Historical Geology of the Period

The Carboniferous period was marked by vast, coal-forming swamps (see also bog) and a succession of changes in the earth's surface that, continuing into the Permian period, ended the Paleozoic era. The Carboniferous is often split into two divisions, the Mississippian and the Pennsylvanian; in the United States the break in the geologic sequence is so sharp that each division is commonly considered an independent period.

The Lower Carboniferous Period

In the Lower Carboniferous, or Mississippian, period, the submersion—on several occasions—of the interior of North America under shallow seas resulted in the formation of limestone, shale, and sandstone. In the Appalachian region, especially in Pennsylvania, great deposits of sandstone and shale were laid down by the erosion products from the eastern coastal highlands. In the far west the Rocky Mt. region was covered by shallow seas that deposited the Madison and Redwall limestones of the Grand Canyon.

The Lower Carboniferous in Europe was a period of submergence and great volcanic activity. E of the Rhine, shales, sandstones, and conglomerates were deposited; and in Russia, the Coal Measures formed. The close of the Lower Carboniferous was marked by mountain building in New Brunswick, Nova Scotia, the S Appalachian region, the SW United States, and Europe.

The Upper Carboniferous Period

In the Upper Carboniferous, or Pennsylvanian, period, there was at least one great submergence. In the E United States great deltas of sediments, now represented by the Pottsville conglomerate, were formed during the early Pennsylvanian. In Kansas, Nebraska, Arkansas, and Texas, the Pennsylvanian beds are chiefly shale, sandstone, and coal; over the Cordilleran (Rocky Mountain) region, marine limestone, with little coal; on the Pacific coast from California to Alaska, limestone and shale. The sea level also oscillated during the period and caused the formation of great marshes with extensive vegetation that was later transformed into coal, with Pennsylvanian strata containing the largest U.S. coal deposits. The Pennsylvanian coal fields of North America include the anthracite field of E Pennsylvania; the Appalachian field, from Pennsylvania to Alabama; the Michigan field; the eastern interior field, in Indiana, Illinois, and Kentucky; the western interior and southwestern field, stretching from Iowa to Texas; the Rhode Island field; and the Acadian field of SE Canada.

In the Upper Carboniferous of Western Europe, the Millstone Grit (the equivalent to the Pottsville conglomerate) is followed by the Coal Measures, which include the Welsh, English, Belgian, Westphalian, and Saar Basin fields. In the Mediterranean region and parts of Asia, the Upper Carboniferous environment resembled that of W North America.

The Upper Carboniferous was a period of marked disturbances caused by collisions of crustal plates. Gondwanaland, the supercontinent containing the continents of Africa and S America, had formed; Euramerica, part of Europe and N America, had fused into a continent to the north; and Angara, today's Asia, was also to the north of Gondwanaland. In Europe the Paleozoic Alps were thrust up; in Asia, the Altai and the Tian Shan; in North America, the Arbuckle and Wichita mts. and the ancestral S Rockies. The Indian peninsula became an active site of deposition; in the Himalayan geosyncline and much of China, mountain building was dominant. Crustal movements in the Andean geosyncline of South America affected the pattern of sedimentation over much of the continent.