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Geologic Structures
Structural processes such as folding and faulting of stratigraphic units creates uplift, which also accelerates the erosional process. In areas where uplift has occurred, erosion has been more extensive and older rocks are exposed. These processes are another part of the geologic history of Kentucky. The oldest rocks in the State occur in central Kentucky where structural events have caused older rocks (Ordovician at the surface) to be uplifted along a domal structure called the Jessamine Dome. The Jessamine Dome is located along an elongate north-trending structural flexure called the Cincinnati Arch. The Cincinnati Arch extends from Cincinnati, Ohio, through Cumberland County in southern Kentucky. These same rocks exposed on the surface in central Kentucky occur below the surface in eastern and western Kentucky, where they are downwarped into geologic structures called basins. Pennsylvanian rocks at the surface in the Eastern Kentucky Coal Field (Appalachian Basin) and Western Kentucky Coal Field (Illinois Basin) are much younger and at one time extended across the State; they have since been removed by erosion in the central part of the State. The Jackson Purchase Region in extreme western Kentucky is part of another basin (sometimes called the Paducah-Memphis Basin) that began formation in the Cretaceous Period. This basin is filled with Cretaceous, Tertiary, and Quaternary strata.
These basins and arches are major structures that are cut by faults caused by breaking and movement of the rocks. The breaking and movement are caused by parts of the earth's crust trying to move past each other. Earthquakes result from this breakage and movement. Several major fault systems are in Kentucky, including the north-trending Lexington Fault System along the Cincinnati Arch and Jessamine Dome in central Kentucky, the east-west-trending Kentucky River and Irvine-Paint Creek Fault Systems in eastern Kentucky, the Rough Creek and Pennyroyal Fault Systems in western Kentucky, and the Pine Mountain Overthrust Fault in southeastern Kentucky.
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