GEOCHEMICAL CORRELATIONS OF LOWER PENNSYLVANIAN STRATA IN THE FOREST CITY BASIN OF SOUTH-CENTRAL IOWA

Lower Pennsylvanian strata of the Forest City Basin in south-central Iowa are extremely heterogenous and contain many marine, marginal marine, fluvial, and lacustrine sedimentary units that make lithologic correlation difficult. The Cherokee Group, including the Kilbourn, Kalo, and Floris formations, records an overall rise in sea level and an up-section shift from predominantly nonmarine to marine depositional environments. The basal Kilbourn Formation is dominated by thick shale sequences and channel-filling sandstone packages that have been interpreted as largely marginal marine depositional environments. The Kalo Formation is comprised of fluvial deltaic deposits consisting of mostly fine-grained clastic sediments in coarsening-upward sequences above coal layers with variable thickness. Finally, the Floris Formation is composed of thick channel-filling sandstones, relatively thicker coal packages, and marine- influenced beds that all together are interpreted to represent rising sea level. Previous studies attempted correlations based on lithologic patterns of sandstone and mudstone or using coal palynology. Our study aims to make improved correlations by constructing an elemental chemostratigraphic framework for these formations from multiple cores within the Forest City Basin. Access to these cores is possible through the Iowa Geological Survey’s Core Repository. We used a portable x-ray fluorescence spectrometer (pXRF) to collect elemental data and determine which element concentrations are best to make distinct correlations between the formations from different cores. Recently collected elemental data will allow us to build upon our previous research in which the elements U, Fe, Rb, Sr, and Y were identified for having the best geochemical signatures to make widespread correlations between formations. U has been used in our initial analysis as a possible indicator of marine bands, which tend to be more continuous and widespread compared to nonmarine strata. The collection of this most recent data will enable us to further construct our chemostratigraphic framework in the context of the preexisting coal palynostratigraphic framework and continue to identify which elements present the best geochemical signatures to accurately make correlations across a large swath of the basin.