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The distribution of potential hydrocarbon source beds within the New Albany Shale group of Illinois was determined by studies of the stratigraphy, lithology, and organic matter of the shales. Shelf-to-basin correlations (across western Illinois to southern Illinois and western Kentucky) reveal a complete and continuous transition from high-energy, aerobic, shallow-water (<50 m ?) environments (fossiliferous limestones) to low-energy, dysaerobic, moderately deep-water (~50 to 150 m ?) environments (bioturbated greenish-gray shales and thickly laminated olive-black shales) to very quiet, anaerobic, deep-water (>150 m ?) environments (finely laminated black shales).

The types and abundance of the organic matter preserved within the shales were predominantly controlled by the depositional environment. Appreciable amounts (3 to 15%) of mixed humic-sapropelic kerogen were preserved in the anaerobic black shale environments. The kerogen assemblage is interpreted to be well-preserved, locally derived organic material. Only small quantities (typically <1%) of humic (degraded ?) kerogen were preserved in the dysaerobic greenish-gray shale environments. This kerogen assemblage is interpreted to result from selective preservation of only the organic constituents most resistant to destruction by benthic invertebrates (detritus feeders) and aerobic bacteria.

Petroleum generation in the New Albany shales is likely to have occurred only in the aerobic black shales where the sapropelic and liptinite fractions have been preserved and where sufficient organic maturation has taken place. Gas generation may have occurred in the greenish-gray shales where humic kerogen has been preserved selectively, but in very small quantities due to the low maturity and paucity of organic matter in these shales.

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