The Mississippian-Pennsylvanian systemic boundary near Somerset, south-central Kentucky, is unconformable. Contact relationships in eastern Kentucky are controversial because of unclear genetic associations displayed by Chesterian(?)-Morrowan Lee Sandstone lobes, which have been interpreted as being of either barrier-beach or fluvial-deltaic origin. The barrier shoreline model stipulates that Meramecian, Chesterian, and Morrowan rocks represent carbonate sediment barriers and carbonate mud islands, offshore clays, quartzarenite barriers, and lagoonal-tidal flat sediments that were penecontemporaneously deposited during north-westerly progradational episodes. The tabular erosion model stipulates that Meramecian, Chesterian, and Morrowan(?) predominantly marine sediments were deposited and lithified as tabular units before and penecontemporaneous with deposition of Chesterian(?)-Morrowan fluvial-deltaic sediments.
Field study of exposures near Somerset indicates that the tabular erosion model satisfactorily explains contact relationships. Tidal flat, tidal channel, and lagoonal lithofacies without barrier sandstones are unconformably overlain by southwesterly progradational fluvial-dominated deltaic lithofacies. Elongate, fining-upward sandstone bodies typically above coal seams, which are oriented parallel with the southwesterly paleoslope, display lag concentrates of carbonized plant debris, epsilon cross-stratification (or apparently lack of stratification), and low-energy ichnofacies, and are enclosed in deltaic lithofacies.