OSL dating of mixed coastal sediment (Sylt, German Bight, North Sea)

Abstract

As part of a study on coastal sedimentary processes this paper presents the OSL dating of mixed coastal sediment samples from the southern North Sea island of Sylt (German Bight). During coring of the swash-bar (beach) sediments, five samples were presumably contaminated by younger overwash and aeolian sediments because of the sampling method employed. To obtain reliable burial ages for these swash-bar sediments, single-grain and small aliquot measurements were used together with the Finite Mixture Model (FMM) proposed by Roberts et al. (2000) to identify the grain population containing the largest doses (from the deepest part of the core). Before the FMM was applied to dating, the parameters and performance of the FMM were first investigated by systematically comparing small aliquot (∼20 grains) and single-grain measurements of an undisturbed aeolian and swash-bar sample and a laboratory mixture of both sediments. This test case demonstrates the advantage of selecting the time interval immediately following the initial luminescence signals for background subtraction because unsuitable quartz grains were removed from the dose distribution. It is concluded that the measurement of small aliquots can be regarded as a reliable proxy for single-grain dose distribution if the sediment contains only a small proportion of quartz grains emitting a luminescence signal and that the FMM results are relatively insensitive to changes of the over-dispersion parameter between 5–40% for small aliquots and 10–40% for single-grains.We show that the burial ages of the contaminated swash-bar samples resulting from the maximum age populations from equivalent dose distributions measured using small aliquots are consistent with the stratigraphy and with ages obtained from uncontaminated samples.