materials that composed the El Limonal Formation at the region of Baní (geological map 6170-IV; Pérez-Varela et al., 2010 a). Heubeck et al. (1991) assumed that the transition to the lower Miocene sequence (the Majagual Formation) is marked by the first massive occurrence of conglomerates containing coral clasts (southwards the studied area, between positions 5 and 6 of figure 4.4.1), while the top is given by an angular unconformity at the base of the middle Miocene sequence (Ingenio Caei Formation). This transition consists of thin- and medium-bedded sandy mudstone and shales (containing clasts of echinoid spines, gastropods, and rhodolites) and to a lesser extent sandstone, calcarenite, shale, conglomerate, and calcareous rubble beds, that could correlate with PVFA4. Other observations in this interval included Thalassinoides as a common trace fossil on bedding planes (Heubeck et al., 1991) and ripples at top (Abad et al., 2010 a). Sandstones present groove and flute cast at base and high regime flux horizontal lamination and cross lamination together with flame structures and rest of plants at top (Abad et al., 2010 a; Pérez-Varela et al., 2010 a). Biju-Duval et al. (1982) studied the presence of “thick coral, algal, and bioclastic limestones of Aquitanian age (lower Miocene) seem to conformably overly older deposits. These rocks pass into breccias with large boulders and blocks derived from erosion of calcareous banks and iden- tified the re-sedimentation of calcareous beds and coral debris with terrigenous influx along chan- nels and slopes. Limestone was deposited until the end of early Miocene when about 2000 m of sandy siltstone and marl accumulated in an open-marine environment”. During the fieldwork, only mid to proximal slope lower Miocene deposits were found and sam- pled at the Fort Resolis hill (figure 4.4.13), while reef facies were not located. This sequence was subdivided into the facies associations FRFA1 (mid-slope deposits) and FRFA2 (shallow depos- its). FRFA1 consists of an alternation of marls and fossiliferous calcarenites, poorly consolidated (figure 4.4.13 B). These facies are cut by channels composed of crystalline limestones with macrofossils, where gastropods were identified, among others, in the field. On thin-sections, this facies association comprises rudstones, packstones and bioclastic grainstone, where depositional components include coral fragments, red algae, and foraminifera, including Miogypsina that dates the sequence in the interval Oligocene – early Miocene (figure 4.4.13 C). 218 FRFA2 correspond with shallow deposits composed of crystalline limestones (figure 4.4.13 A) interpreted as deposited close to a carbonate platform. On thin sections, this association include reefoidal boundstones and framestone, composed of coral fragments, foraminifera, and echino- derms in a micritic matrix. To the south east (between locations 5 and 6 of figure 4.4.1), the presence of shallow-water car- bonate clasts, coarse grain size, and unabraded coral heads is interpreted in Heubeck et al. (1991) as deposited in a distal to proximal fore-reef environment, while interbedded cobble conglomer- ates and well-rounded igneous clasts would indicate that submarine canyons breached the fore- reef, allowing that materials from the exposed island arc were deposited in the basin. The middle Miocene to Pleistocene sedimentary sequences (The Ingenio Caei Group) The middle Miocene sequence, the Río Nizao Formation (location 6 of figure 4.4.1), is composed of a series of sandstones, conglomerates, and marls at base that pass into a succession of forami- nifera-rich grey shales (Abad et al., 2010 a and references therein). The basal member is formed by metric layers of medium grain sandstones and polymictic, well-rounded conglomerates (small clasts, up to 5 cm) and decimetric layers of sandy marls. Conglomerates present inverse grading and sandstones are poorly cemented (Abad et al., 2010 a). On the other hand, the upper section has a clearly shaly nature, consisting of an alternation of dark grey shales, fine-grain sandstones, and siltstones (Abad et al., 2010 a). Shales layers contain a great accumulation of organic matter, composed mainly of vegetal rests, together with planktonic foraminifera. Frequently, it presents also bioturbation produced by Thalassinoides and Planolites (Abad et al., 2010 a). Abad et al. (2010 a) describes the presence of a transgressive unconformity for the middle to upper Miocene outcrops of the Loma de el Peñón member, which is constituted of carbonate materials that where deposited over this erosive surface. They consist of reefal limestones (bound- stones and packstones) and bioclastic calcarenites (with equinoderms, bivalves, gastropods, and macro-foraminifera) with an estimated thickness of 50 m. The presence of small vertical caverns is usual for these facies. Laterally, reef facies pass into marls and limestones alternated in metric layers. The upper Miocene to Pliocene sequence (Ingenio Caei Formation) is heterogenic, with conglom- erates, reefal limestones and calcarenites, sandstones and marls (Abad et al., 2010 a). In general terms, this formation represents a sedimentation change regarding the underlay levels. In this sense, the system evolved from a siliciclastic marine environment to a deeper carbonated one with a great proliferation of corals, echinoderms, and molluscs (Abad et al., 2010 a). 219 Fig. 4.4.13, Examples of lower Miocene outcrops studied along the Fort Resolis section in the San Cristóbal Region. A, General overview of the FRFA2 facies association. B, Example of chan- nel cutting the alternation of marls and calcarenites that composed the association FRFA1. C, Detail of thin section from FRFA1. D, Position of the Fort Resolis (FR) outcrops. E, Detail of thin section from FRFA2. The lower margin of the photomicrograph is equal to 3 mm. 220 4.4.3 Structure and evolution of the Cretaceous to Eocene Basin Domain The structure of this domain is defined by a thrusts and folds belt that occupies the entire terrain. This belt has received different names depending on if authors considered all the materials in- volved as Paleogene or referring only to the central-southern part of the belt, calling it as the Peralta Belt (e.g. Heubeck et al., 1991; Hernaiz-Huerta and Pérez-Estaún, 2002), or the Trois Rivieres – Peralta Belt if assumed the Upper Cretaceous Trois Rivieres Formation and the whole belt (e.g. Bernárdez-Rodríguez et al., 2004). For this work, the definition of the Trois Rivieres – Peralta Belt (TRPB in advance), that comprises the Upper Cretaceous to upper Eocene sequences, has been selected as it is considered more accurate. The TRPB is limited by the SJRFZ and the SJLPFZ (figure 4.4.14; Bernárdez-Rodríguez et al., 2004). The former put in contact the igneous basement of the Tireo Group with the sedimentary formations of the Campanian to Maastrichtian Trois Rivieres Formation and the Peralta Belt, while the latter affects to Paleogene sedimentary rocks of the Peralta Group that thrusts over the San Juan Valley (in the Oceanic Caribbean Do- main, following the division given in this work). Fig. 4.4.14, Above, Schematic cross section of the TRPB at the region of Arroyo Limón, modified from the geological map of Arroyo Limón (5973-III; Bernárdez-Rodríguez et al., 2004). Below, Schematic cross section of south-eastern segment of the TRPB, modified from the geological maps of Constanza (6072-I, Gómez et al., 1999), Sabana Queliz (6072-II, no references available) and Yayas de Viajama (6071-IV, no references available). Locations in figure 4.4.1. Key to acronyms: MZ, Monoclinal Zone; FZ, Folds Zone; THZ, Thrusts Zone. 221 To the north-west, the Campanian to Maastrichtian sequence presents outcrops along a thrusted fold belt (cross-section A-A’ of figure 4.4.14). Faults have traces with a dominant N 55º W trace direction and are essentially inverse. Two kinds of folds have been studied in the area. The first type is characterised by wide, parallel, almost symmetrical folds, while the second type is repre- sented by angular, strong, asymmetric folds. This block has developed an intense foliation that is related with the axial plane of folds (Bernárdez-Rodríguez et al., 2004). Bernárdez-Rodríguez et al. (2004) interprets that both fold systems are syngenetic, related to the main faults, and the difference folding mechanism lies in the anisotropy of the materials. The Yacabueque fault sepa- rates Upper Cretaceous and Paleogene sediments at the region of Arroyo Limón (location 1 of figure 4.4.1). The Paleogene sequences are better studied at the areas from San José de Ocoa (location 2 of figure 4.4.1) to Baní (location 3 of figure 4.4.1; Biju-Duval et al., 1982; Heubeck and Mann, 1991; Heubeck et al., 1991; Dolan et al., 1991; Hernaiz-Huerta and Pérez-Estaún, 2002; Hernaiz- Huerta, 2006; Pérez-Varela et al., 2010 a). There, these sequences are limited by the SJRFZ and the SJLPFZ, having a structure characterized by a system of thrusts and genetically related folds (figure 4.4.12). However, the distribution of structures is not homogeneous, yet there is a clear zonation from NE to SW (figure 4.4.15). To the SW the belt is represented by thrust, which pre- sent high dips (40-60º) with a great lateral continuity, that can reach a length of 20 km before being substitute by folds (Hernaiz-Huerta, 2006 and references therein). Fig. 4.4.15, Main structural zones of the Peralta Belt modified from Hernaiz-Huerta, 2006. Lo- cation in figure 4.4.1. Thrusts and Folds Zones are separated by the El Naranjo Thrust (ENTH). The entire system is limited by the San José – Restauración (SJRFZ) and the San Juan – Los Pozos (SJLPFZ) Fault Zones. 222 In the intermediate zone, separated by the El Naranjo thrust (figure 4.4.15), the deformation is mainly solved by folds and only at discrete place evolve into thrusts. The axis has a NW-SE direction with subvertical axial planes, slightly dipper than the associated thrusts planes (Hernaiz- Huerta, 2006 and references therein). To the southeast, at the area between Nizao and Baní (figure 4.4.9), large-scale northwest-trending folds characterize rocks of the Rio Ocoa Group have been studied (Heubeck and Mann, 1991). They consist of a minimum of five open synclines of 2 to 8 km half-wavelength that alternate with a minimum of four tight anticlines of 1 to 2 km half- wavelength. The anticlinal hinge zones are commonly faulted by subvertical shear zones (Heu- beck and Mann, 1991). Finally, to the NE, the structure consists of a monoclinal series with a general tilting from 30 to 60º to the NE. This zone meets with the upper Eocene - Oligocene sequence (Río Ocoa Group), while the other two with the lower to middle Eocene Peralta Group (Hernaiz-Huerta, 2006 and references therein). The materials involved in this zone show a clearly a synsedimentary defor- mation. At the area between San Cristóbal and Baní, onshore extension of the San Pedro Basin, (repre- sented in figure 4.4.9) the structure of the upper Eocene to lower Miocene sedimentary rocks can be divided into two zones separated by the SJRFZ (Abad et al., 2010 a). To the west of the fault system, only the upper Eocene sediments (Ocoa Formation) crop out, presenting folds and thrust with a SW vergence. This formation also reveals the presence of a high grade of synsedimentary deformation or soft sediment deformation, accompanied by conglomerates and olistoliths. To the east, upper Eocene? – Oligocene to lower Miocene (the El Limonal and Majagua For- mations) have a different deformation style, restrained only to some folds and splays of the SJRFZ. Folds are wide with fold axis that dips 20º to the SE. The Limonal syncline (showed in figure 4.4.9) is a good exponent. It presents the eastern limb cut by a fault (the Loma Desecho Fault, LDF; Abad et al., 2010 a). To the East of LDF, the succession reveals a great monoclinal series with an orientation of NNW-SSE, dipping to the ENE, corresponding with the presence of a great anticline (figure 4.4.9; Abad et al., 2010 a). Middle Miocene to Pliocene formations in the San Cristóbal – Baní area (figure 4.4.9) dip an average of 19º to the southeast (Heubeck and Mann, 1991). The dip corresponds closely to the plunge of most major folds in the underlying upper Eocene to lower Miocene sequences (Heubeck and Mann, 1991). Heubeck et al. (1991) interpret that “the continuous NE-SW strike of bedding and the absence of folds and faults clearly show that these rocks did not undergo deformation by the same event that produced the regional NW-SE strike and large NW-trending synclines in the sedimentary rocks of the Peralta (lower to middle Eocene) and Rio Ocoa Groups (upper Eocene to lower Miocene)”. Regarding to the deformation age, in addition to the three-stages deformation model proposed in Heubeck et al. (1991) and exposed in the section 4.3.1, the integrated analysis of the TRPB and the San Cristóbal region provided new constraints to the evolution of the central and southern margin of Hispaniola. New observations derived from the geology maps of Baní (Pérez-Varela et al., 2010 a) and Nizao (Abad et al., 2010 a), that complete the stratigraphic and tectonic precisions of previous work, have provided the following constraints into the tectonic evolution of the re- gion:  The development of an island arc during the period Albian - Campanian at the island arc domain, and the deposition of volcanic, subvolcanic and volcanic-sedimentary materials of the Tireo Group that could extend into the Cretaceous to Eocene Basin Domain.  After a deformation phase that folded the Tireo Group, the deposition of Campanian to Maastrichtian sedimentary sequences (the Trois Rivieres and Las Palmas Formations) at 223 the back-arc zone, interpreted as turbidite systems fed by materials coming from the is- land arc and limited platforms of mixed sedimentation.  A thick accumulation of sediments along a deep trench parallel to the Cretaceous arc.  The main tectonic event took place during the late Eocene, inverting the Eocene basin, which is associated with the collision between the North American Plate (represented by the Bahamas Banks) and the island. This collision initiated the deformation of the TRPB, with the upper Eocene to lower Miocene sequence being deposited unconformably over the belt. Fault zones, like the SJRFZ, are activated at this time, observing significant lith- ological variations at both sides.  Convergence of the Beata Ridge since early Miocene.  Uplift of Cordillera Central since middle Miocene, registered by the angular unconform- ity identified in the upper Miocene sequence (corresponding to the Ingenio Caei For- mation). Gravity evidences This domain has an imprint on the Bouguer anomaly maps, giving regional gravity minimum (figure 4.4.16). This is related in this work to the great sedimentary accumulation that have been accreted along the Trois Rivieres – Peralta Belt, involving formation at least since the early Cam- panian to the Pleistocene, as recorded at the San Cristobal region. This minimum enters into the San Pedro Basin with a NW-SE tendency. The Beata Ridge, that will be described in the next domain section, draws a local maximum and seems to deform the Peralta Belt, as it is reflected in the direction changes of the SJLPFZ at its proximities. As explained in Section 4.3.1, to the east of Beata, gravity anomalies defined the limit of the basement along the BFZ. Outcrops at the trace of the SJRFZ are represented by Upper Cretaceous sediments, in agreement with the Bouguer anomaly maps. Nevertheless, this relay is poorly understood, and further works must address this relationships Fig. 4.4.16, Bouguer anomaly map of the central segment of Hispaniola Island. Key to acronyms: CC, Cordillera Central; SJRFZ, San José Restauración Fault Zone; SJLPFZ, San Juan -Los Pozos Fault Zone; BFZ, Bonao Fault Zone; PS, Punta Salinas #1 exploration well (Mobil, 1995); SPB, San Pedro Basin. 224 4.4.4 Partial discussion of the Cretaceous to Eocene Basin Domain The Campanian events The first sedimentary record that has been studied into this domain corresponds to the Campanian to Maastrichtian Trois Rivieres and Las Palmas Formations (locations 1 and 5 of figure 4.4.1). The similarities between them are notorious. Both started with the deposition of breccias (figure 4.4.17) derived from the island-arc Tireo Group at the Campanian, that were followed by the deposition of shales and sandstones in a turbidite context (Bernárdez-Rodríguez et al., 2004; Pé- rez-Varela et al., 2010 a). In both cases, outcrops are thrusted by the Tireo Group throughout the San José – Restauración Fault Zone (SJRFZ). It is possible that their origin would be connected to an early stage of the SJRFZ. In that case, if both shared the same kind of facies and tectonic origin, they could be correlated. As it was exposed in chapter 4.3, the development of an extensional back-arc basin has been proposed for the period Campanian to Maastrichtian (Heubeck et al., 1991). However, assuming that all of the following events took place at the Campanian:  End of the subduction-related magmatism (Escuder-Viruete et al., 2007 a).  Inversion of the fore-arc basin at Cordillera Oriental prognosed from the subsidence curves (García-Senz et al., 2007 a).  Start of the exhumation of the metamorphic units at the Puerto Plata Complex (Escuder- Viruete et al., 2014).  Initiation of the collision between Cuba and the North American Plate (García-Casco, 2001).  Deposition of breccias from the island arc of the Trois Rivieres Formation (Ardèvol, 2004) It seems reasonable to propose a compressional event that affected regionally. Following this idea, the Campanian – Maastrichtian formations would have been deposited in a retro-foreland basin. On the other hand, if we assume the extension of the back-arc during this period of time, the SJRFZ could represent a former normal fault reactivated as a reverse fault. Both processes could create a deep trench for the deposition of the Cretaceous and Eocene depos- its. However, from a regional point of view, a compressional event that englobe the formation of a retro-foreland basin has been interpreted as more plausible in this work. The retro-foreland model would include:  The inversion of the island-arc during the Turonian - Campanian, generating thick-skin thrusting, due to the arriving of a thicker crust, belong to the North American Plate, to the subduction zone.  This inversion would have created a retro-foreland basin in the back-arc zone, generating a great accommodation space.  Deposition of a thick-sedimentary sequence from the Campanian to the middle Eocene, corresponding to the Trois Rivieres Formation and the Peralta Group.  At middle – late Eocene, inversion of the Cretaceous to Eocene basin due to the effective transfer of compressional forces derived from the starting of the oblique collision between the island arc and the Bahamas Platform. 225  This inversion would have generated a tectonic change, forming a new thin-skinned tec- tonic, that would have triggered the development of the Trois Rivieres – Peralta (- Muer- tos?) thrust belt.  The upper Eocene to Pliocene sediments of the San Cristóbal region would have been deposited in a new piggy-back like basin. Fig. 4.4.17, Example of the Campanian breccias facies (Arroyo San Pedro member) of the Trois Rivieres Formation taken from Ardèvol (2004). Similarities between the Oligocene – Miocene sequences from Cibao and San Cristóbal A migration of the Oligocene and lower Miocene carbonate platforms to the north, is inferred from the reconstruction of the basin carried out by Biju-Duval et al. (1982), based on stratigraphic and structural analysis. This migration could represent the transgression of the system in a se- quence stratigraphy framework (figure 4.4.18). From a regional point of view, this transgression coincides with those proposed at the Cibao Basin (see Section 4.2.2) which might imply a regional transgression. Lithologies from the Oligocene and lower Miocene sequences seem to share similarities although deposited at opposite sides of Cordillera Central. Oligocene is represented at this domain by a base of conglomerates (PVFA1) followed by an alternation of organic-rich mudstones and micro- conglomerates (PVFA2) and a series of marls (PVFA3) and poorly consolidated calcarenites (PVFA4). These descriptions fit with the most representative lithologies that represent Units O1 and O2 at the forearc / collisional domain. On the other hand, the lower Miocene is represented here by ramp deposits (FRFA1) that passes laterally into reefoidal deposits (FRFA2) in a carbonate ramp system. Following the same argu- ments than given for the Oligocene sequence, FRFA1 and FRFA2 fits with Unit N1 described at the Cibao Basin, specifically with sub-Units N1.2 for FRFA1 and N1.1 for reefoidal facies of FRFA2. 226 This correlation between the Cibao Basin and the San Cristóbal region (and by extension the SPB) implies a regional transgression that make possible to predict formation properties in a sequence stratigraphy framework. The Oligocene to Miocene transgression would have led to the development of a carbonate plat- form over a ravinement surface (Pérez-Varela et al., 2010 a) at middle – late Miocene times (rec- orded in the Río Nizao Formation of the Ingenio Caei Group) together with a change in the geol- ogy record to a more calcareous sedimentation. Tentatively, middle and upper Miocene sandstones could be correlated with those that compose Unit N5 at the Cibao Basin. Note here that while lignite beds are describe in Unit N5, shales layers of this domain also contain a great accumulation of organic matter, composed mainly of vegetal rests (Abad et al., 2010 a). Fig. 4.4.18, Schematic cross section of the San Cristóbal – Bani area modified from Biju-Duval et al. (1982) to adapt their interpretation to a sequence stratigraphy framework. Key to acronyms: FSST/LST. Falling State System Tract / Low stand System Tract; TST, Transgressive System Tract; mfs, maximum flooding surface. 227 Section 4.5: Oceanic Caribbean Domain The Oceanic – Caribbean Domain (OCD) has been proposed for the region that situated south- wards of the SJLPFZ (figure 4.5.1). It is based on the presence of a different basement, in this case CLIP-related (Caribbean Large Igneous Province) basalts that crop out at Bahoruco range (location 1 of figure 4.5.1) and at its Haitian continuation, Chaîne de la Selle and Massif de la Hotte, and it is interpreted to extend below Neiba and the Chaine des Matheux (Corbeau et al., 2017). In addition, there are substantial lithological differences compared to the formations of the northern domains, especially since the base of the Paleogene (mainly carbonates vs. a more terri- genous deposits in the rest of the island). From the point of view of the structure, this domain is mainly characterized by E-W trending bi-vergent thrusts systems that configure the main Cordil- leras (e.g., Neiba and Bahoruco), but above all, by the E-W trending Enriquillo – Plantain Garden Fault Zone (EPGFZ) that cross-cuts the domain from east to west. The stratigraphy was studied by the analysis of 3 selected wells: Maleno DT-1 (MDT-1), Candelon #1 (CAN-1) and Charco Largo #1 (CHL-1). Fig. 4.5.1, Geological maps over digital elevation model of the southern sector of Hispaniola. Key to acronyms: SJLPFZ, San Juan Los Pozos Fault Zone; EPGFZ, Enriquillo Plantain Garden Fault Zone; CAN-1, Candelon #1; CHL-1, Charco Largo #1, MDT-1, Maleno DT1 (at Maleno abandoned oil field); HI-2, Higuerito #2; PA-1, Palo Alto #1. 4.5.1 Lithostratigraphic units description Before the descriptions of the lithostratigraphic units defined for this domain, a brief analysis of the Cretaceous basement results essential to understand the particularities of this domain. Alt- hough not reached by any exploration well, outcrops indicate that the basement of the OCD is composed of CLIP basalts (figure 4.5.2), differing from what has been studied for other domains. After this introduction, every lithostratigraphic unit defined for this domain will be analysed. 228 Fig. 4.5.2, Schematic stratigraphic chart carried out for the Oceanic - Caribbean Domain based on the information gathered from the geological mapping (Pérez-Estaún et al., 2007) and explo- ration wells. The Cretaceous basement Although the origin, composition or extension of the basement of this domain remains partially unknown due to the scarce of data and the lack of geochemical correlations (Wessels, 2018), outcrops indicates a CLIP-related composition. The oldest rocks of this domain correspond to the Upper Cretaceous tholeiitic basalts, limestones and radiolarites of the Dumisseau Formation (Sen et al., 1988; Escuder-Viruete et al., 2016a; Wessels et al., 2019 and references therein) at Ba- horuco and its lateral continuation, Chaîne de la Selle and Massif de la Hotte in Haiti (figure 4.5.1); and to the Upper Cretaceous basalts, terrigenous sequences and epipelagic cherty lime- stones at the Chaîne des Matheux, the lateral continuation of Sierra de Neiba massif (Wessels, 2018). In the Southern Peninsula of Haiti (composed of the Chaîne de la Selle and Massif de la Hotte in Haiti), the bottom sequences of the Dumisseau Formation contain Aptian – Albian rudists that pass laterally and vertically into pelagic facies that domain until late Campanian times (Wessels et al., 2019). The basalts belonging to this formation are part of the Caribbean Large Igneous Province (Wessels et al., 2019; Escuder-Viruete et al., 2016 and references therein). They are divided into a lower section, of Early Cretaceous to Santonian age, and an upper section of Cam- panian age (Maurrasse et al., 1979; Sen et al.., 1988; Sinton et al..,1998; Escuder-Viruete et al., 229 2016). Above these CLIP-related section, Campanian pelagic limestones with chert nodules and occasional claystone and radiolarites crop out in the Southern Peninsula of Haiti (Wessels et al., 2019 and references therein). Similar Campanian to Maastrichtian section has been observed in the Dominican prolongation of the Southern Peninsula, at the Sierra de Bahoruco massif (location 1 of figure 4.5.1). Overlying CLIP-related basalts, there is a succession of dark-grey bio-micritic limestones (wackestones) followed by a conglomeratic section with basaltic and limestones breccias at the geological map of La Salina (5970-IV, Nicol et al., 2004) and dark to brown sandstones, represented by a great proportion of calcareous clasts and marls intercalations at the geological map of Polo (5970-III, Pérez-Varela et al., 2010 d). The presence of organic matter (carbonaceous material) and the development of paleo-soils rep- resents a peculiarity of the Dumisseau Formations at Sierra de Bahoruco massif, reported between the Upper Cretaceous basalts of the formation. The organic matter seems to correspond with car- bonaceous trunks (figure 4.5.3), branches and other vegetal rests that have been replaced, during hydrothermal activity, forming the larimar deposits that are mined in the area (Joubert et al., 2010 b). This larimar is a unique variety of pectolite (NaCa2Si3O8) characterised by a turquoise-blue tone owing to the presence of traces of vanadium (Bente et al., 1991 in Joubert et al., 2010 b) or manganese and copper (Espí, 2007 in Joubert et al., 2010 b). The descriptions of paleo-soils together with the presence of trunks and other vegetal rests in the Dumisseau Formation indicates that at least this part of the island was emerged during a period of time in the Late Cretaceous. Fig. 4.5.3, Evolution of the pectolite substitution of different carbonaceous trunks that configure the larimar deposits in the region of Sierra de Bahoruco massif, from Joubert et al. (2010). 230 Outcrops at the Chaîne des Matheux reveal similar basement units for the central sector of the domain. According to Wessels (2018), they consist of: - A volcano sedimentary sequence of tuffs, greywackes and weathered basaltic flows, in- terbedded with biomicrites of Santonian age. - Massive white epipelagic limestones with chert levels of Campanian age. - A terrigenous sequence consisting of claystones, calcareous fine sandstones and m-scale beds of greywackes of Maastrichtian age. These series could correlate to the outcrops studied in the Southern Peninsula and Sierra de Ba- horuco massif (Vila et al.., 1982; Pubellier et al.., 1991). However, the lack of geochemical data on the tuffs and basalts do not allows a direct comparison with the CLIP basalts (Wessels, 2018). In the Dominican prolongation of Chaîne des Matheux, the Neiba Chain, the Upper Cretaceous is only represented by the El Manguito Formation. It corresponds to a space-limited outcrop, consisting of a series of grey limestones disposed in layer of 30 – 50 cm that alternate with black shales and basalts (Hernaiz-Huerta et al., 2004 b; Hernaiz-Huerta, 2006). The age of the formation is not well constrained. Only the presence of the association Hedbergella sp., Hetterohelix sp. (cf H. globulosa) and Globotruncana allows to assign a Coniacian to Maastrichtian origin (Hernaiz- Huerta et al., 2004 b). The Paleocene sequences The Paleocene record has not been penetrated by any exploration well. According to outcrops, a section of Paleocene conglomerates, containing clasts of massive limestones and tuffs, overlies unconformably the Upper Cretaceous basement and sedimentary rocks. These conglomerates pass into massive limestones of Thanetian age (BouDagher-Fadel, 2008 in Wessels, 2018). At some places “the transition from Maastrichtian to Paleocene is conformable or characterized by an up- per Maastrichtian ravinement surface (Bourgueil et al.., 1988; Desreumaux, 1985 in Wessels et al., 2019), or by K-T impact ejecta material” (Maurrasse and Sen, 1991 in Wessels et al., 2019). According to Wessels et al. (2019), “the Cretaceous basalts and limestones are unconformably overlain by a diachronous transgressive fining-upwards sequence that becomes more calcareous through time (Bourgueil et al.., 1988). This Paleocene sequence commences with shallow water conglomerates and volcaniclastic breccias, clay- silt- and sandstones overlain by turbiditic silty limestones (Amilcar, 1997; Bourgueil et al.., 1988; Van den Berghe, 1983a), and locally possibly platform limestones (Calmus, 1983)”. Unit E1 and E2 Definition: The middle Eocene Unit E1 (defined at the well PS-1-1, see Section 4.4.1), is also reached from 3383 to 3944 m at the well Candelon-1 (CAN-1). This unit passes vertically into the upper Eocene Unit E2 from 3170 to 3383 m (figure 4.5.4). As well as for Unit E1, the strato- type of Unit E2 correspond to Eocene micritic limestones, dominated by planktonic foraminifera and containing silt-sized and coarser clastic carbonate materials together with scattered, reef de- rived fragments and chert. The coarser nature of the sediment in the sequence might indicate a depositional site on a carbonate submarine fan that is closer to a major channel (Robertson, 1984). 231 Well logs are influenced by bad hole conditions (Candelon #1 Executive Summary, 1981) and should be taken cautiously, especially for Unit E1, where the calliper curve shows high values (figure 4.5.5). The deviation of the calliper has an impact on porosity logs, which effect is more notorious in density log. GR remains generally low (values < 40 API) while SP alternates between low (< -30 mV, coinciding with lower resistivities) and high (> - 30 mV) values. In general, neutron porosity, which seems less affected by bore hole conditions, remains low for the intervals were calliper curve in not high (<15 inches), and only a few intervals have fair porosities (between 8 and 10 %). Units E1 and E2 could correlate to the Eocene limestones that crop out at the Sierra de Bahoruco and Sierra de Neiba massifs (locations 1 and 2 of figure 4.5.1) and their extension in Haiti. The oldest Paleogene records described in Bahoruco correspond to lower Eocene carbonates (Abad et al., 2010 b; Pérez-Varela et al., 2010 d; Pérez-Varela et al., 2010 e; Hernaiz-Huerta, 2006) unlike the Southern Peninsula and the Chaîne des Matheux in Haiti, where Paleocene conglomerates and breccias have been differentiated in the geological mapping. At the Sierra de Bahoruco massif, lower to middle Eocene carbonates consists of a succession of white to beige massive limestones (Polo and Aceitillar Members), poorly stratified which main peculiarity is the presence of great accumulations of red algae (forming rhodolites), bio-clasts, shallow fauna (gastropods, bivalves, corals and echinoderms) and benthic foraminifera, disposed in metric banks (Abad et al., 2010 b; Pérez-Varela et al., 2010 d; Pérez-Varela et al., 2010 e). Textures are classified as wackestone and bioclastic packstones. At some places, like at Palo Ar- riba (geological map of Polo, 5970-III Pérez-Varela et al., 2010 d), metric sequences of shallow- ing facies that start with decimetric bioclastic wackestones, continue with rhodolites packstones that pass into metric algae packstones with centimetric rhodolites, corals, gastropods and other shallow fauna. Pérez-Varela et al. (2010 e) interprets these units as a shallow carbonate platform of Bahamas type, with high energy zones, with the development of red algae build-ups (that includes different depositional facies from more energetic oolites deposits to calmer zones of centimetric rhodo- lites), small reef patches and low energy areas with micritic facies. The platform would have occupied a large area that englobes a great part of the current Bahoruco, cropping out at the geo- logical maps of Polo (5970-III, Pérez-Varela et al., 2010 d), La Ciénaga (5970-II, Joubert et al., 2010 b), Puerto Escondido (5870-I, Joubert et al., 2010 c) and Pedernales (5870-II, Pérez-Varela et al., 2010 e), although for the latter two, the most probable age is middle to late Eocene. Laterally and vertically, these bioclastic unit passes into more distal facies that configure the lower and middle Eocene limestones that compose the lower member of the Neiba Formation. The tran- sition to micritic limestones takes place throughout a diversity of facies from mudstones to wack- estones poorly stratified, with sporadic levels of re-worked shallow fauna (Pérez-Varela et al., 2010 d). These distal facies better crop out at the Sierra de Neiba massif (location 2 of figure 4.5.1). The description involves of a monotonous succession of grey-cream limestones disposed in banks and metric layers, rhythmical stratified and separated by centimetric layers of marls (Hernaiz-Huerta et al., 2004 b). The presence of chert layers or nodules is common but irregular. Petrographically, the series could be catalogued as mudstones – wackestones with bioclasts of planktonic and benthic foraminifera, interpreted as belonging to a ramp basin or a low energy platform (Hernaiz-Huerta et al., 2004 b). In the upper part of the series, shallower facies have been identified, consisting of packstones-rudstones where the presence of macro-foraminifera and rests of algae and corals is frequent. 232 Fig. 4.5.4, Units interpreted at the selected wells for the Oceanic Caribbean Domain. See position in figure 4.5.1. Not to scale 233 Fig. 4.5.5, Middle Eocene Units E1, Upper Eocene Unit E2 and Oligocene Unit O3 as seen on CAN-1 well logs. 234 At the same time, sections formed by calcareous breccias are present also at Neiba Cordillera and have been correlated tentatively with this series (Hernaiz-Huerta et al., 2004 b). The total thick- ness of the distal series is estimated of at least 1000-1500 m, not having been observed the base (Hernaiz-Huerta et al., 2004 b). The carbonate sedimentation is disrupted in middle Eocene by the volcano-sedimentary El Agua- cate Formation (51,7 + 0,5 Ma, Friedmann, 2004; 50,1 + 3,4 Ma, Ullrich, 2004, in Hernaiz-Huerta et al., 2004 b) that crops out along the chain. It consists of volcanic breccias, tuffs, basalts and andesites, co-existing with laminated calcarenites, marls, breccias and conglomerates (Hernaiz- Huerta et al., 2004 b) that separates the lower and upper members of the Neiba Formation. Lower to middle Eocene basalts are also encountered in the western part of the Southern Peninsula of Haiti (Calmus, 1987 in Wessels et al., 2019). The upper member has a middle to late Eocene age, having been studied widespread in this do- main, at the Sierra de Bahoruco, Sierra de Neiba and Sierra de Martín García massifs (positions 1, 2 and 4, respectively, of figure 4.5.1). It is composed of an alternation of limestones, marly limestones and marls. The occurrences of chert forming nodules as well as levels is common. In the same way than for the lower member, limestones are catalogued as mudstones and bioclastic wackestones with planktonic foraminifera, which led to a similar depositional ambient (Hernaiz- Huerta et al., 2004 b). The total thickness at Neiba oscillates from 1000 m, at the central segment of the chain, to 300 – 500 m at the septentrional and meridional borders (Hernaiz-Huerta et al., 2004 b). Proximal facies of the upper member have been observed in Bahoruco, corresponding with the geological maps of Polo (5970-III, Pérez-Varela et al., 2010 d), Pedernales (5870-II, Pérez-Varela et al., 2010 e), Puerto Escondido (5870-I, Joubert et al., 2010 c) and Cabo Rojo (Abad et al., 2010 b). They have been named as the Aceitillar and the Trudillé Units in the geological mapping. The main facies consist of white-beige limestones organized in diffused metric banks, composed of accumulations of rhodolites of red algae, bio-clasts and shallow fauna (gastropods, bivalves, cor- als and echinoderms) with concentrations of benthic macro-foraminifera. Petrographically, they are biomicrite or bioclastic packstones and grainstones of algae and macro-foraminifera (Pérez- Varela et al., 2010 e), as shown in figure 4.5.6. Similar formations are described in Haiti. In the Southern Peninsula, distal facies crop out in the southernmost part while to the north, lower Eocene platform limestones rich in benthic forami- nifera progressively change to middle to upper Eocene outer platform limestones (Wessels et al., 2019 and references therein). Proximal facies are also present in the Chaîne des Matheux for the lower to middle Eocene, with massive platform limestones containing large foraminifera and Melobesia algae (Wessels, 2018 and references therein). Middle Eocene basalts separate the upper Eocene chalky limestones with cherts (Wessels, 2018 and references therein). Paleogeographic determinations not only could indicate the geodynamic evolution of the region but also might contribute in the reservoir prediction. In general terms, the Eocene carbonate sys- tem would have occupied the great part of the Oceanic Caribbean Domain. Proximal facies seem to have been deposited in the region of Bahoruco, Southern Peninsula and Chaîne des Matheux, over the volcanic buildings of the Upper Cretaceous Dumisseau Formation. Laterally, they pass into distal deposits towards Neiba in what it has been interpreted as a carbonate ramp system. Distal facies consist of mudstones and wackestones with some bioclastic intercalations coming from the proximal region. This kind of facies have similarities with the tight limestones drilled at CAN-1, fitting well with the depositional model. 235 Deep middle Eocene carbonate facies express in tight carbonates are also reached at PS-1 in the Cretaceous – Eocene Basin Domain. However, the development of a shallow-water clastic sedi- mentation during the Eocene is interpreted as an inversion of the Cretaceous – Eocene Basin during the late Eocene (see section 4.4.1). This sedimentation differs from the development of the carbonate province in the Oceanic Caribbean Domain. The relationship with the middle Eocene limestones of the Peralta group, at the Cretaceous - Eocene Basin Domain, has been proposed in different works (Hernaiz-Huerta et al., 2004 b and references therein). Further works must address these relationships. Fig. 4.5.6, Example of macro-foraminifera accumulations in a transitional section from the Aceitillar Member and the lower Neiba Member from the geological map of Puerto Escondido (5870-I, Joubert et al., 2010 c). Unit O3 Definition: Oligocene Unit O3 is defined at the well CAN-1-1 from 2904 – 3170 m, being also reached at Charco Largo #1 (CHL-1) from 4736 to 4830 m (figure 4.5.4). At the type well, the stratotype correspond to a sequence of pelagic carbonates interbedded with rarer bioclastic layers (Candelon #1 Executive Summary, 1981). This unit is covered by the Miocene shales of Unit N2 (defined in section 4.2.1). Limestones were deposited in a deep-water, possibly middle to upper bathyal environment, with shallow-water material being occasionally introduced by turbidity currents. (Robertson, 1984). Electro facies do not differ from those of the Eocene interval (figure 4.5.5). Only at top, where there is a 50 m transition on resistivity logs, from flat resistivities corresponding to the Miocene shales to the high resistivities of the Oligocene limestones. At Charco Largo #1, the descriptions of the unit O3 are limited to the well summary report, which does not discriminate from the lower Miocene limestones. In general terms, Oligocene to lower Miocene samples are described as “dominantly chalky, lime mudstones, lesser pelagic foram wackestone to packstones, and rare possible skeletal/intraclast/pellet packstones/grainstones. Fos- sil components of the limestone are overwhelmingly pelagic forams; other fauna includes rare 236 benthic forams, echinoderms and corals. These limestones accumulated in open marine, deep wa- ter, clastic-free environments.” (Charco Largo #1 well report, 1981). On the mud logging report, Oligocene samples consist of lite grey / tan and cream, firm, tight, cryptocrystalline limestones with occasionally intervals of earthy and argillaceous limestones (Charco Largo #1 mud logging report, 1981). The carbonates that composed Unit O3 are comparable to those present at the Sierra de Neiba and Sierra de Bahoruco massifs. Similar facies were also identified at the exploration well Palo Alto #1 (location in figure 4.5.1). At Bahoruco (location 1 of figure 4.5.1), over a stratigraphic discontinuity (paraconformity?), there is a succession of Oligocene to lower Miocene marly limestones with cherts nodules (that include molluscs, radiolarian and foraminifera) and decimetric to metric layers of calcarenites with reworked benthic fauna (algae, macroforaminifera and corals), attributed to the upper mem- ber of the Neiba Formation (figure 4.5.7; Pérez-Varela et al., 2010 d; Pérez-Varela et al., 2010 e; Joubert et al., 2010 c; Abad et al., 2010 b and references therein). The presence of gravitational deposits (mainly breccias) and metric slump levels intercalated between the marly limestones has been also noted (Pérez-Varela et al., 2010 d). The estimated thickness at Bahoruco ranges from 250 to 800 m (Joubert et al., 2010 b; Pérez-Varela et al., 2010 e). In general, these limestones are classified as wackestones and packstones or bioclastic grain- stones. The latter could fit well with the intervals or earthy limestones observed at Charco Largo #1. Sedimentary structures and facies lead to interpret them as a part of a distal carbonate platform (Pérez-Varela et al., 2010 d; Pérez-Varela et al., 2010 e; Joubert et al., 2010 c; Abad et al., 2010 b and references therein). This formation passes vertically and laterally into massive bioclastic limestones and micritic lime- stones of the Aguas Negras Member and the calcarenites and massive limestones with micritic limestones of the Pedernales unit (member and unit definitions in Pérez-Varela et al., 2010 e; Joubert et al., 2010 c; Abad et al., 2010 b and references therein). Nevertheless, it should be noticed that these formations are dated as Oligocene to early Miocene, and the limit is not clearly defined. The same limits problem happens for the Sierra de Neiba massif. There, the Oligocene is englobed into the upper member of the Neiba Formation that goes from the upper Eocene to the lower Miocene. At any case, the presence of distal facies should be considered for this part of the domain, as it has been interpreted for this member (Hernaiz-Huerta et al., 2004 b). Fig. 4.5.7, Examples of marly limestones with cherts from the geological map of La Ciénaga (5070-II, Joubert et al., 2010 b). 237 The Aguas Negras Member is composed of a centimetric succession of clear to beige slightly marly mudstones-wackestones with planktonic fauna, levels of packstones with benthic forami- nifera and grainstones of shallow fauna (red algae, corals and macroforaminifera) (Pérez-Varela et al., 2010 e). At some places, micritic limestones have been also described (Joubert et al., 2010 c). The total thickness is estimated around 150 m (Pérez-Varela et al., 2010 e). Laterally it passes into the marly upper member of the Neiba Formation, being interpreted as a transition from me- dium to distal facies of a carbonate ramp (Pérez-Varela et al., 2010 e). Similar to the last member, the Pedernales unit groups a series of different limestones that crop out along the Sierra de Bahoruco massif (figure 4.5.8), which differ in the different facies and depositional styles, configuring the distal, intermediate and proximal zones of a carbonate ramp. The distal facies are composed of beige to pinkish micritic limestones that intercalates thin layers of white more fossiliferous limestones (Abad et al., 2010 b). The intermediate zone is defined thanks to the presence of massive pinkish limestones characterized by the accumulation of plank- tonic foraminifera (globigerina packstones or bioclastic wackestones). There are intercalations of white limestones with benthic foraminifera (specially Lepidocyclina, Operculinoides), corals and algae (Abad et al., 2010 b). Finally, more proximal facies contain white-pink wackestones with planktonic foraminifera that alternate with packstones of reworked shallow fauna (including Nummulites and Lepidocyclina). This unit can reach 300 – 400 m (Pérez-Varela et al., 2010 e). Fig. 4.5.8, Example of thickening upwards Oligocene – lower Miocene alternation of micritic (A) and bioclastic (B) limestones at Bahoruco, from Pérez-Varela and Abad (2010). 238 Unit N1 Unit N1, defined at the well CA-1-1 in Section 4.2.1, englobes a series of lower to middle Miocene limestones (traditionally named the Sombrerito Formation in southern Hispaniola) that are subdi- vided in this work into the subunits N1.1, N1.2 and N1.3 (figure 4.5.9), based on the same crite- rion (lithologies and electro facies) than for the Miocene calcareous sequences of Cibao (see sec- tion 4.2.1). Although the information available is limited, the type well selected for this unit at the Azua basin is the well Maleno DT1 (MDT-1, figure 4.5.4). The division into sub-units follow lithological description from the mud loggings (Maleno DT1 mud logging report, 1960), core descriptions (Maleno DT1 Drilling Steam Test operations report, 1960) and well logs. Unfortu- nately, seismic profiles at the area have not enough resolution to discern the geometry and struc- ture of the different subunits.  Sub-unit N1.1 is delimited from 1400 to 1920 m and consists of a series of white chalky limestones and cream, sucrosic and very fossiliferous limestones that include calcarenites and algal limestones with minor cream, hard, crystalline limestones and marls and chalky limestones at top (figure 4.5.9). This sub-unit is represented by low resistivities (up to 20 Ωm), which increase slightly for the crystalline intervals (up to 30 Ωm). SP remains gen- erally high (> -15 mV). These facies are interpreted as proximal, although unlike its equivalent at the Cibao Basin (drilled at the well CA-1), the well MDT-1 did not reach platform deposits. Core descriptions reveal the presence of fractures and pinpoint to vuggy porosity.  Sub-unit N1.2 is interpreted into two intervals from 1950 to 2850 m and from 1200 to 1400 m (figure 4.5.9). The first interval consists mainly of cream, dense, hard, crystalline limestones and white chalky limestones with minor cream fossiliferous limestones. The second interval, above sub-unit N1.1, is composed of dense limestones, silty shales and chalky limestones. The hardness of this sub-unit might be connected with higher resistiv- ities due to a lower presence of porous intervals filled of saltwater. SP ranges between - 40 and -10 mV. Core analyses reveal the presence of pinpoint to small vuggy porosities at some intervals of fractured, dense, crystalline and fossiliferous limestone of the lower interval with dead oil present along fracture planes. The presence of chalky and massive dense limestone with a lower fossiliferous content is interpreted as a deeper depositional environment.  Sub-unit N1.3 is interpreted at limited intervals by a diminution of resistivities (figure 4.5.9) and the presence of highly fractured fossiliferous limestones and white chalky limestones, interpreted as the potential arriving of reworked shallow fauna. The definitions regarding to the Miocene sequences given in the bibliography results confusing due to the different formations that have been established without a correlation to the prior de- nominations and on the other hand, owing to the determination of units based on different criteria, stratigraphic at some cases and palaeontologist in others (Díaz de Neira et al., 2000). For the new geological mapping, Díaz de Neira et al. (2000) qualifying prior studies (García and Harms, 1988; McLaughlin et al.., 1991) of the Sombrerito (lower to middle Miocene limestones) and Trinchera (middle to upper Miocene shales and marls) Formations, establishing a shallower depositional ambient for the Azua region (geological map of Azua 6071-II, figure 4.5.10). Lower to middle Miocene limestones crop out at the Sierra de Neiba, Sierra de Bahoruco and Sierra de Martín García massifs (Hernaiz-Huerta, 2006 and references therein), see figure 4.5.10. They have been also studied in Haiti at the Southern Peninsula and Chaîne des Matheux (Wessels, 2018 and references therein). 239 Fig. 4.5.9, Unit N1 as seen on Maleno DT-1 well logs. Note the limited data available to interpret the unit. The interval has been subdivided into sub-units N1.1 (consisted of chalky and fossilifer- ous limestones), N1.2 (consisted of hard, crystalline limestones) and N1.3 (consisted of chalky and hard fracture limestones). 