The Romagna Apennines, Italy; an eroded duplex

The study of clast composition carried out on the alluvial gravels of the Romagna Apennines of northern Italy has provided evidence for an extensive covering of allochthonous units (Ligurian nappe and Epiligurian succession) above the Miocene foredeep deposits (Marnoso-arenacea Formation), which has been subsequently eroded during the Late Miocene-Pleistocene uplift. This result is confirmed by the burial history outlined in the Marnoso-arenacea Formation through vitrinite reflectance and apatite fission-track analyses. The Romagna Apennines represent, therefore, a regional tectonic window where the thrust system that displaced the Marnoso-arenacea Formation crops out. The geometric relations between this thrust system and the basal thrust of the Ligurian nappe, exposed at the boundaries of the Romagna Apennines (Sillaro zone and Val Marecchia klippe), are consistent with a duplex structure. Thus, the Romagna Apennines thrust system is an eroded duplex. The duplex roof-thrust corresponds to the surface of the syn-sedimentary overthrust of Ligurian nappe on the Marnoso-arenacea Formation; the floor-thrust is located in the pelagic pre-foredeep deposits (Schlier Formation).