Geological mapping of the Vulture volcanic area: relationships between volcanic activity and sedimentation in the alluvial and lacustrine basins

The Bradano Trough area, included in the watershed of Venosa River, passed from subsidence to regional tectonic uplift with the sedimentation of the Irsina Conglomerate Formation. This period (Middle Pleistocene in age), which was characterized by an alternance of erosional and depositional phases developed on a series of direct faults with a strike-slip component (direction N110°±5°, N130° and east,west) and formed the Venosa Basin palaeovalley. The first erosive phase led to the formation of three alluvial terraces (Ciciriello, Pezza della Breccia e Masseria Impiso Subsynthem) which can be grouped into the Sant'Angelo Synthem. The following depositional event was characterized by the emplacement of by alluvial and lacustrine deposits consisting of conglomerate, mudstone and tuff, which can be grouped into three synthems bounded by stratigraphic unconformities. Sediment composition is mainly volcanic detritus with minor layers of primary volcanic deposits (pyroclastic flow and fall deposits) which can be correlated with the Foggianello, Barile and Melfi Synthem, of Monte Vulture volcano. The three epiclastic units and the Sant'Angelo Synthem have been grouped into the Monte Vulture Supersynthem (from 687±8 ky to 530±22 ky in age). Analysis of the sedimentary facies reveals that the Foggianello Synthem formed in a depositional system of gravelly braided plains and the Barile Synthem formed in small lake basins connected with high sinuosity channels. After the Melfi Synthem sedimentation, on the north-western border of the Venosa Basin, sub-vertical direct faults formed (direction N90°±5° and N103°±2°). Concurrently a new erosional phase, connected with three depositional episodes, occurred. It led to the formation of alluvial deposits that are linked to three terraced stages of fluvial overcutting. Two out of the three units (Li Scafoni and Toppo di Maggio Subsynthem) are included in the Torrente Olivento Synthem and the other one in the Caperroni Synthem. The two synthems are associated with the Monticchio Supersynthem. A palaeogeographic scheme is provided for each synthem, which allows the representation of the evolution of erosion and sedimentation of the Venosa Basin deposits from Middle Pleistocene to Upper Pleistocene.