Abstract

This study suggests that the upper shale (regressive shale) in the Upper Pennsylvanian (Missourian), Lansing-Kansas City Groups D-zone from Hitchcock County, Nebraska, is a paleosol. Pedogenesis of this unit occurred during prolonged subaerial exposure on a semiarid to arid alluvial flood plain. Pedogenesis occurred during maximum retreat of the Late Pennsylvanian sea during the D-zone sedimentary cycle. Initially, clays in this unit were deposited in marine environments but as eustatic sea level continued to drop, deposition became dominated by continental alluvial processes. Characteristics which distinguish the upper shale as a paleosol are the presence of (1) a basal subsoil caliche (C-soil horizon) characterized by weathered limestone regolith clasts, soil nodules, thin-laminated calcrete beds with pseudo-fenestral fabric, pelleted and clotty calcareous and dolomitic caliche, weathered clays, circumgranular cracks, and root casts; and (2) an upper unit (B-soil horizon) characterized by authigenic hematite, intensely weathered clays, soil nodules, slickensides, and gypsum root casts.

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