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.