Palaeoenvironmental analysis and bio- chemostratigraphy during Late Cretaceous Mid-Cenomanian Event 1 (MCE 1): insights from a Tethyan reference section and comparison to the English Chalk

The Mid-Cenomanian Event 1 (MCE 1) is a globally recognised positive carbon-isotope (δ 13 C) excursion of about 1 ‰ that occurred during the middle Cenomanian (Late Cretaceous). Characterized by a distinctive double-peaked δ 13 C signal, it is recorded in marine carbonate and terrestrial organic matter archives worldwide. MCE 1 reflects major perturbations of the global carbon cycle, accompanied by changes in ocean circulation, productivity, and oxygenation. This study presents a new record of MCE 1 from the expanded Vergons section (Vocontian Basin, southeastern France). The section is correlated with the nearby Blieux section using macrofossils and stable-isotope data, and with the Folkestone section (southeastern England), which provides comparable planktonic foraminiferal, isotopic, and macrofossil records. The studied interval spans the upper Thalmanninella globotruncanoides , T. greenhornensis , and lower Rotalipora cushmani zones. Both sections record the appearance of double-keeled, meso-eutrophic Dicarinella species and diversification within the Rotalipora lineage, indicating rapid turnover in single-keeled, oligotrophic taxa. However, differences in the lowest occurrence of R. cushmani and Dicarinella raise questions about their reliability for global correlation. Integrated biostratigraphic, isotopic (δ 13 C and δ 18 O), and sedimentological data reveal contrasting environmental responses across Boreal and Tethyan settings. At Folkestone, cooling episodes associated with positive δ 18 O excursions and Boreal macrofaunal markers suggest incursions of cold, low-salinity waters from the Norwegian Sea that enhanced productivity through water-column mixing, contributing to elevated δ 13 C values. At Vergons, similar cooling trends occurred without Boreal fauna, reflecting its upper-slope Tethyan setting and a more moderate ecological response. These results highlight ocean circulation as a key driver of MCE 1 with continental weathering and runoff providing additional influence.