3D seismic characterization of the Norwegian Channel Ice Stream - bedrock controls on ice streaming behaviour and spatio-temporal evolution of erosion and infill of a major cross-shelf trough through multiple glaciations

The imprint of the Pleistocene glaciations in the North Sea Basin is known from various localities scattered across the North Sea Basin and to a large extent relies on widely spaced cored boreholes linked with 2D seismic profiles. Recent studies have demonstrated that a step change in levels of detail can be achieved when using 3D seismic data to image the glaciogenic sequences. However, to date only a relatively small part of the North Sea has been investigated with these data sets. Because of the long history of hydrocarbon exploration, the North Sea is now covered from coast to coast with high-quality 3D seismic data which allow the glacial succession to be examined in great spatio-temporal detail. This project used a regionally merged (c. 150 km by 150 km, 50 m bin spacing) 'mega survey' 3D seismic dataset to provide, for the first time, a 3D seismic geomorphological characterization of the Norwegian Channel Ice Stream, which records glaciations of the North Sea since at least 1.1 Ma. The project first linked the cored Troll borehole with the 3D seismic dataset, providing age and lithological calibrations of the ice stream base and key glacial surfaces within the fill. The interpretation was then extended to the greater survey extent. The basal ice stream footprint reveals a correlation between km-wide and tens of km long positive landform and dominantly sandy deposits in the substrate. The overall architecture of the infill reveals a progressive filling up of the eastern (proximal) part of the cross shelf trough whilst erosion dominated on the western (distal) flank. This evolution matches the evolution of the trough mouth fan situated on the Atlantic margin which shows a progressive westward migration of depocentres through the Pleistocene. On a smaller scale, the 3D seismic data display the interplay between fjord-supplied ice and the main ice stream conduit. Moreover the analysis suggests the occurrence of numerous grounded as well as floating glacial episodes, separated by marine sedimentation. Some of the marine inter-glacial units show evidence for tidal reworking and tidal cycles are depicted semi-quantitatively by sinuous iceberg scours. Importantly, the cross shelf trough provides a near complete record of glacial and interglacial sedimentation in a proximal setting which is available nowhere else, and yet there is only a single cored borehole within this archive. Clearly only full 3D coverage can ensure that future boreholes target the most complete sections including the oldest part of the ice stream fill which was not sampled in Troll, suggesting perhaps an even older origin of the basal erosion surface.