Landscape evolution in the Tacchi area (Central-East Sardinia, Italy) based on karst and fluvial morphology and age of cave sediments

The east-central part of Sardinia (Italy) is characterised by Jurassic dolomitic mesas (Tacchi, or «table mountains») that overlie a Palaeozoic basement mainly composed of metavolcanics and phyllites. These mountains are the remnants of a continuous carbonate cover, dissected by faults and river erosion, and are now completely isolated hydrological systems. Most of these rivers have cut valleys more than 200 metres deep into the Palaeozoic basement rocks, whose slopes are often characterised by landslides, suggesting their recent oversteepening. Some valleys, on the contrary, have not reached the base of the carbonate sequence and appear to be suspended above the deeper incisions, apparently disconnected by them. Several subhorizontal surfaces can be distinguished on the table mountains, related to local base level stillstands. Also water table caves, scattered along the flanks of the mountains over an altitudinal range of about 200 m, show several stillstands in base level lowering. - (NF).