This volume is devoted to the Phanerozoic sedimentary strata covering the largely, but by no means exclusively, crystalline rocks of that part of the North American craton in the United States (exclusive of Alaska). Readers will note that this opening sentence implies constraints of space, time, and lithology on the subject matter dealt with here. The geographic qualifications derive from the organization structure of The Decade of North American Geology, and it only remains to point out that cratonic rocks and their histories are not delimited by national borders— nor by continental margins where these represent the lines of fission of former megacontinents. The qualifications of age and rock type are discussed on later pages, but first it is necessary to raise the question: “What is a craton?” The term craton stems from the same Greek root as autocrat and bureaucrat and was applied geologically by Hans Stille (1936, 1941) in the sense of a strong, unyielding buckler or shield. In Stille’s time of pre-plate tectonic innocence, he envisaged oceanic as well as continental cratons, the two terranes separated by orthogeosynclines, these being the lineal descendants of the 19th century “geosynclinals” of Dana and Hall. Further, Stille divided orthogeosynclines into eugeosynclines (“true geosynclines”), volcanic-dominated trends outboard with reference to continents, and miogeosynclines (“lesser geosynclines”), inboard nonvolcanic belts. Thus, continental cratons, by original definition, were bounded at the inboard margins of miogeosynclines. Stille advanced these ideas late in his career, and continued development was inhibited by overriding political and military circumstances.
Figures & Tables
Sedimentary Cover—North American Craton
The “sedimentary cover” refers to the stratified rocks of youngest Proterozoic and Phanerozoic age that rest upon the largely crystalline basement rocks of the continental interior. The early chapters of the volume present data and interpretations of the geophysics of the craton and summarize, with sequential maps, the tectonic evolution of the craton. The main body of the text and accompanying plates and figures present the stratigraphy, structural history, and economic geology of specific sedimentary basins (e.g., Appalachian basin) and regions (e.g., Rocky Mountains). The volume concludes with a summary chapter in which the currently popular theories of cratonal tectonics are discussed and the unresolved questions are identified.