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Residual doses in recent alluvial sediments from the Ardenne (S Belgium)

Vandenberghe D., Derese C., Houbrechts G.

Geochronometria

2007

Vol. 28

1-8

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.