Permian outliers in Western Kentucky

Two small, down-faulted outliers of latest Pennsylvanian to Early Permian rocks occur in western Kentucky. These are the youngest Paleozoic rocks in the Illinois basin and are approximately 550 and 750. km, respectively, from strata of comparable age in the Dunkard basin and Midcontinent. A continuous core, Gil 30, was drilled in the eastern (Cap Mauzy) outlier. Fusulinids (Leptotriticies beardi) from a depth of 59.4. m were originally used as evidence for Permian age, although this species is now considered to be latest Pennsylvanian. Ostracods from above the fusulinids support a Permian age. The upper 103.6. m of Gil 30 is assigned to the Mauzy Formation and contains intervals of bedded, micritic, nodular to brecciated limestone of probable lacustrine origin, alternating with marine to brackish-water clastic intervals that tend to coarsen upward, a single upward-fining sandstone interval, and a single 2. cm thick coal layer. Older strata contain much more coal and almost no bedded non-marine limestone. The Grove Center graben, 18. km west of Gil 30, is identified on the basis of an oil-test hole electric log and coal test holes. No core samples are available, but log comparison indicates that the Grove Center outlier contains at least an additional 67. m of younger strata than Gil 30, and is a prime target for further study.Regional coalification and oil-maturation trends, along with lack of evidence for syndepositional tectonic activity in Gil 30, indicate that the Permian rocks preserved in Gil 30, and by extension the Grove Center graben, are likely representative of strata that once occupied much of the Illinois basin, probably in continuity with the Midcontinent. The Kentucky outliers, therefore, provide a link between the Midcontinent and Dunkard basins and may be important in addressing long-standing problems, such as the age of the Dunkard, and paleoclimate reconstructions.