Morphology and Genesis of Some Grayish Claypan Soils of Oklahoma: II. Mineralogy and Genesis

Abstract

Mineralogical determinations and the suggested genesis of two proposed Nardin soils described in the first paper of this series are presented. Weathered and unweathered material of the clayey Wellington formation, Permian Redbeds were also studied to create two models showing that the proposed Nardin soils formed in either Permian Redbeds or Post‐Permian sediments. Cation‐exchange capacity, nonexchangeable K, ethylene glycol retention, and clay mineralogy based on X‐ray diffraction and differential thermal analysis were determined for the clay fraction.The clays are mainly illitic in the surface horizons and interstratified montmorillonite and illite in the argillic horizons. Coarse clays are largely illitic and fine clays, the dominant fraction, are largely montmorillonitic. It is concluded that the proposed Nardin and Waurika soils are developed from similar pedogenic processes from Post‐Permian sediments.