Person:
Fernández López, Sixto Rafael

First Name

Sixto Rafael

Last Name

Fernández López

URI

https://hdl.handle.net/20.500.14352/75204

Affiliation

Universidad Complutense de Madrid

Faculty / Institute

Ciencias Geológicas

Department

Geodinámica, Estratigrafía y Paleontología

Area

Paleontología

Identifiers

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Now showing 1 - 10 of 21

Bajocian ammonoids from Pumani River area (Ayacucho, Peru): Palaeobiogeographical and palaeoenvironmental implications for the Arequipa Basin
(Journal of South American earth sciences, 2014) Fernández López, Sixto Rafael; Carlotto, Victor; Giraldo, Edwing; Chacaltana, César
Deposits of the Socosani Formation in the Pucayacu and Pumani sections (Ayacucho Department, Peru), along several kilometres, have yielded Upper Bajocian ammonoid fossil-assemblages characterized by the occurrence of juvenile individuals belonging to endemic or pandemic genera, such as Megasphaeroceras and Spiroceras respectively. In addition, certain Bajocian genera relatively common in the Mediterranean-Caucasian Subrealm, but very scarce in the Eastern Pacific Subrealm, such as the strigoceratid Cadomoceras and the phylloceratid Adabofoloceras, occur in this area. According to the taphonomic, palaeoecological and palaeobiogeographical evidence from the Pumani River area, the maximum deepening, relative sea-level rise and oceanic accessibility of a BajocianeBathonian, second-order, transgressive/regressive facies cycle in the marine Arequipa Basin were reached during the Late Bajocian Niortense Biochron. However, synsedimentary regional tectonics in the Pumani River area disturbed this general deepening/shallowing cycle of the Arequipa Basin, particularly during the Late Bajocian post-Niortense time-interval of the Garantiana and Parkinsoni biochrons.
Ammonite taphonomy in the Albarracinites beds (Lower Bajocian, Iberian Range, Spain)
(2010) Fernández López, Sixto Rafael
Postulates of the evolutionary taphonomy
(I Simposio Internacional Paleontología del Perú., 2013) Fernández López, Sixto Rafael; Chacaltana, C.; Tejada, L.M.; Morales, M.C.
Late Bajocian bioevents of ammonoid immigration and colonization in the Arequipa Basin (Pumani River area, Ayacucho, southern Peru).
(I Simposio Internacional Paleontología del Perú., 2013) Fernández López, Sixto Rafael; Chacaltana, C.; Tejada, L.M.; Morales, M.C.
Strata of the Socosani Formation in the Pucayacu and Pumani sections (Ayacucho Department, Peru), along several kilometres, have yielded Upper Bajocian ammonoid fossil-assemblages characterized by the occurrence of juvenile individuals belonging to endemic or pandemic taxa, such as Megasphaeroceras and Spiroceras respectively. In addition, certain Bajocian taxa relatively common in the Mediterranean-Caucasian Subrealm, but very scarce in the Eastern Pacific Subrealm, such as the strigoceratid Cadomoceras and the phylloceratid Adabofoloceras, occur in this area. These Late Bajocian bioevents of regional appearance of immigrant ammonoids and even sustained colonization should be associated with an episode of maximum deepening, maximum relative sea-level rise and highest oceanic accessibility of a Bajocian-Bathonian deepening/shallowing palaeoenvironmental cycle in the Arequipa Basin, during the Late Bajocian Niortense Biochron.
New species of Franchia and Protozigzagiceras (Ammonoidea, Middle Jurassic): The phyletic origin of Zigzagiceratinae
(Palaeontology, 2013) Fernández López, Sixto Rafael; Pavia, Giulio
Three genera and seven species belonging to the subfamily Zigzagiceratinae (family Perisphinctidae) are described from the Lower Bathonian of France and Saudi Arabia. Intraspecific dimorphism is recognized. A revision of the genus Franchia proposed by Sturani (1967), based on the syntypes and new specimens from south-east France, is presented. Franchia arkelli Sturani, Franchia subalpina sp. nov., Protozigzagiceras torrensi (Sturani), Protozigzagiceras tethycum sp. nov., Protozigzagiceras flexum sp. nov. and Protozigzagiceras densum sp. nov. are described from the Digne– Castellane region of south-east France. Megazigzagiceras subarabicum, gen. et sp. nov. is described from the Dharma region of Saudi Arabia. The successive Early Bathonian species of Franchia and Protozigzagiceras herein identified in West Tethyan areas, as members of the Mediterranean–Caucasian Subrealm, formed lasting separate