Geochemistry in the Critical Zone: Limestone-Shale and Kimberlite weathering in the Flint Hills, Kansas, USA

Authors: Colleen Gura*, Kansas State University, Saugata Datta, Kansas State University, Pamela Kempton, Kansas State University
Topics: Soils, Environmental Science, Physical Geography
Keywords: geochemistry, Critical Zone, soil weathering, mineralogy
Session Type: Paper
Day: 4/5/2019
Start / End Time: 1:10 PM / 2:50 PM
Room: Jackson, Marriott, Mezzanine Level
Presentation File: No File Uploaded

The Critical Zone is the realm where rocks meet life. In this study, we examine the physicochemical interactions that occur when interbedded limestone-shale systems and kimberlitic eruptive materials weather to form soils. Fast weathering with extensive soil loss has been a major environmental concern in the Flint Hills. Knowledge of soil formation processes, rates of formation and loss, and understanding how these processes differ in different systems are critical for managing soil as a resource. The kimberlites of Riley County, KS, are CO2-rich igneous rocks that are high in Mg and Fe. They are compositionally distinct from the Permian limestones and shales found throughout the rest of the region. Bulk composition and mineralogy of the soils overlying these different bedrock types have been analyzed using X-Ray Fluorescence (XRF), X-Ray diffraction, bulk elemental extraction, and particle size analyses. Results show that the kimberlitic soils have higher concentrations of Fe, Mg, Ca, K and some trace elements (e.g. Ti, Ni, Cu). The resulting clays and other weathering products differ mineralogically as well, e.g. lizardite is abundant in kimberlitic soils and absent from the limestone terrain. As a result, kimberlite-sourced soils have significantly different physical properties than the thin soils surrounding them. Particle size analysis shows that the limestone-shale soils have a higher proportion of silt and clay sized particles whereas the kimberlitic soils have more sand. Kimberlite-sourced and limestone-shale-sourced soils produce different weathering products and could potentially have agricultural significance in terms of ionic and nutrient mobility.

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