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Paleoenvironmental biofacies analysis of recently drilled wells in dark Devonian shales in the Appalachian basin has shown that these facies can be projected to areas with no control points. In particular, the facies distributions in Perry County, Kentucky, were found to be precisely those that were predicted earlier from biofacies and organic geochemical data from the VA-1 well in Wise County, Virginia, and the KY-2 well in Martin County, Kentucky. This demonstrates the importance of these data in assessing the volume of gas in the shale throughout the basin as well as in selecting future test sites.
The recent biofacies and geochemical work combined with a review of the tectonics of the basin have contributed to an evolving interpretation of the geologic control of the biofacies.
While a marine environment persisted throughout the Late Devonian over the Appalachian and Illinois basins (and probably the Michigan basin), dynamic emergent areas controlled an intermittent introduction of large amounts of organic matter. Large amounts of nonmarine organic matter were periodically transported into the basin from a dynamic source provenance on the southeast; massive "blooms" of Tasmanites intermittently spread both east and west from the edges of the emerging Cincinnati arch. At times one or the other of these organic types swept entirely across the basins; at other times a more normal open-marine biota flourished and was deposited, probably under the influence of connections to the open seas on the south and northwest, the north being closed by the collision and sut ring of continental plates and the east by the growing Appalachian Mountains.
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