EVIDENCE OF SYNDEPOSITIONAL FAULTING DURING DEPOSITION OF THE HYDEN FORMATION (MIDDLE PENNSYLVANIAN), EASTERN KENTUCKY COAL FIELD, CENTRAL APPALACHIAN BASIN

New outcrops near Jackson, Kentucky, expose the Pikeville and Hyden Formations (Duckmantian) along the western margin of the Central Appalachian Basin. In this area, the Pikeville Formation is 30 to 40 m thick, and the Hyden Formation is 26 to 30 m thick. Four coal beds are exposed in each unit. Coals are mostly less than 0.5 m thick and several thin or pinch out above paleosols to the northwest. Marine shales are thin; the Betsie Member, at the base of the Pikeville Formation, is less than 5 m thick; the Kendrick Member at the base of Hyden Formation is thin and/or truncated; the Magoffin Member at the base of the Four Corners Formation, is also thin. Basinward, to the southeast, each formation is more than 200 m thick, and there are 5 to 6 major coals in each unit, with several beds occurring in zones of multiple beds. Basinward, correlative coals are more than 1 m thick, and the major marine zones at the base of the formations, are tens of meters thick.

Along the new roadcuts, a sharp increase in dip occurs in part of the Hyden Formation, concurrent with the addition of a 9-m thick channel interval, where the road crosses a basement fault. Additional small faults are noted in the outcrops to the north. Faults were likely reactivated during foreland basin subsidence, and forebulge migration. Successive, downdip movement along basement faults of different scale, and at different times, likely resulted in increased tectonic accommodation and preservation of Pennsylvanian section in a basinward direction.