Early-stage rifting of the Southern Tyrrhenian region: the Calabria-Sardinia breakup

The southern Tyrrhenian Sea is an extensional basins linked to the Neogene evolution of the Calabria subduction zone located in the western Mediterranean realm where controversial kinematic and geodynamical models have been proposed. Our study provides a key to unravel timing and mode of extension of the upper plate and the breakup of Calabria from Sardinia. By combining original stratigraphic analysis of wells and seismic profiles off Calabria with a stratigraphic correlation to onshore outcrops, we re-assess the tectonic evolution that controlled the sedimentation and basement deformation of the Southern Tyrrhenian basin during Serravallian-Tortonian times. We document the tectono-stratigraphic evolution of adjacent extensional basins, characterized by 3rd order depositional sequences (Ser1, Tor1, Tor2) and different modes of extension, subsidence and opposite polarities. Episodic basin development is recorded by a coarsening-up and fining-up trend of the sedimentary succession and by tectonically-enhanced unconformities that reflect three episodes of fault activity. We reconstruct Serravallian-Tortonian paleogeographic maps and propose a block faulting model for the evolution of the Sardinia-Calabria area during the early-stage rifting of the Southern Tyrrhenian region. Sardinia was disconnected from Calabria through N-S normal faults forming Tyrrhenian extensional basins that formed contemporaneously to the E-W opening of the Algerian basin. Unlike published Serravallian-Tortonian reconstructions of the western Mediterranean realm, our results support a geodynamic model characterized by rapid trench retreat, trench-normal extension in the entire overriding plate and very weak coupling between plates