Abstract: Age and Tectonics of Cincinnati Arch in South-Central Kentucky

Richard Q. Lewis, Sr., Paul Edwin Potter

Three major features about the basin-arch relations of the Cincinnati arch in south-central Kentucky have been determined by combining information from 1:24,000 scale geologic maps and subsurface data.

1. The arch, a broad regional structurally positive feature, was active during Late Devonian to Mississippian, and probably into Pennsylvanian, time. The oldest beds exposed at the disconformable base of the Chattanooga Shale and Boyle Limestone of Devonian and Early Mississippian age belong to the Ashlock Formation of Late Ordovician age; the youngest beds belong to the Brassfield Dolomite of Early Silurian age. The Chattanooga Shale thins from more than 400 to less than 20 ft (122 to 6 m) in thickness over the arch and is locally absent near Marrowbone in Cumberland County. Mississippian formations reflect similar but more subdued thinning across the arch.

2. Locally superimposed on the arch are many small curving anticlines and synclines that have typical lengths of 3 to 8 mi (1.8 to 4.8 km) and closures of 20 to 30 ft (6 to 9 m).

3. At the surface on the arch there are some scattered normal faults, a few of which reflect reactivation of Cambrian growth faults.

Although vertical movements of the basement underlying the Cincinnati arch appear to be the dominant factor in its structural style, detailed explanations of the structural features, especially of the small folds, are lacking.

AAPG Search and Discovery Article #90975©1976 GCAGS- GC Section SEPM Annual Meeting Shreveport, Louisiana