Lakes, Loess, and Paleosols In the Permian Wellington Formation of Oklahoma, U.S.A.: Implications For Paleoclimate and Paleogeography of the Midcontinent

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Abstract
: Lower to mid-Permian deposits of the Midcontinent (U.S.A.) record a significant and long recognized aridification because they archive the shift from more humid facies (e.g., coal, organic shale) of the Pennsylvanian to widespread redbeds, semiarid to seasonal paleosols (Calcisols, Vertisols), and evaporites by the mid-Permian. The provenance, transport and depositional processes of the voluminous Permian redbeds of the Midcontinent, however, remain largely undefined. The Artinskian Wellington Formation in Oklahoma exhibits high-frequency cycles comprising organic-rich laminated mudstone with thinly laminated (inferred primary) dolomite, variegated laminated mudstone with gypsum, massive, red to gray-green mudstone with pedogenic overprinting, and pale red siltstone. The gypsum exhibits a distinct 87/86Sr isotopic ratio (0.709199) that is inconsistent with Permian seawater. We suggest that these facies record deposition in ephemeral to perennial lakes during a time of increasing aridity and seasonality, the latter indicated by abundant mudcracks, vertic-type paleosols, conchostracans, and lungfish burrows. The fine and uniform grain size and the geochemistry of the siliciclastic component suggest far-travelled and likely eolian transport that ultimately accumulated in both subaqueous and subaerial environments. Provenance analysis indicates the siliciclastic component was sourced chiefly from the southeastern Ouachita–Appalachian orogen and the Ancestral Rocky Mountains (ARM) or its derivative sediment.

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