Integrated Quantitative Stratigraphy of the Cenomanian-Turonian Bridge Creek Limestone Member Using Evolutive Harmonic Analysis and Stratigraphic Modeling

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Abstract
Secular changes in bulk sedimentation have a significant impact on the preservation of climatic signals in rhythmically bedded strata. In this study a quantitative cyclostratigraphic methodology is developed to use these signal distortions as a means to reconstruct sedimentation. The method exploits a moving-window Fourier tech- nique that we designate ''evolutive harmonic analysis'' (EHA). We cal- ibrate this methodology to a specific set of geologic conditions (i.e., changes in bulk sedimentation) using a series of stratigraphic models and then apply the technique to the Cenomanian-Turonian Greenhorn Formation of the Western Interior basin. Application of EHA to strata that preserve a record of orbital forcing allows the reconstruction of a high-resolution sedimentation history in which bulk sedimentation rates and hiatuses are quantified. Using the data on bulk sedimentation rate, rates of accumulation for geochemical proxies representing de- trital, biogenic, and authigenic contributions to the sediment can be calculated. By integrating these quantitative assessments of siliciclastic dilution, primary production, and depositional redox conditions within a high-resolution chronostratigraphic framework, we are able to de- convolve secular trends in hemipelagic sedimentation during the Late Cenomanian-Early Turonian in the Western Interior basin. This in- tegrated quantitative stratigraphic approach allows a reevaluation of hypotheses for the accumulation of excess organic matter in the West- ern Interior basin during the interval representing Oceanic Anoxic Event II.

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