CENOMANIAN/TURONIAN ORBITAL CHRONOLOGIES AND BURIAL FLUX ESTIMATES: CALIBRATING THE BIOGEOCHEMICAL RECONSTRUCTION OF OCEANIC ANOXIC EVENT II

The calculation of geochemical proxy fluxes and rates of biotic change are critical components of integrated biogeochemical studies of the Earth System. Such estimates provide a decisive tool for interpretation of the causes and consequences of biogeochemical perturbations associated with critical intervals of environmental/oceanographic change. Sufficient time control to constrain these estimates for short-term (<1 Ma) biogeochemical events has largely been limited to the Tertiary. In recent years, however, quantification of Milankovitch orbital cyclicity within strata that record major oceanographic events has made it possible to extend high-resolution burial flux estimates as far back as the mid-Cretaceous. Unfortunately, orbital reconstructions for the same event may vary depending on geographic location, making a global synthesis of temporally constrained biogeochemical data difficult. In this talk we present a new methodology for the quantitative identification and integration of orbital time scales from geographically distant rhythmic sequences. We demonstrate the method with examples from the Cenomanian/Turonian (C/T) Oceanic Anoxic Event II (OAE II), hypothesized to be a global episode of enhanced organic matter burial and oceanographic change. Published orbital timescales for OAE II range from ~320 kyr to ~960 kyr. With our new method, which calculates a misfit parameter between observed and predicted bedding frequencies across a range of sedimentation rates, we are able to identify the best-fit sedimentation rate for a given section. Application of the method to C/T sections from the U.S. Western Interior, Atlantic ODP/DSDP sites, Europe, and the Tarfaya basin allows a quantitative assessment of each orbital record, and construction of a globally coherent C/T time scale. The globally integrated time scale provides an opportunity to assess burial fluxes of organic matter, carbonate, and other constituents at different sites during OAE II, and thus evaluate the relative role of geographically distinct depositional settings on perturbations of the global carbon cycle.