The Rhine-Meuse system in a new light : Optically stimulated luminescence dating and its application to fluvial deposits

Optically Stimulated Luminescence (OSL) dating allows the age determination of sediments deposited during the last glacial-interglacial cycle. Thereby this relatively new technique enables chronological frameworks to be established for fluvial deposits that can often not be dated by other means. The OSL signal of quartz and feldspar minerals is reset by light exposure during fluvial transport, and builds up as a result of ionising radiation after burial of the minerals. Incomplete resetting of the OSL signal, due to inadequate light exposure in the fluvial environment, can result in age overestimations, especially for relatively young samples. Methods used for the detection of incomplete resetting, or poor bleaching, are reviewed. It is argued that techniques measuring the OSL signal from small sub-samples (aliquots) are most promising both for detection of poor bleaching, and for obtaining the true age for a sample in which not all grains had their OSL signal completely removed at deposition. Quartz should be the mineral of choice as it has shown to yield the most reliable results, and because its OSL signal is more rapidly reset than that of feldspar. Aliquot size should be small, with aliquots ideally consisting of a single grain of quartz. Using single-aliquot dating of coarse-grain quartz offsets between zero and a few thousand years have been found for modern fluvial deposits. Validity of single-aliquot quartz OSL dating has been demonstrated by application to known-age samples, but especially for the older age range (> ∼ 13 ka) further prove of the accuracy of the method is essential. The application of quartz OSL dating for geological research of fluvial deposits opens a realm of new possibilities to be explored, as is highlighted by some examples of geological applications