Contribution a l'etude des gisements volcano-lacustres a diatomees de la region de Rochessauve et de Saint-Bauzile (Ardeche)

The upper Miocene diatomaceous sediments of the northeast border of the Coiron massif (Ardeche, France) indicate a shallow-water lacustrine environment. Until now the outcrops at Andance and Ranc-Le Combier have been considered as part of the same lacustrine deposition, but paleoecologic studies suggest that they formed independently. At Andance, diatomaceous sedimentation was continuous until the eruption of the Coiron plateau basalts, while at Ranc a hiatus occurs between the lower and upper diatomites.