240 Fig. 4.5.10, Geological map of the Azua region over digital elevation model. Key to acronyms: QC-1, Quita Coraza #1; MDT-1, Maleno; HI-2, Higuerito; GP-3, Gas Pedom #3; PA-1, Palo Alto #1. Numbers refer to positions mentioned on the text. At the Sierra de Neiba massif (position 3 of figure 4.5.10), the Sombrerito Formation consists of an alternation of calcarenites and marls (Hernaiz-Huerta et al., 2004 b; Díaz de Neira et al., 2004 b and references therein) that have been divided into three sections: - The lower marly section is composed of grey and dark marls with intercalated decimetric bioclastic calcarenites (bioclastic/pellets packstones) with a tabular geometry and grain grading that pass again into the marls, interpreted as basin plain deposits (Hernaiz-Huerta et al., 2004 b; Diaz de Neira et al., 2004 b; Hernaiz-Huerta, 2006). Allochems composed up to the 60% of samples with a moderate micritic content (35-38%) and a low sparite percentage (2-3%). Textural components vary between different outcrops. The fossilifer- ous content ranges from 68-76% to 80-85%, the pellets from 14-20% to 8 – 12% and the minor intraclasts from 10-12% to 5-7% at the geological maps of Galvan (5171-IV, Her- naiz-Huerta et al., 2004 b) and Villarpando (5971-I, Diaz de Neira et al., 2004 b) respec- tively. The thickness of this section is not lower than 300 m according to field observa- tions (Hernaiz-Huerta et al., 2004 b). - The intermediate calcareous section is defined as white limestones and calcarenites dis- posed in banks with thin intercalations of marls. Calcareous levels are decimetric to met- ric, included chert nodules and fossiliferous content, being classified as bioclastic wack- estones and bioclastic packstones/rudstones. This section is interpreted as a carbonate turbidite system. The estimated thickness is 75 m (Hernaiz-Huerta et al., 2004b). - The upper marly section is constituted by a succession of dark marls with decimetric calcarenites and sandstones. This section is considered both the basal sequence of the Trinchera Formation (Cooper, 1983 in Hernaiz-Huerta et al., 2004 b) or the top of the Sombrerito Formation (Mc Laughlin et al.., 1991 in Hernaiz-Huerta et al., 2004 b). Field observations does not allow to define accurately the thickness, which is thought not to be greater than 200 m. At some points, the contact at base is concordant with the Eocene – Oligocene sequences, while at some places a basal conglomerate (with volcanic breccias) layer has been identified in the ge- ological mapping (Hernaiz-Huerta, 2006 and references therein), that is also present at the Sierra de Bahoruco massif (Llinás, 1972 in Hernaiz-Huerta, 2006). 241 Shallower facies have been described at the Azua region (location 1 of figure 4.5.10). As well as at the Sierra de Neiba massif, lower to middle Miocene limestones have been divided into three section: the lower marly section, an intermediate calcareous section and an upper marly section (Díaz de Neira and Solé, 2002). - The lower marly section is composed of lower Miocene marls that intercalate sandstones, constituting both a soft level that influences the landscape. It is a monotonous succession of dark and grey marls and decimetric to metric tabular sandstones, organized in Bouma sequences with flute casts and occasionally, appear disorganized in what is interpreted as debris flows (Díaz de Neira et al., 2000; Díaz de Neira and Solé, 2002). Sandstones has wide composition from calcareous to volcanic clasts or rests of corals and gastropods (Díaz de Neira et al., 2000; Díaz de Neira and Solé, 2002). The thickness is not well- known, although thought to be around 60 m (Díaz de Neira et al., 2000; Díaz de Neira and Solé, 2002). - The intermediate calcareous section consists of a monotonous succession of lower to mid- dle Miocene white limestones, occasionally pink, where locally the calcarenites can be the dominant lithology (Díaz de Neira and Solé, 2002). The base points out a net litho- logical change from the lower section. The thickness is not well-constrained, although a minimum of 500 m should be considered (Diaz de Neira et al., 2000). At Punta Vigía, this section is characterized by the presence of frequent structures with an algal origin like stromatolites, algal balls, oncolites which Díaz de Neira et al. (2000) interprets as an algal mat. Another example of shallow deposition is given at the outcrop of San Francisco steam, where abundant neritic fauna, ripples, wavy and cross stratification, bioturbation and channel and bars morphologies have been identified and interpreted as littoral facies (Diaz de Neira et al., 2000). Petrographically, this section corresponds to bioclastic rud- stones and boundstones (Diaz de Neira et al., 2000). The great fossil content includes red and green algae, equinoderms, bivalves, benthic foraminifera, gastropods, ostracods and corals (Díaz de Neira and Solé, 2002). The depositional structures, architecture and fos- sils of this unit, characteristic of a shallow depositional ambient, differ from other de- scriptions of the Sombrerito Formation given in the bibliography for the same age, where it is considered as a 500 m thick section of pelagic limestones, marls and shallow-marine carbonate debris flows (Mc Laughlin et al.., 1991). This could imply a change of facies to the southwest, to the Sierra the Neiba massif. - The upper marly section is composed of middle to upper Miocene grey to brown marls and decimetric tabular limestones. The latter are basically wackestones with bioclasts. The estimated thickness is about 350 m (Diaz the Neira and Solé, 2002). Description from the shallow intermediate calcareous and the upper marly sections fit well with sub-units N1.1 and N1.2 respectively, described at the well MDT-1. Same as for the Cibao Basin, subunit N1.1 would correlate to the intermediate shallow carbonate section, while subunit N1.2 to the marly section and N1.3 to a marly section with reworked materials, possibly calcarenites. From a regional point of view, a change of facies occurs from the Azua region to the west, where the lower – middle Miocene shallow water carbonates pass into calcarenites laterally and into marls vertically. The lateral changes would explain the presence of a thick Miocene carbonate section at the well MDT-1, that could be interpreted as shallower deposits, and thin deep-water deposits at the well CHL-1. At the Sierra de Bahoruco massif, lower to middle Miocene limestones are similar to those de- scribed in Azua. The Barahona unit, a lateral equivalent of the Sombrerito Formation (Abad et al., 2010 c), consists of a succession of beige to white limestones which include metric banks of corals, molluscs, red algae and benthic and planktonic foraminifera. They intercalate some deci- metric layers of marls and marly limestones, with a high content in planktonic foraminifera (Abad 242 et al., 2010 c). As well as for the Paleogene sequence, proximal facies are associated to the Ba- horuco area while distal facies to the Sierra the Neiba massif. It is notorious that the transition from the intermediate to the upper section took place at the early to middle Miocene, same than for the outcrops at San Cristóbal (Cretaceous to Eocene Basin Domain) and Cibao Basin (Forearc / Collisional Domain). This would imply a regional transgres- sion for this period that was registers in every domain. Furthermore, lower to middle Miocene proximal carbonates of Unit N1 passes vertically into the middle to upper Miocene shales of Unit N2, described below, in what it is a clear deepening of the system and could be assumed in a general transgression of a carbonate ramp system, as previously study in other domains. Unit N2 The Miocene to Pliocene Unit N2, defined at the well LIC-1 in Section 4.2.1, and consisting of an alternation of shales, marls and minor sandstones, is reached at the wells MDT-1 (from 303 to 1225 m), CAN-1 (from 789 to 884 m and from 1859 to 2905 m), and CHL-1 (from 4088 to 4340 m). The description of samples for these intervals are similar. At Maleno DT1, this unit is com- posed of a succession of upper Miocene silty shales with thin silty sandstones layers. Its electro facies are represented by high spontaneous potential values and low resistivities (almost flat) which locally increase due to the growing of sand proportion (figure 4.5.11). Shales consisted of grey, fine, firm, silty shales and marls. At the base, calcareous sandstones became relevant in detriment of shales, expressed in higher resistivities and a slight separation of shallow and deep logs (Maleno DT1 mud logging report, 1960). Another example is the description at Charco Largo #1, where it consists of fossiliferous, grey / dark grey and green chlorite shale, with associated fine clastics and limestones. The fossils are mainly deep-water, pelagic foraminifera (Charco Largo #1 well report, 1981; Charco Largo #1 mud logging report, 1981). The descriptions of this section at Candelon #1 are limited to the presence of Miocene shales and marls with shaly sand- stones so, the limits are based on electric logs (figure 4.5.11). The interval that configures this lithostratigraphic unit has been interpreted as belonging to the Trinchera Formation (Charco Largo #1 well report, 1981; Mann et al., 2008) that crop out along the San Juan – Azua basin (position 2 of figure 4.5.10 is one of the most representative sections of this formation, Hernaiz-Huerta, 2006). The Trinchera Formation is defined as a 1000 to 2650 m thick section of upper Miocene to lower Pliocene (Ardèvol, 2004; Mann et al., 2008 and refer- ences therein) mudstones, siltstones, sandstones and conglomerates that record the onset of clastic sedimentation in the Azua Basin (Mc Laughlin et al., 1991; Mann et al., 2008 and references therein). The transition from calcareous to a clastic sedimentation is gradual as it is recorder at the Gajo Largo Member (Mc Laughlin et al.., 1991). Ardèvol (2004) divided this formation into three sections between Sierra de Neiba and Sierra de Martín García (location 2 of figure 4.5.10). There, the formation has a total thickness of 1500 m. The lower section is composed of shales with intercalations of fine/medium grain sandstones. It is organized into decametric inverse-grading sequences. Sandstones become more relevant for the intermediate section (figure 4.5.12), alternating channelize and non-channelize morphologies. The former forms metric to decametric normal-grading sequences, erosive at base, being consti- tuted by amalgamed bodies. The latter has a metric scale, with fine/medium grains and variable cyclicity. Stratigraphic structures are rare, having a bad classification. This section is interpreted as a normal grading, although slumps and debris flows can appear at top (Ardèvol, 2004). 243 Fig. 4.5.11, Example of Unit N2 (shales) and N5 (sandstones) as seen of Candelon #1 well logs. The upper interval consists of a shaly-marly series that intercalates a decametric progradation of sandy to conglomerate normal grading sequences (Ardèvol, 2004). Ardèvol (2004) interprets this formation as a deltaic-turbiditic progradating system deposited in the middle part of the talus or in a deep ramp, in agreement with McLaughlin et al. (1991). The lower interval is interpreted as a distal channel-levee system. The intermediate interval would correspond to a channel-levee that alternates channels and crevasse lobes. Finally, the upper interval is interpreted as shelfal lobes (Ardèvol, 2004 and references therein). 244 Fig. 4.5.12, Outcrops of the intermediate section of the Miocene to Pliocene Trinchera Formation (Unit N2) at the road from Azua to Barahona, location 2 of figure 4.5.9 (from Ardèvol, 2004). In a tentative well to outcrop correlation, this division seems to fit well with the records at the well Candelon #1 (figure 4.5.13). In this case, the lower Trinchera section would correspond with the deeper interval of Unit N2, the intermediate intervals with the sandstones of sub-unit N5, which is defined in Section 4.2.1 and will be describe later in the text, and the upper interval with the shales and sandstones of Unit N2 and sub-unit N5. Under this interpretation, sandstones bodies of Unit N2 should be considered as channel-levee deposits, while sub-unit N5 would represent an intercalation of channels and crevasse lobes for the deeper interval and as shelfal fans for the uphole interval. Fig. 4.5.13, Tentative correlation between the outcrops of the Trinchera Formation and the Mio- cene shales and sandstones reached at Candelon #1. The stratigraphic column of the Trinchera Formation is taken from Ardèvol, 2004. 245 - Sub-Unit N5 Sub-unit N5, defined at the well SFR-1 in Section 4.2.1 and belonged to Unit N2, is assigned to group those intervals where sandstones dominate over shales. In this domain, it was reached at the well CAN-1 (figures 4.5.11 and 4.5.14), although it is not discarded that some of the sandy intervals at Maleno DT-1 and CHL-1 would correlate with this unit. At CAN-1, sub-unit N5 is interpreted into three intervals, from 509 to 789 m, from 884 to 1859 m and from 2280 to 2400 m. This sub-unit is represented by a decreasing in GR, between 35 and 70 API in front of 90 – 100 API for the shaly Unit N2 (figure 4.5.14), and SPN which passes from a flat curve, around -5 mV, to lower values (< -10 mV). Lower GR and SPN intervals of this unit fit with a slight increase in resistivities, compared with the flat curve that represents the shales from Unit N2. As it was exposed at the outcrop correlation of Unit N2, this unit could be related with the inter- mediate and upper intervals of the Trinchera Formation, where sandstones dominate the sequence, interpreted as intercalation of channels and crevasse lobes for the deeper section, and as shelfal lobes for the upper one (figure 4.5.12). Fig. 4.5.14, Example of the middle interval of Unit N5 at the well CAN-1. 246 Unit N3 Definition: Unit N3 is defined at the well CHL-1 from 2620 to 4088 m. The stratotype correspond to an alternation of lower – middle Miocene anhydrite, salt, shales and dolomites (Charco Largo #1 well report, 1981). Outcrops indicate that this unit is restricted to the Enriquillo basin. This unit is highly variable lithologically (Charco Largo #1 well report, 1981; Charco Largo #1 mud logging report, 1981). At the type well, this unit is overlapped by an alternation of Neogene lime- stones, siltstones and sandstones (Unit N4, defined later in this section). According to the Charco Largo #1 well report (1981), the lithologies suggest that this unit was deposited in a marine to terrestrial evaporite settings. Resistivity and density logs exhibit this alternation with high and low values (figure 4.5.15). Two sills of hornblende diorite occur in the middle of the formation, marked by the highest gamma ray values of the well (figure 4.5.15). They were dated by K/Ar as 12.3 ± 1.3 Ma sill intrusions. This dating is in agreement with the biostratigraphy analysis of the well (Charco Largo #1 well report, 1981). Unit N3 has been correlated with the evaporites of the Angostura Formation (Charco Largo #1 well report, 1981) that crop out at the northern flank of the Sierra de Bahoruco massif (location 3 of figure 4.5.1), limiting with the Enriquillo valley. This formation consists mainly of gypsum (that is interbedded with siltstones) and halite that intercalate with shales, having an estimated thickness of 300 m (McLaughlin et al.,1991). The thicker section reached at Charco Largo #1 may be a secondary effect of salt flowage (McLaughlin et al.,1991). Outcrops present a high grade of deformation that includes folds, faults, thrusts, duplexes and local diapirism (Nicol et al., 2004). The age of the formation is controversial. McLaughlin et al. (1991) and Mann et al. (1999) sup- port an early Pliocene age based on the dating that Bold (1975) established for the Angostura Formation by the identification of ostracods fauna (Cyprideis salebrosa and Ciprideis mexicana). Nevertheless, the dating of the diorite sill implies a middle Miocene or older age. This age, early to middle Miocene, has been considered in this work as it is also consistent with the fauna en- countered in the well. However, further analysis is required owing to the proper dating of this evaporite sequence is essential to better understand the main tectonic events of the Enriquillo Basin. The presence of marine to terrestrial evaporites above marine shales (from Unit N2) might have important impli- cations for the regional dynamics, possibly implying a tectonic inversion of the area. If we assume a middle Miocene age for Unit N3, a tectonic event in the early – middle Miocene is reasonable to be expected. This topic will be argued in Section 4.5.4. 247 Fig. 4.5.15, Evaporites from Unit N3 as seen on the Charco Largo #1 well logs. 248 Unit N4 Definition: Unit N4 is defined at the well CHL-1 from 2118 to 2620 m (figure 4.5.16). The stra- totype correspond to an interval of upper Miocene fine sediments, that includes soft, green, chlo- rite claystones; largely unconsolidated shaly, lithic siltstones; and fine to medium grain sand- stones. This interval was separated in this work from Unit N6 (described below) due to the pres- ence of marine limestones (shaly/silty lime mudstones, miliolid/pellet wackestone to grainstones and shaly bivalve packstones) (Charco Largo #1 well report, 1981). Unit N6 Definition: Above Unit N4, Unit N6 is defined at the well CHL-1 from 1220 to 2118 m (figure 4.5.16). The stratotype correspond to an 898 m thick section of Miocene to Pliocene shales, clays and minor lithic sandstones and conglomerates reached. Unit P1 Definition: Unit P1 is defined at the well CHL-1 from 0 to 1220 m (figure 4.5.16). The stratotype correspond to a section of Pliocene to Pleistocene of cyclic, clastic coarsening uphole sequences of, from base to top, unlithified green clay/shales which become silty and grade up into shaly lithic siltstones. Siltstones pass up into poorly sorted, poorly rounded, very fine to very coarse, unconsolidated lithic sandstones that grade up into thick poorly sorted lithic conglomerates. This unit is also reached at the well MDT-1 from 0 to 304 m. The interval that comprises Units N4, N6 and P1 is correlated to the Las Salinas Formation in the Charco Largo #1 well report (1981). However, a more detail correlation would link the upper part of Unit P1 to the Jimaní Formation (Mann et al., 1999). The Las Salinas Formation is defined as a 2000 m thick section of shallow-marine and marginal marine siliciclastic rocks (McLaughlin et al.,1991 and references therein) that crop out at the northern flank of the Sierra de Neiba massif (location 3 of figure 4.5.1). Unit N4 could be correlated to the massive limestones (“Razorback Ridge” in Mann et al., 1999). Outcrops reveal the presence of a basal level, rich in rest of shells, that presents sigmoidal and unidirectional cross-lamination. The surface of the bank presents also symmetric ripples marks (Nicol et al., 2004 and references therein). Above the bank, the Las Salinas Formation consists of grey and red shales that intercalate deci- metric to metric sandstones and minor limestones and conglomerates (Nicol et al., 2004). The series finalised with section of marly-conglomerates that intercalate sandstones, shell-rich lime- stones and corals (Nicor et al., 2004 and references therein). Paleoenvironmental interpretations assign shallow-marine to lagoonal setting for the area (McLaughlin et al.,1991 and references therein). Finally, the Jimaní Formation consists of a 125 m thick succession of Pleistocene fossiliferous limestones, sandstones and mudstones (McLaughlin et al.,1991 and references therein). An an- gular unconformity separates it from the Las Salinas Formation (McLaughlin et al.,1991 and ref- erences therein). 249 Fig. 4.5.16, Units N4, N6 and P1 as seen on the Charco Largo #1 well logs. 250 4.5.2 Wells correlation Four wells were selected from this domain in terms of their lithologies, total depth and quality of the logs (figure 4.5.17). Although the well Punta Salinas #1 (PS-1) belong to the Cretaceous to Eocene basin domain, it has been included into this section to correlate together all the wells from the southern region of Hispaniola. Fig. 4.5.17, Locations of the selected wells for this domain. Yellow and blue lines show the cor- relation paths of figure 4.5.17 and 4.5.18. Red dashed-line shows the location of cross-sections A-A’ represented in figure 4.5.19 and B-B’ represented in figure 4.5.20. Paleogene sequences are reached at the wells PS-1, CAN-1 and CHL-1, although at CHL-1 the Paleogene only consists of ~ 100 m of Oligocene deep-water limestones. The SJLPFZ juxtaposed the Eocene Units E1 and E3 against the Neogene sediments of the Azua Basin (Units N1 and N2; figures 4.5.18 and 4.5.19). Although separated by a great distance (~ 140 km) there are significant similarities between the middle Eocene limestones reached at the wells PS-1 (belonged to the Cretaceous – Eocene Basin Domain) and CAN-1 (belonged to the Oceanic Caribbean Domain). However, while a similar carbonate pelagic sedimentation continued during the middle to late Eocene (Units E1 and E2) and Oligocene (Unit O3) at CAN-1 (and CHL-1, figure 4.5.19), lime- stones are substituted by mudstones at PS-1 (Unit E3, correlated with El Número Formation, see section 4.4.1). Different facies point out different depositional environment for both domains dur- ing the late Eocene and Oligocene. As previously exposed, further works must address the rela- tionships of middle Eocene limestones of Unit E1 at both domains. In the early Miocene, it is inferred from the well correlation panel I-I’ (figure 4.5.18) a shallower deposition for the Azua Basin. While the well MDT-1 reached lower to middle Miocene car- bonates (Unit N1), including shallow deposits, deep-water mudstones (Unit N2) directly overly the Oligocene carbonates of Unit O3 at the wells CAN-1 and CHL-1. Unit N1 is covered by mudstones of Unit N2, which is interpreted as a transgression of the car- bonate system, like those interpreted in the Cibao Basin. The presence of middle Miocene evap- orites at the well CHL-1 over deep water deposits of Unit N2, which represents a regression of the system, is interpreted as an indicator of early tectonism in the region. Deformation, that would include the uplift of Neiba and Bahoruco, would has led to a great accumulation of upper Miocene sediments at the Neogene depocenter, located at the Enriquillo Basin. 251 Fig. 4.5.18, Well correlation panel I-I’. See figure 4.5.15 for location of wells. 252 Fig. 4.5.19, Well correlation panel I-II’. See figure 4.5.15 for location of wells. 253 4.5.3 Oceanic Caribbean Domain Structure According to Mann et al. (1999), “The regional structure of south-central Hispaniola is dominated by synclinal upper Miocene to Recent sedimentary ramp basins separated by fault-bounded anti- clinal mountain ranges. Major folds nested in the larger scale ramp basins affect upper Miocene to Pleistocene sedimentary rocks and have fold axes ranging in trend from northwest-southeast to east-west. These folds are parallel in profile, lack internal deformation, and formed during pro- gressive closure of the ramp basin in post-early Pliocene time. A shortening amount of 12 percent is estimated for concentric folds in the Azua basin using a regional cross section. The orientations and the sense of slip on major and minor faults are consistent with major fold data and indicate a northeast-southwest- or north-south-directed regional shortening”. The up-lift and the ramp basin formation is, following that interpretation, related to the oblique collision and continued conver- gence between the island-arc related terrains of central Hispaniola and the oceanic-Plateau ter- rains of southern Hispaniola (Mann et al., 1999 and references therein). Different cross-sections that cut the domain from the central segment of the island were ensem- bled (figure 4.5.19) to have a regional picture of the structure. Fig. 4.5.19, Schematic cross-section for the Oceanic Caribbean Domain. Modified from Gómez et al., 1999 2; Díaz de Neira et al., 2004 b; Pérez-Varela et al., 2010 c; Abad et al., 2010 b; and Hernaiz-Huerta, 2006. Location in figure 4.5.15. Key to Acronyms: SJRZ, San José Restauración Fault Zone; SJLPFZ, San Juan Los Pozos Fault Zone. Mann et al. (1991 a) described the Sierra de Martín García and Bahoruco (figure 4.5.19) as large faulted anticlines, considering the Enriquillo and Azua basins as large intervening synclines, where “high-angle faults bounding the mountain ranges exhibit several kilometres of late Neo- gene structural relief between topographically uplifted Paleocene- middle Miocene carbonate rocks in the Sierra de Neiba, Sierra Martín Garcia, and Sierra de Bahoruco and equivalent car- bonate rocks known from exploratory wells in the Enriquillo and Azua basins” (Mann et al., 1991 a). The deformation styles, according with these authors, correspond to dome and basin structures characterized by doubly plunging, parallel anticlines and synclines. Hernaiz-Huerta and Pérez-Estaún (2002) interpreted the Azua Basin as a triangular zone, eastern part of the basin is dominated by the Beata indenter, and the structures of the Sierra de Martín García and Sierra de Neiba as pop-ups (Hernaiz-Huerta 2006). Azua Basin is characterized by folds, some of those related to thrust with minor displacements. The directions are influenced by the frontal thrust of the Peralta Belt (SJLPFZ) and the Sierra de Martín García and Neiba massifs. From the curvature radius of the fault-associated folds, the thrusts should root into a detachment surface located at a minimum estimated depth of 4 km (Hernaiz-Huerta, 2006 and references therein). Nevertheless, it is also assumed a deeper detachment, that could involve even the 254 basement, in based of the analysis of the magnetic anomalies (Hernaiz-Huerta, 2006 and refer- ences therein). The reinterpretation given in these works led the authors to propose the schematic cross sections similar to figure 4.5.19. The indenter of the Beata ridge towards the NNE caused both the structures of the easternmost part of Azua, where the lower – middle Miocene limestones were deformed and exhumed (loca- tion 1 of figure 4.5.10), and the 90º gyro of the Peralta Belt treated at section 4.4.2. This produced the final closure of the Azua Basin in Pliocene times (Hernaiz-Huerta, 2006 and references therein). Hernaiz-Huerta (2006), by the revision of the geological mapping for this region, pro- poses that the infill of the basin is synchronous to the indenter. The frontal part of the indenter meets with the position of a lateral ramp that was conditioned by the advancing of Beata. This gives an older age (Miocene) for the process than the previously proposed by Mann et al. (1991 b). The structure of the Sierra the Neiba massif is defined by kilometric-wavelength folds, generally limited by inverse faults or high-angle thrusts, with an intense development of fractures, that con- figure a great antiform structure with a total height of 2000 m over the San Juan – Azua and Enriquillo basins. (Hernaiz-Huerta, 2006). Regarding to the Sierra de Bahoruco massif, the northern flank has a monoclinal structure to the N/NE together with the development of a frontal deformation zone associated to the thrusting of the mountain range to the Enriquillo basin (Hernaiz-Huerta, 2006). The evolution of this zone would correspond to a compressive context regulated by shear zones in a left-lateral transpres- sional regime (Hernaiz-Huerta, 2006; Pérez-Varela et al., 2010 d and references therein). As it has been exposed along this chapter, the main events that generate regional unconformities detected into this domain took place at the Late Cretaceous – Paleogene (Wessels et al., 2019), Miocene and Pliocene (Hernaiz-Huerta, 2006). The presence of an Late Cretaceous – Paleogene unconformity in Haiti is still subject to debate (Wessels et al., 2019). The presence of an angular unconformity between Cretaceous and Paleo- gene deposits together with a different deformation style of the Cretaceous and the post-Paleocene formations and the identification of Paleocene olistoliths at the Southern Peninsula would point out its existence (Wessels et al., 2019 and references therein). This would agree with the outcrops describes in (Pérez-Varela et al., 2010 d) and the Paleocene unconformably overlying conglom- erates identified in the Chaîne des Matheux (Wessels, 2018). The next episode corresponds to the angular unconformities of early Miocene age locally ob- served in the southwestern and eastern areas of the Southern Peninsula (Wessels et al., 2019 and references therein. This is followed by “a widespread homogenization of pelagic sedimentation marks a phase of tectonic quiescence during the middle to late Miocene” (Wessels et al., 2019 and references therein) while the final stage of uplift of the peninsula took place during the late Miocene. To the north, there is a middle Miocene diachronous evolution of the Chaîne des Matheux (Wes- sels, 2018 and references therein). The development of the Haitian Fold-and-Thrust Belt (HFTB) started in western Hispaniola from the early Miocene onwards (figure 4.5.20). “The HFTB con- sists of a series of stacked NW – SE trending southwest-verging thrust sheets with piggy-back basins on their north-eastern flanks” (Wessels, 2018). The later episode would correspond with the Pliocene final uplift of the Sierra the Bahoruco and Neiba and the closure of the Enriquillo and Azua Basins (Hernaiz-Huerta, 2006 and references therein). 255 Fig. 4.5.20, Schematic cross-section for the Haitian Fold-and-Thrust Belt. Modified from Wessels (2018). Position in figure 4.5.16 (B-B’). 256 4.5.4 Partial discussion for the Oceanic Caribbean Domain The review of the scientific literature together with the study of exploration wells and the defini- tion of lithostratigraphic units indicates that proximal facies were deposited at the Sierra de Ba- horuco and the Southern Peninsula of Haiti since the Late Cretaceous (including the development of high vegetation) throughout Paleogene. On the other hand, deep-water limestones were depos- ited at the territories corresponding to the Sierra the Neiba and its Haitian prolongation (figure 4.5.21). This tendency changed in the early to middle Miocene where shallow water carbonates were de- posited in the Azua Basin (figure 4.5.21). This is interpreted in Hernaiz-Huerta and Pérez-Estaún (2002) and Hernáiz-Huerta (2006) as an interaction of the Beata, whose indenter would have modified the ramp configuration. A regional change to deeper facies at middle Miocene has been recognised into this domain, as well as for the other domains of the island. This would support the idea of a regional transgression that affected the whole island for the Oligocene – middle Miocene period. This has important exploration implications. If the shallow lower – middle Miocene carbonates of Azua, with good reservoir properties, belongs to this Transgressive sequence, the identifications of similar deposits covered by middle Miocene shales became essential for a successful exploration. Fig. 4.5.21, Tentative facies distribution maps for the Paleogene and Miocene based on the anal- ysis of outcrops and well descriptions. 257 Moving to the northwest, the development of the Haitian Fold-and-Thrust Belt (HFTB) took place for the same period of time (early – middle Miocene), equal than the initial uplift of the Southern Peninsula of Haiti (Wessels, 2018; Wessels et al., 2019). The HFTB generated the growing of Miocene piggy-back basins, which genesis could be shared by the Azua Basin. The uplift of the Sierra de Neiba and Sierra de Bahoruco is dated in Mann et al. (1991 a) as Pliocene. This is based, in part, on the dating of the evaporites from the Angostura Formation and the subsequent marginal-marine to terrestrial sedimentation of the Enriquillo Basin. However, as we have seen, the dating of the Angostura Formation is controversial. The presence of two sills dated as 12.3 ± 1.3 Ma (Charco Largo #1 well report, 1981), which agrees with biostratigraphy analysis of the well (Charco Largo #1 well report, 1981), led to a Miocene age for this formation. As an initial hypothesis, an early-middle Miocene aging of the Angostura Formation would change the initial uplift phase of the Sierra de Neiba and Sierra de Bahoruco to that time. This new age would coincide with the deformation events record in Haiti and with a Miocene initiation of the Beata indenter. Furthermore, a Pliocene age of the formation would imply the accumulation of almost 4000 m of sediments in less than 5 Ma at the Enriquillo Basin. Similar thicknesses have been reached at other Cenozoic basins of the island, such as the Cibao Basin (see Section 4.2.2) or the San Pedro Basin indeed (Gorosabel-Araus et al., 2020). In this sense, an accumulation along the Neogene is considered here as more consistent in a regional framework. Nevertheless, further works must support this idea, constraining the age of the evaporite sequence. The final closure of the basins would have taken place along the Pliocene as the increasing in continental facies indicates. 258 259 Section 4.6: General Discussion 4.6.1 The tectono-stratigraphic domains division In this work, a division of Hispaniola into four tectono-stratigraphic domains has been established (figure 4.6.1) as an alternative to others previously proposed in scientific literature (e.g. Mann et al., 1991 b). The purpose of this division is to simplify the resulting model as much as possible and to determine new criteria that helps in future exploration of the island. In this context, one of the objectives has been to clearly delimit the island arc domain, from the adjacent fore-arc and back-arc regions. Fig. 4.6.1, Four-domain division proposed for Hispaniola Island in this work: Forearc / Colli- sional (FACD), Island Arc (IAD), Cretaceous – Eocene Basin (CEBD) and Oceanic – Caribbean (OCD) Domains. Acronyms in Appendix 1. The revision and interpretation of geology and well data of the island support this division. The forearc / collisional domain shares a similar basement, although composed of both volcanic and non-volcanic, it consists of metamorphic suites and differs from the island arc domain, which made up the Cretaceous volcanics and the Cretaceous-Paleogene basaltic intrusions. The limit has been settled along the Hispaniola fault zone (HFZ), a first order fault that divided the whole island, separating different structural styles at both sides of the fault zone. Although, this separation leads to include into the island arc domain ophiolitic materials (like the Loma La Monja assemble), these Upper Jurassic metamorphic suites are interpreted as the substratum in which the island arc was developed in its initial stages (Escuder-Viruete et al., 2009). The analysis of gravity and magnetic anomalies reinforces this initial hypothesis. The island arc domain is represented by a NNW-SSE trending maximum of gravity anomaly (I-I’ on figure 4.6.2). This trend follows a lineament that meets with the main outcrops of Cretaceous vulcanism. 260 In a similar way, the magnetic anomalies caused by the vulcanism-related materials that com- prised this domain follow the same tendency (figure 4.6.2). Although the presence of another maximum at the position of Cordillera Oriental (CO) is also true, it does correspond with the Early Cretaceous initial stages of the island arc. These volcanic remains have been affected by the same tectonic structures as the rest of the fore-arc / collisional domain and differs in position with the mature lower to Upper Cretaceous arc. Furthermore, it constitutes the basement for the main sedimentary sequences studied in this work, in a forearc position since the Aptian. There- fore, the Lower Cretaceous arc has been left in the fore-arc collisional domain. For example, for the Late Cretaceous period, this region included a 5-km-thick sedimentary sequence interpreted as being deposited in the fore-arc region (García-Senz et al., 2007 b). Fig. 4.6.2, Interpretation of the domains of Hispaniola in base of the gravity and magnetic anom- alies. Above, (gravity) Bouguer anomaly map. Below, (magnetic) reduce to pole anomaly map. Red insert indicates the Area of Interest of this work. Dashed lines delimit the different tectono- stratigraphic domains. Letters refer to anomalies mentioned in the text. 261 Between the island arc and the oceanic Caribbean domain, a new division was settled to englobe the Upper Cretaceous to Eocene sedimentary rocks (Cretaceous – Eocene Basin Domain) that crop out in a narrow belt at the southern flank of Cordillera Central. As it has been discussed in this chapter, the composition of rocks for this domain clearly differs from the island arc (volcano- sedimentary sequences and shallow carbonates) and the oceanic Caribbean samples (carbonate sequences), being made up of deep-water sedimentation in a trench parallel to the arc (Hernaiz- Huerta and Pérez-Estaún, 2002). The genesis of this trench has been related to a back-arc exten- sional phase during the Campanian times (Heubeck et al., 1991). From a regional picture a com- pressive back-foreland development fit better with the tectonic events that were taking place in the area at that time. The presence of widespread conglomerates and breccias (Lewis et al., 1991), the accepted arriving to the subduction channel of a thicker crust that starts the initial collision in Cuba (García-Casco, 2001), the possible initial phase of exhumation of the metamorphic suites in Hispaniola (Escuder-Viruete et al., 2014), the inversion of the Upper Cretaceous fore-arc series at Cordillera Oriental (García-Senz et al., 2007 a and b) and an interpreted transpressional regime in the southern flank of Cordillera Central that led to the development of compressional structures adjacent to the back-arc (Escuder-Viruete et al., 2006) for this period of time (Campanian to Maastrichtian) would reinforce this hypothesis. Whether considering a back-foreland model or not, the consequence was the accumulation of a great amount of sediments along this zone that has an imprint on the gravity and magnetic anom- aly maps (A and B anomalies on figure 4.6.2). The main representant is a minimum on the bouguer anomaly (II-II’ on figure 4.6.2) whose origin is interpreted with a thick sedimentary sequence. The established division results useful in the basement prediction for the SPB, and with the inter- pretation of the materials composing the infill of the basin. It is possible to follow the main struc- tures into the offshore section and to extend the limits of the domains on the anomaly maps (fig- ures 4.6.2). Bouguer anomaly maps reflects the continuation of II-II’ anomaly, associated with the Cretaceous to Eocene Basin Domain, into the eastern segment of the basin. In a similar way, the limits of the Island Arc Domain are mapped from the onshore to the offshore, occupying the northern half of San Pedro, and limiting the island arc influence. These basement units seem to be composed of rotated blocks, which could be assumed in a transpressional regime (figure 4.6.3). Finally, the Oceanic Caribbean Domain clearly differs in composition from the other three do- mains. Although the outcrops of the basement are limited, all of them consist of CLIP-related (Caribbean Large Igneous Province-related) basalts (Escuder-Viruete et al., 2016 a) compared to the materials related to the island arc of the other three domains. Furthermore, the sedimentation is eminently and uninterrupted calcareous since the Late Cretaceous to middle Miocene when terrestrial influenced sediments were deposited due to the inversion of the region as a consequence of the collision with the Beata Ridge (i.e. the Beata indenter). In summary, the proposed division seems to be a good approach to analyse the island geology in a simpler although realistic way, with important exploratory implications. For example, Mann et al. (1991 b) divided the island into 13 tectonic terrains (see section 2.4). From those, 10 corre- spond to island arc terrains while only one to the oceanic plateau, corresponding to an area that comprises of the Southern Peninsula and Sierra de Bahoruco. This kind of interpretation could lead to basin modelling that infers a volcanic basement for the San Juan – Azua Basin that englobe the totality of the Cretaceous, instead of having a Turonian CLIP-related material below a Coni- cian to Maastrichtian deep-water sedimentation, similar to the sections reached at the Deep-Sea Drilling Project (DSDP Leg 15 cores from the Venezuela Basin). 262 Fig. 4.6.3, Interpretation of the gravity and anomaly maps for the San Pedro Basin and the adja- cent onshore areas. A, Reduced-to-pole magnetic anomaly map; B, Magnetic tilt derivative map; C, Bouguer anomaly map; D, Gravity tilt derivative map. Purple insert defines the limits of the different domain as exposed in figure 4.6.2. 263 4.6.2 Regional constrains As has been explained in the partial discussions, there was a Campanian event that affected in Hispaniola and Cuba in a similar way. Now, if we considered the Proto-Caribbean as a conse- quence of the separation between North and South America, it is reasonable that its formation had been similar to the processes that generated the aperture of the Gulf of Mexico (Pindell and Ken- nan, 2009). In that respect, the Bahamas margin would have passed progressively from continen- tal crust to an extended crust and finally to an oceanic crust (figure 4.6.4) that would configure the Proto-Caribbean. Therefore, the Campanian event could have been related to the arrival of the subduction zone of a thicker crust, corresponding with an extended continental crust from North America. The arrival of a thicker crust would have interrupted the subduction and generated the compressional regime that inverted the Upper Cretaceous fore-arc basin and the starting of the exhumation of metamorphic complexes. This would also be responsible for a change from the subduction-related vulcanism to the basaltic intrusions of the Pelona – Pico Duarte basalts since the Campanian. The final stage of the collision would have taken place in middle Eocene, with the collision of the continental crust of the Bahamas Banks (non-extended). Fig. 4.6.4, Example of an interpreted seismic profile that shows the transition from a continental crust at the Florida platform to oceanic crust at the Gulf of Mexico, modified from Eddy et al. (2014). Under these premises, Cuba and Hispaniola would correlate as exposed in figure 4.6.5, linking the fore-arc collisional domain with the ophiolites that crop out in northern Cuba and the Albian – Campanian island arcs of both islands following the same trend (figure 4.6.5). Ophiolite com- plexes of the Loma Caribe peridotite have similar geochemical signatures to the Cuban ophiolite belt (Cabrera et al., 2019 and references therein), which lead to propose the same genetic origin and emplacement since the Campanian, finalising with the exhumation at the early Palaeocene. This exhumation would have been registered by the conglomerates with metamorphic clasts of Cuba and Hispaniola (Martín et al., 1999; Monthel et al., 2010 b). Transpressional deformation, with a synkinematic emplacement of batholiths, has been identified at Cordillera Central for this period (Escuder-Viruete, 2006). It is also supposed that compres- sional structures were generated contemporary at the back-arc zone. This could favour the for- mation of a back-foreland basin, in a thick-skin model, that generates the configuration space for the Campanian to Maastrichtian Trois Rivieres Formation and the Palaeocene – middle Eocene Peralta group. 264 Fig. 4.6.5, Suggested correlation for the island arc and metamorphic terrains of Cuba and His- paniola. Above, paleo-reconstruction of the region at middle Eocene times, just before the final collisional stage between the Bahamas Banks and the arc. Below, current configuration of the region. After the collision of Hispaniola Island and the Bahamas Banks in the middle Eocene, compres- sional forces were effectively transferred to the south generating the inversion of the back-fore- land basin and starting the initial stages of the Trois Rivieres – Peralta Fold and Thrust belt. The continuous derive of the Caribbean Plate together with the convergence of the North- and South American Plates would have caused the indenter of Beata and the thrusting of the Trois Rivieres – Peralta Belt (Cretaceous to Eocene Basin domain) over the Oceanic Caribbean Domain of the south of Hispaniola. The aperture of Cayman, the separation of Cuba and Hispaniola and the approaching of Beata would have a common origin and would have generated the main unconformities that affected the island since the Neogene. The aperture of Cayman and the separation of Cuba and Hispaniola has taken place along the Septentrional – Oriente and Enriquillo – Plantain Garden Fault Zones (figure 4.6.6; Wessels et al., 2019 and references therein). 265 Fig. 4.6.6, Above, regional Detail of the structures that affect the Windward Passage, responsible for the separation of Cuba and Hispaniola. Key to acronyms: SFZ, Septentrional Fault Zone; OFZ, Oriente Fault Zone; HFZ, Hispaniola Fault Zone; SJLPFZ, San Juan – Los Pozos Fault Zone; HFTZ, Haitian Fold and Thrust Belt; EPGFZ, Enriquillo Platain Garden Fault Zone. Cross section A-A’ in figure 4.6.7. 266 Following the model proposed throughout this work, a conceptual cross-section of Hispaniola is presented in figure 4.6.7. From north to south we would have the Bahamas Platform, that repre- sents a segment of the North-American continental crust; the Northern Hispaniola Deformed Belt that registers the collision together with the ophiolite complexes that would have been accreted and exhumed; the island arc; and finally, the current configuration of the San Pedro Basin, that has been developed thanks to the accommodation that generates the over-thrusting of the Muertos Thrust Belt (offshore extension of the Trois Rivieres – Peralta Belt) to the Caribbean Plate. Fig. 4.6.7, Conceptual cross-section for Hispaniola Island based on the revision of the geology given in this work. Position in figure 4.64. 4.6.3 Evolution model of the study area By the integration of this model with the main unconformities identified throughout the study of the geology of Hispaniola, a new evolutionary model is proposed for the San Pedro Basin (figure 4.6.8). This model will be the starting point for the interpretation of the basin that will be explained in the next section. The initial stage of the basin would start in Campanian times with the development of a foreland- like basin that involved the thick-skin thrusting of the island arc over the Caribbean Plate. How- ever, it is to be noted that the CLIP magmatism ended during the Turonian so, it is possible that deep-water Turonian to Campanian sediments would be present below the foreland sediments. This stage would have continued up to middle Eocene, when the Cretaceous to Eocene basin would have been inverted due to the final collision between Hispaniola and the Bahamas Banks and an effective transfer of compressional forces to the south, started the thin-skin deformation of the future Muertos Thrust Belt (lateral equivalent of the Trois Rivieres – Peralta Belt). During this process, the basement unit would have accommodated a left lateral transpressional defor- mation (that possibly caused the blocks rotation observed on magnetic anomaly maps, figure 4.6.3), while compression would have been restrained to the Cretaceous to Eocene sediments in a partitioned model. The development of the Muertos Thrust Belt would have generated the ac- commodation for the Neogene to Present sedimentation. The presence of Late Cretaceous, middle Eocene, Oligocene, middle Miocene, and late Miocene unconformities are expected in the basin as the onshore geology suggests. Meanwhile, an Oligocene to middle Miocene transgression is also hoped in the basin. 267 Fig. 4.6.8, Evolutionary model for the San Cristóbal region (modified from Pérez-Varela et al., 2010 a and Abad et al., 2010 a) and the San Pedro Basin following a compressional back-arc model as proposed in this work. 268 269 Section 4.7: Interpretation of the San Pedro Basin This chapter is focused on the interpretation given in this work for the San Pedro Basin (SPB; figure 4.7.2). The final objective is to provide an evolutionary model of the basin, that includes all the constrains proposed in sections 4.1 to 4.6, in order to apply this modelling to the hydrocar- bon potential of the basin. The location of the SPB comprises terrains corresponding to the Island Arc and the Cretaceous – Eocene Basin Domains (figure 4.6.1). The offshore extension of the domains is derived from the analysis of magnetic and gravity anomalies (see Section 4.5). This assumption provides constrains related to the expected basement of the basin and the lithostratigraphic units that can be expected in the basin. This information, derived from the onshore analysis, has been applied to the inter- pretation of the basin. The first stage has been the identification of the main unconformities of the basin and the subsequent division of the sedimentary infill into mega-sequences. The integration of well-tops (from the exploration well San Pedro #1, drilled at the location of a seismic line), together with the comparison with the unconformities identified in the onshore, provides the age of those mega-sequences. The second stage of the interpretation includes the seismic facies anal- ysis. This step is essential to correlate with the lithostratigraphic units described onshore and studied for the different domains. Furthermore, this analysis provides paleo-depositional environ- ments, which results useful to determine the potential elements of the petroleum system studied in Chapter 5. After that, the structure and deformation of the basin will be studied. As a comple- ment of that, different reconstructions of the basin for specific periods of time will be also pre- sented. These kind of methodologies not only give a clear image of the basin at a certain moment but also provides information about the timing of deformational processes. Fig. 4.7.1, Geology maps of Hispaniola Island over digital elevation model of the region. The study area or Area of Interest (AOI) of this work comprises the San Pedro Basin (SPB) and the Muertos Thrust Belt (MTB). See Appendix 1 for acronyms. 