Benthic foraminiferal response to the paleoenvironmental changes during the Late Cretaceous Oceanic Anoxic Event 2 at Clot Chevalier (Vocontian Basin, SE France)

Abstract

The Cenomanian-Turonian boundary interval is characterized by environmental perturbations related to the Oceanic Anoxic Event 2 (OAE 2), affecting marine biota, including benthic and planktonic foraminifera. This study shows a continuous record of benthic foraminifera that, together with published planktonic foraminiferal and geochemical data, allow to interpret the paleoceanographic changes in surface and bottom waters across the OAE 2 interval in the Clot Chevalier section (Vocontian Basin, SE France). The Clot Chevalier section is located at an outer shelf-upper bathyal environment according to benthic foraminifera, and their composition and abundance changes allow the identification of seven distinct faunal intervals. Below the OAE 2 (middle Cenomanian), the seafloor shows moderately oxic conditions and oligotrophic regimes suggested by high species diversity and abundance of infaunal and epifaunal taxa. Within the OAE 2 (upper Cenomanian), characterized by the highest values of Total Organic Carbon (TOC), the benthic calcareous taxa (Gavelinella sp., Gyroidinoides sp., Praebulimina elata, Tappanina laciniosa) are abundant and radiolaria dominate the microfossil assemblages (> 50%) suggesting eutrophy and suboxic conditions at the seafloor. The lowest part of the OAE 2 shows high abundance of the benthic agglutinated taxa Ammobaculites sp., Ammodiscus cretaceus, Gaudryina sp., Textulariopsis bettenstaedti that gradually disappear close to the top of OAE 2. Moreover, at ~1 m above the onset of the OAE 2, and simultaneously to the Plenus Cold Event (PCE), a repopulation event and ventilation at the seafloor is documented by the occurrence of the oxic benthic foraminiferal taxa Frondicularia sp. and Ramulina aculeata. Above the OAE 2 (lowermost Turonian), calcareous and agglutinated taxa re-occur with high species diversity and abundance, identifying moderately oxic conditions and mesotrophic regimes. In conclusion, oxygen and organic carbon variations at the seafloor associated to the OAE 2 can be inferred by the benthic foraminiferal composition and distribution.