High-resolution carbon-isotope stratigraphy across the Campanian - Maastrichtian boundary at Tercis section, SW France.

The transition from the Campanian to the Maastrichtian is characterized by a long-lasting negative carbon-isotope excursion, the so-called Campanian Maastrichtian Boundary Event (CMBE), It is believed that this event was triggered by climatic cooling and sea-level fall. The establishment of a primary marker for the base of the Maastrichtian Stage is undergoing review by the International Subcommission on Cretaceous Stratigraphy. High-resolution carbon isotope stratigraphy can help us understand this event. Here, we present a new, high-resolution carbon-isotope record for the GSSP at Tercis les Bains, France, covering the upper Campanian and the Campanian - Maastrichtian boundary. The carbon isotope record shows a prominent long-lasting negative carbon isotope excursion, known as the Campanian-Maastrichtian boundary event (CMBE), with four superimposed smaller positive excursions in between, and at the uppermost level of the record, there is also a positive carbon isotope excursion (M1). These excursions can be correlated with other sections, such as the Kronsmoor section, located in the North Sea Basin (north Germany), and the Bidart section, which belongs to the Basque-Cantabric Basin (southwest France). These new results contribute to defining a primary marker for the GSSP of the Maastrichtian. Along with the sedimentary cyclicity of the succession to establish an astrochronology, our isotopic data could be used to create an astronomically tuned timescale for the entire Maastrichtian Stage, directly tied to the defined boundary.