Phenomenes epigeniques dans les calcaires toarciens de Saint-Antonin (Aveyron)

Abstract

Nodules in Toarcian (Jurassic) limestones at Saint-Antonin in the valley of the Aveyron, southwestern Quercy, France, which resemble oolites but lack the concentric structure, are described and attributed to deposition of calcite around a nucleus in one single stage. Petrographic study of the limestones also reveals that dolomitization, phosphatization, and silicification have taken place simultaneously, probably as a result of biochemical processes.