ABSTRACT

A data set consisting of 120 miles of seismic data and 44 well logs were used to interpret the structural history of a 25 square-mile area in southern Holmes and northern Coshocton counties. The data show a complicated structural history where compressional and extensional forces alternated over geologic time.

A domal uplift cut by a series of northeast trending anticlines dominates the structural terrain. This structure is called here the Killbuck dome. Four episodes of tectonic activity are documented on the structure: 1) Precambrian thrusting, 2) Upper Cambrian extensional faulting, 3) Upper Cambrian and Lower Ordovician Knox-age uplift and 4) Upper Ordovician, Lower Silurian thrusting. Minor additional uplift occurred after the Mississippian Berea Sandstone was deposited.

Buried faults transect the dome, seen predominantly in the Precambrian through Rome section which probably originated as Grenvillian west-verging thrust faults. The faults were reactivated during Cambrian time when they served as normal faults accommodating regional extension. This is seen clearly on E-W seismic profiles by the thickness variation in the Cambrian section and on well data by the missing Rome and Mount Simon section in certain areas.

Rome time is interpreted from seismic as passive fill of the extensional basin. An episode of uplift is seen following Copper Ridge deposition which may have persisted through Knox unconformity time. Knox-age features are subtle on seismic and difficult to distinguish due to the large degree of subsequent structural overprint, however several erosional remnants have been discovered in the area.

The Cambrian extensional basin was inverted during Cincinnatian time. This age is interpreted from seismic isochrons and isopach maps of well data. In addition, several thrust faults displace seismic reflectors through the Queenston section. Another episode of uplift is recognized during Upper Silurian. Little tectonic activity is recorded on the structure during Devonian time. The structure map on the Top of the Berea Sandstone suggests some movement occurred after Berea time.

Distinguishing the timing of these structural events has proven critical to successfully exploring Knox unconformity traps in this area. Many dry holes have been drilled on late structures which were mistaken for Knox erosional remnants.