VARIATIONS IN SEDIMENT DEPOSITION DUE TO CHANGING WATER REGIMES IN A KARST CONDUIT ON THE SINKHOLE PLAIN, SOUTH CENTRAL KENTUCKY

In karst basins, significant amounts of surface-derived sediment can enter into cave systems. The transport and deposition of these sediments in underground streams is a function of flow velocity, sediment supply and passage morphology. Changes in the surface environment, can affect the water and sediment supplies to subsurface drainage systems. Therefore, recent changes in surface environments may be reflected in the texture and structure of sediment deposits. Sediment deposits in State Trooper Cave, a tributary to the Lost River system in Bowling Green, Kentucky, were studied to evaluate changes in the depositional environment. Passage geometry, sedimentary structure, and texture of the sediment banks adjacent to the cave stream were documented. Samples were collected using coring tubes to preserve the structure within the sediment. These cores were then extracted, dried and analyzed. The structure was documented visually, recording distinct changes in the layering. The texture was determined for different sections through sieving and the passage morphology was documented by detailed mapping of the passage in the vicinity of the sediment banks. The two sediment banks studied were located in different environments within the cave: a meander near the entrance and in a large room near the down-stream sump. The upper foot of the deposits contain a variety of distinguishable sedimentary structures, from laminar bedding to varieties of ripple bedding. This bedding suggests that during flood events, the stream experiences fluctuations in sediment supply and current velocity. Rippled bedding is potentially due to an influx of sediment at the beginning of a flood coupled with higher stream velocity followed by slower velocity as the conduit filled with water, causing laminar bedding. The lower portions of the banks have indistinguishable structures but display variations in grain size that coincide with the structures of the upper portion. This may be due to either pressure from the overlying sediment or eluviation of sediment particles due to percolation of water through the sediment column.