High-resolution biostratigraphy and chemostratigraphy of the Cenomanian stratotype area (Le Mans, France)

Abstract

The definition of the Cenomanian stage was based on the description of several type sections scattered in the vicinity of Le Mans (Sarthe, France). Despite limited exposures nowadays, the area remains a reference for the palaeontology of the Cenomanian due to its outstanding richness in marine macrofossils, especially molluscs, bryozoans, brachiopods and echinoderms. The publication in 2015 of the volume dedicated to the Cenomanian stratotype yielded the opportunity to restudy the last accessible outcrops. This paper provides a high-resolution stratigraphic scheme and palaeoenvironmental reconstruction for the middle and late Cenomanian interval in its type area. La Garenne Quarry is a window on the middle Cenomanian, where Praeglobotruncana rillella nov. sp. has been identified. The δ13Ccarb and δ18Ocarb record of a Cenomanian–Turonian succession close to Le Mans is correlated with the type section of Pueblo (Colorado). Isotopic and biotic events highlight the presence of several hiatuses in the sedimentary record of Le Mans especially around the Cenomanian–Turonian boundary with a dramatic truncation of the plateau of high δ13Ccarb values. Coiling reversal events among the surface dwellers Muricohedbergella delrioensis, indicate sea surface temperature changes with transient coolings, including the Plenus cold event, and warm conditions at the Cenomanian–Turonian boundary. Sandy to chalky facies have yielded empty, well-preserved shells of foraminifera allowing the description of Dicarinella falsohelvetica nov. sp. Oxygen isotopic analyses performed on right- and left-coiled M. delrioensis reveal a systematic offset during cold events which lead to discuss about the potential occurrence of cryptic species in the Mesozoic.