HIGH-RESOLUTION LITHOLOGY AND STRATIGRAPHY OF AN OUTCROP WITHIN THE GRUNDY FORMATION, BREATHITT GROUP (PENNSYLVANIAN), SOUTHEAST KENTUCKY

Thick sequences of stratigraphically continuous exposures of rock occur within the Pennsylvanian section of the Appalachian Mountains that provide opportunities for detailed stratigraphic analysis. During uplift, large amounts of sediment were produced and transported into a foreland basin to the west of the rising Appalachians, and have since been uplifted. Pennsylvanian rocks are dominantly clastics, deposited in broad coastal plains, deltas, and tidal systems. We examine a single roadcut near Coldiron, Harlan County, Kentucky within the Pine Mountain thrust sheet, along KY 119, to determine its high-resolution lithology, stratigraphic relationships, and depositional environments.

The outcrop is comprised of mudstone, siltstone, and sandstone with thin intervals of coal in the Grundy (formerly Hance) Formation (Lower Pennsylvanian). We measured 81 meters of stratigraphic section using a Jacob’s staff, and sampled pertinent rock units for detailed examination. The stratigraphic section shows several coarsening-upward sequences from 6 to 20 meters in thickness, capped by coal and/or organic-rich shale about a decimeter thick. Clastic lithologies pervasively exhibit lamination in mudstones and fine cross-lamination in siltstones and sandstones. Woody fragments and plant material are common in several units. The lithology and sedimentary structures of marine mudstone are consistent with deposition in shelf (prodelta?) depositional environments. Overlying sandstones are deposited in deltaic and tidal systems, which are capped by coal and/or organic-rich mudstone that likely formed in coastal, freshwater environments.

Ultimately, contextual information, lithologic descriptions, the measured stratigraphic column, and photographs of key features and samples will be posted on the Kentucky Geological Survey (KGS) website as a story map. Samples will be archived at the KGS Earth Analysis Research Laboratory (EARL).