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Les dép ts continentaux du Jurassique moyen au Crétacé inférieur dans le Haut Atlas oriental (Maroc) : paléoenvironnements successifs et signification paléogéographique [Middle Jurassic to Lower Cretaceous continental deposits from eastern High Atlas (Morocco): successive paleoenvironments and paleogeographic significance]

Keywords: Continental

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Abstract:

In the eastern High Atlas (Morocco), continental "Red Beds" overlying the last marine deposits of Jurassic age consist of three main lithostratigraphic units: the Anoual Formation, the Ksar Metlili Formation and the Dekkar Group, bounded by two sharp sedimentary discontinuities. The Anoual Formation is a fluvial dominated deltaic plain deposit. It is followed by a final marine transgression of Early Bathonian age. The Ksar Metlili Formation found only in some subsident areas represents a renewal of fluvio-deltaic environments with a flora of Late Tithonian-Early Berriasian charophytes. The Dekkar Group occupies a larger area of sedimentation, its limits overlap the whole domain. From bottom to top, the succession indicates the existence of three paleoenvironments: alluvial fans deposits locally associated with Barremian?-Aptian lacustrine sediments containing charophytes and ostracods, alluvial plains deposits and finally, marine coastal to brackish plains deposits of the Cenomanian.After the closure of the Jurassic Atlasic marine trough, the eastern Atlasic "Red Beds" were deposited in response to three main geodynamic events: * the filling of the Atlasic trough with very thick deposits in subsiding areas linked to tectonic rifting during the Early Bathonian; * the emergence of this area caused a hiatus in sedimentation involving strata ranging in age from Bathonian to Barremian?-Aptian. However, continental sediments are preserved in some onshore geomorphological depressions at the Jurassic/Cretaceous boundary; * the opening of new basins, continental during the Barremian?-Aptian, that became marine during the Late Cenomanian as the result of Cenomanian-Turonian transgression. A comparison of the succession of events recorded in different parts of the Atlasic belts allows reconstruction of the three phases of paleogeographic evolution in these southern Tethyan areas during Middle Jurassic to Late Cretaceous times.

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