GENERAL FRAMEWORK The Tacchi area (Central Sardinia): geomorfological and paleogeographical premise In Central-Eastern Sardinia (Gerrei, Barbagia, Ogliastra, Sarcidano), a definitely peculiar scenery appears to the traveller: dubtless the Jurassic “Tonneri” or “Tacchi” (Plateau) area is a natural landscape showing one of the most peculiar morphological varieties in the multifaceted Sardinian geological area. This landscape is marked by flat- topped highlands, plateau, mesas and buttes built of Jurassic carbonate rocks horizontally stratified and often separated from each other by deep gorges.Those flat relieves located at different topographic levels ranging from 350 m (Tacco di Escalaplano) to 1300 m (Tacco di Seui) for the differentiated Tertiary uplifting tectonic movements of the area. This tectonics, together with the Cenozoic-Quaternary erosion, leaded to the present scattered distribution of the Jurassic outcrops. These outcrops represent the remnants of a former widespread and uninterrupted Mesozoic continental to marine cover, which posed most likely over the whole Sardinia island and repeatedly emerged and was eroded: this is confirmed also by the correlatable carbonate rocks of the Eastern - Northeastern Sardinia (Supramonte, Golfo di Orosei, Isola di Tavolara, Capo Figari), of the Nurra N to Alghero (NW Sardinia) and of the Sulcis in the SW Sardinia (Porto Pino, S.Antioco). Geological setting 1. Variscan Paleozoic Basement and Permo- Carboniferous covers In Central Sardinia (Fig. 1) the Mesozoic outcrops cover mainly the Variscan metamorphics through an angular unconformity. More rarely, they could be posed unconformably over Permo-Carboniferous molassic sediments. In Central Sardinia the Variscan lithologies (Late Cambrian-Early Carboniferous) transgressed by the Mesozoic deposits are assigned to different tectonic units, each one of them interested by deformation and metamorphic degree growing up to North. Those units pertain to the Outer Nappe Zone and to the Inner Nappe Zone (Carmignani et al., 1992; 1994). Here and there, little remains of sediments belonging to the limnic sediments cycle (Late Carboniferous – Early Permian) and/or to the red beds sediments cycle (Permian) cover unconformably the Variscan metamorphics, reaching a maximum thickness of 400 m (Cassinis et al., 2000). The allochton Variscan units are formed by low- to middle grade metamorphics deriving mainly from terrigenous deposits: volcanics and carbonates are subordinate protoliths. 1 MESOHELLENIC PIGGYBACK BASIN EVOLUTION FROM EOCENE TO MIOCENE - FIELD TRIP A2 F I E L D T R I P 5 Evidences and consequences of the breakup of the Pangea and the opening of the alpine tethys in the Triassic Jurassic Sedimentary cycles of central sardinia (Tacchi Area) Luca Giacomo Costamagna*, Sebastiano Barca**, Luciano Lecca*** * lucakost@unica.i, **barcas@unica.it, leccal@unica.it Fig. 1 – Geological sketch of the Tacchi area: the location of the Barbagia Paleohigh is evidenced (M.B.H.) (modified after Costamagna et al., 2007).