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RESEARCH PRODUCT

Lower Cretaceous formations (Berriasian/Valanginian to Albian) from the East of the Paris Basin: lithostratigraphy and depositional environments.

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description

The Paris Basin is a Meso-Cenozoic intracontinental basin characterised during the Early Cretaceous by a continental evolution. However, in its southeastern part, due to transgres­sions originating from the Tethys, the Lower Cretaceous conti­nental deposits were occasionally interrupted by the deposition of marine sediments. In this area, the sedimentary succession includes above the Lower Tithonian “Calcaires du Barrois”, the transgressive “Sables de Soulaines” Formation on the Late Jurassic emersion surface. This formation showing facies characteristic of a tidal flat is reputed to be Valanginian in age, but there is no dating element and could as well begin in the Late Berriasian. Above, after a major discontinuity, the succes­sion continues with the "Calcaires à Spatangues" Formation. The facies point to open marine environments, also evi­denced by the presence of ammonites which indicate an Early Hauterivian age (Acanthodiscus radiatus to Lyticoceras nodoso-plicatum Zones). The sedimentary succession continues with the “Argiles ostréennes” reputed to be of Barremian age, but this stratigraphic attribution would imply the absence of the entire Upper Hauterivian, while the transition from the “Calcaires à Spatangues” to the “Argiles ostréennes” is gradual without discontinuity. It seems probable that the “Argiles ostréennes” deposited in very-shallow environments with possible occasional emersions, are of upper Hauterivian age at the base where the occurrence of a Faraoni-equivalent level is suspected, and Barremian at the top. During the Late Barremian, an emersion occurred, and the study area was subjected to deep continental weathering under hot and humid climates leading to the for­mation of lateritic weathering profiles. A major transgressive event occurred in the Early Aptian leading to the deposition of lower offshore clays called“Argiles à Plicatules Formation” dated using ammonites from the base of the Aptian (probably Deshayesites forbesi Zone) to the Dufrenoyia furcata Zone. In this formation, a chemostratigraphic approach based on δ13C has allowed the identification of an OAE1a equivalent in the Deshayesites deshayesi Zone. After the deposition in shoreface environments of the “Sables verts de l’Aube” (Greensands), Late Aptian/Early Albian in age, the succession is dominantly composed of Albian clays and marls constituting the “Argiles tégulines de Courcelles” Formation and the Marnes de Brienne well-dated by numerous ammonites. The Albian transgression leading to clayey deposits punctuated by numerous marker beds in an offshore environment marks the onset of a period of high sea level and the long-lasting installation of open marine deposits throughout the Upper Cretaceous, starting in the study area by the cenomanian Craie de Laubressel Formation.