The Triassic Buntsandstein sedimentary basins of Sardinia (Italy) and their transition to the Brianzonese ridge (Western Alps): crossroads through the Western Tethys areas

Sardinia represented a key area during the Western Tethys opening in late Early–early Middle Triassic times as it was located at the nodal point of several palaeogeographical domains. New and revised sedimentological data and petrographical investigations provide evidence that the Sardinian Buntsandstein Group formational units differ from each other and were deposited in different alluvial to transitional depositional systems related to Alpine rifting basins. Petrographic analysis revealed north–south and east–west compositional differences: they hint at morphotectonic rises separating the diverse depositional areas through lasting barriers related to palaeoeuropean ridges in progressive dismantling. The data suggest that the dominant environmental and (micro)climate conditions varied from area to area and the sedimentary basins evolved differently through time and were diachronous in timing. Moreover, the sources of debris were variable, both in morphology and substrate composition, with relief from articulated to smoothed. A stratigraphic and sedimentological framework for the Sardinian Buntsandstein is suggested. Comparison analysis with close coeval successions of the Western Tethyean area, particularly regarding the Upper Permian?–Lower Middle Triassic deposits of the Brianconnais ridge, have been attempted, as well as their palaeogeographical location, to frame the Sardinian Buntsandstein Group with the coeval units of SW Europe.