Terrestrial and Marginal-Marine Record of the Mid-Cretaceous Oceanic Anoxic Event 2 (OAE 2): High-Resolution Framework, Carbon Isotopes, CO2 and Sea-Level Change

Document Type


Publication Date



Oceanic Anoxic Event 2 (OAE2; c. 94.5–93.9 Ma) offers insight into the mechanisms of past climate change linked to organic productivity and carbon sequestration. It has been studied extensively, but the vast majority of data come from marine records, thus providing an incomplete view of past climate dynamics. Here we integrate new high-resolution data and published records on depositional environments, the carbon-isotope composition of bulk organic carbon (δ13Corg) and plant cuticles (δ13Ccut), and stomatal-index values, a proxy for pCO2, in well-preserved terrestrial through marginal-marine archives of the initial phase of OAE2. The study area is located on the western margin of the Western Interior Seaway (southwestern Utah). Age constraints are based on a new U-Pb bentonite age and correlation to an orbitally calibrated interval of the Bridge Creek Limestone. nAlkane abundance suggests predominance of terrestrial contributions to bulk organic carbon for most samples. Despite similarities between carbon-isotope variations and transgressive-regressive shoreline movements, it is argued that δ13Corg and δ13Ccut are not strongly affected by local variables. A series of negative, ~2‰ carbonisotope excursions is identified and attributed to changes in the size and isotopic value of the atmospheric CO2 reservoir. The temporal spacing of these anomalies (80–120 kyr) is consistent with changes in insolation modulated by orbital eccentricity. A systematic, phase-shifted relationship between the negative carbon-isotope excursions and transgressive increments further suggests a link between carbon-cycle perturbations and meterscale sea-level change on the 100-kyr time scale. A conceptual model involving insolation-controlled aquifer charge/discharge and biomass burial/degradation in the monsoonal belt is proposed. The framework presented here is available to facilitate further research on the interplay of terrestrial and oceanic carbon reservoirs during OAE2.