Lineamenti geomorfologici dell’Alta Valle del Tirso (Goceano, Sardegna)

Geomorphological outlines of the Upper Tirso Valley (Goceano, Sardinia, Italy)

Abstract

The plain of the Tirso River, like the other main plains of Sardinia, is found in a valley originated by tectonic movements of distensive nature. These movements began in the Late Tertiary and continued in subsequent phases up to the Middle and Late Pleistocene. They originated an asymmetric graben located in the ancient (Paleozoic) crystalline basement. The landscape was condicioned by periodic uplifting movements. The stages of the geomorphological evolution are shown by the relics of the ancient post-hercynic peneplain and by the marked slopes along the northern and southern parts of the region. In particular, a continuous hilly piedmont runs along the northern slopes of the plain (Costera); it originated from the modelling of this area during and after the first uplifting. In this area magnificent inselberg forms can be seen. In the Miocene the products of a vulcanic calc-alkaline activity fell in the valley and the consequent damming originated a lake, which estinguished later on. The modelling of the large surface which connects the most central part of the valley to the slopes, in particular in the North, began in an indefined moment. This gently dippin surface is covered by detritic deposits and was originated by a mechanism of crio-pedimentation. The deposits of glacis cover and mask previous alluvial deposits, probably Middle Pleistocene in age, of the ancient Tirso River. Evidently, the river flowed at the northern end of the valley. This fact shows that the river migrated towards the South owing to the contiuous uplifting of the northern slopes.The central part of the plain is the site of the present Tirso River and in this zone Holocenic and recent sediment with related forms can be seen.