Early Holocene loessic colluviation in northwest England: new evidence for the 8.2 ka event in the terrestrial record?

Abstract

Vincent, P. J., Lord, T. C., Telfer, M. W. & Wilson, P. 2010: Early Holocene loessic colluviation in northwest England: new evidence for the 8.2 ka event in the terrestrial record? Boreas, 10.1111/j.1502-3885.2010.00172.x. ISSN 0300-9483. Twelve new samples of loessic silts from widely spaced locations on the karst uplands of northwest England have yielded Optically Stimulated Luminescence (OSL) dates that fall within or overlap with (within uncertainties) the early to mid-Holocene period (11.7–6.0 ka), and support three already-published Holocene ages from similar sediment from this region. Nine of the 15 dates are coincident with the hypothesized climatic deterioration at 8.5–8.0 ka in the North Atlantic region and eight are coincident with the 8.2 ka event. These dates demonstrate that the silts are not primary air-fall loesses of deglacial/Lateglacial age (c. 18.0–11.7 ka) but have been reworked and now consist of loess-derived colluvial deposits; we consider the ages to be reliable as there is no compelling evidence to indicate that the samples are partially bleached. There is no substantive archaeological or palynological evidence for Late Mesolithic hunter-gatherers having had a major impact on the landscape, and it is considered highly unlikely that these people triggered colluviation. We estimate that during the 8.2 ka event there was a reduction in mean annual air temperature at these upland locations of ∼2.6–4.6 °C, and proxy evidence from other sites indicates a shift to wetter conditions. It is inferred that there was greater snow accumulation in winter, that the snowpack survived for longer periods, and that there was an increase in the magnitude and frequency of frost-related processes and meltwater flooding. Together, these changes in climate and their associated (sub)surface processes were responsible for the reworking of the loess. The OSL dates indicate climatically induced landscape dynamism in Great Britain during the latter half of the ninth millennium.