Person:
Fernández López, Sixto Rafael

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First Name
Sixto Rafael
Last Name
Fernández López
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Geológicas
Department
Geodinámica, Estratigrafía y Paleontología
Area
Paleontología
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UCM identifierORCIDScopus Author IDWeb of Science ResearcherIDDialnet IDGoogle Scholar ID

Search Results

Now showing 1 - 10 of 55
  • Publication
    Ammonites from lumpy limestones (Lower Pliensbachian, Portugal). Taphonomic analysis and palaeoenvironmental implications.
    (Sociedad Geológica de España, 2000) Fernández López, Sixto Rafael; Duarte, Luís Vitor; Henriques, María Helena Paiva
    Preservational features of ammonites recorded in the Lower Pliensbachian lumpy limestones of the Lusitanian Basin confirm the deep marine origin previously established for this facies. These deposits can be subdivided into three main taphofacies which are distinguished by preservational ammonite features: 1) lumpy limestones and marly intervals with reelaborated ammonites, 2) laminated marls and bituminous shales with accumulated ammonites, and 3) homogeneous limestones with resedimented ammonites. The background sedimentation of suboxic (dysaerobic, bioturbated lumpy muds; taphofacies 1) to anoxic conditions (anaerobic, laminated muds; taphofacies 2) on deep zone was interrupted by depositional events related to distal gravity flows (taphofacies 3). Lumpy limestones containing reelaborated ammonites, and showing gradational boundaries and inverse grading developed in deep environments due to sedimentary starving. The stratigraphic intervals of taphofacies 1 represent the lowest values of sedimentation and accumulation rates. Taphofacies of type 1 alternate with taphofacies of type 2 composing stratigraphic cycles of metric order. Such cycles resulted from cyclical environmental changes of hundreds of thousands of years. Deepening episodes of 4th-order led to the development of dysaerobic to anaerobic environments, whilst subsequent shallowing episodes increased the levels of bottom oxygenation.
  • Publication
    Los yacimientos paleontológicos del Jurásico de la Sierra de Albarracín (Rama Castellana de la Cordillera Ibérica): aspectos estratigráficos y patrimoniales
    (Instituto de Estudios Turolenses, 2002) Meléndez Hevia, Guillermo; Fernández López, Sixto Rafael; Soria Llop, Celia; Pérez Urresti, Isabel; Bello, Julia; Delvene, Graciela; Comas Rengifo, María José; Goy, Antonio; Clemente, Elena; Rodríguez Mora, Montserrat; Meléndez Hevia, Guillermo; Peñalver Mollá, Enrique
    Los yacimientos paleontológicos del Jurásico en la Sierra de Albarracín (Temel) presentan un especial interés tanto científico, por la importancia y diversidad de los grupos fósiles representados y el desarrollo de las unidades estratigráficas, como patrimonial, por la excelencia de los afloramientos y su riqueza fosilífera, e histórico, por la gran tradición de estudios llevados a cabo desde el siglo XIX. En el presente trabajo se analizan los aspectos estratigráficos y patrimoniales de ocho de ellos, seleccionados por su riqueza paleontológica y su valor patrimonial, incluyendo la descripción de su contenido paleontológico, la evaluación de los riesgos y las posibles medidas de protección de los mismos. El gran interés del registro fósil ha llevado a la definición de muchos nuevos taxones en esta región, como es el caso de los braquiópodos Aulacothyris iberica u Homoeorhynchia meridionalis, y de algunos taxones de ammonites, como los géneros Albarracinites, Microbajocisphinctes o Melendezia. Por otra parte, el conjunto de rasgos patrimoniales que convergen en la Sierra de Albarracín, unido al hecho de encontrarse en un marco paisajístico de gran belleza, ha llevado a la Administración a una toma de Jconciencia en lo referente a la necesidad de protección y conservación del patrimonio histórico y cultural, y a la declaración de una parte de la sierra como Parque Cultural. El proyecto de gestión patrimonial, cultural y turística iniciado recientemente en la Sierra de Albarracín, con la participación del Gobierno de Aragón y otl;as instituciones (Dinópolis) aún en fase embrionaria, contempla la creación de un parque temático de carácter eminentemente recreativo y turístico, aprovechando los recursos paleontológicos de la provincia. Un correcto planteamiento de este proyecto permitirá, sin duda, la integración en el mismo de los trabajos de investigación, por un lado, y la protección del patrimonio paleontológico por otro.
  • Publication
    Fossilization of ammonites and sedimentary events in deep environments of carbonate platform (highest Middle to lowest Upper Oxfordian, Iberian Range, Spain).
