ABSTRACT: Basement Tectonics in the Eastern Illinois Basin and Their Effect on Early Paleozoic Sedimentation

FURER, LLOYD C., Indiana Geological Survey, Bloomington, IN

A unifying regional tectonic working model is proposed as an alternative explanation for several anomalous geologic features that have been observed for many years in the Illinois basin. Studies are in progress on all deep wells in Indiana to delineate more accurately structural deformation that may have affected the initiation and distribution of some Silurian reefs within the Terre Haute Bank. An estimate of the general location of concealed early Paleozoic faults in Indiana is based on several lines of evidence, including detailed subsurface field studies, reinterpretation of published structure maps, anomalous bedding dips in outcrops, historical earthquake distribution, anomalous thermal events, published gravity/ magnetic studies, and limited seismic data.

One model that explains the Silurian data is as follows. In southern Indiana, the northeast-trending basement faults parallel faults of the Wabash Valley Fault System. Movement on these faults has occurred during Paleozoic periods of compression or extension as these faults became reactivated. This fault movement has had subtle effects on the thickness and/or facies distribution of certain lower Paleozoic internals, including the Cambrian Mount Simon Sandstone, Cambrian Eau Claire Formation, Cambrian-Ordovician Knox Supergroup, Ordovician Trenton Limestone, and Ordovician Maquoketa Group. In most cases the faulting occurred in conjunction with the formation of a regional unconformity.

Proterozoic (1.2-1.0 Ga) faulting was a key mechanism in forming the very thick (18,000 ft; 5487 m) recently recognized Precambrian basin of Indiana, Ohio, and Kentucky. The basin was formed by plate-margin rifting along a series of very steep northeast-trending faults in the older Precambrian granitic basement. These faults are intersected by a set of northwest-trending basement faults. The location of some individual reefs within the basin-rimming Terre Haute Bank may have been controlled by positive structural features formed by the intersection of this northeast and northwest conjugate fault system.

AAPG Search and Discovery Article #91013©1992 AAPG Eastern Section Meeting, Champaign, Illinois, September 20-22, 1992 (2009)