GNGTS 2014 - Atti del 33° Convegno Nazionale

The availability of the processed and interpreted seismic dataset of Western Sardinia [WS10 project, partly published by Geletti et al. (2014) and Del Ben et al. (2014)] and the processed and partly interpreted profiles of South Balearic margin (Salt deformation and sub-salt fluid circulation in the Algero-Balearic abyssal plain (SALTFLU) SF12 project, Camerlenghi et al., submitted), allowed us to focus on some analogies in the seismic facies of the sedimentary sequences that deposited after the drifting phases of both basins during the MSC and in the Pliocene and Quaternary. We paid particular attention to differences and analogies concerning the thickness of the Messinian evaporitic units, evidences of depositional depths, erosive events and discontinuity surfaces. Salt tectonic activity involving the Upper evaporite Unit and the Plio-Quaternary deposits will be discussed based on different kinds of salt-induced deformation in the lower slopes and abyssal plains already identified by Camerlenghi et al. (2009, 2014), Geletti et al. (2014) and Del Ben et al. (2014). Given the absence of calibrating boreholes in the deep Mediterranean basins and the difficult penetration of seismic energy below the evaporitic layers, the comparison of these datasets is a contribution to the comprehension of the evaporitic deposition, margin erosion, and early-stage salt deformation during the MSC in the Mediterranean sea. Geological setting. The present distribution of the geological domains in the west Mediterranean Sea is the product of mainly extensional processes that followed the Late Cretaceous to Early Tertiary counterclockwise rotation of Iberia and the compression of the Pyrenees until about 20 Ma (Carminati et al. , 2004). Beginning in the Late Oligocene, a rifting phase affected most of the region; during the Early Miocene, a WNW-ESE extension was associated to detachment �� ��� �������������� of the Corso-Sardinia microplate and Balearic promontory from the Iberian plate (Sabat et al. , 1995). The Sardo- Provençal basin and Valencia Trough started to open while the southestern part of the Balearic promontory underwent NW-SE compression originating the Betic-Balearic thrust belt (Gelabert et al. , 1992). Following the continental collision, an extensive rifting phase begun initiating the opening of the N-S opening of the Algero-Balearic basin. Between the Alboran block and the Balearic Promontory a right lateral movement generated the transpression along the Emile Baudot Escarpment (EBE) (Acosta et al. , 2001). In the EarlyMiocene, the Corso-Sardinia microplate started a counter-clock rotation reaching the actual position in the Middle Miocene (Cohen, 1980). The Provençal basin opened as back- arc basin between 19 and 16 Ma (Speranza et al. , 2002). The Sardinia Block migrated along the right lateral north Balearic fault Zone and displaced the Balearic Promontory with a coeval rifting in the Valentia Trough. The Algero-Balearic basin has a thin and uniform oceanic crust (Sabat et al. , 1995) and the N-S trending Hannibal Ridge is considered the spreading center of the Algero oceanic basin, that ended its activity 8 Ma (Mauffret et al. , 2004). The authors consider the NW-SE magnetic anomaly 160 km far from the east side of the Hannibal ridge, as the boundary between the Sardo- Provençal and Algero-Balearic basins. The sedimentary sequence is characterized by the post drift Messinian Salinity Crisis (MSC), resulted by a complex combination of tectonics, precession controlled oscillations and glacio eustatic processes which progressively contributed to restrict and finally isolate theMediterranean Sea from the ocean. Collected literature analyzed by CIESM (2008) lead to agreement on beginning of the evaporitic sequence at 5.96 Ma until 5.33 Ma, with re-connection between Mediterranean and Atlantic basins and restoration of water circulation (Hsü et al. , 1973). The “Messinian trilogy” recognized in the West-Mediterranean abyssal plain (Rehault et al. , 1984), is characterized by different seismic facies: the Lower evaporite Unit (LU), the salt Mobile Unit (MU) and the Upper evaporite mainly gypsiferous Unit (UU) (Lofi et al. , 2011). In the eastern Sardo-Provençal basin, the Upper Unit has been identified as nine-ten cycles of high reflecting layers interpreted as gypsum with alternation of transparent layers associated to halite lithology (Geletti et al. , 2014). The authors have recognized a thicker GNGTS 2014 S essione 1.2 157