INITIAL ASSESSMENT OF THE PRE-CHATTANOOGA TECTONIC HISTORY ALONG THE SOUTHERN CINCINNATI ARCH USING AUTOMATED GIS TOOLS

The Cincinnati Arch is a regional structure that extends from northern Alabama to southern Ontario. The initial uplift of this structure has been attributed to formation of the Taconian peripheral bulge cratonward of the Appalachian foreland basin during the Middle to Late Ordovician. The tectonic history during and following the initial uplift of the Cincinnati Arch and the formation of the Nashville and Jessamine domes along this feature are not well understood. This study attempts to determine the timing of deformation of the Ordovician section in these structures and relate it to potential far-field effects of the Neoacadian and Alleghanian orogenies, or to other events.

This study developed an automated process using GIS software and Python™ scripts to produce structure contour maps from surface 7.5-minute 1:24,000 geologic quadrangle maps and subsurface well data. The subsurface data were compiled from oil and gas well logs, mineral exploration holes, mineral resources summary reports, oil and gas well databases, and 1:24,000 scale geologic maps from published and unpublished sources including the TN Division of Geology, KY Geological Survey, USGS, and AL Geological Survey. Specific stratigraphic horizons were particularly useful for correlation, including the unconformities between the Stones River (Black River) and Nashville (Trenton) Groups, and beneath the Devonian-Mississippian Chattanooga (New Albany-Ohio) Shale. In addition, the regionally extensive Millbrig and Deicke K-bentonites provide convenient chronostratigraphic markers permitting correlation of time-equivalent surfaces across the domes.

The structure contour maps were used to identify 1:24,000 map-scale folds and faults where point density was high enough to resolve them; several were identified along the southern flank of the Nashville dome. These findings have implications for oil and gas exploration by identification of folds and faults which may have produced fractures to enhance local reservoirs. Both the data and the technology being developed during this research should have wider applications to other structures in the Appalachian region and continental interior. Automating the production of high-resolution maps permits larger areas to be studied in a reasonable time frame.