Buried iceberg ploughmarks in the early Quaternary sediments of the central North Sea: A two-million year record of glacial influence from 3D seismic data

Buried linear to curvilinear depressions, interpreted as iceberg ploughmarks, were identified through most of the 2 Ma-long and about 700 m thick early Quaternary sedimentary record in two 3D seismic cubes from the central North Sea Basin (56-58°N, 2-3°E). The mean width of 402 features measured at 6 time slices in cube C08 was between 49 and 63 m and mean length was 2.5 to 3.7 km. Mapping the < 2.75 Ma old base-Quaternary horizon enabled the approximate shape of the central North Sea Basin to be estimated. The basin provided accommodation space for sediments, delivered in part by glacial processes from Scandinavia and northern Britain and from European rivers during the Quaternary. Images of seismic time slices of the chaotic and irregular features found in these sediments are similar to multibeam swath-bathymetric images of iceberg ploughmarks from modern polar shelves. The buried features indicate drifting icebergs in the central North Sea Basin through most of the early Quaternary. Lack of iceberg ploughmarks in the last few hundred thousand years of the North Sea Basin record suggests that by the Middle/Late Quaternary the basin was largely sediment filled. The iceberg source was probably an early Quaternary Scandinavian ice sheet extending intermittently onto the westward prograding shelf of western Norway. N-S orientated ploughmarks indicate iceberg drift from the north and a W-E component suggests iceberg circulation within the basin. By analogy with maximum thickness of modern icebergs, water depths were < 600 m at most when ploughing took place.