Cenozoic evolution of the eastern Danish North Sea

Abstract

This paper provides a review of recent high-resolution and conventional seismic investigations in the eastern Danish North Sea and describes their implications for the development of the eastern North Sea Basin. The results comprise detailed time-structure maps of four major unconformities in the eastern Danish North Sea: the Top Chalk surface (mid-Paleocene), near top Oligocene, the mid-Miocene unconformity, and base Quaternary. The maps show that the eastern Danish North Sea has been affected by faulting and salt diapirism throughout the Cenozoic. Carbonate mounds, erosional valleys and pockmark- or karst-like structures were identified at the top of the Upper Cretaceous–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 southeastern North Sea at the Eocene/Oligocene transition and in the post-Middle Miocene appear to correlate with similar events world wide and with long term δ18O 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 hundreds of metres less than previously suggested. It is argued that late Cenozoic 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 created in the Paleogene. The late Cenozoic periods of accelerated denudation and incision rates were most likely driven by climatic deterioration and long term eustatic lowering rather than active late Cenozoic tectonics, the cause of which is conjectural.A series of shallow thrust structures and an associated system of deep, buried valleys were mapped. Thrust faulting most likely occurred in response to gravitational loading at the margin of an advancing ice sheet, and it was followed by deep incision due to subglacial melt-water erosion, probably during the Elsterian glaciation.