Oceanic Anoxic Event 2 (OAE 2; ~94 Ma) was one of the most significant carbon cycle perturbations in Earth's history, characterized by a global positive carbon isotope excursion, widespread deposition of black shales, and major shifts in marine redox conditions. However, previous studies have predominantly focused on the southern sector of the Western Interior Seaway (WIS), leaving the central WIS largely unexplored and thereby constraining regional and global assessments of redox evolution. In this study, we present a geochemical record from the Highwood River section in Alberta, Canada, using carbon isotope stratigraphy, iron speciation, and redox-sensitive trace element analysis. Our results confirm the expression of OAE 2 in the central WIS (southwestern Canada) and reconstruct the phased evolution of bottom-water redox conditions. Correlation of the δ¹³C_org record from the Highwood River section with the δ¹³C_carb record from the Gongzha section and the δ¹³C_org record from the Iona-1 core enables subdivision of the OAE 2 interval into five stages (C2–C6), establishing a chemostratigraphic framework for this event in the study area. Redox proxy data reveal that the C2 and C3 stages were characterized by ferruginous anoxic conditions; the C4 stage marks a transition from ferruginous to euxinic conditions, representing the most intense bottom-water anoxia of the entire interval; and the C5 and C6 stages returned to stable ferruginous anoxic conditions. Collectively, the Highwood River section records a phased alternation between ferruginous anoxic and euxinic conditions at the shelf margin of the central WIS during OAE 2. Integration of global datasets further indicates that marine redox conditions during OAE 2 exhibited both temporally staged evolution and spatially differentiated patterns: bottom waters were more hypoxic than surface waters, and upwelling processes, driven by paleogeographic configuration and oceanic circulation, likely coupled surface-water hypoxia in upwelling-dominated regions with bottom-water anoxic conditions.
Keywords: Oceanic Anoxic Event 2 (OAE 2); Highwood River section; Western Interior Seaway (WIS); Redox conditions; Iron speciation; Carbon isotope stratigraphy

 

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