Ofioliti, 2001, 26 (2a), 371-380 371 C - EASTERN SECTOR OF THE VOLTERRA BASIN Fabio Sandrelli Dipartimento di Scienze della Terra, Università di Siena, via Laterina 8, 53100 Siena, Italy (e-mail:
[email protected]). Keywords: field trip, Neogene sediments, Unconformity bounded units, Volterra Basin. Italy. INTRODUCTION A different hypothesis on the geodynamic evolution of Southern Tuscany, considers that the first compressional The geological setting of Southern Tuscany, where the phase acted until the end of the Neogene. In such a case, the Volterra Basin is located, is due to two different tectonic sedimentary basins of western Tuscany would have formed phases. The first one, compressional, is linked to the conver- as piggy-back or thrust-top basins (Bonini et al., 1994; Boc- gence and collision between the Adriatic Microplate and the caletti et al., 1994; Bonini and Moratti, 1995; Boccaletti et European Plate and occurred from the Late Cretaceous to al., 1997). the Early Miocene. The second one is consequence of the During the field trip, we will visit the Volterra Basin be- extensional tectonic regime active since the Early-Middle tween Spicchiaiola and Pignano. This area is particularly Miocene (Carmignani and Kligfield, 1990; Jolivet et al., important because it lies on the western margin of the Mid- 1990; Bertini et al., 1992; Carmignani et al., 1994; 1995; El- dle Tuscany Ridge and recorded most of the depositional ter and Sandrelli, 1995a; Baldi et al., 1995; Dal Mayer et al., events which occurred in Southern Tuscany from Late 1996). According to Elter and Sandrelli (1995a; 1995b), the Miocene to Pliocene.