GNGTS 2015 - Atti del 34° Convegno Nazionale

102 GNGTS 2015 S essione 1.2 Complex geometries in the Plio-Quaternary sequence in the West Sardinian margin G. Guion 1 , A. Del Ben 1 , A. Mocnik 1 , R. Geletti 2 1 DMG, University of Trieste, Trieste, Italy 2 OGS, Trieste, Italy Introduction. During Autumn 2010 the R/V OGS Explora acquired a seismic dataset in the western Sardinian offshore within the framework of the WS10 project (Fig. 1). The acquired profiles covered a wide region between the west Sardinian shoreline and the oceanic Sardo- Provençal basin, crossing the entire Sardinian continental slope and platform. In the continental crust the data explore the entire sedimentary sequence and reach the geological basement, well depicting the rift and post-rift phases. Furthermore, many interesting information were outlined about the Messinian Salinity Crisis (MSC) that produced thick evaporite sequences in the deep basin. In the upper slopes and shelves around the Mediterranean Sea margins, as well as locally in the onshore, the MSC originated the erosional surface known as Messinian Erosional Surface (MES). In this study we have focalized our analysis upon the Plio-Quaternary (PQ) sequence of the Sardinian shelf and upper slope. The base of the PQ sequence is generally clearly highlighted by the MES or, locally, by a thin seismic package of high amplitude reflectors that has been ascribed to Messinian evaporite of the Gessoso-Solfifera Fm (Geletti et al. , 2014). In the continental slope and in the deep basin, the MSC features are generally covered by the typical semi-transparent layer of Lower Pliocene; it, in its turn, is covered by the Upper Plio-Quaternary sediments, characterized by medium/high amplitude reflectors. Also in the Sardinian shelf we can recognize the semi-transparent Lower Pliocene sequence, often onlapping the MES. It is covered by wavy sediment strata that we ascribe to the depositional and erosional effects of the sea bottom currents (contourites). Locally, the Plio-Quaternary sequence shows very peculiargeometries that needadifferent explanation. An investigation of the sediment geometries and a correlation with local events have allowed us to hypothesize the relationships between cause and effect of the observed features. Geological setting. Oligo-Miocene opening of the west Mediterranean basin. A spreading phase between the African and European plates originated the development of the Tethyan oceanic crust (135 Myr). This process was followed by the subduction of the same oceanic crust and the consequent collision of the African and European plates. The subduction of the oceanic crust under the European margin took place in the Oligo-Miocene; it is associated with the calc-alkaline volcanism of the Sardinia and with the opening of the back-arc basins of the west Mediterranean Sea. The Fig. 1 – Map of the study area and position of the interpreted seismic profiles.