An Orbital Time Scale for the Turonian Stage and Carbon Isotope Chemostratigraphy from Demerara Rise (ODP Site 207)

Matthew M. Jones
Northwestern University, Department of Earth and Planetary Sciences, Evanston, Illinois, USA 60208
[email protected]

In recent years, the Geologic Time Scale has been fine-tuned through the Cenozoic Era via the detection of orbitally driven changes in solar insolation recorded in sedimentation patterns. Cyclic variations in Earth’s orbit (Milankovitch Cycles) have well-defined periods that can be used to construct an in-situ time scale in sedimentary sequences where lithology or geochemical properties are sensitive to fluctuation in climate. A current goal of stratigraphers is to extend this astronomical tuning of the Geologic Time Scale into the Mesozoic Era. This study will test whether a statistically significant orbital signal is preserved in the western tropical Atlantic at Demerara Rise (Ocean Drilling Program Site 207) through the Late Cretaceous Turonian Stage. This will serve to create a robust chronostratigraphic framework for geologists studying the interval’s climate, biologic trends, and energy resources globally.

Geophysical logs and geochemical data from the organic-rich and interbedded mudrock and carbonate sequence will be analyzed using specialized algorithms designed for spectral analysis of stratigraphic datasets. Initial results suggest that an orbital signal exists through the Turonian at Demerara Rise, so a carbon isotope (dC13) chemostratigraphy is being developed from the core to correlate the orbital timescale to sections elsewhere (e.g. Western Interior Seaway and the Gulf Coast). The combination of the cyclostratigraphic record with the dC13 record will provide quantitative estimates for the timing, duration, and orbital forcing of organic carbon burial events in the Turonian.

AAPG Search and Discovery Article #90183©2013 AAPG Foundation 2013 Grants-in-Aid Projects