Paper No. 6
Presentation Time: 10:15 AM
STRUCTURAL CONTROLS ON CONDUIT DEVELOPMENT IN OHIO CAVERNS
Ohio Caverns is an extensive, horizontal, multi-conduit cave system developed in the Columbus Limestone, Champaign County, Ohio. Conduit development is focused along a single bedding plane. Individual conduit (passage) profiles are cross-shaped, with enlargement along the horizontal bedding plane as well as upward in to joints. Lower portions of the cross-section are filled with up to several meters of clastic material. To understand the structural controls on conduit development we examined and measured joints within the cave, and compared them to conduit segments, local topographic aspect, and regional jointing. We found that: 1) There are many joints with no predominant orientation; 2) The direction of jointing varied between beds (as shown in peeled away sections of ceiling); 3) Passages in some beds don't seem to be controlled by a joint (or that joint has now been completely dissolved away); 4) Many of the "major" joints, which are controlling passages, are very curvilinear. In the historic section, conduits follow joints more clearly. In the other section there are many, many joints, most of which do not serve as loci for conduit growth. Some passages that are quite linear show clear joint control in the ceiling. Although some of these joints are straight, many are curvilinear. There are also passages that are straight in which no joints are apparent in the ceiling. In some places, we see a thin bed (a few inches) at ceiling level that does not have a joint, but the overlying bed has a joint that the conduit follows. There are instances of en-echelon jointing where the conduit seems to "shift" from, one to the other joint. The regional trend for joints in Ohio is ENE, which has the same orientation as the contemporary stress field. The highly fractured nature of the rock may be related to loading and shear stresses induced by glacial override of this small knob. Also, the anisotropic stresses generated by glacial override are expected to develop curved fractures. Fractures measured by Codispoti (2011) show that the dominant joint direction is north-northwest and the secondary is northeast. This, in conjunction with very localized water inputs, result in an overall cave form that does not exhibit a distinct bedding-plane or joint control as typically found in fluviokarst.