A thrust-stacked origin for inter-stratified till sequences : an example from Weybourne town pit, North Norfolk, UK

Subglacial processes, and their temporal and spatial variations, play a significant role in controlling the behaviour of ice masses. The processes leading to the formation and emplacement of inter-stratified sequences of subglacial tills are, however, particularly poorly understood. Such sequences are relatively widespread, having been found in, for example, the UK, Canada and Germany. Those of the Weybourne area of north Norfolk, UK, are especially interesting in that the majority of the sediment pile is composed of repeated, inter-laminated subglacial till units with very few non-till units present. Many contrasting mechanisms for this highly contorted sequence have been suggested throughout a long history of investigation at the site and even the direction of ice advance that produced the deformation has proved difficult to resolve. In order to address this, the current study combines lithological, structural and palynological techniques to investigate the exposure at Weybourne Town Pit. A re-interpretation of the sequence is presented in which the tills are seen to have been derived initially as subglacial tills from advances of the Middle Pleistocene British Ice Sheet flowing southwards along the east coast of England. A stage of brittle deformation linked to oscillation of the ice margin is identified as occurring after the primary deposition phase. This secondary deformation phase was responsible for localised thrust-stacking of the till blocks and resulted in the inter-stratified sequence seen today.