CYCLES IN THE PENNSYLVANIAN ROCKS OF THE CENTRAL APPALACHIAN BASIN
CHESNUT, Donald R., Jr., and COBB, James C., Kentucky Geological Survey,
University of Kentucky, Lexington, KY 40506-0107

Stratigraphic analysis of the Lower and Middle Pennsylvanian rocks of the
Central Appalachian Basin reveals three orders of depositional cycles which, in
order of decreasing duration, are: the Breathitt coarsening-upward cycle, the
major marine transgression cycle, and the coal-clastic cycle.
	The coarsening-upward sequence of the coal-bearing rocks represented by the
Breathitt Group was deposited during Early and Middle Pennsylvanian times,
approximately 20 million years in duration. This rock sequence corresponds to
the Breathitt coarsening-upward cycle which was probably caused by the
increasing intensity of the Alleghenian Orogeny.
	The Breathitt Group is informally subdivided into eight formations,
approximately equal in thickness, based on the occurrence of laterally extensive
and commonly recognized marine and brackish shale members. These formations
correspond to the major marine transgression cycles that lasted approximately
2.5 million years. Sinusoidal functions of coal resources and sulfur content in
some of the formations also reflect this cycle. The cause of the major marine
transgression cycle is unknown, but may be tectonic in origin.
	An average of six major-resource coal beds occurs in each formation. Each
major coal and associated clastic rock sequence represents the coal-clastic
cycle that lasted several hundred thousand years. A 400,000-year duration is
equivalent to the mesocyclothem and also to the Long Earth Orbital-Eccentricity
Cycle, thought to control glaciation.
	Autocyclic processes such as delta switching have been attributed as the
cause of the coal-clastic cycles, and were thought to mask any allocyclic
control of deposition in the Appalachian coal-bearing rocks. Although only one
radiometric date is available for these rocks, the possibility exists that
glacio-eustatic allocyclic processes controlled deposition in the Appalachian
Basin during Pennsylvanian time.