peramorphoclines characterized by increasing hydrodynamic coiling of the shell. In contrast, rapid proterogenesis originated and diversified the earliest Bathonian zigzagiceratin lineages, giving paedomorphic members, commonly neotenic and more scarcely progenetic. Procerites–Siemiradzkia seems to be the oldest zigzagiceratin member in the French Subalpine, Iberian and Lusitanian basins, branched off by paedomorphosis from leptosphinctins at the Bajocian–Bathonian transition. The Mediterranean–Caucasian genera Franchia, Zigzagiceras, Zigzagites and Wagnericeras branched from successive species of Protozigzagiceras, in turn, a direct derivative of Procerites. The oldest lineages of the clade Zigzagiceratinae evolved by iterative, rapid, paedomorphic changes and additional, lasting, peramorphic modifications during the Early Bathonian.
Le GSSP du Bathonien à Bas Auran (réserve naturelle géologique de Haute-Provence, France)
(Géologie de la France, 2010) Olivero, Davide; Pavia, Giulio; Fernández López, Sixto Rafael; Mangold, Charles; Guiomar, Myette
Le Bathonien est le troisième étage du Jurassique moyen. Son nom dérive de la « Bath Oolithe », une formation définie près de Bath (Somerset, Angleterre). Mais, dans cette région, les niveaux condensés ne sont pas favorables pour définir le stratotype de l’étage. On ne peut pas sélectionner d’affleurements pouvant permettre de définir le stratotype de limite de l’étage. En France, trois coupes dans les environs de Bas Auran (Alpes de Haute-Provence, France) ont donc été proposées en 1967. En 1990, ces mêmes localités ont été présentées officiellement comme possible stratotype de la limite basale de l'étage (GSSP). Enfin en 2007, le GSSP a été formellement accepté par le « Bathonian Working Group » et, en 2008, par l’IUGS. Les coupes ont été levées dans les ravins du Bès, d'Auran et des Robines, près du hameau de Bas Auran (commune de Chaudon-Norante, Alpes de Haute-Provence). Elles montrent une alternance marno-calcaire, d'une épaisseur de 13 mètres environ, coiffée par une surface durcie (hard-ground), constituant le mur de la formation des Terres Noires. Les âges s’étendent de la sous-zone à Bomfordi (Zone à Parkinsoni, Bajocien supérieur) à la Sous-zone à Tenuiplicatus (Zone à Aurigerus, Bathonien inférieur). Des travaux récents ont permis de compléter et d’affiner les données existantes concernant les assemblages d’ammonoïdes, la sédimentologie et l'ichnologie. Les associations d’ammonoïdés, les microfossiles, le nannoplancton, les assemblages ichnologiques et surtout, l'absence de discontinuités notables, permettent de proposer la base du banc 71 de la coupe du Ravin du Bès comme stratotype de la limite inférieure du Bathonien. Atout non négligeable, Bas Auran se situe au sein de la Réserve Géologique de Haute-Provence, ce qui permet la sauvegarde de ce site, très facile d'accès. [ABSTRACT] The Bathonian is the third stage of the Middle Jurassic System. Its name derives from the “Bath Oolithe” formation, cropping out in the surroundings of Bath, in southern England. However, in this country, no outcrops make it possible define the stratotype of the Bathonian Stage, as the succession is taphonomically and stratigraphically condensed. The Ravin du Bès section at Bas Auran was thus suggested as the bounding stratotype in 1967. Only later, in 1990, this section was officially proposed as possible stratotype (G.S.S.P.) of the basal boundary of the Bathonian Stage. Lastly, in 2007 this G.S.S.P. was formally accepted by the Bathonian Working Group and, in 2008, the proposal was ratified by the I.U.G.S. Three sections were studied in the surroundings of the Bas Auran farm (Alpes de Haute-Provence, France). The succession is composed of marly and calcareous beds that alternate on nearly 13 metres, and is unconformably overlain by the “Terres Noires” Formation with a sharp hard ground at the lithostratigraphic boundary. The studied interval spans the Bomfordi Subzone (Parkinsoni Zone, late Bajocian) to the Tenuiplicatus Subzone (Aurigerus Zone, early Bathonian).
Taphonomic analysis and sequence stratigraphy of the Albarracinites beds (lower Bajocian, Iberian range, Spain). An example of shallow condensed section
(Bulletin de la Société géologique de France., 2011) Fernández López, Sixto Rafael
