Depositional environments and chronology of Late Weichselian glaciation and deglaciation in the central North Sea
Geological constraints on ice-sheet deglaciation are essential for improving the modelling of ice masses and understanding their potential for future change. Here we present a detailed interpretation of depositional environments from a new 30-metre long borehole in the central North Sea, with the aim of improving constraints on the history of the marine Late Pleistocene British–Fennoscandian Ice Sheet. Seven units characterise a sequence of compacted and distorted glaciomarine diamictons, which are overlain by interbedded glaciomarine diamictons and soft, bedded to homogeneous marine muds. Through correlation of borehole and 2D/3D seismic observations, we identify three palaeo-regimes. These are: a period of advance and ice-sheet overriding; a phase of deglaciation; and a phase of postglacial glaciomarine-to-marine sedimentation. Deformed subglacial sediments correlate with a buried suite of streamlined subglacial bedforms, and indicate overridding by the SE–NW-flowing Witch Ground ice-stream. AMS 14C dating confirms ice-stream activity and extensive glaciation of the North Sea during the Last Glacial Maximum, between c. 30 and 16.2 14C ka BP. Sediments overlying the ice-compacted deposits have been reworked, but can be used to constrain initial deglaciation to no later than 16.2 14C ka BP. A re-advance of British ice during the last deglaciation, dated at 13.9 14C ka BP, delivered ice-proximal deposits to the core site and deposited glaciomarine sediments rapidly during the subsequent retreat. A transition to more temperate marine conditions is clear in lithostratigraphic and seismic records, marked by a regionally-pervasive iceberg-ploughmarked erosion surface. The iceberg discharges that formed this horizon are dated to between 13.9 and 12 14C ka BP, and may correspond to oscillating ice-sheet margins during final, dynamic ice-sheet decay.
Authors: Graham, Alastair G.C., Lonergan, Lidia, Stoker, Martyn S.