CORRELATION OF UPPER MISSISSIPPIAN (CHESTERIAN) ROCKS IN SOUTH-CENTRAL KENTUCKY

Upper Mississippian (Chesterian) strata in western and south central Kentucky are divided into a variety of formal stratigraphic units. In the vicinity of Bowling Green, Kentucky, the Girkin Formation is widely recognized, whereas in counties to the southwest and northeast, the interval occupied by the Girkin is subdivided into several thinner stratigraphic units. Because the Girkin occupies a relatively thick portion of the Chester Series in Kentucky, a field investigation is underway to ascertain if formations recognized outside of the Bowling Green area can be correlated into strata commonly recognized as the Girkin Formation. Two stratigraphic units equivalent to the uppermost Girkin have thus far been studied: the Elwren Formation and the Beech Creek Limestone Member of the Golconda Formation. The Elwren Formation consists of a heterogeneous assemblage of thin-bedded mudstones, shales, and siltstones. A distinctive paleosol occurs near the top of this unit which, along with associated lithologies, suggests deposition in a marginal marine environment with some subaerial exposure. The overlying Beech Creek Limestone consists of fossiliferous packstones and grainstones interpreted to have been deposited in more open marine conditions. Both the paleosol of the Elwren and the distinct fossils of the Beach Creek have been recognized in Girkin outcrops in the Bowling Green area. Additional work is underway to correlate other formations and members into the Girkin and to determine the depositional and structural controls on the occurrence of Chesterian strata in south-central and western Kentucky.