High-resolution bio- and chemostratigraphy of an expanded record of Oceanic Anoxic Event 2 (Late Cenomanian–Early Turonian) at Clot Chevalier, near Barrême, SE France (Vocontian Basin)

Abstract

A newly located exposure of the Niveau Thomel, an organic-­‐rich level at the Cenomanian–Turonian boundary, provides a highly expanded record of Oceanic Anoxic Event (OAE) 2, excepted for the lower relatively condensed glauconite-­rich part of the section. The new locality, close to Barreme in the Vocontian Basin, SE France, is developed in deep-­water hemi-­pelagic facies (shales, marls, marly limestones, variably enriched in organic matter) and provides an improved understanding of palaeoceanographic events associated with OAE 2. Investigation of the biostratigraphy (nannofossils and planktonic foramininfera), organic and inorganic geochemistry (bulk carbonate δ18O, total organic carbon (TOC), bulk organic, biomarker-specific and carbonate δ13C, major and trace elements, and Rock-­Eval data) has allowed characterization of the sediments in great detail. The combined study further constrains the detailed relationship between bio-­ and chemostratigraphy (particularly with respect to the details of the well-­displayed positive carbon-­‐isotope excursion) for this interval. The section also provides new evidence, in the form of a positive oxygen-­isotope excursion and an offset between carbonate and organic-­carbon carbon-­isotope records, which confirms the importance of cooling accompanied by a drop in dissolved CO2 in near-­surface waters during the Plenus Cold Event that characterized the early part of OAE 2. Evidence for increased oxygenation of bottom waters, together with elevated concentrations of redox-­sensitive and chalcophilic elements registered elsewhere through the level of the Plenus Cold Event, may be reflected in enhanced concentrations of iron (in glauconite) and nickel in coeval strata from the Clot Chevalier section.