Magnetostratigraphic calibration of the Oligocence to Middle Miocene (30-15 Ma) mammal biozones and depositional sequences of the Swiss Molasse Basin
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Cited by 14 publications
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[1] The Penninic nappes in the Swiss Alps formed during continental collision between the Adriatic and European plates in Cenozoic times. Although intensely studied, the finite geometry of the basement-bearing Penninic nappes in western Switzerland has remained a matter of debate for decades (e.g., "Siviez-Mischabel dilemma") and the paleogeographic origin of various nappes has been disputed. Here, we present new structural data for the central part of the Penninic Bernard nappe complex, which contains pre-Permian basement and Permo-Mesozoic metasedimentary units. Our lithological and structural observations indicate that the discrepancy between the different structural models proposed for the Bernard nappe complex can be explained by a lateral discontinuity. In the west, the presence of a Permian graben caused complex isoclinal folding, whereas in the east, the absence of such a graben resulted mainly in imbricate thrusting. The overall geometry of the Bernard nappe complex is the result of three main deformation phases: (1) detachment of Mesozoic cover sediments along Triassic evaporites (Evolène phase) during the early stages of collision, (2) Eocene top-to-the-N(NW) nappe stacking (Anniviers phase), and (3) subsequent backfolding and backshearing (Mischabel phase). The southward localized backshearing is key to understand the structural position and paleogeographic origin of units, such as the Frilihorn and Cimes Blanches "nappes" and the Antrona ophiolites. Based on these observations, we present a new tectonic model for the entire Penninic region of western Switzerland and discuss this model in terms of continental collision zone processes.
[1] The Penninic nappes in the Swiss Alps formed during continental collision between the Adriatic and European plates in Cenozoic times. Although intensely studied, the finite geometry of the basement-bearing Penninic nappes in western Switzerland has remained a matter of debate for decades (e.g., "Siviez-Mischabel dilemma") and the paleogeographic origin of various nappes has been disputed. Here, we present new structural data for the central part of the Penninic Bernard nappe complex, which contains pre-Permian basement and Permo-Mesozoic metasedimentary units. Our lithological and structural observations indicate that the discrepancy between the different structural models proposed for the Bernard nappe complex can be explained by a lateral discontinuity. In the west, the presence of a Permian graben caused complex isoclinal folding, whereas in the east, the absence of such a graben resulted mainly in imbricate thrusting. The overall geometry of the Bernard nappe complex is the result of three main deformation phases: (1) detachment of Mesozoic cover sediments along Triassic evaporites (Evolène phase) during the early stages of collision, (2) Eocene top-to-the-N(NW) nappe stacking (Anniviers phase), and (3) subsequent backfolding and backshearing (Mischabel phase). The southward localized backshearing is key to understand the structural position and paleogeographic origin of units, such as the Frilihorn and Cimes Blanches "nappes" and the Antrona ophiolites. Based on these observations, we present a new tectonic model for the entire Penninic region of western Switzerland and discuss this model in terms of continental collision zone processes.
Sédimentologie, paléontologie et paléoenvironnements côtiers de la région de Porrentruy (Sud-Rhénan, Paléogène, Jura, Suisse): implications géodynamiques
Located in the distal part of the Swiss Molasse Basin and in the southern extension of the Rhine Graben, the conglomeratic deposits belonging to the Gompholithes & Conglomérats stratigraphic group have been the object of detailed sedimentological and paleontological studies. The great number of outcrops that came into sight during the building works of the Transjurane highway in the vicinity of Porrentruy (Swiss Jura) lead to a better understanding of Rupelian paleoenvironments (Early Oligocene).The sedimentological and paleontological studies reveal the existence of coastal environments with Mesozoic limestone cliffs notched by canyons with torrential rivers. Those rivers eroding the Mesozoic series create pebbles deposits forming marine deltas prograding towards North. In protected areas, some lacustrine environments can develop.These conglomeratic deposits are strongly bound to the Rupelian tectonic activity. The rhenish distension and the activity of the transform faults located between the Rhine Graben and the Bresse basin divide the Mesozoic blocks in horst and graben structures, thus allowing the erosion of sediments in higher regions (horst) and their transport in lower zones (graben).The discovery of rare pebbles made of endogene and