Upper Campanian-Maastrichtian calcareous nannofossil biostratigraphy of the Stevns-1 borehole, Denmark

The Stevns-1 borehole (Stevns Klint, eastern Denmark) penetrated lowermost Danian bryozoan limestone and Maastrichtian chalk before reaching a terminal depth of 456.1m in the Campanian/Maastrichtian boundary interval. The borehole, drilled as part of a project to study the Earth System in a Greenhouse World, provides the most complete and expanded section through the Maastrichtian in NW Europe. Consequently, it constitutes a significant biostratigraphic reference for this interval. This work presents the biostratigraphy of the borehole, underpinning palaeoecological research that is in progress. 
Application of existing northern high-latitude calcareous nannofossil biozonation schemes to the biostratigraphic data has revealed some previously unsubstantiated/unreported nannofossil events. These include the extinction of Helicolithus trabeculatus and increase in abundance of Prediscosphaera grandis in the Upper Maastrichtian, and extinction of Zeugrhabdotus praesigmoides in the Campanian/Maastrichtian boundary interval. These may prove to be useful in further subdividing this interval, or of particular palaeoecological relevance. Additionally, some nannofossil events appear to contradict those of the established schemes, such as higher than expected extinctions of Zeugrhabdotus bicrescenticus and Gartnerago segmentatum, and the lower than expected extinction of Calculites obscurus. The significance of these, in biostratigraphic or palaeoecological terms, remains to be assessed.