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Abstract: Stratigraphic and Structural Framework Of Granville-like Lithologies in the Tanglewood Member, Middle and Upper Ordovician Lexington Limestone, Central Kentucky

ETTENSOHN, FRANK R., and MARK A. KULP

The Granville is a driller's term applied to a series of clean, porous to tight, fossiliferous limestones that form local pay zones in the upper Lexington Limestone of south-central Kentucky. Throughout most of Kentucky, the Lexington Limestone is 50- to 60-m thick and reflects a deepening-upward trend in depositional environments. In the Jessamine dome area of central Kentucky, however, a pronounced episode of regressive shoaling produced three series of Granville-like lithologies represented by the Tanglewood Member, resulting in a thicker (>100 m.) and younger accumulation of Lexington Limestone called the Tanglewood buildup, which grades laterally into deeper water facies in all directions. Sedimentary structures, lithology, and paleontology indicate that the Tanglewood represents a series storm-influenced shoals that grade laterally into shallow, open-marine nodular limestones and shales. Mapping the distribution of the Tanglewood Member shows that the buildup is a roughly triangular body bound by fault zones and that individual shoal complexes in the buildup are also commonly delimited by faults. It is difficult to escape the conclusion that this anomalous buildup of shoal complexes reflects periodic uplift into wave base during reactivation of the basement precursors of the present surface faults due to Taconian far-field tectonism. Although pay zones are absent in central Kentucky, the occurrence there of Granville-like lithologies at similar stratigraphic horizons, apparently related to reactivation of local structures, may provide models that are useful in the search for pay zones at this horizon elsewhere in Kentucky.

AAPG Search and Discovery Article #90939©1997 AAPG Eastern Section and TSOP, Lexington, Kentucky