Luminescence dating of mass-transport sediment using rock-surface burial methods: a test case from the Baksan valley in the Caucasus Mountains

Mass-transport sediments are generally difficult to date directly by existing methods. Conventional luminescence dating of sand is unsuitable because the short transport distances provide little opportunity for bleaching. However, larger clasts are often exposed to sunlight for prolonged periods before becoming entrained in mass-movements, and these clasts have the potential to be used for rock-surface luminescence dating. Mass-transport is a major component of landscape change in mountain regions; in the Baksan valley, Caucasus Mountains, high uplift rates and high precipitation create a rapidly eroding landscape where preservation of sediments is poor. The area is particularly prone to destructive debris flows, because of the large quantity of detrital material in the catchments. The debris-flow and hillslope sediment the Baksan valley are used here to test the applicability of rock-surface burial dating to mass-transport sediment. We find that colluvial clasts show a high degree of bleaching and give reproducible ages, with a large colluvial deposit dated to the early-mid Holocene. The bleaching of debris flow clasts is more variable - we suppose due to the more complex transport history of the clasts, with opportunities for lengthy storage in moraines or colluvium. Overall, the results are encouraging, and suggest that rock-surface methods can provide a useful approach to mass-transport dating in mountainous regions. However, improved targeting of samples and measurement efficiency is desirable for widespread application.