Depositi lacustri infrapleistocenici con intercalazioni vulcanoclastiche (Bacino di Sant'Arcangelo, Basilicata)

Abstract

Infrapleistocene lacustrine deposits cropping out in the North-central part of Bacino di Sant'Arcangelo (Southern Italy) were investigated in order to define stratigraphic and sedimentological features. Lacustrine deposits form a 200 m thick succession made up of clays and silts, interbedded with sandy or calcareous beds, passing into a 50 m thick conglomeratic- sandy unit. Ashy volcani clastic intercalations, consisting essentially of glass fragments, have been recognized at various levels within the succession. A detailed chemical, structural and textural study of these volcaniclastic intercalations was carried out. These deposits have log-normal and well sorted grain size distribution. They are composed of vesiculated clasts due to magmatic fragmentation processes. On this basis it was possible to suggest a plinian-type eruption for these deposits. A K-Ar age of 1.1 ± 0.3 Ma was obtained for the volcanic glasses. This allowed to detail the tectonic - sedimentary evolution of the Bacino di Sant'Arcangelo. The information gained from the volcaniclastites allow to frame more precisely the evolutive phases of the Apennine chain during Quaternary age.