15th International Permian-Triassic Field Workshop Permian-Triassic of Sardinia 13-18 May 2019

This field trip presents a general overview of the stratigraphical, sedimentological and paleogeographic evolution of the post-Variscan Permian-Triassic successions of Sardinia. These successions were deposited in continental to marine environments and represent from Permian to Early Triassic terrestrial sedimentation phases interrupted by erosive periods and are thus separated by several unconformities. They were followed by Middle to Late Triassic marine deposits. All these deposits laid down under active extensional-tectonic conditions. The post-Variscan successions of Sardinia rest unconformably on a Variscan basement of Early Cambrian to Early Carboniferous age: the metamorphic grade of the basement strata varies from the anchimetamorphic zone (SW Sardinia) to the high-grade metamorphic zone (NE Sardinia). The post-Variscan successions start with Late Carboniferous–Early Permian limnic to Early–Middle Permian red-bed molassic discontinuous sedimentary covers deposited in collapse basins related to the post-Variscan trans-tensional to extensional tectonic phases. They are followed by the early Middle Triassic Sardinian continental to marine deposits. They belong to Germanic Triassic Domain and rest unconformably on older successions. They comprise thin transgressive siliciclastic alluvial deposits (Buntsandstein Group) that pass into marine carbonates (Muschelkalk Group).

In SW and NW Sardinia there is stratigraphic continuity from the Triassic to the Cretaceous carbonate marine deposits. In contrast, in SE Sardinia the Middle Triassic deposits are unconformably succeeded by a Middle Jurassic transgressive siliciclastic fluvial succession that passes up into Middle Jurassic to Cretaceous marine carbonates of shallow to deep-water environments. Above this, scattered Paleogene deposits include carbonates and terrigenous or mixed deposits cropping out extensively only in the SW sector of the island where they form the “Lignitifero Basin”, an Early Eocene marine to coalrich transitional succession. Emersion (following the Alpine Pyrenean phase) led in SW Sardinia to the deposition of the Eocene–Oligocene molassic continental deposits of the Cixerri Fm. Conversely, in E Sardinia the Jurassic carbonate deposits are unconformably covered by the lower continental to marine, terrigenous to carbonate Early Eocene Monte Cardiga Fm. Both the Cixerri Fm, and possibly the Monte Cardiga Fm, are related to the development of an articulated fluvial to littoral system fed by the denudation of the older relief.

Above this, the Late Oligocene to Early Miocene Flumentepido (SW Sardinia) and Ussana Fms (Central to SE Sardinia) rest unconformably on the earlier formations. They are featured by coarser grain-sizes throughout and are related to the extensional tectonics that started the Sardinian Rift and restored a rugged landscape in Sardinia. They represent fan deltas and short depositional systems elongated on active extensional tectonic lines. They dip steeply into the Miocene N-S tectonic rift, which was later filled by carbonate to marly deposits. In Pliocene to Quaternary times further rifting occured followed by infilling by marine to continental terrigenous deposits.