The subglacial and ice-marginal signature of the North Sea Lobe of the British–Irish Ice Sheet during the Last Glacial Maximum at Upgang, North Yorkshire, UK

Abstract

Abstract A stratigraphic sequence of glaciogenic sediments at Upgang on the North Yorkshire coast records the advance, recession and re-advance of the North Sea Lobe of the British–Irish Ice Sheet during the Last Glacial Maximum. Two lower deposits (LFA 1 and 2) are interpreted respectively as a glaciotectonite comprising large Liassic bedrock rafts and a subglacial traction till. These deposits are overlain by an extensive body of upward-coarsening stratified sediments (LFA 3) which firstly record deposition into an ice-marginal lake as a result of ice recession, and then the deposition of a sandur complex due to glacier re-advance, which finally resulted in the emplacement of an overlying subglacial traction till (LFA 4). This upper till grades vertically into a stratified diamicton documenting ice-marginal and submarginal subaqueous sediment gravity flows and suspension sedimentation during final deglaciation of the site. Using regional sedimentological, vegetation and varve records, together with lithostratigraphic correlation of the Upgang tills with those at Dimlington, allows the production of a chronostratigraphic framework for this sedimentary sequence. This suggests that the initial ice advance occurred shortly after 22.3–20.9 cal. k yrs BP and correlated with the Dimlington Stadial, while the second advance and emplacement of LFA 4 occurred after 16.2 ka, but before 14.7 cal. k yrs BP. Ascertaining whether these advances of the North Sea Lobe were a response to climate forcing, or to shifts in BIIS internal ice sheet dynamics, remains a difficult challenge.