Pennsylvanian Rocks of New England1
Several basins of probable Pennsylvanian rocks are downfolded or downfaulted into the older rocks of New England. The largest of these, and definitely of Pennsylvanian age, is the Narragansett basin of Rhode Island and Massachusetts. Smaller nearby or connected basins are the North Scituate basin, the Woonsocket basin, and the Norfolk basin. Pennsylvanian rocks seem to be present at Worcester, Massachusetts, also, but their extent and relations are not known. The rocks of the Boston basin may be Pennsylvanian or older.
The Narrangansett basin is a complex synclinal mass of clastic sedimentary rocks trending northward through eastern Rhode Island, and northeastward into Massachusetts. These rocks lie with marked discordance upon older metamorphic and igneous rocks of Precambrian? and Paleozoic age.
The rocks of the basin are chiefly gray and black shale, sandstone, conglomerate, and meta-anthracite. In the northwest part of the basin similar clastic rocks are red. All are of continental origin.
The lowermost Pennsylvanian formations are the Pondville and the Bellingham comglomerates. Above the Pondville, or lying directly upon basement, is the Rhode Island formation, which is by far the thickest and the most extensive of the Pennsylvanian formations. The uppermost Pennsylvanian formation is the Dighton conglomerate. The red Wamsutta formation in the northwest is equivalent in part to the Pondville and in part to the lower part of the Rhode Island formation. Basaltic and felsitic rocks are interbedded with the Wamsutta formation. The Purgatory conglomerate may be equivalent to the Dighton or it may be a conglomerate facies of the Rhode Island formation. The total thickness of Pennsylvanian rocks has been estimated to be 12,000 feet.
Fossils are mostly of plants, but also include insects and other animals; these suggest an Allegheny to Monongahela age. The sedimentary and structural features characterize the basin as an epieugeosyncline and also relate it to the limnic basins of Europe.
The rocks in the northern part of the basin are essentially unmetamorphosed. To the south and southwest they are progressively metamorphosed to garnet staurolite schist and coarse mica schist.
The chief mineral resource is meta-anthracite, which has been used only sparingly because of its high ash content and low combustible volatile content.
Figures & Tables
Pennsylvanian System in the United States
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