Cenozoic evolution of the eastern Danish North Sea

This paper provides a review of recent high-resolution and conventional sei smic investigations in the eastern Danish North Sea and describes their imp lications for the development of the eastern North Sea Basin. The results c omprise detailed time-structure maps of four major unconformities in the ea stern Danish North Sea: the Top Chalk surface (mid-Paleocene), near top Oli gocene, the mid-Miocene unconformity, and base Quaternary. The maps show th at the eastern Danish North Sea has been affected by faulting and salt diap irism throughout the Cenozoic. Carbonate mounds, erosional valleys and pock mark- or karst-like structures were identified at the top of the Upper Cret aceous-Danian Chalk Group. Strike-parallel erosional features and depositional geometries observed at near top Oligocene and at the mid-Miocene unconformity indicate that these major sequence boundaries can be attributed to large-scale lateral changes in sediment supply directions. Increases in sediment flux to the southeaste rn North Sea at the Eocene/Oligocene transition and in the post-Middle Mioc ene appear to correlate with similar events world wide and with long term d elta O-18 increases, indicating forcing by global factors, i.e. eustasy and climate. Stratal geometries observed on the seismic data indicate that the so-called 'Neogene uplift' of the eastern Danish North Sea may have been h undreds of metres less than previously suggested. It is argued that late Ce nozoic uplift of the basin margin and of mountain peaks in southern Norway may have been caused entirely by isostatic uplift of the crust in response to accelerated late Cenozoic denudation and dissection of topography create d in the Paleo.-ene. The late Cenozoic periods of accelerated denudation an d incision rates were most likely driven by climatic deterioration and long term eustatic lowering rather than active late Cenozoic tectonics, the cau se of which is conjectural. A series of shallow thrust structures and an associated system of deep, bur ied valleys were mapped. Thrust faulting most likely occurred in response t o gravitational loading at the margin of an advancing ice sheet, and it was followed by deep incision due to subglacial melt-water erosion, probably d uring the Elsterian glaciation. (C) 2001 Elsevier Science B.V. All rights r eserved.