Geomorphology, stratigraphy and facies analysis of some Late Pleistocene and Holocene key deposits along the coast of Sardinia (Italy)

Two major synthems have been recognised along the coasts of Sardinia. The older one is composed of two sub-synthems, the oldest of which was formed in high-energy boulder beaches, and is a thin condensed transgressive sequence usually located at the foot of a marine cliff. The overlying sub-synthem was generated by aeolian, slope, interdunal ponds and alluvial depositional environments. It is widespread, and terraces and relict dune fields are usually deeply dissected. Its deposition is associated with a cold and arid climate. The aeolian and alluvial deposition was interrupted by the evolution of steppe-prairie soils. A more evolved reddish brown Bt paleosol is locally found at the top of the sequence. The younger synthem is made of beach and coastal lagoon and swamps. It is more variable in thickness, rests unconformably over the older, one and has no sedimentary cover. It is laterally correlated to the present-day depositional environments such as alluvial plains and beaches. Unfortunately, because beach deposits of this synthem are found up to 6 m asl and a marine notch is present at 5–6 m (Capo San Marco), the widespread idea that Sardinia is a stable area and that marine sea level during the Holocene was never higher than nowadays led to their previous attribution to MIS 5e. However, all the stratigraphic, geomorphic and pedological evidence indicates that only the older sub-synthem can be correlated with the MIS 5e high stand. The younger sub-synthems made of aeolian lacustrine and alluvial deposits at Cala Gonone, Santa Reparata, Capo S.Marco and S.Giovanni di Sinis were deposited during the rest of the Late Pleistocene. The younger synthem evolved during the Holocene, and this is the chronological setting of the beach deposits at Is Arenas, Scala e´ Croccas, Santa Reparata, and Capo San Marco. Radiocarbon dating confirms these attributions. Unfortunately, OSL dating suggests an older chronology for these deposits, and therefore it seems that further investigations are needed.