Pennsylvanian Rocks of Southern Appalachians1
Pennsylvanian rocks generally underlie the Cumberland Plateau and Warrior plateau. To the south and west they continue beneath Mesozoic sediments of the Coastal Plain. To the north they form the Allegheny plateau.
Lithologically, the strata consist of sandstone, shale, conglomerate, coal, underclay, and minor ironstone and limestone. Black shale is prominent in western Mississippi.
Geology of the Pennsylvanian is illustrated by five correlation sections, four isopach and lithofacies maps, and three structure maps.
Deposition began during the early Pottsville in two separated areas and then spread by basal onlap beyond the present day erosional limits. By middle Pottsville time, Pennsylvanian deposits were continuous with those of the Eastern Interior basin. Thickest connection was probably across the Clifton saddle in western Tennessee, and even the Nashville dome was covered.
Trends of deposition were generally parallel to the Cincinnati arch, swinging from northeast in Kentucky and Tennessee to northwest in Mississippi, as the arch similarly swings to join the Ozark dome.
Pennsylvanian rocks were later folded and thrust in southwest-trending “no-basement” structure of the Appalachian revolution. This structure system may intersect or join with northwest-trending Ouachita structure deep in the subsurface in southeast Mississippi.
More recent epeirogenic movements have formed a broad southeast-plunging nose in southern Tennessee and northern Alabama where Pennsylvanian beds have been most deeply eroded.
Figures & Tables
Rocks of the Pennsylvanian System are the bed rock of approximately 10 per cent of the land area of continental United States. These rocks yield 17 per cent of the petroleum, most of the coal, and most of the ceramic raw material of the United States.
Areas of deposition of Pennsylvanian rocks are naturally discriminated as the New England trough, the Appalachian trough, the Eastern Interior basin, the Michigan basin, the Western Interior basin, the Ardmore basin, the Ft. Worth syncline, the Permian basin, the Rocky Mountain geosyncline, and the Cordilleran trough. These genetic areas and the Ouachita fold belt are the regions described.
The Pennsylvanian System in Michigan has been described in detail by W. A. Kelly (Mich. Geol. Survey, Pub. 40, part 2, p. 155-226, 1936). The section is truncated and consists of the Parma sandstone (below), the Saginaw group of cyclical formations, and the Grand River group, which contains red sandstones and gypsum. The Parma and Saginaw are Pottsvillian in age; possibly, Atokan and Desmoinesian. The Grand River, placed by some geologists in the Permian, is probably early Missourian.
The project for a special volume was initiated in 1953, at which time it was decided that the Springer Series was tobeconsidered as Pennsylvanian, the Wolfcamp and Admire-Council Grove-Chase, as Permian. Evidence has since accumulated that the Springer is Mississippian, that the Ouachita Jackfork and Stanley are Mississippian, that the Dunkard is, atleast in part, Pennsylvanian, and that the “Lyon series” and Wolfcamp formation might better be classed