ALLOSTRATIGRAPHY AND SEISMIC STRATIGRAPHY OF THE MIOCENE SEDIMENTS OFTHE SPICCHIAIOLA-POMARANCE AREA, SOUTHERN SIDE OF THE VOLTERRA BASIN (TUSCANY, ITALY)

The objective of this work is to analyze the Miocene depositional unit s of the southern side of the Volterra Basin (Tuscany, Italy) utilizin g outcrop and seismic data and to establish the major events that led to their formation. Four depositional units have been recognized: Unit 1 is characterized by marine sediments of late Serravallian-early Tor tonian age; Unit 2 is characterized by fluvio-lacustrine and brackish deposits of late Tortonian-early Messinian age; Unit 3 is characterize d by marine deposits of early Messinian age; Unit 4 is characterized b y the lacustrine deposits (''Lago-mare'' facies) of late Messinian age . The deposition of these four units is associated with an extensional tectonic regime that has been active in Tuscany at least since the la te Tortonian. This regime generated half graben type structures in whi ch deposition occurred. The recognized unconformities between the unit s are mainly related to uplift as a consequence of the extensional tec tonic regime.