Transgressive dune formation along a cliffed coast at 75 ka in Sardinia, Western Mediterranean: A record of sea-level fall and increased windiness

Transgressive dunes develop frequently along strandplain coastlines; however, they may also form along rocky coasts dominated by cliffs and embayments. Two lithified transgressive dune systems developed along the cliffed Alghero coast (NW Sardinia, Italy) have been investigated. One aeolian system forms a cliff-front anchored aeolian dune accumulation; the other is a valley-head anchored sand-ramp system. Optically stimulated luminescence ages indicate that both systems formed around 75 ka. This period, which corresponds to the beginning of MIS 4, was characterized by a relatively low sea-level stand (15 m below the present sea level) and was preceded by a sea-level highstand (+1 m asl) around 81 ka (MIS 5a). Our results show that this rapid sea-level fall exposed an enormous amount of marine sand, which was transported inland by strong northerly winds and deposited in front of cliffs or in valley heads. Therefore, sediment supply and sea-level fall seem to be critical factors controlling dune formation along rocky coasts, which generate time-transgressive aeolianites.