La base dell’Arenaria di Ponsano nella sua area tipo e nella zona di Casole d’Elsa

The base of the Arenaria di Ponsano in the typearea and in the Casole d’Elsa zone (Tuscany). Lithological and micropaleontological characters of the lowermost sediments of the Miocene Ponsano Sandstone, cropping out in the south of Volterra (Pisa) area, have been studied. A first outcrop is located at Fattoria Tignano, close to the type-area of the formation, the other is near the village of Casole d’Elsa, about 5 Km SE of the former. The contact with the Pre- Neogene substratum is not directly observable at Fattoria Tignano, however it seems to be primary and unconformable. On the other hand, the contact with the Pre-Neogene units is well exposed in the Casole d’Elsa outcrop. Only marine deposits, Late Serravallian in age, have been recognised in the outcrop of Fattoria Tignano. They are sandstones in the lower part (Paragloborotalia partimlabiata Zone, Globoturborotalia decoraperta Subzone of foraminifers and Discoaster kugleri Zone of calcareous nannofossils) and marls in the upper (Neogloboquadrina atlantica praeatlantica Zone and D. kugleri Zone). At Casole d’Elsa, a basal limestone attributed to a continental environment is overlain by sandstones of marine littoral environment. Calcareous plankton is absent in the sandstones, therefore it has not been possible to date the outcrop. However, the closeness between the two outcrops allows us to refer the sediments of Casole d’Elsa to the Late Serravallian.