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© 2016 GEUS. Geological Survey of Denmark and Greenland Bulletin 35, 51–54. Open access: www.geus.dk/publications/bull The chemical composition of chalk and marl reflects the mixture of carbonate particles and clastic input deposited on the seabed together with growth of authigenic minerals and diagenesis. The Rørdal quarry in Jylland (Fig. 1) is known for its alternating chalk–marl succession (Surlyk et al. 2010) and the aim of this article is to investigate how this cyclicity is reflected in the geochemical signature of the sequence and test if this has implications for the interpretation of the depositional environment as well as the chemostratigraphy in the chalk. The observed variation in the benthic fauna and the cyclic character of the chalk–marl succession may reflect an environmental response to orbital forcing. The benthic fauna shows higher species diversity and density in the chalk than the marl layers, suggesting more favourable living conditions in the former (Lauridsen & Surlyk 2008), whereas no differences in environmental stress between the two environments could be derived from a study of the trace fossils (Lauridsen et al. 2011). The c. 10 m thick Rørdal Member was established as a lithostratigraphic unit by Surlyk et al. (2010) and recognised as an expression of a late Maastrichtian cooling event. X-ray diffraction (XRD) analysis indicates that the marly layers represent a relative increase in smectite clays and illite together with some quartz and analcime. The inorganic geochemical evolution in Maastrichtian chalk was investigated by Jørgensen (1986) who noted changes in Sr/Ca and Mn/Ca ratios towards the end of the Maastrichtian in the North Sea Central Graben, leading to the conclusion that geochemistry is a “conceivable tool in basin analysis in the lithologically rather monotonous chalk sequence” (p. 267). However, a systematic geochemical analysis of the chalk has never been undertaken and this work is an attempt to look into the potential of understanding the geology of the chalk by analysing a wide range of elements in chalk and marl.

Geochemistry of the Maastrichtian Rørdal Member, Jylland, Denmark: Ce anomaly as a palaeo-redox proxy