An Early Pleistocene grounded ice sheet in the Central North Sea

Evidence is presented for an Early Pleistocene grounded ice sheet in the Central North Sea (CNS). Dated basal Quaternary deposits from UK well 30/13-2 Josephine coincide with the lowest iceberg ploughmarked horizon in a southern CNS depocentre. This horizon has been traced northwards into the central CNS where it is identified as the Crenulate reflection, which exhibits a series of deep, channel-like features, interpreted as subglacial meltwater channels. Further north, a seismic reflection at the same level is characterized by megascale lineations that are interpreted to be the result of erosion, deposition and deformation of sediment beneath an advancing ice sheet. An overlying seismic reflection is characterized by a well-developed channel system that is thought to have drained the retreating ice sheet prior to a post-glacial marine transgression. A southern CNS Early Pleistocene depocentre is shown to have become inactive sometime in the Early to Middle Pleistocene and was replaced by a developing depocentre in the central and northern CNS that remained active into the Late Pleistocene. Evidence for an Elsterian or older grounded ice sheet in UK Continental Shelf Quad 22 is presented in the form of glaciotectonic thrust features.