Reconstruction of the Sardinia North-West coast evolution: a chronologic and sedimentologic approach

The Middle-Upper Pleistocene Sardinian stratigraphy is analysed to identify the role played by sea and climate changes, in controlling sedimentation. The studied deposits crop out along the NW Sardinia coast were dated with Optically Stimulated Luminescence on both quartz and k-feldspar grains. The Quaternary successions were grouped in four major stratigraphic units mainly represented by shallow marine coastal dunes and alluvial systems, spanning from MIS 6 to MIS4. Stratigraphic and chronologic data allow some considerations on climate changes occurred within the last interglacial (MIS 5) to the early glacial phase (MIS4, post 80 ka). The last interglacial MIS 5 (130-80 ka) is subdivided in five substages (e-a) and MIS 5e (Eemian) is considered the climatic optimum. During the MIS 5e sea level was +46 m higher than today and climate conditions were warmer and more humid. The NW Sardinia coast paleogeography was dominated by wave cut platforms colonized by carbonate intertidal deposits (algal rim) and small gravelly to mixed sandy-gravelly pocket beaches which developed at the base of the cliff-wall. Occasionally, in the wider embayment well developed sandy barrier-lagoon systems occurred. During MIS 5b sea level drop of 15 m and the Mediterranean region was characterized by alternated dry and wet condition. At the end of MIS 5b temperature increased, most of the ice formed melted and a new interglacial phase (MIS 5c) took place. During MIS 5c (100-95 ka) the sea level rose up to ~2 m above the present and the North-west coast of Sardinia was dominated by prograding sandy-mixed pocket beaches. At the end of MIS 5c a climate deterioration led to a progressively cooler condition and sea level drop again of about -20m and alluvial plain and regressive coastal dunes developed.