A morphometric analysis of tunnel valleys in the eastern North Sea based on 3D seismic data

A 1250km(2) 3D seismic volume is used to provide a detailed spatial and geometrical analysis of fifteen Pleistocene tunnel valleys in the Danish North Sea. All the valleys are buried; they are up to 39 km long, 3-4 km wide and up to 350 m deep. The valleys are part of a vast tunnel valley province covering an area of some 0.5 million km(2) of the formerly glaciated lowland areas of North West Europe. The valleys consist of non-branching, non-anastomosing troughs; they exhibit strongly undulating bottom profiles with numerous sub-basins and thresholds, and are characterised by adverse end slopes. Cross-cutting relationships and theoretical considerations suggest the occurrence of seven major episodes of valley incision attributed to ice marginal oscillations within a few glacials. Calculations considering the valley end gradients and theoretical ice-surface profiles suggest that the valleys were formed by pressurised subglacial meltwater erosion. Given a range of theoretical ice-surface profiles, the adverse end slopes are well beyond the supercooling threshold, which suggests that the water was not in thermal equilibrium with the basal ice and that flow was concentrated in substantial conduits with sufficient mass and flux to maintain water temperature well above the freezing point. Copyright (C) 2007 John Wiley & Sons, Ltd.