270 4.7.1 Identification of main unconformities After the examination of the data, five main unconformities have been identified on seismic pro- files based on the onlap and downlap of reflectors (figure 4.7.2). The corresponding horizons have been mapped along the basin, being possible to tie three of them to the well San Pedro #1 (SP; figure 4.7.3) which correspond with the Top Cretaceous, middle Miocene and upper Miocene (or Miocene). The other two have been interpreted as corresponding to the middle Eocene and Oli- gocene (- early Miocene) unconformities, according with the observed onshore geology (e.g. Abad et al., 2010 a; Pérez-Varela et al., 2010 a). These five unconformities agree with the main events identified on the onshore analysis of the geology. Each interpreted horizon will be dis- cussed independently. Fig. 4.7.2, Main unconformities interpreted on seismic profile WGC08, modified from Gorosabel- Araus et al. (2020). Cretaceous, middle Miocene and upper Miocene unconformities are tied to the well San Pedro #1. The other two (Top middle Eocene and Oligocene) are inferred from the onshore constrains. Top Cretaceous Top Cretaceous unconformity has been identified in multiple forms on seismic profiles, either representing angular unconformities or erosional surfaces. This horizon was reached at San Pedro #1, at top of Units K1 and K2 (figure 4.7.3), assigning a Late Cretaceous age for the materials that englobe. Below this horizon, there is a generalized loss in reflectors amplitude and frequency 271 spectrum, which might indicate a wide range of processes including high deformation, incipient metamorphism or an abrupt acoustic impedance step that absorbs a great proportion of energy. As a widespread silicification was observed on outcrops of Units K1 and K2 (see section 4.2.1), which could fit with an absorption of the acoustic energy at this level (note the great change on density logs at Top Cretaceous, figure 4.7.3 A). Nevertheless, as the subsurface information is limited, a low grade of metamorphism should not be totally discarded, especially for the area of the basin that correspond with the Island Arc Domain. At other places, a high grade of defor- mation, that have eroded the Cretaceous sedimentary sequence, could have contributed to a reso- lution loss (figure 4.7.3 B). Below the Top Cretaceous, an intra Cretaceous unconformity is inter- preted when the seismic resolution allows it (figure 4.7.3 B). This inner unconformity is tenta- tively interpreted as belonged to the Campanian event (see Sections 4.2.3 and 4.6.2). The sedi- ments below this unconformity have suffered a higher deformation. Fig. 4.7.3, Top Cretaceous interpreted on different TWT seismic profiles. A, correlation with well San Pedro #1 located at the trace of seismic line SP-4. B, Example of Top Cretaceous acting as an erosional surface that eroded Upper Cretaceous sedimentary sequences, previously deformed. Note the loss in amplitude and frequency content for the levels below Top Cretaceous (black arrows). An intra Cretaceous unconformity (IKU) has been identified in the basin and interpreted as belonged to the Campanian event. 272 Top middle Eocene This horizon represents an angular unconformity that is identified along the basin. Sediments above onlap into this surface (figure 4.7.4) that locally appears eroded. Its situation above Top Cretaceous, together with the angular unconformity represented by this onlap, lead to interpret the sedimentary sequence enclosed below this horizon as Paleocene? – lower Eocene to middle Eocene. The onlap would be, in this sense, a consequence of the inversion of the former Creta- ceous to Eocene Basin due to the collision between the island arc and the Bahamas Bank, that took place in middle – late Eocene times (see Sections 4.4.2 and 4.4.3). Fig. 4.7.4, Interpretation of progressive onlap into middle Eocene horizon on TWT seismic profile WGC08. Note the different seismic facies below and above Top Cretaceous unconformity. Top Oligocene Top Oligocene is characterized by a progressive onlap of the sequence above (figure 4.7.5). Alt- hough locally the transition between both sequences appears conformable, at the edges it is pos- sible to identify an angular unconformity. Onshore, between the Late Cretaceous and middle Mi- ocene intervals there are two unconformities, the middle – late Eocene and the Oligocene - early Miocene (see section 4.6). Therefore, this horizon is set as Top Oligocene. In addition, other arguments that reinforce this interpretation will be explained in the seismic facies (4.7.3) and deformation styles (4.7.2) sections. 273 Fig. 4.7.5, Interpretation of progressive onlap into the interpreted Top Oligocene horizon as viewed on different TWT seismic profiles. Above, southern onlap of interpreted lower Miocene sequence on line WGC08. Below, northern onlap on seismic line MDRH-55. 274 Top middle Miocene This unconformity, interpreted as the top of middle Miocene, not only represents a progressive onlap of the section above but also spots a clear change of seismic facies (figure 4.7.6). Seismic facies go from high-amplitude and lateral-continuous reflectors to low-amplitude reflectors (see section 4.7.3). This horizon also confines amplitude anomalies detected on seismic profiles (figure 4.7.6) that will be treated on section 4.7.4. This anomaly clearly cuts lower to middle Miocene reflectors, indicating a potential fluids contact. As it is enclosed in a broad anticline, further surveys should determine the nature of the anomalies by an Amplitude Versus Offset (AVO) analysis and the closure of the structure to delimit potential traps and the lateral extension of these amplitude anomalies. Fig. 4.7.6, Example of vertical change of seismic facies on TWT seismic line SD6. The section above progressively onlaps Top middle Miocene horizon. Note the change in seismic facies from high-amplitude and lateral-continuous (1) to low-amplitude reflectors (2) and the amplitude anomalies (3) restrained by this horizon. 275 Top upper Miocene Finally, Top upper Miocene, identified at San Pedro #1 (figure 4.7.3), is mapped along the basin and represented by the wedge and onlap of Pliocene to Present sediments into this horizon (figure 4.7.7). Fig. 4.7.7, Example Top Miocene horizon in the basin. Pliocene to Present sediment wedge into this horizon. 276 4.7.2 Seismic facies analysis and units correlation After the examination of seismic data, a wide variety of seismic facies that composed the sedi- mentary infill of the basin and the basement were identify. The aim of this section is to analyse these facies, providing an interpretation of the lithologies that they might represent. The combi- nation of these lithologic prognosis with the interpreted sequence will lead to the assignation with those units established for the onshore geology. Each sequence, defined by the Late Cretaceous, early – middle Eocene, late Eocene – Oligocene, early – middle Miocene and late Miocene un- conformities, will be study independently along the section. Upper Cretaceous seismic facies The subsurface image of the sedimentary sequence defined by the Top Cretaceous is generally very poor, with a limited resolution that makes difficult a detailed interpretation. At the same time, the correct identification of this sequence is highly depending on the seismic survey and the acquisition date and parameters. In general terms, when recognisable, Cretaceous series consists of medium-to-high amplitude and laterally discontinuous reflectors. This poor image might be a consequence of a frequency loss observed for this interval (figure 4.7.8 and figure 4.7.9). This effect is amplified at the zones with a great deformation, where this sequence appeared eroded. At some zones of the Island Arc Domain, the limited resolution does not allow to discern clearly between the basement and sedimentary levels (figure 4.7.8). Nevertheless, it should be noted here that there was still a volcanic activity during the Late Cretaceous (arc-related and basic vulcanism and intrusions), and the possibility of having this type of materials coeval with a sedimentary deposition is reasonable. Another option is the possibility of having suffered some degree of met- amorphism due to that magmatic activity. For this domain, Upper Cretaceous seismic facies are interpreted as correlated to the Campanian - Maastrichtian Units K1 and K2 which, although de- fined as forearc deposits (García-Senz et al., 2007 b), seismic data indicate their continuation into the basin (figure 4.7.3). Their relationship with volcanic systems must be addressed in further studies with an improve resolution. The frequency loss suffered by this units is interpreted here as a consequence of either the silicification of the level (as observed in the field, see section 4.2.1) or an early stage of contact metamorphism product of a posterior magmatic activity. The presence of an intra Cretaceous unconformity (figure 4.7.8) could be indicate the preservation in the basin of pre-Campanian intervals like the Las Guayabas Formation studied at Cordillera Oriental (section 4.2.1) or the Río Blanco Formation, described between the volcanic Tireo Group at Cordillera Central (section 4.3). Seismic facies consist of medium to high amplitude reflectors with a low to medium continuity that could correspond with mudstones of the cited formations At the zone that corresponds to the Cretaceous – Eocene Basin Domain, although with a slight frequency and amplitude loss, the Cretaceous sequence recovered its lateral continuation (figure 4.7.9), being conformed of medium to high amplitude and parallel reflectors. This interval, in- volved into the MTB, is interpreted as a deep-water deposition, correlated in this case with the Trois Rivieres and Las Palmas formations (see section 4.4). A certain degree of silicification was also observed for the Las Palmas Formation in the field and might be the responsible of the fre- quency loss also for this domain. Nevertheless, while for the Island Arc Domain reflectors seem to have been highly deformed and altered, for the Cretaceous – Eocene Basin Domain, they only have been deformed in a compressional style coherent with a thrust belt, where the upper sheet of the thrust shows a low grade of deformation (figure 4.7.9) 277 Fig. 4.7.8, Examples of Cretaceous seismic facies at the Island Arc Domain. Above, commonly observed medium-to-high amplitude and discontinuous reflectors that characterised this interval. IKU refers to an intra Cretaceous Unconformity interpreted in this interval. Below, dominant frequency attributes extracted from profile LSP1 (NORCARIBE-2013). Note the frequency loss for the Upper Cretaceous interval. 278 Fig. 4.7.9, Example of Cretaceous seismic facies at the Cretaceous – Eocene Basin Domain cor- responding to the upper thrust sheet of the MTB. Note the recovering of lateral coherency of this level in comparison with the Island Arc Domain. Lower to middle Eocene seismic facies This sequence is represented by two different seismic facies (figure 4.7.10). Eocene seismic facies 1 consists of a thin layer (up to 0.3 sTWT) of high-amplitude and lateral-discontinuous reflectors. This set of seismic facies onlaps the Cretaceous sequence northwards. Its position in the basin meets the area where the magnetic and gravity anomalies define the limits of the island arc domain (figure 4.7.11). These facies are interpreted as proximal carbonates that were deposited over the island arc domain, in what are thought that represent paleo structural highs or islands. This idea is supported by the erosion, thinning or non-deposition (figure 4.7.11) of these facies detected over these paleo-highs. They would correlate to the Paleocene to Eocene shallow water carbonates that crop out at the southern flank of Cordillera Central in the San Cristóbal Basin, onlap the volcanic basement (Biju-Duval et al., 1982). Eocene seismic facies 2 correspond to a series of high- and low- amplitude reflectors laterally continuous to semicontinous (figure 4.7.10), although this last might be a consequence of the seismic quality (high dips and deformation of this area do not allow a proper imaging), located at the Cretaceous – Eocene Basin Domain and mainly incorporated to the MTB. These facies are interpreted as deep water deposits, where high amplitude reflectors would correspond with mud- stones and low-to-medium amplitude intervals might correspond with a more calcareous deposi- tion or the arriving of gravity deposits into the basin. Eocene seismic facies 2 are associated here with the lower to middle Eocene Units E1 and E3 reached at Punta Salinas #1 (section 4.4.1). 279 Fig. 4.7.10, Examples of lower to middle Eocene seismic facies. Above, Eocene seismic facies 1, interpreted as proximal carbonates like those that crop out at Cordillera Central and described in Biju-Duval et al. (1982). Below, Eocene seismic facies 2, interpreted as deep-water carbonates and correlated with Units E1 and E3. 280 Fig. 4.7.11, Interpreted paleo-structural highs in the middle segment of the San Pedro Basin. The upper map represents the reduced-to-pole magnetic anomaly map where the interpreted location of group 1 is given by the blue area. Red insert gives the location of the seismic line. Upper Eocene to Oligocene seismic facies Upper Eocene to Oligocene sequence is characterised in general by high-amplitude and parallel to semi-parallel reflectors (figure 4.7.12). Nevertheless, in a similar way than for the lower to middle Eocene sequence, there are significant differences between the facies on the Island Arc Domain and those deposited to the south, at the Cretaceous – Eocene Basin Domain. A similar division is studied in Pérez-Varela et al. (2010 a) for the upper Eocene? to Oligocene outcrops of the El Limonal Formation (see section 4.4.2) Over the Island Arc Domain, this sequence consists of a thin layer (from 0.2 to 0.3 sTWT) of semi-parallel, continuous and medium to high amplitude reflectors that are interpreted in this work as deposited over a structural high (figure 4.7.12). In general terms the upper Eocene to Oligocene sequence are interpreted as corresponding to Units O1 and O2. This interval starts with moderately chaotic reflectors of medium amplitude and lateral continuity which pass vertically into high-amplitude, laterally continuous and plane-parallel reflectors. This transition is similar to what was observed in the field, where Oligocene conglomerates from the facies association PVFA1 pass vertically into a shaly section of mudstones with minor micro-conglomerates and sandstones intercalated defined as PVFA2 (see section 4.4.2). At top of this section, a layer of transparent facies (low-amplitude reflectors) is identified where the resolution of the seismic al- lows it. This is interpreted as a thin calcareous deposit that would give pass to the lower Miocene calcareous sequence that will be described in the next section (Lower to middle Miocene seismic facies) and correlated with the facies association PVFA4. 281 Fig. 4.7.12, Example of upper Eocene to Oligocene semi-parallel, continuous and high amplitude reflectors interpreted as a sedimentary sequence deposited over the island arc domain. Dashed line indicates the limit between the Island Arc (IAD) and the Cretaceous – Eocene Basin (CEBD) domains. Southwards the interpreted structural highs, at the Cretaceous – Eocene Basin Domain, the upper Eocene to Oligocene sequence evolves into a thick interval (up to 1.2 sTWT) of high-amplitude, parallel to semi-parallel and continuous reflectors accompanied by others with low amplitude and a hummocky structure. This interval is interpreted as a lower-slope to deep-water sedimentation (high-amplitude facies) sequence disrupted by the arriving of slumps or large lithified collapse blocks (low-amplitude and chaotic reflectors). It fits well with the onshore upper-Eocene to Oligocene Río Ocoa group (Pérez-Varela et al., 2010 a; Abad et al., 2010 a; Heubeck et al., 1991 and references therein) that consists of “a series of conglomerates and sandstones at base that passes into a rhythmic succession of marls and turbidite sandstones with intercalations of calcarenites and conglomerates with olistoliths” (Pérez-Varela et al., 2010 a). Chaotic facies become dominant conforming we approach to the northern limit. This reinforce the interpretation of mass-transport deposits for them, having recorded the dismantling of a pre- vious platform (Olistoliths of the Río Ocoa group are composed of Cretaceous to Eocene lime- stones, Heubeck et al. (1991), Heubeck (1992)). High amplitude reflectors could be also corelated to the organic-rich shales previously mentioned (PVFA2) and, considering the presence of other intervals of Oligocene organic-rich shales at the Cibao Basin, this interval might correspond, potentially, with a regional source rock. 282 Fig. 4.7.13, Example of upper Eocene to Oligocene sequence interpreted as deposited to the south of a structural high. Chaotic facies are interpreted as conglomerates and olistoliths from a pre- vious platform. They become dominant to the north, while to the south are replaced by high- amplitude, parallel and continuous reflectors. Dashed line represents the limit between domains. Lower to middle Miocene seismic facies This sequence is characterized by the presence of low-amplitude and mound-shaped structures that are identified along of at least two different levels on seismic profiles (L1 and L2 on figure 4.7.14), especially at the central and western sections of the basin (this subject will be address in section 4.7.4). The seismic facies of these mound-structures consist of chaotic and discontinuous reflectors, alt- hough a certain degree of coherence is identified when the resolution of the seismic allows it (i.e., NORCARIBE 2013 profiles, figure 4.7.14). On dip-sections, mound-shaped bodies have a wedge structure with coherent internal reflections. Laterally and vertically low-amplitude facies grade into high-amplitude and continuous to semicontinuous reflectors. This change of seismic facies is interpreted as a transition from proximal to distal deposits, forming part of what is interpreted as a carbonate ramp system that retrogrades to the north (i.e., landwards). This back-stepping architecture is thought to represents a general transgression of the system. In a sequence stratig- raphy framework, the maximum flooding surface seems to meet the interpreted middle Miocene top. Considering that, the age of this transgression of the system fits with the interpreted regional transgression based on the onshore geology (see section 4.4.3). At some points, high-amplitude and low-frequency contorted to mound-shaped reflectors (figure 4.7.14) have been identified and tentatively interpreted as karstified limestones, which could represent higher frequency sea-level variations, inside a general transgression. 283 Fig. 4.7.14, Lower to middle Miocene sequence. Above, strike-section from NORCARIBE 2013 cruise, highlighted in red on the location map. Mound structures consist of low-amplitude reflec- tors interpreted as carbonate build-ups that pass laterally into high-amplitude reflectors inter- preted as reef-channels. At some points, low-frequency and high-amplitude mounds (blue insert) have been identified and interpreted as potential karstified limestones. Below, dip-section high- lighted in yellow on the location map. Mounds have a wedge structure on dip-profiles. They pass laterally into high-amplitude reflectors interpreted as the upper slope and the pelagic zone. In- tersection of both profiles are represented by dashed lines. 284 Towards the basin interior, this interval is divided into two main facies (figure 4.7.15). The Type 1 consists of high-amplitude, parallel and continuous reflectors with minor low-amplitude ones. Type 2 is composed of subparallel to hummocky reflectors where it is possible to identify chan- nels. Both are interpreted as a turbidite system, where Type 2 facies represents a higher energy interval with the arrival of a greater amount of clastics and possibly material derived from the carbonate platforms located northwards. At the onshore extension, for this period of time, Heu- beck et al. (1991) identified deposits related to a proximal to distal fore-reef environment (i.e., it consists of shallow-water carbonate clasts and unabraded coral heads) and interbedded cobble conglomerates and well-rounded igneous rocks clasts that would indicate the presence of subma- rine canyons that breached the fore-reef, allowing materials from the exposed island arc to be deposited in the basin. Fig. 4.7.15, Example of different kind of facies for the lower to middle Miocene infill of the basin. Type 1 facies consist of high-amplitude, parallel and continuous reflectors. Type 2 facies are defined by subparallel to hummocky reflectors where different channel systems have been identi- fied. These channels could be the same system identified on seismic profiles (figure 4.7.14) that by- passed sediments derived from the exposed terrains of the extinct island-arc to the basin through- out a carbonate system. Both the interpreted karstification of the shallow facies and the presence of channels at the reef zone, coincide with the deposition of the Type 2 seismic facies. This coincidence could be con- nected with a tectonic event, which led to the exposition of the platform due to a relative falling of the sea-level and leading to the arriving at distal environments of a coarser sedimentation. An early stage of the Beata Ridge indentation might be a good candidate for this process. Neverthe- less, a higher cyclicity stage or even a combination of both processes should not be discarded. At any case, the origin of this process must be regional owing to a similar regression is observed on seismic lines at the Cibao Basin (see section 4.2.2). 285 Assuming the karstification of Miocene limestones, this process might be the origin of cavernous porosity identified on core samples at Maleno DT1 (Maleno DT1 DSTs report, 1961) and Maleno #7 where a water blow-out took place while drilling these lower to middle Miocene limestones. “Although there are few cores, the Maleno #7 and Maleno DT-1 both appear to have drilled thick shallow-marine limestone sections. There were 3,000' of limestone below the abrupt Trinchera contact in the Maleno #7, with hydrocarbon shows and lost circulation throughout. The well fi- nally had a water blowout from vuggy and cavernous porosity at TD, and the well was abandoned. Flows from the blowout zone were estimated at 50 MBFPD” (Munthe, 1995). Regarding the correlation of seismic facies, the interpreted carbonate ramp system is connected with Unit N1. Onshore, the lower Miocene platform (sub-unit N1.1), composed of reefoidal and shallow-water deposits with a back-stepping architecture (see section 4.2.1 and 4.5.1), passes lat- erally into ramp deposits consisting of chalky limestones (sub-unit N1.2) with reworked material from the platform (sub-unit N1.3) and finally into mudstones corresponding to basin plain depos- its (Units N2). Under the interpretation given in this work, reef limestones assigned to sub-unit N1.1 would be represented by the mound-shaped transparent facies (figure 4.7.16). Along a lateral change of facies, sub-unit N1.1 wedges and passes into high amplitude reflectors interpreted as ramp deposits (sub-unit N1.2) and basin-plain deposits (Unit N2). Chaotic facies are interpreted as reworked material from the platform (Unit N1.3). Fig. 4.7.16, Interpretation given for a Lower to middle Miocene carbonate ramp system, based on the seismic facies analysis. 286 Upper Miocene to Present seismic facies The upper Miocene and Pliocene to Present sequences are differentiated by the presence of a shallow area with well-developed platforms and a deep region of a turbidite sedimentation. The seismic facies that configure the interpreted upper Miocene platform consists of low- to medium- amplitude and parallel reflectors (figure 4.7.17). They grade into medium- to high- amplitude and semi-continuous reflectors that thinning out towards the interpreted platform, composing the up- per slope deposits. Finally, the hemi-pelagic to pelagic section would be constitute by low- to medium-amplitude and parallel reflectors. The amplitude loss is interpreted as the arriving to dis- tal areas of a greater proportion of turbidite sandstones and calcarenites than for the middle Mio- cene sequence. Distal section recovered to high-amplitude reflectors for the Pliocene to Present sequence. Upper Miocene platform facies, assigned to Unit N1, are represented by banks of me- dium amplitude instead of the moundy and transparent lower to middle Miocene. Distal deposits are equally represented by high-amplitude basin plain deposits (Unit N2) and sandstones and cal- carenites (Unit N5). Pliocene to present carbonates are represented by Units P2 and P3 reached at the well San Pedro #1. Onshore, this section correlates to the upper Miocene to Pliocene Ingenio Caei Formation. Abad et al. (2010) describes the presence of upper Miocene reefoidal limestones above a ravinement surface. They consist of boundstones and packstones accompanied by bioclastic calcarenites that laterally grade into marls. Deep-water deposits go from a basal member of metric layers of me- dium grain sandstones, conglomerates and marls to an upper section of shales layers that contain a great accumulation of organic matter, composed mainly of vegetal rests and planktonic foram- inifera (Abad et al., 2010 a). Fig. 4.7.17, Example of upper Miocene to Present sequences, differentiated by the presence of a well-developed platforms and a deep region of a turbidite sedimentation. 287 4.7.3 Structure of the basin The current configuration of the SPB bounds to the south with different structural systems. While the western section of the basin is limited by the compressive structures of the MTB, the south- eastern border is defined by the Saona Escarpment (figure 4.7.18), interpreted here as a transpres- sive system. In order to facilitate the comprehension of the tectonism that affected to the basin, this section has been subdivided into 2 parts to addressed the compressional structures that com- posed the MTB and the shearing system separately. Compressional structures The main exponent of compressional structures in the study area is the Muertos Thrust Belt (or Muertos Fold-and-Thrust Belt, MTB), offshore extension of the Trois Rivieres – Peralta Belt (TRPB; Biju-Duval et al-. 1982; Heubeck et al., 1991) which development has generated the configuration space for the San Pedro Basin since middle Eocene times. It shows “a stepped slope resulting from long-lived active folding and thrusting in a thin-skin tectonic style” where the “northward steeply-dipping reflectors suggest highly deformed materials forming a fold-and- thrust belt with a prevailing south-verging imbricate structure over a detachment located within the Dominican sub-basin sedimentary section” (Granja-Bruña et al., 2014). Fig. 4.7.18, Digital elevation model of the study area with the main structures and the domain limits (FACD, ISD, KEBD and OCD). The current configuration of the SPB bounds to the south with the MTB for the western section of the basin and with the Saona Escarpment for the eastern. See Appendix 1 for acronyms. 288 The interpretation of the basin meets the structural classification given for the onshore TRPB, where the distribution of structures is heterogeneous (Hernaiz-Huerta and Pérez-Estaún, 2002; Hernaiz-Huerta, 2006). There is a clear zonation, from SW to NE, of thrusts, folds and monoclines (figures 4.7.19). Rotation of structures has been interpreted as an effect of Beata Ridge indentation since the Miocene (Hernaiz-Huerta and Pérez-Estaún, 2002; Granja-Bruña et al., 2014). Seismic profiles show the same zonation affecting the same materials as in the onshore extension. Fig. 4.7.19, Interpretation of the SPB and the MTB at the western sector modified from Gorosa- bel-Araus et al. (2020). A, geology map of the onshore NW extension of the SPB (geology sheets of Sabana Buey 6070-I, Baní 6170-IV and Nizao 6170-I). B, Cross-section modified from Pérez- Varela et al. (2010 a) and Abad et al. (2010). C, interpretation given for the seismic profile SD5. The MTB consists of a series of thrusts and duplex (forming an antiform stack) in a thin-skinned model (Granja-Bruña et al., 2014). Interpreted horizons corresponds with the main unconformi- ties explained in 4.7.1. The division of zones follows the same criteria given in Hernaiz-Huerta (2006) for the onshore Trois Rivieres - Peralta Belt. See figure 4.7.18 for location of seismic and 289 geology map. See Appendix 3 for a non-interpreted section. Key to numbers: 1, Upper Cretaceous Las Palmas fm; 2, lower to middle Eocene Peralta Group; 3, upper Eocene to Oligocene El Limo- nal fm; 4, upper Eocene to Oligocene Ocoa fm; 5, lower Miocene Majagual fm; 6, middle – upper Miocene Río Nizao fm; 7, upper Miocene – Pliocene Ingenio Caei fm. Some of the structural features inferred on seismic lines, such us the accretion of duplexes land- ward, forming antiformal stacks, and an imbricate thrust system developed seaward over a de- tachment surface, practically undeformed (figure 4.7.19), are characteristic of a thin-skinned tec- tonic (Granja-Bruña et al., 2014). The hypothesis of a non-implicated basement into the defor- mation of the MTB was tested by the elaboration of gravity models for this region of the basin (figure 4.7.20). For that, the resulting surfaces obtained for the main unconformities of the basin, previously described in section 4.7.1, were integrated into the model. Densities were obtained by calculating the average values between seismic rms (root mean square) velocities and from the interval velocities given at the exploration wells for every level (see Chapter 3.3.1 for more in- formation). Thickness of the Caribbean Plate in the Venezuelan Basin was constrained following the values given in Granja-Bruña et al. (2010) and Núñez et al. (2016) and references therein. The results of the model reinforce the interpretation of a thin-skinned model for the MTB, where the deformation only implicates the upper sedimentary cover over a detachment surface that sep- arates a low-deformed basement. Fig. 4.7.20, Gravity model built for the San Pedro Basin and the Muertos Thrust Belt for the same location than seismic profile SD5 (figure 4.7.19). Note that the minimum observed in the Bouguer anomaly are caused by the accumulation of at least 8 km of sediments without the implication of the basement into the deformation belt. Regarding the structure of the system SPB-MTB, seismic lines reveal the same zonation affecting the same materials as in the onshore extension, considering that Miocene sediments that fossilized the main structures have been eroded onshore due to the progressive exhumation of the San Cris- tóbal Basin, while the offshore sedimentation have continued until present. Onshore, lower to middle Eocene rocks are affected by a high-dip (40-60º) thrust system with great lateral continuity (Hernaiz-Huerta, 2006 and references therein); while folds involve outcrops of the upper Eocene to Oligocene Río Ocoa Group (Pérez-Varela et al., 2010 a; Abad et al., 2010 a and references therein). Furthermore, dimensions of the thrust zones, 12 km-long in the offshore and 8 km in the onshore, and the fold zones, 38 km-long in the offshore and 30 km in the onshore, together with half-wavelengths of folds between 2 and 6 km in the offshore and 2 to 8 km in the onshore (Heu- beck and Mann, 1991), support this interpretation (figures 4.7.19 and 4.7.21). Note here that the interference of the Beata indenter decreases while entering into the offshore. 290 Fig. 4.7.21, Zoom to structural interpretation for the rear thrust system of the MTB on seismic profile SD5 interpreted on figure 4.7.20. Seismic image corresponding to the attribute 3D Edge Enhancement extracted with Petrel. Modified from Gorosabel-Araus et al. (2020) The rear imbricate thrust system would be limited by the SJRFZ to the north and the SJLPFZ to the south (figure 4.7.19). Thrusting activity would fault the Cretaceous to middle Eocene sedi- mentary rocks while the upper Eocene to Oligocene sequence would be folded. The thrust zone consists of a series of south-verging imbricate thrusts that show high dips, close to the vertical in some cases. The imbricate system would accommodate the shortening produced by a series of out of sequence basal thrusts, finalising with a master thrust that splays to the surface with a lower dip than the imbricate fan (figure 4.7.21). Under the interpretation given for the basin, this system would root into the Top Upper Cretaceous, which would explain the absence of Upper Cretaceous outcrops at the onshore thrust zone. The southern limit of the system is interpreted as the lateral continuation of the SJLPFZ. Southwards, the frontal thrust system would have incorporated younger sedimentary sequences and could be correlated with the Azua Group units. The folds zone comprises the central and rear part of the MTB with an estimated extension of 25 km. It is characterized by the presence of broad anticlines and synclines, with half-wavelength between 2 and 6 km, that mainly affect to the upper Eocene to Oligocene sequence. These folds accommodate the deformation produced by the structures below, like the interpreted SJRFZ or the duplex accretion (figures 4.7.19 and 4.7.21). Shallow normal faults (figures 4.7.19 and 4.7.21) affect to the Miocene to present section generating escarpments on the seafloor morphology (Granja-Bruña et al., 2014). They are the result of the ongoing growth of the MTB and the over- 291 steepening of the slope which causes this local shallow extensional regime that contributes to the balance of the thrust belt critical taper angle (e.g., Dahlen, 1990). The first nappe of the MTB is interpreted that took place through the SJRFZ (figures 4.7.19 and 4.7.21). The different thrusts of this zones would have affected to the Cretaceous and Eocene sequences, allowing the outcropping of Cretaceous sedimentary rocks in the onshore extension as is reflected in Abad et al. (2010) and Pérez-Varela et al. (2010 a). The lack of Eocene outcrops along the trace of the SJRFZ might imply the erosion of this sequence during the inversion of the zone. This process would have been recorded by the deposition of Olistoliths with remains of Upper Cretaceous and middle Eocene limestones (Heubeck, 1992). The activity of the SJRFZ since the late Eocene has been established by a differential sedimentation at both sides of the fault zone (see section 4.4.2). The back-stop of the system (figure 4.7.19), limited by the offshore prolongation of the BFZ, would form part of the island arc domain. This zone could have accommodated the strike-slip offset generated by the northern Caribbean Plate dynamic since the late Eocene – Oligocene (Pin- dell and Kenan, 2009), as it is inferred from the presence of transpressive structures. This kind of processes will be addressed in the Shearing structures section. Evolution of the SPB-MTB system The timing of the main deformation pulses of the basin is estimated by the flattening of main unconformities on seismic lines (figure 4.7.22). This method is possible when the horizon repre- sents a sedimentary layer that was deposited horizontally, such as basin floor deposits. Under the model presented in this work (discussed in section 4.6), the first deposits of the basin would have arrived in the back-arc region by the Conician – Danian (Heubeck et al., 1991). As a tentative interpretation, the hypothetical arrival of thicker crust at the subduction zone in the Campanian could have been responsible for all these processes, having inverted the island arc throughout a proto- BFZ, generating structural highs at the Island Arc Domain (Gorosabel-Araus et al., 2020; figure 4.7.22 A). This would have started the deposition, above Coniacian sediments of the Car- ibbean Plate, of Campanian deposits in a back-foreland basin. The Paleocene? – middle Eocene sequence was deposited unconformably above Top Cretaceous, reflecting a Late Cretaceous un- conformity as registered onshore (García-Senz et al., 2007 b). The depocenter was located at the Cretaceous – Eocene Basin Domain, in what is interpreted the fore deep of the basin. Sedimentation continued until the late Eocene, when the collision between the island arc and the Bahamas Banks took place. An effective transmission of compressional forces to the south driven by the oblique collision between the North American and Caribbean plate (see Granja-Bruña, 2008; ten Brink et al., 2009) would have inverted this Cretaceous to Eocene back-foreland basin through the SJRFZ (figure 4.7.22 B), initiating the development of the south-verging imbricate MTB (and its onshore continuation the TRPB) until Present. In a partitioned model, shearing deformation would have been absorbed by the basement units of the Island Arc Domain, possibly reactivating basement structures, like the BFZ. In this new tectonic configuration, the inversion of the Cretaceous to upper Eocene sequences lead to the migration of the depocenter of the basin to the north. During the early and middle Miocene, new structures appeared in the limit region between both domains (figure 4.7.22 C), including the development of broad anticlines at the rear zone of the MTB and the accommodation of deformation through normal faults to the north. 292 Fig. 4.7.22, Reconstruction of seismic line WGC08 since middle Eocene (A), throughout Oligo- cene (B), middle Miocene (C), upper Miocene (D) and Present day (E). Compressional forces effectively transferred to the south led to the inversion of the Cretaceous to Eocene Basin. During the upper Eocene to Oligocene, there is a reactivation of former basement structures in a trans- pressional regime. Although the tectonic climax took place for the period Oligocene to middle Miocene, the deformation has continued until Present. Location in figure 4.7.18. 293 294 The continuation of the deformation since late Eocene times until Present is recorded by the land- wards migration of depocenters (figure 4.7.22 C-D). In summary, it has been interpreted that there is a “strain partitioning in the forearc and in the inner island arc and convergence in the retroarc” (Granja-Bruña et al., 2014 and references therein). This would lead to have an effective shorten- ing accommodation in the MTB, which would correspond to the Cretaceous to Eocene Basin Domain, while left-lateral shearing would dominate on the Island Arc Domain since the Oligo- cene / early Miocene (see next section, Shearing Structures). Shearing structures As a consequence of the oblique collision between Hispaniola and the Bahamas Banks, the de- formation in the island has followed a partitioned model in space and time, involving compressive and shearing structures (Calais and Mercier de Lépinay, 1995; Dolan and Mann, 1998; Mann et al., 1991 a, 1998; in Pérez-Estaún et al., 2007). This partitioned deformation has led to kilometric structural domains separated by coetaneous strike-slip faults, common feature in transpressive regimes (Pérez-Estaún et al., 2007 and references therein). Under the interpretation given in this study for the SPB, transpressional forces would have been mainly absorbed by the Forearc and Island Arc Domains, constituted of Cretaceous volcanics and Upper Jurassic to Cretaceous metamorphic suites, while the MTB, composed of a thick sedimen- tary accumulation during the Campanian – middle Eocene period, would have accommodated the shortening derived from the effective transmission of compressional forces to the south, due to the collision with the Bahamas Banks and the indentation of the Beata Ridge (Granja-Bruña et al., 2014). The interpretation of magnetic anomalies (figure 4.7.23) reveals the counter-clockwise rotation and eastward tectonic escape of crustal blocks and the presence of a left-lateral strike-slip faults, such as the HFZ, that penetrated into the basin along the northern border, or the interpreted pro- longation of the BFZ, which limited the Island Arc Domain in the SPB to the south. On the other hand, faults like the Saona Fault Zone (SAFZ, named here; Saona Escarpment in Granja-Bruña et al., 2014), accommodates part of the share dividing the island arc basement into two different maximum zones (A and B, figure 4.7.23) as revealed by the limited displacement of local anom- alies (1 and 2, figure 4.7.23). On seismic profiles (figures 4.7.24 and 4.7.25), these tectonic features are interpreted as trans- pressive structures that inverted sections of the basement of the basin, resulting in a disposition of elevated blocks (figure 4.7.24). Oligocene and middle Miocene flattening sections reveal the initiation of this deformation at the back-stop zone for this interval, comprising the basement (volcanic and metamorphic units) of the Island Arc Domain (figure 4.7.22). Later normal faulting during Miocene would have accommodated the deformation. The age and deformation style ob- served here is similar to the deformation described within the Southern Puerto Rico Fault Zone (Erikson et al., 1990; Erikson and Pindell, 1991). On a large-scale setting, this transpression could have accommodate part of the east-west strike-slip offset generated by the Cayman opening (Pin- dell and Kenan, 2009) through the HFZ, BFZ and SAFZ (Gorosabel-Araus et al., 2020). 295 Fig. 4.7.23, Structural interpretation over reduced-to-pole magnetic anomaly map. Under the interpretation given in this work, the Island Arc Domain (IAD) in the SPB would have been de- formed by a left lateral shear strain, resulting in the eastward tectonic escape of crustal blocks. The Saona Fault Zone (SAFZ) would have separated two main anomaly zones (A and B) as indi- cating by the displacement of local anomalies (1 and 2). See Appendix 1 for acronyms. Fig. 4.7.24, Interpretation of crustal-scale structures on seismic profiles at the Island Arc Do- main. Elevated sections of the basement are the result of a transpressive regime that led to a disposition of rotated blocks controlled by the main left-lateral strike-slip fault systems, like the HFZ and BFZ. Location given in figure 4.7.23. 296 Fi g. 4 .7 .2 5, In te rp re ta tio n of s ei sm ic p ro fil e SD 9. S tru ct ur al h ig h id en tif ie d at th e ea st er n re gi on o f t he b as in is in te rp re te d as a p os iti ve fl ow er . T he gr ow in g of th is k in d of tr an sp re ss iv e fe at ur es h as le d to th e de ve lo pm en t o f s ec on da ry st ru ct ur es li ke ro ta te d bl oc ks d ue to g ra vi ty -d ri ve n no rm al fa ul ts . 297 The SAFZ was interpreted as an old normal fault along the Saona Escarpment in the scientific literature (Granja-Bruña et al., 2014). Nevertheless, a new subsurface image provided by new available seismic lines and the reprocessing of previous surveys, has led to identify the presence of a transpressive structure along its trace (figures 4.7.26 and 4.7.27). Under this new interpreta- tion, the SAFZ would have affected the basement of the island arc, leading to a limited displace- ment of the southern blocks in a transpressive regime. As a consequence, sedimentary sequences above were inverted, with an estimated uplift of at least 800 ms TWT (figure 4.7.26), having its surface expression along the Saona escarpment. Fig. 4.7.26, Interpretation of transpressive structures along the trace of the SAFZ. This crest would have accommodated the deformation due to the left-lateral displacement of crustal blocks. Fig. 4.7.27, Flattening to Top Miocene at the SAFZ. The inversion of sedimentary sequences is constrained to the middle Miocene, as the onlap of upper Miocene sediments might indicate. 298 The transpressive uplift generated by the action of the STFZ seems to have started at middle Miocene, as the onlap of upper Miocene sediments against the structure indicates (figure 4.7.27). Assuming this age, the action of the SAFZ would be posterior than the initiation of the transpres- sive deformation of the island arc basement, which is constrained to the Oligocene – middle Mi- ocene. In this sense, the SAFZ could be a secondary structure that accommodates part of the share between the main faults of the system, the HFZ and the BFZ. Fig. 4.7.28, Schematic deformation model for the Island Arc in a transpressive regime for the Oligocene – middle Miocene and upper Miocene periods. The resulting uplift seems to have triggered an asymmetric gravity-driven normal fault system that accommodate the deformation to both sides of the structure (figures 4.7.29). To the north of the SAFZ, seismic profiles disclose the presence of rotated blocks which root into the lower to middle Eocene level (figures 4.7.26 and 4.7.29). The initiation of the normal-faulting system is constrained to the late Miocene, having continued until Present. While at the northern side of the fault zone, normal faults occupied an extension of 5 km, to the south the system extends up to 30 km (figure 4.7.29), establishing the asymmetry of the resulting SAFZ structure, with a northern higher dip. The southern fault system roots into the same level, which could imply the presence of a shale package for this interval at this part of the basin, similar to the Eocene El Número Formation described onshore (see section 4.4.1). Shales are proved as good decollement levels in similar gravity-driven systems of the world, like in the Orange Basin of Namibia (e.g. Scarselli et al., 2016) that could be a good analogue. The presence of compressional structures to the south, resulted from this gravity system is not discarded. Unfortunately, the seismic coverage does not allow to identify it. A mound-shaped structure that affected the Oligocene and the lower Miocene sequences (figure 4.7.29) was initially interpreted as a structural anticline. Nevertheless, its morphology does not fit with the kind of structure expected in a normal-faulting setting. Furthermore, the absence of deformation in the levels below (lowermost Oligocene, represented by almost flat reflectors) would point out a different cause. As a tentative interpretation, this mound could consist of reefoidal limestones or another kind of bioconstruction. Further studies should address its origin. 299 Fig. 4.7.29, Above: Seismic interpretation of the southern section of the gravity-driven system identified at both sides of the SAFZ. It is supposed that the transpressive uplift of the STFZ during the lower to middle Miocene triggered the process. Below: Detail of the rotated blocks located at the northern side of the SAFZ. Note that normal faults root in the same lower to middle Eocene sequence at both sides. 300 4.7.4 The Oligocene to middle Miocene sequence As previously explained in section 4.7.2, the Oligocene to middle Miocene period is characterized by the presence of a series of mound- and wedge-shaped which, based on their seismic facies (see section 4.7.2), are interpreted as a carbonate ramp system. It is possible to explain the evolution of this system from a sequence stratigraphy framework (figures 4.7.30 and 4.7.31) throughout the architecture and facies analysis. For that, different profiles were flattened on the Top of middle Miocene, that covered the carbonates and is interpreted as the maximum flooding surface, giving a good reconstruction of the system. The lower sequence boundary is defined close to the Top Oligocene. Above, the first level is interpreted as a Falling-Stage System Tract (FSST 1, figures 4.7.30 and 4.7.31) with a stratal forestepping with downstepping stacking pattern. This level is followed by a stratal forestepping with upstepping stacking pattern, interpreted as a Lowstand System Tract (LST 2 figures 4.7.30 and figure 4.7.31). As observed on different sections, this relative sea level fall would have ex- posed the previous Oligocene sequence, where an amplitude and lateral continuation loss has been identified and interpreted as a potential karstification of the previous sequence (figure 4.7.31, see section 4.7.2). Fig. 4.7.30, Seismic interpretation of a carbonate ramp system in a sequence stratigraphy frame- work. Key to acronyms: FSST, Falling-Stage System Tract, LST; Lowstand System Tract; TST, Transgressive System Tract; HST, Highstand System Tract; mfs, maximum flooding surface. *Secondary variation on the sea level. Seismic profile flattened to middle Miocene horizon. 301 Fig. 4.7.31, Seismic interpretation of the carbonate system. Different potential karstification zones are connected with low sea level periods. Key to acronyms: FSST, Falling-Stage System Tract, LST; Lowstand System Tract; TST, Transgressive System Tract; HST, Highstand System Tract; mfs, maximum flooding surface. *Secondary variation on the sea level; SB, Sequence Boundary. 302 On seismic profiles, the third stage would correspond with the Transgressive System Tract (TST 3, figures 4.7.30 and 4.7.31), characterized by a back-stepping architecture to the north of mound- shaped deposits, similar to those proposed for the onshore San Cristóbal region or the Cibao Basin (see sections 4.2.2 and 4.4.2). Seismic facies consist of low-amplitude reflectors that laterally pass into high-amplitude and laterally continuous (figure 4.7.31) that would correspond with ramp and basinal deposits, respectively. Although the system exhibits a generalise transgression to the north, a secondary regression is identified on seismic profiles by the appearance of prograde reflectors (figure 4.7.32). According to their morphology, the first deposits coincide with a FSST (FSST 4 on figures 4.7.30 and 4.7.31), possibly derived from the exposition and erosion of the transgressive platform (TST). This process would have been recorded by the incised valleys interpreted on strike sections (figure 4.7.31 C). At the same time, potential indicators of karstification were observed on seismic lines, such as the loss of lateral continuity of reflectors, due to karst fractures. This process could be connected with the development of cavernous porosity in the lower – middle Miocene limestones observed in onshore exploration wells (e.g., Maleno #7, Munthe, 1995). This stage is followed by a wedge with an upstepping stacking pattern, considered as a Lowstand System Tract (LST 5 on figures 4.7.30 and 4.7.31). Basinwards, this regression,composed of the FSST and the LST, is accompanied by the deposition of chaotic reflectors, interpreted as a higher-energy sedimentation in the basin. Although a higher cyclicity could explain this regression, its coincidence with other tectonic events that took place at the early Miocene makes the latter more plausible. In this sense, the uplift of basement blocks studied in last section (4.7.3) or the indenter of the Beata Ridge in southern Hispaniola might have caused the relative sea level fall. Nevertheless, a combination of both explanations is not totally discarded. After this impasse, the system retrograded again landwards (to the north) finalising with the de- velopment of an upper Miocene platform that would represent the Highstand System Tract (HST on figure 4.7.30). The maximum flooding surface is located close or over the Top of the middle Miocene sequence. At the onshore extension, Abad et al. (2010) describes also de presence of a ravinement surface, on which upper Miocene reefal limestones and bioclastic calcarenites were deposited, supporting this interpretation. Fig. 4.7.32, Detail of the carbonate system at the San Pedro Basin. (location in figure 4.7.31 B). Note the presence of bead-like reflectors for the Oligocene reef that could imply karstification. 