Regional Variations in Pennsylvanian Lithology

Recurring similar sequences of strata characterize the Pennsylvanian in most regions in the United States. The Illinois type of sequence has been called the "cyclothem" and the Kansas type the "mega-cyclothem." There are many variations in the pattern of these rhythmic successions, and within the Pennsylvanian areas of the United States they include representatives of nearly all kinds of sedimentary rocks. Thirty-six representative Pennsylvanian successions, two from the Mississippian, and one from the Lower Permian are graphically represented. The rhythmic successions may record diastrophic or climatic fluctuations of continent-wide extent, and the varied type of successions composing them may result from locally variable features of environment, topography, climate, or the configuration of land and sea. Data sheets to record quantitative lithologic variations in the Pennsylvanian and its principal subdivisions have been devised. From these sheets, prepared on the basis of one for each county, various types of lithologic-variation maps and isopach maps can be prepared.