Evidence for a major breach of the roof units of the Southern Apennine duplex system in the Picentini Mountains

In the Picentini Mountains (Southern Apennines), Mesozoic shallow-water carbonates belonging to the Campania-Lucania platform overlie with a low-angle thrust surface Mesozoic-Tertiary deep-water deposits belonging to the Lagonegro domain (Ietto 1963a, b; 1965; Scandone et al. 1967). The tectonic contact is exposed in several tectonic windows. In the Campagna window, the most important structural feature in the region, the Lagonegro units, in turn, tectonically overlie Lower-Middle Miocene siliciclastic flysch deposits (Vallimala sandstones and limestones in Scandone and Sgrosso 1974) stratigraphically covering Triassic to Paleogene carbonates. These carbonates and the overlying siliciclastic deposits are known in the geological literature as Monte Croce Unit (Scandone et al. 1967). Lagonegro deposits sandwiched between two carbonate units, known only in the Campagna tectonic window, have been matter of debate in the geological literature and three different interpretations have been proposed. Recently, the Monte Croce unit has been penetrated by the Acerno 1 well, a borehole located in correspondence to the northwestern margin of the Campagna tectonic window that has reached a depth of 4625 metres.The information provided by Acerno 1, together with the evidence derived from the surface geology, allowed as to interpret the superposition of the Lagonegro units on the Monte Croce Unit as a major breach cutting across the primary tectonic couple made up of the Campania-Lucania and Lagonegro thrust sheets.