Geological and Geophysical Study of the Maunie Fault in the Wabash Valley of the Illinois Basin

By

Milton P. Smith¹, John L. Sexton¹

(1) Southern Illinois University at Carbondale, Carbondale, IL

 The Wabash Valley Fault Zone, located in southwestern Indiana and southeastern Illinois, contains more than 26 separate oil fields in Illinois that have produced over 400 million barrels of oil since its discovery in 1938. Understanding the nature and origin of these faults is important to future exploration and development of the oil and mineral deposits of this area. This structural zone has been proposed to be the result of reactivation of the New Madrid Rift Complex. The Wabash Valley Fault Zone is composed of many faults that run north from the northern bounding fault of the Rough Creek Graben approximately 55 miles to the LaSalle Anticline. The faults are typically high angle, 60¡ to 90¡ normal faults which have a tendency to splinter as they approach the surface. The Maunie Fault lies on the eastern side of the Illinois Basin. Deep seismic, shallow seismic, georadar, and electric log data from drill holes, show a graben-like feature northeast of Maunie, IL. From electric log data, displacement along the edge of this feature is approximately 90 feet at the top of the Beech Creek limestone. Shallow seismic and georadar data show that the Maunie Fault was reactivated as recently as the Quaternary and possibly during the Holocene. These data are all generally consistent with the hypothesis that the faults are related to a reactivated rift complex.