Tunnel valley deposits from the southern North Sea – material provenance and depositional processes

This study offers new insights into the origin and depositional history of the mixture of sediments infilling one of the largest offshore, northward-orientated, clinoform-structured, tunnel valleys (TVs) of Elsterian age in the southern North Sea (SNS). Specifically, the study sheds light on the provenance of TV deposits based on K-Ar dating of illite, QEMSCAN^® heavy mineral assemblage study, and U-Pb and fission track dating on single grains of apatite. Early Pleistocene substrate and the TV infill demonstrate provenance from the Scandinavian and Baltic realms as well as from Renish central Europe and the Alps. Prior to Elsterian glaciation fluvial transport to the SNS increasingly switched from Baltic sources to a more central European influence. However, based on similar provenance of both the substrate and TV infill, the episode of subglacial tunnel valley formation interrupted this central European influence. Glacial erosional processes associated with the expansion of the Elsterian ice sheet to the SNS reworked a large amount of sediment from the Early Pleistocene deposits of the SNS. The sediment was eventually deposited as the tunnel valley infill. Taking into account a high uncertainty related to the facies of TV sedimentary infill, which thus far has been inferred from seismic reflection surveys only, this study offers the first comprehensive set of data on the composition and provenance of the offshore Elsterian TV sediment.