Erosional and depositional features in upper Meramecian and lower Chesterian (Mississippian) carbonate rocks of south-central and east-central Kentucky suggest the influence of coeval structural activity. The study area, which extends from Pulaski County northeastward into Powell County, is underlain by (1) the Greenwood Anomaly, a large north-trending gravity anomaly, which probably represents part of a Precambrian rift system, and (2) the western part of the Rome Trough, an east-trending graben-like structure, which represents a Late Precambrian to Cambrian continental rift zone. The study focused on the St. Louis Limestone and lower Monteagle Limestone of south-central Kentucky and correlative carbonate rocks of the Slade Formation in east-central Kentucky.
Several lines of evidence suggest Mississippian reactivation of rift-related faults associated with the Greenwood Anomaly and the Grenville Front, which extends along the west side of the anomaly: (1) local subaerial exposure of St. Louis sediments, (2) local depositional thinning of lower Monteagle sediments, (3) relatively widespread erosion during early Monteagle time, and (4) thickness variation in Mississippian units across the anomaly.
In east-central Kentucky, erosional and depositional features suggest Mississippian movement along the Locust Branch and Glencairn Faults of the Irvine-Paint Creek Fault System in the interior of the Rome Trough during deposition of the Slade Formation. Reactivation along the projected trend of the Locust Branch Fault in Estill and Jackson Counties apparently resulted in (1) abrupt thinning of the Renfro Member, (2) penecontemporaneous soft-sediment deformation of Big Sinking bed deposits, and (3) extensive erosion of the Burnside member. Movement along the Glencairn Fault in Powell and Wolfe Counties is indicated by more pronounced erosion of the Burnside member along the border of the upthrown side.
Mississippian reactivation of faults apparently was caused by migration of lithospheric bulges through the area. Based on recent investigations that relate Mississippian depositional sequence to lithospheric flexure, passage of an east-migrating, relaxation-phase, Acadian bulge and a north-migrating Ouachita bulge seems to have been contemporaneous with the fault movements and may explain evidence of fault reactivation and its consequences on Mississippian carbonate deposition in the area.
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© 1999 Kentucky Geological Survey, University of Kentucky