Analyzing the Cenozoic Depositional History of Western Kansas: A New Approach Using Paleosol Zircon Geochronology

Abstract

Correlation of terrestrial strata is challenging due to the lack of continuous outcrops, limited biostratigraphy, and poor preservation of useful marker beds such as tephra layers. This improved understanding of its internal architecture could lead to more effective management of groundwater, which is presently declining at an unsustainable rate. Chronostratigraphic correlation of paleosols in these formations is a promising new technique for continental deposits. Paleosols are time-rich sections in the terrestrial realm, and this study tests the hypothesis that they concentrate volcanogenic zircons from eruptions coincident with pedogenic processes. A section of stacked paleosols in the Ogallala Fm. from the Lake Scott area in Scott County, KS was sampled for zircon U-Pb by LA-ICP-MS. Paleosols yielded grains whose ages are consistent with local biostratigraphic data, and are stacked in normal superposed order, ranging from ca. 10.6 – 6.3 Ma. These dates are also consistent with ages from previously dated ashes from the Ogallala Fm. and allow detailed correlation among measured sections. Results from a sediment core from Harvey County, KS did not yield ages consistent with biostratigraphic suites, but the organization of the youngest zircon populations suggest that these units were deposited through unroofing of sediments in the source region. This study reveals the utility of paleosols as chronostratigraphic marker beds, units that can determine the depositional age of sediments, and as units that can provide information about the depositional nature of continental basins.