Processi di erosione e sedimentazione nei campi carsici: un esempio dai Piani d’Ischia, Monte Terminio, Italia meridionale

Erosional and sedimentary processes in polje: example from the “Piani d’Ischia” polje, Terminio mount, Southern Italy

Abstract

The Mt. Terminio karstic area is characterized by the occurrence of many structural polje within which, during the Quaternary, pyroclastic fall deposits deriving from the Phlegrean-Vesuvio volcanic district accumulated. The upper part of the succession filling the polje is well exposed on the slopes of a ponor located ill the Piani d’Ischia polje. Such stratigraphic succession allowed us to reconstruct the geomorphological evolution of the area from the end of the Upper Pleistocene until the Holocene. Furthermore, chemical analysis of the pyroclastic fall deposits and the correlation of these tephra layers with the main eruptions of Vesuvio volcanic complex allow us to date the main erosional and depositional processes occurred in the area. At the end of the last glaciation (17ka) a little lake existed in the area as testified by the presence of a six meter thick sequence of silts and clays with frequent micro and meso sedimentary structures (parallel and convolute lamination, slumping). A paleosol located on the top of the clayey deposits, which has a ¹⁴C age of 10 ka, testifies that the lake filled up at the beginning of the Holocene. The area then became a little swamp similar to the present one. Starting from that moment, the morphological evolution of the area has been controlled by karst processes and particularly by the opening of collapse dolines which induced new erosional and depositional processes to take place within the polje.