303 The distribution of the carbonate ramp system occupied fundamentally the central and western region of the basin, coinciding with the magnetic anomaly attributed to the island arc domain, especially at its southern limit (figure 4.7.33). This would point out an Oligocene transgression that favoured the development of a carbonate ramp system over the island arc domain, which would have been exposed previously. Fig. 4.7.33, Distribution of the interpreted carbonate ramp system over Reduce to Pole anomaly map. According to the interpretation, the carbonate system was developed over the southern limit of the island arc domain. Comparison with Puerto Rican analogues “Reef development increased worldwide during the late Eocene and Oligocene” (Pomar et al., 2017 and references therein) and the Oligocene eustatic rise, which flooded shelf margins, led to the zenith of Tertiary reef-building, being reported extensively from the Caribbean-Western At- lantic, Mediterranean, middle-East and near Eastern regions (Frost et al., 1983 and references therein). On the southern margin of Puerto Rico (figure 4.7.34), middle and late Tertiary rocks are divided into three main sequences (from Frost et al., 1983 and references therein):  A late Oligocene transgressive cycle that comprises basal clastic units and shelf/reef tract as well as deeper shelf to slope sediments.  A major flooding cycle of the reef tract in the early Miocene with the onlap of hemipelagic and deep slope and marls and chalks.  A thick, carbonate shelfal sequence of middle and late Miocene age. 304 Fig. 4.7.34, Position of the main carbonate systems described on text: San Pedro Basin (green), Puerto Rican (Blue) and location of Perla Field (red) over regional digital elevation model of the Caribbean region. Note as San Pedro and Perla could be mirror basins for the Oligocene to Miocene period. Puerto Rican Oligocene reef complex was exposure above the sea level by the end of the Oligo- cene and/or earliest Miocene (figure 4.7.35), which could be associated to the FSST-1 and LST- 2 stages interpreted at the SPB. Nevertheless, an extensive diagenetic solution stage did not occur during this exposition in Puerto Rico. “Three factors likely played a role in shielding the reef sediments from meteoric waters: (1) the porous sandstones of the underlying Juana Diaz For- mation as well as the inshore shelf sandstone equivalents of the reef may have captured the down- dip flow of water to a degree where it essentially bypassed the package of reef sediments; (2) the reef is overlain in part by poorly permeable forereef and island slope muds that may have created an overlying diagenetic seal; and (3) the reef sediments were fairly tight prior to the exposure due to the large amount of lime mud matrix and internal sediment along with cementation by marine and equant calcite spar cements” (Frost et al., 1983). The mud-rich composition of the Oligocene reef could be the responsible of the high-amplitude seismic facies on seismic profiles (4.7.30), which might correspond with a sedimentation similar to the PVFA2 (see section 4.4.2). Never- theless, at the SPB, interpreted Oligocene reefs are not cover by the lower Miocene deep-water facies at its northern section. This could have led to a hypothetical karstification of the sequence that favoured porosities and permeabilities. Figure 4.7.32 shows that FSST top is below Oligocene reef top. Furthermore, bead-like reflectors might imply caves formation during karstification pro- cesses (e.g. Li, 2017; Tuyl et al., 2018). Lower to middle Miocene (NN1 to NN6 nannozones) facies at San Cristóbal (onshore extension of San Pedro Basin, see section 4.4.1) vary from algal limestones, to bioclastic and sandy limestones, marls, siltstones and conglomerates with abundant Oligocene reworked fossil assembles (Biju-Duval et al., 1982). This section is interpreted to be related to the FSST and LST deposits identified on seismic profiles, where reworked material demonstrates the exposition of the Oligocene reef at the SPB same as in Puerto Rico. 305 The early Miocene flooding fits with the TST-3 stage observed in the SPB. In addition, the un- conformity study in southern Puerto Rico (figure 4.7.35), that eroded the lower Miocene, would be related to the secondary regression of the system proposed under the interpretation given in this work and corresponding to the stages FSST-4 and LST-5. After this episode, middle and upper Miocene limestones would represent the final transgression and Highstand of the system. Fig. 4.7.35, Schematic stratigraphic model of the Oligocene – Miocene carbonate system that crops out at the southern margin of Puerto Rico. Modified from Frost et al. (1983). Comparison with Venezuelan analogues As exposed in section 4.2.1, “the approximately 300-m (984.2 ft)-thick Oligo–Miocene car- bonates of the Perla field consist of an overall deepening-upward sequence predominantly com- posed of larger benthic foraminifera and red algae (oligophotic production) with a minor contri- bution from shallow-water (euphotic) carbonate components (green algae and corals)”. They were deposited “in a context of tectonic subsidence, the building blocks progressively onlapped with backstepping configuration onto a paleo-island” (Pomar et al., 2015). This architecture favours that the distal facies of the system cover former deposits, creating stratigraphic traps (figure 4.401). The sedimentological model includes (from Pomar et al., 2016):  “Poorly sorted skeletal packstones and grainstone with micropeloidal muddy matrix rep- resent the shallowest, fully marine deposits, in which mastophoroid red algae and codia- cean green algae point to shallow euphotic conditions”, Pomar et al., 2016.  “Downdip of the shallow sea grass meadows, red algae dominated production and accu- mulation. Coarse branching red algae packstone/ floatstone with larger benthic foramin- ifers (LBF; Amphistegina, Heterostegina, Lepidocyclina and Miogypsina), passing downdip into rhodolithic floatstone with grainstone tomud-lean packstone, and subse- quently into fine branching red algae floatstones/rudstone and “LBF rudstones” that in- dicates a significant amount of carbonate production in the meso- and oligophotic zones. In the most distal part of the ramp, red algal fragments and LBF occur in structureless, 10- to 35- cm-thick intervals in which LBF are randomly oriented. They are separated by 306 thin (5 to 20 cm thick) intervening layers in which LBF predominate and are all sub- horizontally oriented, parallel to the bedding. Although these zones occur below the ac- tion of surface waves, episodic turbulence, enough to winnow the mud and turnover the rhodoliths would have been needed”. “To explain this apparent paradox, internal waves (IWs) in the oligophotic zone are a good candidate”. “In this context, the “LBF rudstones” represent gravity flow deposits accumulated on the aphotic outer ramp”, Pomar et al., 2014. This depositional environment has led to a good porosity preservation of the system. This is rel- evant due to Oligocene – Miocene carbonates at the San Pedro Basin follow a similar back-step- ping architecture (figure 4.95) for the same period of time and also, over what is interpreted as paleo-islands or structural highs (see section 4.7.2). Aquitanian (lower Miocene) carbonates exposed at San Cristóbal (Fort Resolue Formation), in- terpreted as similar to the TST deposits at San Pedro Basin, consists of a “thick coral, algal and bioclastic limestones that pass into breccias and resedimentation of calcareous beds and coral debris along. This carbonate sequence was deposited until the end of the early Miocene, when sandy siltstones and marls were accumulated in an open-marine environment” (Biju-Duval et al., 1982). Although this sector was not mapped at the recent SYSMIN project and the description are limited, depositional model seems to be in agreement with the propose for Perla. Fig. 4.7.36, Three-steps deposition model for the Perla Carbonates in northern Venezuela, mod- ified from Pomar et al. (2015). Note how distal facies of every new step cover previous deposits favouring the formation of stratigraphic traps. 307 4.7.5 Integrated discussion and main conclusions for the San Pedro Basin evolution After the study of the main unconformities, seismic facies, structures interpreted in the basin and the evolution of a carbonate system identified on seismic profiles, it is possible to propose an evolution model that includes all the constrains established along the chapter. The integration of this model with the lithostratigraphic units, established from exploration wells and the revision of the onshore geology, will give us the tools for the study of the hydrocarbon potential of the basin in next chapter. The analysis of the onshore geology of each tectono-stratigraphic domain provides the following constrains:  A Campanian event that folded the fore-arc region (García-Senz et al., 2007 a; see Section 4.2.3) and could be registered by the deposition of breccias in the barck-arc (Ardèvol. 2004; see Sections 4.4.1; 4.4.2 and 4.4.4). This is accompanied by a change in the geo- chemistry of vulcanism, stopping the subduction related volcanic activity at this time (Es- cuder-Viruete et al., 2007 a; see Section 4.3.2).  A Turonian – Campanian shortening in the island arc that produced NE and SW vergent folding and thrusting, concluding a shortening across the southern domain that had taken place concurrently with sinistral strike-slip movement along the crustal scale BFZ (see Section 4.3.1). In addition, faults were re-activated during the late Eocene – Oligocene thrusting and Miocene to Present Uplift of Cordillera Central (Escuder-Viruete et al., 2006; see Section 4.3.1).  Deposition of deep-water series in the back-arc (Trois Rivieres and Las Palmas for- mations; Abad et al., 2010 a; Pérez-Varela et al., 2010 a; See Section 4.4.1 and 4.4.2).  A top Cretaceous event registered by the erosion of the Maastrichtian platform and reg- istered by Paleocene conglomerates (such as the Don Juan Formation; García-Senz et al., 2007 a; see Sections 4.2.1 and 4.2.3).  Deposition of the Paleogene? – Upper Eocene sequence along a deep trench parallel to the arc (Hernaíz-Huerta, 2006; see Section 4.4.1).  Inversion of the Cretaceous to Eocene sequences due to the collision of Hispaniola with the Bahamas Platform (Hernaiz-Huerta, 2006; Pérez-Estaún et al., 2007; Abad et al., 2010 a; Pérez-Varela et al., 2010 a and references therein). This inversion was recorded by the deposition of conglomerates and olistoliths since the late Eocene to the early Mi- ocene (see Section 4.4.2).  The activity of the SJRFZ started at least in the late Eocene, with a differential sedimen- tation at both sides of the trace (Abad et al., 2010 a; Pérez-Varela et al., 2010 a; see Section 4.4.2).  Oligocene – middle Miocene transgression of a carbonate system as identified on seismic profiles in the Cibao basin (see section 4.2.2) and the deepening of stratigraphic columns in San Cristóbal (Biju-Duval et al., 1982; see Section 4.4.4) or Azua (see Sections 4.5.1 and 4.5.4).  Early Miocene indentation of the Beata Ridge in southern Hispaniola (Hernaiz-Huerta and Pérez-Estaún, 2002; Abad et al., 2010 a; Pérez-Varela et al., 2010 a; see Sections 4.4.4 and 4.5.4).  Late Miocene tilting of the San Pedro Basin and inversion of the San Cristóbal Region (Biju-Duval et al., 1982; Heubeck and Mann, 1991; see Sections 4.4.3). 308 After the analysis of constrains that could have played a role in the SPB, the following evolution model was proposed for the south-eastern margin of Hispaniola.  The development of a back-foreland basin in the retro-arc since the Campanian times, as a consequence of the inversion of the island arc.  The inversion of the Campanian – Eocene basin due to the collision of the island with the Bahamas Banks and an effective transmission of compressional forces to the south, start- ing the development of the MTB in the late Eocene.  Accommodation of shearing in the island arc domain as registered by the identification of rotated blocks in magnetic anomaly maps.  Transgression of carbonate platforms during the Oligocene and the early Miocene.  Middle Miocene unconformity derived from the indentation of the Beata Ridge.  Late Miocene unconformity as a consequence of the tilting of the basin and the exhuma- tion of the San Cristóbal region. The combination of seismic data and potential fields with the prognosed model of the basin has led to the interpretation presented in section 4.7. This integration has not only allowed to reinforce the model but has also provided new observations on the SPB dynamics not observed onshore due to the limited access to outcrops. Furthermore, the structural analysis has reinforced the divi- sion into main tectono-stratigraphic domains established for Hispaniola Island. The first unconformity that could be mapped along the basin corresponds with the Top Creta- ceous, which was tied to the exploration well San Pedro #1 (section 4.7.1). Over the Island Arc Domain, this sequence presents a high-grade of deformation and implies a change in seismic at- tributes, with a frequency, coherency and amplitude loss. In addition, an intra-Cretaceous uncon- formity was identified for those locations where the seismic resolution allowed it. This uncon- formity is interpreted as corresponding to the Campanian event. On the other hand, further studies must address the relationship between the Upper Cretaceous sediments and vulcanism, not possi- ble with the current subsurface image of the basin. The high-deformation observed for the Island Arc Domain is not observed (or in a lower degree) when moved to the Cretaceous – Eocene Basin Domain, where the Cretaceous sequence is represented by lateral continuous reflectors only de- formed by the structures hoped in a thrust belt system in a thin-skin model, that comprises of the MTB. The paleo-reconstructions of the basin provided by the flattening of the main unconformities (when possible), suggests the presence of structural highs in the island arc domain and the depo- sition of a thick sedimentary sequence at the Cretaceous – Eocene Basin Domain (with a footprint on gravity anomaly maps). Although further studies with an improved image of structures must confirm the hypothesis, this disposition, together with the regional geodynamics constrains, rein- forces the back-foreland model for the period Campanian – late Eocene. The final collision with the Bahamas Platform took place in middle / late Eocene times and gen- erated the Top middle Eocene Unconformity. The origin of this unconformity is assumed to relate to an effective transfer of the compressional forces to the south (Granja-Bruña, 2008; Granja- Bruña et al., 2009) which would be involved in the inversion of the Cretaceous to Eocene basin, recorded by the interpreted Top middle Eocene unconformity. At the Cretaceous – Eocene Basin Domain, seismic facies analysis for the late Eocene to Oligo- cene period reveal the presence of transparent and hummocky reflectors close to the main fault zones. These facies are interpreted as the seismic expression of the Olistoliths, mass transport and conglomerates identified at the onshore El Limonal Formation (Pérez-Varela et al., 2010 a). They progressively pass into high-amplitude and lateral continuous reflectors to the south, giving us the transition from a lower slope to a deep-water environment. 309 Landwards, at the Island Arc Domain, this sequence is interpreted as a shallower sedimentation deposited over a structural high and the upper slope. They are correlated with the Oligocene out- crops of San Cristóbal (Biju-Duval et al., 1982, Pérez-Varela et al., 2010 a and references therein) and Puerto Rico (Frost et al., 1983), where clastics leads to upper Oligocene limestones that were exposed at lowermost Miocene times. The analysis of seismic sections provides indicators of the exposition and potential karstification of the Oligocene reef. Since the late Eocene, deformation has not been accommodated in a similar way for the other different domains. While shearing has been accommodated in the Island Arc Domain, compres- sion dominates to the south, developing the MTB (figure 4.7.37). Fig. 4.7.37, Schematic deformation models proposed for the western and eastern sectors of the SPB. In a partitioned, shearing is mainly accommodated by the island arc basement while com- pressional forces are effectively transmitted to the south, generating the MTB in a thin-skinned model. The accommodation of shearing took place between the Hispaniola and Bonao Fault zones, limits of the Island Arc Domain in the SPB. This process started in Oligocene – Lower Miocene (figure 4.7.38), generating the anti-clockwise rotation and elevation of crustal blocks and coincide with the deformation observed also in southern Puerto Rico (Erikson and Pindell, 1991). This process could have accommodated the deformation derived from the aperture of Cayman and the east- wards tectonic escape of the Caribbean Plate. In the late Miocene, there is a change in the eastern sector of the basin with the appearance of the SAFZ, which generates the inversion and a left lateral displacement of the southern zone, possibly a consequence of the regional geodynamic change. The uplift produced by the SAFZ would have triggered diverse normal fault systems, like rotated blocks or gravity-driven faults. Both seem to take root at the lower to middle Eocene sequence, which acts as a detachment level. Compressional forces are accommodated along the MTB through the inversion of the Cretaceous – Eocene Basin Domain (figure 4.7.38). Following the same criteria for onshore studies, the MTB has been divided into thrusts, folds and monocline zones, revealing the same disposition and ex- tension. The rear zone of the system would be composed between the SJRFZ and the SJLPFZ, leading to the correlation of the Azua Basin with the frontal Thrust of the MTB. The configuration space for the SPB since the late Eocene has been controlled by the development of the MTB, and since the late Miocene by the SAFZ in the eastern sector of the basin. An Oligocene flooding over the Island Arc Domain would have started the evolution of a car- bonate ramp system. This evolution has been set in terms of the sequence stratigraphy, prognosing a general transgression of the system, given by its back-stepping architecture, and interrupted in the early – middle Miocene by a secondary regression of the system. 310 Fig. 4.7.38, Evolution model of the south-eastern margin of Hispaniola as proposed from onshore studies (Abad et al., 2010 a; Pérez-Varela et al., 2010 a) and observed on seismic profiles. 311 This episode would have been recorded by the potential karstification of the lower Miocene plat- form and by the deposition of high-energy deposits in the basin. This evolution is in consonance with what is observed in the onshore. The potential karstification is connected with the develop- ment of cavernous porosities in lower – middle Miocene limestones in Azua, and the transgression is in agreement with the interpretation of seismic profiles in the Cibao Basin or the stratigraphic columns in the southern region of Hispaniola. After this early to middle Miocene regression, the transgression continued landwards, and these deposits were covered by the distal facies of the next stage (which represents the maximum flooding surface in the middle Miocene). Finally the effect of the Beata indentation could have influenced the secondary regression in the early Miocene, and caused the inversion and exhumation of the westernmost area of the Basin (San Cristóbal region), from the late Miocene, generating the late Miocene unconformity, which revealed the tilting of the basin. This new tectono-sedimentary model of the basin opens a new window for future exploration activities in the SPB providing new constrains on the hydrocarbon potential of the basin. The correlation between onshore and offshore units (summarized in figure 4.7.39) might be applied to the play prediction, being possible to identify key elements of the petroleum system of the basin, such as the source rock and the reservoir seal of the system. On the other hand, the structural analysis provides potential traps and the age estimation of structures might constrain the timing. All these topics will be addressed in next chapter: Hydrocarbon Potential of the SPB. Fig. 4.7.39, Schematic stratigraphic chart of the southern margin of Hispaniola (not to scale). This chart was built by the integration of the onshore and offshore geology. 312 313 Chapter 5: Petroleum system for the San Pedro Basin 314 315 Section 5.1: Exploration background This chapter will attempt to answer two main questions, have oil and gas been generated in the south-eastern margin of Hispaniola? And, in that case, is it possible to identify areas where com- mercial accumulations could be discovered? The answer to the first question is easy: yes, oil and gas have been generated as it is proved by the presence of oil and gas shows along Hispaniola and the limited oil production that took place in Azua, at the Higuerito and Maleno oil fields. However, the response to the second question is not obvious. Despite of the drilling of up to 71 onshore wells in the Dominican Republic until Present, a big discovery has not been made. Nev- ertheless, it should be noted that most of the exploration wells were drilled before 1965, mostly based on surface geology and without a good seismic control, and targeting, in most cases, the shallower section (figure 5.1.1). This chapter is an additional effort to understand the hydrocarbon potential of the island, and in particular within the offshore SPB. For that, the results of the previous exploration activities were evaluated, including the analysis of 60 exploration wells provided by Banco Nacional de Datos de Hidrocarburos (BNDH) of the Dominican Republic, processing of new 2D multi-channel seis- mic data from the Spanish Research Project NORCARIBE, re-processing of legacy seismic pro- files and interpretation of gravity and magnetic data.. This study describes and discuss the avail- able evidences to support the presence of main elements of the petroleum system, it´s evolution, the associated exploratory geological risk, and suggests critical aspects that should be addressed in the future of the exploration in SPB. For that, 10 representative wells were evaluated by a post- mortem analysis in order to determine the main elements of the petroleum system (section 5.2), integrating the results with the evolution model presented in Chapter 4 to determine a reviewed hydrocarbon potential of the basin (section 5.3). Fig. 5.1.1 Summary of main exploration activities in Hispaniola since the first geological map of the island that reported the presence of oil seeps (Gabb,1872), through the Maleno discovery during the forties and until the first license round that started in July 2019, from Gorosabel-Araus et a. (2020). 316 The history of hydrocarbon exploration in Hispaniola dates back to Spanish colonial times when natural seeps were already known. In 1862, Nelson worked on the first report that addressed the presence of oil in the Dominican Republic (Mann et al., 2008). It was required by the American consul in the island, under the administration of President Abraham Lincoln. From 1869 to 1871, the American geologist William Gabb carried out the first systematic geological mapping in the Island. His work conducted to the Geological Map of the Republic of Santo Domingo (figure 5.1.2). In this document, for instance, Gabb describes: ‘the presence of “viscid” oil in an artesian well where the tube of the well is filled with oil and water with an inodorous and non-inflammable gas bubbles to the surface’ (Gabb, 1872). It is also remarked in Gabb (1872) the words of Taylor in Statistic of Coal, p.247: “the entire chain of the West India and Windward Islands present similar phenomena of petroleum springs, beds or veins of asphaltum and accumulation of mineral pitch”, with a special emphasis on Cuba and Barbados. In the same way, Schomburgk (1848) described in detail oils seeps and bituminous coals for these two islands. These contributions emphasise the knowledge of the presence of energetic resources for the whole chain of island that configure the Greater and Lesser Antilles since the nineteenth century. Fig. 5.1.2 Geological Map of the Republic of Santo Domingo (current Dominican Republic) elab- orated by William M. Gabb in 1872. In the early twentieth century, eight wells were drilled in the Azua area (figure 5.1.3) by the Lancaster & Kreider Company (Mann et al., 2008). Their results were published in the report elaborated by the United States Geological Survey (USGS) (Vaughan et al., 1921) during the American occupation of the island, between 1915 and 1923. The goal of the project was to study the oil, gas and mineral potential resources of the country. According to that statement, these wells were drilled at the location of the main oil seeps. The total depths were a few hundred meters, with the deepest one reaching only 400 m. Oil signs and small accumulations of it were found in all of them. The estimated production goes from a dozen up to several hundred barrels per day. The description given for the oil is “dark brown, very liquid and of high gravity, the results of various tests showed a gravity of 19º to 21º Baumé” (table 5.1.1). 317 Fi g. 5 .1 .3 , D ig ita l e le va tio n m od el o f H is pa ni ol a sh ow in g th e av ai la bl e ex pl or at io n w el ls . R ed in se t s ho w s th e st ud y ar ea o r Ar ea o f I nt er es t (A O I) . W el ls se le ct ed fo r t he w el ls p os t-m or te m a pp ea r l ab el le d wi th th ei r a cr on ym s. 318 Table 5.1.1 Geochemical results from the oils of Azua from Vaughan et al.(1921). Vaughan et al. (1921) also described the presence of oil seeps eastward the Azua Basin, at about 16 km northwest of Baní, at the TRPB, onshore extension of the MTB, where Cretaceous to Oli- gocene sediments crop out this fold-and-thrust belt. Previous field works of exploration geologists had reported the collection of samples of oil from this place. Unfortunately, at the moment that Vaughan’s team visited the area, they noticed that “much rain had recently fallen, and with the rise of the creek the indications may have been obscured” (Vaughan et al., 1921). The mud in the stream bed had an odour of hydrogen sulphide. This area was not considered of exploratory in- terest due to the high grade of deformation and faulting. Nevertheless, it should be notice here, that this zone has not been included in any recent field survey nor the new geological mapping. The presence of an oil seep in this position could imply the existence of a Cenozoic or older source rock that open the window for a petroleum system in the TRPB-MTB system and should be addressed in future studies. After this initial phase, most of the exploration in Hispaniola was focused in the San Juan – Azua Basin (figure 5.1.4) for the next decades. The production was limited with a cumulative of 25000 bbl (barrels, 200 BOPD or barrels of oil per day) in Maleno #1 (Mann et al., 2008 mention an estimated cumulative production between 23,000 and 45,000 bbl for the Maleno field) and 4500 bbl in Maleno #1A. Other wildcats were drilled in Cibao Valley (Villa Isabel #1 and Licey #1), the San Juan Basin (Comendador #1) or Enriquillo (Charco Largo #1) during this period (figure 5.1.4). None of them resulted productive. However, the presence of oil and gas shows holds com- pany’s attention, and, during the eighties, exploration activities moved to other basins of the Do- minican Republic. For the period 1979-1984, Petrolera Las Mercedes carried out geophysical surveys in the sur- roundings of Santo Domingo city and the San Pedro Basin. As a result, Las Mercedes drilled 3 wildcat wells next to Santo Domingo (Santo Domingo #1, San Pedro #1 and #2), and another in the San Juan Basin (Candelon #1; see figure 5.1.4 for locations). They resulted dry holes after testing, except for the oil shows detected at San Pedro #1. 319 Fig. 5.1.4 Main sedimentary basins of Hispaniola at present day; Enriquillo, San Juan – Azua, San Pedro and Cibao. The position of the wells cited in the text is included: VI-1, Villa Isabel #1; LIC-1, Licey #1, COM, Comendador #1; CAN-1, Candelon #1; CHL-1, Charco Largo #1; PS-1, Punta Salinas #1; SD1, Santo Domingo #1; SP-1, San Pedro. Red inset shows the study area. In 1981, Charco Largo #1 (figure 5.1.4) was drilled in the Enriquillo Basin to a total depth of 15,847 ft (4830 m), the deepest well in Hispaniola until present. It was the final phase of an exploration survey by Canadian Superior Oil (now integrated into Exxon-Mobil) which consisted of the analysis of gravity anomalies and the acquisition of more than 1000 km of 2D seismic data. After testing, the well was abandoned as a dry hole. Ten years later Mobil resumed the exploration in the San Juan - Azua and San Pedro Basins. By a new approach of the basins and the acquisition of new seismic and geochemical data this com- pany drilled Punta Salinas #1 in the nearby of San Pedro Basin in 1995. It resulted a dry with shows of gas and bitumen. At the same time, Petrolera ONCE-ONCE performed new seismic surveys in Cibao Valley which combined with the information coming from two wildcats drilled in the fifties led to a perforation program in the area in two phases. The first one, consisted of four wells, encountered non-commercial gas accumulation and oil shows. In the second phase, Pe- trolera ONCE-ONCE acquired new seismic and drilled five wells, all of them with gas shows only. In summary, a total of 72 exploration wells were drilled in the Dominican Republic (according to the BNDH database), demonstrating the presence of oil shows and little accumulations which join to a variety of seeps along the country. Nevertheless, a big discovery is still elusive and additional exploratory work must be done in order to understand the petroleum systems of the island. 320 Section 5.2: Available exploration data 5.2.1 Surface geology Geology mapping in Hispaniola started in the second part of the XIX century with the work of the American geologist William Gabb and continued with the analysis of the geology and the oil, gas and mineral potential of the island by Vaughan et al. (1921) for the USGS (Mann et al., 2008). In the period 1939 – 1947, Dominican Seaboard Company, a subsidiary of Standard Oil of New Jersey, carried out additional geologic mapping with a special focus on the central and meridional segments of Hispaniola (Dohm, 1941, a,b,c in Mann et al. 2008). This field work, combined with gravity and seismic data, resulted in the drilling of two wells in the Higuerito structure, seven wells at the Maleno anticline (including Maleno #1) and two wells next to Maleno at El Mogote and Las Hormigas anticlines (Mann et al. 2008), figure 5.2.1. Fig. 5.2.1 Geology and digital elevation maps of the Azua region with the position of the Azua and Higuerito fields. Bowin, Palmer and Nagle continued going in depth of the geology of Hispaniola, studying the Central and Septentrional Cordillera and the Cibao valley (Antonini, 1979; Bowin, 1960, 1966; Palmer, 1963, 1979; Nagle et al., 1979). During the seventies the exploration was focused on the ophiolite and metamorphic complexes of Central Hispaniola (Kesler et al., 1975, 1977; Kesler and Sutter, 1977). Their studies were used for the develop of the mining industry. During the eighties and nineties numerous scientists studied the geology of the Dominican sector of the island contributing with new constrains on the deformation events and the stratigraphy and evo- lution of the main sedimentary basins (e.g. Mann 1983; Mann et al. 1991 a, b; Mann et al. 1999; Pindell and Draper, 1991; Duval et al., 1982; Heubeck et al., 1991; Heubeck and Mann, 1991; Heubeck, 1992). It is also in this time when Mobil resumed its interest in the region acquiring the Azua and San Pedro blocks and between 1991 and 1995 carried out field studies, gravity and geochemical studies of the Azua oils and rock-eval analyses of outcrops. The programmes SYSMIN I (1994-2001) and SYSMIN II (2007-2010), founded by the European Union and leaded by Dominican General Mining Direction (DGM; Dirección General de Minería) and the Dominican Geological Survey (SGN; Sevicio Geológico Nacinal) respectively, produced the systematic geological cartography of the Dominican Republic to 1:50,000 scale. These studies were carried out in collaboration with the Spanish Geology Survey (IGME; Instituto Geológico y Minero de España), the French Bureau de Recherches Géologiques et Minières (BRGM) and companies like PROINTEC and INYPSA. The systematic geology mapping contributed signifi- cantly to the understanding of the geology and evolution of the island. Nevertheless, it did not cover strategic areas for the present study, such as the geographic quadrants 5972 and 6171 cor- responding with the sectors of San Juan and San Cristobal (figure 5.2.2), which are the lateral continuation of the Azua and San Pedro Basins respectively. 321 Fig. 5.2.2 Distribution of the 1:50.000 geology sheets of the SYSMIN I and II programmes, mod- ified from SGN (2007). Red inserts show the quadrants of San Juan (5972) and San Cristóbal (6171) not included in the cartography project. 5.2.2 Geochemical data The level of geochemical knowledge of the island could be considered as relatively poor (this will be addressed at Section 5.3). In general, geochemical state of art faces the following issues:  From wells, rock-eval analyses are limited. Most of them do not include pyrolysis data to determine kerogen type.  Only eight of the seventy exploration wells perforated in the Dominican Republic had vitrinite reflectance analyses.  Outcrops samples are scarce and non-systematic.  Oil and gas samples from Azua have been analysed. However, an oil-to-source correla- tion has not been stablished.  From observations taken during the geology mapping of the Dominican Republic, out- crops from the Cretaceous, Oligocene and Miocene have been considered as potential source rocks. However, no rock-eval analyses has been carried out and, in most cases, these appreciations are based on visual recognition by the field geologist. 5.2.3 Seismic data All the seismic data acquired in Hispaniola is 2D. Since the creation of “Banco Nacional de Datos de Hidrocarburos” (BNDH) in 2016, 805 seismic lines were released, covering more than 12500 km. They have been classified in terms of the quality as follows:  Very poor: It is difficult even to discern between the acoustic basement and the reflections corresponding to the sedimentary infill of the basin  Poor: It is possible to discern between the basement and the sedimentary sequences. 322  Fair: It is possible to distinct seismic facies. A resume of all the seismic acquired in the Dominican Republic is shown in Table 5.2.1 while the representation of all the seismic lines included for this thesis is shown in figure 5.2.3. Company or Insti- tution Year Area Quality Format Dominican Seaboard Co. 1945 San Juan and Azua Basins Not available. - Petrolera Dominicana 1960 Enriquillo Not available. - Teneco (1) 1969 Offshore Azua, San Cristo- bal and Cibao Basins Poor to Fair quality. Digitalized University of Texas (2) 1975 Muertos Thrust Belt and Caribbean Plate Poor quality. SEGY University of Texas (3) 1977 San Pedro Basin Poor to fair quality. SEGY Las Mercedes (4) 1977 Llanura Oriental Poor quality Digitalized Canadian Superior Oil Co. (5) 1979 Enriquillo Poor quality. Digitalized Cariboil (6) 1979 San Juan Poor quality. Digitalized University of Texas (7) 1980 Beata Ridge and Muertos Thrust Belt Poor quality. SEGY Weeks Petroleum Lim- ited (8) 1982 Cibao Basin Poor quality. Digitalized Western Geophysical Co. (9) 1982 Offshore San Pedro Basin Poor to fair quality. Digitalized ONCE ONCE (10) 1991 Cibao Basin Poor to fair quality. Digitalized Mobil Oil 1992 Offshore San Pedro Basin Fair quality SEGY LDEO (11) 1995 Beata Ridge Fair quality. SEGY Murfin Dominicana (12) 1996 Azua and San Cristobal Basins Only available profiles in Azua. Poor quality. Digitalized Complutense Univ. of Madrid (13) 2013 Offshore San Pedro and Hispaniola Trench Good quality. SEGY Table 5.2.1 Seismic acquisition summary in Hispaniola. The position of the available surveys is represented in figure 5.2.3. 323 Fig. 5.2.3 Location of seismic surveys acquired in Hispaniola and available in the BNDH data- base. See table 5.2.1 for survey information and quality. In terms of sedimentary basins, the seismic coverage comprises:  Enriquillo: 65 seismic lines with a total length of 1007.23 km.  Azua – San Juan: 30 seismic lines with a total length of 303.74 km.  San Pedro – Muertos Thrust Belt: 75 seismic lines with a total length of 2329.45 km.  Llanura Oriental: 9 seismic lines with a total length of 193.36 km.  Cibao: 62 seismic lines with a total length of 631.72 km.  Other marine sections: 99 seismic lines with a total length of 8126.72 km. 5.2.4 Gravity and magnetic data Since the decade of the forties, geophysical regional surveys have been carried out on the island. They consisted of gravity and magnetic data. Nevertheless, in most cases the access to the survey details and quality criteria is not possible. The coverage and resolution could be classified as fair to good, covering the whole country and offshore. A resume of data acquisition is shown in Table 5.2.2. The information has been collected from Mann et al. (2008), Marrero et al. (2006) and the BNDH database. Company or Institution Year Area Data Dominican Seaboard Oil Co. 1945 San Juan and Azua Basins Gravity. Residual gravity map 1:100000 with a contour interval of 5 mGal Pohly Exploration Co. 1956 Cibao Basin Gravity maps 1:800000 with a contour interval 0.5 mGal. Petrolera Las Mercedes 1978 Azua and San Pedro Basins Bouguer gravity anomaly maps 1:50000 with a contour interval of 1 mGal and a density recuction of 20 g/cm3 and mag- netic anomaly maps 1:250000 324 Quisquella Oil Co. 1979 Cibao Basin Bouguer gravity anomaly map 1:50000, with of 1 mGal. Western Geophysical Co. 1982 Dominican Repub- lic Bouguer gravity anomaly map with 5 mGal contours and total magnetic anomaly with 10 gammas contours. Maps 1:250000. CGG 1996 Dominican Repub- lic Aeromagnetic acquisition for SYSMIN projects. Flight height 120 m, lines sep- arations of 500, 1000, 2000 m (N-S) and 5000, 10000 (E-W). Total coverage of the Dominican territory. Complutense Univ. of Ma- drid (UCM) 2006 Offshore Hispaniola Gravity and Magnetic Complutense Univ. of Ma- drid (UCM) 2009 Offshore Hispaniola Gravity and Magnetic Complutense Univ. of Ma- drid (UCM) 2013 Offshore Hispaniola Gravity and Magnetic Table 5.2.2 Gravity and magnetic data acquisition summary in Hispaniola. In addition, the American National Geospatial-Intelligence Agency (NGA) gathered all the grav- ity data collected by Institut Français de recherche pour l'exploitation de la mer (IFREMER), the Royal Astronomical Society, Cambridge University and Lamont-Doherty Geological Observa- tory (LDEO) between the years 1939 and 1991. This dataset was integrated and processed for this work. For this thesis, potential fields data come from the following sources:  Gravity: NGA collection combined with the data set of Sandwell et al. (2014).  Magnetic: CGG 1996 survey combined with the UCM and WMAG datasets See Section 3.3 for a detail description of gravity and magnetic data used for this work, together with the processing and methods. 325 Section 5.3: Wells post-mortem analyses Despite of the drilling of up to 72 onshore wells in the Dominican Republic until Present (accord- ing to the BNDH database), a big discovery has not been made. Nevertheless, it should be noted that most of the exploration wells were drilled before 1965 (figure 5.3.1), mostly based on surface geology and without a good seismic control, and targeting, in most cases, the shallower section. More than 50% of the wells reached a total depth lower than 1,000 m. The only discovery took place in the San Juan - Azua Basin, producing in shallow reservoirs consisting of Miocene – Pliocene sandstones and following a Miocene play. To determine the strengths and weaknesses of the exploration in Hispaniola, a post-mortem analysis of the main exploration wells was carried out. These analyses are useful to identify regional elements of the petroleum system which will be applied to determine the hydrocarbon potential of the SPB. Fig. 5.3.1 Exploration wells distribution in terms of time (left) and total depth (right). The available information corresponding to the totally of the wells stored at the BNDH database (72) were examined. From those, 9 were selected for a well post-mortem analysis: Charco Largo #1, CHL-1; Candelon #1, CAN-1; Maleno DT-1, MDT-1; Punta Salinas #1, PS-1; San Pedro #1, SP-1; Caño Azul #1, CA-1; San Francisco Reef #1, SFR-1; Licey #1, LIC-1; and Villa Isabel #1, VI-1. The location is represented on Figure 5.2. They were chosen on account of the most com- plete penetrated stratigraphic section, available files, lithologies and results, in an attempt of giv- ing the most complete image of the subsurface as possible (Table 5.3.1). Well logs and geological or lithological sample reports are available for all of them. The integra- tion of the wells with the seismic profiles (in time) had to be using Delta Times (DT) due to there is no check shot file. Tops and basic descriptions are only accessible for the wells CHL-1, CAN- 1, MDT-1, PS-1 and SP-1. The correlation with the remaining ones was completed by the analysis of logs and the description of samples. Only CHL-1 and PS-1 have End of Well Reports (EOWR). Completion of testing files are attached for CHL-1, MDT-1, PS-1 and SP. As it was mentioned, the geochemistry is poor studied in the island and only four of these wells have rock-eval and/or vitrinite reflectance results. A penetration chart for these wells is represented on Figure 5.3.3. The great part of the record is Cenozoic (Neogene in particular) with basement units reached only at CA-1 (quartzites and dio- rites) and SFR-1 (possibly ophiolite material, quartzite with glauconite re-crystalized, biotite, traces of graphite). Three source rocks were identified from Cretaceous, Oligocene and Miocene. Drilling stem tests reveal the presence of good porosity reservoir for Neogene and Oligocene carbonates and clastics. Differential pressures and changes in fluids compositions reveal the pres- ence of seals. And finally, oil and/or gas shows were detected for 7 of 9 selected wells. 326 Fig. 5.3.2 Location of wells selected for a post-mortem analysis. Key to acronyms: VI-1, Villa Isabel; LIC-1, Licey-1; SFR-1, San Francisco Reef-1; CA-1, Caño Azul-1; SP-1, San Pedro-1; PS-1, Punta Salinas-1; MDT-1, Maleno DT-1; CAN-1, Candelon-1; CHL-1, Charco Largo-1. Well Logs Check shots WELL REPORTS Geochem. TD (m) / Age Tops and basic re- sults EOWR Geological Completion of testing CHL- 1 X X X X X X 4,830 / Oli? CAN- 1 X X X X X 3,944 / Eoc. MDT- 1 X X X X 3,023 / Mio. PS-1 X X X X X X 1,575 / Eoc. SP-1 X X X X X 2,040 / Cret? CA-1 X X X X X 1,060 / ? SFR-1 X X X X 1,844 / Oli? LIC-1 X X X 3,666 / Oli? VI-1 X X 3,318 / Oli? Table 5.3.1 Available data for the most representative wells in Hispaniola that were selected for the post-mortem analysis. EOWR refers to the End of Well Report. Red X show the information does not proceed from a report but from annotations in well logs or mentioned on other docu- mentation. TD = Total Depth. 327 Fi g. 5 .3 .3 , P en et ra tio n C ha rt o f t he se le ct ed w el ls fo r t he w el ls p os t-m or te m a na ly si s w he re d ri lli ng st ea m te st a nd sh ow s a re re pr es en te d. 328 5.3.1 Villa Isabel #1 (VI-1): post-mortem analysis Villa Isabel #1 (VI-1, figure 5.3.4) was drilled in 1958 by HS Cole & Son to a total depth of 3318 m. The information of this well is limited to well logs (resistivities, spontaneous potential, mag- netic mark detector and calliper), the perforation records with lithology descriptions, the palaeon- tological summary and personal communications. The objective of the well is not defined in the available documentation. It is supposed that Villa Isabel #1 tried to reach a structure interpreted from gravity data and surface geology. Nevertheless, this structure is not clearly identified on new cross sections (geological map 5975-III, Urien et al., 2010 b), neither on potential fields (figure 5.3.4). The target of the well is not indicated in the available information. However, since the well TD at top Oligocene, it is possible to asume that the well targeted Miocene reservoirs, following a Miocene play similar to those in the Azua Basin. Figure 5.3.4, A, Bouguer anomaly map over digital elevation model. B, Reduce-to-Pole anomaly map. C, Cross section modified from the Geology map of Villa Vazquez (5975-III, Urien et al., 2010 b). Location in A and B. Results: The information relative to hydrocarbon shows (figure 5.3.5) is limited to annotations on well logs, all of them catalogued as non-productive.  From 397 to 480 m dry gas (methane) was detected in drilling fluids, no gas and no flu- orescence in cuttings. Similar gas shows (methane) were detected at 826 m and from 939 to 972 m.  Another gas show from 1272 to 1274 m with 85% methane was classified as possible productive, although there is not more information about.  The first oil show appeared from 1508 to 1509 m that was described as a residual show.  From 1767 to 1790 m oil and gas shows were detected, with fluorescence in cuttings, 25 units of 95% wet gas in mud and 9 units – 95% wet in cuttings.  From 2320 to 2321 m and 2405 – 2407 m two oil and gas shows are described. The former exhibited 26 units of 75% wet gas in mud 6 units of 95% wet gas and fluorescence in cuttings. The later had 30 units of 95% wet gas in mud and 30% of fluorescence in cut- tings. Both were declared non-productive. 329 Fig. 5.3.5 Summary of Villa Isabel #1 post-mortem analysis (see Appendix 2 for the legend). 330  From 2804 to 2808 m there was a gas show with 44 units of 50% dry gas in mud and 14 units of 10% dry gas in cuttings. Non-productive.  From 2969 to 2971 m oil was detected in mud with good fluorescence in cuttings and 24 units of 99% wet gas in mud.  From 3119 to 3121 m oil appeared in mud with 38 units of 99% wet gas and trace of fluorescence in cuttings. There is no information about pro- duction tests. Rock-eval or vitrinite analyses are not available if they were carried out. Despite of the lack of formal analy- sis, the study and correlation of litho- logical units and well logs determine intervals with source rock potential. Black shales are described along Unit O1 (see Sections 4.2.1 and 4.2.2). The presence of potential Oligocene source rocks in Hispaniola for the same interpreted units leads to the hypothesis of considering the pres- ence of a potential source rock. Fur- ther studies and analysis are neces- sary to determine their source rich- ness and kerogen type. Furthermore, the current geothermal gradient calculated from the cor- rected Bottom Hole Temperatures (BHT, figure 5.3.6) indicates that sediments at total depth are entering the oil generation window (100 ºC). Figure 5.3.6, Geothermal gradients calculated from corrected BHT for Villa Isabel #1 and His- paniola. Stratigraphy summary: Based on sample descriptions and well logs interpretation, Villa Isabel #1 record has been divided in this work into the following lithological units (figure 5.3.5):  Unit N6: From 0 to 400 m, this unit consists of Miocene grey to dark grey, firm to brittle shales; and grey, firm, fine grain and well consolidated sandstones. SP remains generally high (> -10 mV) with values locally lower corresponding to sandier intervals. Resistivity curves are flat, indicating the shaly character of the unit, with values lower than 5 Ω·m.  Sub-unit N5: From 400 to 732 m, this unit is composed of grey, fine grain, well consoli- dated, silty - calcareous sandstones that contain ash and lignite; alternated with grey, soft to brittle, sandy to silty shales. The presence of sandstones confers to this unit a lower SP (< -10 mV) and resistivities slightly higher than for Unit N6 (between 5 and 10 Ω·m).  Unit N2: From 732 to 1414 m, this interval is characterized by dark grey, soft to firm, calcareous, silty shales; accompanied by grey, fine to medium grain, well consolidated, 331 silty sandstones; and grey, soft, fine grain, earthy and poor consolidated sandstones. SP is characterised by high values (> -10mV) in consonance with the shaly character of the unit. Resistivities show low values (< 10 Ω·m) that increase to base where the long nor- mal log separates from short normal giving way to the next section. Unit N2 has been proved as a regional seal in other wells of Hispaniola (e.g. Maleno DT-1, Section 4.3.7)  Sub-unit N5: From 1414 to 1890 m, this unit consists of grey, very/to fine grain, well consolidated sandstones with traces of limestones; combined with dark grey to black, calcareous, silty and soft to hard shales. Despite of the dominance of sandstones, this interval shows a higher SP (~10 mV) than the upper N5 section, possibly determined by a lower grain size and a greater proportion of shales. Resistivities increase slightly to low- medium values (between 10 and 30 Ω·m) with long and short normal logs separated.  Unit N2: From 1890 to 2504 m, this interval is composed of dark grey to black, hard, silty, calcareous shales; and grey/white to tan, very fine grain, well consolidated sand- stones. Well logs are similar to the interval above (Sub-unit N5), although with a higher SP (< 10 mV), implying a greater shale content.  Unit N1.2 / O2: From 2504 to 2743 m, this interval is represented by grey/tan/milky, hard and buff/milky, chalky, soft to very hard limestones; black, very hard and very calcareous shales; and minor grey, very fine grain, very calcareous sandstones. They present high resistivities with a great separation on long and short normal logs (from 20 to 40 Ω·m for the shallow resistivity and between 60 and 120 Ω·m for the deep). Spontaneous potential change abruptly to the lowest values of the well (< -20 mV) and only alternates with medium values for shaly intervals. However, it is possible that their thickness would be lower than the resolution of the tool. Lithologies together with the unconformity detected on well logs lead to interpret this section as Oligocene (see section 4.2.1 and 4.2.2), alt- hough the presence of lower Miocene sediments is not totally discarded for the upper section. Palaeontological Summary included good lithology descriptions. However, from Unit N1.2/O2 samples were described as washed residues, with no fauna. Therefore, it is not possible to confirm their Oligocene age.  