Comparison of OSL ages from young dune sediments with a high-resolution independent age model

Abstract

In order to test the accuracy of quartz optically stimulated luminescence (OSL) dating for young dune sediments (<100a), a series of aerial images of a migrating sand dune is used to cross validate OSL ages. The investigated dune is situated on the northern part of the island of Sylt (southern North Sea). Based on aerial images and a map from 1925 to 2009 and the internal architecture of the dune obtained by ground-penetrating radar (GPR), an independent age model has been developed to attribute sedimentary-architectural elements of the dune to time. The annual rate of dune migration is calculated to be around 4.1m/a. Along a 245m transect oriented parallel to the direction of dune movement, 13 samples for OSL dating were collected at equidistant locations. Sand-sized quartz (150–250μm) was used for determining the equivalent dose (De) applying a single-aliquot regenerative-dose (SAR) protocol. Results show that the oldest OSL age from the investigated recent dune appeared to be 110±10a, whereas the modern analogue was dated to 34±3a. In comparison with the aerial images, the OSL ages show a systematic overestimation of 10–40a for six out of seven younger samples, which are expected to be younger than ∼60a. This offset is negligible for older samples, but a substantial error in these younger ages. The overestimation is originated from a combination of small thermal transfer of 4–12mGy during preheat and incomplete bleaching in medium OSL component causing a residual dose of about 15mGy. The contribution of the incompletely bleached medium component cannot be removed totally by an early background subtraction approach. Despite the observed offset for youngest samples, this study corroborates the suitability of the OSL technique to date young dune sediments (<100a).