ABSTRACT: Evolution of the Illinois Basin

KOLATA, DENNIS R., and W. JOHN NELSON, Illinois State Geological Survey, Champaign, IL

The origin and evolution of the basin are closely related to the development of the Reelfoot rift and Rough Creek graben, a failed rift situated at the south end of the basin. The rift system formed during breakup of a supercontinent, apparently during late Precambrian to Early Cambrian time. Lithospheric extension within the rift system resulted in tensional block faulting and relatively rapid subsidence. By Late Cambrian, the tectonic setting changed from a rift basin to a broad cratonic embayment centered over the rift. During the remainder of the Paleozoic Era, the proto-Illinois basin was a broad trough extending from the continental margin in central Arkansas northward through Illinois, Indiana, and western Kentucky. Widespread structural deformation in the basin began in Valmey ran time concurrent with the initial accretion of continents that later formed the Pangea supercontinent.

Compressional stresses emanating from the Allegheny and Ouachita orogenies were transmitted to the continental interior, reactivating faults within the Reelfoot rift and Rough Creek graben and causing uplift of basement-block structures throughout the Illinois basin. The compressional phase was followed by a post-Early Permian episode of extension that apparently coincided with the breakup of Pangea. Tensional stresses reactivated faults within and adjacent to the Reelfoot rift and Rough Creek graben. Post-Pennsylvanian, pre-Late Cretaceous uplift in the area of the Reelfoot rift structurally closed the southern end of the Illinois basin, creating the present basin geometry.

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