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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Now showing 1 - 10 of 22
  • 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
    Aalenian Tmetoceras (Ammonoidea) from Iberia: taxonomy, habitats and evolution.
    (Kluwer, 1999) Fernández López, Sixto Rafael; Henriques, María Helena Paiva; Linares Rodríguez, Asunción; Sandoval Gabarrón, José; Ureta Gil, María Soledad; Olóriz Aguilera, Federico; Rodríguez Tovar, Francisco J.
    Several hundred Aalenian Tmetoceras from the Iberian Peninsula (N Lusitanian Basin, Asturias, Basque-Cantabrian Basin, NE Cameros, NW Iberian Basin, Aragonese Platform, Tortosa Platform, Castilian Platform, Majorca and Betic Basin) have been reviewed. Two species of Aalenian Tmetoceras have been identified on the basis of morphological, biochronological and palaeobiogeographical data: T. scissum and T. regleyi. T. scissum was dominant among the Tmetoceras populations developed in the Betic and Lusitanian basins during Opalinum, Murchisonae and Bradfordensis biochrons. Populations composed by evolute individuals of T. scissum inhabited shelfal or oceanic environments. A chronocline, from rectiradiate and primitive forms to flexicostate and derived forms, can be recognized in these populations of T. scissum. In contrast, shallow epicontinental platforms were inhabited by involute individuals of T. regleyi. This second species was phyletically derived from T. scissum, representing an adaptive radiation from populations of shelfal or oceanic basins to populations of epicontinental platforms.
  • Publication
    Taphonomy of ammonite condensed associations. Jurassic examples from carbonate platforms of Iberia
    (Geologische Bundesanstalt., 1999) Fernández López, Sixto Rafael; Henriques, María Helena Paiva; Duarte, Luís Vitor
  • Publication
    Reelaborated ammonites as indicator of condensed deposits from deep marine environments. Case study from Lower Pliensbachian limestones of Portugal.
    (Euroean association paleontological, 1999) Fernández López, Sixto Rafael; Duarte, Luís Vitor; Henriques, María Helena Paiva; Rocha, Rogério B; Silva, C.M.; Caetano, P.S.; Kullberg, J.C.
    Lumpy limestones with reelaborated ammonites are a typical facies in the Lower Pliensbachian of the Lusitanian Basin. They were developed in deep marine environments, induced by sedimentary starving. Reelaborated ammonites, with various taphonomic attributes, provide a key to recognition of condensed deposits developed in deep offshore environments during intervals of low sediment input. [RÉSUMÉ]: Les calcaires grumeleux avec des ammonites réélaborées, correspondent a un facies très typique dans le Pliensbachien inférieur du Bassin Lusitanien. Ils se sont développés en milieu marin profond, sur conditions de bas taux de sédimentation. Ces ammonites réélaborées, avec des différents attributs taphonomiques, sont un moyen important pour la reconnaissance de dépôts condensées en milieu marin profond.
  • 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
    The Cabo Mondego section as a possible Bajocian boundary stratotype
    (Servizio geologico nazionale, 1990) Rocha, Rogério B; Henriques, María Helena Paiva; Soares, Antonio; Mouterde, René; Caloo, Brigitte; Ruget, Christiane; Fernández López, Sixto Rafael
    The Cabo Mondego section situated on the Atlantic coast, 160 km north of Lisbon, presents characteristics of a good boundary stratotype section (G.S.S.P.). The outcrop is easily accessible and well exposed near the sea where the erosion process is continuous. The section shows a thick succession of clay limestones with a regular sedimentation and belongs to a sedimenrary basin whose palaeogeography is already well established. The variety and abundance of cephalopods provide good correlation between the submediterranean and the subboreal provinces. This section has already been considered during the discussion on the definition of the boundary stage (Orsay meeting, 1970).
  • Publication
    The base of the Zigzag Zone in the Ravin du Bès Section (Bas-Auran, Subalpine Basin, SE France) as the GSSP for the base of the Bathonian Stage
    (2008) Fernández López, Sixto Rafael; Pavia, Giulio; Erba, Elisabetta; Guiomar, Myette; Henriques, María Helena Paiva; Lanza, Roberto; Mangold, Charles; Morton, Nicol; 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 first occurrence level of Gonolkites convergens Buckman and the renewal of parkinsonids. This level coincides with the first occurrence of Morphoceras parvum Wetzel. Calcareous nannofossils, as secondary global marker, are present in all beds, enabling documentation of the Bajocian-Bathonian transition. 3) Regional analyses of sequence stratigraphy and manganese chemostratigraphy are available. Spectral gamma-ray data corroborate interpretation of 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 on the ammonite succession in 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
    Le Bajocien Inferieur du Cap Mondego (Portugal) - Essai de biozonation
    (Centro de Estratigrafia e Paleobiologia da Universidade Nova de Lisboa (INIC),, 1988) Fernández López, Sixto Rafael; Henriques, María Helena Paiva; Mouterde, René; Rocha, Rogério B; Sadki, Driss; Rocha, Rogério B; Soares , A.F.
