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Continued interest in the carbon-rich shale of Devonian and Mississippian age in Kentucky is reflected by intensive leasing and drilling to evaluate the potential reserves of oil shale. Hydrocarbons and heavy metals are associated with layers rich in organic matter (OM). Thicker accumulations of shale suitable for surface extraction lie along the flanks of the Cincinnati arch in both the Illinois and Appalachian basins. Distribution of the OM-rich shale is not uniform, but is controlled by subtly defined lithostratigraphic units. The shale tends to thin across the Cincinnati arch by an order of magnitude (100 versus 10 m, 330 versus 33 ft), and individual units disappear entirely. Key beds have been used with mixed success in tracing these changes.
Recognition of these key beds in cores provided by a recently completed 70-core drilling program in and near the outcrop is the basis for revising earlier suggested correlations. One key bed, marked by the occurrence of the alga? Foerstia (Protosalvinia), occurs in the lower part of the lower (Huron) member of the Ohio Shale in the Appalachian basin. The Huron Member is overlain by a lithostratigraphic marker, the Three Lick Bed. The Foerstia Zone has been traced in core and outcrop to the upper part of the uppermost (Clegg Creek) member of the New Albany Shale in the Illinois basin.
Discovery in this widespread continuous biostratigraphic marker at the top of the upper (Gassaway) member of the Chattanooga Shale near the designated reference section in Dekalb County, Tennessee, suggests that the Three Lick Bed of the Ohio Shale does not correlate with the middle unit of the Gassaway Member of the Chattanooga Shale as thought. Field relations indicate that the Three Lick Bed is absent by nondeposition, and starved-basin conditions prevailed into Early Mississippian time in this part of Tennessee. These stratigraphic revisions become significant in a regional synthesis of the anoxic-basin depositional model of OM--rich shale and syndepositional tectonics during Late Devonian time in Tennessee and Kentucky.
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