Mapping the rise and demise of Urgonian platforms (Late Hauterivian - Early Aptian) in southeastern France and the Swiss Jura |
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| Institution: | 1. 24 Chemin des Champs d’Amot, F-74140 Messery, France;2. 71 Chemin de Planta, CH-12223 Cologny, Switzerland;3. Chemin Meruzin, F-69370 St Didier au Mont d’Or, France;4. Département de Géologie et de Paléontologie, Sciences de la Terre et de l’Environnement, 13 Rue des Maraîchers, CH-1211 Genève 4, Switzerland;5. Université de Brest, UMR 6538 Domaines Océaniques, 29238 Brest, France;6. CNRS, UMR 6538 Domaines Océaniques, 29238 Brest, France;1. Lerchenauerstr. 167, D-80935 München, Germany;2. Babe?-Bolyai University, Department of Geology and Center for Integrated Geological Studies, Str. M. Kog?lniceanu 1, 400084 Cluj-Napoca, Romania;1. CNRS-UMR6249, Laboratoire Chrono-Environnement, UFR des Sciences et Techniques, 16 Route de Gray, 25030 Besançon, France;2. Fachbereich Geowissenschaften, Forschungsbereich Paläobiologie, Universität Tübingen, Hölderlinstras., 12, D-72074 Tübingen, Germany;3. Equipe d''Archéologies Environnementales, Maison de l''Archéologie et de l''Ethnologie René Ginouvès, ArScaAn-UMR 7041, case courrier 05, 21 allée de l''Université, F-92023 Nanterre Cedex, France;4. Fachbereich Geowissenschaften, Forschungsbereich Urgeschichte und Naturwissenschaftliche Archäologie, Universität Tübingen, Rümelinstrs. 23, D-72070 Tübingen, Germany;1. Departament de Geologia, Facultat de Ciències, Universitat Autònoma de Barcelona, Edifici C, E-08193 Bellaterra, Barcelona, Spain;2. Institut Català de Paleontologia Miquel Crusafont, Carrer de l’Escola Industrial 23, E-08201 Sabadell, Catalonia, Spain;3. Institut de Ciències de la Terra Jaume Almera-CSIC, E-08028 Barcelona, Spain;4. Grupo Aragosaurus-IUCA, Dpto. Ciencias de la Tierra, Facultad de Ciencias, Universidad de Zaragoza, Calle Pedro Cerbuna 12, E-50009 Zaragoza, Spain |
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| Abstract: | Lower Cretaceous carbonate deposits historically called “Urgonian limestones” are widely exposed around the margins of the Vocontian basin in southeastern France and in the adjacent Swiss Jura. This paper presents the history of their rise, growth and sudden demise. Eleven maps were constructed for deposits ranging in age from the Late Hauterivian pro parte to the Early Aptian (Bedoulian) pro parte. Based on sequential interpretations, they illustrate the present geographical distribution of the inner platform facies (Urgonian limestones stricto sensu, with rudists), the outer platform facies (essentially bioclastic deposits) and the basinal facies (slope, hemipelagic, pelagic deposits). These maps depict only the final terms of each successive sequence (the late highstand intervals). Chronostratigraphy is constrained by ammonites found mainly in basinal deposits, by echinoids, by rudists and to a lesser extent by dinoflagellates and calcareous nannoplancton. Inner platform, outer platform and slope (talus) deposits are dated by rich assemblages of orbitolinids and dasycladalean algae. Currently 39 species of orbitolinids have been recognized and their ranges collated with those of the ammonites in the area.In the Jura and in Provence the oldest Urgonian deposits are dated early Late Hauterivian, thus showing the synchroneity of the onset of platform carbonates development on both the southern and northern margins of the basin. Thereafter, growth of the platforms led a clearly regressive shallowing-upward trend, resulting from a stepwise progradation toward the center of the Vocontian area, coordinated with cyclical exposures in the inner platform areas. The maximum reduction of the platform deposits occurred early in Late Barremian times, coeval with a noticeable turnover in the orbitolinids assemblages.Thereafter, carbonate platform deposition shifted toward the margins of the Vocontian basin. In Early Aptian time, a well-dated discontinuity of regional extent marks the sudden, almost synchronous disappearance of the Urgonian deposits. |
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