LOWSTAND VERSUS HIGHSTAND EUSTATIC MODELS FOR PEAT PRESERVATION:
THE COAL-BEARING ROCKS OF THE BREATHITT GROUP, EASTERN KENTUCKY
CHESNUT, Donald R. , Jr. , and GREB, Stephen F. , Kentucky Geological
Survey, University of Kentucky, Lexington, KY 40506-0107.

Stratigraphic and chronologic studies suggest that the alternation between major coal beds and clastic rocks of the Lower and Middle Pennsylvanian Breathitt Group (Central Appalachian Basin) resulted from glacial eustacy. The typical Coal-Clastic cycle (CC or Appalachian cyclothem) starts at the top of a major coal bed and consists of a coarsening-upward sequence of marine or brackish-water strata which is commonly truncated and overlain by a fining-upward sequence. The fining-upward sequence is overlain by a rooted paleosol which is overlain by a coal bed. Two differing scenarios have been developed to explain the sequence of strata observed in the CC. In one scenario (highstand peat preservation), the peat is deposited during the stable highstand period. Because of subsidence, the highstand peat deposit is drowned and covered by marine sediments. During the subsequent lowstand the marine strata, are eroded to varying degrees and bare channels are developed, causing an erosional unconformity surface on the marine strata. During transgression, the rise in base-level causes sediments to aggrade within the channels, creating fining-upward sequences above the marine strata. Paleosol development and peat deposition begin again at the next highstand.
	In another scenario (lowstand peat), peats are deposited in a coastal setting during lowstand. As transgression proceeds from lowstand, channels backfill and all low-lying areas including peat are covered by marine muds. Near the next highstand, sediments begin to accumulate as coarsening-upward sequences. Peats are then deposited on exposed platforms during highstand. During the subsequent drop in sea level, channels are incised and highstand peats and part of the coarsening-upward sediment package is eroded.
	The second scenario implies a preservation bias to cyclothems caused by eustatic rates being greater than subsidence rates. Peats are probably deposited during both lowstand and highstand, but lowstand peats are more likely to be preserved. If there were always a surplus of sediments, fluvial sandbelts would have been deposited at all sea levels and fining-upward sequences could represent sediments deposited at different phases including lowstand.