Towards an orbitally-tuned Maastrichtian Stage

After the peak warmth’s of mid-Cretaceous times, progressive climate cooling occurred during the late Cretaceous, with a global temperature decline in the order of Cenozoic cooling without signs of major and persistent glaciation. Thereby, the Maastrichtian marks a cool greenhouse period with different non-analog boundary conditions in comparison to today. Global mean temperatures, polar ice extents, regions of deep-water formation, types of vegetation, as well as patterns and variability of precipitation and evaporation were all different. Repeated multi-million-year long periods of climate cooling and warming occurred during the cool Maastrichtian greenhouse. Particularly, the latest Campanian–early Maastrichtian witnessed substantial deep-water cooling as well as a carbon cycle perturbation expressed by a long-lasting negative carbon isotope excursion. Our understanding of climate and carbon cycle dynamics is still limited for times prior 66 million years, particularly for the Campanian–Maastrichtian transition. The lack of highly resolved stratigraphy introduces severe uncertainties in the quality and interpretation of global correlation. Here we present the present state in the development of an astrochronology for the Maastrichtian stage that integrates sedimentary cyclicity, carbon isotope and magnetostratigraphy in combination with biostratigraphic events from the successions of Zumaia, Sopela, Bidart and the GSSP locality Tercis-les-Bains belonging to the Basque-Cantabrian and Aquitain basins in Spain and France. The development of a Bay of Biscay Maastrichtian record will provide new insights about the phase relation between orbital forcing and carbon cycle response, as well as temporal relations to changes in ocean chemistry, circulation and sea level, and the ecosystem response.