    Des récoltes récentes et la révision du matériel déja recueilli dans la coupe du Bajocien inférieur du Cap Mondego ont permis de distinguer quatre zones et quelques sous-zones. Le groupe des est relativement abondant dans les couches de passage de l'Aalénien au Bajocien. Pour établir la limite entre la Biozone a Concavum et la Biozone a Discites on a utilisé comme critere la présence des représentants les plus anciens du groupe Hyperlioceras-Toxolio-ceras. Sont aussi fréquents dans la Biozone a Discites les Euoploceras, Sonninia, fontannesia, Zurcheria et Parasurcheria. La fréquence des représentants d'Emileites, Witchellia et Fissilobiceras permet de caractériser la Biozone a Laeviuscula ouA deux sous-zones peuvent étre distinguées. La base de la sous-zone a Ovalis est marquée par le plus ancien représentant des Witchelliaj localement prédominent les Otoitidés, notamment "Docidoceras" gr. longalvum, Emileites, Trilobiticeras s .1. La sous zone a Laeviuscula se distingue de la sous-zone la présence du premier représentant de l'espece-indice, w.laeviuscula. Les Haplopleurocératinés sont fréquents: Bradfordia, Protoecotraustes, Toxamblytes, Microtoxamblytes et Lissoceras. La Biozone a Sauzei a été caractérisée par l'apparition des Labyrinthoceras et l'albense des Frogdenites. Les Haplocératidés sont fréquents dans la plupart des couches. A la partie supérieure, les Sonninidés sont bien représentées et la sous-zone a Hebridica a été bien caractérisée. Dans la Biozone a Humphriesianum, espece caractéristique rencontrée est 3ephanopheras nodosum; Emileites et Otoites sont absents, mais Dorsetensia et Nannoceras persistent.
  • Publication
    El Jurásico Medio de la Cuenca Catalana: unidades litoestratigráficas y elementos paleogeográficos.
    (Museo Nacional de Ciencias Naturales: Sociedad Española de Paleontología, 1996) Fernández López, Sixto Rafael; Aurell, Marcos; García Joral, Fernando; Gómez Fernández, Juan José; Henriques, María Helena Paiva; Martínez Gutiérrez, Gemma; Meléndez Hevia, Guillermo; Súarez Vega, Luis Carlos
    The palaeogeography and facies distribution of the Catalan Basin during the Middle Jurassic are reconstructed, on the basis of outcrops and logs data. A new lithostratigraphic classification valid for the Catalan Basin is defined and its equivalence with the correlative units in the lberian Basin and Majorca is discussed. A system of arched, listric-shaped faults dipping towards the Mediterranean sea was a major factor determining the differentiation of the subsident Platform of Tortosa. From a palaeobiogeographical point of view, the ammonite and brachiopod recorded associations from the Platform of Tortosa are taxonornically similar to the associations of the epicontinental European basins. The Catalan Basin and Majorca were two geographically separate areas, maintaining separate biogeographical and taphonomic dispersal ways in the Middle Jurassic. Yet in the Catalan Basin expanded, outer shelf sections were developed during the Garantiana Biochron (Upper Bajocian). During this episode the basin reached the maximum bathymetric values and acted as a biogeographical dispersal area for some taxonomic groups characteristic of the West-Tethys.
  • Publication
    La Plataforma de Tortosa (Cuenca catalana) durante el Jurásico Medio: unidades litoestratigráficas, paleogeografía y ciclos ambientales
    (Universidad Complutense de Madrid. Departamento de Estratigrafía, 1998) Fernández López, Sixto Rafael; Aurell, Marcos; García Joral, Fernando; Gómez Fernández, Juan José; Henriques, María Helena Paiva; Martínez Gutiérrez, Gemma; Meléndez Hevia, Guillermo; Súarez Vega, Luis Carlos
    El presente trabajo constituye una guía de campo de un transecto de la Plataforma de Tortosa, en dirección SW-NE, desde el Estrecho de Beceite hacia las proximidades del Alto de Tarragona. Los afloramientos situados en las proximidades de Alfara, Tivenys, Llaberia y Cap Salou permiten reconocer las sucesivas unidades litoestratigráficas, así como las variaciones de espesor y facies en los distintos sectores, facilitando la reconstrucción paleogeográfica y secuencial de la Cuenca Catalana para este intervalo temporal, entre el Toarciense y el Oxfordiense. Los materiales del Jurásico Medio en la Cuenca Catalana forman una potente sucesión carbonática que sobrepasa los 350 m de potencia, y muestran una fuerte reducción de espesor hacia el norte (área de Llaberia) y el nordeste (el llamado Alto de Tarragona). Estos materiales han sido estudiados a partir de los datos de superficie (más de 30 perfiles estratigráficos) y de subsuelo (más de 30 sondeos petrolíferos). Se han reconocido tres formaciones que habían sido previamente definidas: la Fm. Sant Blai, preferentemente carbonatada (Toarciense inferior a Bajociense inferior), la Fm. Cardó, preferentemente margosa (Bajociense inferior a Bajociense superior), y la Fm. La Tossa, formada por calizas y dolomías (Bajociense superior a Calloviense medio). En la Fm. Sant Blai se distingue a su vez cinco miembros estratigráficamente sucesivos. Por encima de la Fm. La Tossa se desarrolla la Fm. Serra de la Creu, formada por calizas bioclásticas y peloidales (Oxfordiense medio a superior). Las variaciones de facies y de espesor son indicativas de que la sedimentación estuvo controlada por fracturas de basamento, que condicionaron el desarrollo de diversas plataformas carbonáticas así como sucesivos cambios relativos del nivel del mar. No obstante, las discontinuidades de mayor amplitud, localizadas en el Aaleniense (Biozona Murchisonae), en el límite Batboniense - Calloviense (Biozona Discus) y en el límite Calloviense - Oxfordiense, se encuentran también en la Cuenca Ibérica y fueron debidas a factores alocíclicos. Las profundidades relativas de estas áreas de plataforma epicontinental alcanzaron valores mínimos durante el desarrollo de estas tres discontinuidades mencionadas, que localmente pudieron corresponder a episodios prolongados de exposición subaérea. Los máximos valores batimétricos se alcanzaron durante el Bajociense superior (Biocrón Niortense) y durante el Oxfordiense medio (biocronos Schilli y Rotoides). Durante estos intervalos de máxima profundización relativa se registraron las únicas evidencias de colonización generalizada de la Cuenca Catalana por poblaciones de ammonites.