The effect of thermal transfer on the zeroing of the luminescence of quartz from recent glaciofluvial sediments

Abstract

The natural optically stimulated luminescence (OSL) response of quartz grains extracted from a range of recent glaciofluvial and other glaciogenic sediments from Western Greenland is presented. All samples were deposited within the last 10 years, many only days or hours before collection. Consequently we would expect to measure zero or very small D E values had optical resetting of the OSL signal been complete. In the case of most samples. D E values in the range 0.5–10 Gy are observed, while higher values are observed for a handful of samples. However, the regenerated OSL growth curves, constructed after daylight exposure of at least several hours, also show large apparent D E values (negative x-axis intercepts). Corresponding samples from four different locations in the Indian Himalaya display similar OSL characteristics. The measurement of several regenerated OSL growth curves omitting the preheat procedure which normally precedes OSL measurement, confirms that a significant degree of thermal transfer is occurring during the preheating. It is this thermal transfer of charge during the preheat which is responsible for a significant contribution to the large apparent D E values observed for the regenerated OSL growth. In this paper we describe combined OSL and TL measurements which have been used to monitor the charge transfer in detail for one sample. An attempt is made to describe the charge transfer behaviour, and we discuss methods appropriate to eliminating the unwanted effects of this phenomenon during OSL dating. Preliminary results from the application of these techniques are presented, and the implications of these observations for the OSL dating of glaciogenic sediments are discussed.