Unit O1: From 2743 to 3088 m, this unit is defined by brown, chalky, soft and buff, crystalline very hard limestones; dark grey to blue, hard, brittle and black, hard, very calcareous shales; and minor grey, fine grain to coarse, well consolidated, soft to hard, calcareous sandstones. As above, limestones are represented by a low SP, increasing for shale intervals (up to -10 mV). In a similar way, resistivities go from low values for shales to the highest values for the limestones (between 20 and 50 Ω·m)  Unit O2: From 3088 to 3318 m (TD), it is composed of tan, sandy, earthy, soft and milky/white/grey, chalky, hard limestones; unconsolidated sandstones; and black to blue- ish, very hard, calcareous shales. The behaviour of the wireline logs is similar to Unit O1, with low SP and resistivities for limestones and high values for shaly intervals. With the limited available information, it is not possible to determine good reservoir intervals. However, high spontaneous potential and lithology descriptions suggest that sandstones from Sub-unit N5 and O2 and carbonates from Units O2 (N1?) and O1 could be good candidates. Other wells in Hispaniola have demonstrated good reservoir properties for the same units, like Caño Azul #1, San Francisco Reef #1 or Maleno DT-1 (described along this section). A similar argu- ment could be applied for the seal capacities of Units N1 and N2 (see Section 4.2.2 for unit cor- relation). Conclusions:  The identification of oil and wet gas while drilling indicates the presence of a mature source rock in the basin.  Slight accumulations of methane could be associated with the beds of lignite and shales of Sub-unit N5 and O1. The origin of this methane would be biogenic.  There is no information about tests at this well. 332 Source rock  No rock-eval or vitrinite reflectance analyses are available, if they were carried out.  From lithology description and well logs, black shales from Units N1/O2 and O1 could have a source rock potential. This potential has been confirmed in other wells of Hispan- iola, like Caño Azul #1 (section 5.3.4), Maleno Dt-1 (section 5.3.7) or Cul du Sac #1 (in Haiti).  The calculated current geothermal gradient indicates that the bottom of the well is enter- ing the oil generation window. Therefore, potential source rock above this level remain immature and should be considered only for biogenic gas generation. Reservoir  From lithology description and well logs, clastics of Units N5 and O2 and carbonates of Units N1/O2 and O1 could have good reservoir properties. Seal  It is not possible to determine any regional seal with the available information. However, the composition of Units N2 and O2 and their seal capacities in other places of the island postulates these units as potential seals (see wells Caño Azul and Maleno Dt-1). Timing / Preservation  The presence of oil shows but the lack of oil accumulations could be related with a tim- ing/migration, trap integrity, lack of trap or preservation issue.  The oil expulsion and migration could be prior to the trap development or, the absence of an effective migration pathway to reservoirs at the well position.  On the other hand, the proximity to the first order SFZ could have generated a traps preservation issue. It should be considered that this strike-slip system has been active at least since Miocene times (De Zoeten and Mann, 1999), which could have affected the potential traps integrity. Trap  No seismic available to test the presence of traps. The slight amounts of hydrocarbons restrained to porous levels between shales could point out potential stratigraphic traps.  Geological cross sections (figure 5.3.4) suggest the presence of structural traps in the area. Nevertheless, as explained for the timing/preservation, the presence of an active fault system such as the SFZ points toward preservation as a key exploration risk. 333 5.3.2 Licey #1 (LIC-1): post-mortem analysis Licey #1 (LIC-1, figure 5.3.7) was drilled in 1958 by HS Cole & Son to a total depth of 3666 m. The information of this well is limited to well logs (resistivities, spontaneous potential, magnetic mark detector, calliper and mud logging report) and personal communications. The objective of the well was a structure interpreted from gravity data, called “Este de Santiago” structure. Nev- ertheless, this structure is not clearly identified on new cross sections (geological map 6074-II, Urien et al., 2010 a), neither on potential fields (figure 5.3.4). The target of the well is not indi- cated in the available information. However, since the well TD at top Oligocene, it is possible to asume that the well targeted Miocene reservoirs, following a Miocene play similar to those in the Azua Basin. Figure 5.3.7, A, Bouguer anomaly map over digital elevation model. B, Reduce-to-Pole anomaly map. C, Cross section modified from the Geology map of Santiago (6074-II, Urien et al., 2010 a). Location in A and B. Results: Oil and gas shows were recorded on well logs (figure 5.3.8), but all of them were classified as of non-commercial value (Licey #1 mud logging report, 1958).  From 1003 to 1006 m, there was an oil show classified as non-productive. Fluorescence was believed to be from residual oil in thin sand stringers interbedded in shale.  From 1818 to 1819 m a gas show was detected. It consisted of fair saturation of gases in drilling fluids but absence in the cuttings.  At the intervals 2835 – 2838 m ft (A) and 2841 – 2846 m (B) oil shows were detected. Fluorescence was observed in interval A and traces of paraffin were observed in both intervals. Interval B had “a little more gas” and a greater percentage of fluorescence.  A dry gas show was detected at 2918 – 2925 m. It was defined as an interval of good gas saturation.  A similar dry gas show occurred at 3004 – 3015 m with fair saturation of gases in drilling fluids. 334 Fig. 5.3.8 Summary of Licey #1 post-mortem analysis. 335 From the documentation available at the BNDH database, 7 DST were performed. DST #1 run in the interval 3210 – 3220 m (Unit N1/O2) producing water (figure 5.3.8). Cores from this interval determined porosities of 15% in sands. The rest of the DST were misrun. There is no rock-eval or vitrinite reflectance analyses available. Therefore, there is not any information about the pres- ence of source rock and its maturity along the sedimentary record. Stratigraphy summary: Based on sample descriptions and well logs interpretation, Licey #1 record has been divided in this work into the following lithological units (figure 5.3.8):  Unit N7: From 0 to 671 m, this interval is composed of grey well-consolidated sand- stones; grey, soft to firm and silty shales; and limestones. They are characterized by a high SP at top (> -10 mV) that changes into low values at base (from -30 to -15 mV), where it seems that sandstones and limestones dominate the section over shales. Resis- tivities remains generally low (< 5 Ω·m) for the entire unit.  Unit N6: From 671 to 1158 m, there is an interval of grey, silty to sandy, soft to firm shales; and minor sandstones. They are characterized by low and flat resistivities (< 5 Ω·m) and a high spontaneous potential (> -10 mV).  Sub-unit N5: From 1158 to 1737 m, this interval is composed of grey, very fine grain, well consolidated, hard sandstones with ash; and minor clear to milky, crystalline, chalky, hard limestones; and grey, hard siltstones. Spontaneous potential reached the lowest val- ues for the whole well record (from -30 to -20 mV) and resistivities increase the unit above up to medium values (30 Ω·m).  Unit N2: From 1737 to 2164 m, this unit consists of grey, sandy to silty shales; and minor grey, well consolidated to earthy and limy sandstones. Electro facies of Unit N2 consists of a high SP (> -10 mV) combined with flat and low resistivities (< 5 Ω·m).  Sub-unit N5: From 2164 to 2646 m, there is a second alternation of grey, poor to well consolidated, silty sandstones; and grey / grey to black, sandy to silty, hard shales; with a 140 ft thick limestone section at top. Similar than for the well VI-1 (Section 5.3.1), this second interval of Sub-unit N5 is characterized by a higher SP, which increases downhole leading to the shales of Unit N2 below.  Unit N2: From 2646 to 3090 m, this interval is composed of grey to dark grey and soft shales; and black and hard shales; with minor well consolidated sandstones. This unit slightly coarsens downhole as it is reflected in subtle decrease on the SP curve, although its electro facies correspond with those expected for this unit.  Unit N1.3 / O2: from 3090 to 3283 m, there is an interval of white, hard, sandy to chalky limestones; grey, hard, very calcareous shales; and minor grey, consolidated, limy sand- stones. This interval is interpreted as belonged to the Oligocene (see section 4.2.1 and 4.2.2), although the presence of lower Miocene sediments at top is not totally discarded.  Unit O2: From 3283 to 3667 m, this unit is composed of dark grey, hard to soft and earthy, calcareous shales; together with grey, consolidated to poorly consolidated, silty sand- stones (from the top of the unit to 3459 m) and white, earthy, sandy limestones and grey, grey, fine grain, poor consolidated sands to TD (3666 m). The presence of shales together with earthy limestones and poor consolidated sands makes this section a good candidate for belonging to Oligocene, as well as the resistivity logs, similar to San Francisco Reef #1 and Villa Isabel #1 (see Sections 4.2.1 and 4.2.2). Outcrops at the borders of Cibao Basin show similar earthy facies and black shales with lignite beds for the late Oligocene. 336 Conclusions:  The available information is limited. Only well logs, mud logging reports and internal project communication have been preserved in the BNDH database.  There are gas shows at sections next to shales (Unit N2). These shows were described as dry gas. Although it is not mentioned for this well, the presence of lignite beds was re- ported in correlated units of Cibao. This could indicate a biogenic origin for most of the gas shows.  Oil shows and paraffins or bitumen are detected for the Units N6 and N2. The origin is unclear and further studies are essential. Source rock  No rock-eval or vitrinite reflectance analyses are available, if they were carried out.  Black shales from Units N1/O2 were not penetrated at this well. Only shales from Unit N2 could be considered as potential source rocks, although their quality must be ad- dressed in further works. Reservoir  Unit N1.3 andO2 were tested as potential reservoirs, although it only produced water. Seal  With the available data it is not possible to determine the presence of a regional seal. However, Unit N2 that consists of 427 and 444 m of shales could act as regional seals. Although its equivalent in San Juan – Azua has been tested, the seal capacity in the Cibao Basin must be addressed in future works. Timing / Preservation  No conclusion with the information available, although hydrocarbon shows suggest that migration could happen at some time. Trap  No seismic available to test potential traps. As a hypothesis, the slight amounts of hydro- carbons restrained to porous levels between shales are tentatively interpreted as potential stratigraphic traps.  Geological cross sections (figure 5.3.7) suggest the presence of structural traps in the area. Nevertheless, due to the presence of an active fault system such as the SFZ close to the drilled area, the preservation of traps is suggested as a key exploration risk. 337 5.3.3 San Francisco Reef #1 (SFR-1): post-mortem analysis San Francisco Reef #1 (SFR-1, figure 5.3.9) was drilled in 1995 by Petrolera ONCE ONCE to a total depth of 1844 m. It forms part of the first stage of exploration activities in the Cibao Basin by the company Petrolera ONCE ONCE. This activity comprises the re-interpretation of previous 2D seismic profiles and the acquisition of a new 2D seismic survey together with the drilling of three exploration wells (Pimentel Reef #1, Rio Güiza #1 and San Francisco Reef #1). San Fran- cisco Reef #1 was located 7 km southwards San Francisco de Macoris, next to the location of the Shot Point 132 of the seismic line ‘Once #5’ (figure 5.3.9). Target objective: Based on the interpretation of 2D seismic data, the primary objective of the well was established in the upper part of a prognosed platform, defined as the San Francisco Reef, from 1830 to 1981 m, where oil and gas were expected to be present. In addition, secondary objectives were selected from the interpretation of 2D seismic profiles (figure 5.3.8): 1. Sandstone interval prognosed to be at 550 m that was hoped to have gas accumulations. 2. Amplitude anomaly at 600 m interpreted as a gas accumulation. 3. Turbidite sequence, interpreted to appear at 1175 m, thought to be gas bearing. Detailed information about the prospect, such as the closure of the traps is not available, and according to available information, this well was drill only based on 2D dip seismic lines (San Francisco Reef #1 operations summary, 1995) with limited information on the strike direction. Other information, like lithologies or DSTs results, is limited to well logs and the mud logging report (figure 5.3.10). Figure 5.3.9, San Francisco Reef #1 and the seismic line Once 5. Gamma ray, in black, and spontaneous potential, in blue, are represented to the left of the well track and resistivity to the right. 338 Fig. 5.3.10 Summary of San Francisco Reef #1 post-mortem analysis. 339 Results: The information available regarding to DSTs carried out at this well is only limited to annotations on well logs. From there, seven tests were carried out:  DST #1, from 1770 to 1847 m, was emplaced at the basement (ophiolite section from Unit A1) and produced slight amounts of gas (non-productive). There was an initial very strong blow and a final very strong blow with gas to surface in 30 minutes that burned a 2-3 ft flare.  DST #2, from 1540 to 1622 m, only recovered drilling mud.  DST #3, from 1495 to 1510 m, after an initial and final fair blow, it produced water with gas shows.  DST #4, from 1185 to 1273 m, after an initial very strong blow and a final strong blow, it recovered water with gas shows.  DST #5, from 782 to 850 m, there was an initial strong blow and a final strong blow that decreased and died in 10 minutes. It produced water with gas shows.  DST #7, from 698 to 709 m, there was an initial strong blow and a final strong blow that decreased. The pipe recovered a total of 27.96 barrels, consisted of 1.42 bbls of gas cut mud and 26.54 bbls of gas cut formation water.  DST #6, from 686 to 698 m, here was an initial strong blow and a final strong initial blow that steadily decreased recovering water and gas shows. In addition to the gas shows, as- phalt in fractures was also reported at the interval 1631 to 1634 m (cor- responding to the lithostratigraphic Unit O2). However, this infor- mation comes only from notes on the mud logging report. There is no analysis or well completion report available that complete the infor- mation. No rock-eval or vitrinite reflec- tance analyses are available. Only one BHT appears on the documen- tation. This temperature fits with the Hispaniola geothermal gradi- ent (figure 5.3.11). If we assume that San Francisco Reef #1 follows this gradient, the entire section should be immature. The presence of asphalt in frac- tures could imply a timing. It is possible that oil was generated in a deeper part of the basin in an early stage previous to the trap generation. On the other hand, this presence might imply a preservation issue. Figure 5.3.11, Geothermal gradients calculated from corrected BHT for San Francisco Reef #1 and Hispaniola. 340 Stratigraphy summary: The lithological information is limited to the mud logging report (San Francisco Reef #1 mud logging report, 1995). According to cutting descriptions and the study of well logs, the San Fran- cisco Reef #1 record has been divided in this work into the following units (figure 5.3.10):  Unit N6: From 0 to 540 m, this interval is composed of Miocene mudstones, siltstones and minor sandstones. Mudstones were described as greenish to dark grey to yel- low/brown, soft to massy with micro carbonaceous flecks and foraminiferous and shell fragments. Siltstones samples are dark grey, firm to hard with an argillaceous matrix. Sandstones are represented by brown, cemented and hard samples. This unit is character- ized by high GR and SP curves (> 50 API and > -25 mV, respectively), only deviated to medium values for sandstone intervals. The electric logs reveal low values for the whole unit (< 3 Ω·m). The reservoir value is low. No information relative to pressure differen- tials nor variations on fluid composition is available, therefore the seal capacity of this unit is unknown.  Sub-unit N5: From 540 to 975 m, this interval consists of Miocene sandstones (with lay- ers of coal), siltstones and occasionally limestones. The sandstones are grey, fine grain, well cemented, hard and with crystalline veins of quartz. DST #6 was carried out in these sandstones. From 792 to 853 m sandstones are described as grey, microconglomeratic, with silt, lithic clasts and coal, firm to unconsolidated. DST #5 correspond to this interval. Siltstones samples are described as dark green to grey, with an argillaceous matrix and firm to hard. Limestones consist of grey to orange/pink, microcrystalline, fossiliferous and hard. DST #7 was emplaced at these limestones. Finally, coal consisted of bed of black, subbituminous, hard with brittle fractures. The variability of lithologies of this unit is expressed in low to medium values on the GR curve, although generally lower than 50 API. SP remains in low (< -25 mV), although for more shaly intervals this log increases up to values higher than -10 mV. Low SP values combined with a medium GR could be correlated with the presence of coal in the record. Good reservoir properties could be expected for zones with a lower SP, as the DSTs seem that point out. Resistivities are low to relatively low, with values between 2 and 9 Ω·m.  Unit N1 (Sub-unit 1.2): From 975 to 1189 m, this interval is composed of grey, micro- crystalline and hard limestones with coral and shell fragments; grey to hard siltstones in argillaceous matrix with foraminiferous and traces of coral fragment; brown to grey mud- stones; and minor grey, microconglomeratic, well sorted and firm to unconsolidated sand- stones. Electro facies of this interval consists of a high SP (> -10 mV), almost flat, ac- companied by low resistivities (~2 Ω·m), also flat. This behaviour coincides with those defined for Unit N2 at the wells LIC-1 and VI-1. Sub-unit N1.1 has been differentiated from Unit N2 due to a higher proportion of materials from the platform, being consider as ramp deposits in front of the basinal deposits of Unit N2. DST #4 was located at the base this unit and the top of unit N5. Good flow is interpreted here as coming from the Sub-unit N5 below, acting sub-unit N1.1, tentatively, as a potential seal.  Sub-unit N5: From 1189 to 1341 m this interval is defined by the presence of grey, fine to medium grain, with trace of calcite cement sandstones; and grey to yellow/brown, soft to firm siltstones in an argillaceous matrix. At top, resistivities increase slightly although remains relatively low (up to 8 Ω·m) and come to low values to the lower half of the section (~ 2 Ω·m). This tendency is followed by the SP (with values < -50 mV), although with higher values than the upper member of Sub-unit N5. This behaviour is also ob- served for both intervals of Sub-unit N5 at the well Licey #1.  Unit N1 (Sub-unit 1.2): From 1341 to 1494 m, this lower interval of sub-unit N1.1 is composed of orange/yellow to grey, crypto to micro-crystalline, slight silty, massy and hard limestones; and grey to black, slight sandy, firm to soft siltstones with traces of coral fragments. Electro facies correspond with those defined for this sub-unit.  Unit N1.3/O2: From 1494 to 1576 m, this interval consists of Oligocene yellow to grey, cryptocrystalline, soft to hard limestones; and green to black, slight sandy, hard siltstones 341 in an argillaceous matrix with pyrite and calcite cement. GR and SP remain low (< 50 API and < -90 mV, respectively) which could indicate good permeabilities, postulating this unit as a potential reservoir. Resistivities increase for this interval, variating from 2 to 30 Ω·m. DST #2 and #3 were emplaced at this unit. DST #3 could point out a strati- graphic trap. Distal facies could be represented by tight carbonates that cover potential reservoirs which could have led to the formation of a stratigraphic trap, where a slight amount of gas was detected. This interval is separated here from Unit O2 (below), as the presence of lower Miocene sediments is not totally discarded  Unit O2: From 1576 to 1844. As it can be shown on well logs, this unit is separated into two intervals in terms of their well logs. - From 1576 to 1676 m, this interval consisted of yellow to grey, micro/crypto- crystalline, silty, bulky, micritic and hard limestones; grey to black, firm to hard siltstones in argillaceous matrix with carbonaceous materials; and grey, clean, microconglomeratic, well cemented sandstones. They are represented by a high SP (> -10 mV) and flat resistivities between 3 and 4 Ω·m. - From 1676 to 1731 m, the lower interval consisted of grey, fine to medium grains, unconsolidated sandstones; grey to orange, micro/crypto-crystalline, laminal, hard limestones with traces of corals; and grey to black, soft to firm, siltstones with pyrite, glauconite and carbonaceous materials. They are represented by a low spontaneous (< -50 mV) potential and high resistivities (between 50 and 80 Ω·m). As explained in Sections 4.2.1 and 4.2.2, Unit O2 is dated as Oligocene due to the litho- logical and electro facies correlation with the Oligocene section at the well Caño Azul #1 (Section 5.3.4) and similarities with outcrops.  Unit A1: From 1731 to 1844 m, this unit would correspond with the Basement of the basin at this area. Descriptions on the mud logging report correspond to quartzites re- crystalized with, glauconite, pyrite and biotite with minor layers of mudstones with kao- linite. As it was presented in Section 4.2, this unit has been interpreted as an ophiolite complex. Low SP intervals wouls indicate the presence of permeable rocks with some degree of reservoir properties, as the production of water with slight amounts of gas dur- ing DST-1 would prove. The presence of unconsolidated sands above the basement (belonged to Unit O2) could imply that these sands belong to a fossilized regolith, caused by the action of weathering on the quartzites of Unit A1. Conclusions:  The information concerning to this well is limited. Only well logs and mud logging are available.  This well reached the basement of the basin, consisting of metamorphic materials.  Oil was detected in fractures of sandstones belonged to Unit O2 and must have been produced in the Basin.  Slight amounts of gas were detected during DST #1 and from DST #3 to DST #7. All of them are of non-commercial value. At least part of this gas could be related with the presence of beds of coal with a biogenic origin.  The origin of the gas found at the ophiolite unit (DST #1) is unknown. There is no infor- mation about its composition (dry or wet gas). 342 Source rock  No rock-eval or vitrinite reflectance analyses are available. However, from sample de- scriptions, two potential source rocks could be present. The beds of coal of Sub-unit N5 could act as potential source rock for biogenic gas and the black siltstones with carbona- ceous materials of Unit O2 for oil and gas. Further analysis must determine the source rock potential of Miocene and Oligocene intervals at the Cibao Basin. Reservoir  From annotations on well logs, up to 7 DSTs were carried out in this well. It seems that Units A1, N1.3/O2 and N5 could be considered as potential reservoirs. Seal  With the information available it is not possible to determine the presence of regional seals.  In the case of SFR-1, instead of the deep-basin shales of Unit N2 (reached at the wells VI-1 and LIC-1), shallower deposits were penetrated with a greater proportion of plat- form-derived materials (sub-unit N1.2). The seal capacity of this interval is not known, and further works must address this subject. Timing / Preservation  The presence of oil in fractures only for the Oligocene section could reveal a timing or preservation issue. It is possible that oil was generated in a deeper part of the basin and migrated before the traps creation, or the system was not preserved due to the high grade of tectonism that affected the basin. It is important to remind that oil shows were detected also for the Oligocene section of Caño Azul #1. Trap  According to the reprocessed seismic data (figure 5.3.9), structural traps are not expected at the position of the well.  The primary objective of the well does not work as an effective trap.  Nevertheless, the identification of limited gas accumulations at Units N5 and N1/O2 could point out the presence of stratigraphic traps working in the basin (secondary objec- tives of the well), where shaly formations cover reservoir intervals. However, this is only a hypothesis, impossible to test with the available information. 343 5.3.4 Caño Azul #1 (CA-1): post-mortem analysis Caño Azul #1 (CA-1, figures 5.3.12 and 5.3.13) was drilled in 2000 by Petrolera ONCE ONCE to a total depth of 1060 m. This well belongs to the second exploration phase of Petrolera ONCE ONCE in the Cibao Basin (figure 5.1.4). Previous wells had demonstrated the presence of non- commercial gas accumulations in Miocene carbonates and Sandstones and registered slight oil shows (Rio Güiza #1, Pimentel Reef #1 and San Francisco Reef #1). Preliminary efforts of Pe- trolera ONCE ONCE in the Cibao Basin included the acquisition of 2D seismic profiles and the interpretation of previous seismic and gravity surveys. Target objective: The principal target of this well was a flat spot identified on an irregular 2D seismic grid of 1 x 1 km in what was thought to be Oligocene limestones (figure 5.3.12). At the same time, secondary targets consisted on the testing of massive Miocene reefs interpreted on the seismic and the nature of the basement. The play was Oligocene – Miocene. Source rocks were hypothetical Oligocene – Miocene shales and lignite beds for gas. Reservoir was represented by the Oligocene and Miocene carbonates with Oligocene and Miocene shales acting as regionals seals. The trap that completed the prospect was stratigraphic, Oligocene and Miocene shales layers that onlap landwards and cover potential reservoirs. There is no information available about the closure or volumetric potential of the main targets. Figure 5.3.12, Caño Azul #1 and the seismic line Pet Once 7 (TWT). 344 Fig. 5.3.13 Summary of Caño Azul #1 post-mortem analysis. 345 Results: The primary target was reached at 823 m. It resulted to be a gas-liquid contact, proved to be a relatively small gas cap overlying a zone of sulphur water, in an interval of Oligocene earthy and highly fossiliferous limestones. The sulphur water contained minor liquid hydrocarbons in the C30 to C42 range (Caño Azul #1 well summary, 2000). Formation pressure push the mud out of the well and started the blowout preventers. According to the well summary, this blow out caused damages in the borehole and in uphole sections, altering porous formations for their evaluation. Gas shows were reported along the Miocene limestones in the range of 100-300 units. Downhole, at 700 m, readings of 1,800 units were detected in the limestones corresponding to the Unit N 1.3. There was a heavy oil show in the Unit O1. Although in organic-rich shales, it is interpreted to have migrated from a deeper part of the basin, as according to the well executive summary, the whole interval is immature (Caño Azul #1 well summary, 2000), although this information is not confirmed by any vitrinite reflectance analyses included in the report. This show could represent a failure in timing/preservation. Rock-eval analysis determined that beds of organic-rich Oligo- cene shales from the Unit O1 had a TOC content as high as 1.05 (Caño Azul #1 well summary, 2000; no rock-eval analyses available). It is also referred on this summary the presence of lignite layers with a TOC of 14 Wt %. This information is only referred in the well summary, and rock- eval results are not included. The well CA-1 produced a number of significant gas shows but failed to bring in commercial quantities of hydrocarbons despite attempts to complete several zones for production. A total of 9 tests were carried out.  The first DST was emplaced in the basement, at 861 m, comprising up to 97 m of base- ment rocks. Only 2 barrels of drilling mud were recovered, without any hydrocarbon con- tent.  At the primary objective (823 m), no test was made because the formation fluids were ejected together with the drilling mud and flowed to the surface, being identified as a gas- liquid contact, consisting of liquid sulphur water that contains minor liquid hydrocarbons.  DST #2 was located at the interval 700 – 711 m in the Unit N 1.3. This test produced a small flare for a minute as fluid rose to 340 m below the surface when movement stopped and the well became static. 25 barrels of water were pumped into the formation, which broke down at 1,700 pounds of surface pump pressure and thereafter taking water at 1,100 pounds pressure. After recovering the same barrelage that injected the well was again static, indicating an open formation pressure of 1,142 pounds. This zone was then swabbed for 3 ½ days, 77 swab runs, giving up 500 barrels of sulphur water. It was con- cluded that this zone was damaged due to sulphur water invasion that came from 823 m.  DST #3 to DST #8 were performed in the massive Miocene reef of the Unit N 1.1. After the testing zones were swabbed, DST #3 (from 488 to 491 m), #4 (from 465 to 469 m) and #5 (from 456 to 458 m) produced fresh sulphur water which changed to saltwater with gas in solution. Gas released from fluid flared while being ejected. DST #6 (from 446 to 447 m) was inconclusive because there was little or no cement behind the casing, even though some gas flared. DST #7 (from 446 to 447 m) only produced sulphur water. It was concluded that this section was damaged by sulphur water invasion and was aban- doned. DST #8 (from 353 to 355 m) in a chalk section concluded that the chalk was tight, and no oil or gas was in place.  DST #9 was located at 214 m in limestones of the Unit N 1.2. Due to cementing problems the entire section from 200 to 274 m had to be tested. After 15 swab runs producing sulphur water the wellbore was emptied of fluid. From well summary: Test results demonstrate gas shows throughout the well mostly in the form of gas in solution. All test zones above basement, except the chalk zone, carried gas including the sulphur water zone (Caño Azul #1 well summary, 2000). 346 Stratigraphy summary: The lithological information is limited to the mud logging report. According to biostratigraphy report, well log analysis and cutting descriptions, Caño Azul #1 record has been divided in this work into the next units (figure 5.3.13):  Unit N6: middle Miocene sands and silts from 0 to 154 m where the top of an unconform- ity was encountered. Below the unconformity, there is an alternation of lower to middle Miocene limestones, reefs and chalks from 154 to 732 m that configure the Unit N1. This Unit is subdivided into the sub-Units 1.1, 1.2 and 1.3 in terms of their electro-facies and lithological features:  Sub-Unit N1.2: From 154 to 335 m, this interval is composed of chalky limestones and minor reef facies. The chalky limestones are white to cream, bulky, with traces of calcite. At 224 m, an 18 m Miocene reef exhibited vuggy porosity and took over 1,000 barrels of drilling fluid during a loss of circulation. This section is characterized by medium to high resistivities (between 50 and 70 Ω·m in average, although they can reach values up to 120 Ω·m locally), while the SP remains high (> -10 mV) and the GR exhibits low values in general (< 40 API).  Sub-Unit N1.1: From 335 to 616 m this sub-unit comprises a massive lower Miocene reef. This interval consists of white/tan/pink, hard, bulky and firm limestones with inter- vals of vuggy porosity. The electro facies of this section revealed a low SP (< -20 mV) and GR (< 40 API), combined with a reduction of resistivities (RILM between 8 and 10 Ω·m and RILD between 3 and 6 Ω·m), including the separation of the deep and shallow curves. This could lead to the presence of good reservoir intervals, with a developed po- rosity filled with low resistivity fluids.  Sub-Unit N1.2: From 616 to 671 m there is an interval of white/cream, bulky and chalky limestones. Resistivity increased to medium values (10 – 30 Ω·m) with both curves joined together. This tendency was register also on SP going from high to low values (from -40 to -1 mV) while gamma ray remains low (< 40 API).  Sub-Unit N1.3: From 671 to 732 m, this interval consists of lower Miocene limestones and shales. While GR alternates from high to medium values (from 20 to 50 API) indi- cating the alternation of limestones and shales, SP remains high (> -10 mV). Resistivities alternates also from low (4 Ω·m) to medium (30 Ω·m) values. At the top of this sub-unit the calliper curve becomes chaotic (from 8 to 17 in, behaviour that continues to the base of the Unit O2 below), which is correlated with the abruptly changes in Neutron logs and may represent the alternation of consolidated and unconsolidated layers in the borehole.  Unit O1: At 732, this unit is separated to define a 16 m thick Oligocene layer of organic- rich shales.  Unit O2: From 748 to 853, this unit represents an Oligocene alternation of unconsolidated sands, earthy limestones, dolomites and shales with lignite beds. They are represented by a high SP (> -10 mV), a calliper that ranges between 8 and 17 in and low to medium resistivities (between 4 and 30 Ω·m).  Units A1 and A2: This units represent the basement, being reached at 853 m. They consist of a 6 m layer of quartzite and quartz diorite (Unit A1) followed by Granite to TD (Unit A2). This unit is characterized by a low SP (< 40 mV) and high resistivities (between 100 and 2000 Ω·m). As explained in Section 4.2.1, lower Miocene limestones (Unit N1) were divided into three sub- units which are interpreted in terms of their depositional environment. While sub-unit N1.1 rep- resents the platform of a carbonate system that has retrograded to the south (as interpreted on seismic profiles, figure 5.3.14), sub-units N1.2 and N1.3 represent ramp deposits, including distal deposits (sub-unit N1.2) that correlate with shales of Unit N2 and reworked materials (sub-unit N1.3) with rests of corals between others. 347 Conclusions:  Caño Azul #1 reached the primary objective at 823 m. It had been interpreted as a flat spot based on 2D seismic profiles. However, it resulted a gas-sulphur water contact.  This well reached the basement at 853 m, consisting of a quartzites itruded by a granite.  Gas shows were detected along Unit N1. The composition of this gas is not available. Nevertheless, the little amounts of gas, together with the presence of lignite beds, shales and the thin burial, lead to the tentative interpretation of a biogenic origin.  A heavy oil show was detected at unit O1. From well summary, this samples are assumed that has migrated from a deeper position in the basin, where the oil generation window has been reached. Source rock  According to the well summary report, an Oligocene potential source rock, with a TOC of 1.05%, was reached at 732 m. However, rock-eval analyses and vitrinite reflectances are not included and further analysis are necessary to establish the source rock potential of Oligocene levels in the Cibao Basin.  The presence of lignite beds and carbonaceous rests in other interpreted Oligocene inter- vals could indicate gas prone source rock intervals for these levels. Reservoir  Despite the limited information, Units O2 and N1 were proved as reservoirs, since they were able to produce formation water and very minor gas.  The primary objective at Unit O2 was not tested. However, the blow-out preventers had to be used when drilling this unit at 822 m. The presence of high-pressure formation fluids that caused damages in up-hole sections indicates its good reservoir properties. Formation fluids consisted of mainly sulphurous water with slight amounts of gas that invaded the upper sections.  DST #2 tested Unit N1.3, resulting 500 barrels of sulphurous water, concluding that this unit was damaged during the blow-out.  DST #3 to DST #8 tested Unit N1.1. Although initially all of them produced sulphurous water, DST #3 (from 488 to 491 m), #4 (from 465 to 469 m) and #5 (from 456 to 458 m) turned into saltwater with gas in solution. Seal  Overpressures of Unit O2 at the primary objective tested the seal capacity of Oligocene shales (Units O1/O2).  At Caño Azul #1, Miocene shales corresponding to Unit N2 are absented. Nevertheless, tight carbonates, such as those belonged to sub-unit N1.2, could act as internal seals of the carbonate system. The presence of slight gas accumulations in the system is inter- preted as an indicative of their seal capacity. Trap  The presence of a stratigraphic trap was tested for the primary objective. Unfortunately, only little accumulations of gas and sulphurous water were trapped. This trap consists of Oligocene unconsolidated sands and earthy limestones that acted as reservoirs with Oli- gocene shales sealing the system.  The evolution of a complex carbonate system could have favoured the creation of strati- graphic traps, where porous limestones are covered by tight/distal carbonates. Gas shows identified along the well are located at zones where GR, SP, resistivities and density logs suggest good reservoir intervals, being covered by layers with a high GR, indicating their shaly composition. This is reinforced by the disposition of the platforms interpreted on seismic profiles (figure 5.3.14). 348 Timing / Migration / Preservation  There was a heavy oil show at the Unit O1 (figure 4.3.13). It is interpreted to have mi- grated from a deeper part of the basin (Caño Azul #1 well summary, 2000). This could represent a migration issue from deeper to shallower sections. However, as it happens in other parts of the Cibao Basin, this show could also represent a timing issue. It is possible that oil was generated at a moment when the main traps did not exist yet. At the same time, a preservation issue could also explain the absence of hydrocarbon accumulations. Nevertheless, in this case, the presence of high-pressure fluids at the Oligocene interval points out the preservation of traps, being a preservation issue less likely. Fig. 5.3.14 Seismic interpretation given for the seismic line PET-7 with the well Caño Azul #1 tied. The evolution of the carbonate system could have generated stratigraphic traps as the slight accumulations of gas might indicate. 349 5.3.5 San Pedro #1 (SP-1): post-mortem analysis San Pedro #1 (SP-1, figure 5.3.15) was drilled in 1979 by the company “Petrolera Las Mercedes” to a total depth of 2040 m. This well was a wildcat drilled to determine the geology and potential of the region known as Llanura Oriental, northwards extension of the SPB, after a poor quality 2D seismic reflection survey and gravity data. Target objective: The target objective of San Pedro #1 was an interpreted horst structure based on seismic interpre- tation and on a maximum of gravity anomalies (San Pedro #1 well summary, 1979). This structure was thought to act as a potential trap. Nevertheless, due to the limited information the hypothetical closure was not determined. The prognosed geology of the well is also unknown. In addition, after the reprocessing of 2D seismic lines during the current work, it was concluded that the expected horst was not present. Figure 5.3.15, San Pedro #1 and the seismic lines SP4 and 91MDRH-55A. The step registered on resistivity and density logs coincides with the top of the Cretaceous sequence (Unit K2). Results: According to well reports, up to 7 oil shows were reported during the drilling of the Cretaceous sequence, at depths corresponding to black shales intervals (figure 5.3.16). These shows consisted of paraffin residues in the shaker and hydrocarbon material expulsed from shale fragments when heating them. Shows were re-evaluated by Mobil in the 90s, and the results identified a high- molecular weight wax, which was considered a refined product. However, other samples contain hydrocarbon suites, petroliferous in origin, characteristic of oils derived from carbonates or marly source rocks (Munthe, 1996). As these hydrocarbons appeared between Upper Cretaceous black shales and marls, being considered as indigenous bitumen. Upper Cretaceous shales that crop out at Cordillera Oriental could fit with this interval. Under the interpretation given for this work, Units K1 and K2 (figure 5.3.16) are correlated with the Río Chavón Formation. See Chapter 4.2.1 for the complete interpretation. 350 Fig. 5.3.16 Summary of San Pedro #1 post-mortem analysis. 351 Rock-eval analysis were carried out by Mobil for the interval 1119 - 1525 m that corresponded to black shales where oil shows were reported. TOC are low in general, although for the interval from 1518 to 1519 m, the TOC content resulted 0.52 Wt %, classifying this as marginal Type III source rock. Tmax from rock-eval is low, with values from 380 ºC to 421 ºC (Munthe, 1996). Complete results are included in Section 5.4 dedicated to source rocks. Vitrinite reflectance anal- yses were not carried out or are not available. Core analyses at the Cretaceous section determines that three samples had porosities higher than 10% (22.3 at 1123 m, 15.6 at 1419 m, 10.2 at 1562 m). Nevertheless, the permeability is low (0.1 – 4.8). Two tests were emplaced next to oil and paraffin shows in the Cretaceous section without recovering any fluid due to no apparent porosity. Stratigraphy summary: The information about this well is, in part, not reliable. From the well summary, San Pedro #1 penetrated:  From 0 to 674 m Plio-Pleistocene unconsolidated sands, shales and sandstones.  From 674 to 1094 m Miocene sandstones, shales and limestones  From 1094 to 2040 m (TD) Oligocene siltstones and shales with thin beds of limestones and lignite. However, this information does not fit with cuttings descriptions on the mud logging report (San Pedro #1 mud logging report, 1979). In 1990 Mobil acquired the Azua Block which included the San Pedro Basin and the Llanura Oriental. They re-evaluated the well by studying the cuttings and cores. Their results agreed with the mud logging report, being considered as valid for this work. The record has been divided into the following lithostratigraphic units (figure 5.3.16):  Unit P3: From 0 to 518 m, this unit consisted of Pliocene – Pleistocene carbonates with low resistivities (up to 6 Ω·m). Sonic log alternates from low to medium velocities (be- tween 90 and 140 µ/ft), increasing slightly towards the base.  Unit P2: This unit is defined from 518 to 674 m. There was a samples gap, but they are supposed to be Pliocene limestones. The presence of bad hole conditions, supposed to be caused by caverns, could relate to the intense karstification that has been reported in Pli- ocene – Pleistocene limestones. Sonic log seems to follow the same tendency than for Unit P3 and the division between both is based on the increase in resistivity logs, from a flat resistivity for Unit P3 to a sharp curve for Unit P2 with values between 2 and 46 Ω·m.  Unit N4: From 674 to 908 m this interval is composed of middle – upper Miocene lime- stones at top that alternate with sandstones and shales at base. This change is noted on well logs with a decrease on sonic velocities (from 90 µ/ft for the upper interval to an alternation between 90 and 120 µ/ft for the lower one) and a subtle increase on the GR.  Unit N2: From 908 to 1094 m the succession turned completely into an alternation of middle Miocene sandstones and shales.  Unit K2: This Unit has been defined in this work from 1094 to 1798 m and separated from the underlying Unit K1 in based on lithological and electrical changes. According to Mobil reports, from 1094 to TD the sediments have suffered a low grade of metamor- phism. During our field work, only a regional and well-developed process of silicification was found in Upper Cretaceous sediments, which has provided samples a great hardness. Nevertheless, due to the proximity to the Hispaniola Fault Zone, the development of a low-grade of metamorphism is not totally discarded. Considering metamorphism or not, hardening of this level has been recorded on well logs. While GR and SP are not affected, there is a step of sonic, resistivity and density logs at top of this unit. This interval has been considered as an undifferentiated Cretaceous sequence that consisted of dark and black shales and sandstones with minor limestones, marls and beds of lignite. (see Section 4.2.1 for a complete description and correlation of Unit K1 and K2) 352  Unit K1: from 1798 to 2040 m (TD) Unit K2 turned into Cretaceous sandstones and shales with a decrease in GR and resistivities, with a separation between deep and shallow curves. Despite of a greater proportion of sandstones together with a reduction in density logs and the increase of permeability inferred from resistivities, this section was not tested. Conclusions:  San Pedro #1 reached undifferentiated Cretaceous sediments which have been correlated in this work with the Upper Cretaceous sequences that crop out at Cordillera Oriental (Section 4.2.1).  There is a hiatus from the Late Cretaceous to the middle Miocene interval.  Several oil shows were reported along the Upper Cretaceous section. analysis performed by Mobil in the 90s revealed that some of these materials consisted of waxes and were catalogued as contaminated samples. However, other samples contained hydrocarbon suites, petroliferous in origin, and could be indigenous. Extra analysis must be carried out to determine their origin.  Two tests were located along the interval where the oil shows were detected (Unit K2). Both did not recover any fluid. Source rock  Unit K2 consisted of a succession of black shales, shales and sandstones. Rock-eval anal- ysis determined a type III kerogen with a TOC up to 0.52 Wt % for the interval where the shows were detected.  No vitrinite reflectances are available. Tmax from pyrolysis are low, with values from 380 ºC to 421 ºC. Reservoir  The Neogene interval was not tested as potential reservoir.  Core analysis revealed porosities higher than 10 % for samples belonged to Unit K2 yet with low permeabilities.  Gamma ray indicates that the proportion of sandstones for Unit K1 is greater and resis- tivity logs points to an increase of permeability. Nevertheless, this unit was not tested. Seal  No regional seal is inferred from the available information.  Further analysis must address the seal capacity of the Cretaceous shales. Timing / Migration / Preservation  Considering the oil shows as reliable, only local migration due to an incipient generation has took place, because they are located at the source rock intervals. Trap  The review of the reprocessed seismic data and the limited information available at public databases concludes the trap was absent. 353 5.3.6 Punta Salinas #1 (PS-1): post-mortem analysis The well Punta Salinas #1 (PS-1, figure 5.3.18) was drilled in 1995 by MOBIL to a total depth of 1575 m and was plugged and abandoned in January 1996, after finding only little amounts of combustible gas. The well was located at the south-western flank of the foothills of the Cordillera Central. This well represent the final stage of an exploration program carried out in the area that consisted of the re-processing of previous offshore 2D seismic profiles, the acquisition of new on-shore 2D seismic data, a new gravity survey, the geology mapping of the area and the re- evaluation of the Azua Basin petroleum geology. Interpreters expected to find Miocene series like those reached at the abandoned Maleno oil field. Target objective: The objective of the well was an anticlinal structure with an area closure of 27 km2. This prognosis was based upon a Mobil gravity survey that reveals a large gravity anomaly, the reprocessing of a 2D offshore seismic grid of 2 x 2km and new onshore seismic sections acquired to correlate with the onshore geology. They expected to drill 914 m of Eocene sandstones and shales and, directly below, a Miocene sequence in a sub-thrust contact. Miocene limestones were hoped as potential reservoirs (Punta Salinas #1 well report, 1996). The play was a Maleno like one and the prospect would comprise deep-water Miocene shales acting as source rocks, Miocene reservoirs in sandstones and carbonates, Miocene shales as seals and structural compressive anticlines as traps. Results: Small amounts of combustible gas were de- tected along the well with a pick of 100 units at the top of the Eocene limestones. Trace amounts of black material (bitumen?) were observed in sample cuttings from 405 m to TD. This material did not fluorescence or give a cut fluorescence. Intermittent traces of a black material (bitumen?) were found as coatings in apparent fractures of middle Eocene limestones, providing a milky white cut fluorescence and left a brown stain residual cut from 1454 to 1521 m. According to lithological analysis, no po- tential source rock was recognised from cuttings. No vitrinite reflectance or rock- eval analyses were performed. The corrected BHT at TD was 125 ºF (51.6 ºC). Although this temperature implies a lower geothermal gradient in the area than expected (Punta Salinas #1 well report, 1996), this temperature fits with the His- paniola tendency (figure 5.3.17). Figure 5.3.17, Geothermal gradients calculated from corrected BHT for Punta Salinas #1 and the rest of Hispaniola exploration wells. 354 Fig. 5.3.18 Summary of Punta Salinas #1 post-mortem analysis. 355 No DST was carried out for this well due to the lack of any indicator of potential reservoir or hydrocarbon accumulations. Stratigraphy summary: According to stratigraphy and palaeontology analysis (Punta Salinas #1 well report, 1996), the Punta Salinas #1 record has been subdivided in this work in the following units (figure 5.3.18):  Unit Q1: Quaternary dunes and beach sands up to 87 m.  Unit E4: From 87 to 305 m this unit is composed of upper Eocene sandstones and silt- stones. From GR log, this unit shows an uphole coarsening (from 26 API at bottom to 13 API at top of the unit).  