No abstract

The Upper Cretaceous chalk of the Danish Basin has been interpreted as a major contourite complex on the basis of high-resolution seismic data. The sea floor had a pronounced topography with kilometre-wide ridges and valleys up to almost 200 m deep, interpreted to have been formed by contour-parallel bottom currents. Only few ancient contourite systems have been recognized, mainly based on sedimentary facies and only rarely on architecture and morphology. Two cored boreholes, 345 and 443.3 m deep through the Danish chalk contourite complex, offer a unique possibility to compare seismic and sedimentary facies. The contourite chalk is completely bioturbated except for thin intraclast conglomerates and a few thin levels, showing possible primary lamination. In terms of lithology and trace fossils the contourite chalk is similar to horizontally bedded pelagic chalk uninfluenced by bottom currents. Published contourite models cannot normally be used for the chalk because of the very fine grain size, generally complete bioturbation, and lack of any vertical trends in grain size on a millimetre to centimetre scale. It is thus only rarely possible to document the influence of bottom currents on the basis of facies analysis alone and this can be inferred only by architectural analysis of seismic-scale outcrops.

The Upper Cretaceous – Danian succession in Denmark and most of NW Europe is composed mainly of chalk and associated shallower water carbonates deposited in a wide epeiric sea during an overall global sea-level highstand (e.g. Surlyk 1997). The Maastrichtian–Danian chalk has been intensely studied over the last 20 years, since it forms the most important reservoir rock for hydrocarbons in the North Sea Central Graben (e.g. Surlyk et al. 2003; Klinkby et al. 2005). In Denmark, thousands of water wells have been drilled through the succession as about 35% of the water consumption is from Maastrichtian chalk and Danian bryozoan limestone. During 2005 the new Cretaceous Research Centre (CRC) was established jointly at Geocenter Copenhagen by the Geological Institute, University of Copenhagen and the Geological Survey of Denmark and Greenland (GEUS) with financial support from the Danish Natural Science Research Council (FNU). CRC aims at studying the Earth System in a Greenhouse World, with special emphasis on the Upper Cretaceous – Danian chalk of NW Europe. The stable, longlasting marine macro-environment represented by the chalk sea provides a unique opportunity to analyse and link the depositional, geochemical and biological responses to external forcing at time scales ranging from the sub-Milankovitch to the million year range. The studies will be based on a wide range of methods, including seismic stratigraphy, palaeoecology, sequence-, cyclo- and biostratigraphy, isotope geochemistry, sedimentology and time series analysis. This paper presents the first preliminary results of a CRC drilling campaign at Stevns Klint, eastern Denmark (Fig. 1), where two shallow boreholes were drilled and logged from near the base of the Danian bryozoan limestone and down through the upper 350–450 m of the very thick Upper Cretaceous chalk section (Vejbæket al. 2003). The cores represent the first complete sections through the Maastrichtian chalk of eastern Denmark.