THE EFFECT OF THERMAL TRANSFER ON THE ZEROING OF THE LUMINESCENCE OF QUARTZ FROM RECENT GLACIOFLUVIAL SEDIMENTS

The natural optically stimulated luminescence (OSL) response of quartz grains extracted from a range of recent glaciofluvial and other glaci ogenic sediments from Western Greenland is presented. All samples were deposited within the last 10 years, many only days or hours before co llection. 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, DE values in the range 0.5-10 Gy are observed, while higher values are observed for a handful of samples. However, th e regenerated OSL growth curves, constructed after daylight exposure o f al least several hours, also show large apparent DE values (negative x-axis intercepts). Corresponding samples from four different locatio ns in the Indian Himalaya display similar OSL characteristics. The mea surement of several regenerated OSL growth curves omitting the preheat procedure which normally precedes OSL measurement, confirms that a si gnificant degree of thermal transfer is occurring during the preheatin g. It is this thermal transfer of charge during the preheat which is r esponsible for a significant contribution to the large apparent DE val ues 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 descri be the charge transfer behaviour, and we discuss methods appropriate t o eliminating the unwanted effects of this phenomenon during OSL datin g. Preliminary results from the application of these techniques are pr esented, and the implications of these observations for the OSL dating of glaciogenic sediments are discussed. (C) 1997 Elsevier Science Ltd .