Shallow core drilling of the Upper Cretaceous Chalk at Stevns Klint, Denmark

Abstract

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.

Controls on upper Campanian–Maastrichtian chalk deposition in the eastern Danish Basin

“…The Stevns-2 borehole is in the Boesdal limestone quarry, close to the coastal cliffs of Stevns Klint, 3 km north-east of Rødvig and 75 km south of Copenhagen (Stemmerik et al, 2006). It is located approximately 8 km south of the Stevns-1 borehole described by Rasmussen & Surlyk (2012) (Fig.…”

“…1B and C). Stevns-1 and Stevns-2 were drilled on the Stevns Klint coastline at the culmination and depression of the Cretaceous-Palaeogene (K-Pg) boundary, respectively (Lykke-Andersen Stemmerik et al, 2006;Surlyk et al, 2006). The Stevns-2 core is thus located where the K-Pg boundary is at its lowest topographic position, which is interpreted to reflect a depression on the late Maastrichtian sea floor, whereas the high topographic position of the K-Pg boundary at Stevns-1 is interpreted to reflect a depositional ridge (see Rasmussen & Surlyk, 2012) (Fig.…”

Early diagenetic evolution of Chalk in eastern Denmark

“…This study mainly focuses on the Campanian and Maastrichtian Chalk which has been cored in the Stevns-1 and Stevns-2 boreholes (Figs 1 and 2; Stemmerik et al, 2006). The overall stratigraphy and depositional evolution of the cored succession is presented by Surlyk et al (2013) and a detailed description of the Stevns-2 core is given by Boussaha et al (2016).…”

“…The Stevns-1 and -2 boreholes are entirely cored with excellent recovery (>98%; Stemmerik et al, 2006). A suite of geophysical measurements have been logged in the boreholes (spectral gamma ray, neutron density, sonic) and on the core (gamma ray, density).…”

“…1; Nielsen et al, 2011). Previous studies of the area have documented the stratigraphy, depositional facies, porosity variations with depth and the associated seismic velocities (Frykman, 2001;Lykke-Andersen & Surlyk, 2004;Stemmerik et al, 2006;Surlyk et al, 2006Surlyk et al, , 2013Anderskouv et al, 2007;Esmerode et al, 2007;Nielsen et al, 2011). These studies allow the seismic response of the Chalk to be assessed according to stratigraphic variations and compositional changes, and in particular, the impact on porosity and seismic velocities (Nielsen et al, 2011).…”