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Deeply rooted glaciotectonism in western Denmark: geological composition, structural characteristics and the origin of Varde hill-island



We investigate a hill-island in western Denmark, a major cupola-hill-type thrust complex generated by ice-marginal glaciotectonism. The study uses a unique dataset of densely spaced airborne electromagnetic data, high-resolution seismic data and borehole information to document the complexity of deeply rooted thrust sheets comprising Miocene to middle Pleistocene deposits. The deformation spans at least 150 m of sediment thickness, placing this complex among the largest glaciotectonic features on record. The main stages of formation of the hill-island were (1) erosion of Miocene deposits by subglacial tunnel valleys and infill of these valleys in the pre-Elsterian and Elsterian time, (2) two phases of glaciotectonic thrusting during the Saalian glaciation, (3) erosion by the Saalian ice sheet removing a significant part of the thrust complex and (4) periglacial and postglacial erosion of the hill-island excavating the glaciotectonic elements. Palaeoglaciological calculations suggest that the Saalian ice sheet that caused the thrusting was thick, had a steep profile, rested on a permafrost wedge and moved slowly, which contrasts with the highly mobile, thin ice lobes of the Last Glaciation.