GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 145-5
Presentation Time: 2:45 PM


JONES, Matthew M., Earth and Planetary Sciences, Northwestern University, 2145 Sheridan Road, Technological Institute, Rm. F374, Evanston, IL 60202, SAGEMAN, Bradley B., Department of Earth and Planetary Sciences, Northwestern University, Evanston, IL 60208, SELBY, David, Department of Earth Sciences, University of Durham, Science Labs, Durham, DH1 3LE, United Kingdom, OAKES, Rosie L., Department of Geosciences, The Pennsylvania State University, University Park, PA 16802, PARKER, Amanda L., University of Massachusetts Amherst, Department of Geosciences UMass, 611 N. Pleasant St, Amherst, MA 01003, LECKIE, R. Mark, Department of Geosciences, University of Massachusetts Amherst, 611 N. Pleasant St, 233 Morrill Science Center, Amherst, MA 01003 and BRALOWER, Timothy J., Department of Geosciences, Pennsylvania State University, 503 Deike Building, University Park, PA 16802,

Arthur and colleagues in the 1970s were the first to recognize Mesozoic oceanic anoxic events based on positive carbon isotope (δ13C) excursions and show the utility of these major perturbations in the global carbon cycle as chemostratigraphic tools. Since then, other proxies for changes in ancient ocean chemistry, such as initial osmium isotope ratios (Osi), have been implemented as high-resolution chemostratigraphic markers; they have potential to record the onset of submarine large igneous province (LIP) volcanism, such as that which occurred at the onset of Oceanic Anoxic Event 2 (OAE2) (~94 Ma).

Our recent work correlates high-resolution δ13C and Osi chemostratigraphies from key Western Interior Basin (WIB) localities preserving OAE2 along a distal to proximal and depth transect. Although lithofacies from the different localities are distinct, each site records prominent excursions to unradiogenic Osi compositions signaling enhanced submarine volcanism, which are followed by increased global organic carbon burial (as indicated by positive δ13C shift). Using a published astrochronologic time scale, the time lag between the onset of LIP volcanism before OAE2 and the carbon cycle response is quantified at 2-2.5 precession cycles (~40-50 kyr). The presence of this lag between Osi and δ13C excursions in the Portland Core indicates that the hiatus in the uppermost Hartland Shale near the Cenomanian-Turonian Stage GSSP is relatively brief (<40 kyr) compared to the duration of OAE2.

Within the refined chronostratigraphic framework of bentonite stratigraphy, Osi and δ13C chemostratigraphies, and biostratigraphy, changes in the depositional environment of the WIB can be evaluated at the highest temporal resolution to-date. Notably, carbonate content decreased synchronously in two intervals during the lag between Osi and δ13C excursions in the WIB, and near Bentonite “A” where Osi decreases subtly again. The compilation of datasets from a range of depositional settings demonstrates that carbonate sedimentation was suppressed in the Western Interior Seaway during these two intervals of OAE2. This suggests that the injection of large quantities of CO2 to the ocean-atmosphere system from LIP volcanism altered marine carbonate chemistry or other factors governing carbonate production in the WIB.