BURIED ARCHITECTURE OF THE VITTORIO VENETO BASIN (NE ITALY)

A geological survey and analysis of the borehole stratigraphies enabled us to characterise the buried architecture of the Quaternary basin of Vittorio Veneto (NE Italy). The study area belongs to the Neogene-Quaternary front of the eastern Southern Alps: the Montello and the Cansiglio thrusts show much evidence of Quaternary activity and are considered seismic sources capable of destructive earthquakes. As a result of the 1936 earthquake, strong site effects became manifest in Ceneda and Serravalle, located respectively to the south and north of Vittorio Veneto. A geological and geomorphological survey enabled us to point out the surficial characteristics of the Vittorio Veneto basin, carved in the Tertiary Molasse. In order to characterize lithology and geometry of the Quaternary sediments and reconstruct the geometry of the bedrock-surface, about sixty borehole stratigraphies were analyzed. Bedrocksurface dips gently northwards: an effect of the tectonic activity of the Montello thrust. Maximum thickness of Quaternary sediments (more than 80 m) is located south of the Serravalle gorge. Three Quaternary sedimentary units have been recognised in the subsurface of the Vittorio Veneto basin: 1) a sandy-gravelly body (with maximum thickness of about 70 m) of alluvial and glacial origin that almost completely fills the Vittorio Veneto basin and contains an important aquifer; 2) thinner sedimentary bodies (with medium thickness about 10-15 m) that form the alluvial fans at the base of the reliefs and are composed of a close sequence of silts, muds and clays interbedded with thin gravelly levels; 3) finally in the Lapisina valley, north of Serravalle gorge, prevailing sands with lenses of lacustrine silts and peat deposits form a sedimentary body that locally reaches 20-30 m in thickness.