Overdeepened Quaternary valleys in the eastern Danish North Sea: morphology and origin

A system of 100-350 m deep, overdeepened and buried valleys has been mapped in the eastern Danish North Sea. Individual valleys can be traced for several tens of kilometres, and valleys generally begin and terminate abruptly. A correlation to buried valleys onshore southwest Denmark is possible. The valleys post date glaciotectonic structures, and are interpreted to be Elsterian and possibly Saalian in age. The origin of valleys in the eastern Danish North Sea is explained by repeated cycles of sub-glacial down-cutting of meltwater channels and channel closure due to ice creep, eventually producing deeply incised valleys. Glacial erosion may have been significant in cases where valleys are broad and shallow. The origin of overdeepened Quaternary valleys in general can be attributed to a combination of three end-member processes: (i) steady-state drainage of meltwater; (ii) catastrophic outbursts of meltwater; and (iii) glacial erosion. The main requirement for sub-glacial valley formation is the presence of a melting ice sheet overlying a poorly consolidated substrate. Permeability variations of the substrate may produce subregional variations in the pattern of valley incision, while pre-glacial rivers, faults or salt structures are of local importance only. (C) 2000 Elsevier Science Ltd. All rights reserved.