Planar detaching faults in the southern Horn Graben, Danish North Sea

Abstract

The Danish Horn Graben is located in the south-eastern North Sea and suffered fault controlled differential subsidence during the Triassic. Within the Horn Graben, several faults cut the Triassic succession but detach at or close to the Top pre-Zechstein surface. An E-W striking trend of planar detaching faults is mapped using 2-D seismic sections and the displacement on the faults is analysed with respect to timing and spatial distribution of the displacement. The spatial distribution of the displacement is analysed using the Fault Analysis Projection System (Badley Earth Sciences), whereas the timing is analysed by reconstructing the seismic sections and thus obtaining the spatial distribution of displacement at different times. The occurrence of the detaching planar faults appears to be controlled by the difference in basal friction across the pinch-out line of the mobile Zechstein sediments. A dipping detachment surface is necessary to create a driving mechanism but is of minor importance in initiating the faulting. The timing of the faulting is controlled by a general change in tectonic pattern enabling a N-S extension of the sediments covering the Top pre-Zechstein surface.