Person:
Fernández López, Sixto Rafael

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

Search Results

Now showing 1 - 10 of 43
  • Publication
    Sistemas tafonómicos: función y evolución
    (Museo Nacional de Ciencias Naturales: Sociedad Española de Paleontología, 1991) Fernández López, Sixto Rafael
    El sistema conceptual de la Paleontología ha sido radicalmente modificado desde el siglo pasado hasta la actualidad. La Paleobiología ha desarrollado nuevos conceptos, presupuestos, métodos y procedimientos. En la actualidad se requiere de una Táfonomía sistemista y evolucionista para garantizar la congruencia de los resultados paleontológicos. En el presente trabajo se explicita y discute el significado de algunos conceptos referentes a la funcionalidad y evolución de los sistemas tafonómicos. La producción tafogénica y la alteración tafonómica hacen que la fosilización, en vez de ser un proceso paleobiológico destructivo, sea un proceso negentrópico que no implica pérdida o disminución de la información paleobiológica y en el cual se incrementa la información tafonómica. Los conceptos de producción tafogénica y alteración tafonómica proporcionan los fundamentos teóricos para interpretar los mecanismos de fosilización. [ABSTRACT] The conceptual system ofPaleontology has beendrastically modified from the last century to the present, new concepts, methods, assumptions and paleobiological procedures having been developed. In the present state of knowledge a systemist and evolutionary taphonomy is required in order to guarantee the consistency of the paleontologicalresults. The meaning of some concepts concerning the functionality and evolution of taphonomic systems is discussed and precised. Such processes as taphogenic production and taphonomic alteration make fossilization become a taphonomic, negentropic process, in which taphonomic information increases and which does not involve any loss or(ceduction of paleobiologic information, instead of a destructive process. The concepts of taphogenic production and taphonomic alteration provide the theoretical foundations to intepretate the mechanisms of fossilization.
  • 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
    Utilidad sedimentológica y estratigráfica de los fósiles reelaborados.
    (Dpto. de Paleontología de la Fac. de Ciencias Geológicas, Instituto de Geología Económica, Museo Nacional de Ciencias Naturales, 1990) Fernández López, Sixto Rafael; Gómez Fernández, Juan José; Fernández López, Sixto Rafael
    In many cases the reelaborated fossils are the best preserved of the assemblages. Even they can not be used to establish and identify biostratigraphical or chronostratigraphical units, the reelaborated fossils are useful for sequential and discontinuities analysis, for location of source areas of sediments, as indicators of paleocurrents, and for identification of sedimentary environments and paleogeography. Some reelaborated fossils are the only existing record of eroded sediments. They permit the obtention of data on episodes of the Geological History of which the stratigraphic record is not available anymore.
  • Publication
    Evolution tectono-sedimentaire et genese des associations d'ammonites dans le secteur central du Bassin Iberique (Espagne) pendant l'Aalenien.
    (Assoc. des Facultés Catholiques de Lyon, 1990) Fernández López, Sixto Rafael; Gómez Fernández, Juan José
    A la limite Lias-Dogger, le Bassin Ibérique correspondrait a une marge passive se disloquant en panneaux montrant des facies différents. Un des meilleurs exemples du comportement différentiel des blocs limités par des failles actives se trouve dans le secteur central du bassin, où la Faille de Noguera-Aguaton individualisait deux secteurs : celui d' Albarracin et celui de Menera. La discontinuité stratigraphique de plus grande amplitude se situe a la limite Toarcien-Aalénien dans le secteur d'Albarracin et a l'intérieur de l' Aalénien dans le secteur de Menera. Le changement paléogéographique le plus important pour la plate-forme se produit a la limite de l'Aalénien inférieur/Aalénien moyen . La sédimentation de ces secteurs correspond a un environnement de plate-forme externe tres peu profonde, soumise a des émersions locales répétées et les associationss uccessives d'ammonites sont surtout le résultat de nécrocinese régionale a partir d'aires épicontinentales plus septentrionales. [ABSTRACT] At the Lias-Dogger boundary the Iberian Basin corresponded to a passive margin where different facies conditioned by the presence of several faulted blocks were developped. One of the best examples showing the synsedimentary differential behaviour of the fault-bounded blocks was found in the central sector of the basin, where the Noguera-Aguaton Fault individualized two blocks : the Albarracin and the Menera ones. The most important stratigraphic discontinuity in the Albarracin Sector is located in the limit between the Toarcian and the Aalenian. However in the Menera Sector the most important stratigraphic discontinuity is located within the aalenian sediments. The biggest paleogeographical change in the platform occurred in the boundary between Early and Middle Aalenian. Sedimentation in this sectors corresponds to a very shallow external platform environment with repeated local emersions. The successive ammonite associations were mostly the result of regional nekrokynesis from septentrional epeiric seas
