The potential of optically stimulated luminescence for dating periglacial slope deposits - a case study in the Taunus area, Germany
Periglacial deposits overlying bedrock are widespread in the German low mountain ranges. The age of these deposits is still a matter of debate and therefore, three sections in the Taunus area were investigated with luminescence dating techniques. In general, the heterogeneity of the sediment, which is characterized by a mixture of grain sizes from clay to cobbles, is the main problem for dating as dose-rate determination is complicated. This is demonstrated based on comparisons of high resolution γ-ray spectrometry, neutron activation analysis, β-counting and in-situ measurements of the γ-dose-rate. Insufficient bleaching due to the transport mode, and consequently age overestimation, was expected to be a major problem for luminescence dating of periglacial slope deposits. In order to get a detailed insight into equivalent dose variations due to partial bleaching, single aliquot regenerative dose (SAR) protocols have been applied to the polymineralic fine-grain fraction, sand-sized K-feldspar and quartz extracts. Our results do not confirm partial bleaching as a problem, except for the basal layer. The luminescence properties vary substantially depending on the site, the layer and the mineral fraction that is measured for equivalent dose determination. However, hardly any systematic tendencies can be observed. Micromorphology analysis indicates post-depositional mixing which complicates the equivalent dose estimation even further. Due to the lack of accuracy, the relevance of the presented data for palaeolandscape reconstruction is limited. Based on these observations, suggestions are made to improve future attempts of dating periglacial cover beds with optically stimulated luminescence (OSL).
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