EXPLORING EARLY EOCENE HYPERTHERMALS FROM AN ONSHORE COREHOLE ON THE NEW JERSEY PALEO-CONTINENTAL SHELF (ODP 174AX)

Hyperthermals, episodes of abrupt global warming associated with the release of ¹³C–depleted carbon into Earth’s system, have been documented in the early Eocene and may represent analogs for future climate change. These negative excursions in ¹⁸O and ¹³C have been identified in deep-water DSDP/ODP/IODP sites, although constraints on the timing, magnitude, duration and a comprehensive study on the response of microfossil assemblages and abundances associated with these events is lacking. Here, we study early Eocene hyperthermals by complementing bulk carbonate isotopes with benthic foraminiferal assemblages, planktonic foraminiferal abundances, and ostracod assemblages and abundances from the Bass River site (ODP 174AX), a shallow marine onshore corehole on the New Jersey paleo-continental shelf. Results from our bulk carbonate isotopes display distinct negative ¹³C and ¹⁸O excursions, primarily from sequence E2 (53-54 Ma GTS2012). These excursions, which appear in a step-wise pattern, exhibit maximum decreases of ~1‰ in¹⁸O and ~1.5‰ in ¹³C records. Micropaleontological data indicate a biotic response to these events as well, with shifts in dominant species (e.g., Trifarina wilcoxensis, Osangularia expansa, Cibicidoides pseudoungerianus) corresponding with the excursions. Findings at Bass River endorse our hypothesis that early Eocene hyperthermals are recoverable at shallow-water sites, display prominent negative ¹³C and ¹⁸O excursions, and record a biotic response to environmental changes, with the potential to further constrain the hyperthermals through the use of quantitative faunal analysis in a shallow-water setting.