Tracking palaeotemperatures in Coniacian–Maastrichtian seas

Abstract

In this study the stable isotopes of belemnites, are presented from the Coniacian–Maastrichtian interval (∼76–66 Ma) derived from the chalks of Yorkshire and Norfolk, UK, deposited on the western North Atlantic shelf. Cathodoluminescence and elemental geochemistry of the belemnites reveals that most of the rostra were well preserved. If interpreted in terms of temperature, our oxygen isotope record reveals that during the Coniacian (at ∼43 °N) the climate was relatively warm, with maximum mean temperatures of ∼26 °C, followed by cooling to <∼21 °C during the Campanian and Maastrichtian. This overall stratigraphic trend is similar to other records, suggesting that the cooling pattern was not a regional trend and, therefore, driven predominantly by global mechanisms. Within our belemnite data, we also observe a decline in δ¹³C at the Campanian- Maastrichtian boundary, again consistent with other records. This trend has been interpreted as a result of an increased ratio of organic to inorganic carbon introduced into the oceans, driven by increased weathering and reworking of organic-rich sediments exposed on continental shelves during a sea-level fall. The latter related to a build-up of polar ice. Although our oxygen isotope data point to a cooling this was not necessarily linked to polar ice formation.