Residual Doses in Recent Alluvial Sediments From the Ardenne (S Belgium)

We report on our first investigations into the potential of optical dating for determining the rate of river flood sedimentation in the Ardenne region (S Belgium). Two samples collected from a recent alluvial deposit were used to investigate the extent of resetting in different particle size fractions of quartz (4-11 μm, 63-90 μm, 90-125 μm, 125-180 μm, 180-212 μm and 212-250 μm) as well as in polymineral fine (4-11 μm) grains. Both samples show satisfactory OSL and IRSL characteristics. The IRSL signals from the polymineral fine grains yield an equivalent dose (De) of 3-4 Gy, while a De of 0.3-0.6 Gy was measured using large aliquots of quartz. Small aliquot analyses of 63-90 μm and 212-250 μm quartz grains confirm that the coarser fraction contains more grains with lower De's. Furthermore, for a modern sample (< 3 years old), ~60% of the aliquots yields a De consistent with zero, indicating that these contain only well-bleached grains. These findings suggest that it might be possible to extract the true burial dose from dose distributions measured using small aliquots of coarse-grained (e.g. 212-250 μm) quartz.