THE ORIENTATION, SIZE, AND SPACING OF JOINTS IN SANDSTONES OF THE UPPER CONEMAUGH GROUP (LATE PENNSYLVANIAN) IN SOUTHEASTERN OHIO

Fracture and joint studies of sedimentary rocks provide information regarding not only the tectonic history of a region, but also permeability and strength of the rocks. Of the few studies of joint patterns in the distal portion of the Appalachian basin in southern Ohio, none have been restricted to a single lithology or included information on joint spacing. This study has acquired data from a series of multi-storey, medium- to coarse-grained fluvial sandstones present within the upper Conemaugh Group (Late Pennsylvanian). Individual channel thickness varies from 6 to 12 meters. The strata are undeformed (dip is ~0.3° SE) and exposed on valley walls east of the city of Athens, OH. A total of 347 joint orientations were recorded using traditional field methods.

The data show that there are two main fracture sets oriented approximately 35° apart. The dominant set (42% of all measurements) has a mean direction of 340° and joint spacing that varies between 0.01 to 0.04 m. A subordinate set (26% of all measurements) has a mean orientation of 015° and a joint spacing that varies between 0.05 and 0.4 m, and more commonly extends through the entire exposure of the sandstone. The joint patterns are similar to those of the previous studies. The dominant set, which is parallel to the inferred axis of principal stress in this region, is also oriented parallel to the mean flow direction of the sandstones. This coincidence of sandstone orientation and stress pattern is considered to be responsible for the differences in spacing and length between the two sets of joints.