Fig. 8. Lommel
(1) is in northern Belgium, near the border with the Netherlands. At 12.94 ka (2), this site was a large late Glacial sand ridge covered by open forest at the northern edge of a marsh. ….Then, just before the Younger Dryas began, a thin layer of bleached sand was deposited and, in turn, was covered by the dark layer marked "YDB" above
. That stratum is called the Usselo Horizon and is composed of fine to medium quartz sands rich in charcoal. The dark Usselo Horizon is stratigraphically equivalent to the YDB layer and contains a similar assemblage of impact markers (magnetic grains, magnetic microspherules, iridium, charcoal, and glass-like carbon). The magnetic grains have a high concentration of Ir (117 ppb), which is the highest value measured for all sites yet analyzed. On the other hand, YDB bulk sediment analyses reveal Ir values below the detection limit of 0.5 ppb, suggesting that the Ir carrier is in the magnetic grain fraction. The abundant charcoal in this black layer suggests widespread biomass burning. A similar layer of charcoal, found at many other sites in Europe
, including the Netherlands (3), Great Britain, France, Germany, Denmark, and Poland (4)
, also dates to the onset of the Younger Dryas (12.9 ka) and, hence, correlates with the YDB layer in North America.