Tectonic vs gravitational processes affecting Ligurian and Epiligurian units in the Marecchia valley (Northern Apennines)

Thrusts of the Northern Apennine tectonic units are currently referred to horizontal compression, even if some authors still attribute the emplacement of the Ligurian and Epiligurian units to gravitational mechanisms. This research aims to contribute to the distinction between tectonic and gravitational processes, by means of structural, sedimentological-stratigraphic and geotechnical investigations on some Ligurian and Epiligurian formations of the Val Marecchia thrust sheet (central Italy). The identification of syntectonic Epiligurian basins describing antitaxial arcs and of structures related to Neogene brittle tectonics in the Ligurian units, shows that the emplacement of the Val Marecchia thrust sheet was probably due to compressive tectonics. This assumption is furthermore corroborated by geotechnical tests. Gravitational processes are limited to episodic submarine landslides, during the Neogene stages of advancement of the deformation front, and to recent subaerial active and dormant mass movements linked to superficial erosion and softening processes.