An Application of High Resolution Marine Chemostratigraphy as a Chronostratigraphic Control for "Mid" Cretaceous Oxygen-Isotope Records in Amalgamated Non-marine Paleosols

White, T.S., Dept. of Geology, University of Iowa, Iowa City, IA, Ludvigson, G.A., Iowa Dept. of Natural Resources-Geological Survey Bureau, Iowa City, IA, and Young, L.D., Dept of Geology, University of Iowa, Iowa City, IA

Ongoing sequence stratigraphic reconstructions have led to correlation of Albian-Turonian non-marine-marine strata in a transect perpendicular to the eastern-margin paleoshoreline of the Western Interior Seaway. In the nonmarine strata, we have developed a high resolution palynostratigraphy and oxygen isotope chemostratigraphy from amalgamated Albian-Cenomanian kaolinitic mudrock paleosols in Iowa and Nebraska. Our results suggest, that meteorological conditions were stable in the late Albian/early Cenomanian of the midwestem U.S. However, an enrichment in ¹⁸O values from -4.5 to -3.5 ⁰/₀₀. occurred in the late Albian, followed by a return to more depleted values of -4.5 ⁰/₀₀.

The sequence stratigraphy was used to tie detailed midbasin geochemical profiles of %CaC031, %TOC, HI and Ol to nearshore geochemical profiles. Correlation of these profiles uses a model for the development of geochemically-defined parasequences which provides -100,000 year resolution. In Kansas, these parasequences interfinger with non-marine paleosols. Here, oxygen isotopic profiles generated from the paleosol sphae roside rites allow us to tie the non-marine oxygen isotope chemostratigraphy to the geochemically defined marine parasequence. This approach allows us to better define the amalgamated non-marine chronostratigraphy, and therefore better interpret the paleoclimatological record.