Late Maastrichtian warming in the Boreal Realm: Calcareous nannofossil evidence from Denmark

The climate of the mid to Late Cretaceous was probably one of the warmest of the Phanerozoic, but by the late Maastrichtian distinctly cool high latitude regions had developed. Studies from low latitude sites have demonstrated that the late Maastrichtian cooling was punctuated by two pulses of warming, but the response of nannoplankton to climatic fluctuation in the mid to high northern latitudes is not well documented. A high-resolution nannofossil study was undertaken on subsurface chalk sections of Denmark which provide a stratigraphically complete record of late Maastrichtian sedimentation of nannofossil ooze in an extensive mid to high latitude carbonate province. The quantitative nannofossil data from cored sections through the upper Maastrichtian chalk reveal subtle but significant shifts in taxa interpreted as having been sensitive to temperature fluctuations (Arkhangelskiella cymbiformis, Kamptnerius magnificus, Lucianorhabdus cayeuxii, Nephrolithus frequens, and Watznaueria barnesiae), and indicate two late Maastrichtian warming events correlatable with those of low latitude records, and a decrease in surface water temperatures in the latest Maastrichtian.