GNGTS 2015 - Atti del 34° Convegno Nazionale

GNGTS 2015 S essione 1.2 105 it is generally recognizable on the base of clear toplap termination. In some shallow basins the MSC is characterized by the deposition of the Gessoso-Solfifera Formation, whose top is generally a high amplitude reflector due to the high contrast of acoustic impedance between the PQ sediments and the gypsum layer. According to this regional conditions, in the west-Sardinian continental slope we recognize (example in Fig. 3) a clear erosional truncation (orange horizon on the left of Fig. 3) or, in any case, a high amplitude reflector which generally lays at the base of the semi-transparent Lower Pliocene. Locally we can see also a high amplitude seismic package that Geletti et al. (2014) ascribed to the Gessoso-Solfifera Formation. Sometimes the MES results to be crossed by some conical buildings, locally outcropping on the sea bottom with a circular section, observed by Geletti et al. (2014) in the Mulibeam data and interpreted as volcanic bodies. Generally Lower Pliocene sediments onlap the top of these buildings and they show to be undeformed, so testifying a deposition following the magmatic activity. This magmatic activity could be assigned to the magmatic event occurred between 5.3- 5.0 Myr in the SE Sardinian onshore, discussed by Lustrino et al. (2000). In some profiles the Pliocene sediments, laying above the volcanic buildings, show a smeared setting: this could be explained by a deformation due to the magmatic intrusion occurred after the deposition. This magmatic activity could be assigned to an event occurred between 0.9 and 0.1 Myr in northern Sardinia, as discussed by Lustrino et al. (2000). Also, this attribution would be coherent with the basaltic layer covering a Pliocene calcarenite described by Cornée et al. (2008) in the Sinis peninsula (Fig. 1). As already outlined, a semi-transparent layer can be recognized on the Sardinian continental shelf and upper slope. It has been regionally interpreted on the whole Mediterranean Sea and has been joined to the marls of the Trubi Formation, representing the Lower Pliocene deposition after the re-opening of the Strait of Gibraltar at the end of the MSC. This sequence onlaps or concordantly overlays the MES. It is not homogenously present or recognizable on all the continental shelf, where it tends to thinning or, more often, it changes from the semi-transparent seismic facies to a more reflective package. In view of the total absence of calibrations this could have occurred due to a different sedimentary supply. In particular, we can observe that the higher reflectivity of the Plio-Quaternary sequence corresponds to some geometries characterized by undulations, inclination and changing thicknesses of the strata. Some internal erosional surfaces have been also recognized. These geometries can be related to mound drift, to Fig. 2 – Part of stack seismic profile: comparison between the data before and after the multiple attenuated processing.