Luminescence Rock Surface Dating of Pleistocene gravelly beaches and marine terraces

The reconstruction of the Quaternary to present-day coastal evolution according to very high frequency “natural” fluctuations (ca. 103-104 ka) and increasingly human impacts represents the tool to forecast the possible scenarios of environmental changes. Particular interest is focused on Last Interglacial (LIG) or Marine Isotopic Stage (MIS) 5e (124-119 ka) a period of warmer conditions than the present, without a human fingerprint and with a higher sea-level up to 9 metres above the modern. Several MIS 5e paleo-shorelines are well preserved along the coasts of the Mediterranean basin and studied that to unravel potential patterns of future sea-level rise caused by global warming. Nevertheless, perform an accurate geochronological framework on the most precise sea level marker such as Marine terraces are quite often extremely difficult and traditional dating methods such as radiocarbon and U/Th frequently are unenforceable. Luminescence methods is giving interesting results in dating Late Pleistocene sequence filling marine terraces worldwide, but it is suitable only for silty to sandy grained deposits. Recently the new Rock Surface Dating (RSD) method has been developed, that use luminescence principles to date rock surfaces. It is based on the ability of light to penetrate in rocks and to bleach luminescence signal in depth and afterwards the signal can be rebuilt during burial. The analysis of residual luminescence signal with depth allows to obtain burial or exposure ages. This method demonstrated to give reliable ages when used in Holocene cobbles or surfaces and recently has been tentatively performed on Pleistocene deposits. Aim of this work is to test the reliability of RSD on three well known Late Pleistocene gravelly deposits filling the marine terrace of: Cala Mosca, and Cala Viola Porto Palmas (Sardinia, Italy). A total of 17 partially buried cobbles were collected, made up of different lithologies (siliciclastic sandstone; bioclastic-rich sandstone, slate, quartz vein). Performed RSD on the samples had different outcomes: only two out of seventeen samples coming from the Cala Mosca and Cala Viola sites gave RSD reliable ages of 131 ± 8 ka and 126 ± 9 ka, referring the gravelly deposits to the LIG and confirming the published independent ages; several samples resulted affected by a negligible or partial resetting of the signal prior to the burial event and thus were considered unsuitable for RSD dating; others show inadequate luminescence characteristics (dim signal). Results from this work points out that RSD is a promising dating method for Late Pleistocene gravelly coastal sequences but also confirm how mineralogical composition and depositional context can affect the suitability of surface for RSD.