Unit E3: from 305 to 745 m, this interval is defined by the presence of upper Eocene siltstones and siliceous mudstones. Well logs are characterized by a high SP (> -8 mV), combined with almost flat resistivity curves, empathises the shaly character of the unit, which is interpreted that interferes in the sonic porosity curve. Only a limited interval (from 500 to 540 m) reveals fair porosities keeping a low GR, possibly due to the presence of sandstone levels. This unit is correlated in this work with the El Número Formation (see Section 4.4.1).  Unit E1: from 745 to 1575 m the well reached middle Eocene limestones, occasionally siliceous mudstones and silty siliceous mudstones. They are represented by a low non- corrected GR (~10-20 API) that only increases for the shaly intervals (~30-40 API). This behaviour is followed by the sonic log, that reveals high velocities for limestones (< 70 µs/ft), decreasing for the shaly intervals (> 70 µs/ft). Sonic porosity revealed intervals with a poor to fair porosity (3% to 7 %), while the higher values resulting from shale interference (figure 4.4.4). On the other hand, SP is relatively high (> -20 mV), and only decreases for some limestone intervals at bottom (< -20 mV), possibly indicating a lack of permeability for most of the unit. Resistivity curves have low – medium values (10 – 60 Ω·m) increasing to high (290 Ω·m) for the intervals with the lowest SP. In general terms, lithologies and wireline logs indicate that this unit is constitute by hemipelagic limestones. No hydrocarbon show was detected while drilling this unit. Nevertheless, the presence of black coats and bitumen (specially for the lower interval) and a small gas show (at top of the unit) were included in the mud logging report (Punta Salinas #1 mud logging report, 1995). This unit is correlated in this work with limestones of the Peralta Group that crop out in the southern flank of Cordillera Central (see Section 4.4.1). The well is interpreted to have penetrated thrust-faulted, easterly-dipping sediments. Although seismic line 70D-BE (not available) appearing to show some east-west rollover at the well posi- tion, field evidence strongly indicates the lack of a four-way closure (Punta Salinas #1 well report, 1996). The Eocene sediments are in an angular unconformable contact with the overlying Qua- ternary sands. Field work in the nearby El Numero mountains demonstrates that these sediments dip 70 degrees to the east (Punta Salinas #1 well report, 1996). The presence of shows is tentatively interpreted as an older hydrocarbon migration. The lack of a regional seal, good reservoirs and traps could have led to the absence of oil or gas accumulations. Therefore, timing/migration represents a key risk for exploration activities that included the mid- dle – upper Eocene sequence. Conclusions:  Punta Salinas #1 did not encounter the prognosed Miocene objective nor any sub-thrust structure.  From 87 m to TD this well penetrated Eocene sediments. 356  Little amounts of gas, with a peak at the top of the middle Eocene limestones, and black material (bitumen?) with milky white cut fluorescence in fractures were identified. Source rock  No potential source rock was identified. Reservoir  Reservoir potential of Eocene limestones is limited, only some intervals have poor to fair porosities. Seal  No regional seal could be inferred from well data. Trap  The trap was not tested. The sub-thrust objective was not penetrated. Timing / Migration / Preservation  The objective of the well was a Miocene play that was not encountered.  The presence of oil (bitumen) and gas shows could represent a former hydrocarbon mi- gration. This information should be considered at the time of proposing an Eocene Play. 357 5.3.7 Maleno DT-1 (MDT-1): post-mortem analysis Oil production in Azua: The Azua Basin is the only area in Hispaniola where oil have been produced, at the Maleno and Higuerito structures (figure 5.3.19). The main filed, Maleno, had a limited cumulated production of 25000 bbl (200 BOPD) at Maleno #1 and 4500 bbl at Maleno #1A, both operated by Seaboard (Mann et al., 2008). They produced a 20º API oil from upper Miocene - Pliocene sandstones (Units N2 - P1). Additionally, good oil and gas shows have been reported at deeper formations like at the lower – middle Miocene carbonates. Figure 5.3.19, Geology map of the Azua region with the main exploration features. A-A’ section indicates the location of figure 5.3.22. Oil origin is controversial. Some intervals of deep-water Miocene carbonates and shales show a good TOC content. However, oil to source correlations remain unknown. Available vitrinite anal- ysis (table 5.3.1 and figure 5.3.20) reveal that all Miocene samples are immature (below 0.60 %Ro). Other potential source rocks, like those from the Upper Cretaceous and Paleogene se- quences, have been proposed yet their presence deeper in the basin and their quality are only hypothetical. Table 5.3.1 summarise all the samples with the best genetic potential in terms of TOC (values higher than 0.45 %WT) and the deepest vitrinite reflectance value from wells in the Azua - San Juan basin and its continuation in Haiti (represented by the well Jurinet #1). Well or outcrop Depth (m) TOC (WT %) Vitrinite Reflectance (% Ro) Maleno #2 133 0.66 0.24 Maleno #2 202 - 0.31 Maleno #7 178 0.68 0.33 Maleno #7 556 - 0.41 Higuerito #1 625 0.76 0.24 Las Hormigas #1 1530 - 0.33 Candelon #1 2291 0.56 - Comendador #1 (Robertson 1984) 782 0.46 - Comendador #1 (Robertson 1984) 642 - 0.33 Jurinet #1 (Robertson 1984) 836 0.83 0.34 Jurinet #1 (Robertson 1984) 909 0.64 0.29 Jurinet #1 (Robertson 1984) 1138 0.49 - Jurinet #1 (Robertson 1984) 1551 - 0.44 Table 5.3.1 Most representative values of TOC and Vitrinite reflectance for Miocene samples in Hispaniola. 358 Oil production in Azua was limited to sandstones bodies enclosed into the Miocene – Pliocene Trinchera Formation. This level consists of soft to hard shales and two critical turbidite sandstone intervals, informally named the “A” and “B” sands (Mobil, 1996). In Azua, these intervals are in a shallow position, and exploration wells have reached them at depths lower than 300 m. This limited burial may have caused the biodegradation of accumulated oils, explaining their heavy character (18-20 ºAPI). In addition, biodegradation could also explain the difficulties on the oil to source correlation. However, not only not-enough burial could be an issue, but also their lateral continuation. Maleno East #1 was drilled in 2003 by Murfin Dominicana at the eastern flank of Maleno anticline to a total depth of 357 m. It found the A sand at 235 m with a thickness of 14 m and the B sand developed into two couplets, B1 from 287 to 311 m and B2 from 317 to 332. After plugged and abandoned, Maleno East #2 was drilled at the northern crestal position finding only the A sand at 275 m with a thickness of 5 m. On the other hand, deeper Miocene limestones with a good lateral extension and reservoir prop- erties (an estimated average porosity of 12% from wireline logs, Mobil, 1996) have been studied at Maleno #7 and Maleno DT-1 and might represent potential reservoirs. Figure 5.3.20, Geothermal gradients calculated from corrected BHT and Vitrinite Reflectances for the Azua – San Juan basin and Hispaniola. Vertical lines represent the oil generation, expul- sion and wet/dry gas limit calculated from the geothermal gradient. Maleno DT-1: Most of the information from the Azua exploration wells has not been preserved or is not availa- ble. Maleno DT-1 (figure 5.3.21) has been selected as a representative well of the Maleno struc- ture (figure 5.3.19) due to it is the deepest well of the basin, well logs are available, and reaches the same lithological units than Maleno #1 and #1A. Maleno DT-1 was drilled in 1960 by Pe- trolera Dominicana in the Azua Basin to a total depth of 3023 m. The objective of the well was a broad anticline (figure 5.3.22) usually known as Maleno structure or anticline. There, Miocene sands and carbonates were hoped to have good reservoir properties. 359 Fig. 5.3.21 Summary of Maleno DT1 post-mortem analysis. 360 Target objective: The objective of the well was the structure known as the Maleno anticline (figure 5.3.22), which has been interpreted as a thrust-related anticline (Mann et al., 2008). Nevertheless, the information about the prospect, closure and net thickness of the expected reservoirs is limited. Figure 5.3.22 shows a regional cross section for the Azua Basin with the most representative wells. Maleno DT- 1 is located at the southern flank of the Maleno anticline. Maleno DT-1 targeted the same play than other wells in Azua. As it was mention on the introduc- tion, an oil – source rock correlation is not stablished. Lower Miocene shales and marls were expected to have good source quality. Good reservoir intervals were prognosed for the upper Miocene – Pliocene turbidite sandstones and the lower - middle Miocene limestones. The seal was represented by middle Miocene to Pliocene shales and the lower - middle Miocene tight carbonates (Munthe, 1996). Figure 5.3.22, Regional cross section for the Azua Basin where the most representative wells are represented. Maleno DT-1 is highlighted in yellow. Modified from Murfin Dominicana, 2002. Location in figure 5.3.19. Results: Oils shows were identified during core operations along Unit N1. Cores from 1445 to 1460 m had good fluorescence, up to 20%. Slight to good gas odors and oil along fractures were reported on the core record from 1272 to 2911 m. Core analysis revealed the presence of good gas odors, stains on the samples and dead oil on fracture planes and pinpoint to vuggy porosity were noted but not quantified on the available reports. The presence of dead oil in fractures, as interpreted in this work for other wells in Hispaniola, could indicate a timing/migration or preservation issues, or the absence of an effective trap. Note that the limited seismic available at the Azua Basin does not allow to determine the closure of the Maleno anticline. The well logging determines intervals that could be oil and gas saturated. Logs of Unit N2, from 304 to 1225 m, are characteristic of shales and sandy shales with low resistivities and high spon- taneous potential (Maleno Dt-1 well logging report, 1960). Unit N1, from 1225 m to TD (3024 m), consisted of limestones interrupted by shale brakes. These limestones exhibit high resistivities and low spontaneous potential which should lead to good permeabilities, postulating them as po- tential reservoirs, this will be study in Chapter 5.3. Quantitative analysis was carried out by means of both Archie and Tixier methods (Maleno DT-1 Drilling Steam Test operations report, 1981). 361 A good example of the high resistivity limestones is the interval from 1252 to 1276 m. For this interval the results are summarized in Table 5.3.2: Table 5.3.2 Estimated porosities for the interval 1252 to 1276 m (Unit N 1.1) from well logging. Since the porosity is consistent throughout the section, 14 tests were performed in Maleno DT-1. All of them had a fair blow although producing only saltwater.  DST #1 from 1270 to 1283 m recovered 9 m of oil and gas cut mud.  DST #2 from 1445 and 1460 m had an immediate good blow and gas to surface in 30 minutes recovering saltwater with oil and gas cuts. This test was unsatisfactory, it was unable to close the tool due to a stuck pipe.  DST #6 from 2316 to 2362 m had immediate good flow that continued through test (no pressure gauge used).  DST #9 from 1618 to 1644 m had an immediate good blow that became weak to the end of the test recovering 1470 m of saltwater.  DST #11 from 1431 to 1445 m had an immediate slight blow that increased to fair blow with a recovery of 1221 m of saltwater.  DST #12 from 1362 to 1469 m had a fair blow through the test producing 1300 m of saltwater with slight gas cut.  DST #14 from 1247 to 1268 m had an immediate good blow and gas to surface in 15 minutes (no surface gauge used). 76 m of gas and saltwater cut mud was recovered. Packer failed for DST #3, #4 and #5 (from 2719 to 2748 m), DST #7 and #8 (from 2058 to 2109 m), DST #10 (from 1453 to 1473 m) and DST #13 (from 1242 to 1268 m). No potential source rock was identified. There are no rock-eval or vitrinite reflectance analyses. The geothermal gradient, calculated from empirical corrected BHT, and vitrinite reflectances (fig- ure 5.3.20), from wells with available data in the Azua - San Juan Basin, reveal that all the pene- trated sections are immature. At TD (3024 m), Unit N1 would be entering the oil generation win- dow (100 ºC). The lateral equivalent of Unit N2 (Miocene shales) has resulted immature at other wells of the San Juan – Azua Basin, with a maximum vitrinite reflectance of 0.33 %Ro at 1529 m in Las Hormigas #1 well, 0.41 % Ro at 556 m in Maleno #7 and 0.24 % Ro at 615 m in Higuerito #1 (location of wells in figure 4.319). Stratigraphy summary: According to stratigraphy and palaeontology analysis, Maleno DT-1 penetrated:  Unit P1: from surface to 304 m, Plio-Pleistocene sandstone and gravel with low to me- dium resistivity values. This sequence is cyclic clastic that coarsens uphole. From base to top, silty shales grades up into silts and silty sands. Sandstones pass up into claystones, sandy conglomerates and conglomerates.  Unit N2, from 304 to 1225 m is a succession of upper Miocene silty shales with thin silty sandstones layers. Its electro facies show a high SP and low resistivities (almost flat) which slightly increase from the middle of the section due to the increase of the sand proportion. Shales consisted of grey, fine, firm, silty shales and marls. At the base, cal- careous sandstones became relevant in detriment of shales, expressed in higher resistivi- ties and a slight separation of shallow and deep resistivity logs. However, they consisted Tixier Archie Neutron Water saturation 31% 18% Porosity 6.5% 6.5% Fm water resistivity: 0.13 ohm 362 of grey to white, fine and cemented calcareous sandstones, alternated with sandy shales with low reservoir potential. Finally, from 1225 to 3024 m middle Miocene carbonates (Unit N1) were identified. Well logs reveal intervals with low spontaneous potential and medium to high resistivities that alternates with intervals of high spontaneous potential and low resistivities. From cuttings and core record this unit has been divided into three sub-units (figure 5.3.21), following the same criteria than for the well Caño Azul #1, in Cibao (see Section 4.5.1).  Sub-unit N1.1: From 1400 to 1920 m, this interval is composed of a series of white chalky limestones and cream, sucrosic and very fossiliferous limestones that include calcarenites and algal limestones with minor cream, hard, crystalline limestones and marls and chalky limestones at top. This sub-unit is represented by low resistivities (up to 20 Ω·m), which increase slightly for the crystalline intervals (up to 30 Ω·m). SP remains generally high. These facies are interpreted as proximal, although unlike its equivalent at the Cibao Basin (drilled at the well Caño Azul #1), the well Maleno DT-1 did not reach platform deposits. Core descriptions reveal the presence of fractures and pinpoint to vuggy porosity.  Sub-unit N1.2 is interpreted into two intervals from 1950 to 2850 m and from 1200 to 1400 m. The first interval consists mainly of cream, dense, hard, crystalline limestones and white chalky limestones with minor cream fossiliferous limestones. The second in- terval, above sub-unit N1.1, is composed of dense limestones, silty shales and chalky limestones. The hardness of this sub-unit might relate to higher resistivities due to a lower presence of porous intervals filled of saltwater. SP ranges between -40 and -10 mV. Core analyses reveal the presence of pinpoint to small vuggy porosities at some intervals of fractured, dense, crystalline and fossiliferous limestone of the lower interval with dead oil present along fracture planes. The presence of chalky and massive dense limestone with a lower fossiliferous content is interpreted as a deeper depositional environment.  Sub-unit N1.3 is interpreted at limited intervals by a diminution of resistivities and the presence of highly fractured fossiliferous limestones and white chalky limestones, inter- preted as the potential arriving of reworked shallow fauna. Conclusions:  Maleno DT-1 did not encounter sediments older than early Miocene.  Hydrocarbon shows were detected at the limestone of Unit N1. At the same interval, DSTs recovered oil and gas cut mud. Core analysis revealed the presence of good gas odors, stains on samples and dead oil on fracture planes. Source Rock  According to well reports, no potential source rock was identified although there is no rock-eval analyses available.  Vitrinite reflectance analysis are also not available. Vitrinite reflectances from other Mi- ocene intervals in the San Juan – Azua Basin revealed an immature stage.  BHTs fit with the calculated geothermal gradient of Hispaniola. At TD (3023 m), Unit N1 would be entering the oil generation window (100 ºC). Reservoir  Although production in Maleno #1 and #2 was limited to Units P1 – N2, Maleno DT-1 did not reach any potential clastic reservoir for this interval.  Lower to middle Miocene carbonates were tested as reservoirs. 14 DST were carried out for these limestones. Half of them produced saltwater with a good blow while for the other half the packer failed. Core analysis revealed pinpoint and fair vuggy porosities. 363 Seal  Unit N2 seal capacity has been tested at Maleno #1 and Maleno #2 as well as in other wells in Hispaniola (see Charco Largo #1). Trap  Due to low seismic quality and resolution, it is not possible to conclude if the well targeted a valid trap for the carbonate section. Timing / Migration / Preservation  The presence of shows together with the absence of accumulations could point out to a timing issue. It is possible that oil, stains and dead oil on fractures, and gas shows repre- sent a former migration prior to traps generation or the absence of an effective trap that comprises the Miocene limestones.  On the other hand, due to the high tectonic deformation occurred in the region since the late Eocene to present (Hernaiz-Huerta, 2006), it is possible that the petroleum system had not been preserved. In this case, shows would represent former hydrocarbon accu- mulations. More information about the seal integrity is mandatory to evaluate this possi- bility. 364 5.3.8 Candelon #1 (CAN-1): post-mortem analysis Candelon #1 (CAN-1, figure 5.3.23 and 5.3.24) was drilled in 1981 to a total depth of 3944 m by the consortium CARIBOIL / Anschutz Company in the San Juan area, at the north-western region of the San Juan – Azua Basin. The primary objective of the well was to test the potential of the Oligocene limestones where good primary porosity was expected but also a secondary porosity within massive limestones was supposed to be present. The top of this limestones was predicted to occur at 3120 m (Norconsult, 1982). The well was abandoned as dry after reaching the main target. Target objective: Based on an irregular 2 x 3 km 2D seismic grid and geology maps, the prospect of this well included two structural closures (figure 5.3.23), consisting of an almost symmetrical anticline, where Oligocene to Eocene reservoirs were expected. The first one corresponds with the mapped Top Oligocene, interpreted as a thrust-faulted anticline covering an area of approximate 30 km2. Below, another closure was mapped in a deeper event (interpreted as Eocene) covering an area of 20 km2 (Candelon #1 Executive Summary, 1981). From the documentation available it is not totally clear the play targeted by this well. It is sup- posed that they expected a Paleogene? source rock, potential reservoirs in the Eocene – Oligocene limestones and Miocene shales acting as regional seals. Results: Test reports are not available. However, from annotations on well logs, it seems that there was at least one Drilling Stem Test (DST) at the interval 3495 – 3509 m for the middle Eocene carbonates (Unit E1). Recovering a 3,000 ft water cushion cut with CO2, with no formation liquids according to the available information, indicating the presence of tight limestones at this interval. The pres- sures registered during the DST are shown in Table 5.4. IHP 6850 FHP 6850 ISIP 4644 FSIP 3802 60 min 90 min IFP 845 FFP 1390 Table 5.3.3 Results from the DST carried out at the interval 3495 – 3509 m (Unit E1) found at annotations on the mud logging report. Key to acronyms: IHP, Initial Hydrostatic Pressure; FHP, Final Hydrostatic Pressure; ISIP, Initial Shut-In Pressure; FSIP, Final Shut-In Pressure; IFP, Initial Flowing Pressure; FFP, Final Flowing Pressure. No hydrocarbon shows were detected. Rock-eval analysis for the Miocene section (Unit N2) indicate that samples for the interval 2257 – 2290 m could be classified as marginal source rock in terms of organic richness, with TOC values of 0.53 – 0.56 WT % (Robertson, 1984). In addition, the presence of an interval of Paleo- gene limestones with a good organic content is included in the well summary (Candelon #1 Ex- ecutive Summary, 1981). However, this affirmation is not backed by any analysis. Vitrinite reflectance analyses are not available. The current geothermal gradient of Hispaniola Island, obtained from the corrected bottom hole temperatures, indicate that the deepest interval of Candelon #1 would be entering into the oil expulsion window (120 ºC; figure 5.3.25), 1000 m below the Miocene potential source rocks. 365 Stratigraphy summary: According to the well report, Candelon #1 penetrated 2905 m of Miocene shales and shaly sands and 1040 m of Oligocene limestones up to TD (Candelon #1 well report, 1981; Norconsult, 1982). Robertson Research (1984) reviewed the biostratigraphy and redefined as Eocene the section be- tween 3170 m and TD. This reviewed stratigraphy has been considered for this work (figure 5.3.24). Figure 5.3.23, Seismic line Cariboil SJ80 12 and the well Candelon #1. Markers indicate the main objectives included in the prospect, consisting of an almost symmetric anticline. 366 Fig. 5.3.24 Summary of Candelon #1 post-mortem analysis. 367 Mud logging is only available from 2905 m to TD and stratigraphy reports has not been preserved or are not available at public databases. The information concerning to the formations from 0 to 2905 m comes only from summary reports (Candelon #1 well report, 1981; Norconsult, 1982). With this limited information, it is not possible to define Units with reasonable accuracy. Units classification has been based on certain electro facies that define Neogene units in other wells on the island. That is the reason for presenting first a general description of the interval from 0 to 2905 m and then the division into Units based on the well logs response.  Units N2, N5 and N6: From surface to 1220 m this interval is composed of consisted of Neogene shales and shaly sandstones. This section of the well represents shallower ma- rine environments and changes from 1220 to 2905 m where lower to upper bathyal marine deposits have been identified. By the analysis of well logs, the whole interval has been divided into the following units (figure 5.3.24): - Unit N6: From 0 to 509 m, this unit is represented by a high SP (> -10 mV, local intervals between -15 and -10 mV). Resistivity decrease from ~20 Ω·m at top of the unit to ~5 Ω·m at base, while the GR passes from values lower than 40 API at top to greater than 70 API at base. - Sub-unit N5: From 509 to 789 m, this unit is represented by a SP that ranges from low – medium (< -20 mV) to high values (> -10 mV), predominating the first. Lower SP intervals coincide with sections where resistivities increase slightly (from 2 to 10 Ω·m) in a similar way than middle Miocene sandstones at the Cibao Basin (e.g. Licey #1 or San Francisco Reef #1, Sections 5.3.2 and 5.3.3, respec- tively). GR remains generally high (> 60 API), indicating the shaly character of the interpreted sandstones. - Unit N2: From 789 to 884 m, this unit is represented by a high SP (> -10 mV) and low, flat resistivities (~2 Ω·m). - Sub-unit N5: From 884 to 1859 m, this lower interval of Sub-unit N5 is repre- sented by a decrease of the SP (up to -15 mV) and increase in resistivity curves (up to ~20 Ω·m) in comparison with the Unit N2 above. Nevertheless, the in- crease in the SP log is lower than for the upper interval of Sub-unit N5. This behaviour is also observed in sandstone intervals at the Cibao Basin (e.g., San Francisco Reef #1, Section 5.3.3) - Unit N2: From 1859 to 2905 m, this unit is represented by a high SP (< -10 mV) together with low and flat resistivities (~4 Ω·m). According to well report, sand deposits resulted shaly with poor reservoir quality. Wire- line logs together with lithology descriptions settle the lower part of N2 as a potential seal as determined at the Azua exploration area. However, it is not possible to test the seal capacity without any data regarding pressures or fluid contents that support its potential.  Unit O3: From 2905 to 3170 m. Oligocene limestones did not show good porosity inter- vals. Both SP and resistivity logs are high (greater than -10 mV and 1000 Ω·m, respec- tively). This section has been interpreted as part of sequence of pelagic carbonates inter- bedded with rarer bioclastic layers. Deposition was occurring in a deep-water environ- ment, possibly middle to upper bathyal, with shallow water material being occasionally introduced by turbidity currents. (Robertson. 1984)  Units E2 and E1: From 3170 to 3944 m. Eocene limestones are micritic dominated by planktonic foraminifera and containing silt-sized and coarser elastic carbonate material, together with scattered, reef derived fragments. The coarser nature of the sediment in the sequence might indicate a depositional site on a carbonate submarine fan that is closer to a major channel (Robertson, 1984). The logs show that the limestones are usually tight with a low porosity. However, a few intervals of poor to fair primary porosity were identified (Table 5.5): 368 Interval (m) Thickness (m) Average porosity % 3258 – 3273 14 6 – 8 3322 – 3330 8 8 3342 – 3346 4 8 3372 – 3374 2 7 3408 – 3421 13 9 3421 – 3450 29 10 – 13 3496 – 3502 6 11 3514 - 3520 5 7 Table 5.3.4 Average porosities calculated from well logs for the interval 3258 – 3520 m (Norcon- sult, 1982). Neutron - density cross plots and well site description shows that the limestones are locally dolo- mitic. This would suggest that dolomitization of micritic limestone is occurring a resulting local increase in porosity (Candelon #1 well report, 1981). Evidence of fracturing is often noted on the microscopic examination of the cuttings. Although the contribution of fractures to the porosity should not represent an increment greater than 2% to the porosity (Norconsult, 1982), it could contribute to the permeability. Figure 5.3.25, Candelon #1 and Hispaniola geothermal gradients calculated from corrected BHT. 369 Conclusions:  Candelon #1 did not encounter sediments older than middle Eocene (Unit E1).  No hydrocarbon show was detected. Source Rock  Rock-eval analysis of Unit N2 revealed fair source rocks with a TOC between 0.53 – 0.56 WT % for the interval 2257 – 2290 m.  No vitrinite analyses are available.  Present-day geothermal gradient (figure 5.3.25) indicates the deepest section of the well would be entering the oil expulsion window (120 ºC), 1000 m below the Miocene source rocks. Reservoir  Intervals of tens to one hundred feet of Units E1 and E2 presented poor to fair porosities according to well logs.  Test reports are not available. From annotations on well logs, there was one DST at 3495 – 3509 m. The results seem to point out Unit E1 consists of tight carbonates. No more information is available. Seal  Seal capacities are only based on lithology description. The lower part of Unit N2 rep- resents of 1675 m of shales and minor shaly sandstones that might act as a potential seal, similar than for the San Juan – Azua Basin, covering the Paleogene limestones that could act as reservoirs. Timing / Migration  With the available data, the absence of a mature source rock does not allow the presence of hydrocarbons at the location of the well. Trap  Available seismic indicate the presence of a structural trap at the location of the well. 370 5.3.9 Charco Largo #1 (CHL-1): post-mortem analysis Introduction: Charco Largo #1 (CHL-1, Figure 5.3.26) was drilled in 1981 by the Canadian Superior Oil Com- pany to a total depth of 4,830 m at the Enriquillo basin (location in Figure 5.3.26). This well represents the final stage of an exploration program which included more than 1000 km of 2D seismic and gravity data acquired in Enriquillo Basin to define what is called the Charco Largo Structure (Figure 5.3.27). The aim of the well was to test the hydrocarbon potential of the En- riquillo Basin considering that it is located next to the San Juan - Azua Basin. The presence of hydrocarbon seeps in the Enriquillo Basin is known since the beginning of the last century. In 1953, the company Petrolera Dominicana carried out a reconnaissance of the San Juan - Azua and Enriquillo basins to locate and catalogue oil and gas seeps (Guerra-Peña, 1953). It was included in the first stage of its exploration activities. The result was positive locating several oil and gas superficial leaks in both basins (figure 5.3.26). At Enriquillo, the following seeps were identified:  1 salt sulphurous water with natural gas seep located next to sulphur deposits between Jimaní and Boca Cachón (location 1, figure 5.3.26)  4 saltwater and natural gas seeps located at La Playa and La Lancha (both in Boca Cachón, location 2, figure 5.3.26).  1 oil seep between Mella and Bermesí, named as Boqueron Chico oil seep. It is located at a fault plane, producing saltwater and intermittently oil (location 3, figure 5.3.26).  1 oil seep in Barahona, at Salinas, that was blocked off in order to avoid the periodic cleaning of the area (location 4, figure 5.3.26).  1 gas seep northern the locality of Mella (location 5, figure 5.3.26). Fig. 5.3.26 Location of wells selected for a post-mortem analysis. Key to acronyms: SPB, San Pedro Basin; PS-1, Punt Salinas; MDT-1, Maleno DT-1; CHL-1, Charco Largo. White insert indicates de location of figure 5.3.27. 371 Figure 5.3.27. Seismic line Canadian 111, which intersects Charco Largo #1 (location in figure 5.3.26). GR and SP are represented to the right of the well track and resistivities to the left. Units tops are represented by circles and other features, like shows or DSTs locations by squares. The dash line indicates the top of the Charco Largo Structure. In addition, during the SYSMIN geology mapping, two more oil seeps were discovered at Peder- nales and Cabo Rojo, southwards Sierra of Bahoruco (location 6, figure 5.3.26; Pérez-Varela et al., 2010 e; Abad et al., 2010 c). Although potential source rocks were identified and despite of the presence of oil shows (figure 5.3.28), the entire section resulted immature and no hydrocarbon accumulation was detected. Be- cause of that, the well was plugged and abandoned. Target objective: According to the well report (Charco Largo well report, 1981), the objective was a broad anticline where Eocene and lower-middle Miocene reservoirs were expected (figure 5.3.27). The Charco Largo Structure was delimited by 2D seismic profiles forming an irregular grid (averaged grind interval 2 km) and supported by 3,000 stations of gravity data. It was interpreted as a NW-SE trending anticline rooted by a major thrust fault parallel to the structure. The upthrown block of the thrust is to the northeast and has approximately 790 m of dip displacement (Charco Largo #1 well report, 1981). Minor imbricate thrusts are also present. This trap was classified as a struc- tural-compressional thrust related-fold derived from the interpreted basin inversion. It was con- cluded that the structure had 10 km2 of horizontal closure at its lowest contour and 240 m of vertical closure at its culmination (Charco Largo #1 well report, 1981). 372 Fig. 5.3.28, Summary of Charco Largo #1 post-mortem analysis. 373 At the Maleno oil field in the San Juan – Azua Basin, oil was produced in upper Miocene / Plio- cene sandstones with multiple shows in lower to middle Miocene limestones. The source rock for these oils has not been confirmed by geochemical analysis, although Miocene shales and marls have been proposed as the best candidates. As Enriquillo Basin was defined at the time of this well as an elongated ESE-WNW graben bordered by Eocene to Miocene limestones, Charco Largo Structure represented an attractive prospect. The play for Charco Largo was Eocene - Mi- ocene. It was hoped that middle to lower Miocene and Eocene shales would provide source rocks, middle to lower Miocene and Eocene carbonates provide reservoirs and Miocene evaporites the seals. Results: The review of well cuttings at the laboratory revealed the presence of sections with porous and permeable sands, silts and dolomites interbedded in salts. These samples showed apparent indi- cations of hydrocarbons when cut with solvents. The interpretation of wireline logs suggested the presence of permeable intervals. The main indicator was the separation between the shallow and deep resistivity curves that in the case of salt mud logging would normally be interpreted as mov- able hydrocarbons (Charco Largo #1 well report, 1981). These two evaluations (samples and logs) led to propose four zones for production testing, all of them in the Unit N3 at the intervals:  3,437 – 3,453 m: Claystones.  3,632 – 3,643 m: Claystones.  3,673 – 3,678 m: Claystones.  3,872 – 3,883 m: Dolomites and claystones. The results were negative because no formation fluids were recovered, and all the formations appeared to have a lack of permeability. According to well reports, these tests did not produce even under large pressure differentials. It took large pressure differentials to pump fluids into the formations, possibly exceeding frack pressures (Charco Largo #1 well report, 1981). No hydro- carbon was detected. A revaluation of the section of interest determined the absence of potential reservoir formations. Fresh drill cuttings were washed with a saturated brine revealing that the samples were composed of salt and soft clay/shale aggregates with embedded salt cubes, silt and sand grains. A total of 17 of hydrocarbon shows are described on the mud-logs from 2800 to 4200 m (Units N3 and N2). They range from petroliferous odors to viscous oils and yellow fluorescence cuts. 13 shows were in claystones and shales, while the remaining 4 shows were in carbonates. The best shows tool place at dolomite intervals. However, the thickness was only ~2 ft (0.6 m). The C15 to C35 normal paraffin distributions of samples examined in this interval are not typical of crude oil, although the number of heavy hydrocarbons is typical of oil or residual bitumen. Hydrocarbon shows were interpreted as a possibly early expulsion from Miocene shales (Charco Largo #1 well report, 1981). Source richness was examined for the interval 2633 – 4789 m. The results will be discussed in detail in the Section 5.4. As a summary:  From Composited samples, the intervals 3627 – 3718, 3864 – 3929 and 4075 – 4130 m presented TOC values of 1.60, 1.58 and 0.9 Wt % (Unit N3). From 4276 to 4773 m the analysis indicated TOC values of 0.44 – 0.57 Wt % (Unit N2).  TOC of hand-picked shales fragments for the interval 2588 – 3929 m (Unit N3) showed values as high as 4.95 Wt %. 374 No rock-eval analyses are available and samples were only classified in terms of their TOC and Kerogen identification. The entire section is thermally immature (Figure 5.3.29) with a vitrinite reflectance value of 0.34 – 0.40 % Ro at TD (4830 m) which implies a reflectance gradient of 0.02 % Ro per 1,000 ft (304.8 m). With this gradient, oil generation would be reached between 6400 and 8200 m, which implies a deviation from the Hispaniola tendency. Although some shales were organic-rich, they had only generated an early-expulsion product. In the proximities of the hornblende intrusions (at Unit N3, two sills between 3280 and 3375 m) the reflectance was slightly higher (0.68 % Ro surrounded by samples with vitrinite values of 0.35 – 0.31 % Ro) and it is not clear if the intrusion had any impact in an early generation process. Figure 5.3.29, Charco Largo and Hispaniola geothermal gradients, calculated from corrected BHT, and Vitrinite Reflectance values. The first hypothesis would be related with the location of Charco Largo #1, one of the southern- most wells drilled in Hispaniola. According to the island division proposed in this work (Chapter 4), this well is emplaced at the Oceanic Caribbean Domain. However, unlike those drilled in the San Juan – Azua Basin (belonged to the same domain), a greater distance to the island arc might have influenced the heat flow of the area. In addition, recent works have attributed a lower heat flow for the Enriquillo Basin and its prolongation in Haiti, more connected with the Caribbean Plate than with the island arc (Rolandone et al., 2019). A second hypothesis for the low vitrinite reflectance values could be the thermal effect of a salt package, in this case represented by Unit N3. Corrected BHTs of Charco Largo #1 fit with the current Hispaniola geothermal gradient for the measures above and into the evaporite interval (Unit N3). However, BHT below this interval are lower than expected. The effect of a salt level Diorite intrusion 375 on the thermal gradient at Charco Largo #1 could be related with the high thermal conductivity of salts, which produces a negative thermal anomaly below the salt bodies (Petersen and Lerche, 1995). This could explain the low values below Unit N3. On the other hand, lower values between the salt levels could be a consequence of overpressure. This has been recognized in other petro- leum basins such as the North Sea, the South of China and in Pyrolysis Rock Eval experiments (McTavish, 1978; Zou and Peng, 2001; Hao et al., 1996; Dalla Torre et al., 1997; Carr et al., 2009; Uguna et al., 2012, 2014; Schito et al., 2016). The highest value coincides with the depth where the diorite intrusions were encountered and could be consequence of them. Finally, the low vitrinite reflectance values could be a consequence of a vitrinite reflectance sup- pression. This is expected to occur in the following circumstances (Carr, 2000):  Transgressive sequences containing higher proportions of marine deposits.  Oxygen-deficient, alkaline depositional conditions producing aliphatic/bitumen-rich vit- rinite.  The presence of high liptinite contents.  When vitrinite has been formed from waxy, aliphatic-rich plant species. However, from geochemical reports, none of these cases were reported. Moreover, Thermal Al- teration Indexes (TAI) fit with vitrinite reflectance results (Charco Largo #1 well report, 1981). In summary, although the first and second hypothesis could be consistent with the data, a lower heat flow for the Enriquillo basin and a high thermal conductivity of salt layers, the first one is interpreted in this work as the main cause. This interpretation is based on the prognosed heat flow of the basin on account of the domain where it is located. Nevertheless, it is also assumed that the presence of the evaporites from Unit N3 might have magnified the effect. Stratigraphy summary: According to stratigraphy and palaeontology analysis, Charco Largo #1 record has been divided in this work into the following units (figure 5.3.28):  Unit P1/N5: from 0 to 1220 m this interval consists of upper Miocene to Present of cyclic, clastic coarsening uphole sequences of, from base to top, unlithified green clay/shales which become silty and grade up into shaly lithic siltstones. Siltstones pass up into poorly sorted, poorly rounded, very fine to very coarse, unconsolidated lithic sandstones which finally grade up into thick poorly sorted lithic conglomerates. Logs responses confirm this tendency with a SP that passes from high values at base (> -10 mV, although it alter- nates levels lower than -20 mV) to low values for the upper interval (< -15 mV) and resistivities passing from flat al low values at base (~2 Ω·m) to slightly higher values at top (between 8 and 15 Ω·m). However, the shallow position, and the poorly sorted com- position discards its reservoir potential.  Unit N6: from 1200 to 2118 this unit is characterized by an 898 m thick section of middle to upper Miocene shales, clays and minor lithic sandstones and conglomerates. The most abundant clay/shale is red brown colour and often well laminated. Resistivity decreased to low values (~2 Ω·m, flat curve). Normal pressure was encountered up to 1220 m, where pressure progressively increased to 13.0 lb/gal gradient at 2659 m. From logs and pressures, shales of Unit N6 could be considered as potential seals.  Unit N4: From 2118 to 2620 m this interval is composed of middle Miocene sediments characterized by the presence of marine limestones, which consist of shaly/silty lime mudstones, miliolid/pellet wackstone to grainstones and shaly bivalve packstones. How- ever, the main lithology of this Unit is composed of soft green chlorite clay/shale and 376 largely unconsolidated shaly lithic siltstones together with fine to medium sandstones. Deep resistivity is slightly higher for this interval (always lower than 5 Ω·m) which could imply certain degree of permeability. Nevertheless, porosities seem to remain low in general, leading to a low reservoir properties.  Unit N3: From 2620 to 4088 m there is a lower – middle Miocene alternation of anhydrite, salt, shales and dolomites. This unit is highly variable lithologically. The lithologies sug- gest that this unit was deposited in in terrestrial to coastal evaporite settings. Resistivity and density logs exhibit this alternation with high and low values. Pressures raised to 17.0 lb/gal gradient from 2659 m and continued to a maximum of 18.6 lb/gal gradient by 3295 m. The pressure remained high to 4008 m where a pressure decreased to a 11 lb/gal gra- dient at 4468 m. In this sense, the integrity of the salt package was settled, lending to proposed Unit N3 as a good regional seal.  There was an occurrence of two sills of hornblende diorite in the middle of the formation (between 3280 and 3375 m), marked by the highest GR values (up to 115 API). They were dated by K/Ar as 12.3 ± 1.3 My intrusions.  Unit N2: Below this salt package, the lithology turned into lower Miocene shales with low resistivities (~2 Ω·m) and high SP (> -10 mV) from 4088 to 4340 m. Unit N2 is composed of fossiliferous, green chlorite shale, with associated fine clastics and lime- stones. The fossils are mainly deep-water, pelagic foraminifera.  Unit N1: From 4340 to 4736 m there is a lower Miocene limestone section with limy shales at top and limestones from 4541 m. These limestones are dominantly chalky, lime mudstones, lesser pelagic foram wackstone to packstones and rare possible skeletal/in- traclast packstones/grainstones. Resistivity log shows an increase from Unit N2 to me- dium values for unit N1 (between 10 and 20 Ω·m). Neutron porosity reveals that these limestones represent the higher net fair to good porosity of the well. However, this could have been altered due to the presence of shales and deep-water carbonates, not showing the real porosity. Pressures reached a normal 9.0 lb/gal gradient at 4572 and continued constant to TD.  Unit O3: from 4736 m to TD (4830) Oligocene? earthy carbonates and silty shales with a similar electric response than Unit N1. Conclusions:  Charco Largo #1 did not encounter sediments older than Oligocene.  Hydrocarbon shows detected were interpreted as an early expulsion of Miocene shales (Charco Largo well report, 1981). Source rock  Potential source rocks were identified by geochemical analysis. Units N2 and N3 had good TOC content for composite samples (averaging 1.50 – 1.60 WT %), while hand- picked samples reveal TOC values as high as 4.95 WT %.  However, the entire section is immature, with a maximum vitrinite reflectance of 0.34 % Ro at total depth.  Vitrinite Reflectance values are lower than the Hispaniola tendency observed in other wells. It could be a consequence of a lower heat flow corresponding to its position in the Oceanic Caribbean Domain, which could have been magnified by the presence of the evaporites belonged to Unit N3. 377 Reservoir  All the tested reservoirs resulted to have no porosity. According with available data there is no reservoir interval at the location of this well Seal  Pressures differentials confirm the seal properties of Miocene shales (Unit N4) and evaporites (Unit N3). Timing / Migration  Only local migration due to an incipient generation. Trap  Although a structural trap is present at the location of CHL-1, no reservoir intervals has been identified therein. No hydrocarbon accumulation was encountered, and the well was plugged and abandoned.  Further studies should address the presence of other potential traps associated to the halokinesis. 378 5.3.10 Post-mortem conclusions The post-mortem evaluation summary (tables 5.3.5 and 5.3.6), simplified by a three colour-coded system, clarifies the hydrocarbon exploration features in Hispaniola: • Potential source rocks, good reservoirs, effective regional seals and traps have been iden- tified in exploration wells (figure 5.3.30). • However, mature source rocks and Timing/Migration represent the main issues. In this section, every component of the petroleum system will be analysed in order to identify the strengths and the weaknesses for the exploration in the area and which lessons could be learned for our Area of Interest (AOI). Table 5.3.5, Post-mortem summary using a three colours system. See table 5.3.6 for the followed guideline. Source rock Identified by rock eval analysis. Only based on description of for- mation. No potential. Mature source rock Confirmed by analysis. HC accumulation indicates its presence although not confirmed by wells HC Shows suggests the presence of mature SR but not proved by anal- ysis Proved immature. No evidence of HC. Reservoir Good porosity and permeability. Fair to good porosities. No potential. Seal Regional effective seal identified. Formation with seal potential. No potential. Time Mi- gration Hydrocarbon accumulation. HC shows suggest migration can be working Timing failure. Accu- mulation not pre- served Trap Effective. Potential. No potential. ? Must be present but the well did not reach it Table 5.3.6, Guideline for the post-mortem analysis followed in this work. 379 Figure 5.3.30, Penetration chart updated with the information derived from the Section 5.3. 380 Source rock The level of geochemical knowledge of the island could be considered as relatively poor (see Section 5.2.2). The limited information represents a drawback when studying a potential play in the area, leading to propose only potential source rocks, with a low grade of knowledge. From the evaluated wells in the post-mortem analysis, three potential source rocks have been identified:  Miocene shales of Units N2 and N3 (Charco Largo #1 and Maleno #1).  Oligocene shales and lignite beds of Unit O1 (Caño Azul #1, San Francisco Reef #1 and Vila Isabel #1)  Cretaceous black shales and marls of Unit K2 (San Pedro #1) Maturation Despite the production of oil and the recognition of shows and seeps along the island, none of the exploration wells have identified a mature source rock that had generated hydrocarbons. From Vitrinite Reflectance data (figure 5.3.31), none of the samples have reached a maturation stage enough for the hydrocarbon generation. Nevertheless, the accumulation of oil at the abandoned fields of Higuerito and Maleno (at the Azua region) together with the presence of multiple oil and wet gas shows suggest the presence of mature source rocks in the area. In this sense, it is necessary to stablish the burial history of the AOI the determine the location and timing of potential kitchens for the different potential intervals (see Section 5.4.5). Figure 5.3.31, Vitrinite reflectance from the exploration wells in Hispaniola. 381 Reservoir Oil production in Hispaniola has been limited to the upper Miocene – Pliocene sandstones inter- preted as limited channel and fan submarine systems. Sand B at Maleno is composed of 95% fine to medium grains poorly sorted with a quartz content up to 75% for some intervals (Maleno East- 1 well report, 2003). However, as it was exposed in the Maleno DT-1 post-mortem analysis (Sec- tion 5.3.7), this sand bodies Have a limited lateral extension with a net gross between 14 and 24 m. Besides the upper Miocene – Pliocene sandstones, the following units have demonstrated good reservoir intervals.  Middle Eocene limestones of Unit E2 at Candelon #1 and Punta Salinas #1 have poor to fair porosities from 6-8 % to 10-13% producing water at the interval 3495 – 3509 m.  Oligocene limestones and sandstones of Unit O2 produced water at the wells Caño Azul #1 and Licey #1. On the one hand, Carbonates consisted of highly fossiliferous and earthy limestones, containing overpressure gas and sulphurous water. On the other hand, sand- stones exhibit porosities up to 15 %. However, the lack of quartz is common in Paleogene and Neogene sandstones of Hispaniola and should be considered (see Section 4.2.1).  Miocene limestones of Unit N1 produced water with oil and gas shows at Maleno DT-1, having vugular porosities and fractures. Their potential as reservoir has been verified in other wells in Azua (e.g. Maleno #1, Maleno #2 or Maleno #7 which had a water blowout occurred from vugular and cavernous porosity). The estimated average porosity of the lower Miocene limestones is 12 % from wireline logs. In Cibao Basin, Miocene reef fa- cies produced water at the well Caño Azul #1 with a good blow during DSTs.  Miocene sandstones belonged to Unit N5 have demonstrated good reservoir intervals, with a porosity up to 15%, in the Cibao Basin at the well San Francisco Reef #1. Seal From the available data, the following intervals have been tested as regional seals:  Oligocene shales belonged to Units O1 and O2: The well Caño Azul #1 proved its seal capacity by confining overpressure sulphurous water below them. They are com- posed of grey to black, organic-rich silty shales. Biostratigraphy reports interpret their deposition at the neritic zone (Guerra and Percival, 2000)  Miocene shales: Accumulations at Maleno #1 probed the capacity of Miocene shales belonged to Unit N2. They consist of deep-marine grey to black silty shales. Moreo- ver, Miocene shale section is thick enough (640 m at Maleno DT1) to seal a substan- tial hydrocarbon column (Munthe, 1995).  Tight limestones and marls are interpreted as internal seals for the Oligocene – middle Miocene carbonate system. The wells Caño Azul #1 and San Francisco Reef #1 pre- sent limited methane accumulations restrained to porous limestones covered by these internal seals, forming stratigraphic traps.  