OSL dating of Upper Pleistocene littoral sediments: a contribution to the chronostratigraphy of raised marine terraces bordering the Gulf of Taranto, South Italy

Abstract

The lower three of a flight of raised marine terraces bordering the northern side of the Gulf of Taranto, close to Metaponto (Basilicata and Puglia, South Italy) were studied using optically stimulated luminescence (OSL) dating techniques plus sedimentological and mineralogical criteria. Deduced from geomorphological correlation and independent age control, these littoral deposits, reaching up to 60 m a.s.l., represent late Middle Pleistocene and early Upper Pleistocene coastlines. OSL dating was carried out using single aliquot regeneration (SAR) protocols on coarse grain quartz and potassium feldspars as well as multiple aliquot additive (MAA) protocols on coarse grain feldspar and polymineral fine grain samples. Results obtained by multiple and single aliquot techniques for feldspar and fine grain samples are in good agreement; however, they underestimate the expected age ranges significantly, by more than 25%. Age determinations exceeding 90 ka are not feasible. Nevertheless, fading tests carried out over a time span of 11 months gave no indication for instabilities of the feldspar signals. Age estimates obtained by SAR dating on coarse grain quartz exceed the feldspar dating limit. They reveal saturation doses between 150 and 200 Gy and accordingly show low reproducibility and large uncertainties. Feldspar results obtained for the youngest terraces T2 and T1, which are correlated with marine isotope stages (MIS) 5.5 and 5.1, respectively (cf. Brückner, 1980a), indicate an accumulation of the littoral marine sediments during the transition time from MIS 4 to MIS 3. OSL-dating terrace T3, correlated with MIS 7, rendered feldspar age estimates of MIS 5.1. The study shows that OSL dating of marine deposits is far from being a routine technique.