Progradational and Retrogradational Trends in Pennsylvanian Fluvio-Deltaic Successions of the Grundy Formation (Appalachian Foreland, SE Kentucky): Implications for the Interpretation of Cyclothems of the Breathitt Group

Pennsylvanian strata of the Breathitt Group, in eastern Kentucky, are a world-class exam- ple of complex, glacioeustatically controlled stratigraphy developed in continental to mar- ginal-marine environments of the Central Ap- palachian foreland Basin. Although the upper formations of the Breathitt are well studied, the more areally restricted, coal-bearing parts of the Lower Pennsylvanian Breathitt Group, including the Grundy Formation are less well known. This article provides a detailed sedi- mentological and stratigraphic analysis of the Grundy Formation (late Early Pennsylvanian), based on new, extensive roadcut exposures. The Grundy Formation is dominated by shallow- and marginal-marine deposits and coals, as well as continental facies associations, which are commonly preserved in incised-val- ley fills. Detailed mapping, shows facies which can be divided into progradational and retro- gradational packages similar to the younger formations of the Breathitt, but forming two superposed genetic-stratigraphic cycles, based on, a thick, mid-formation marine interval, the larger number of coal-clastic cycles, and the greater stratigraphic thickness of the Grundy Formation. Comparison of the two Grundy sequences to overlying Breathitt sequences fur- ther confirms the general progradational trend within the Group. Furthermore, comparison of high-resolutioncyclicityindicatesoverprinting of high-frequency base-level fluctuations onto genetic-sequence scale cycles, thus providing a detailed sequence-stratigraphic framework for sediment repartition in time-equivalent series