STRUCTURAL AND PALEOTOPOGRAPHIC CONTROLS ON PRINCESS NOS. 8 AND 9 COALS, BREATHITT GROUP (MIDDLE PENNSYLVANIAN), ALONG THE NORTHERN MARGIN OF THE CENTRAL APPALACHIAN BASIN

The Princess Formation is exposed in the northeastern part of the Eastern Kentucky Coal Field, on the northern margin of the central Appalachian Basin. New exposures of the Princess No. 8 and Princess No. 9 coal zones in Greenup County illustrate varied local controls on thickness and coal-bench architecture. Exposures of the Princess No. 8 coal bed indicate that the coal drapes an irregular surface, sometimes thickening into scours. In one well-exposed scour, multiple coal benches complexly fill two scours. Two coal benches, separated by a thick claystone, thicken into the northern scour and thin or pinch out on the scour limb. In the south channel fill, three benches of coal thicken into the scour; the lower two benches reach their greatest thickness close to the northern margin of the channel and are restricted to the scour.

At another location, an extra bench in the Princess No. 8 coal is developed adjacent to a listric fault for a distance of 3 m, in a narrow, V-shaped scour or graben. A subjacent structural ramp leads to the merging of at least two coal benches on the upthrown margin of the ramp. Merging rather than syndepositional splitting due to clastic influences can be interpreted, based upon the truncation of an underclay developed beneath one of the coal benches. At the same location, multiple, thin coal beds in the Princess No. 9 coal zone drape a scour cut 3 m into the underlying floodplain facies, nearly to the top of the uppermost bed in the Princess No. 8 zone.

These dramatic local changes in bench architecture and coal thickness illustrate the profound effect of paleotopography and possibly syndepositional structural movement on peat accumulation on the northern margin of the basin. The low accommodation setting resulted in a complexly incised surface upon which peats accumulated. Bench architecture and coal thickness shows vary laterally relative to that surface, even across short distances. Low accommodation also resulted in relative thinning of the stratigraphic interval between coal beds, such that beds may come close to merging along structures and beneath channels. The complex bench-architecture and zoning of the coals that results from the paleotopographic and tectonic influences can lead to problems in lateral correlation of beds where the coal zones are not as well exposed.