Subsidence history from a backstripping analysis of the Permo-Mesozoic succession of the Central Southern Alps (Northern Italy)

摘要

Seven tectonic subsidence curves, based on outcrop data, have been calculated in order to constrain the geodynamic evolution of the Permian-Mesozoic sedimentary succession (up to 10 km thick) of the Central Southern Alps basin (Italy). The analysis of the tectonic subsidence curves, covering a time span of about 200 Ma, allowed us to quantify the subsidence rates, to document the activity of syndepositional fault systems and calculate their slip rates. Different stages, in terms of duration and magnitude of subsidence-uplift trends, have been identified in the evolution of the basin. The fault activity, reconstructed by comparing subsidence curves from adjacent sectors, resulted as highly variable both temporally and spatially. Strike-slip tectonics was coeval to Permian sedimentation, as suggested by the strong differences in the subsidence rates in the sections. The evolution and subsidence rates suggest a continental shelf deposition from Early Triassic to Carnian, when subsidence came to a stop. A rapid resumption of subsidence is observed from the Norian, with a subsidence pulse in the Late Norian, followed by the regional uplift, in the Late Rhaetian. The following Early Jurassic subsidence is characterized by tectonic subsidence similar to that of the Norian. The Norian and Early Jurassic pulses were characterized by the highest slip rates along growth faults and are identified as two distinct tectonic events. The Norian-Rhaetian event is tentatively related to transtensional tectonics whereas the Early Jurassic event is related to crustal extension. The Early Jurassic subsidence records a shift in space an time of the beginning of the extensional stage, from Late Hettangian to the east to Late Pliensbachian-Toarcian to the west. From the Toarcian to the Aptian, the curves are compatible with regional thermal subsidence, later followed (Albian-Cenomanian) by uplift pulses in a retrobelt foreland basin (from Cenomanian onward).