Coal Exploration Model for Lower Pennsylvanian Rocks of South-Central Kentucky
Jay C. Close, Wayne D. Martin
Recognition of laterally extensive, delta-margin sheet sandstone facies in the Lower Pennsylvanian Breathitt and Lee Formations of Kentucky has enabled us to identify laterally persistent coal seams directly overlying sheet sandstones. The Mississippian-Pennsylvanian systemic contact is a pronounced unconformity, and relief on the erosional surface exceeds 30 m. Discontinuous coal and coal-bearing rock units directly overlie the unconformity because precursor peats and associated deltaic sediments were deposited in topographic lows, which prevented blanketlike sedimentation. Southwesterly progradational deltaic sediments progressively filled in topographic lows, and eventually the lower delta plain became nearly flat and horizontal. The interplay between subsidence, detri al influx, clay dewatering, and wave loading influenced the development of sandy substrate locations on the lower delta-plain surface at which peats could accumulate. The sand platforms were required for widespread accumulation of peats because the platforms provided surfaces of considerable areal extent on which vegetation could establish. Depositional sites on the upper delta and lower fluvial plain were more localized; therefore, peat accumulations in those areas were areally restricted.
Surfaces that experienced optimum conditions for peat and sheet sand deposit accumulation are preserved as laterally persistent complexes of delta-margin sheet sandstone-coal facies, elongated parallel to the northwesterly depositional strike and dipping gently southwest. Coal exploration programs focusing on the Lower Pennsylvanian rocks of south-central Kentucky should concentrate on delineating similar delta-margin sheet sandstone-coal facies complexes.
AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.