Evidence for the presence of hydrocarbon charge in the Knox and pre-Knox rocks of the Rough Creek Graben

REYNOLDS, DOUGLAS W., JR., Reynolds Resources, Inc., Owensboro, KY

Concerning the presence of hydrocarbons in the Knox and pre-Knox rocks of the Rough Creek graben (RCG), only scant evidence exists in the public domain. Evidence developed on data from rocks above the RCG are suggestive of hydrocarbon charge in these rocks.
1. A review of seismic data from the RCG revealed a zone in the Knox that may be interpreted as a zone bearing gaseous hydrocarbons.
2. Geochemical analysis was performed on two oil samples from the Mississippian and one from the Pennsylvanian, and also one gas sample from the Pennsylvanian. All three oil samples had properties consistent with other oils throughout western Kentucky and the rest of the Illinois Basin. The gas sample was dry gas and, by comparison with published empirical data, isotopic data indicated that the gas had a mixed biogenic and thermogenic origin. The thermogenic component implies generation from sources with maturities beyond those observed from the New Albany Shale.
3. Oil in the Illinois Basin is ubiquitous and mostly consistent in its geochemical properties. Distribution of mature New Albany Shale is consistent with the observed distribution of oil occurrence.
Non-associated gas is more significant in western Kentucky than in other areas of the Illinois Basin, so New Albany maturity patterns do not explain the distribution of gas fields nearly as well as they explain oil distribution. A more closely correlated source for dry gas is the thick pile of pre-Knox rocks present in the RCG.

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