THE CRETACEOUS OCEANIC ANOXIC EVENT 2 (OAE2) INTERVAL DOCUMENTED IN THE IONA-1 CORE, WESTERN INTERIOR SEAWAY, NORTH AMERICA: A RE-ANALYSIS

Cretaceous Oceanic Anoxic event 2 (OAE2) occurred near the Cenomanian-Turonian Boundary (CTB, ~93.9 Ma) and represents one of the most pronounced environmental and biotic perturbations in the Mesozoic that is characterized by widespread marine anoxia, pronounced biotic turnover, and distinct geochemical anomalies including a prominent positive carbon isotope excursion (CIE). The Western Interior Seaway (WIS) in North America has been a focus of study of OAE2 given that it hosts the CTB GSSP and a rich sedimentary record of OAE2. Among outcrops and drilled cores, the Iona-1 core, which was situated at the southern gateway of the WIS, documents one of the most expanded OAE2 interval and thus has great potential to depict the detailed evolution of OAE2. Yet, different definitions of the carbon isotope excursion (CIE), varying duration estimates for OAE2, and apparently slightly older numerical age models for the OAE2 interval of the Iona-1 core have led to differing proposed correlations with other OAE2 records, thus hampering this archives full potential. Here we re-analyze the available datasets for the Iona-1 core with an aim to improve the definition of the CIE in the OAE2 interval archived in this core and to propose a refined numerical age model. This effort aims to permit high-resolution correlation of the Iona-1 core with other OAE2 records and to test whether the temporal and spatial evolution of OAE2 can be better delineated. Our analysis integrates the biostratigraphy, C and Os isotope chemostratigraphy, cyclostratigraphy, and the GSSP CTB ages. The results reveal that the CIE in the OAE2 interval of the Iona-1 core spans ~94.7 Ma to ~93.7 Ma, lasting for ~1.0 Myr, a duration that is substantially longer than estimates for several other OAE2 records. Our analysis distinguishes the prolonged CIE interval of the Iona-1 core into two segments: a globally correlative segment spanning ~94.5 Ma to ~93.7 Ma and a predating regional segment spanning ~94.7 Ma to ~94.5 Ma. We further present a proposed correlation of the Iona-1 core CIE with other OAE2 records and discuss the associated implications for the evolution of OAE2.