Evidence for Late Pleistocene ice stream activity in the Witch Ground Basin, central North Sea, from 3D seismic reflection data

Buried submarine landforms mapped on 3D reflection seismic data sets provide the first glacial geomorphic evidence for glacial occupation of the central North Sea by two palaeo-ice-streams, between 58-59 degrees N and 0-1 degrees E. Streamlined subglacial bedforms (megascale glacial lineations) and iceberg plough marks, within the top 80m of the Quaternary sequence, record the presence and subsequent break-up of fast-flowing grounded ice sheets in the region during the late Pleistocene. The lengths of individual mega-scale glacial lineations vary from similar to 5 to similar to 20 km and the distance between lineations typically ranges from 100 to 1000 m. The lineations incise to a depth of 10-12 m, with trough widths of similar to 100 m. The most extensive and best-preserved set of lineations, is attributed to the action of a late Weichselian ice stream which either drained the NE sector of the British-Irish ice sheet or was sourced from the SW within the Fennoscandian ice sheet. The 30-50 km wide palaeo ice-stream is imaged along its flow direction for 90 km, trending NW-SE. An older set of less well-preserved lineations is interpreted as an earlier Weichselian or Saalian ice-stream, and records ice flow in all SW-NE orientation. Cored sedimentary records, tied to 3D seismic observations, support grounded ice sheet coverage in the central North Sea during the last glaciation and indicate that ice flowed over a muddy substrate that is interpreted as a deformation till. The identification of a late Weichselian ice stream in the Witch Ground area of the North Sea basin provides independent geomorphic evidence in support of ice-sheet reconstructions that favour complete ice coverage of the North Sea between Scotland and Norway during the Last Glacial Maximum. (c) 2006 Elsevier Ltd. All rights reserved.