Geology and Structure of the Rough Creek Area, Western Kentucky

• Main Authors: Johnson, William D., Jr., Schwalb, Howard R.
• Format: Text
• Language: unknown
• Published: UKnowledge 2010
• Subjects: Rough Creek; geology; structure; Western Kentucky; basement; Illinois Basin; Geomorphology; Payne; Ice Sheet
• Online Access: https://uknowledge.uky.edu/kgs_b/1; https://uknowledge.uky.edu/cgi/viewcontent.cgi?article=1000&context=kgs_b

The Rough Creek area is a rectangular area about 113 mi east to west and 35 mi north to south encompassing about 3,900 mi2 in west-central and western Kentucky. The Ohio River delineates most of the western border with Illinois and locally also part of the northern border with Indiana. The northeast corner of the area is about 27 mi southwest of Louisville. The principal cities are Owensboro and Henderson. The Precambrian basement has been penetrated in only two wells in western Kentucky at depths somewhat greater than 14,000 ft. Basement is projected to underlie much of the area at a depth of more than 25,000 ft, and perhaps locally even more than 30,000 ft, in this, the deepest part of the Illinois Basin. Rocks of all geologic ages from Cambrian to Quaternary, except those of Mesozoic age, are present within the Rough Creek area; Upper Cretaceous strata occur as close as 20 mi south of the southeastern corner, however. All Paleozoic rocks older than Early Mississippian are restricted to the subsurface, so that the exposed rocks are dominantly of Mississippian (Meramecian and Chesterian) and Pennsylvanian ages. Strata of the Fort Payne Formation (Osagean) are present locally in the Rough Creek Fault Zone. Also, rocks of Early Permian age have been identified in a graben in the fault zone. Although no Pleistocene ice sheets penetrated south of the Ohio River in the Rough Creek area, the river valley was a major sluiceway for glacial debris from the Wisconsinan ice sheet, so the valley is filled with outwash, and loess blown from the valley blankets the area adjacent on the south. Remnants of Tertiary and Quarternary stream terraces are present in the Ohio and Green River Valleys, and thick lacustrine deposits covered by younger alluvium fill the larger stream valleys tributary to the Ohio River. The Rough Creek area is in the southern part of the Illinois Basin, and the principal structural features of the region that are present within or close to the study area, and at times influenced depositional patterns during the Paleozoic, include the Rough Creek–Shawneetown Fault System, the Moorman–Eagle Valley Syncline, the Pennyrile Fault System, and faults of the Illinois-Kentucky Fluorspar District. The Rough Creek–Shawneetown Fault System, which extends from western Kentucky into southeastern Illinois, where it is called the Shawneetown Fault Zone, is defined on its northern and western margins in Illinois by a southward-dipping, high-angle reverse fault with as much as 3,500 ft of reverse displacement. The frontal fault extends into Kentucky, but the degree of displacement is less than in Illinois; eastward along the structure, the frontal fault is broken into several long, arcuate segments by high-angle normal faults, and is displaced southward until it is no longer the frontal fault. In Kentucky, the Rough Creek zone is characterized by many steeply dipping fault blocks bounded by high-angle normal and reverse faults. The Moorman–Eagle Valley Syncline lies immediately south of the Rough Creek–Shawneetown Fault System, and that structure forms its steep northern and western limbs; the Kentucky part is the Moorman Syncline. The Pennyrile Fault System defines the gentle southern limb of the Moorman Syncline. In the deepest part of the composite syncline, which is close to its northern limb, structural relief on the Precambrian basement is more than 30,000 ft. The Moorman–Eagle Valley Syncline overlies the Rough Creek Graben in the basement. The Pennyrile Fault System, which lies mostly south of the Rough Creek area, is a broad feature composed of three branches of east- to northeast-trending, high-angle normal faults in an en echelon pattern that break the gently dipping strata into a series of fault blocks. Displacement on the faults generally increases to the west toward the junction of the fault system with faults of the Illinois-Kentucky Fluorspar District. The Pennyrile overlies the southern margin of the Rough Creek Graben, a structural feature in basement rocks.