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Geochemical Analysis of Stanley Shale Concretions in Southern Oklahoma

Abstract

The Ouachita Mountains of Arkansas and Southern Oklahoma are known for their serenity, unique geology, and perhaps most notably hydrothermal springs, but they also contain ore deposits of significant economic and industrial importance. Hydrothermal deposits produce valuable and unique mineralization all around the world; the Ouachita Mountains are no exception. These mountains contain thousands of feet of sedimentary beds that have undergone rapid deposition in the Late Paleozoic and intense deformation associated with the assimilation of Pangea. A particularly thick and highly deformed sedimentary unit is the Stanley Shale Group, which is primarily a black marine mudrock deposited in a deep trough during the Mississippian. This shale unit contains numerous physical and chemical features unique to its depositional environment and subsequent diagenesis, including concretions or nodules that have an unknown origin and a previously unstudied chemical composition. The concretions' distinctiveness is their appearance to be lithified “cow patties” but internally these concretions have an outer crust or shell and a differing but homogeneous core.

Concretions are classified by their chemical and physical attributes; they are also indicators of the environment and physical processes which acted upon the lithology. They may record the changes in hydrothermal solutions over time, be indicators of ore bearing deposits, or even form from hydrocarbon seeps on the ocean floor. Petrographical analyses, chemical analyses, and theoretical modeling of these particular concretions provide insight to syndepositional environment, post-depositional diagenesis, and changes to hydrothermal solutions, providing evidence to track fluid migration in this intensely fractured and faulted fold belt.