Holocene reworking of drift-mantled hillslopes in Glen Docherty, Northwest Highlands, Scotland

Abstract

Sections exposed within a colluvial debris cone in Glen Docherty, Scotland, reveal in-situ palaeosols intercalated with debrisflow diamictons and horizons of slopewash deposits. Radiocarbon dating of the palaeo sols suggests that drift reworking at this site involved brief, intermittent episodes of debrisflow and slopewash activity since c. 6.5 cal. ka BP. At least four such phases can be recognized: c. 6.5–6.2, 5.6–5.3, 4.9–4.6 cal. ka BP and after c. 450 cal. BP. The palaeosols examined show no evidence of local burning of vegetation. A calibrated radiocarbon age for the onset of the most recent phase of reworking may be interpreted as reflecting woodland clearance and/or the influence of extreme rainfall events during the ‘Little Ice Age’ period of regional climatic deterioration. The combined chronostratigraphic and palaeoecological evidence points to discrete, local rainstorms that are seemingly unrelated to long-term climatic change as the most likely cause of enhanced slope reworking, at least prior to c. 450 cal. BP. If this interpretation is valid, it implies that the formation of Holocene debris cones elsewhere in upland Britain may have been due primarily to a small number of localized, extreme rainstorm events. Consequently, caution is necessary in using debrisflow chronostratigraphy alone as a means of reconstructing long-term climate patterns.