Base Quaternary in the Danish parts of the North Sea and Skagerrak

Over the years, several maps of the base Quaternary surface of the Danish area have been published. However, the maps have either been local in character (e.g. Håkansson & Pedersen 1992; Huuse et al. 2001) or have concentrated on special topics such as tunnel valleys (e.g. Huuse & Lykke-Andersen 2000) or glaciotectonic features (e.g. Klint & Pedersen 1995; Andersen et al. 2005). The only published map of a more regional character is that of Binzer & Stockmarr (1994) that covers onshore Denmark and eastern Danish waters. Here we present for the first time a regional map of the base Quaternary surface for the entire Danish sector of the North Sea and Skagerrak based on interpretations of reflection seismic data at the Geological Survey of Denmark and Greenland (GEUS) (Fig. 1). The new map has been depth-converted and merged with the onshore map of Binzer & Stockmarr (1994) and thus the first map covering the entire Danish land and sea areas has been compiled. The definition of the base Quaternary is a current issue of debate. In this article, we follow Gradstein et al. (2004) who place the base Quaternary at base Gelasian, which is dated to 2.59 Ma. In parts of the studied area, glacial tectonic features in the form of thrust complexes can be seen on the seismic data. Here the base Quaternary surface has been placed at the base of the dislocated thrust units, corresponding to the basal décollement horizon. The base Quaternary surface is of both academic and practical interest. The depth to the base Quaternary surface and its morphology are of interest to the understanding of the Quaternary development of the region, but are also important in relation to offshore constructions such as oil and gas platforms, pipelines and wind mills