WHITE, T. S., Dept. of Geology, University of Iowa, Iowa City, IA; G. A. LUDVIGSON, Iowa Dept. of Natural Resources-Geological Survey Bureau, Iowa City, IA; and L. D. YOUNG, Dept of Geology, University of Iowa, Iowa City, IA

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

Ongoing sequence stratigraphic reconstructions have led to correlation of Albian-Turonian nonmarine-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 midwestern U.S. However, an enrichment in d¹⁸O values from -4.5 to -3.5 o/oo occurred in the late Albian, followed by a return to more depleted values of -4.5 o/oo.

The sequence stratigraphy was used to tie detailed midbasin geochemical profiles of %CaCO₃, %TOC, Hl 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 nonmarine paleosols. Here, oxygen isotopic profiles generated from the paleosol sphaerosiderites allow us to tie the nonmarine oxygen isotope chemostratigraphy to the geochemically-defined marine parasequence. This approach allows us to better define the amalgamated nonmarine chronostratigraphy, and therefore better interpret the paleoclimatological record.

AAPG Search and Discovery Article #90921©1999 AAPG Mid-Continent Section Meeting, Wichita, Kansas