Late Quaternary geology of a potential wind-farm area in the Kattegat, southern Scandinavia

Following the proposal of the offshore Anholt wind-farm project with an energy capacity of 400 megawatt in the Kattegat, southern Scandinavia, an evaluation of the geotechnical properties of the subsurface of the area is required. As a first step to map the seabed geology the Geological Survey of Denmark and Greenland (GEUS) conducted a geophysical survey (Leth et al. 2009) which, together with cone penetration tests and data from boreholes, lead to a greater understanding of the geological architecture and development of the 144 km 2 survey area (Figs 1, 2). Methods We used a multibeam echo-sounder for detailed mapping of the bathymetry, and shallow seismic equipment and coring to map the shallow seabed geology including the distribution and thickness of the main geological units. A combination of two seismic devices (chirp and sparker systems) was chosen to ensure good penetration and high resolution. The sparker system provides data from the sea floor down to about 45 m into the seabed with a vertical seismic resolution in the order of 50 cm, while the chirp system provides high-resolution seismic data from the upper 5–10 m of the seabed with a vertical seismic resolution at decimetre scale. A side-scan sonar was used for mapping of surface sediments. At seven sites, boreholes were made to a depth of 40 m and selected intervals sampled. Cone penetration tests were carried out at the same sites (Fig. 2) and surface sediment samples collected for biological studies.