PRECAMBRIAN CRYSTALLINE BASEMENT TOPOGRAPHY, BELLEFONTAINE OUTLIER AREA, OHIO

Previous GSA poster sessions have discussed a gravity and geomagnetic survey of 550 common data points within 9 USGS quadrangles in the Bellefontaine Outlier area of west central Ohio located over part of the East Continental Rift Basin (ECRB). Processed using SURFER, complete Bouguer gravity and magnetic anomaly maps were produced between West longitude 83.50 and 83.85 degrees and North latitude 40.12 and 40.50 degrees. The Average data point separation of both data sets is 1km.

Previously the data was manually analyzed for maximum gravity and magnetic anomaly gradients ascribed to faulting in the crystalline Precambrian basement. The vertical components of fault throw were calculated using corresponding gravity and magnetic anomaly gradients and found to be in good agreement in location and magnitude.

We are now using ROCKWARE to assist in a higher resolution analysis of this data to locate only the steepest anomaly gradients. We have identified the location and have calculated the vertical components of fault throw of two major sub-parallel faults of similar length and in the south central part of the survey area. The faults bound the region of the minimum gravity and magnetic anomalies over the subjacent ECRB. The faults are south of the COCORP OH-1 seismic survey. A recent analysis and interpretation by graduate students at Ohio State University using PROMAX of seismic profiles on lines north of our survey area have given us estimates of depth to crystalline basement and also suggest the presence of other basement faults.

Anomaly Maps, cross-sections, and 3-D models of the Bellefontaine Outlier area are shown to illustrate the crystalline basement topography and estimated total thickness of overlying Precambrian through Paleozoic sediments.