It is the intent of this chapter to summarize the tectonic history of the North American Craton south of the Canadian border and north of the Mojave-Sonora megashear (see Anderson and Schmidt, 1983) of northern Mexico from the latest Proterozoic to the present. The tectonic evolution of cratons is most readily deciphered by analysis of the preserved cover rocks, their distributions and thickness, their petrologic characteristics and fossils, and the regional and interregional unconformities that punctuate the stratigraphic record.
The pattern of preserved distribution of cover strata of a particular age is a measure of the minimum area below depositional base level during the time in question. Such patterns, especially where marine and intertidal deposits are involved, and the extremes of distributions represented by erosional outliers, isolated fault blocks, and xenoliths in diatremes, are important to studies of ancient sea levels. The form and pattern of preserved thicknesses of strata are of greater utility in tectonic analysis than geographic distribution alone. The great majority of preserved cratonic cover rocks were deposited at or near depositional base level and thus within a few tens of meters of sea level. Dewatering and compaction are relatively rapid processes at cratonic time scales as continuing sedimentation imposes loads in excess of hydrostatic pressure; therefore, the thickness of strata representing a significant span of geologic time in the absence of evidence of monotonic deepening or shallowing is a meaningful approximation of the degree of subsidence of the depositional site relative to base level (and, by extension, relative to sea level).
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.