Sedimentology of Pennsylvanian Sandstone from Bedding-Plane Exposures, Laurel Dam Spillway, Eastern Kentucky Coalfield
Stephen F. Greb, Donald R. Chesnut, Jr.
Exposures of bedding planes in a coarsening-upward sequence of the Breathitt Formation at the Laurel Dam spillway in Whitley County, Kentucky, were analyzed by surveying a 250,000-ft2 area on a 10-ft grid and mapping within grids.
Detailed mapping of sedimentary structures revealed several internal facies within the coarsening-upward sandstone unit. The lower facies is fine grained, thin bedded, and dominated by asymmetric current ripples except for a narrow area of large-scale trough stratification. The troughs have asymmetrical limbs with ripple fans commonly developed on the shallow dipping limbs. The lower sandstone is truncated by a series of small channel facies that contain a siderite-pebble lag and massive sandstone grading upward into current-ripple-bedded sandstones that exhibit parting lineations and flat-topped ripples interpreted to represent sheared ripples during upper-regime flow. The upper sandstone facies is a large channel that truncates underlying facies. Channel fill consists of plant-debris lags and abundant planar cross-beds deposited by paleocurrents to the west.
These types of exposures provide a detailed three-dimensional look at a typical Pennsylvanian bay-fill deposit as well as an exceptional view of the microforms and mesoforms within that environment.
AAPG Search and Discovery Article #91023©1989 AAPG Eastern Section, Sept. 10-13, 1989, Bloomington, Indiana.