    (Università degli studi di Milano. Dipartimento di Scienze della Terra "A. Desio", 2004-03) Fernández López, Sixto Rafael; Meléndez Hevia, Guillermo
    In the Ricla area (Zaragoza, Aragonese Branch of the Iberian Range), at the top of the Yátova Formation, grey-reddish wackestone limestones grade into yellow-green siliciclastic limestones of the Aldealpozo Formation. These changes of facies between the two successive formations are associated with syndepositional palaeoreliefs developed during the Late Oxfordian. The uppermost deposits of the Yátova Formation represent an Oxfordian condensed section, from the upper Bifurcatus Zone (Middle Oxfordian) and Hypselum Zone (Upper Oxfordian). These deposits are interpreted as developed in an open marine, moderately deep carbonate platform, showing uniform lowenergy conditions with extremely reduced carbonate and terrigenous background sedimentation, and very low sedimentation rates. The low diversity of the benthic fauna, scarce development of sponge bioherms and ammonite populations inhabiting the platform are palaeobiological criteria which corroborate these palaeoenvironmental conditions. Ammonite assemblages are composed of Sub-Mediterranean taxa. Over 900 ammonite specimens have been collected from the upper Bifurcatus and Hypselum zones. Oppeliidae (45,2%) and Perisphinctidae (37,9 %) are dominant. Aspidoceratidae (14,3%) are common. Haploceratidae (2,2%) are scarce. Two phylloceratids and a lytoceratid have been found. Ammonoids are commonly preserved as concretionary calcareous internal moulds of reelaborated elements. Resedimented shells are scarce. The degree of packing of ammonite remains and the stratigraphical persistence display high values. Taphonomic features indicative of sedimentary starving in deep carbonate platform environments are: 1) high concentrations of reelaborated ammonites, 2) taphonic population of type two, 3) phragmocones completely filled with sediment, and 4) homogeneous concretionary internal moulds, bearing no signs of abrasion, bioerosion or dense encrusting by organisms (such as serpulids, bryozoans or oysters). In conclusion, the occurrence of these ammonite associations confirms the development of an advanced deepening phase, within a 3rd order deepening/shallowing cycle, in the Aragonese platform, during the late Bifurcatus to Hypselum zones.
  • Publication
    Taphonomy of an ammonite recorded association (Murchisonae Zone, Aalenian, Iberian Range, Spain). Palaeoenvironmental implications.
    (International Subcommission on Jurassic Stratigraphy, 2002) Fernández López, Sixto Rafael; Martínez Gutiérrez, Gemma; Martire, Luca
  • Publication
    The limit between biostratinomy and fossildiagenesis
    (Ayuntamiento de Valencia, 2002) Fernández López, Sixto Rafael; Fernández Jalvo, Yolanda; Renzi, Miguel D.; Pardo Alonso, Miguel V.; Belinchón, Margarita; Peñalver, Enrique; Montoya, Plinio; Márquez Aliaga, Ana
  • Publication
    Morphological taphonomic transformations of fossil bones in continental environments, and repercussions of their chemical composition
    (Wiley-Blackwell, 2002) Fernández Jalvo, Yolanda; Sánchez Chillón, B.; Andrews, Peter; Fernández López, Sixto Rafael; Alcalá Martínez, L.
    The aim of this paper is to provide a summary of structural or surface modifications of vertebrate bone remains in continental palaeoenvironments that may have repercussions on their chemical composition. Both before and after burial, a different set of physical, chemical and biological agencies may produce modifications of the bone morphological structure and/or bone chemical composition. Several of these morphological modifications are diagnostic of particular agents, which otherwise may not be noticed or identified in a fossil association. In order to understand diagenesis, those events that occurred before final burial have to be considered, as they may strongly modify the bone morphological structure and influence post-burial changes.
  • Publication
    Formal proposal for the Global Boundary Stratotype Section and Point (GSSP) of the Bathonian Stage, at the base of the Zigzag Zone in the Ravin du Bès Section (Bas-Auran, Subalpine Basin, SE France).
