GNGTS 2014 - Atti del 33° Convegno Nazionale

50 GNGTS 2014 S essione 3.1 oceanic lithosphere. The process progressively evolved into a south-eastward slab rollback and was responsible for the spreading stage that lead to the opening of the North-Western Mediterranean as a back-arc basin, during the Miocene (Carminati et al. , 2012). This occurred in association with the formation of oceanic crust (Carminati and Doglioni, 2005) and the rotation of the Corso-Sardinian block until its collision with the NWAdria plate (Finetti et al. , 2005). The oldest units of the sedimentary sequence of the north-western Mediterranean basin and related slopes, comprise rift and post-rift Oligo-Miocene sediments. They correspond, respectively, to discontinuous reflectors with variable amplitude, related to probable continental syn-extensional clastic deposits and to more continuous reflectors possibly related to pelagic deposition (Rehault et al. , 1984; Geletti et al. , 2014). During the Messinian age an extreme and relatively brief geological event occurred in the Mediterranean basin and surrounding areas in response to about 1500m sea level drop principally due to a closure of the gateway between the Atlantic and Mediterranean Sea (Clauzon et al. , 1996; Krijgsman et al. , 1999; CIESM, 2008). This event, known as the Messinian Salinity Crisis (MSC), is generally accepted to have onset 5.96 My ago (Krijgsman et al. , 1999; CIESM, 2008; Krijgsman and Meijer, 2008). In the western Mediterranean basin the MSC deposits consist of evaporite lithologies with an average thickness ranging between 1600-2100 m (Geletti et al. , 2014) that have not been sampled by boreholes except for the uppermost part. These units were Fig. 1 – A) Position of the analysed seismic reflection lines in the Sardo-Provençal basin of the north-western Mediterranean Sea: WMR profiles (by TGS) in blue; WS profiles (by OGS) in green; CROP profiles in orange. Red segment: reprocessed C88M1 REPRO, part of CROP C88M1. B) Morphology of the western Mediterranean Sea. Study area bounded by the red polygon. C.i) Seismic line recorded in the deep basin domain of the north-western Mediterranean (Finetti and Morelli, 1973). C.ii ) Seismic velocities (Montadert et al. , 1978) that permitted C.iii) the identification of the Messinian Trilogy (modified, Rehault et al. , 1984).