Miocene evaporites: Although their deposition seems to be limited to the Enriquillo Basin and linked to its tectonic evolution, the presence of a thick alternation of shales and evaporites (Unit N3) results attractive in terms of exploration. The seal capacity of Unit N3 has been tested at Charco Largo #1 in account of the pressures differentials registered in the well. In summary, Oligocene and Miocene shales intervals are widespread and have been reached at most of the studied wells (except at San Pedro #1 and Punta Salinas #1). 382 Timing / Migration / Preservation Timing and hydrocarbon migration are one of the puzzles to solve for a satisfactory exploration in Hispaniola. Seven of the nine wells studied in this chapter had hydrocarbon shows, yet none of them presented satisfactory accumulations of oil or gas, beyond the limited production at the fields of Higuerito and Maleno. As oil or gas are being or were generated at any time in Hispaniola, the absence of a big discovery could be related with a timing/migration issue. It is possible that oil generation and expulsion happened before the creation of effective traps, representing a timing issue in the area. On the other hand, traps at Maleno and Higuerito abandoned oil fields are recent (late Miocene / Pliocene). This led to another question: did the hydrocarbon migration fail to deeper reservoirs or the migration was effective but not preserved? The first scenario represents a migration issue, to be treated in each case, or an ineffective trap. More seismic data are required to analyse the effectiveness of deeper traps to determine if wells such as MDT-1 penetrated valid traps. The second scenario could signify a regional issue of preservation. In this case, hydrocarbon shows would represent former accumulations where the trap has not been preserved. Due to the high tectonism that has suffered the island since late Eocene times, it is mandatory to evaluate the preservation risk of the AOI. To reduce the exploration risk, it is necessary to evaluate the right timing of the petroleum system at the AOI and the regional tectonic events that could have affected it. Another issue associated to timing is the burial of reservoirs in order to prevent oil biodegradation, owing to Pliocene and Quaternary thickness does not exceed 300 m at any of the wells in the San Juan – Azua Basin. Trap While structural traps have produced oil at the Higuerito and Maleno fields at Azua, stratigraphic traps have been also tested by the presence of high-pressure sulphurous waters or limited bioge- netic (?) gas accumulations at the wells Caño Azul #1, San Francisco Reef #1 or Villa Isabel #1 at the Cibao Basin. In the Cibao Basin, stratigraphic traps with porous limestones, that pinch out landwards and are cover by shales or tight limestones, produced limited amounts of gas and sulphurous water. This carbonate ramp system works in other hydrocarbon productive provinces of the world, such as the Perla field in Venezuela (see Section 4.2.3). Porous carbonates are covered by younger distal facies due to the back-stepping architecture of the carbonate systems generated during transgres- sion, developing stratigraphic traps. Variations of the sea level could expose shallower limestones propitiating the development of secondary porosities. In the San Juan - Azua Basin, thrust-related anticlines accumulated oil in upper Miocene / Plio- cene sandstones. The age for this trap is late Miocene / Pliocene. However, since the late Eocene Hispaniola have suffered a transpressional regime that has generated thrust and fold belts which have created a wide variety of structural traps. 383 5.3.11 Lessons learned for the San Pedro Basin The San Pedro Basin in a regional framework As it was presented in Chapter 4, Hispaniola island has been divided in this work into four main tectono-stratigraphic domains (figures 5.3.32 and 5.3.33). The first relevant lesson derived from the post-mortem analysis is that the generation of hydrocarbons is regional, having been reported at every domain, except for the Island Arc Domain, where most of the sedimentary record has been eroded. This division has been extended into the SPB by the interpretation of gravity (figure 5.3.32) and magnetic (figure 5.3.33) anomalies. According to that, the SPB would comprise ter- rains of the Island Arc, the Cretaceous – Eocene Basin and the Oceanic – Caribbean Domains. The SPB is bounded to the west by the Azua Basin which has a proven petroleum system and small oil production has been recovered from the Maleno and Higuerito fields, located at the limit between the Cretaceous – Eocene Basin and the Oceanic Caribbean Domains. While in the scien- tific literature the SPB and the Azua basins have been considered as disconnected sedimentary systems, this study suggests both that shared a common tectonic evolution and therefore the pres- ence of an untested petroleum system in the SPB can be expected (Gorosabel-Araus et al., 2020). Structurally, the rear imbricate thrust system would be limited by the SJRFZ to the north and the San Juan–Los Pozos Fault Zone (SJLPFZ) to the south (see Section 4.7.3). Thrusting activity would fault the Cretaceous–middle Eocene sedimentary rocks, while the upper Eocene– Oligo- cene sequence would be folded. The frontal thrust system, limited to the north by the SJLPFZ, incorporates younger sedimentary sequences and could be correlated with the Azua Group units (Gorosabel-Araus et al., 2020). While the Azua Basin was finally exhumed after the Miocene– Pliocene, most of the SPB continued as an actively subsiding basin. The Higuerito and Maleno fields were emplaced in a gravity minimum which would correspond to thick sedimentary accumulation (see Section 4.7.3). This trend enters into the Area of Interest (AOI) at its north-western sector. As an initial hypothesis, this fact together with the interpreted presence of lithostratigraphic Units which have been classified as potential source rock, would open the way for the generation of oil and gas in the basin, conferring certain grade of hydrocar- bon potential to the basin that will be analysed in the following sections (5.4 to 5.10). Play elements prognosed for the San Pedro Basin By the combination of the results coming from the interpretation of the basin (Section 4.7) and the post-mortem analysis (Section 5.3), it is possible to identify potential plays in the SPB. For that, units susceptible to be considered as a potential element of a play are classified in table 5.3.7. Under the interpretation given in this work, different plays could be proposed for the basin, com- prising Cretaceous, Paleogene and Miocene units, leads to the possibility to explore new plays in the area beyond the Azua play. Source rock Reservoir Seal Wells post-mortem K2, O1, N2, N3 E2? O2, N1, N5 O1/O2, N1*, N2, N3 Interpreted at SPB K2, O1, N2 E2, O2, N1, N5 O1/O2, N1*, N2 *Internal seals in the carbonate system. Not regional. Table 5.3.7, Units considered as elements of the petroleum system that have been identified in the post-mortem analysis and Units interpreted to be present at the San Pedro Basin. 384 Figure 5.3.32, Regional domains division over Bouguer anomaly map with the main exploration results represented. 385 Figure 5.3.33, Regional domains division over Reduced-to-pole magnetic anomaly map with the main exploration results represented. 386 Section 5.4: Source rock The wells post-mortem evaluation identifies the presence of three potential source rocks in His- paniola Island: Upper Cretaceous marls and shales (Unit K2), Oligocene shales and lignite beds (Unit O1) and Miocene marls and shales (Units N2 and N3). The new interpretation given for the SPB in this work prognoses the presence of these three potential levels in the basin. In order to get a better regional framework, rock eval information from well reports, public databases (BNDH) and the scientific literature (e.g. Robertson, 1984) has been gathered and completed with regional data from Puerto Rico (Robertson, 1984), Jamaica, Saba (Robertson, 1984) and the Car- ibbean Plate (Munthe, 1995). The results were represented in terms of the kerogen type, genetic potential, thermal maturity and kerogen conversion (figure 5.4.1) and were compared with the observations derived from the field work carried out in November 2019 where Cretaceous, Eo- cene and Oligocene outcrops were sampled and analysed for their Total Organic Carbon (TOC) composition (table 5.4.1) and rock eval analysis (results not available at date June 2020). Figure 5.4.1, Source rock evaluation for all intervals (Cretaceous, Eo- cene, Oligocene and Miocene sam- ples). Triangles represent data from field work. 387 Along Sections 5.4.1 to 5.4.4, the different intervals will be studied individually. However, there are some observations that could be inferred from the general results of the source rock evaluation. In figure 5.4.1, all data are plotted grouped into age intervals. There is a clear differentiation of the kerogen type depending on the interval. While Miocene and Cretaceous samples range from type II to type III (oil and gas prone), Paleogene is represented by a Hydrogen Index (HI) below 200 mgHC/gTOC, classifying this interval only as type III or corresponding to a gas prone source rock. In terms of the genetic potential, samples from the Cretaceous, Oligocene and Miocene could be classified as good to very good. Nevertheless, the thermal maturity indicates a general immature stage close to the oil window, and only some Oligocene samples are entering into the oil zone according to the kerogen conversion. During the field work carried out for this work, Cretaceous to Oligocene outcrops were sampled to determine their source rock potential. Although a potential Eocene source rock was not prog- nosed in the post-mortem evaluation, this interval was sampled in account of field observations. At the southern flank of Cordillera Central, the upper Eocene El Número Formation consisted of a ~500 m interval of deep-water deposits, characterised by an alternation of thin-bedded turbidites and mudstones. At base, the lower interval of this formation (facies association ENFA1 in Section 4.4.1) is composed of dark grey to black mudstone beds in a strong dominance over sandstones, being sampled in order to determine the presence of source rock intervals deposited during the Eocene. The preliminary results (only TOC analysis is completed at the time of this work) confirm the potential of the Upper Cretaceous, Eocene and Oligocene source rocks (table 5.4.1). According to TOC, the Cretaceous samples could be considered as very good (based on Peters, 1986) and should be considered as the best exploration target. On the other hand, Eocene and Oligocene samples could be considered as fair to good. Further analysis, including rock eval and vitrinite reflectance, must address the quality of these intervals and their maturation to stablish the final source rock evaluation of these formations. Table 5.4.1, Total Organic Carbon (TOC) analysis derived from the field work carried out in November 2019 in the Dominican Republic. TC, Total Carbon; IC, Inorganic Carbon; TOC, To- tal Organic Carbon.. 388 5.4.1 Cretaceous Source Rock Cretaceous samples have demonstrated the best source rock quality between the samples available both in terms of their kerogen type and the genetic potential (figure 5.4.1). Despite of that, the grade of knowledge of the Cretaceous interval in Hispaniola Island is limited. Rock eval analysis are only available for the well SP-1, where samples demonstrate a type III kerogen with a low genetic potential (figure 5.4.2), having only a fair TOC (up to 0.52 wt %). Conversely, samples obtained at the Caribbean Plate for the Deep-Sea Drilling Project (DSDP) reveal the presence of type II and III source rock intervals, with a very good to excellent genetic potential and a TOC up to 6.81 wt % (Bode, 1971; Munthe, 1995). Regarding the thermal maturity and the kerogen con- version, all samples resulted immature, with a maximum Tmax of 433 ºC (figure 5.4.2). Neverthe- less, despite of the maturation results, this interval should be considered as the most attractive for future exploration projects in the island as will be explained in this section. Figure 5.4.2, Source rock evaluation for Cretaceous samples from His- paniola, Jamaica, Puerto Rico and the Caribbean Plate. Triangles rep- resent data from field work. 389 In the first place, the scarce of data provides a limited vision of the Cretaceous potential. Onshore Hispaniola, the Cretaceous has not been systematically sampled, and only data from the well SP- 1 is available, revealing a type III kerogen with a fair TOC (figure 5.4.2). In order to improve the knowledge of this interval, outcrops at the Cordillera Central and the Cordillera oriental were sampled during the field work carried out for this work. Although the final results are not available at the time of this work, preliminary results indicate the presence of good source rock intervals at both locations (figure 5.4.3) with TOC as high as 3.6 wt % at Cordillera Central and 0.53 at Cordillera Oriental (the Río Blanco and Las Guayabas Formations, respectively; table 5.4.1). At both locations, the sedimentary record indicates the deposition in a deep-water environment dur- ing the Coniacian – Santonian (see Section 5.2.1 and 5.3.1) in a pre-tectonic geodynamic setting, which could favour the presence of widespread regional source rocks. Further analysis (rock eval and vitrinite reflectance) must determine the real potential of the Cretaceous, although prelimi- nary results point the good direction. Figure 5.4.3, Overview of Cretaceous outcrops at Cordillera Central and Oriental. Above, Re- gional division of Hispaniola into Domains based on gravity (A) and magnetic (B) anomalies (see Appendix 1 for acronyms). Centre, example of the Río Blanco Formation at Cordillera Central (C), including a detail of the organic-rich black mudstones (D). Below, example of the Las Guay- abas Formation at Cordillera Oriental (E and F). 390 According to the division of the island proposed in this work, samples would include formations of the Forearc - Collisional and the Island Arc Domains. Samples obtained during the DSDP (site 144/149), composed of type II and III kerogens with a good to excellent genetic potential (figure 5.4.2; Bode, 1971; Munthe, 1995), could be considered as belonged to the Oceanic – Caribbean Domain. From a regional point of view, it is possible to correlate the stratigraphy of the Turonian to San- tonian record reached at the Deep-Sea Drilling Project (DSDP) leg 15 wells at the Venezuelan Basin and outcrops from Cordillera Oriental and Central. In summary:  At the site 146/49 of the DSDP (belonged to the Oceanic – Caribbean Domain), Turonian Dolerites and basaltic ash pass up into Coniacian to Santonian radiolarian limestones. The upper part is a fairly homogeneous light grey limestone and the lower part is a varicol- oured limestone with contrasting lithologies, including white radiolarian sands and very dark carbonaceous layers (Bode, 1971; Munthe, 1995) with a TOC up to 6.81 wt %.  At Cordillera Oriental (at the Forearc – Collisional Domain), dolerite sills and basaltic flows have been identified and dated as Turonian (García-Senz et al., 2004 a, b). Above these basaltic units, there are a succession of shales and sandstones that passes up into radiolarian cherts identified as Coniacian in age (García-Senz et al., 2004 a, b; 2007).  At Cordillera Central (at the Island Arc Domain), the stratigraphy of the Coniacian to Santonian Río Blanco Formation consists of an alternation of sandstones and black shales with a TOC up to 3.6 wt %. This sequence is followed vertically by the ‘El Convento’ member, consisting of a succession of limestones, shales, sandstones and radiolarian cherts (Gómez et al., 1999). Since the Campanian and following the evolution model given in Chapter 4 for the southern mar- gin of Hispaniola, Campanian to Maastrichtian sediments would have deposited over the Carib- bean Plate in a back-foreland model (see Section 4.7.5). According to this model, similar intervals to those reached at the site 146/149 of the DSDP or at Cordillera Central (Río Blanco Formation) could be expected at base of the Cretaceous – Eocene Basin Domain. This sequence would have been covered by the Campanian to Maastrichtian Trois Rivieres Formation, composed of a suc- cession of shales and sandstones interpreted as a thin-bedded turbidite system dominated by mud- stones (figure 5.4.4; Ardèvol, 2004 b; Goulet-Lessard, 2012). Unfortunately, this formation has not been sampled or the rock eval and vitrinite reflectance analysis are not available. Further works must address the source rock potential of the Trois Rivieres Formation in order to complete the information concerning the Late Cretaceous. Regarding the maturity and the low Tmax obtained for Cretaceous samples at the site 146/149 of the DSDP and the well San Pedro #1, it should be noted that this should not represent an issue for the SPB, where a thick sedimentary sequence has been accumulated since the Cretaceous and tectonically stacked at the MTB (up to 8 km of sediments stacked, see Section 4.7.3). In the case of samples obtained at the Caribbean Plate, the sedimentary cover of the Venezuelan Basin is mainly formed by abyssal plain deposits which do not represent the enough burial to entering to the oil generation zone. On the other hand, the well San Pedro #1 was drilled close or above a basement high (see location on figure 5.4.3). Therefore, a higher maturation is prognosed for the depocenter of the SPB and will be studied in Section 5.4.5. In summary, Upper Cretaceous potential source rock intervals have been identified or prognosed by models at each domain, and therefore, it should be considered as a regional source rock. The identification of intervals with a good TOC in the onshore extension of the basin (up to 3.6 wt %) together with the good source quality determined for samples of the Caribbean Plate postulate the Cretaceous as the main source rock to be considered in the SPB. 391 Figure 5.4.4, Above (TR1), Chevron fold at the Trois Rivieres Formation at Cordillera Central in the Dominican Republic, from Ardèvol (2004 2), interpreted as deposited in a turbidite setting. Below (TR2), detail of an interpreted turbidite deposit of the Trois Rivieres Formation at the Libon river in Haiti, from Goulet-Lessard, 2012. 392 5.4.2 Eocene Source Rock Although the interval corresponding to the Eocene was not prognosed as a source rock potential interval by the post-mortem evaluation, it was sampled on account of field observations. At the southern flank of the Cordillera Central, the El Número Formation consists of an alternation of mudstones and sandstones interpreted as a thin-bedded turbidite system (figure 5.4.5; see Section 4.4.1). The formation has been divided in this work into two facies associations based on the proportion of sandstones (ENFA1 and ENFA2). Figure 5.4.5, Examples of the Eocene El Número Formation (EN), corresponding to the ENFA1, sampled during the field trip. Numbers refer to samples of Table 5.4.2. 393 The main component of ENFA1 is bed configuration with thin bedded fine to very fine-grained carbonate sandstones, and medium- to thick-bedded mudstones. In this facies association, dark grey to black mudstone beds are in a strong dominance and often take up 80% of the total thick- ness of the outcrops. The composition varies from bottom to top, passing vertically form a variety of foraminifera and peloids to packstones of globigerina which could indicate a deepening upward of the marine environments recorded in the sampled section (Canales, personal communication). In this sense, sediments deposited in a deeper environments have higher TOC content, from 0.24 wt % at base to 0.98 wt % at top (table 5.4.2). TOC analysis indicates the presence of fair intervals into this Eocene formation. Nevertheless, further works must determine the kerogen type and the maturation of these intervals in order to assess the source rock potential of the Eocene. Table 5.4.2, Total Organic Carbon (TOC) of Eocene samples obtained during the field work car- ried out in November 2019 in the Dominican Republic. TC, Total Carbon; IC, Inorganic Carbon; TOC, Total Organic Carbon. 394 5.4.3 Oligocene Source Rock The source rock potential of the Oligocene was pointed at the well CA-1. The well summary describes the presence of organic-rich Oligocene shales from the Unit O1 had a TOC content of 1.05 wt % (Caño Azul #1 well summary report, 2000). Unfortunately, rock eval and vitrinite reflectance data are not available. Units O1 and O2 include the presence of black shales and beds of lignite which are also described at the wells SFR-1 and VI-1 (Villa Isabel #1 mud logging report, 1958; San Francisco Reef #1 mud logging report, 1995). Despite of the lack of rock eval data of Units O1 and O2 from exploration wells, a good approach to this intervals could be pro- vided by outcrops at the Cibao Basin and the San Cristóbal region (onshore extension of the SPB, see Section 4.4.2) which were completed with regional data from Puerto Rico and Saba (figure 5.4.6; data from Robertson, 1984). Figure 5.4.6, Source rock evaluation for Oligocene samples from Hispan- iola, Puerto Rico and Saba. Trian- gles represent data from field work. 395 All samples are catalogued as type III - IV with a HI lower than 200 mgHC/gTOC (figure 5.4.6). In this case, the available data classify potential Oligocene source rocks are gas prone. Kerogen conversion indicates that this interval is entering into the oil window, with a vitrinite reflectance up to 0.58 %Ro for samples at the San Cristóbal region (table 5.4.3). Nevertheless, as the exhu- mation of this zone started at the late Miocene (Heubeck and Mann, 1991) a higher maturation is expected for this interval at the offshore, where most of the SPB continued as an actively subsid- ing basin. Finally, the genetic potential chart indicates that samples from Saba and San Cristóbal could be classified as very good. Table 5.4.3, Source rock evaluation for Oligocene outcrops at the San Cristóbal Region, the San Pedro onshore extension (* data from Robertson, 1984). The Oligocene differs clearly from the Cretaceous in the kerogen type (there are no data regarding the Eocene). While Cretaceous samples range from type II to type III, the Oligocene is only rep- resented by type III kerogens. Samples collected during the field work demonstrate the presence of carbonaceous material (figure 5.4.7), which suggests a type III kerogen in the sampled area. This change could have been influenced by the tectonism of the island. Upper Eocene and Oligo- cene sequences are marked by the presence of widespread conglomerate intervals and olistoliths (see Sections 4.2.1 and 4.4.2). An Oligocene terrestrial source rock is coherent with the tectonic evolution of the Hispaniola, which was partially in subaerial conditions since the Eocene. Lignite beds identified on exploration wells (e.g. CA-1) might correspond to this process. At the San Cristóbal region the Oligocene record (Presa Valdesia Formation) has been divided into 4 facies associations (see Section 4.4.2). Belonged to this interval, PVFA2 consists of an alternation of mudstones, microconglomerates and coarse grain sandstones, where grey/dark grey mudstones take up more than 70% of the total thickness. The presence of organic matter, consist- ing of carbonaceous materials, is usual in mudstones (figure 5.4.7), revealing a TOC up to 0.95 wt %, although TOC of samples in Robertson (1984), gathered at the same sector, can be as high as 4.18 wt%. Poorly sorted polymictic conglomerates and coarse sandstones are dominated by pieces of coral/algal/larger foraminiferal limestone, volcanic and metamorphic clasts. At top of this association a level of metric blocks was observed although due to bad-access conditions, it could not be studied in detail. Carbonaceous clasts are interpreted in this work as vegetal rests that arrived at a deep-water en- vironment, yet close to the exposed area (see Section 4.4.2). This proximity is also inferred by the appearance of conglomerates and Olistoliths coming from a near platform. Other Oligocene outcrops in Hispaniola reveal similar intervals, such as the La Toca Formation at the Cibao Basin, defined by an alternation of polymictic conglomerates, sandstones and mud- stones which includes levels with lignite fragments (figure 5.4.7; Monthel et al., 2010 b). 396 Figure 5.4.7, Example of Oligocene organic-rich intervals at the San Cristóbal Region (Presa Valdesia Formation, PV) and the Cibao Basin (La Toca Formation, LT, from Monthel et al., 2010 b). 397 5.4.4 Miocene Source Rock A Miocene source rock has been proposed as the most likely origin for oils in Azua (Mann et al., 2008). Samples of Hispaniola coming from exploration wells and outcrops (data from Robertson, 1984) determine type II and III kerogens (figure 5.4.8). Oil prone intervals have been identified at the Haitian well Cul-de-Sac with a good to very good genetic potential, while the others fall into the Type III, gas prone, and Type IV, non-source rocks. Nevertheless, the kerogen conversion and the thermal maturity charts (figure 5.4.8) indicate that all of samples are immature, therefore having a mature Miocene source rock represents an exploration risk. This immature stage is sup- ported by vitrinite reflectances at the San Juan – Azua and Enriquillo Basins (see Section 5.3.7, figure 5.3.20 and Section 5.3.9, figure 5.3.29). During the field work, no Miocene interval was sampled. While Oligocene samples are close or entering into the oil zone, all Miocene samples are imma- ture. Maturity maps must be calculated for this interval for determining its generation potential. Figure 5.4.8, Source rock evaluation for Miocene samples of Hispaniola, from exploration wells (Candelon, Jurinet and Cul de Sac) and out- crops of the Cibao Basin. 398 5.4.5 Maturation Bottom Hole Temperatures (BHT) have been gathered from exploration wells in Hispaniola to stablish the current geothermal gradient of the island. These temperatures were corrected to com- pensate the effect of drilling fluids in the borehole. BHT were corrected empirically (Dowdle and Cobb, 1975) since the duration of the sampling, for a proper correction, was not available. The results are plotted in figure 5.4.9. Figure 5.4.9, Left, Hispaniola geothermal gradient from empirical corrected BHT. Right, Vit- rinite reflectances from exploration wells. Excepting the well Charco Largo #1, located at the Oceanic – Caribbean Domain and distant from the Island Arc Domain (see Section 5.3.9), all the measures follow the same tendency, resulting a geothermal gradient of 3,52 ºC / 100 m. Vitrinite reflectance data support this geothermal gra- dient, obtaining the following necessary burial for the main oil and gas generation windows:  Oil generation (100 ºC / 0.55 % Ro): ~3,300 m.  Expulsion (120 ºC / 0.8 % Ro): ~4,200 m.  Wet / dry gas (150 ºC / 2 % Ro): ~5,500 m. Under the assumption that this geothermal gradient would have been constant in time and apply- ing it to the basin reconstruction of Section 4.7.3, five flattened profiles were created, in the depth domain, for different moments of the San Pedro Basin evolution: middle Eocene, Oligocene, middle Miocene, late Miocene and Present (figure 5.4.10). These charts have been created for the Neogene basin and the main thrust sheet, due to the seismic profiles do not allow the precise interpretation of the underlying thrusts and duplex. Different scenarios were assumed for the elaboration of maturity maps. In the case of a Cretaceous source rock (table 5.4.4 and figure 5.4.10 A to E), the first scenario assumed that the source rocks 399 interval is located 500 m below the Cretaceous top, at the depth where black shales with a fair TOC were reached at the well San Pedro #1. In order to cover the possibility of a deeper source, a second scenario comprises a source rock interval 1000 m below the Cretaceous top. For the Oligocene (figure 5.4.10 F and G), the first scenario assumed a source rock interval 100 m below the Oligocene top and another 800 m below the Oligocene top, both cases based on the study of outcrops at the San Cristobal Region and the geological mapping (Abad et al., 2010 a; Pérez-Varela et al., 2010 a). Table 5.4.5, Different scenarios proposed for the elaboration of maturity maps. The main conclusions obtained from the maturity maps include:  Maturity maps reveal that the main kitchen follows a NW-SE trend divided since the middle Miocene by the Saona Fault Zone (SAFZ; figure 5.4.10).  The Cretaceous source rocks would have entered the oil window at the depocenter of the basin for a period between the Oligocene and the middle Miocene, with the main gener- ation occurring during the Miocene through Present (figure 5.4.10 C to E).  Regarding the Oligocene, the early generation window is reached at the late Miocene for the deeper scenario (figure 5.4.10 F). However, the oil peak did not start before Pliocene to Quaternary when the shallower section entered the oil generation window (figure 5.4.10 G).  However, as rock eval data indicate that the Oligocene would only include a Type III source rock, it is expected the volume of oil generated was small and needs an extra burial to reach the peak of gas production. Oligocene production of gas should be considered as riskier due to the not-enough burial, and it is possible that only biogenic gas had been produced from this level.  Under the assumed premises, the entire Miocene section is immature, yet it is possible that some of the deepest sediments had got and early generation stage. In consequence, with the available data, a Cretaceous source rock represents a lower risk and should be considered as the best candidate for the oil and gas generation. Regarding the Oligocene source rocks, they should be considered only for gas production. 400 Figure 5.4.10 A, Source rock maturity evaluation for a potential Cretaceous source rock. Above, seismic line WGC08 depth converted and flattened to the Top middle Eocene. Centre and below, maturation maps for a source interval 500 m and 1000 m the Top Cretaceous. Yellow line indi- cates the position of the seismic profile. 401 Figure 5.4.10 B, Source rock maturity evaluation for a potential Cretaceous source rock. Above, seismic line WGC08 depth converted and flattened to the Top Oligocene. Centre and below, mat- uration maps for a source interval 500 m and 1000 m the Top Cretaceous. Yellow line indicates the position of the seismic profile. 402 Figure 5.4.10 C, Source rock maturity evaluation for a potential Cretaceous source rock. Above, seismic line WGC08 depth converted and flattened to the Top middle Miocene. Centre and below, maturation maps for a source interval 500 m and 1000 m the Top Cretaceous. Yellow line indi- cates the position of the seismic profile. SAFZ, Saona Fault Zone. 403 Figure 5.4.10 D, Source rock maturity evaluation for a potential Cretaceous source rock. Above, seismic line WGC08 depth converted and flattened to the Top upper Miocene. Centre and below, maturation maps for a source interval 500 m and 1000 m the Top Cretaceous. Yellow line indi- cates the position of the seismic profile. SAFZ, Saona Fault Zone. 404 Figure 5.4.10 E, Source rock maturity evaluation for a potential Cretaceous source rock. Above, seismic line WGC08 depth converted. Centre and below, maturation maps for a source interval 500 m and 1000 m the Top Cretaceous. Yellow line indicates the position of the seismic profile. SAFZ, Saona Fault Zone. 405 Figure 5.4.10 F, Source rock maturity evaluation for a potential Oligocene source rock. Above, seismic line WGC08 depth converted and flattened to the Top upper Miocene. Centre and below, maturation maps for a source interval 100 m and 800 m the Top Oligocene. Yellow line indicates the position of the seismic profile. SAFZ, Saona Fault Zone. 406 Figure 5.4.10 G, Source rock maturity evaluation for a potential Oligocene source rock. Above, seismic line WGC08 depth converted. Centre and below, maturation maps for a source interval 100 m and 800 m the Top Oligocene. Yellow line indicates the position of the seismic profile. SAFZ, Saona Fault Zone. 407 Section 5.5: Reservoir The limited oil production in Azua was limited to upper Miocene – Pliocene sandstones (see Section 5.3.7). Nevertheless, the Drilling Steam Tests (DSTs) carried out in Hispaniola demon- strate the presence of additional reservoir intervals for the period Oligocene – late Miocene (figure 5.5.1) which include carbonates and sandstones from the following Units:  Oligocene: Carbonates and sandstones from Unit O2  Miocene: Carbonates from Unit N1 (comprising sub-units N1.1, N1.2 and N1.3) and sandstones from Unit N5. Based on the stratigraphic interpretation given in this work for the Cenozoic infill of the SPB and the Cibao Basin (see Section 4.2), it is possible to infer reservoir properties for the Oligocene to Miocene sequences interpreted as a carbonate ramp system with a similar evolution for the same period of time. In addition, although Eocene limestones from Unit E1has not been tested, this interval is included into the analysis on account of the identification of fair porosity intervals on well logs (see Sections 5.3.6 and 5.3.8 corresponding to the wells Punta Salinas and Candelon). Figure 5.5.1, Schematic stratigraphic cross sections of the San Pedro (above) and Cibao (below) Basins. According to the interpretation given in this work, similar properties than obtained at the Cibao Basin could be expected for the SPB. 408 Petrophysics has been studied individually for each Unit by the analysis of well logs data in order to obtain the following parameters (see Section 3.5).  Gross thickness: The measured thickness from the top of the Unit to the base, including intervening non-reservoir lithologies.  Net thickness: The measured thickness of limestones or sandstones with reservoir prop- erties (gross thickness minus thickness of shale and other intervening lithologies). May also indicate total thickness of porous sandstones of limestones, in which case, a cut-off porosity must be given.  Net/Gross: Net thickness divided by the gross thickness, expressed as a decimal. Volume of shale and porosities have been calculated through gamma ray (GR) values and density logs. As permeability values are limited, spontaneous potential (SP) has been selected as an indi- cator of it, constraining the results to the intervals where SP points out fair to good permeabilities. 5.5.1 Unit E1 Eocene Limestones of Unit E1 were reached at the wells Candelon #1 and Punta Salinas #1, se- lecting Candelon #1 as the type well for this Unit. This interval is composed of micritic lime- stones, dominated by planktonic foraminifera, containing silt sized and coarser carbonate materi- als such as reef derived fragments. Unit E1 is interpreted as deposited in deep water environment, where coarser intervals might indicate the presence of carbonate submarine fans, closer to a major channel (Robertson, 1984). Evidence of fractures is often noted on the microscopic examination of cuttings. The results of the petrophysics analysis for Unit E1 at the well Candelon #1 are represented in figure 5.5.2. Porosity cut-off was settled to 8 %, volume of shale to 40% and SP at the middle value between shale line and SSP (-25 API). According to this criterion, this Unit is defined by the following parameters:  Gross thickness: 561 m.  Net thickness: 75 m.  Net/Gross: 0.13. Two intervals of 78 and 19 m were selected on account of their properties (figure 5.5.2). Porosities of interval 1 range from 0.1 to 28 % with an average porosity of 15% and in the case of interval 2, from 1 to 28% with an average of 14%. Net/gross ratios improve to 0.40 for interval 1 and 0.85 for interval 2. Nevertheless, this Unit was tested from 3495 to 3509 m (corresponding to the in- terval 1) resulting to be tight carbonates (see Section 5.3.8), although the information of the DST is limited. In this sense, although logs of Unit E1 indicates the presence of fair porosity intervals, it should be considered as tight reservoirs. The implication of this unit into highly deformed areas could have favour the development of permeability. However, in terms of reservoir, Unit E1 should be consider as a high-risk reservoir. Middle Eocene Carbonates are present in outcrops and exploration wells of Cordillera Central, Neiba, Bahoruco, San Cristobal and Cordillera Septentrional (figure 5.5.2; Candelon #1 well re- port, 1982; Heubeck and Mann, 1991; Punta Salinas #1 well report, 1991; Hernáiz-Huerta et al., 2000; Hernáiz-Huerta, 2006; Mann et al., 2008; Abad et al., 2010 a, Zoeten and Mann, 1999). 409 Figure 5.5.2, Well logs corresponding to Unit E1 at the well Candelon #1, selected as the type well for this Unit. The graphics correspond to the petrophysical analysis of Unit E1 carried out to determine the net thickness of the Unit. 410 5.5.2 Unit O2 According to the correlation established in this work, Unit O2 was reached at Charco Largo #1, Candelon #1 Caño Azul #1, San Francisco Reef #1, Licey#1 and Villa Isabel #1. The type well selected has been Caño Azul #1. Although the upper part consisted of hard limestones and well cemented sandstones, this unit is characterized by the presence of unconsolidated sands and lime- stones (figure 5.5.3). The alternation of unconsolidated levels with consolidated sandstones and dense limestones confer a chaotic character to the calliper. This seems to have an impact on den- sity log quality. To evaluate the effect on porosity, neutron density has been evaluated together with density porosity. Figure 5.5.3, Examples of outcrops of Unit O2 at the Cibao Basin from Escuder-Viruete et al. (2010). The results of the petrophysics analysis for Unit O2 at the well Caño Azul #1 are represented on figure 5.5.4. With a porosity cut-off settled at 8% (considering neutron and density porosities), the volume of shale to 40% and SP at the middle value between shale line and SSP (-5 API), the following parameters were calculated:  Gross thickness: 105 m.  Net thickness: 87 m.  Net/Gross: 0.83. It should be noted that the petrophysical information of this interval is limited. There is no data available regarding to permeabilities and porosities from well cores. Average porosity for reser- voir intervals is as high as ~30% (ranging from 6 to 40%). Nevertheless, the bad hole conditions consequence of the lithological characteristics of this unit could have influenced the register. This effect has a lower impact on the neutron porosity log, obtaining a similar average porosity of ~30%. However, there is no information about the matrix calibration, and this value should be taken carefully. 411 Figure 5.5.4, Well logs corresponding to Unit O2 at the well Caño Azul #1, selected as the type well for this Unit. The graphics correspond to the petrophysical analysis of Unit O2 carried out to determine the net thickness. 412 This unit was the primary objective at Caño Azul #1 at 822 m. No test could be carried out at this zone due to blow-out preventers had to be activated when high pressure sulphurous water was ejected from this level. The liquids contained at this unit caused damages in uphole sections. Oligocene limestones and sandstones like those of Unit O2 are present in outcrops and exploration wells of Bahoruco, Enriquillo, Azua – San Juan, San Cristóbal, Cibao and Cordillera Septentrio- nal (figure 5.5.4; Pérez-Varela et al., 2010 a; Charco Largo #1 well report, 1981; Maleno DT1 well report, 1960; Biju-Duval et al., 1982; Abal et al., 2010; Caño Azul executive summary, 2000; San Francisco Reef well report, 1995; Zoeten and Mann, 1999). 5.5.3 Unit N1.1 Unit N1.1 was reached at the wells Maleno DT1 and Caño Azul #1. At Maleno DT1, Unit N1.1 is composed of a series of white chalky limestones and cream, sucrosic and very fossiliferous limestones that include calcarenites and algal limestones, presenting pinpoint to small vugular porosities (Maleno DT-1 Drilling Steam Test operations report, 1981). At Caño Azul #1, samples are described as reef facies that consisted of white / cream to tan, hard, firm, with vugular poros- ities intervals (Caño Azul #1 executive summary, 2000; Caño Azul #1 mud logging report, 2000). The results of the petrophysics analysis for Unit N1.1 at the well Caño Azul #1 are represented on figure 5.5.5. Porosity cut-off was settled to 8 %, the volume of shale to 40% and SP at the middle value between shale line and SSP (-5 API), the following parameters have been calculated:  Gross thickness: 230 m, at Caño Azul #1.  Net thickness: 201 m, at Caño Azul #1.  Net/Gross: 0.88, at Caño Azul #1. Porosities of Unit N1.1 range from 10 to 34 %, with an average porosity of 26% obtained from the density log and of 31% from the neutron. However, it should be noted that the petrophysical information of this interval is limited as there is no data available regarding to permeabilities and porosities from well cores. 5.5.4 Unit N1.2 Unit N1.2 was reached at the wells Maleno DT1 and Caño Azul #1. At Maleno DT1, Unit N1.2 consisted of cream, dense, hard, crystalline limestones and white chalky limestones with minor cream fossiliferous limestones. It presented pinpoint and small vugular porosities (Maleno Dt1, well report, 1960). At Caño Azul #1, this unit consisted of white to cream, chalky, fossiliferous limestones (Caño Azul executive summary, 2000). The results of the petrophysics analysis for Unit N1.2 at the well Caño Azul #1 are represented on figure 5.5.5. Porosity cut-off was settled to 8 %, the volume of shale to 40% and SP at the middle value between shale line and SSP (-5 API), the following parameters have been calculated:  Gross thickness: 55 m, at Caño Azul #1.  Net thickness: 19 m, at Caño Azul #1.  Net/Gross: 0.35, at Caño Azul #1. 413 Porosities range from 4 to 24 %, with an average porosity of 13% obtained from the density log and of 25% from the neutron. However, it should be noted that the petrophysical information of this interval is limited as there is no data available regarding to permeabilities and porosities from well cores. 5.5.5 Unit N1.3 Unit N1.3 was reached at Maleno DT1 and Caño Azul #1. At Maleno DT1, Unit N1.3 consisted of grey, fractured, sucrosic to slight chalky, fossiliferous limestones (Maleno DT1 well report, 1960). The results of the petrophysics analysis for Unit N1.3 at the well Caño Azul #1 are represented on figure 5.5.5. Porosity cut-off was settled to 8 %, the volume of shale to 40% and SP at the middle value between shale line and SSP (-5 API), the following parameters have been calculated:  Gross thickness: 60 m.  Net thickness: 32 m.  Net/Gross: 0.53. Porosities range from 6 to 40 %, with an average porosity of 24% obtained from the density log and of 32% from the neutron. However, it should be noted that the petrophysical information of this interval is limited as there is no data available regarding to permeabilities and porosities from well cores. Miocene limestones produced water with oil and gas shows at Maleno DT-1 having vuggy poros- ities and fractures. Their potential as reservoir has been verified in other wells in Azua such as at Maleno #1, Maleno #2, Maleno #7 that had a water blowout occurred from vugular and cavernous porosity. The estimated average porosity of the shallow marine lower Miocene limestones in Azua is estimated on 12 % from wireline logs (Munthe, 1996). At Caño Azul #1, DST #3 to DST #8 tested Unit N1.1. Although initially all of them produced sulphurous water, DST #3 (from 488 to 491 m), #4 (from 465 to 469 m) and #5 (from 456 to 458 m) turned into salt water with gas in solution. Neogene limestones similar to those of Unit N1 are present in outcrops and exploration wells of Bahoruco, Enriquillo, Neiba, Azua – San Juan, San Cristóbal, Cibao and Cordillera Septentrional (figure 5.5.5; Pérez-Varela et al., 2010 a; Charco Largo well report, 1981; Hernáiz Huerta, 2006, 2004; Maleno DT1 well report, 1960; Mann et al., 1991 a; Biju-Duval et al., 1982; Caño Azul executive summary, 2000, Zoeten and Mann, 1999; Escuder-Viruete et al., 2010, Abad et al., 2010 a and c). 414 Figure 5.5.5, Well logs corresponding to the different sub-units of Unit N1 at the well Caño Azul #1, selected as the type well for this interval. The graphics correspond to the petrophysical anal- ysis of Unit N1 carried to determine the net thickness. 415 5.5.6 Sub-unit N5 Unit N5 was reached at the wells Candelon #1, San Francisco Reef #1, Licey #1 and Villa Isabel #1. The type well selected in this work is San Francisco Reef #1. There, Unit N5 consisted of sandstones, siltstones and occasionally limestones with layers of coal. The results of the petrophysics analysis for Unit N5 at the well San Francisco Reef #1 are repre- sented on figure 5.5.7. Porosity cut-off was settled to 8 %, the volume of shale to 40% and spon- taneous potential at the middle value between shale line and SSP (-50 API), the following param- eters have been calculated:  Gross thickness: 347 m.  Net thickness: 45.6 m.  Net/Gross: 0.13. Two intervals of 35 and 84 m were selected on account of their properties (figure 5.5.7). Porosities of interval 1 range from 4 to 24 % with an average porosity of 15% and in the case of interval 2, from 5 to 24% with an average of 16%. Net/gross ratios improve to 0.16 for interval 1 and 0.44 for interval 2. Despite these good reservoir intervals, quartz content might represent an issue in Hispaniola that must be addressed. Figure 5.5.6 represents QFL triangular diagrams for different basins in Hispaniola. Despite quartz content increases since the Late Cretaceous to the Miocene, it remains generally low. Further analysis for the Miocene sequence at the vicinity of San Pedro Basin must be carried out to determine the reservoir potential of Neogene clastics. Neogene sandstones intervals similar to those belonging to Unit N5 have been described in out- crops and exploration wells of Azua – San Juan, San Cristóbal, Cibao and Cordillera Septentrional (figure 5.5.7; Candelon #1 well report, Biju-Duval et al., 1982; Heubeck et al., 1991; San Fran- cisco Reef mud logging report, 1995; Licey mud logging report, 1958; Villa Isabel mud logging report, 1958). Figure 5.5.6, QFL triangular diagrams from samples of Llanura Oriental, San Cristobal Basin and Cibao Basin. Modified from García-Senz et al., 2007 b; Heubeck et al., 1991; De Zoeten and Mann, 1999. 416 Figure 5.5.7, Well logs corresponding to Unit N5 at the well San Francisco Reef #1, selected as the type well for this Unit. The graphics correspond to the petrophysical analysis of Unit N5 carried out to determine the net thickness. 417 5.5.7 Reservoir summary Petrophysical analysis have demonstrated the presence of good reservoir intervals for the period Eocene – Miocene, corresponding to Units interpreted in the SPB (table 5.5.1). Among the pro- posed intervals, the Oligocene to Miocene record, corresponding to an interpreted carbonate ramp system, could be considered as the best candidate to constitute the reservoir of a petroleum sys- tem. This interval owns the higher porosities and net /gross ratios. In addition, the Neogene sand- stones belonged to Unit N5 might be considered also as potential reservoirs. Nevertheless, the quartz content might represent an issue and further studies must address it. On the other hand, despite of the identification of potential reservoir intervals, DSTs results indi- cate that Unit E1 is composed of tight carbonates. It should be noted that the wells that reached this interval, Candelon and Punta Salinas, were located at positions were deep-water carbonates are expected. In the case of the well Candelon #1, drilled at the Oceanic – Caribbean Domain, Paleogene proximal facies are expected only at the Bahoruco massif (see Section 4.5.3). This is also the case of the well Punta Salinas #1, drilled at the Cretaceous – Eocene Basin Domain. The seismic facies analysis determine that proximal facies would occupy a position constraint to the Island Arc Domain, while for the Cretaceous – Eocene Basin Domain, Eocene sequences would be represented only by deep-water deposits (see Section 4.7.2). Table 5.5.1, summary of petrophysical information for potential reservoirs in Hispaniola. These values come from the type wells: Candelon #1 for Unit E1, Caño Azul #1 for Units O2 and N1; and San Francisco Reef #1 for Unit N5. 418 Section 5.6: Seal The post-mortem evaluation (Section 5.3) determines the seal capacity of Units O1/O2, N2 and N3. The study of unconformities and the seismic facies analysis prognosed the presence of Units O1/O2 and N2 in the basin (figure 5.6.1; see Sections 4.7.1 and 4.7.2 for more information re- garding the interpretation of units in the SPB). These units are represented by high-amplitude and laterally continuous reflectors which are interpreted as distal deposits composed of shales and marls. With the information available, it is not possible to determine the seal capacity of this units in the basin, nor the integrity. The only indicator could be the presence of certain amplitude anom- alies at the central segment of the basin, which seem to be confined by different levels of Unit N2 (figure 5.6.1). Outcrops from other units could be considered as potential seals, such as the shales belonged to Unit E3 (the El Número Formation). Nevertheless, the seal capacity of these units has not been demonstrated and further studies must address their potential. Figure 5.6.1, Details of the seismic lines SD5, above, and SD6, below (TWT). High amplitude and lateral continuously seismic facies are interpreted as distal deposits with seal capacities. Amplitude anomalies are confined between different levels of Unit N2. 419 Section 5.7: Trap A trap consists of a geometric arrangement of permeable (reservoir) and less-permeable (seal) rocks which, when combined with the physical and chemical properties of subsurface fluids can allow hydrocarbons to accumulate. Three main trapping elements comprise every subsurface hy- drocarbon accumulation (Vincelette et al., 1999): 1. Trap reservoir: storage for accumulating hydrocarbons and can transmit hydrocarbons. 2. Trap seal: an impediment or barrier that interferes with hydrocarbon migration from the reservoir. 3. Trap fluids: physical and chemical contrasts—especially differences in miscibility, solu- bility, and density—between the common reservoir fluids (primarily water, gas, and oil) that allow hydrocarbons to migrate, segregate, and concentrate in the sealed reservoir They could be classified into two trap systems following the definitions given by the same authors (Vincelette et al., 1999).  Structural: Post- or syn-depositional deformation or displacement of reservoir and/or sealing units.  