PALEOHYDROLOGY OF OHIO CAVERNS: AN ABANDONED GROUNDWATER CONDUIT

Ohio Caverns is an abandoned groundwater conduit located in Champaign County, Ohio. The cave is formed in a small hill that is capped with the Ohio shale, and cored with the Columbus Limestone. This hill is within the Bellefontaine Outlier, a bedrock high that disrupted glacial ice flow. The origin of the clastic sediments and the paleohydrologic function of the cave were investigated. Passage morphology shows that the cave initially formed under phreatic conditions, primarily along one bedding plane. The following sequence of phases then occurred: 1) vadose incision (resulting in keyhole conduit profiles); 2) deposition of clastic sediments (nearly filling the cave); 3) localized collapse of the walls and ceiling (breakdown); 4) deposition of dark red speleothems (localized mainly on ceiling joints, and characterized by micro-gours); and 5) deposition of brilliant white speleothems (not usually localized on joints). The last phase is presently active.

Twenty-six clastic sediment samples were collected from a 6-meter thick deposit. The sediment size fractions were analyzed, and indicated the possible presence of five distinct depositional units. Sand ranged from under one to over ninety percent. Clay had a similar range, and silt varied from one percent to sixty-nine percent. There was zero calcite in seventeen of the twenty-six samples. The remainder had one to seven percent. Dolomite was consistent with values around ten to fifteen percent. There were two spikes of dolomite of twenty-five and forty-three percent. Statistical analysis of the grain size data from the cave sediments verifies the presence of five different episodes of clastic deposition. For the most part there is no connection between the five depositional phases and the carbonate present in the samples. There is no correlation between the silt and clay fractions and total carbonate. There is a weak positive correlation between sand and total carbonate.

Phases 1 and 2 of cave formation were related to either downcutting of the valleys surrounding the cave or rearrangement of local drainage due to glaciation. Phase 3 was caused by loss of buoyancy when the cave was drained. The shift from Phase 4 to 5 indicates a change of infiltration mode and chemistry of the drip waters, probably due to a change in the overlying regolith.