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Zeroing of the osl signal as a function of grain size: investigating bleaching and thermal transfer for a young fluvial sample

Truelsen J. L., Wallinga J.

Geochronometria

2003

Vol. 22

1-8

Previous studies have indicated that the OSL signal from coarser grain-size fractions might be more completely reset during fluvial transport. In this study we investigate whether this feature is real, or rather an artefact of thermal transfer effects that might affect finer grains more due to smaller thermal lag during heat treatment. Our experimental results obtained on three grain-size fractions (90-125, 180-212 and 425-500 mm) clearly show that better bleaching of coarser grains is not caused by differences in thermal transfer. On the basis of our results we advise selecting a coarse grain size for analysis when dating young fluvial deposits.

On the detection of OSL age overestimation using single-aliquot techniques

Wallinga J.

Geochronometria

2002

Vol. 21

17-26

Optically stimulated luminescence (OSL) dating is a quantitative dating method to determine the time of last exposure of sand and silt to (sun) light. However, insufficient resetting of the optically stimulated luminescence signal prior to sediment deposition can result in overestimation of the age of a sample. Therefore detection of so-called poor bleaching is of prime importance in OSL dating. Several methods proposed in the literature for detection of poor bleaching are based on the scatter in equivalent doses obtained by singlealiquot methods. In this paper numerical simulations are used to assess the validity of these methods. The simulations show that scatter in equivalent doses is largely dependent on the number of grains contributing to the luminescence signal of each aliquot, and proportion of poorly-bleached grains in the mixture under study. Thresholds for detection of poor bleaching based on inter-aliquot scatter in equivalent doses are therefore not valid. It is concluded that tight, symmetrical dose distributions obtained on small aliquots (ultimately consisting of a single grain) provide the best indication that the sample is homogeneously bleached.