Geomorphology and neotectonic evolution of a sector of the Tyrrhenian flank of the southern Apennines (Region of Naples, Italy)

Summary. The western slope of the campanian Apennines is characterized by graben-like coastal depressions some thousands of metres deep, separated by structural promontories several hundred metres high. The depression floors are occupied by broad alluvial plains (Garigliano, Campana and Sele plains). This structure is the result of extensional tectonics that affected the region after a relatively quiet period that had allowed a mature erosional landscape to develop across the complex litho-structural situation left by the preceding compressional events during the Early Miocene to Middle Pliocene. Biostratigraphic, geocronologic and geomorphological data suggest that the subsidence of the coastal grabens began during the Early Pleistocene and was accompanied by repeated uplifts of the main chain and of its south-westward protruding ridges separating the grabens. This caused severe erosion of the rising uplands and the accumulation of huge conglomeratic sequences in the depressions. The latter deposits are today exposed only at the inner part of the Sele Plain, which passed from the subsiding to the rising domain at the beginning of the Middle Pleistocene, following a westward migration of the tectonic inner rim of that- graben. Yet during the Middle Pleistocene the same graben broadened laterally at the expense of the Sorrento Peninsula, the narrow "horst'' that separates the Sele Plain from the Campana Plain. The latter plain is characterized by a very flat topography and steep marginal fault scarps. Another difference between the Sele Plain graben and the other two is the presence in the latter of numerous volcanic centres whose products and landforms are found throughout the entire depositional sequence. Ancient beach deposits of the region ·show that the Campanian coast-maintained its fragmenting tectonic behaviour also during the Upper Pleistocene. The Sele Plain has been subject to moderate uplift, while the Campana Plain continued to subside (its volcanic portions had a more complex evolution). The structural promotories (M. te Massico, Sorrento Peninsula and Cilento) and the Garigliano Plain gained tectonic stability not later than the Last Interglacial.