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Geografia Fisica e Dinamica Quaternaria, 2012, Issue 35, p. 119-127
Landscape evolution in the Tacchi area (Central-East Sardinia, Italy) based on karst and fluvial morphology and age of cave sediments
Abstract:

 

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.


 


26Al and 10Be burial dating of sediments in four caves located at different


elevations on the flanks of the suspended Taquisara Valley show


an Upper Pliocene or Lower Pleistocene age. Thus, this valley appears to


be of Late Tertiary age. The deeper valleys, such as Riu Pardu, that dissect


the Tacchi mountains completely, cutting deeply into the basement


rocks, are much younger, as their unstable slopes suggest. Knickpoint retreat


in Riu Pardu and estimated valley erosion rates suggest the capture


of Riu Pardu by Rio Pelau to have occurred in the last 100 ky.