Pre-Mount Simon Basin in Southwestern Ohio

L. H. Wickstrom, D. L. Shrake

The Ohio Division of Geological Survey recently drilled a continuously cored hole in Warren County, in southwestern Ohio. This hole was projected to encounter crystalline Precambrian basement at a depth of approximately 3,500 ft. However, after drilling a normal stratigraphic section, additional sedimentary strata were encountered below the Mount Simon Sandstone (Cambrian) at a depth of 3,450 ft. Approximately 1,200 ft of this newly discovered sequence has been cored. Preliminary analyses show this rock to be, for the most part, a lithic arenite.

Through a cooperative agreement between the Ohio Division of Geological Survey, the University of Cincinnati, Wright State University, and a consortium of interested industry representatives, an 8-mi long, east-west seismic profile across the area was obtained. The profile revealed that the pre-Mount Simon sedimentary section thickens to the east and may reach in excess of 5,000 ft. Furthermore, below this interval lies a series of deep, east-dipping reflectors broken by low-angle thrust faults and normal (block) faulting.

It is not possible to identify unequivocally the origin of this "basin" at this time, although some very exciting prospects exist. This basin may represent an extension of the Mid-Michigan Keweenawan rift system or possibly a faulted foreland basin related to the Grenville orogeny and subsequently infilled by detritus from the eroded Grenville highlands.

This exploration effort has shown additional, previously unrecognized, sedimentary strata and the presence of relatively shallow crustal disconformities in southwestern Ohio that may be of future geologic and economic significance.

AAPG Search and Discovery Article #91023©1989 AAPG Eastern Section, Sept. 10-13, 1989, Bloomington, Indiana.