Reconstructions of the Late Devensian (Dimlington stadial) British-Irish Ice Sheet: the role of the upper Tees drumlin field, north Pennines, England

摘要

It has long been known that the upland areas of the Pennines, northern England, were a local ice source during the Late Devensian (Dimlington Stadial) glaciation of Britain. However, there has been little detailed work on their significance for ice sheet reconstructions. The presence of drumlins at high elevations within the northern Pennines is reported from the upper reaches of the Tees valley and Harwood Beck. Geomorphological mapping has identified 134 drumlins occurring up to an elevation of 662 m OD in association with superimposed drumlins and drift tails. These landforms, particularly the presence of superimposed forms, enable the reconstruction of two ice flow events associated with a local ice centre that formed during the Late Devensian glaciation in northern England. The earlier flow event was directed straight down the upper Tees valley from a limited source area on the high ground to the east of Cross Fell. The later event indicates a flow direction more transverse to the valley, from a more extensive source area that had migrated and expanded westwards across the high plateau of Cross Fell and southwards towards Dufton Fell. The presence of drumlins at this high altitude indicates sufficient ice thickness to allow basal deformation and suggests that drumlin upper elevation defines a thermal regime above which the plateau ice field was cold based and frozen to the bed. This requires the area to be completely covered by ice. This study demonstrates the importance of these upland areas in detailed reconstructions of a multi-domed, British-Irish Ice Sheet (BIIS).