A TROPICALLY HOT AND SALTY WESTERN INTERIOR SEAWAY (USA) SPANNING CRETACEOUS OCEANIC ANOXIC EVENT 2

The Cretaceous Thermal Maximum (KTM) is considered Earth’s warmest sustained interval for at least the past 100 Ma. Oceanic Anoxic Event 2 (OAE2) – a 600-800 kyr interval of widespread ocean deoxygenation linked to large igneous province (LIP) volcanism – has been hypothesized to represent a hyperthermal event punctuating the KTM, beginning at ~94.5 Ma. Here, to quantify paleotemperatures in the Western Interior Seaway (WIS) of North America spanning OAE2, we present new carbonate clumped isotope geochemical analyses (Δ₄₇) of fossil marine oysters. Diagenetically altered specimens are screened from the dataset using trace element contents and a calcite preservation index from SEM images. Following screening, mean Δ₄₇ temperatures of precipitation for oyster calcite range from 28-40˚C in the pre- and syn-OAE2 specimens of the WIS, quantitatively signifying the extreme regional and global warmth during OAE2 and the broader KTM. Additionally, values of δ¹⁸O_w (~-2 to +0.5‰ SMOW), derived from Δ₄₇ temperatures and δ¹⁸O_carb values, indicate a dominantly marine salinity regime in the WIS with implications for longstanding interpretations of biotic assemblages and water mass circulation in the vast epicontinental seaway.