Person: Fernández López, Sixto Rafael
Loading...
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
5 results
Search Results
Now showing 1 - 5 of 5
Item Ammonoid taphonomy, palaeoenvironments and sequence stratigraphy at the Bajocian/Bathonian boundary on the Bas Auran area (Subalpine Basin, south-eastern France)(Lethaia, 2007) Fernández López, Sixto RafaelBas Auran, in south-eastern France, is the candidate area for Global Boundary Stratotype Section and Point (GSSP) of the base of the Bathonian Stage (Middle Jurassic). In the Bas Auran area, upper Bajocian and lower Bathonian deposits are made up of limestone beds alternating with marls that correspond to the ‘Marno-calcaires à Cancellophycus’, below the ‘Terres Noires’ Formation. Taphonomic analyses of the successive ammonoid fossil assemblages provide new and complementary data for biostratigraphic completeness, palaeoenvironmental setting and sequence stratigraphy. Lithologic differentiation between limestone and marl intervals resulted from alternating episodes of carbonate input and starvation. Both lithologic phases may contain evidence for sedimentary and taphonomic reworking, associated with scours, that reflects low rates of sedimentation and stratigraphic condensation. Three successive types of elementary cycles resulted from increasing rates of stratigraphic condensation, sedimentary condensation and substrate stabilization during early Bathonian. The occurrence of reelaborated ammonoids (i.e. exhumed and displaced before their final burial) implies that tractive current flows or winnowing affected the burial of concretionary internal moulds. In the lower Bathonian strata, the dominance of homogeneous concretionary internal moulds of phragmocones, completely filled with sediment, is indicative of low rates of sedimentation and sediment accumulation, respectively associated with low degrees of stratigraphic and sedimentary condensation. However, at the Bajocian/ Bathonian transition, hemipelagic, bed-scale limestone–marl alternations show a maximum value of biostratigraphic completeness and there is no evidence for taphonomic condensation in the ammonoid fossil assemblages. Taphonomic analyses of the successive ammonoid fossil assemblages and taphofacies confirm the development of a deepening phase associated with sedimentary starvation, which characterizes the last episode within the deepening half-cycle of third and second order cycles, in the Bas Auran area of French Subalpine Basin during early Bathonian.Item Candidate sections for the GSSP of the base of the Bathonian Stage (Middle Jurassic)(Volumina Jurassica, 2009) Fernández López, Sixto RafaelIn accordance with the recommendations of the International Commission on Stratigraphy (ICS), the leading candidate for the Global Boundary Stratotype Section and Point (GSSP) of the base of the Bathonian Stage is located in the Ravin du B¯s (Bas Auran area, SE France). This section was formally proposed as candidate nineteen years ago. A second potential candidate section is located in the Cabo Mondego area (Portugal). This Portuguese section, however, has not been formally proposed as a candidate for the Bathonian basal boundary stratotype. The formal selection and proposal of a GSSP for the Bathonian Stage is the responsibility of the Bathonian Working Group (BtWG) and is expected by September 2007. In accordance with the procedures to ratify GSSPs, a formal ballot on the selection and proposal of a GSSP for the Bathonian Stage, by post or email, by all members of the BtWG is the responsibility of the convenor and the International Subcommission on Jurassic Stratigraphy Executive, and will be carried out within this time scale.Item Le stratotype de la base de l’Etage Bathonien à Bas-Auran (Réserve Géologique de Haute Provence)(2008) Olivero, Davide; Pavia, Giulio; Fernández López, Sixto Rafael; Mangold, CharlesItem Ammonoid succession at the Bajocian-Bathonian transition in the Bas Auran area, Digne district, South-East France.(Rivista italiana di paleontologia e stratigrafia, 2008) Pavia, Giulio; Fernández López, Sixto Rafael; Mangold, CharlesThe uppermost Bajocian to lowermost Bathonian ammonoid succession has been studied in the Bas Auran area in view of choosing one of its sections as the Global Stratotype Section and Point (G.S.S.P.) of the Bathonian Stage. The Bas Auran ammonite assemblages display exceptional values of record quality. The stratigraphic distribution of 629 specimens referred to 63 species and 35 genera, collected during the last forty years from three sections (Ravin du Bès, Ravin d'Auran, Ravin des Robines), is plotted and analyzed, bed by bed. Over 85 stratigraphic levels, through 9 m in thickness, have been studied at the top of the "Marno-calcaires à Cancellophycus" formation, ranging from the latest Bajocian (Parkinsoni Zone, Bomfordi Subzone) to the earliest Bathonian (Zigzag Zone, Convergens Subzone) and the base of the Macrescens Subzone. Ammonoid assemblages are composed of Northwest European and Mediterranean elements, associated with Sub-Mediterranean ones, allowing chronocorrelation between the Northwest European Convergens Subzone and the Sub-Mediterranean Parvum Subzone. The basal boundary of the Zigzag Zone and of the Bathonian Stage is placed at the base of Sturani's bed 23 in the Ravin du Bes section and is identified by the first occurrence of Gonolkites convergens, and coincides with the loest occurrence of Morphoceras parvum. Features of the ammonoid succession indicate relatively homogeneous and good record quality, gradual biostratigraphic change and high degree of taxonomic similarity between the Bomfordi and Convergens subzones. Palaeontological criteria also indicate relatively high values of palaeontological and stratigraphic completeness at the base of levels RB070-RB071 (= level 23 in Sturani 1967) which corresponds to the Bajocian/Bathonian boundary. The Ravin du Bès Section, with forty-six successive ammonoid fossil-assemblages of the Convergens Subzone belonging to three biohorizons through five metres of thickness, shows maximum values of biostratigraphic and biochronostratigraphic completeness, being one of the most complete in the world. Therefore, the Ravin du Bès Section should be chosen as the Global Stratotype Section and Point for the base of the Bathonian Stage. Two biostratigraphic logs summarize the ammonite content from the uppermost Bomfordi to basal Macrescens subzones. Three plates illustrate the most characteristic ammonoid taxa at the Bajocian-Bathonian passage in the Bas Auran succession.Item Formal proposal for the Bathonian GSSP (Middle Jurassic) in the Ravin du Bès Section (Bas-Auran, SE France)(Swiss Journal of Geosciences, 2009) Fernández López, Sixto Rafael; Pavia, Giulio; Erba, Elisabetta; Guiomar, Myette; Henriques, María Helena Paiva; Lanza, Roberto; Mangold, Charles; Olivero, Davide; Tiraboschi, DanieleThe Bathonian Global Stratotype Section and Point (GSSP) is proposed at the base of limestone bed RB071 (bed 23 in Sturani 1967) in the Ravin du Bès Section (43º 57' 38" N, 6º 18' 55" E), Bas-Auran area, “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: 1) The exposure extends over 13 m in thickness. At the Bajocian-Bathonian transition, no vertical (bio-, ichno- or tapho-) facies changes, condensation, stratigraphic gaps or hiatuses have been recorded. Structural complexity, synsedimentary and tectonic disturbances, or important alterations by metamorphism are not relevant constraints. 2) There is a well-preserved, abundant and diverse fossil record across the boundary interval, with key markers (ammonites and nannofossils) for worldwide correlation. The base of the Bathonian Stage and Zigzag Zone in Bas-Auran corresponds to the first occurrence level of Gonolkites convergens Buckman, which 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. 4) The criteria of accessibility, conservation and protection are assured by the “Réserve Naturelle Géologique de Haute Provence”. The Cabo Mondego Section (Portugal) is suggested as the Bathonian auxiliary section and point (ASSP) within this GSSP proposal.