NEW STRATIGRAPHIC AND SEDIMENTOLOGIC DATA ON THE MIOCENE OF NORTH-WEST SARDINIA (ITALY)

New planktonic microfauna dating shows that Miocene echinofauna evolves in the same way both in Provence and in Sardinia. These facts plus a sedimentologic study allow us to establish close correlations between these two Mediterranean provinces and to better situate the Sardinian evolution of the Miocene in Western Mediterranean geodynamics. The Burdigalian marine transgression takes place in the TB 2.1 cycle on a topography generated by volcanic episodes which started in the Oligocene and continued until the lower Burdigalian. Volcanism is of the same period as three important events: the Oligocene rifting, the oceanic opening which caused the Corsica-Sardinia plate to drift S-E, and finally the stopping of the drift at the beginning of the Burdigalian. The TB 2.2 cycle begins with a lowstand wedge and is then followed by facies of highstand deposits. On top comes the 16.5 Ma discontinuity. The Miocene succession ends with the TB 2.3 cycle characterized by highstand deposits with a rich planktonic fauna. The nature of the facies, the situation of the Miocene sediments and the localization of the high and low bedrocks enable us to envisage the existence of a marine passage. It lies in the N-W of Sardinia between a large emerged piece of land in the E and an island in the W. The fringes of this channel are faulted and the occurrence of these accidents interferes with the positive eustatic variations.