Evidence for changes in Holocene sediment flux in Semer Water and Raydale, North Yorkshire, UK

We present preliminary results from studies carried out in the lake and extensively gullied drainage basin of Semer Water in North Yorkshire, England. The results obtained so far are limited by physical problems encountered during coring at the present day lake, the complex nature of the sedimentary infill upstream in Raydale, and difficulties experienced in establishing a continuous Holocene chronology for the site. Both magnetic measurements and organic geochemical analyses show that the bulk of the sediment sampled in Semer Water and in the alluvial area of Raydale, just upstream, is derived from the catchment, although in some cases the allochthonous magnetic signature is overprinted by contributions from bacterial magnetosomes growing in the lake or surface sediments. Significant traces of polyaromatic hydrocarbons (PAHs) in sediments contemporary with the Mesolithic occupation of the Pennines reinforce evidence from elsewhere for the use of fire at this time. Several lines of evidence identify a mid-Holocene period of reduced allochthonous input. Rapid sediment accumulation during the period between 4200 and 3500 cal. BP points to the likelihood of increased erosion during the Bronze Age. Geomorphological studies point to periods of alternating dissection and aggradation in the catchment during the last 2000 years. The record presented gives some indication of the potential for uniting geomorphological, palaeolimnological and organic geochemical research in an effort to trace the Holocene evolution of a complex, highly eroded system.