Late Pleistocene coastal evolution of San Giovanni di Sinis, west Sardinia (Western Mediterranean)

摘要

The Upper Pleistocene succession of coastal deposits outcropping at San Giovanni di Sinis (west Sardinia) has been studied since the 1960s. However, the absence of consistent radiometric ages has allowed the production of competing stratigraphic subdivisions of these deposits with different Isotopic Stage (OIS/MIS) attributions. The succession is composed of sandy to gravelly shallow-marine, coastal aeolian and alluvial fan/plain deposits. Facies analysis and log correlations show the presence of three unconformities (T1, T2, T3) always overlain by shallow-marine deposits, cutting through the substrate, alluvial fan or aeolian sediments. We have collected three samples for Optically Stimulated Luminescence (OSL) dating at the top of each shallow-marine deposit. The succession is composed of four unconformity-bounded units (U1, U2, U3, U4), and the new OSL dates indicate the presence of three different sea-level highstands. The first Unit (U1), which is composed of shallow-marine to aeolian deposits and overlies transgressive surface Tl, is related to a marine transgression during OIS 7 (186 ±13 ky). Unit 2 is composed of continental deposits and formed during OIS 6. Unit 3 represents OIS 5 and overlies a transgressive surface (T2). More precisely, Subunit U3a is related to OIS 5e (120 ±10 ky; Eu-Tyrrhenian or Eemian sensu strictu) and is characterized by shallow-marine to aeolian deposits developed during both transgressive and highstand phases. The following bay deposits of Subunit 3b are associated with OIS 5c (100 ± 5 ky) and record a second transgressive event (T3) and highstand phase occurred during the Neo-Tyrrhenian. The succession of San Giovanni di Sinis ends with continental deposits of Unit 4 associated to a sea-level fall that took place at the beginning of the last glacial phase (OIS 4).