Cilia Derese

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

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 Des. 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.

The timing of aeolian events near archaeological settlements around Heidebos (Moervaart area, N Belgium)

At the locality of Heidebos (Moervaart area, N Flanders, Belgium), a sedimentary core was taken in the Maldegem-Stekene coversand ridge and dated using optically stimulated luminescence (OSL). The study aimed at contributing to an improved understanding of the evolution of the physical landscape around archaeological settlements in this area. The core comprised a 7 m thick series of laminated and massive aeolian sands, in which several organic layers were intercalated. From this sequence, 11 samples were collected for quartz-based SAR-OSL dating; an internally consistent dataset was obtained. The ages of the lowermost 1 m of the sedimentary sequence (15.5±1.1 ka and 17.3±1.3 ka) imply that these sediments may represent the time-equivalent deposit of a deflation phase that occurred during the Late Pleniglacial and led to the formation of a widespread desert pavement, regionally known as the Beuningen Gravel Bed. However, a significant part of the sediments (at least 4 m) was deposited later, i.e. during the Allerod and/or the Late Dryas. As such, the results allow establishing the genesis of the coversand ridge at the Heidebos locality on the basis of direct age information. The relatively high sedimentation rate and the absence of extensive soil formation in the record reflect periods of pronounced aeolian activity and landscape instability during the Late Glacial, which provides part of the environmental framework for human occupation in the area.