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Far-field Tectonic Controls on Deposition of the Ordovician Utica/Point Pleasant Play, Ohio using Core Logging, Well Logging, and Multi-variate Analysis


The Ordovician Utica shale is an extensive and important part of the Appalachian Basin subsurface, providing a source for hydrocarbon reservoirs, acting as an unconventional hydrocarbon reservoir, and of interest as in impermeable cap rock for carbon dioxide sequestration in Cambrian formations. The Utica shale and adjacent formations (Point Pleasant Formation, Trenton/Lexington Limestones) are a mixed siliciclastic-carbonate system that is mostly in the subsurface in areas of interest within the Appalachian Basin. Most outcrops are located to the east, in the Appalachian fold and thrust belt, and few public cores are available for study from key areas in the basin. Using a combination of core/well logging and multi-variate analysis with GAMLS software, lithofacies based upon mineralogical variations and sedimentology were extrapolated to electrofacies across the state of Ohio. These electrofacies were then mapped to identify controls on deposition during the Upper Ordovician time in Ohio. It typically is assumed that the primary control on regional deposition during this time period was the Taconic tectophase of the Taconian Orogeny; however, Precambrian basement structures appear to have localized influence on deposition also, such as the Waverly Arch, Utica Mountain Fault, and Harlem Fault. Also, the Sebree Trough has previously been reported to end in southwest Ohio, yet electrofacies mapping shows that the dark, calcite-poor shales that infilled the Sebree Trough continue towards northeast Ohio in a possible trough-like feature. These shales may have later timing compared to the Sebree Trough proper. Overall, lithofacies mapping combined with electrofacies mapping indicates that these Upper Ordovician formations are not homogenous rock types deposited across the state (such as layer-cake stratigraphy), but rather vary in mineralogy and thickness both horizontally and vertically across the region due to multiple controls on deposition.