Atmospheric CO2 through Oceanic Anoxic Event II, Late Cretaceous (94Ma)
To provide a rigorous test of the primary productivity hypothesis we are applying the stomatal index method for estimating pCO2 using plant cuticles from paralic sections of the Dakota Sandstone in Utah. This has been correlated to the CTB stratotype in Colorado using bio-, chemo-, & bentonite-stratigraphy. Terrestrial organic matter coeval with the onset of OAEII in the marine section documents a positive δ13C isotopic shift known globally in marine carbon. This validates the correlation and provides evidence for terrestrial and marine carbon cycle linkage via the atmosphere. Stomatal index values rapidly decrease prior to OAEII. If confirmed, this suggests increasing pCO2 before the positive δ13C excursion. It may coincide with a short negative δ13C excursion observed in the Bonarelli at Gubbio, corresponding with high sea temperatures in δ18O and Tex86 proxies in the Atlantic. A pulse of CO2 before the event could have enhanced hydrologic cycling, delivering nutrients to the ocean and triggering anoxia. Both stomatal index and density increase at the onset of OAEII, supporting increased marine primary production as the driving mechanism.