EVOLUTION OF THE SURFACE AND SUBSURFACE DRAINAGE OF THE SINKHOLE PLAIN, CENTRAL KENTUCKY KARST, USA

The Mammoth Cave system of central Kentucky, USA, is developed largely in the sandstone-capped Chester Upland in response to incision by the Green River. To the south, the upland gives way to the sinkhole plain of the Central Kentucky Karst. The sinkhole plain lies about 50 m lower in elevation and is internally drained by sinkholes that connect to the Green and Barren Rivers. Previous studies have used cosmogenic radionuclide (CRN) dating to link the incision history of the Green River and the development of Mammoth Cave as far back as 3.25 Ma. However, the temporal relationship between Mammoth Cave and the relict passages in knobs that stand above the sinkhole plain, such as Prewitts Knob, Bald Knob, and Huckleberry Knob, is not clear. To constrain the age of this stage of karst development, and to provide an estimate of the long-term erosion rate of the sinkhole plain, we present results of CRN burial dating on sediments from Crystal Onyx Cave in Prewitts Knob. These data complement new detrital cosmogenic results suggesting that catchments of the small sinking streams on the sinkhole plain are eroding very slowly, about 4.5 m/Myr, on 200-kyr timescales. Ultimately, the sinkhole plain and the Mammoth Cave system share the same base level (the Green-Barren R. system), so differences in erosion rate over differing timescales may reflect changes in erosional efficiency as karst systems respond to incision of their base level streams. The results of this work have implications for understanding timescales of the evolution of karst systems in unconfined carbonate sequences as well as the response of karst terrains to transience in surface drainage networks.