effusive rocks in those conglomeratic deposits shows a transport coming from the Vosges massifs towards south to the Porrentruy region, probably with the support of a littoral drift. Although the surrection of the Vosges and Schwarzwald massifs (and the beginning of their erosion) is normally attributed to the base of the Miocene, the presence of those pebbles attests the existence of faults putting the basement of the Vosges massif to erosion since the base of Rupelian. RESUME Situés dans la partie la plus distale du bassin molassique suisse et dans le prolongement sud du fossé rhénan, les dépôts conglomératiques appartenant au groupe stratigraphique des Gompholithes & Conglomérats ont fait l'objet d'une étude sédimentologique et paléontologique détaillée. La multitude des affleurements réalisés lors des travaux de construction de l'autoroute Transjurane dans la région de Porrentruy (Jura), permet d'appréhender ces paléoen-vironnements rupéliens (Oligocène inférieur).Les études sédimentologiques et paléontologiques révèlent l'existence d'environnements côtiers avec des falaises de calcaires mésozoïques entaillées par des canyons où se trouvent des rivières au régime torrentiel. Ces rivières qui érodent les couches du Mésozoïque créent des galets qui sont déposés sous la forme de deltas marins progradant vers le nord. A l'abri des exutoires des canyons se développent quelques environnements lacustres.Ces dépôts conglomératiques sont fortement liés à l'activité tectonique rupélienne. La distension rhénane et l'activité de la faille transformante située entre le fossé rhénan et le bassin de la Bresse subdivisent les différents blocs mésozoïques en horsts et grabens, permettant ainsi l'érosion des sédiments dans les parties hautes (horst) et leur transport dans les zones basses...
Integrated stratigraphy and paleoenvironmental reconstruction of the Miocene series of the Châteauredon Dome, S.E. France
This study presents the results of a palynological analysis (dinocysts, spores and pollen) that are discussed with those obtained from stable isotopes geochemistry (δ 13 C and δ 18 O) on Miocene coastal and continental deposits in the southern area of the Digne Valensole Basin. Palynology study has been conducted on dark levels while isotopic analysis was performed on paleosol carbonate nodules.Stratigraphic attributions based on palynology are restricted to dinoflagellate cysts associations as spore and pollen assemblages are scarcely identified. They confirm the stratigraphy based on the micromammal fossil sites and propose an Aquitanian to early Serravallian age. From a selection of ODP-DSDP sites, the marine δ 13 C chemostratigraphy shows several characteristic isotopic intervals. These were also identified on the continental signal from the paleosols.Stratigraphic interpretation from the isotopic continental signal is in good agreement with both palynological data and micromammal sites attributions. It can offer a high resolution correlation, a few 100 kyr when paleosols are frequent and δ 13 C fluctuations significant. The method puts also in evidence hiatuses (during middle Aquitanian and late Burdigalian) and precise the age of formations interbedded between micromammal sites.Regarding paleoenvironmental reconstruction, the palynological study is more efficient than isotopic data and shows a flora evolution from mesothermic riparian and coastal vegetation during Aquitanian/Burdigalian to herbaceous and more open vegetation during the Langhian period in association to a drier and warmer climate.This study brings also new insights on paleogeographic reconstructions. The studied area was located close to the sea coast during the lower Miocene. Marine incursions occurred during the middle Aquitanian and from late Burdigalian to early Serravallian. These are characterized by tidal facies as well as dinoflagellate cysts and benthic foraminifera occurrences. These marine incursions, better recorded in the eastern part of the Châteauredon Dome, argued for a northern or a southern connection with the Miocene sea in relation to the foreland basin geodynamic evolution. RESUMECette étude présente les résultats de la palynologie (kystes de dinoflagellés, spores et pollen) discutés avec ceux de la géochimie des isotopes stables (δ 13 C et δ 18 O) réalisée sur les séries côtières et continentales d'âge miocène dans la partie sud du bassin de Digne. L'étude palynologique a été réalisée sur des niveaux noirs et les analyses isotopiques sur les nodules carbonatés des paléo-sols.Les attributions stratigraphiques sont basées sur la palynologie établie à partir des associations de dinokystes et non sur les assemblages de spores et pollen, peu diversifiés. Elles confirment la stratigraphie établie d'après les sites fossilifères de micromammifères et proposent un âge Aquitanien à Serravallien inférieur. A partir d'une sélection de plusieurs sites ODP-DSDP, la chimiostratigraphie δ 13 C marine montre plusieurs intervalles isotop...
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