Contact: Dave Harris
From: Geological Society of America, 1999 Abstracts with Programs, v. 31, no. 5, p. A13.
DRAHOVZAL, James A., and HARRIS, David C., Kentucky Geological Survey, 228 Mining and Mineral Resources Bldg., University of Kentucky, Lexington, KY 40506-0107, firstname.lastname@example.org
Rocks of the East Continent Rift Basin are a succession of Precambrian siliciclastic (Middle Run Formation) and volcanic rocks that have been variously interpreted. One interpretation holds that these rocks represent a rift sequence that was subsequently deformed during the Grenville Orogeny, becoming part of the Grenville foreland fold and thrust belt. This interpretation is based on seismic and well data from near the Grenville Front in western Ohio and central Kentucky. Additional seismic data suggest that the same folded and thrust-faulted succession is present in southern Indiana and western Kentucky.
Interpretation of seismic data and recent deep wells in west-central Kentucky has resulted in defining some previously unrecognized characteristics for the East Continent Rift Basin. The rift succession in west-central Kentucky is thinner than in many of the areas previously studied. At least part of the relative thinness may be caused by tectonic inversion of the East Continent Rift Basin succession, because the overlying Cambrian section is also anomalously thin over this Precambrian basin. In addition, much of west-central Kentucky does not appear to exhibit the typical fold and thrust structures interpreted elsewhere. Instead, the area is cut by listric faults that likely indicate an east–west wrench motion. A new lithofacies for the Middle Run Formation also has been recognized in this area of Kentucky. A clean quartzose sandstone of possible marine origin is present in a recently drilled well.
These thickness, tectonic, and lithologic differences in the rocks of the East Continent Rift Basin in west-central Kentucky raise several basic questions and have important implications for understanding the regional tectonic evolution and for developing future natural-gas resources.