STRUCTURAL ANALYSIS SUGGESTS BEDROCK JOINTS IN OHIO ARE TECTONIC RATHER THAN GLACIAL IN ORIGIN

Subvertical joints are prominent in bedrock exposures throughout Ohio. Similar joints in younger, unconsolidated material across the region are attributed to Pleistocene glacial loading and freeze-thaw processes; alternatively, bedrock joints elsewhere in the Appalachian region have been interpreted as resulting from tectonic forces associated with the Alleghenian Orogeny. Joints formed by glacial loading should be subvertical but without a preferred azimuth, and should only be found within the maximum extent of Pleistocene ice cover. Joints formed by the tectonic model should be subvertical, with one population striking NW-SE and a secondary group striking ENE-WSW. Joints resulting from tectonic forces should be present throughout the region, and not limited by Pleistocene ice extent.

To investigate whether bedrock joints are glacial or tectonic in origin, we identify and document joints in bedrock exposures in northeast, central, and southeast Ohio, both within and beyond the maximum Pleistocene glacial extent. The joints we observe are subvertical with two primary preferred azimuths: 085 ± 10° and 170 ± 10°. We suggest that these preferred orientations are consistent with the tectonic model of joint formation, where regional joint patterns are influenced by stresses associated with the Alleghenian orogeny.