STRUCTURAL AND STRATIGRAPHIC FRAMEWORK OF THE CARBONIFEROUS ROCKS OF THE CENTRAL
APPALACHIAN BASIN, EASTERN U.S,A.
Chesnut, Donald R., Kentucky Geological Survey, Lexington, Kentucky, 40506,
U.S.A.
Although the Carboniferous rocks of the central Appalachian Basin are very
important economically and academically, many important features such as the
presence or absence of a regional unconformity and an understanding of the
regional stratigraphic and structural relationships are poorly known. A series
of highly detailed cross sections reveal new structural and stratigraphic
features and provide the basis for a structural and stratigraphic framework for
this basin.
	These sections reveal the extent.and nature of the Mississippian-
Pennsylvanian unconformity, sequential truncation of underlying units including
buried topography, buried fault-controlled valleys, and deep channels at the
unconformity. The Early Mississippian-age (Tournaisian) Borden delta front is
also located, as well as extensive marker beds in the Pennsylvanian-age rocks.
These marker beds are generally easily identified marine shale intervals and
include the Cannelton Member, Kendrick Shale, Magoffin Member, and the Stoney
Fork Member. The extensive occurrence of these beds provides the basis for a
stratigraphic framework of the coal-bearing rocks (Pennsylvanian-age). The
Middle and Lower Pennsylvanian-age rocks are divided into two dominant
lithologic facies: a quartz-rich sandstone lithofacies called the Lee Formation
and a coal-bearing subarkosic sandstone and shale lithofacies called the
Breathitt Group (informal terminology). The Breathitt Group is divided into
subequal, informal formations separated by the marine shale marker units and
quartz-rich sandstones. These informal formations, in ascending order, are the
Pocahontas, New River, Grundy, Pikeville, Hyden, Four Corners, and Princess
formations. The use of the Pocahontas and New River formations is a different
concept than the formal units mapped as the Pocahontas Formation and New River
Formation in Virginia and West Virginia. Overlying the Breathitt Group are the
Upper Pennsylvanian Conemaugh and Monongahela Formations.
	Structural features include buried faults (Dorton-Hellier Fault), buried
folds, the Silurian- and Devonian-age rocks in part of the allochthonous block
of the Pine Mountain Thrust Sheet, and numerous anticlines and synclines. The
disparities between the surface structural features and the subsurface features
are also demonstrated; surface beds (Pennsylvanian age) in the area of the
Allegheny Front Uplift dip to the northwest, while subsurface units
(Mississippian-age) dip to the southeast. The Eastern Kentucky Regional
Syncline was probably formed as a consequence of the Allegheny Front Uplift.
	Thicknesses of the units in the cross sections reveal the tectonic
development of the central Appalachian Basin. During Upper Devonian (Famenian)
deposition, the basin subsidence increased due eastward. During Borden
deposition (Tournaisian), a delta system prograded to the southwest.
Disregarding paleotopography at the delta front, the Borden deposition thickness
indicates fairly even subsidence across the study area. Significant subsidence
of the basin in the study area did not begin again until Pennington Group
deposition (Serpukhovian). At this time, subsidence increased to the southeast.
During Early Pennslyvanian time (Bashkirian) uplift(?) caused extensive erosion,
resulting in the unconformity. After this event, the thickness of coal-bearing
units indicates that the basin resumed subsidence, which increased to the
southeast. Most present structural features were deformed during the maximum
development of the Allegheny Orogeny.