Lower Aptian ammonite biostratigraphy and potential for further studies of OAE 1a in Bulgaria |
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| Institution: | 1. Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad Universitaria, Coyoacán, 04510 México, D.F., Mexico;2. Département des Sciences de la Terre, Université de Nice-Sophia Antipolis, 28 Avenue Valrose, F-06100 Nice, France;3. Departamento de Estratigrafía y Paleontología, Facultad de Ciencias, Universidad de Granada, Avenida Fuentenueva s/n, 18002 Granada, Spain;4. Departament de Geoquímica, Petrologia i Prospecció Geològica, Universitat de Barcelona Martí i Franquès s/n, 08028 Barcelona, Spain;1. Department of Earth and Planetary Sciences, Faculty of Science, Hokkaido University, N10W8, Sapporo 060-0810, Japan;2. Tohoku University Museum, Tohoku University, Sendai 980-8578, Japan;1. Université de Lyon, UCBL, ENSL, CNRS, LGL TPE, Bâtiment Géode, 2 rue Dubois, 69622 Villeurbanne, France;2. Hungarian Natural History Museum, Department of Palaeontology, 1088 Ludovika tér 2, Budapest, Hungary;3. IDEAN, Instituto de Estudios Andinos Don Pablo Groeber, Departamento de Ciencias Geológicas, Universidad de Buenos Aires, Ciudad Universitaria, Pabellón II, 1428 Buenos Aires, Argentina;4. Departamento de Paleontología, Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad Universitaria, Delegación Coyoacán, CP 04510, Ciudad de México, Mexico;5. Departamento de Estratigrafía y Paleontología, Facultad de Ciencias, Universidad de Granada, Campus de Fuentenueva s/n, 18002 Granada, Spain;6. Groupement d''Intérêt Paléontologique, Science et Exposition, 60 bd Georges Richard, 83000 Toulon, France;7. Djanelidze Institute of Geology, Polytkovskaja St. 5, 0186 Tbilisi, Georgia;8. Demmerik 12, 3645 EC Vinkeveen, Netherlands;9. Geological-Palaeontological Department, Natural History Museum, Burgring 7, A-1010 Vienna, Austria;10. Chemin du Battoir 7, 1337 Vallorbe, Switzerland;11. Polish Geological Institute, National Research Institute, 4 Rakowiecka, PL-00-975, Warsaw, Poland;12. Geology Department, Faculty of Science, University of Birjand, PO Box 97175/615, Birjand, Iran;13. Institute of Geonics, Academy of Sciences of the Czech Republic, Studentská 1768, CZ-70800 Ostrava-Poruba, Czech Republic;14. Geological Faculty, Moscow State University, 119234 Leninskie Gory, Moscow, Russia;15. Borissiak Palaeontological Institute of RAS, Profsoyuznaya 123, Moscow, 117647 Russia;p. Cherepovets State University, Lunacharskogo 5, Cherepovets, 162600 Russia |
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| Abstract: | Sediments of Early Aptian age in Bulgaria can be assigned to four different facies: platform carbonates (Urgonian complex), shallow-water siliciclastics, hemipelagic and flyschoid siliciclastics. The taxonomic analysis of the ammonite faunas of 18 sections from these four different facies resulted in a revision of the existing ammonite zonation scheme so far applied in Bulgaria and adjoining areas. A new biostratigraphic scheme, which bridges the western and eastern Tethys, is thereby proposed for the Lower Aptian of Bulgaria.The Upper Barremian Martelites sarasini Zone is characterized in its upper part by the Pseudocrioceras waagenoides Subzone in the shallow-water sections and by a horizon with Turkmeniceras turkmenicum in the deep-water settings. The Upper Barremian/Lower Aptian boundary is fixed by the first appearance of Paradeshayesites oglanlensis. For the Lower Aptian the following ammonite zones were established (from bottom to top): The Paradeshayesites oglanlensis Zone, the Deshayesites forbesi Zone (= formerly Paradeshayesites weissi Zone) including the Roloboceras hambrovi Subzone in the upper part, the Deshayesites deshayesi Zone including the Paradeshayesites grandis Subzone in the upper part and the Dufrenoyia furcata Zone. The Lower–Middle Aptian boundary has been defined by the appearance of species belonging to the genera Epicheloniceras and Colombiceras.The Lower Aptian ammonite faunas of Bulgaria, allow an interregional correlation with other areas of the Tethyan Realm. The presence of Turkmeniceras in the Upper Barremian enables a correlation with the Transcaspian region, whereas Roloboceras, Koeneniceras and Volgoceratoides found in the middle part of the Lower Aptian are more typical representatives of the ammonite faunas in northern Europe (England, Germany, Volga region).The analysis of the ammonite successions in combination with sedimentological observations enable us to conclude that the marls and marly limestones of the Lower Aptian studied here also cover the interval of the Oceanic Anoxic Event 1a. An interval of thin-laminated clays, rich in organic matter, was identified in the upper part of the D. forbesi Zone (Roloboceras hambrovi Subzone). This interval is characterized by a total lack of benthic faunas. |
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