Quaternary deposits and geomorphological evolution of the Telesina Valley (Southern Apennines)

Abstract

In this paper, we outline the results of a geologic and geomorphologic survey carried out in a sector of the Calore River basin (Telesina Valley), located in the Benevento Province (Southern Apennines, Italy). The data analysis conducted allowed to reconstruct of the morpho-evolutionary sequence of events that occurred in the study area during the Quaternary. The pre-Quaternary substratum of the Telesina Valley is made of tectonically deformed carbonatic, pelitic and arenaceous terrains, whose ages range from Late Triassic to Early Pliocene. A gentle erosional landscape (Paleosuperficie, Auct.) was cut on these terrains between the Late Miocene and the upper Early Pleistocene. Most probably 1.3 My B.P., a first tectonic phase disrupted the Paleosuperficie and a subsident depression was formed in the study area. It was bounded by morphostructural highs subject to severe erosional processes which led to the emplacement of large amounts of detritus in the morphostructural depression. During the same phase, in the northern part of the valley, a glacis developed partly on the detritus and partly in the underlying substratum. A new tectonic phase, probably dating about 700 ky B.P., disrupted the glacis and enlarged the valley floor, which was subsequently filled by a thick succession of alluvial deposits. The dating of an ignimbrite interbedded in the upper part of the alluvial succession allows the end of the valley-infilling to be fixed at ~540 ky B.P. The alluvial deposits were then terraced in three orders by phases of downcutting and lateral erosion of the Calore River. Afterwards, the valley was partly filled by Campanian Ignimbrite, (~39 ky B.P.) and then affected again by deep downcutting and lateral erosion which led to an almost complete removal of the Campanian Ignimbrite from the valley-axis and, finally, to the formation of a fourth order of erosive terraces in the Early Holocene. During the Middle and Late Holocene, the Calore River experienced a new phase of downcutting, followed by an aggradation of a few decametres of silt-sand alluvial deposits and to the forming a V order of depositional terraces. The current a notable instability of the valley sides appears to be strongly related to recent and still ongoing deepening of the drainage network.