Chasing sand: evolution of the surface and subsurface drainage of the Sinkhole Plain, Central Kentucky Karst, USA

This work extends the established geochronology of the Mammoth Cave region, Kentucky, USA, spatially and temporally, to infer evolution of the karst landscape and to consider the shifting drainage basins of the Barren River and the Green River in relation to regional drainage rearrangements. Previous studies have focused on the Mammoth Cave System and used cosmogenic radionuclide dating to link the incision history of the Green River and the Cave as far back as 3.25 Ma. We posit that prior to the wide-spread karstification that produced Mammoth Cave, drainage consisted of a purely fluvial stream network flow on the youngest clastic rocks. When this caprock was breached, carbonate dissolution ensued and the system transitioned to fluviokarst. Relict large trunk passages that originated at that time can be found in features such as Prewitts Knob, Bald Knob, and Huckleberry Knob. We intend to use sediments and speleothems collected from Crystal Onyx Cave in Prewitts Knob 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 surrounding the knob. These relict trunks were also used for cave stream profile reconstruction in combination with the east-west trending uvalas and sets of steep, deep sinkholes. We interpret that paleodrainage as having been west-flowing into the Barren River which then served as regional base level. Thus, we infer that as the rivers incised, this drainage was pirated to the north and began flowing to the Green River. The system then evolved into a more mature karst, large conduits near the surface collapsed, and dissected the landscape into isolated depressions. The collapsed limestone formed red soil and the sandstone produced angular clasts scattered throughout that soil. The retreating Chester Cuesta, marking the boundary between the Sinkhole Plain and the sandstone-capped Chester Upland, eroded most rapidly where limestone was exposed to the surface and more slowly where it was sandstone-capped leaving abandoned isolated cave trunk passage segments in remnant knobs. The results of this work have implications for understanding timescales of the evolution of karst systems in unconfined carbonate sequences as well as the interaction of karst areas with the transience in drainage networks.