PROPOSED MECHANICAL CONNECTIONS BETWEEN THE ROME TROUGH AND THE ROUGH CREEK GRABEN ACROSS CENTRAL KENTUCKY

The structure of the Rome Trough (RT) beneath the Appalachian Basin in eastern Kentucky and West Virginia has been documented though well, seismic, and potential fields data analysis. Similarly, the Rough Creek Graben (RCG) beneath the Illinois Basin in western Kentucky has also been demonstrated with subsurface data. Because these graben structures are in close proximity and are filled with sediments of similar ages and lithologies, a probable connection between these features has been proposed by previous researchers, but the exact locations of the connecting structures or fault systems have not been established. Using a combination of surface and subsurface geologic and geophysical data, the connecting structures between these two graben systems are proposed here.

The western limit of the RT is considered to be the down-to-southeast normal faults of the Lexington Fault System, exposed in Jessamine, Garrard, Lincoln, and Casey Counties, Kentucky. The southern limit of the RT is poorly defined west of the Rockcastle River Uplift, and appears to include a southern extension into northern Tennessee. The eastern limit of the RCG has been considered to be the down-to-southwest normal faults exposed in southeastern Grayson and western Hart County, Kentucky, between the Rough Creek Fault Zone on the north and the Pennyrile Fault System on the south.

USGS 1:24,000-scale Geologic Quadrangle maps are available across the study area, but because of the high cost of deep drilling and seismic acquisition, data densities decrease dramatically with depth. Regional subsurface structure maps of the base of the Devonian New Albany Shale and the top of the Ordovician Trenton Formation, however, indicate that an east-west oriented structural depression is present to at least those depths between the two defined grabens. Closer analysis of the surface structure contours suggests that the brittle deformation that created the Pennyrile and Rough Creek Fault Systems continues eastward at least to central Adair and Marion Counties, respectively. Linear trends of monoclinal surface structures are interpreted to be drape folds that formed over deeper fault offsets, connecting these two grabens. The identification of these through going fault trends further suggests that the RCG and RT formed as part of a single intracratonic rift event.