    (2007) Fernández López, Sixto Rafael; Pavia, Giulio; Erba, Elisabetta; Guiomar, Myette; Henriques, María Helena Paiva; Lanza, Roberto; Mangold, Charles; Olivero, Davide; Tiraboschi, Daniele
    The Global Boundary Stratotype Section and Point (GSSP) for the base of the Bathonian Stage is proposed at the base of limestone bed RB071 (bed 23 in Sturani 1967) in the Ravin du Bès Section (43º57’38’’N, 6º18’55’’E), Bas-Auran area, in the Chaudon-Norante commune, around 25 km at the South-Southeast of Digne-les-Bains, in the “Alpes de Haute Provence” French department. The Ravin du Bès Section, as formal candidate GSSP for the base of the Bathonian Stage, satisfies most of the requirements recommended by the International Commission on Stratigraphy (ICS): 1) The exposure extends over 13 m in thickness, comprising more than five metres of fossiliferous levels below and above the boundary. The Bathonian basal bed corresponds to the “Marno-calcaires à Cancellophycus”, is located 7.8 m below the “Terres Noires” Formation and forms part of a transgressive-facies cycle. At the Bajocian-Bathonian transition, no vertical (bio-, ichno- or tapho-) facies changes, stratigraphic gaps or hiatuses have been recorded. There is no evidence of taphonomic condensation (i.e. mixture of fossils of different age or different chronostratigraphic units). Structural complexity, synsedimentary and tectonic disturbances, or important alterations by metamorphism are not relevant constraints in the Bas-Auran area. 2) There is a well-preserved, abundant and diverse fossil record across the boundary interval, with key markers (ammonites and nannofossils) for worldwide correlation of the uppermost Bajocian and Lower Bathonian. The boundary can be characterized by both primary and secondary (auxiliary) biostratigraphic markers. The section appears to be suitable for biostratigraphic study of microfossils, such as foraminifera, but as yet there are no published studies. The base of Bathonian Stage and Zigzag Zone in Bas-Auran corresponds to the renewal of parkinsonids and the first occurrence level of Gonolkites convergens Buckman. This level coincides with the first occurrence of Morphoceras parvum Wetzel. Calcareous nannofossils, as secondary global marker, are present in all beds and allow characterizing the Bajocian-Bathonian transition. 3) Regional analyses of sequence stratigraphy and manganese chemostratigraphy are available. Spectral gamma-ray data corroborate an Early Bathonian deepening half-cycle of second order. No data are currently available for strontium isotope (87Sr/86Sr ratio), oxygen isotope (δ18O) or carbon isotope (δ13C) chemostratigraphy. Bajocian and Bathonian deposits have been remagnetized with a steady normal polarity. Volcanogenic deposits suitable for direct radio-isotope dating are not known in the section. 4) The criteria of accessibility, conservation and protection are assured by the “Réserve Naturelle Géologique de Haute Provence”, protected under national law as recognised by UNESCO. The Cabo Mondego Section (Portugal), which provides complementary data of the ammonite succession at the Sub-Mediterranean Parvum Subzone and its chronocorrelation with the Northwest European Convergens Subzone, is suggested as the Bathonian auxiliary section and point (ASP) within this GSSP proposal.
  • Publication
    Diagnóstico paleontológico de ciclos paleoambientales en plataformas epicontinentales carbonáticas. Ejemplos del Jurásico Medio de la Cordillera Ibérica
    (Alcalá de Henares (Madrid): Museo Arqueológico Regional, 2004) Fernández López, Sixto Rafael
    Aunque parece haber un acuerdo general entre los geólogos en cuanto a que el registro estratigráfico ha estado influenciado por ciclos paleoambientales, pocos estudios hacen referencia a la naturaleza del registro fósil y su carácter cíclico. Sin embargo, los ciclos estratigráficos representan fluctuaciones paleoambientales que también han influido en las entidades paleobiológicas y en la conservación de sus restos y señales. Por analogía con el modelo desarrollado en Estratigrafía Secuencial, la Paleontología puede proporcionar un modelo referente a procesos de distintas escalas representados por ciclos tafonómicos y ciclos paleobiológicos. Los conocimientos paleontológicos pueden ser aplicados en las investigaciones estratigráficas para identificar los ciclos y las discontinuidades del registro estratigráfico. De manera análoga, los conocimientos estratigráficos proporcionan un sistema conceptual en el que es posible contrastar los ciclos paleontológicos y las discontinuidades del registro fósil. La Estratigrafía Secuencial y la Paleontología Aplicada pueden desarrollar un sistema conceptual, integrado y predictivo, para interpretar y contrastar el carácter cíclico del registro geológico y los ciclos paleoambientales, analizando independientemente la ciclicidad del registro estratigráfico y la del registro fósil.
  • Publication
    Evolución orgánica y diseño inteligente
    (Universidad Complutense, 2006) Fernández López, Sixto Rafael; Viedma Molero, Cristóbal
  • Publication
    Primera fase de post-rifting: Jurásico Inferior y Medio.
    (Sociedad Geológica de España, 2004) Gómez Fernández, Juan José; Fernández López, Sixto Rafael; Goy, Antonio; Vera, J.A.