Geological map of Quaternary deposits and Geomorphological map of the Upper Volturno River Valley (Molise, Southern Italy)

Abstract

A Geological and a Geomorphological map have been elaborated on the basis of morphostratigraphical studies carried out in the Upper Volturno River Basin, an area located between the towns of Isernia and Roccaravindola (Isernia Basin). A fluvial-lacustrine succession, broadly outcropping in the basin, has been mapped and divided into two main morpho-lithostratigraphic units: Main Infill Unit and Valley Floor Unit. The Main Infill Units, made up of different members with various facies associations (gravelly, silty and clayey deposits of alluvial fan, fluvial and lacustrine environments), represent the first cycle of Quaternary deposition. Several tephra layers are intercalated in this succession, presumably originated from the eruptive activity of the Roccamonfina Volcano. Recent radiometric data related to some of the above-mentioned stratigraphic markers, confirm the attribution of such continental deposits to the Middle Pleistocene. Notwithstanding many geomorphological observations suggest that the idrographic network is conditioned by the structure, the Quaternary deposits rarely show fault evidence. The Valley Floor Units, overlaying the dissected Main Infill Units, are mainly made of poligenetic gravels; also alluvial fanglomerates and scree deposits occur. On the Geomorphological map great attention has been given to those landforms which can give some information on the morphoevolutive trend of the area. Particular emphasis has been given to fluvial processes (largely prevailing in comparison to gravity phenomena) and to their status of activity. Four orders of terraces ranging in age from Middle Pleistocene to Holocene, have been distinguished. The I order terraces, the most widespread in the area, have been interpreted as depositional terraces located at the top of the Main Infill Units. The following orders can be found in the principal rivers of the area (T. Lorda, F Cavaliere, T. Vandra and F. Volturno): the II order surfaces are mainly erosional surfaces cut in the Main Infill Units, while the III and IV order terraces are depositional surfaces related to the Valley Floor Units.