Timing and significance of talus slope reworking, Trotternish, Skye, northwest Scotland

Abstract

Exposures through the upper rectilinear (or near rectilinear) segment of vegetated, relict talus slopes at the foot of the Trotternish escarpment, northern Skye, exhibit stacked debris flow diamictons intercalated with surface wash horizons and occasional buried organic palaeosols, thus indicating a long history of reworking at this site. Radiocarbon dates for the tops of buried palaeosols indicate that reworking of sediment locally predates 5.9–5.6 cal. ka BP, and has been intermittently active throughout the late Holocene. Broad coincidences of timing are evident for the onset of reworking of different sectors of the talus slope at c. 5.9–5.6 cal. ka BP, c. 2.3–1.7 cal. ka BP and c. 0.7–0.5 cal. ka BP, that may represent more widespread reworking. Analysis of subfossil palynomorphs within some buried palaeosols suggests that most reworking postdates the main period of local, anthropogenic woodland clearance dated to the mid-Holocene. Buried palaeosols examined contain no evidence of local burning of vegetation. These findings appear to exclude anthropogenic interference with vegetation as a possible cause of late-Holocene erosion of this talus. Evidence for alternative causes of reworking is largely inferential. One hypothesis is that the timing of phases of reworking may reflect the occurrence of climatic events of sufficient magnitude to induce talus slope failure (extreme events). If so, an implication of this finding is that talus deposits may be highly sensitive to climate and could ultimately yield a proxy-record of extreme event occurrence.