Interpretation of Recent Seismic Data from a Frontier Hydrocarbon Province: Western Rough Creek Graben, Southern Illinois and Western Kentucky

Allen J. Bertagne, Eugene T. Pisasale, Tim C. Leising

The northern basement fault of the Rough Creek graben is seismically discernible and has surface expression in the Rough Creek fault zone. The southern basement fault is not clearly defined seismically, but can be inferred from shallow faulting and gravity data. This fault is roughly coincident with the Pennyrile fault zone. Extensional faults that formed the rift boundaries were the sites of late-stage compressional and extensional tectonics. Flower structures observed along the graben boundaries probably indicate post-Pennsylvanian wrench faulting. The basement within the graben plunges north-northwest, with the lowest point occurring south of the Rough Creek fault zone. Pre-Knox sediments thicken to approximately 12,000 ft in this area.

The Knox Megagroup thickens toward the Mississippi Embayment, ranging from 4,800 ft (southeastern graben area) to more than 7,000 ft (west end of graben). Upper Ordovician to Devonian units also display westward thickening. The top of the Meramecian, New Albany, Maquoketa, and the base of the Knox generate continuous, high-amplitude seismic reflections due to large impedance contrasts between clastic and carbonate units.

Shallow oil and gas production (Mississippian and Pennsylvanian) is present in this area. However, deep horizons (Knox, Lower Cambrian) remain relatively untested. Potential hydrocarbon traps in the pre-Knox sequence observed on seismic include fault blocks and updip pinch-outs.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.