GNGTS 2014 - Atti del 33° Convegno Nazionale

GNGTS 2014 S essione 3.1 49 REPROCESSING, DEPTHMIGRATIONAND INTERPRETATIONOF SEISMIC PROFILES IN THE NORTH-WESTERN MEDITERRANEAN SEA M. Dal Cin a , A. Del Ben a , F. Accaino b , A. Birch-Hawkins c , P. Conn c , D. Chisari c , R. Geletti b , W. Toson b , M. Tyrrell c a Dipartimento di Matematica e Geoscienze (DMG), Università di Trieste, Italy b Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS), Trieste, Italy c TGS, Surbiton, Surrey, United Kingdom Introduction . The geological genesis, evolution and depositional settings of the Mediterranean Sea have been studied for decades by the scientific community which, for some aspects, combines research with the Petroleum Industry to enhance hydrocarbon exploration. It is in these circumstances that the geophysical study hereafter described was conceived. Two research bodies and a multi-client geophysical company have been involved in this project: the Department of Mathematics and Geosciences of the University of Trieste (DMG), the Italian National Institute of Oceanography and Experimental Geophysics (OGS) and TGS Geophysical Company ASA. The paper presents a geophysical analysis, based on interpretation of ten 2D multichannel seismic reflection profiles located in the eastern Sardo-Provençal basin of the north-western Mediterranean crossing domains from the outer west Sardinian shelf to the deep basin (Figs. 1A, 1B). The post-stack time migrated lines have a total length of 1545 km and cover an area of about 35.000 km 2 . The profiles belong to three distinct datasets (WMR, WS, CROP, location on Fig.1A) recorded by different geophysical projects, each of them using specific acquisition parameters. The five WMR (West Mediterranean Regional) profiles were provided by TGS. The three WS (West Sardinia) profiles were acquired by their owner OGS. The two CROP (CROsta Profonda) lines, provided by the DMG, were originally sponsored by AGIP-ENI, CNR & ENEL. The presence of the Messinian rock salt, that within a sedimentary sequence produces halokinesis and scatters most of the acoustic energy, suggested the reprocessing in time domain of a part of a CROP seismic profile in order to improve the imaging of those reflections that are strongly deformed or masked. To enhance image accuracy assessing size and location of geological structures beneath the Messinian salt, a pre-stack depth migration (PSDM) was executed using the Kirchhoff algorithm. The processing outcomes were useful not only to enhance and better define the entire seismic interpretation on the available datasets, but also allowed the evaluation of the peculiar lithologic/ stratigraphic conditions of the basin. The integration of the three datasets gave better coverage of the study area and supplied complementary information thanks to different resolutions. On the whole, the work presented hereafter aimed at better knowledge of the depositional history, starting from the Messinian Age, of the North-Western Mediterranean basin. Geological setting. According to Gennesseaux and Vanney (1979) and Rehault et al. (1984), the western Mediterranean Sea can be classified into four main morphological domains (Fig.1B). On the bathyal plain (or deep basin), on average, the water column is 2700 m thick. The Corso-Sardinian shelf has a minor extension compared with that of the Gulf of Lion and the Corso-Sardinian slope is steeper than the French-Spanish mainland slope. This last is overlapped by large amounts of sediments from the Rhône river, which contribute to the large deep-sea fan of the Gulf of Lion. The back arc basin of the north-western Mediterranean Sea is confined to the east by the passive margin of the Corso-Sardinian block and to the northwest by the conjugate continental margin of the Gulf of Lions and Provence, to the SW by the Valencia basin and the Balearic promontory and to the south by the Algerian and Alboran basins. The actual isolated position of the Corso-Sardinian block is the result of a NE-SW striking rifting stage due to extensional field stress induced since Late Eocene-Oligocene by the north-westward subduction of the Tethys