Geophysical exploration of the West Sardinian continental margin and Sardo-Provençal oceanic basin (West Mediterranean Sea)

Geophysical exploration of the West Sardinian continental margin and Sardo-Provencal oceanic basin (West Mediterranean Sea). Del Ben A.1, Geletti, R.2, Zgur F.2, Brancatelli G.2, Camerlenghi A.2, Dal Cin M.2, Fais S. 3, Forlin E.2, Lanzoni A.1, Romeo R.2 1 Dipartimento di Matematica e Geoscienze, Università di Trieste. 2 Istituto Nazionale do Oceanografia e di Geofisica Sperimentale OGS, Trieste. 3 Dipartimento di Ingegnaria Civile, Ambientale e Architettura, University of Cagliari Corresponding author: delbenan@units.it Keywords: West-Sardinian margin, Sardo-Provencal Basin, Seismic reflection, Messinian, Evaporites The Sardo-Provencal Basin and its eastern continental West Sardinian margin represents one of the less explored Italian sea. During the year 2010 the Explora acquired a new geophysical dataset (W-Sardinia_2010) represented by seismic reflection and chirp profiles and Multibeam and Magnetic data. The dataset acquisition was designed on the base of results provided by previous seismic profiles of the MS (Mediterranean Sea), CROP (CROsta Profonda) and ViDEPI (Visibility of Petroleum Exploration Data, public data available in the Sardinian offshore, near the shoreline) projects. Integration of all the different dataset allowed us to interpret the main geological structures produced during the Upper Oligocene-Lower Miocene, when the rifting phase was followed by the oceanic opening of the West Mediterranean Sea. On the continental margin seismic waves have explored the whole sedimentary sequence, reaching the geological basement and showing the horst and graben system produced by the extensional tectonics (Geletti et al., 2014; Dal Cin et al., 2016; Del Ben et al., 2018). On the oceanic abyssal plain the MS and CROP profiles depicted some deep reflectors, generally ascribed to the top of the basaltic basement, while not good information is available about the Moho reflector. The new W-Sardinia_2010 dataset, due to its higher resolution, highlights very clearly the Messinian evaporate sequence, characterized by the typical Messinian trilogy (Rehault et al., 2004). The evaporate sequence is represented by i) a high amplitude stratified upper unit (UU), of mainly gypsum lithology, ii) a transparent salt unit (MU for Mobile Unit), characterized by strong halocinetic tectonics, and iii) a stratified lower unit (LU), never crossed by boreholes, probably also represented by gypsum. This trilogy gradually onlaps the lower continental slope, disappearing toward east, substituted by a marked erosional truncation (MES, for Margin Erosional Surface: Lofi et al., 2011) representing a variable hiatus, locally evident also in the Sardinia onshore. The Plio-Quaternary sequence, clearly depicted by the seismic reflection, was highly deformed, especially during the Lower Pliocene, by halocinetics. Sometimes this process is still active, producing some circular structures in the sea bottom, which are well imaged in detail by the chirp and multibeam data. The different resolution of the available data represents the best condition to study the whole sedimentary sequence and to correlate deep structures with their local effect on shallow youngest sediments. References Dal Cin M., Del Ben A., Mocnik A., Accaino F., Geletti R., Wardell N., Zgur F. & Camerlenghi A. (2016) - Seismic imaging of Late Miocene (Messinian) evaporites from Western Mediterranean back-arc basins. Petr. Geosci. 22, 297–308. Del Ben, A., Mocnik A., Camerlenghi A., Geletti R., Zgur F., 2018. – 9.A-D- Western Sardinia. In: J. Lofi, Ed., Seismic atlas of the Messinian Salinity Crisis markers in the Mediterranean sea. Volume 2. - Mem. Soc. geol. fr., n.s., 2018, t. 181, and Commission for the Geological Map of the World, 32-35. Geletti R., Zgur F, Del Ben A. , Buriola F. , Fais S., Fedi M., Forte E., Mocnik A., Paoletti V., Pipan M., Ramella R.,. Romeo R., Romi A. (2014) - The Messinian Salinity Crisis: new seismic evidence in the West-Sardinian Margin and Eastern Sardo-Provençal Basin (West Mediterranean Sea). Marine Geology, 351, 76–90. Lofi, J., Deverchère, J., Gaullier, V., Gillet, H., Gorini, C., Guennoc, P., Loncke, L., Maillard, A., Sage, F., Thinon, I. (2011). Atlas of the Messinian seismic markers in the Mediterranean and Black Seas. Memoir Societe Geologique de France n.s. 179 and World Geological Map Commission (72 pp.). Rehault, J.P., Boillot, G., Mauffret, A., 1984. The Western Mediterranean Basin geological evolution. Marine Geology 55, 447–477.