High-Resolution Correlation of Mid-Cretaceous Strata in the Cretaceous Western Interior Basin

Philip Morath, The Pennsylvania State University, Department of Geosciences, University Park, PA, [email protected]

In this project we correlate paleosol-bearing nonmarine sections to a well-developed record of coeval marine chronostratigraphy using high-resolution chemostratigraphy.  This provides a better understanding of the timing and development of a thick stack of amalgamated paleosols in northwestern Iowa along a northwest transect across the Western Interior Basin to coeval marine strata in Wyoming.  In particular, this study focuses on a mid-Cretaceous (Albian-Cenomanian) regressive/transgressive event during which cross-basin paleosols likely formed.

Four cores and intervening outcrops located in Iowa, South Dakota, and Wyoming were lithologically described and sampled.  Total organic carbon (TOC), carbonate content (CaCO₃), total sulfur (S), and Hydrogen Index (HI) values from Rock Eval pyrolysis are performed on the samples and used to establish parasequence-scale correlation by pattern matching.  Using this approach, low TOC-CaCO₃-S-HI horizons are interpreted to represent terrestrial progradation, whereas horizons with higher TOC, CaCO₃, S, and HI values are interpreted to represent marine flooding.

Paleosols on the eastern margin of the Western Interior Basin are widely developed and amalgamated, whereas to the west in coeval marine sections, paleosols are primarily found at sequence boundaries.  This study provides insight into the timing and cyclicity of paleosol development along the eastern margin of the Western Interior Basin by applying a higher-resolution marine chronostratigraphy to coeval nonmarine strata.  Paleosols can act as reservoir seals, so by understanding the cyclicity and extent of paleosols across the Western Interior Basin, the distribution of fossil fuel resources within the basin could be better understood.