Le gisement « Purbeckien » de vertébrés de Cherves-de-Cognac, Charente (SW France) : nouvelles données biostratigraphiques

The Purbeckian facies of the Aquitaine Basin northern margin outcrop has a thickness of about 30 m in the gypsum quarry of Champblanc, Cherves-de-Cognac, located about 10 km northeast of Cognac (Charente, SW France). Two lithological units have been identified. The basal unit (U1) is an alternation of gypsum and finely bedded black marls sometimes stromatolitic. The upper unit (U2) is a limestone-marl alternation, more or less fossiliferous. In the upper part of the unit, a one meter thick level has yielded a rich vertebrate fauna. A micropaleontological analysis of these levels, until now considered as Uppermost Jurassic age, has provided rich and diversified associations of brackish and fresh-water ostracodes and charophytes allowing them to be dated as Berriasian and to be related with the lower part of the Middle Purbeck of southern England.