Stratigraphy, facies analysis and chronology of Quaternary deposits at Capo S. Marco (Sinis Peninsula, west Sardinia, Italy)

Capo S. Marco is the southernmost termination of the Sinis Peninsula in the northwestern border of the Oristano Gulf (western Sardinia, Italy). In the area, there are some of the most controversial and debated Quaternary deposits of Sardinia, consisting of beach, aeolian and slope sediments, whose chronological attribution changed according to different authors and, in different times, by the same authors. These discrepancies have not been solved by new radiometric dates, as radiocarbon and Optically Stimulated Luminescence (OSL) methods provided ages that are significantly different. During recent investigations at Capo S. Marco, beach notches filled with bioclastic sands, gravels, and boulders were discovered up to an elevation of w4.5 m, which is the highest elevation of the known beach notches. These sediments rest on aeolian deposits and form a marine terrace in two sites. In some places, these sediments also include small colonies of the coralCladocora caespitosa in living position that have been recently dated by U/Th at 70 4 ka and attributed to the end of MIS 5. Here, we report new U-series analyses of two samples of C. caespitosa collected on the uppermost part of the sequence. The U/Th ages of 153 0.8 and 149 0.6 kawould correspond to MIS 6, but the high values for the initial d 234U (177 and 179) compared to the modern seawater value (147) point to an open-system addition of 234U and/or 230Th. The corrected ages using the open-system model of Thomson et al. are 141.6 2 and 132 2 ka. However, these deposits and the beach notches are not buried under aeolian or colluvial sediments, as are almost all the Tyrrhenian marine deposits found in Sardinia. They also rest on aeolian sediments, which, at San Giovanni di Sinis, were dated to MIS4 or Late MIS2 by OSL and radiocarbon dating of buried organic palaeosols, respectively. Accordingly, the stratigraphic evidence would suggest their attribution to the Holocene, although this contrasts with the Holocene sea level models available and the U/Th dating results.