Late Holocene debris cone development and vegetation and land-use history in the Pasture Beck valley, Lake District, NW England

Abstract

SUMMARY Investigations of a sedimentary sequence exposed in the distal margin of a small debris cone in the valley of Pasture Beck, eastern Lake District, have yielded detailed information concerning the time and nature of cone aggradation phases and the local vegetation and land-use history. Radiocarbon dates from two buried peat beds indicate that the cone surface was generally stable from the late 8 th to the early 13 th centuries AD (1165–736 cal. BP). An interlude of colluvial gravel deposition interrupted peat accumulation and was probably the result of a single short-lived event. Gravel-dominated beds represent deposition of reworked rockfall debris and glacial drift by cohesionless debris flows, whereas finer-grain beds are probably the result of sheet-flows derived by washout of fines from debris-flow deposits. The stratigraphic evidence indicates that the minerogenic sediments accumulated in quick succession. Pollen and charcoal data from peat samples reveal intensification of land-use before burial of the peats by minerogenic sediments. It is proposed that landscape instability was associated first with Norse-Irish settlement and woodland clearance, and later, probably, to the expansion of upland pastures and more intensive grazing in the 13 th century AD. When the Pasture Beck data is considered along with information from elsewhere in the British Isles, it is apparent that not all patterns of Late Holocene landscape change in upland areas can be ascribed to a single cause.