Late Weichselian deformation of glaciomarine clays in Hesselo Bay, Denmark

Ultra-ultra-high resolution (UUHR) seismic reflection data were acquired in 2020 as part of a preliminary geophysical site survey covering the original Hesselo Offshore Wind Farm Site in the southern Kattegat, Denmark. Improved seismic processing techniques revealed the subsurface geology in greater detail than seen previously. The study area comprises an approximately 40 m thick unit of glaciomarine clays. The seismic character is generally well-stratified. Within this unit, two distinct and previously unidentified deformation events were recognised. The deep level deformation is characterized by acoustically chaotic to transparent intervals, which are interbedded with well-stratified intervals at the base of a clay unit. Acoustically transparent intervals are interpreted to be the result of glaciotectonic deformation during ice sheet advance. The shallow deformation generally comprises small-scale normal faults which cut through a well-stratified unit and acoustically transparent intervals. The small-scale normal faulting maybe contributed to frost-thaw action. Spatially, the presence of the shallow acoustically transparent succession can be correlated to the Sorgenfrei-Tornquist Fault Zone and the deformation is likely the result of gravitation induced mass movements above the deeper fault system.