Tracking Palaeotemperatures in Coniacian–Maastrichtian Seas

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 of the belemnite revealed some diagenetic alteration occurring around the margins, central apical canal and prominent fractures, although large portions of the rostra were well preserved. 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 global rather than regional and, therefore, driven predominantly by global mechanisms – likely declining atmospheric CO2 levels. 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 was 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 it does not necessarily point to polar ice formation.