--> ABSTRACT: Hydrocarbon Potential of Early Paleozoic Rocks of the Illinois Basin, by Norman C. Hester; #91003 (1990).

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ABSTRACT: Hydrocarbon Potential of Early Paleozoic Rocks of the Illinois Basin

Norman C. Hester

Deep seismic reflection profiles gathered in the southern part of the Illinois basin define an east-west-trending wedge-shaped trough south of the Rough Creek fault zone and the Shawneetown fault. The asymmetry of the trough indicates a northward overthickening of the pre-Knox (Cambrian) rock sequence that developed as a result of growth faulting. Despite the fact that the total sedimentary sequence approaches 25,000 ft in thickness, the southern part of the Illinois basin remains as one of the very few coal- and oil-producing basins in our nation that is essentially untested at depth in the lower Paleozoic sequence.

In the trough, four pre-Knox tests, the deepest of which was drilled to 15,200 ft, indicate (1) a minimum of 5000 ft of pre-Knox shale; (2) an increase of total organic carbon in the Cambrian section both westward and with increasing depth; and (3) a repeated section that resulted from 3300 ft reverse faulting.

Two major tectonic events make this trough an attractive target for petroleum explorationists. First, extensional tectonics during the late Precambrian resulted in the sediment trap that allowed the accumulation of as much as 10,000 ft of Cambrian terrigenous clastics, potentially including both source rocks and reservoirs. Second, compressional tectonics during the Late Pennsylvanian and Permian provided the mechanism for mobilizing and trapping the hydrocarbons.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990