GNGTS 2013 - Atti del 32° Convegno Nazionale

No seismic evidences of Messinian trilogy have been recorded in the present shallow basins. In the Adriatic Basin the Messinian sequence is absent or mainly represented by gypsum and anhydrite with marls intercalation, named Gessoso Solfifera formation. It is calibrated by a great number of boreholes and reaches a thickness of about 120m. Also in the Sicily Channel we can recognize hiatus related to the MES or, alternatively, the Gessoso Solfifera layer, calibrated by some boreholes. The Tyrrhenian Basin opened, from west to east, since the Tortonian age. No relevant presence of Messinian evaporite units has been recorded, just some samples of gypsum lithologies are testified along the continental margins (Fabbri and Curzi, 1980). Discussion. In Fig. 2 the WS10-07 seismic profile crosses with an east-west direction the Sardinian slope of the continental margin till the deep Balearic Basin. In the detail B we have highlighted the Messinian trilogy where the thick and high reflecting UU covers the MU which is deformed by halokinetics processes; the LU is partially masked by the signal absorption due to the diapir presence. In the frame C the typical seismic signature of the MES is evident along the upper continental slope by a prominent reflector that truncates the pre-Messinian horizons. In Fig. 3 four seismic portions of a virtual profile starting from the Adriatic Basin, crossing the Ionian Basin and reaching the Levantine Basin are described. A portion of seismic profile ADRIA-95 (Fig. 3A) shows the Messinian layer as a prominent reflector that encompasses the entire gypsum deposits of about 100 m, as calibrated by Eterno 1 borehole. It is covered by the thick low reflecting Pliocene sediments and by the Quaternary prograding sequences originated by the erosion of the Apennine Chain. Moving to the deep Ionian Basin the Gessoso Solfifera formation turns on the thick salt layer of the abyssal plain, as shown along the seismic profile CROP-22 (Fig. 3B); the bottom of its characteristic transparent facies is well evidenced by a prominent reflector, west-tilted and giving a structural high. The pre-Messinian horizons show toplap terminations on the salt bottom that is probably associated to a sub-aerial exposure due to the joint effects of the Messinian sea level drop and of the tilting. Toward west the compressive tectonics originate more and more irregular reflectors on the top and inner the salt layer producing typical diffractions. The thick layer of Messinian salt is proved to be present till the eastern sector of the Mediterranean Sea: the portion of the seismic profile MS-50 (Fig. 3C) shows an eastward increasing of salt deformation, where the deep Nile fan delta has been deposited after the Messinian crisis. The underlying salt layer is squeezed by the Plio-Quaternary sediment load and a single high amplitude reflector identifies the remaining discontinuity . In the West Cilicia Basin, along the seismic profile MS-49 (Fig. 3D) the salt layer clearly pinches out toward the margin. A high reflecting upper sequence, interpreted by Bertoni and Cartwright (2006) as deep-water clastic sediments, are very similar to the seismic facies of the UU in the Balearic Basin, suggesting their possible ascription to gypsum layer. Conclusions. The MSC, even if it is well documented in the whole Mediterranean Sea by several different seismic markers, is a still open question. The interpretation of the seismic signatures let to distinguish alternated phases of exposure and flooding of the different basins which often result to be hardly correlated to one another. In the Adriatic basin and in the Sicily Channel the Messinian layer, where it is not replaced by an erosional surface, is present as a thin evaporate layer mainly constituted by Gessoso Solfifera formation. The Messinian trilogy has been observed only in the deep Balearic Basin, while in the Ionian and Levantine Basins it shows a mainly salt seismic facies. The presented seismic data aim to contribute to the recognition of the different seismic facies which characterize the different units; their comparison could improve the comprehension of the processes that affected the Messinian events in the Mediterranean region, specially because of the critical lacking of boreholes. 58 GNGTS 2013 S essione 3.1