Revisiting a type locality for Late Glacial aeolian sand deposition in NW Europe: Optical dating of the dune complex at Opgrimbie (NE Belgium)

The Late Glacial dune complex at Opgrimbie (NE Belgium) is thought to represent a complete record of the Late Pleniglacial to Holocene change at the southernmost part of the coversand area. In this work, the chronology of the site was reinvestigated using quartz-based single-aliquot optical dating. Nine samples in total were collected from sediments above and below a bleached horizon, the Opgrimbie layer, which laterally passes into a sandy peat layer; earlier radiometric radiocarbon dating and pollen analyses showed the latter to be of Bølling age (14.8–14.1 ka cal. BP). The sampled sequence is overlain by a second horizon, the Usselo horizon, for which an Allerød age (14.0–13.0 ka cal. BP) was deduced from one radiometric 14C age and palynological evidence. This was confirmed by AMS data obtained as part of this study. ne quartz samples showed satisfactory luminescence characteristics, and yielded an internally consistent set of optical ages. The dataset contains no clear outliers and the observed variation is not much larger than that expected from uncertainties. The sediments over- and underlying the lowermost bleached horizon are dated at 12.9 ± 0.9 ka (n = 6) and 13.0 ± 0.8 ka (n = 3), respectively. These ages do not confirm the Bølling age that was previously established for this horizon; the optical ages are, however, consistent with the chronostratigraphical position of the sediments below the Usselo soil of Allerød age. As such, the OSL ages question if the Lateglacial aeolian succession is fully developed at Opgrimbie, and they challenge its significance as a type locality.