Several ammonite fossil assemblages from Sierra de Albarracín (Teruel, Castilian Branch) contain abundant specimens of the Ovale and Laeviuscula zones (lower Bajocian, Middle Jurassic), including microconchs and macroconchs of the characteristic genus Albarracinites. Over 1500 ammonites from the type horizon of the species A. albarraciniensis, in the outcrop of Masada Toyuela, have been studied. Ammonites are commonly preserved as phosphatized, calcareous, concretionary internal moulds (mean size = 50.5 mm) of unflattened shells, partially or completely filled with relatively heterogeneous mudstone to wackestone sediment. Incomplete, fragmented phragmocones with calcitic septa are the dominant remains, generally bearing traces of rounding, incrustation and bioerosion. Taphonomic data, such as the predominant taphonomic populations of type 3, composed of reelaborated, relatively heterogeneous concretionary internal moulds, isolated concretionary body chambers and hollow ammonites, bearing traces of abrasion, bioerosion and encrusting organisms, are indicative of low rate of sedimentation and occasional high rate of sediment accumulation, due to sedimentary winnowing and bypassing interrupted by storm depositional events, in shallow-water marine environments. The exceptional occurrence of taphonic populations of type 2 belonging to Albarracinites and Hebetoxyites, with dominant shells of pre-adults and absence of juveniles, suggests autochthonous biogenic production of shells by indigenous populations of Sub-Mediterranean taxa at the Iberian platform system. In the outcrop of Masada Toyuela, the Albarracinites beds correspond to a condensed section, developed in shallow- water, open-marine, carbonate environments of the External Castilian platform. The sharp, irregular base of beds and the normal grading of reworked elements suggest these carbonate deposits were affected by tractive currents, scouring and redeposition. Limestone beds represent storm-related sedimentary events, whereas the local marly intervals represent background-sedimentation time-intervals of winnowing and bypassing on the seafloor. This condensed section is composed of at least four, decimetric or centimetric, expanded-deposit intervals, stacked and showing an overall thinning upward, which constitute a deepening sequence developed during two biochrons. Taphonomic results also corroborate the development of an incipient-deepening phase, which represents the first episode of a deepening half-cycle of third order, in the Albarracín area within the Castilian platform, during the Ovale and Laeviuscula biochrons (early Bajocian).
First Circum-Pacific Record of Dimorphinites (Ammonoidea, Upper Bajocian) in the Precordillera of Northern Chile
(Earth Science Frontiers = Dixue qianyuan, 2010) Fernández López, Sixto Rafael; Chong Díaz, G.B.
Examples of reelaborated ammonites
(Reduca. Geología, 2011) Fernández López, Sixto Rafael
Identify reelaborated fossils requires knowing the meaning of the term taphonomic reelaboration and the diagnostic criteria that can be used to test such preservation state. In the present work: 1) we make explicit the meaning of the taphonomic terms: accumulation, remotion or reworking, resedimentation and reelaboration, understood as diverse categories of the same taphonomic classification system; 2) showing a model of the process of taphonomic reelaboration; and 3) displaying diverse examples of accumulated (2), resedimented (2) and reelaborated (16) ammonites.
Dimorphism and endemism in Hebetoxyites (Ammonoidea, lower Bajocian) from the Iberian Range (Spain)
(Revue de Paléobiologie, 2012) Fernández López, Sixto Rafael
New findings of lower Bajocian, haploceratid ammonites (Cephalopoda, Mollusca) of the genus Hebetoxyites from the Albarracín area are described and revised alongside specimens previously collected from the Iberian Range. Three species have been identified: H. hebes Buckman, H. incongruens Buckman and H. mouterdei Fernández-López. Indigenous populations of these Tethyan species in the Iberian carbonate platform system, including macroconchs and microconchs, are interpreted as immigration and colonization of shallow-water marine environments by Submediterranean taxa during a short interval of the early Bajocian. As peramorphic result of palingenetic evolution, a chronocline from strongly ribbed, stout forms of the Ovale Zone (including H. mouterdei), to oxycones with blunt, simple or irregularly branched ribbing of the Laeviuscula Zone (including H. incongruens), through intermediate forms belon-