Mise en évidence d’une formation siliceuse oligocène de type meulière dans le nord du bassin d’Aquitaine (Saint-Jean-d’Angle, Charente-Maritime, SO France)

Abstract

Outcrops of fossiliferous Palaeogene deposits are identified for the first time in the northern part of the Aquitaine Basin, at Saint-Jean-d’Angle, locality of Malaigre, in the Rochefort area (Charente-Maritime). They provide silicified deposits of a millstone facies, with a fossiliferous content rich in charophyte remains (gyrogonites, stems, “roots”) and in freshwater gastropods (hydrobioids, limnaeids). A preliminary study of the charophytes allowed to observe in the more or less translucent siliceous matrix gyrononites close to the genera Lychnothamnus, Sphaerochara and Harrisichara. On the palaeogeographical and palaeoenvironmental points of view, these silicified facies give evidence of the marine regression started during the late Eocene that lead to the continentalisation of the northern Aquitaine and the regional development of lacustrine areas.