A MIS 5a attribution to the deposits of the type-section of the Tyrrhenian Stage at Cala Mosca-Is Mesas (South East Sardinia, Italy)?

The Tyrrhenian Stage was created by Issel (1914) to designate a time interval postdating the Sicilian and predating the Holocene. The type section mostly comprises beach deposits and is located at Cala Mosca - Is Mesas on the Sant'Elia headland near Cagliari (South East Sardinia). The attribution to the Last Interglacial was made because of the occurrence of a warm-water mollusk assemblage that, among others, contains Strombus bubonius, a gastropod nowadays thriving along the Senegalese coast. This species is considered as an index fossil of the Last Interglacial along the Mediterranean shorelines. Early chronological data, including amino-acid racemization and U/Th dating of mollusks and corals found in the beach sediments, confirmed this attribution. However, ages obtained from the latest U/Th dating, despite a good correlation with the Last Interglacial, showed inconsistent isotopic ratios. Recent investigation at the type-locality revealed the occurrence of a small cave carved in Miocene limestone, the Is Cocciulas cave, which was largely colluvium-covered in the past years, but has been re-opened by modern erosion processes. The cave, many tens of meters long, shows a pristine tidal notch at ca. 6 m asl, as well as lithophaga borings up to ca. 9.0 m asl. The elevation of the tidal notch is lower than the tidal notch exposed in coastal cliffs along the Orosei Gulf to the north and in the past assigned to the highest MIS 5e highstand. The lower elevation of the notch has to be associated with the occurrence of negative tectonic movements in the Campidano area. The intermediate marine sequence and terrace in the central part of Cala Mosca - Is Mesas at ca. 5 m asl could possibly represent a MIS 5c highstand. Therefore, the sediments containing the Senegalese fauna and capping a marine abrasion platform at +1.5 m asl in the southern part of the area, that were previously attributed to MIS 5e, could actually represent a later highstand, possibly MIS 5a. Nonetheless, all these indicators could also reflect millennial sea-level fluctuations during MIS 5e. New U/Th dating of corals found in the inner part of the Is Cocciulas cave are in progress, and should hopefully shed light on these questions.