ANALYSIS OF POLYPHASE DEFORMATION OF THE SOUTHERN CINCINNATI ARCH USING PYTHON AND GIS APPLICATIONS

The initial formation of the Cincinnati arch has been attributed to the peripheral bulge of the foreland basin formed during the Mid to Late Ordovician Taconic orogeny. The tectonic history following the initial uplift of the arch and the formation of the Nashville and Jessamine domes is poorly understood. This is due in part to the complexities of the interplay of unconformities and structural overprinting resulting from subsequent Paleozoic orogenies. This study attempts to determine the timing of deformation of the unconformity-bound sequences exposed along the southern Cincinnati arch by generating high resolution structure maps of the Mid-Ordovician to Mississippian formations. These maps were used to identify structures relating to potential far-field effects of the Taconian, Neoacadian, Alleghanian, and possibly Ouachita orogenies. Structures previously identified in large-and small-scale geologic maps and other published works across central Kentucky, Tennessee, and northern Alabama were also incorporated.

Due to the large volume of data available for this study, we developed a semi-automated process for data collection, cleaning, and cross-verification using Python™ and ArcGIS™. This process was used to compile data from 887 published and unpublished digital 1:24,000-scale geologic quadrangle maps acquired from the Tennessee Geological Survey, Kentucky Geological Survey, USGS, and Alabama Geological Survey. Subsurface data from 24,833 wells were also compiled from oil and gas well logs, mineral exploration boreholes, resource summary reports, and state oil and gas well databases. We then generated structure maps of key surfaces and identified multiple sets of map-scale folds across the study area. Along the southern Nashville dome these folds frequently trend N-S, with a second set trending NW-SE at a similar orientation to a series of faults. E-W-trending folds occur on the flanks of the Jessamine dome. Silurian formations that outcrop around the Jessamine dome are limited to the cores of N-S trending synclines along the eastern and southern Nashville dome due to truncation by the unconformity at the base of the Devonian Chattanooga Shale. Combining information about fold orientations and unconformities over a large area is the key to unraveling the tectonic history of the Cincinnati arch.