Formation and widening of a North Sea tunnel valley - The impact of slope processes on valley morphology

Over the past two decades, seismic data from the hydrocarbon industry have become a popular tool for investigating shallow Quaternary formations in the North Sea Basin, revealing multiple buried tunnel valleys and other features of glacial origin. In this study, we incorporate 3D seismic analysis with 2D high-resolution seismic data to describe a tunnel valley system in the southern part of the Danish North Sea Basin. We document pervasive slumping as the main driver for valley widening in the southern part of the system. The slumping and the lateral distribution of slump scars were seemingly controlled by valley steepness and the shape of the valley profile, which is partly controlled by the infill rate. The system evolved through multiple erosional and depositional phases in the subglacial environment, with continued deposition after deglaciation. The study provides further evidence of large-scale channelized subglacial drainage under past ice sheets and documents a strong impact of valley slope processes in the shaping of the morphology of the upper slopes and shoulders of tunnel valleys.