Stratigraphic: Depositional, erosional, or diagenetic configuration of reservoir and/or sealing units. To characterise a trap, it is necessary to identify the trap closure. Vincelette et al., 1999 defines it as “a measure of the potential storage capacity or size of the trap defined by the trap boundaries. Vertical closure is a measure of the maximum potential hydrocarbon column of the trap. Areal closure is a measure of the maximum area of the potential hydrocarbon accumulation within the trap boundaries. Volumetric closure integrates vertical and areal closure with pay thickness, po- rosity, and hydrocarbon saturation to provide the volume of the potential hydrocarbon accumula- tion within the trap boundaries”. As a consequence of the complex evolution of the SPB, a wide variety of potential traps have been interpreted in the basin, including structural and stratigraphic traps which have been gathered into diverse groups. Structural traps have been grouped on account of their origin and will be presented in this section individually. As it was explained in Section 4.7.3, the structures of the basin can be separated into compressional and shearing structures. Compression dominates the frontal and the rear thrust system, while shearing is constrained to the backstop, which represent the Island Arc Domain (figure 5.5.9). The main traps that can be identified on seismic profiles associated to the compression at the rear zone of the MTB would include thrusts and fault related anticlines. On the other hand, the backstop is represented by transpressive structures, which could have evolved from former compressional structures since the Oligocene (see Section 4.7.3). In addition, normal faults present in the basin would have accommodated part of the deformation, especially at the Saona Fault Zone (located in figures 5.4.10 C to G). Stratigraphic traps are composed of two main trap systems. The first is associated to the evolution of a carbonate ramp system in a similar way than interpreted for the well Caño Azul #1 (see Section 5.3.4) and the second would include the pinch outs of younger sequences against inverted sections of the basin. 420 Figure 5.7.1, Overview of the different structures and stratigraphic features that could have been involved in the generation of traps. These systems comprise the compressive (1), shearing (2) and accommodation (3) faults involved in deformation of the basin or the stratigraphic record (4) that includes the evolution of a carbonate ramp system and the onlap over former strata. 5.7.1 Structural traps associated to compression. The workflow and formal definition and classification of traps is based on the criterion given in Vincelette et al. (1999) where structural traps are subdivided into the following trap systems:  Fold Traps: A fold trap is formed by syn- or post-depositional processes that deform geological surfaces into a curved or nonplanar arrangement (Biddle and Weilchowsky, 1995).  Fault Traps: Fault(s) forms part or all of the closure of the trap by sealing the reservoir either laterally and/or from the top (after Biddle and Wielchowsky, 1995).  Fracture Traps: Trap in which lateral boundaries of the trap are provided by change from fractured reservoir to unfractured or less fractured rock or by change from open, permeable fractures to cement-filled or narrow-aperture, low-permeability fractures. The proposed classification scheme places traps into four ranked levels, from general to specific: 1, System; 2, Regime; 3, Class (Superclass if necessary); 3.a, Subclass; 3.b, Style (if necessary); 4, Family (Superfamily if necessary); 4.a, Subfamily; 4.b, Variety (if necessary). The structural traps associated to compression are associated to the development of a thrust and folds belt, the MTB. Unfortunately, the seismic resolution and coverage at this zone of the basin is limited. Only the seismic line SD5 (figure 5.7.1) crosses the belt completely with enough pen- etration to discern structures. At the same time, the seismic grid available does not allow to de- termine the vertical and areal closure of structures. Nevertheless, the information provided by available data provides a good approach to the potential traps that could be present and with the information derived from the interpretation of the basin, it is possible to determine the age of the different traps. 421 Formal classification of Compressional Group 1: Structural; Regime: fold; Class: local anticline; Superfamily: Tectonic; Family: Compressional; Subfamily: Thrust-belt fold. Age: Late Eocene – Miocene. This classification is applied to the group of traps encloses at the rear thrust system of the MTB (figure 5.7.2). Their origin is a direct consequence of the development and growing of a thin-skin thrust belt. The result is a trend of folds with an average wavelength of 7 km. However, due to their own particularities, this system could be subdivided into three sub-groups. Sub-groups 1 and 2 occupied the folds zone of the belt and sub-group 3 the thrust zone, according to the division stablished in Section 4.7.3, based on the classification given in Hernaiz-Huerta (2006). Sud-group 1 includes the structures resulted from the evolution of the interpreted SJRFZ (San José – Restauración Fault Zone). Onshore, the age of this fault system is constrained to the late Eocene (e.g. Pérez-Varela et al., 2010 a) based on a differential sedimentation at both sides of the fault zone for this period. This system would have registered the initiation of the deformation in the area, after an effective transmission of the compressional stressed to the south after the colli- sion of the arc with the Bahamas Banks (Granja-Bruña, 2008; Granja-Bruña et al., 2014). The result is the formation of two faulted anticlines, with half-wavelengths of 2 and 6 km, which comprise Oligocene and older sedimentary sequences. As lower Miocene sediments fossilised the structure, their age is constrained to the period late Eocene – early Miocene. Sub-group 2 include a trend of wide folds resulted from the deformation at the lower part. On- shore, folds are constituted by upper Eocene and Oligocene sedimentary rocks (Heubeck and Mann, 1991; Abad et al., 2010 a). Despite of the limited resolution of the seismic, it is possible to infer that thrust and duplexes of the belt are behind the origin of these folds (figure 5.7.2). Regarding the timing, the unique precision with the available data is late Eocene to early Miocene, and further work should address the tectonic evolution of the belt to constrain the age. Finally, sub-group 3 is composed of an imbricate system which include middle Eocene and older sediments that are covered by Miocene deposits. Nevertheless, burial could represent an issue for this system and should be considered as a potential risk. The available seismic grid does not allow to characterise these traps and further seismic surveys must determine their closures. Hypothetical prospects would include Units E1 and O2 acting as reservoirs and shales from Units O1/2 and N2 as the regional seals. Figure 5.7.2, Interpretation given for the Muertos Thrust Belt over profile SD5 (location in figure 5.7.1) and potential structural traps identified. 422 Formal classification of Compressional Group 2: Structural; Regime: fold; Class: regional anti- cline; Superfamily: Tectonic; Family: Compressional; Subfamily: Thrust-belt fold. Age: Late Oligocene / early Miocene to present. This group corresponds to broad and elongated fault related folds generated at the rear zone of the Muertos Thrust Belt (figure 5.7.3). Their origin is a combination of the compressional stresses transferred from the north and the development of the thrust belt. Gravity models for this structure reveals that no basement unit is implicated, being its origin on account of the sedimentary rocks’ deformation. Internal faults accommodate the deformation while the pinch-outs are a consequence of the progressive syn-sedimentary growing of the thrust belt. This last group will be explained in Section 5.7.4. In a geodynamic context, this fold system is related to the development and growing of the Muertos Thrust Belt which was initiated at middle / late Eocene times with the inversion of the Cretaceous – Eocene Basin Domain and has continued to present time. The origin is related to the transfer of compressional stresses from the north, due to the collision with the Bahamas Banks, and the presence of the Beata Ridge at the south. According to the reconstruction carried out for the basin (see Section 4.7.3), these traps started at a point between the late Oligo- cene and the early Miocene, where the middle Miocene flattening revealed the presence of an anticline deforming Eocene to Oligocene sequences. Deformation has remained active until Pre- sent, deforming the current seabed. A hypothetical prospect would include Units E1, O2 and N5 acting as reservoirs and shales from Units O2 and N2 as regional seals for both structure styles. Figure 5.7.3, Section of the seismic line WGC 08 interpreted. Note the progressive pinch outs of the Oligocene and Miocene record over the previous sequence. 423 5.7.2 Structural traps associated to shearing Formal classification of Shearing Group 1: Structural; Regime: fold; Class: regional anticline; Superfamily: Tectonic; Family: Transpressional; Subfamily: Inverted structure. Age: Oligocene – Miocene. Under this classification, a series of transpressional structures, which affect to the basement and the Cretaceous and Paleogene sedimentary cover, have been grouped. Their location corresponds to the island Arc Domain. However, the seismic resolution for the lower units and the irregular grid available in the basin does not allow to define their closure. Under the evolution model proposed in this work, these traps would have been created in two main deformation stages. The first was dominated by compression, generating first order faults that affected the basement since the Campanian, folding the Cretaceous sequence and resulting in structural highs. After that, in a second stage, the island arc basement would have accommodated the shearing stress, propitiating the development of transpressive structures since the Oligocene – early Miocene. This latter stage generated the final geometry of the potential traps, possibly destroying traps created during the first stage, reason to consider only the latter as potential traps. The interpretation of magnetic anomalies (discussed in Section 4.7.3) reveals the counter-clock- wise rotation and eastward tectonic escape of crustal blocks together with the presence of a left- lateral strike-slip faults. On seismic profiles (figure 5.7.4), these tectonic features are interpreted as transpressive structures that inverted sections of the basement of the basin, resulting in a dis- position of elevated blocks. Oligocene and middle Miocene flattening sections reveal the initia- tion of this deformation at the back-stop zone for this interval, comprising the basement (volcanic and metamorphic units) of the Island Arc Domain and part of the Paleogene cover. Figure 5.7.4, Interpretation of crustal-scale structures on seismic profiles at the Island Arc Do- main. Elevated sections of the basement are the result of a transpressive regime that led to a disposition of rotated blocks controlled by the main left-lateral strike-slip fault systems. 424 Hypothetical prospects that include these traps should consider Unit E1 and fractures that involve the basement and the Cretaceous units as the main reservoir. Cretaceous basement units have been tested at the Jatibonico oil field in Central Cuba. This oil field is emplacement at a basement structural high composed of Cretaceous island arc materials (Cruz-Osora et al., 2012 a,b; Gómez- García and Prol, 2001; Bandt, 1958). However, it should be considered that the integrity of any potential seal for these ages must have been destroyed owing to the high tectonism, and an effec- tive seal was not provided until the deposition of shales from Units O2 and N2. Formal classification of Shearing Group 2: Structural; Regime: fold; Class: regional anticline; Superfamily: Tectonic; Family: Transpressional; Subfamily: Inverted structure. Age: Lower? – middle Miocene. Although traps associated to the Saona Fault Zone would belong to the same regime that the previous group, they have been separated owing to the entity of this system. They are interpreted as 4-way dip traps that comprise materials from the Upper Cretaceous to the Miocene. However, the available seismic grid does not allow to quantify the resulted closures. The origin of this groups lies in a transpressive structure interpreted on seismic profiles (5.7.5), having affected the basement of the island arc, leading to a limited displacement of the southern blocks under a transpressional regime. Consequently, sedimentary sequences above have been inverted, with an estimated uplift of at least 800 ms TWT, having its surface expression along the Saona escarpment. This system is interpreted in this work as a secondary structure that accom- modates part of the share between the main faults that affected the Island Arc Domain (the His- paniola and Bonao Fault Zones). The transpressive uplift generated by the action of the STFZ seems to have started at middle Miocene, as the onlap of upper Miocene sediments against the structure indicates. The resulting uplift seems to have triggered an asymmetric gravity-driven normal fault system that accommodate the deformation to both sides of the structure, described in next section. Figure 5.7.5, Interpretation given for the Saona Fault Zone. The growing of this transpressive structure (in red) triggered the accommodation of deformation along normal faults (in black). 425 5.7.3 Structural traps associated to accommodation of deformation Formal classification of Accommodation Traps: Structural; Regime: fault trap; Class: normal fault; Subclass: tilted fault block; Superfamily: Tectonic; Family: Extensional; Subfamily: Growth fault. Age: Middle Miocene. Traps Group 5 represented a series of normal faults presented at the backstop part of the Muertos Thrust Belt confined to the eastern part of the San Pedro Basin. These faults are interpreted to be part of a gravity-driven system that sole into a low-angle basal detachment. Under the interpreta- tion proposed for this system, the initiation of the normal-faulting system is constrained to the middle – late Miocene, having continued until Present. While at the northern side of the SAFZ, normal faults occupied an extension of 5 km, to the south the system extends up to 30 km. Reservoirs of a hypothetical prospects would be represented by Units E1 and O2, and N1/N5 while shale deposits from Units O1/2 and N2 would be the seal. Figure 5.7.6, Interpretation given for the gravity driven system generated by the action of the Saona Fault Zone. The growing of this transpressive structure has triggered the accommodation of deformation along normal faults. 426 5.7.4 Stratigraphic traps The geological controls for stratigraphic system traps are stratigraphic in nature and formed as a result of depositional, erosional, or diagenetic processes. These processes are the basis for the three regimes of the stratigraphic system (Vincelette et al., 1999). In the case of the San Pedro Basin, stratigraphic traps belong to the depositional regime. Traps in the depositional regime are formed primarily by processes that created facies changes between reservoir and seal-quality rocks. Besides deposition by sedimentary processes, this regime also includes deposition by igneous processes (Vincelette et al., 1999). Formal classification of Stratigraphic Group 1: Stratigraphic; Regime: Depositional; Class: Dep- ositional pinch-outs; Subclass: Regional sandstones and carbonate pinch-outs; Superfamily: Ma- rine pinch-outs; Reservoir variety: Deep marine; Seal variety: Turbidite. Age: Oligocene – Miocene. The origin of the pinch-outs from Stratigraphic Group 1 lies in the progressive inversion of the Cretaceous to Eocene sedimentary sequence due to the development and growing of the Muertos Thrust Belt, which allowed the on-lap of younger units. There are 3 main zones of pinch out (figure 5.7.7 A). The first one involves the basinwards onlap of the upper Eocene – Oligocene sequence that onlap against a thrust sheet composed of deep- water Cretaceous to Eocene sedimentary rocks. The second comprises the landwards onlap of the same sequence against a structural high. Finally, the third zone includes the onlap of Miocene deposits against the norther flank of the syn-tectonic early Miocene fold. Reservoirs could be represented by the Units O2 and N1/5 and seal by the sales present in Units O1/2 and N2. Formal classification of Stratigraphic Group 2: Stratigraphic; Regime: Depositional; Class: Dep- ositional relief; Subclass: Carbonate; Superfamily: Marine carbonate reservoirs; Family: Bio- herms; Subfamily: Platform reefs. Age: Lower to middle Miocene. Under the interpretation proposed in Section 4.7.4 for the Oligocene to middle Miocene sequence, based on the seismic facies analysis, the transgression of the carbonate ramp led to a back-step- ping architecture of the system. This evolution has the peculiarity that the distal part of the younger parasequences cover the proximal series of the previous parasequence. Therefore, prox- imal facies with good reservoir properties are covered and sealed by shales and tight limestones (distal facies), generating an effective stratigraphic trap (figure 5.7.7 B). As it was exposed for the reservoir (Section 5.5), these deposits have been tested as good reser- voirs at the exploration wells Caño Azul #1 and San Francisco Reef #1. The trap system was also tested in Caño Azul #1, where overpressure sulphur water was encounter at Unit O2 and non- commercial accumulations of gas and formation fluids at the reef limestones of Unit N1. The reservoirs for this system are the Units O2 and N1.1/1.3 while the seals correspond with shales of the Units O1/O2 and N2 and tight limestones of Unit N1.2. 427 Figure 5.7.7, A, Interpretation given for the seismic line SD6 in depth domain. Note the progres- sive onlap of Oligocene and Miocene deposits over previous sequences, corresponding to the Stratigraphic Group 1. B, Back-stepping architecture of carbonate ramp system that configures the Stratigraphic Group 2. Black horizons represent distal facies characterized by high amplitude reflectors. A tentative analogue of this kind of trap could be the Oligocene to Miocene carbonates of the Perla field in Venezuela. Figure 5.7.8 represents the conceptual model for the deposition of car- bonates at Perla (Pomar et al., 2015). According to Pomar et al., 2015: “The approximately 300- m (984.2 ft)-thick Oligo–Miocene carbonates of the Perla field consist of an overall deepening- upward sequence predominantly composed of larger benthic foraminifera and red algae (oligo- photic production) with a minor contribution from shallow water (euphotic) carbonate compo- nents (green algae and corals). Deposited in a context of tectonic subsidence, the building blocks progressively onlapped with backstepping configuration onto a paleo island”. Figure 5.7.8, Conceptual model for deposition of the main reservoirs at the Perla Field, from Pomar et al. (2015). 428 Section 5.8: Timing and preservation The results of the post-mortem evaluation bring to light the two main risks for a successful ex- ploration in Hispaniola Island: a mature source rock and the timing. According to this work, the presence of a mature source rock does not represent a risk for the San Pedro Basin (see Section 5.4). The maturation of a potential Cretaceous source rock should be granted (figure 5.8.1) and the risk is associated to the kerogen type. On the other hand, the Oligocene would have started the generation in the late Miocene – Pliocene. Nevertheless, it should be contemplated that cal- culations were carried out considering a constant heat flow based on the Present geothermal gra- dient. In addition, the identification of an organic-rich interval for the upper Eocene could open new doors and further analysis must determine the real potential of the Eocene. Considering this, the main exploration risk in the basin would be the timing for the remaining elements of the play and the traps creation and preservation. Figure 5.8.1, Evaluation of the petroleum system for the San Pedro Basin. The best reservoir intervals are limited to the period Oligocene to early Miocene, composed of Oligocene sandstones and limestones (Unit O2) and lower to middle Miocene carbonates (Unit N1). Other intervals, like the corresponding to the middle Eocene limestones, have not been proved. Unit E1, reached at the wells PS-1 and CAN-1, consisted of deep-water tight limestones. Nevertheless, the seismic facies analysis (Section 4.7.2) prognosed the presence of shallow water carbonates deposited over structural highs at the Island Arc Domain. This could fit with observa- tions in outcrops at the San Cristóbal region (e.g. Biju-Duval et al., 1982) and further studies must explore their reservoir properties. Regarding the seal, exploration wells demonstrated the seal capacity of Oligocene and Miocene shales and tight carbonates. This might represent an issue since their deposition is close to the hypothetical generation of hydrocarbons in the basin prognosed in this work. Finally, the high grade of tectonism suffered by the region not only have propitiated the creation of a wide variety of traps but also represents a preservation issue (figure 5.8.2). In this sense, traps created before the middle – late Eocene event have not been considered because structures impli- cated in the creation of traps would have been reactivated in further events. Based on these results, the Critical Point of the petroleum system is emplaced at the early – middle Miocene, when the main elements of the play are present in the basin, coinciding with the devel- opment of stratigraphic traps and the generation of hydrocarbons. 429 Figure 5.8.2, Synthetic column for the San Pedro Basin with the major regional events and the elements of the petroleum system. 430 Section 5.9: Summary Despite the demonstrated generation of oil on the island, confirmed by the limited production in Azua, the widespread oil and gas shown in exploration wells and the identification of the main elements of the petroleum system, the success rates are limited to two abandoned fields with a cumulative production of ~45000 bbl. In order to get a realistic perspective of the exploration opportunities in the SPB, the risk associated to each element of the petroleum system interpreted in the basin has been analysed (figure 5.9.1), providing an overview of the further works that could improve the numbers and the best plays that should be considered. Figure 5.9.1, Schematic cartoon for the main elements of the petroleum system proposed in this work for the San Pedro Basin. Source rock Three different intervals have been identified with a source rock potential:  Upper Cretaceous, Type II and III  Oligocene, Type III  Miocene, Type II and III According to the basin modelling proposed in this work, the Upper Cretaceous would have reached the main generation window for a period between the early and the middle Miocene. Although the recognition of organic-rich intervals points in the right direction, the presence in the basin is only prognosed by models, leading to an associated risk of 60%. Under the assumptions considered in this work, the Oligocene would be entering into the oil gen- eration window in recent times and the burial would not be enough for a type III kerogen. This interval should be considered for biogenic gas, representing an associated risk of 50%. Finally, Miocene potential source rocks present in the basin are interpreted to be immature, rep- resenting the highest risk of 40%. 431 In order to reduce the exploration risk associated to source rock, field work is required to sample potential intervals not studied in this work, such as the formations deposited in the Cretaceous – Eocene basin (e.g. the Trois Rivieres Formation). In addition, rock-eval analysis of the Upper Cretaceous and the Eocene are essential to determine their real potential. Reservoir Petrophysics reveals the presence of good reservoirs for the intervals:  Middle Eocene (limestones, Unit E1).  Oligocene (sandstones and limestones, Unit O2).  Miocene (limestones, Unit N1, and sandstones, Unit N5). Except for Unit E1, all of them were tested positively, producing formation waters during DSTs together with slight oil and gas shows. Since the seismic facies analysis prognose their presence in the basin, the associated risk is 70%. Seal The seal capacities of three intervals have been proven in exploration wells:  Oligocene shales (Unit O1 and O2).  Miocene shales and marls (Units N1 and N2).  Miocene evaporites (Unit N3). According to the interpretation of the basin only Units O1/O2 and N1/N2 would be present in the basin. Both, Oligocene and Miocene shales and marls have been tested in exploration wells and were deposited regionally. Consequently, and despite the lack of seismic data with a good reso- lution that allows confirming their integrity, the associated risk to the seal is set at 70%. Traps Although different events, corresponding to the main unconformities localized in the basin, might have created effective traps, only those generated after the middle – late Eocene are considered owing to their preservation. At the same time, the available seismic data does not allow to deter- mine the associated risk to any prospect in particular, only identifying conceptual traps. On ac- count of this, the risk associated to a structural trap is restrained to 50%. This number could be improved with a better seismic coverage that allows to determine the effectiveness of structural traps and their closure. On the other hand, the Oligocene – Miocene evolution of the carbonate ramp system might have favoured the creation of stratigraphic traps, similar to those tested in the Cibao Basin at the well Caño Azul #1. The associated risk to stratigraphic traps is 60%. Timing and migration The critical point for the petroleum system is emplaced at the early Miocene, coinciding with the formations of the main stratigraphic traps (which includes the best reservoir and seals) and the development of the main structural traps. This fact represents the greatest exploration risk as the 432 period of creation of traps is close to the main oil window. Therefore, the associated risk to timing is 50%. A better understanding of the reservoir properties and seal capacity of the Eocene sequences would help to reduce this associated risk. At the same time, an improved image from the subsur- face of the basin could improve the associated risk of timing providing a better control on the events and the resolution of these deeper sequences. Finally, the accumulations of oil discovered at the abandoned fields of Higuerito and Maleno were limited to recent traps (Pliocene to Present; see Section 5.3.7), while deeper structures resulted dry. This fact could be interpreted as a preservation issue and must be considered in future explo- ration activities, considering that the island is located in an tectonically active region. 433 Section 5.10: Conclusions and forward look of exploration activities The wells post-mortem evaluation has resulted in a useful tool to determine the main regional elements of the petroleum system that can be expected in the basin. This information integrated with the interpretation of the basin proposed in Section 4.7 has led to identify the main elements of the petroleum system in the SPB. This work prognoses the presence of three potential source rocks in the basin, good reservoir intervals for the Oligocene and Miocene and the deposition of regional seals for the same period of time. In addition, potential traps have been dated thanks to the evolution model proposed in Section 4.7.3. All this information led to propose an exploration risk of 9% for the basin. While this number could be considered low, before the new constrains provided in this work, the exploration risk would be non-existing. It should be noted that the latest interpretation of the basin considered it to be a Neogene basin. Furthermore, the margin can be reduced in the future with new studies that address the following key points: First of all, the most important point concerns the source rock. Geochemical data on Hispaniola Island is scarce and does not cover the whole sedimentary record. More information, especially regarding the Upper Cretaceous interval and its connection with samples of the Caribbean Plate (e.g. DSDP site 146/149), would reduce its associated risk substantially. Secondly, although the middle and upper Eocene sequences are well known in scientific literature (e.g. Hernaiz-Huerta, 2006), there is no information about their properties as elements of the pe- troleum system. More information regarding the shallower facies at the Island Arc Domain (for their reservoir properties) and the deepest sections (for source rock and seal potential) is required to better understand this interval. The incorporation of these elements into the petroleum system of the basin would reduce the associated risk of timing. Finally, new seismic surveys in the basin result essential to delineate potential traps and for a better understanding of the MTB-SPB system and their evolution. The seismic resolution that is currently available is fairly limited for the more deformed areas of the basin. Along the same lines, the seismic image of the deepest reflectors, such as the Upper Cretaceous sequences, is limited and do not allow discern between the sedimentary cover and the basement at some regions of the basin. This information would improve the knowledge about the tectonic and sedimentary evolution of the basin, allowing an improved basin modelling and reducing the risk of future exploration activities. 434 435 Chapter 6: Summary and conclusions 436 437 Section 6.1: The tectono-stratigraphic domains division In this work, a division of Hispaniola into four tectono-stratigraphic domains has been established as an alternative to others previously proposed in scientific literature (e.g. Mann et al., 1991 b). The purpose of this division is to simplify the resulting model as much as possible and to deter- mine new criteria that help in future exploration of the island. This division has been extended into the offshore SPB by the interpretation of potential fields, resulting in the following domains:  A Forearc – Collisional Domain (FACD) delimited by the Hispaniola Fault Zone to the south and the Northern Hispaniola Deformed Belt to the north. The basement is composed mainly of Mesozoic metamorphic complexes, overlaid by Cenozoic sedimentary se- quences.  The Island-arc Domain (IAD) is limited by the Hispaniola Fault Zone to the north and to the south, by the San José – Restauración Fault Zone for the western and central sectors of the island and by the Bonao Fault zone for the eastern sector. It is composed of Creta- ceous to Paleogene volcanic and volcaniclastic suites and Mesozoic metamorphic mate- rials.  The Cretaceous – Eocene Basin Domain (CEBD) would be delimited by the San José – Restauración and Bonao Fault Zones to the north and the San Juan – Los Pozos Fault Zone to the south. The thrust and folds belt, known as the Trois Rivieres – Peralta Belt, is interpreted in this work as an inverted back-foreland basin that developed between the Island arc and Oceanic Caribbean Domain from the Late Cretaceous (possibly Campa- nian) to the middle Eocene.  The Oceanic – Caribbean Domain (OCD) would comprise the region southwards the San Juan – Los Pozos Fault Zone, whose basement would be related to the Caribbean Plate. The established division has been used for the basement prediction of the SPB, which would occupy a position between the IAD and the CEBD. This prediction has been reinforced by the joint seismic interpretation of unconformities, seismic facies and the structural analysis of the basement. Firstly, the correlation of seismic facies and lithostratigraphic units seems to be consistent with those prognosed for each domain. Paleo-structural highs have been interpreted over the IAD, where shallower facies were deposited. This differential deposition could have important impli- cations for the hydrocarbon potential of the basin. Eocene limestones reached at the exploration wells PS-1 and CAN-1, drilled at the CEBD and the OCD, consisted of deep-water deposits with bad reservoir properties. However, shallower facies could be expected for the IAD, similar to those described at its onshore prolongation (e.g. Biju-Duval et al., 1982). In the same way, an Oligocene flooding over the IAD would have started the evolution of a carbonate ramp system. This evolution has been set in terms of the sequence stratigraphy, prognosing a general transgres- sion of the system, given by its back-stepping architecture, and interrupted in the early – middle Miocene by a secondary regression of the system. The potential karstification is connected to the development of cavernous porosities in the lower – middle Miocene limestones in Azua, and the transgression agrees with the interpretation of seismic profiles in the Cibao Basin or the strati- graphic columns in the southern region of Hispaniola. This system is not only relevant for the reservoir predictions but also for the creation of stratigraphic traps, owing to reef facies, which are prognosed as good reservoirs, would be covered by younger distal deposits, acting as the seal of the system. 438 To the south of the IAD, a deep-water sedimentation has been interpreted for the CEBD based on the seismic facies analysis. The Cretaceous sequences, tied to the exploration well San Pedro #1, are represented by high-amplitude and laterally-continuous reflectors with a low grade of defor- mation than for the IAD. This interval is correlated with the onshore Trois Rivieres (Ardèvol, 2004) and Las Palmas (Pérez-Varela et al., 2010 a; Abad et al., 2010 a) formations, corresponding with an alternation of Campanian to Maastrichtian shales and turbidites. Under the evolutionary model of the basin, these sediments would have been deposited over Turonian – Coniacian Car- ibbean deposits after the inversion of the IAD in a foreland setting. The identification of Creta- ceous potential source rocks in the onshore results determining the potential of the basin. Basin modelling results indicate that this level could have started the generation of hydrocarbons in the middle Miocene. Seismic facies of the upper Eocene to Oligocene sequence reveal the presence of disorganized deposits, close to the main fault zones, which have been correlated with the onshore olistoliths and conglomerates (Pérez-Varela et al., 2010 a; Abad et al., 2010 a, and references therein) a consequence of the inversion of the zone after the collision between the island and the Bahamas Banks in the middle Eocene. The final Miocene to present infill of the SPB corresponds to basin deposits, where sandy intervals have been prognosed by the facies analysis, connecting them to the middle Miocene sub-unit N5. These deposits have demonstrated the presence of good porosity intervals interbedded with shales and should be considered as potential elements of the petroleum system of the basin. 439 Section 6.2: The structure of the SPB The structural interpretation of the basin indicated a partitioned strain model for the SPB-MTB system. The accommodation of shearing took place between the Hispaniola and Bonao Fault zones, limits of the IAD, starting in the Oligocene – Lower Miocene, and generating the anti- clockwise rotation and elevation of crustal blocks and coinciding with the deformation observed also in southern Puerto Rico (Erikson and Pindell, 1991). This process could have accommodated the deformation derived from the aperture of Cayman and the eastwards tectonic escape of the Caribbean Plate. In the late Miocene, there is a change in the eastern sector of the basin with the appearance of the SAFZ, which generates the inversion and a left lateral displacement of the southern zone, possibly a consequence of a regional geodynamic change. Compressional forces are accommodated along the MTB through the inversion of the Cretaceous – Eocene Basin Domain. Following the same criteria as for onshore studies, the MTB has been divided into the thrusts, folds and monocline zones, revealing the same disposition and extension. The rear zone of the system would be comprised between the SJRFZ and the SJLPFZ, leading to correlate the Azua Basin with the frontal Thrust of the MTB. The configuration space for the SPB since the late Eocene has been controlled by the development of the MTB, and since the late Miocene by the SAFZ on the eastern sector of the basin. Both deformation systems could be implicated in the traps creation of the basin. However, alt- hough different events might have created effective traps, only those generated after the middle – late Eocene have been considered in this work owing to their preservation. At the same time, the available seismic data does not allow the determination of the closure of most of the structures and further surveys must address this subject. 440 Section 6.3: The evolutionary model of the SPB After the revision of the onshore geology, the main regional constrains that could have played a role in the SPB. The integration with the joint interpretation of the basin has led to propose a new evolutionary model which could be applied to the south-eastern margin of Hispaniola.  The development of a back-foreland basin in the retro-arc since Campanian times, a con- sequence of the inversion of the island arc.  The inversion of the Campanian – Eocene basin due to the collision of the island with the Bahamas Banks and an effective transmission of compressional forces to the south, start- ing the development of the MTB in the late Eocene.  Accommodation of shearing in the island arc domain as registered by the identification of rotated blocks in magnetic anomaly maps.  Transgression of carbonate platforms during the Oligocene and the early Miocene.  Middle Miocene unconformity derived from the indentation of the Beata Ridge.  Late Miocene unconformity as a consequence of the tilting of the basin and the exhuma- tion of the San Cristóbal region. The first application of this model to the exploration of the basin refers to the development of a Campanian to middle Eocene basin at the back-arc region over former Caribbean deposits. The immediate consequence is the possibility of finding potential Cretaceous source rocks in this zone, similar to those described in the onshore and samples from the Deep-Sea Drilling Project. Ac- cording to the maturity maps calculated with the geothermal gradient obtained for Hispaniola, the Cretaceous interval could have generated hydrocarbons since middle Miocene. Secondly, the development of thin-skin folds and a thrust belt, at the CEBD, and the transpres- sional structures, in the IAD, could have generated the necessary traps for the accumulation of hydrocarbons since the middle Eocene. The transgression of a carbonate ramp system could have been implicated in the creation of strat- igraphic traps, where reef facies are prognosed as good reservoir and distal deposits as the regional seal of the system. Finally, according to this model, the key factor for successful future exploration in the SPB is the timing, and further studies must address this subject to reduce the associated risk. 441 Section 6.4: Conclusions The integration of geological and geophysical data has allowed reinterpretation of the San Pedro Basin (SPB), providing a new evolutionary model that could have implications for future explo- ration. During the Late Cretaceous, inversion of the island arc basement resulted in deposition of Campanian–Maastrichtian sediments in a foreland setting (at the back-arc region) over Turonian– Coniacian Caribbean deposits. This inversion continued until middle Eocene times, when the in- itial stage of collision with the Bahamas Banks prompted inversion of the former Cretaceous– Eocene basin, with translation of compressional forces to the back-arc. This triggered the devel- opment of the Muertos Thrust Belt (MTB) and the current configuration of the SPB. A review of previous exploration work in Hispaniola has led to the identification of the main regional elements of the petroleum system. Three potential source rocks are postulated at the SPB, which involve Cretaceous, Oligocene and Miocene sections. Maturation maps indicate that a po- tential Cretaceous source could have started the generation of hydrocarbons in middle Miocene time, while the Oligocene levels would mature between the late Miocene and the Present. The Miocene section would remain immature. Good reservoir intervals are known and interpreted in the basin for the Eocene–Miocene section. Transgressive–regressive cycles might have favoured good reservoir intervals, as seen in the Maleno DT-1, Maleno #2, Maleno #7 and Caño Azul #1 wells. Oligocene shales, and the Miocene shales, marls and evaporite are known to provide seals onshore. However, only Oligocene and Miocene shales and marls are proposed in the basin. Moderate–high deformation of the area is likely to have generated different traps since Cretaceous times. However, trap preservation represents a main risk. Traps formed since the Oligocene–mid- dle Miocene are the primary objective. They are structural and stratigraphic and include internal stratigraphic traps within an interpreted carbonate system. However, limited seismic data does not allow the delineation of closures, and traps remain conceptual. Finally, the critical point of the petroleum system is emplaced in middle Miocene times, when the generation of hydrocarbons would have started, and the main traps were being created. While the main elements of a petroleum system seem to be present in the basin, timing is a key issue for any future exploration in the basin. At the same time, the preservation of the system must be cautiously considered as it could represent an exploration risk. 442 443 Chapter 7: Forward look 444 445 Section 7.1: Forward look After the review of the onshore geology and exploratory data, together with the interpretation of the basin provided in this work, different subjects have been identified which need a deeper study beyond the objectives of this work. In most cases, it is a matter of the quality or absence of data, being needed as additional information. These topics can be divided into academic and explora- tory subjects and could be considered for future works in the Hispaniola Island. Regarding the academia, the following topics should be analysed in the future for a better under- standing of the geology of the island:  It has been interpreted in this work a relay from the SJRFZ and the BFZ as the limit between the IAD and the CEBD. This change is based on the gravity data and outcrops at the onshore extension of the SPB, where only Cretaceous sediments are exposed along the trace of the SJRFZ. Further studies should study the zone where the relay.  The relationships between the middle Eocene limestones at the CEBD and the OCD are poorly understood and should be study. In addition, a more detailed study of proximal facies at the CEBD should be carried out, as it is only mentioned in the work of Biju- Duval et al. (1982).  The seismic quality of Hispaniola is generally poor. Further surveys must improve the resolution of the Cenozoic sequences, providing a clear image of the Mesozoic and the basement.  Accordingly, the seismic image of the most deformed areas, such as the Muertos Thrust Belt is quite poor. New surveys must provide an image of these areas to understand the tectonic evolution of the belt.  In addition, with the current available data it is not possible to discern between Cretaceous sediments and island arc materials. Further studies must address the relationship between the Upper Cretaceous sediments and vulcanism.  Finally, the seismic quality at the Cibao Basin is also poor. Further studies must determine the shape of the basement and the configuration of the Oligocene sequences.  The age of the evaporites deposited at the Enriquillo Basin has been questioned in this work. Further works must sample this formation as it is the key to understand the tectonic evolution of the southern region of Hispaniola.  An angular and erosive unconformity was found in the upper interval of the upper Eocene sediments studied at the CEBD. This might imply some degree of deformation at the time of the deposition of this interval. Further investigations must address if the shallowing of the sequence is related or not with an early stage of deformation of the basin. Along with the aforementioned, the following topics should be treated in the future to improve the exploratory perspective of the region.  The available geochemical data of Hispaniola is limited, and more samples are necessary to understand the real potential of the region. A better understanding of the Cretaceous, Eocene and Oligocene potential would improve the exploratory perspective of the north- ern Caribbean in general, and The Dominican Republic in particular. In this respect, new rock eval and vitrinite reflectance data is required.  At the same time, the source rock potential of the Campanian Trois Rivieres and Las Palmas Formation should be determined by the sampling of outcrops. 446  The reservoir properties of the main intervals considered in this work were obtained with- out permeability data. Additional information results are essential to determine the best reservoir intervals.  In addition, more data regarding the quartz content of the Miocene sandstones at the on- shore extension of the SPB should be acquired to determine the real reservoir potential of this interval.  More data is required to determine the seal capacity of the Upper Cretaceous shales (e.g. Units K1 and K2 reached at the well SP-1) and the Miocene and Oligocene shales (e.g. Units O1/O2 and N2 reached at the Cibao and San Juan – Azua Basins).  The seismic quality of the basin must be improved to better identify the main elements of the basin. 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Geol. 18.6, 707e713. 470 471 Appendices 472 473 Appendix 1: List of Commonly Used Acronyms AOI Area of Interest BFZ Bonao Fault Zone CA-1 Caño Azul-1 CAN-1 Candelon-1 CARIB Caribbean Plate CEBD Cretaceous – Eocene Basin Domain CHL-1 Charco Largo-1 CLIP Caribbean Large Igneous Province EPGFZ Enriquillo-Plantain-Garden Fault Zone FACD Fore Arc – Collisional Domain HFZ Hispaniola Fault Zone IAD Island Arc Domain LIC-1 Licey-1 MDT-1 Maleno DT-1 MTB Muertos Thrust Belt OCD Oceanic Caribbean Domain PS-1 Punta Salinas-1 RYFZ Río Yabón Fault Zone SAFZ Saona Fault Zone SFR-1 San Francisco Reef-1 SFZ Septentrional Fault Zone SJLPFZ San Juan – Los Pozos Fault Zone SJRFZ San José – Restauración Fault Zone SP-1 San Pedro-1 SPB San Pedro Basin TRPB Trois Rivieres – Peralta Belt TWT Two-way Travel Time VI-1 Villa Isabel-1 474 475 Appendix 2: List of acronyms (complete) AOI Area of Interest BFZ Bonao Fault Zone BHT Bottom Hole Temperature BNDH Banco Nacional de Datos de Hidrocarburos CA-1 Caño Azul-1 CAN-1 Candelon-1 CARIB Caribbean Plate CDP Common Depth Point CEBD Cretaceous – Eocene Basin Domain CIA Caribbean Island Arc CMP Common Mid-Point CHL-1 Charco Largo-1 CLIP Caribbean Large Igneous Province CC Cordillera Central CO Cordillera Oriental CS Cordillera Septentrional DC Duarte Complex DPHI Density Porosity DMO Dip Move Out DSDP Deep Sea Drilling Project DST Drilling Stem Test ENFA El Número Facies Association EPGFZ Enriquillo-Plantain-Garden Fault Zone FACD Fore Arc – Collisional Domain FSST Falling Stage System Tract FRFA Fort Resolis Facies Association GR Gamma Ray HFTB Haitian Fold-and-Thrust Belt HFZ Hispaniola Fault Zone HI Hydrogen Index 476 HST Highstand System Tract IAD Island Arc Domain IKU Intra-Cretaceous Unconformity LBF Larger Benthic Foraminifers LCP Loma Caribe Peridotites LIC-1 Licey-1 LLM Loma La Monja Formation LST Lowstand System Tract MDT-1 Maleno DT-1 MTB Muertos Thrust Belt NMO Normal Move Out NOAM North American Plate NPHI Neutron Porosity OCD Oceanic Caribbean Domain OI Oxygen Index PIA Primitive Island Arc PPC Puerto Plata Complex PS-1 Punta Salinas-1 PVFA Presa Valdesia Facies Association QA Quality Control and Data Assessment RMS Root Medium Square RSJC Río San Juan Complex RTP Reduce to Pole RYFZ Río Yabón Fault Zone SAFZ Saona Fault Zone SFR-1 San Francisco Reef-1 SFZ Septentrional Fault Zone SJLPFZ San Juan – Los Pozos Fault Zone SJRFZ San José – Restauración Fault Zone SOAM South American Plate SOFZ Septentrional Oriente Fault Zone SP Spontaneous Potential 477 SP-1 San Pedro-1 SPB San Pedro Basin TD Total Depth TIA Tholeiitic Island Arc TST Transgressive System Tract TOC Total Organic Carbon TRPB Trois Rivieres – Peralta Belt TWT Two-way Travel Time VI-1 Villa Isabel-1 478 479 Appendix 3: Supplementary material Sup. 1, Non interpreted and interpreted section SD-5 of figure 4.7.19. 480 Sup. 2, Location of cross-sections in App. 3 and 4. 481 Su p. 3 , C om po sit e cr os s- se ct io ns fr om th e ge ol og ic al m ap pi ng o f t he D om in ic an R ep ub lic (S YS M IN I an d II P ro gr am s) 482 Su p. 3 , C om po si te c ro ss -s ec tio ns fr om th e ge ol og ic al m ap pi ng o f t he D om in ic an R ep ub lic (S YS M IN I an d II P ro gr am s) Tesis José Miguel Gorosabel Araus Portada Acknowledgements Funding Content Resumen Abstract Chapter 1: Introduction 1.1 Introduction and objectives 1.2 Organization of this volume Chapter 2: Geological setting 2.1 Tectonic overview for the Caribbean Region 2.2 Crustal structure (and composition) of the interior CARIB 2.3 Tectonic evolutionary models for the Caribbean Region 2.4 The border region between the CARIB and the NOAM 2.5 Hispaniola Island 2.6 The San Pedro Basin Chapter 3: Data and methods 3.1 Preliminary research 3.2 Integrated geological model 3.3 Elements of the petroleum system 3.4 Basin modelling Chapter 4: Basin Modelling 4.1 Tectono-Stratigraphic Domains 4.2 Fore arc - collisional domain 4.3 Island Arc Domain 4.4 Cretaceous to Eocene Basin Domain 4.5 Oceanic Caribbean Domain 4.6 General Discussion 4.7 Interpretation of the San Pedro Basin Chapter 5: Petroleum system for the San Pedro Basin 5.1 Exploration background 5.2 Available exploration data 5.3 Wells post-mortem analyses 5.4 Source rock 5.5 Reservoir 5.6 Seal 5.7 Trap 5.8 Timing and preservation 5.9 Summary 5.10 Conclusions and forward look of exploration activities Chapter 6: Summary andconclusions 6.1 The tectono-stratigraphic domains division 6.2 The structure of the SPB 6.3 The evolutionary model of the SPB 6.4 Conclusions Chapter 7: Forward look 7.1 Forward look References. Appendices Appendix 1: List of Commonly Used Acronyms Appendix 2: List of acronyms (complete) Appendix 3: Supplementary material