Assemblage of buried and seabed tunnel valleys in the central North Sea: from morphology to ice-sheet dynamics

Abstract

Tunnel valleys are kilometre-scale, channel-like, incised subglacial landforms usually associated with glaciated lowlands (O Cofaigh 1996). Tunnel valleys related to the Pleistocene glaciations are present onshore and offshore of NW Europe (e.g. Huuse & Lykke-Andersen 2000; Van der Vegt et al. 2012). In the central North Sea, tunnel valleys are found buried in the Quaternary succession and as bathymetric deeps at the seabed. Three-dimensional (3D) seismic data from the central North Sea image extensive networks of buried tunnel valleys that consist of multiple generations of cross-cutting landforms (Stewart et al. 2013). Seabed tunnel valleys are identified in high-resolution bathymetric data, and form another set of younger glacial landforms. Morphological measurements of the buried and seabed tunnel valleys are compared to infer their relationship to past ice-margins and highlight the differences in ice-sheet configuration over time. In the central North Sea, over 180 buried tunnel valleys are clearly imaged within 14 overlapping 3D seismic datasets originally acquired for the hydrocarbons industry (Fig. 1a; Stewart et al. 2013). The survey area lies within 56–59° N and 1° W to 2° E, in water depths of 90–150 m. The buried tunnel valleys form part of the extensive erosive surface at the top of the Aberdeen Ground Formation, usually related to the Pleistocene glaciations of the region from the middle Quaternary onwards (Stoker et al. 1983; Graham et al. 2011). The buried valleys overlie the Bruhnes–Matuyama magnetic reversal (dated at 780±5 ka BP from boreholes in the region, Stoker et al. 1983) and are overlain by sediments dated to 30 14C ka BP (Graham et al. 2010). Fig. 1. ( a ) Location of the study area, three-dimensional (3D) seismic volumes and examples in the central North Sea. Map from GEBCO_08. WB, Witch Ground Basin. ( b ) All the tunnel valley outlines mapped within …