Abstract

The central Irpinia area lies in a key sector of the southern Apennines, near the link between the Molise-Sannio segment and the Lucania-Campania segment of the belt. We present new stratigraphic and structural data and discuss correlation with regional geological features. The central Irpinia area comprises a widespread Quaternary cover, a few outcrops of Pliocene clastic deposits, and various Tertiary sedimentary successions, consisting of three stratigraphical-structural units. These are the Daunia Unit and two Lagonegro Units-the Frigento Unit (formerly samnitic units Auct. p.p.), composed of the Flysch Rosso Auct. Formation, and the Numidian Flysch, and the Fortore Unit, formed by the Argille Varicolori Auct. Formation and Frigento Formation p.p. The Numidian Flysch, not previously mapped in the area, outcrops along the "Vallone dei Bagni" talweg and our data allow correct evaluation of its local thickness. The Frigento Formation p.p. is formed by locally siliceous limestones, marls and clays, which sometimes look like the "galestri", dated in the literature with very different ages from Lower Cretaceous to Miocene. We postulate an Eocene-Oligocene age for these deposits, and correlate them with the Corleto Perticara Formation. The Daunia Unit, which is formed by the Faeto Flysch, the Toppo Capuana clayey Marls, and Messinian clastic deposits and evaporites, usually crops out along the eastern margin of the southern Apennines, near the front of the chain, as this unit is referred to a foreland domain or to the undeformed sector of the Miocene foredeep. However the Daunia Unit here lies in an axial portion of the belt; its deposits are stratigraphically connected to the Inner Apulian Platform, which forms a buried structural high. Our data confirm the presence of important duplex structures (Apulian thrust system), which tectonically double the flexured Inner Apulian Platform and uplifts it so that it almost outcrops in the central sector of the Irpinia area, where the top of the Apulian carbonate sequences has been recognized at a depth of about 500 m. The very complex geometrical and tectonic relationships among the outcropping units suggest a complex tectonic history of this sector of the Apennines belt. The overthrusting of a nappe, formed by the basinal deposits of the Lagonegro Units, towards the foreland domain, represented by the Daunia Unit, occurred after the Messinian evaporitic events and lasted till the early Pliocene. Later tectonic evolution was characterized by out-of-sequence thrusting, which has involved a deep portion of the belt and caused the doubling of the nappes pile, with the thrusting of the Daunia Unit over the Lagonegro Units.

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