Tectonic-Sedimentary evolution of the Tuscan shelf (Italy): seismic-stratigraphic analysis of the Neogenic succession in the northern Tyrrhenian Sea between Elba Island and Monte Argentario promontory

Abstract

The northern Tyrrhenian Sea separates the northern Apennines of the Tuscany coast (Italy) from the Corsica island (France). A comprehensive revision of a vast dataset of vintage public seismic reflection profiles was conducted, re-elaborating via dedicated vectorization codes to improve their resolution and interpretability. The bathymetry of this sector shows a very regular and almost flat geometry of the seafloor. Despite this, a close look at seismic profiles reveals an articulated topography of the pre-Neogenic deformed acoustic basement. This is organized in thrust-related structural highs and narrow, N-S and NNW-SSE trending basins, filled by sedimentary successions separated by unconformities.Nowadays, the sedimentary sequences associated with the most recent evolution of the Tyrrhenian Sea completely sutured the previous morphology.To date, we found strong evidence regarding the role of structural inheritance in shaping the current architecture of the shallow crust. We identified an intimate relationship between the thrust-related structural highs and the basins' position at the antiforms' forelimb and backlimb. Indeed, the Tuscan Shelf neogenic basins started to develop as intermontane fault-controlled basins along the flanks of the inherited antiforms.We performed a structural analysis of the faults bounding the basins and a detailed seismic-stratigraphic analysis of the Neogenic succession deposited into such basins to reconstruct the Tyrrhenian Sea extension's initial phases and embed it into the broader evolution of the Mediterranean region.The evolution of the sedimentary basins from the middle Miocene to the Pleistocene provides a more comprehensive and robust picture of the Tyrrhenian Sea. We were able to track the progressive activation and deactivation of high-angle normal faults controlling the basins deposition and the eastward migration of the extensional front. Such a setting influenced the asymmetrical or symmetrical evolution of the basins. Intriguingly, and partially in contrast with previous works, no evidence of low-angle normal fault was observed.We also present the first reconstruction of a 3D geological model of the southern Tuscany offshore between Elba Island and Monte Argentario promontory (Italy). Such a model poses new questions on the crustal-scale mechanisms responsible for the extensional process, also establishing a unique starting point for fully unraveling the Tuscan Shelf and the Tyrrhenian Sea early stages of evolution.