HIGH RESOLUTION CHEMOSTRATIGRAPHIC CORRELATION OF AMALGAMATED PALEOSOLS AND COEVAL MARINE UNITS: THE DAKOTA FM. OF KANSAS, NEBRASKA, AND IOWA
L. D. Young, T. S. White, B. J. Witzke, and G. A. Ludvigson
The Geological Society of America
1999 Annual Meeting and Exposition
Denver, Colorado, October 25-28, 1999
1999 Abstracts with Programs, p. A-291
Oxygen isotope data obtained from sphaerosiderites formed in Cretaceous wetland paleosols of the Dakota Fm. have been used to construct paleolatitudinal d18O gradients of mean annual rainfall along the Cretaceous Western Interior Seaway. In Iowa, Kansas and Nebraska, amalgamated Cretaceous sphaerosiderite-bearing paleosols provide an opportunity to assess variations in rainfall chemistry, which may be linked to fluctuations in atmospheric circulation, precipitation rate and temperature change. Our results suggest that meteorological conditions varied in the late Albian of the midwestern United States leading to fluctuations in the d18O record ranging between ~ -2.7 and -5 per mil. In Kansas and Nebraska, the variations in d18O values between paleosols is ~ 0.6 per mil; apparently the temporal variation was muted in the more seaward sections. Furthermore an ~ 0.5 per mil enrichment is observed between western and central Kansas, which we tentatively attribute to a continental rain-out effect. Using sequence stratigraphic methodology, high resolution geochemical profiles of %CaCO 3, %TOC, HI and OI were tied to nearshore geochemical profiles, using a parasequence model for the development of geochemical facies. This model provides ~ 100,000 year resolution. In Kansas, paleosols exist within the marine parasequences, so here oxygen isotope profiles can be tied directly to the marine chemostratigraphic record. Once constrained, the combined record is used to better define the amalgamated non-marine chronostratigraphy, and therefore better interpret the paleoclimatological record.