Environmental Changes Across the Cenomanian-Turonian Boundary as Revealed by Biostratigraphic and Magnetic Analyses of Continental Shelf Sediments from the Holland Park Core, Virginia

Oceanic Anoxic Event 2 (OAE2, ~94 Ma ago) occurred near the Cenomanian-Turonian (Ce-Tu) boundary. OAE2 is associated with widespread black shale deposits in the deep ocean—which are products of rapid redox changes triggered by the massive release of volcanic CO2. Although the mechanisms that triggered OAE2 are distinct from Anthropogenic climate change, changes in nutrient cycling, primary productivity, and carbon burial during OAE2 may help us better understand the long-term impacts of modern climate change on biogeochemical cycles. Here we investigate some of the immediate and long-term environmental changes that resulted from OAE2 using marine sediments from the Holland Park core, drilled by the Virginia Department of Environmental Quality, in the City of Suffolk, Virginia. Using a combination of biostratigraphic and magnetic analyses, we provide a window into how the iron and hydrologic cycles may have changed in response to this carbon cycle perturbation. Calcareous nannofossils confirm that these sediments span the Ce-Tu boundary. Eiffelithus turriseiffelii, Garnerago obliquum, and Lithraphidites acutus mark the Cenomanian from 124.0-100.2 m; the base of the Turonian is marked by the appearance of Eprolithus moratus at 96.6 m. Based on lithology and microfossil abundance, deposition is inferred to have occurred in a middle to outer neritic environment. Bulk magnetic measurements show a decrease in saturation magnetization over the Cenomanian and an increase in remanent magnetization after the Ce-Tu boundary. Magnetic coercivity is variable throughout the section. Magnetic component analysis reveals that these changes are driven by varying proportions of single domain magnetite and hematite over these intervals, which implies changes in coastal runoff. Our results also suggest changes in redox states, further demonstrating that these sediments did not undergo anoxia and were, at times, well-oxygenated.