HIGH RESOLUTION CHEMOSTRATIGRAPHIC CORRELATIONS AND THE DEVELOPMENT OF ACCOMMODATION SPACE, MID CRETACEOUS STRATA, EASTERN MARGIN WESTERN INTERIOR SEAWAY, CENTRAL UNITED STATES

This study examines changes in a suite of geochemical parameters recorded in an onshore-offshore transect approximately perpendicular to the eastern paleoshoreline of the Cretaceous (Albian-Cenomanian) Western Interior Seaway (KWIS). Data were collected from two cores in Kansas (Kansas Geological Survey Jones #1 Core and Amoco Rebecca K. Bounds #1 Core), and one core from coeval strata in Iowa (Hawarden Core). Mostly marine or marine-influenced sediments are present in the base of the three cores, and are overlain by mostly non-marine fluvial sediments. An up-section shift back to mostly marine sediments was deposited during the Greenhorn Transgression. Our data set consists of lithologic descriptions, carbonate content, total organic carbon content (%TOC) and organic matter type as determined by Rock Eval pyrolysis. A conceptual parasequence model for the development of geochemical facies was applied to better understand observable trends in the data sets as a function of the processes affecting accommodation space development in the basin. In this model, marine flooding surfaces (MFS) usually contain higher carbonate contents, higher Hydrogen Index (HI) and lower Oxygen Index (OI) values, whereas progradational sediments contain more terrestrial organic and clastic detritus. The parasequences are represented in these study sections as ~7 meter thick packages consisting of ~4-50% CaCO3, ~1-6% TOC and HI values between ~100 and 600 at the MFS with values from ~0-4% carbonate content, ~<1% TOC and HI values ranging from 0-800 in the progradational sections. Literature citations of stratigraphic ages were used to identify an ~300,000 year cyclicity in parasequence distributions, and explored potential causes for changes in Cretaceous sedimentation rates to explain the observed stacking patterns. Parasequence-scale data trends are most easily explained by eustatic sea level changes, but the processes causing the eustatic changes are not clearly understood. Waxing and waning of global ice sheets was ruled out solely due to the lack of evidence for their existence. The most likely cause for the parasequence scale stacking patterns was a combination of paleoclimatically-modulated changes in sedimentation rates combined with the thermal expansion of global oceanic waters.