EXTRACTING PALEOCLIMATIC DETAILS FROM PERMIAN REDBEDS OF THE MIDCONTINENT: A CASE STUDY FROM THE WELLINGTON FORMATION (OKLAHOMA)

Lower/mid Permian redbeds and intercalated evaporites in the Midcontinent are of interpreted arid marine/sabhka origin. This interpretation hinges on the evaporites, without detailed study the associated (voluminous) clastics. The provenance, transport, and deposition of the redbeds remain unconstrained. Sedimentologic and geochemical data from a core of the Wellington Formation (Kungarian), Oklahoma, suggest these represent continental environments, including perennial freshwater and ephemeral saline lakes. The Wellington comprises organic-rich laminated mudstone with laminated dolomite, variegated laminated mudstone with bottom-growth gypsum, massive, red to green mudstone with pedogenic overprinting, and red siltstone. Taken together, the finely laminated dolomite and gypsum, mudcracks, vertic-type paleosols, conchostracans, and lungfish burrows suggest a lacustrine rather than marine origin. The dolomite consists of micron-scale crystals interlaminated with clay and associated pyrite, suggesting deposition in a permanent, stratified, anoxic lake. The evaporites record saline lake deposition. Facies stacking consists of basal interlaminated dolomite and organic-rich mudstone, variegated mudstone with vertic features, and siltstone. At least 30 of these cycles occur in the (90 m) section, recording perennial freshwater lake, ephemeral saline lake, dry saline pan, and loess input. The geochemical signature and uniform, fine grain size of the clastics suggests far-traveled dust. Geochemistry of the clay indicates affinities to Ouachita-Appalachian-derived sediment. The silt is compositionally variable, and the chemistry and detrital zircon data suggest a western source. During more humid (interglacial?) phases clastics were sourced primarily from the Ouachita-Appalachian system and subsequently deposited into an anoxic, stratified freshwater lake. With aridification, the lake became saline. During arid (glacial?) periods, silt derived from the Ancestral Rocky Mountains accumulated as loess over the desiccated lake basin within a westerly wind regime. If our interpretation of an eolian origin for these redbeds is correct, then there may be a causative link between dust flux and regional climate of mid Pangaea, e.g. aridification and formation of saline brines.