ZEROING OF THE OSL SIGNAL IN QUARTZ FROM YOUNG GLACIOFLUVIAL SEDIMENTS

The natural luminescence of quartz samples from recent (<200 yr old) glaciofluvial sediments collected from a range of distances from the snout of the Gangotri glacier in the Garhwal Himalaya, India, was measured. Six measured D-E (equivalent dose) values ranged from 35 to 175 Gy, strongly suggesting that these samples had been exposed to daylight only poorly before deposition. However, regenerated growth curves constructed after exposure to several hours of natural daylight gave apparent D-E values ranging from 10 to 30 Gy. Detailed measurements of one sample confirm that these observations are due to a hugh recuperation effect. The ''shine plateaux'' observed in the majority of these D-E determinations showed little increase of D-E with increasing exposure time. The mechanisms of this unexpected behavior, and the implications for the detection of partial bleaching, are discussed.