Evidence for a Major East-West Structural Discontinuity in Southern Indiana –— A Possible Marginal Fault Zone of the Rough Creek Graben

Kenneth B. Horrall¹ and Matthew S. Stone²
¹Consulting Geologist-Geophysicist, Olney,IL 62450,[email protected]
²Barger Engineering, Inc., Evansville, IN 47728, [email protected]

Research on the attitude of jointing and small-scale thrust faulting in Indiana by Smith and Ault (1985) resulted in a proposed stress-field boundary in the southern part of the state. The boundary separates two major stress fields: the Midcontinent Stress Province north of the boundary and the Ohio Valley Stress Province south of the boundary. The Midcontinent Stress Province is currently under the contemporary geotectonic stress field shown by the rest of eastern North American - - maximum horizontal compression along an axis trending slightly north of east. The Ohio Valley Stress Province exhibits a strongly different stress field -- maximum horizontal compression along an axis trending north or slightly east of north.

A major structural discontinuity closely tracks the proposed stress-field boundary in southern Indiana. Evidence comes from two geotectonic features. First; detailed mapping using a LANDSAT- 7,infrared, color-composite, space image; has revealed a 70 miles (112 kilometer)- long, discontinuous, composite lineament zone that strikes east-west from westcentral Harrison County westward to the northwest corner of Warrick County. Second, an aeromagnetic map of Indiana shows flattened anomalies that strikingly align along the lineament zone.

The large structural discontinuity may be a major east-west fault zone similar to the Rough Creek - Shawneetown fault system of southeastern Illinois and northwestern Kentucky. If ground-truth checks verify this hypothesis, the discontinuity could be a marginal fault zone of the Rough Creek Graben arm of the New Madrid Rift Complex.

AAPG Search and Discovery Article #90095©2009 AAPG Eastern Section Meeting, Evansville, Indiana, September 20-22, 2009