An examination of the Geochemical properties of late devensian glacigenic sediments in Eastern England

Abstract

Onshore advance of the North Sea lobe of the Late Devensian British Ice Sheet the last glaciation resulted in the deposition of thick multiple till sequences along the coasts of east Yorkshire and north Lincolnshire. Despite an abundance of sedimentological and stratigraphical data, the origin of these tills remains controversial, and their correlation along the coast is poorly understood. These multiple till sequences provide an excellent opportunity to test models of large-scale subglacial sediment transport and deposition beneath soft-bed ice sheets using geochemistry. Such geochemical analysis has been used extensively in other formerly glaciated areas, notably Canada, to identify till characteristics and dispersal patterns. However, to date it has not been applied in any detail to glacial sediments in the UK and its potential as a tool for till correlation and understanding till genesis remains relatively undeveloped. A detailed sampling method was employed at seven sites in eastern England; Filey, Skipsea, Dimlington, South Ferriby, Kirmington, Welton-Le-Wold and Morston; to investigate vertical and lateral changes in till geochemistry in this region. Particle size analysis of the till matrix was used as an additional tool to provide extra sedimentological data. Complete linkage and Ward's method cluster analysis was used to establish groups of geochemically similar diamicton samples. Geochemical results suggest that there are vertical changes in till geochemistry, which are likely to be related to a change in provenance from local to more distal sources. Geochemistry and particle size results were also unable to precisely differentiate between the Basement, Skipsea and Withernsea till types. Instead, the repeated nature of the geochemical signature at larger sites, such as Dimlington, and the lateral discontinuity of some geochemical groups suggests that the till sequences at Filey, Dimlington, and Skipsea are comprised of a number of lithologically distinct rafts which have been tectonically stacked or elevated to higher levels in the sediment pile. At Dimlington the production of a glacitectonically folded and stacked moraine is proposed as a mechanism to explain the remarkably thick sequence of Withemsea Till and the repeated nature of the geochemical signature at this site. This research therefore provides new evidence for our understanding of glacial stratigraphy and former ice dynamics in eastern England, suggesting that till composition and the mechanics behind its production are more complex than the traditional stratigraphic division allows.