GNGTS 2017 - 36° Convegno Nazionale

540 GNGTS 2017 S essione 3.1 the origin and the characterization of the event is still debated. The study of evaporitic series and the relation between the post and pre-event sediments are the key to try to explain this unresolved question. Previous study of reflection/refraction seismic, combined to gravimetric and magnetic data, allowed to divided the two associated margins and the basin in five distinct domains (Moulin et al. , 2015; Afhilado et al. , 2015). The domains I and V, on the Gulf of Lion and eest Sardinia margins, respectively, correspond to the continental slope domain. The nature crust of domain III is assumed oceanic. In the center of basin, the magnetic anomaly pattern is different from the adjacent domains, showing a concomitant low gravity anomaly. The domains II and IV are the transitional area, called OCT (Ocean-Continent Transition). The crust velocities are high and this is still matter of debate. Several hypothesis have been proposed, as the exhumation of lower crust material (Bache et al. , 2010) or mantle material, serpentinized by water (Le Douaran et al. , 1984). The aim of this study is the analysis of several seismic profiles in order to correlate the different seismic evidences of the MSC markers across the margins and the Sardo-Provençal basin. Furthermore, the work tries to explain if a correlation between the deformation of salt domes and the crustal domains really exists. Geological setting. The central-western Mediterranean consists of a sub-basins series, developed from Oligocene time onward in the context of back-arc extension contemporaneous to the eastward to southward roll-back of the originally W-directed Apennine-Maghrebide subduction zone (Carminati et al. , 2010; Rehault et al. , 1984). During back-arc spreading, blocks moved radially, from NE-ward to southward, and rotated both clockwise (southern arm, African Atlas) and counter-clockwise (northern arm). About 60° counter-clockwise rotation affected the Sardinia-Corsica continental block (Speranza et al. , 2002). The Corso-Sardinian shelf is steeper and was affected by a minor extension than the slope of the Gulf of Lion, where the Rhone River provides an important contribution to the large deep- sea fan of the French margin. The rift and post-rift Oligo-Miocene sediments are the basal oldest units of the sedimentary sequence of the north-western Mediterranean basin. The Upper Oligocene (?)- Lower Miocene continental syn-rift sediments are covered by Neogenic pelagic deposition (Geletti et al. , 2014). In the western Mediterranean, during the MSC event, about 1600-2100 m of evaporites series are deposited (Geletti et al. , 2014). Only the uppermost part has been sampled by boreholes. This scarcity of calibration makes difficult the exact identification of the different facies interpreted along the seismic profiles. Lofi et al. (2011) proposed a new terminology for evaporites units, which were already identified by Rehault et al. (1984), and include Lower Unit (LU), Mobile Unit (MU) and Upper Unit (UU). On the continental slope, in the lower part, a thinning salt layer overlaid by the Upper Unit, turns into the Messinian Erosional Surface, which is generally a strong reflector that truncated the pre-Messinian reflectors (Geletti et al. , 2014). The abrupt restoration of marine conditions at the beginning of the Pliocene is another point not completely defined. In a recent study, Bache et al. (2012) suppose a two-step reflooding of the western Mediterranean Basin at the end of the MSC. The first step is characterized by a relatively moderate sea-level rise (500 m), resulted from the beginning of erosion of the Gibraltar barrier. The second step (5.46 Ma) was dramatic, due to the collapse of the Gibraltar channel and the following sea level rise of 600-900 m. The Lower Pliocene unit has a typical semi-transparent seismic facies. Above it, Upper Pliocene and Quaternary turbiditic layers of sediments, transported by the Rhone (Aslanian et al. , 2012), present a more reflective facies (Rehault et al. , 1984). On the Sardinian slope the PQ units are thinner than the Gulf of Lion or on the deep basin. Seismic dataset. The profiles that we interpreted belong to different datasets: West