Systematic high-sampling resolution OSL dating of a well-preserved river dune in the Lys valley (Sint-Martens-Latem, NW Belgium)

During the Late Glacial recolonization of NW Europe, hunter-gatherers preferably settled in sheltered environments and along river valleys and lake edges. However, in the Scheldt basin of NW Belgium (which includes tributaries such as the Lys river) remains of these Late Glacial settlers are scarce. Due to the lack of an in-depth assessment of Final Palaeolithic sites in the Scheldt basin, it is not clear at present whether this scarcity is related to specific taphonomic factors and/or corresponds to a prehistoric reality. Moreover, the few known sites in the floodplains of the Scheldt and its tributaries all seem to date to the Younger Dryas (final stage of the Late Glacial), which recently led to the hypothesis of a possible population shift from the inland lakes towards the rivers at the abrupt transition from the warm AllerOd to the extreme cold Younger Dryas. We seek to investigate this hypothesis through intensive geoarchaeological research of aeolian river dunes in this area, as they represent dry elevations bordering a wet landscape, making them attractive spots for occupation. This study reports on quartz-based optically stimulated luminescence (OSL) dating of an exceptionally well-preserved dune, as one of those potential contexts of sealed Final Palaeolithic sites. The dune, locally called “Molenberg” (Lys valley, municipality of Sint-Martens-Latem, NW Belgium), is more than 10 m high (top is 24.82 m a.s.l.). Samples for OSL dating were collected systematically at 50 cm vertical intervals by hand coring at two localities, allowing for a complete sequence from top to base and resulting in a total of 31 samples. These were processed in the usual manner for OSL dating using sand-sized (125-180 m) quartz and the single-aliquot regenerative-dose (SAR) protocol. All samples exhibit satisfactory luminescence characteristics (in terms of purity, signal intensity and composition, and SAR procedural tests). The optical ages range from 11.6 ± 1.1 ka at the top, to 14.9 ± 1.4 ka at the base of the dune, placing its formation in the Late Glacial. In general, the dataset is internally consistent although, further down the sequence, the observed variability appears somewhat larger than expected from measurement uncertainties (2 sigma) only. We consider additional sources of (partial) random uncertainty (such as water content) and use Bayesian chronological age-depth modeling to improve the chronological precision and connect the sedimentation ages with the different climatic and environmental changes during the Late Glacial. Our case study not only illustrates the importance of OSL dating for prospecting potential contexts for hunter-gatherer finds dating to the Final Palaeolithic; it also contributes to a chronological framework for the changing aeolian landscape in the Lys valley during the Late Glacial, which is somewhat contentious untill now. Finally, we show that results from a high-sampling resolution strategy contribute to debates on expected and observed variability, and hence the time-resolution that can reasonably be achieved for the sandy archives under consideration here.