  • 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
    Ammonites, ciclos tafonómicos y ciclos estratigráficos en plataformas epicontinentales carbonáticas.
    (Museo Nacional de Ciencias Naturales: Sociedad Española de Paleontología, 1997) Fernández López, Sixto Rafael
    Algunas variaciones de los caracteres tafonómicos y la distribución de las asociaciones registradas de ammonites en las plataformas epicontinentales carbonáticas permiten distinguir secuencias tafonómicas elementales, tafosecuencias, taforregistros, tafociclos, megatafosecuencias y supertafociclos que son el resultado de cambios relativos del nivel del mar. La identificación de los ciclos tafonómicos es de máxima importancia para la interpretación de los ciclos estratigráficos de las plataformas epicontinentales mesozoicas, cuando no hay evidencias de las variaciones de la línea de costa y los sedimentos fosilíferos de plataforma externa están ampliamente desarrollados. Cinco ciclos ambientales de profundización/somerización se desarrollaron en las plataformas Castellana, Aragonesa y de Terrosa durante el Jurásico Medio: cuatro de profundización media (durante el Aaleniense inferior, el Aaleniense medio-Bajociense inferior, el Bathoniense y el Calloviense) y uno de profundización avanzada (durante el Bajociense superior). Los taforregistros de ammonites de la Biozona Opalinum representan los últimos términos de una megatafosecuencia de somerización iniciada durante el Toarciense superior. La máxima profundización y el máximo transgresivo se alcanzó durante el Biocrón Niortense (Bajociense superior). Los episodios de máxima somerización durante el Jurásico Medio, que representan máximos regresivos, corresponden a las discontinuidades del Aaleniense medio (Biocrón Murcbisonae) y del Calloviense superior (Biocrón Lamberti). Los sedimentos del Jurásico Medio comprendidos entre estas dos discontinuidades estratigráficas, desde el Aaleniense medio basta el Calloviense superior, representan un superciclo de segundo orden en la Cuenca Ibérica. [ABSTRACT] Same varialions of the taphonomic fearures and the distribution of the recorded assoc iations of ammonites enable to distinguish elemental taphonomic sequences, taphosequences, taphorecords, taphocycles, megataphosequences and supertaphocycles in carbonate epi continental platforms resulting of relative sea- level changes. The identification of taphonomic cycles is important in interpreting stratigraphic cycles of epicontinental platforms, when no evidence of coastal on lap is preserved and fossil iferous sed iments of outer platforlll are wide ly developed. Five environlllental cycles of deepening/shallowing were developed in the Castiliane, Aragonese and Tortosa platforms during the Middle Jurassic: four of them of median deepen ing (early Aalenian, middle Aalenian-early Bajocian, Bathonian and Callovian) and one of them of advanced deepening (late Bajocian). Ammonite taphorecords of the Opalinum Biozone represent the last terms of a shallowing upwards megataphosequence which began in the late Toarcian. The maximum relative sea-Ievel rise and the maximum deepening were reached during rhe Niortense Biochron (late Bajocian). Episodes of maxilllum relative sea-Ievel faH during the Middle Jurassic correspond to tbe stratigraphic discontinuities of middle Aalenian (Murchisonae Biochron) and late Callovian (Lamberti Biochron). The Middle Jurass ic sediments between these stratigraphic discontinuities, from middle Aalenian to Upper Callovian, represent a supercycle of second order in the Iberian Basin.
  • Publication
    El significado de la autoctonia/aloctonia tafonomica
    (Instituto de Geología Económica, Museo Nacional de Ciencias Naturales, 1990) Fernández López, Sixto Rafael; Fernández López, Sixto Rafael
    The different meanings with which the terms authochthonous and allochthonous are generally used, in order to interpretate the fossils, are discussed and analyzed. The spatial reference that should be used in Taphonomy is the place or the are a where the remains and/or traces were produced, neither the life position nor the place or area occupied by the paleobiological entities.
  • Publication
    Tafonomía y fosilización
    (Consejo Superior de Investigaciones Científicas, 1999) Fernández López, Sixto Rafael; Meléndez, Bermudo; Meléndez Hevia, Guillermo