Deposition and diagenesis of a marine-swamp margin; the providence limestone and adjacent coals, western Kentucky

Marine limestones, terrigenous siltstones, shales, and coals exhibit complex stratigraphic relationships in the western Kentucky coal fields at the southern margin of the Illinois Basin. The Providence Limestone member of the Sturgis Formation (Pennsylvanian) is a mixed siliclastic-carbonate unit bounded by the No. 11 (Herrin) and No. 13 (Baker) coal seams. The coals contain fractured and brecciated horizons, cemented by sparry calcite and dolomite. Shallow-marine limestones and clastic rocks are interbedded with coals; lateral thickness and lithologic changes are abrupt. Up to 6.6 ft (2 m) thick beds of limestone are brecciated, with abundant intraclasts and disrupted fabrics. Slickensided claystones containing plant debris (underclays) directly underlie the coal seam deposits. The coals are overlain by thin shales with limestone nodules, followed by normal marine limestones. The limestones are generally disrupted, with pedogenic features overprinting the original marine fabric. Hard claystones overlie the disrupted limestones. The coals and Providence lithologies have complex diagenetic histories. Early lithification of brecciated coal fragments prevented complete organic decay, and the brecciated coals have well-preserved macerals. Petrographic examination of the Providence shows an original marine faunal assemblage in wackestones, packstones, and grainstones. Multiple episodes of carbonate cementation, silicification, and pedogenic alteration have altered the primary textures, creating a diverse suite of microfabrics.