Le Cretace des environs de Chabrieres (Basses-Alpes)

Abstract

Abstract The results of lithologic and paleontologic study of Cretaceous rocks of the Vocontian facies demonstrate that the massive upper Jurassic limestones are separated from Valanginian (lower Cretaceous) deposits by an erosion surface. Two series distinguishable in the Valanginian include a lower zone of marls and limestone containing a Berriasian fauna, and an upper zone of marls and limestones, less compact than those below, containing an upper Valanginian fauna. The Hauterivian is represented by a transitional zone of marls and limestones overlain by blue fossiliferous marls. The passage to the Barremian (lower Cretaceous) is transitional, marked by a zone resembling the thick-bedded Barremian limestones in which two members are recognized --thick-bedded limestone with interbedded schistose marl and fossiliferous marls and limestones with Emericiceras and Acrioceras in the lower part, and Holodiscus above. The uppermost Barremian bed is corroded, corresponding to an interruption in sedimentation. This surface is directly overlain by lower Albian-upper Aptian black marls, glauconitic in the upper part. Blue marls with Pervinquieria represent the Vraconian (upper Cretaceous). The Cenomanian, sparsely fossiliferous, is represented by blue marly limestones, sandstones and glauconitic sandy limestones. The Chabrieres Cretaceous series resembles the neritic facies to the south and the surrounding Vocontian domain. Sedimentation in the area is a result of slow uplift and subsidence, especially in the Valanginian.