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 Kilbourn, Kalo, and Floris formations are part of the Cherokee Group, which 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 have 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 are using a portable x-ray fluorescence spectrometer (pXRF) to collect elemental data and determine which element concentrations and/or element ratios are best to make distinct correlations between the formations from different cores. Uranium (U) has been used initially in our analysis as spikes in U concentrations across the formations, mostly within shale or siltstone units, has previously been used in other basins as an indication of a marine band. Marine bands should be more widespread and continuous than the interbedded nonmarine and marginal marine strata. Our chemostratigraphic framework will be built in the context of the existing coal palynostratigraphic framework. The continuation of this research aims to find which elements make for the best geochemical signatures to use to accurately make formation-wide correlations across a large swath of the basin.