Blake Nose stable isotopic evidence against the mid-Cenomanian glaciation hypothesis

Abstract

Detailed multitaxon stable isotope (ŸA18O and ŸA13C) data from Blake Nose (western North Atlantic) argue against a mid-Cenomanian glaciation event during the mid-Cretaceous greenhouse. Results generated are precisely correlated to sea-level changes inferred from European sequence stratigraphy using the twin ŸA13C excursions mid- Cenomanian event (MCE) Ia and MCE Ib. Microfossils analyzed (surface-dwelling to deep-dwelling planktonic foraminifera, benthic foraminifera, coccoliths) show remarkably consistent intertaxon ŸA18O and ŸA13C offsets; comparative scanning electron microscope and Sr/Ca analyses allow some ŸA18O data to be eliminated because of selective diagenesis. Across MCE Ia, the proposed interval of major glacioeustatic regression, the planktonic ŸA18O values are constant for each taxon. The absence of a mean seawater ŸA18O shift contradicts predictions for the mid-Cenomanian glaciation episode. The benthic ŸA18O records show signifi cant fl uctuations during MCE I, implying short-term variability in North Atlantic intermediate-water and deep-water circulation patterns and/or sources at that time.