Early in the Decade of North American Geology, a planning document was assembled and published as Perspectives in Regional Geological Synthesis (Palmer, 1982). This collage of diverse contributions included an item devoted to the North American Craton in the United States that closed with several “unresolved questions” (Sloss, 1982a, p. 39):
What is the significance of episodic emergences of the craton responsible for the sequence-bounding unconformities? The natural corollary is the meaning of the several episodes of cratonic submergence. In both cases the magnitude of vertical movement far exceeds that which could be ascribed to any combination of eustatics and loading-unloading by sediment and water. Is there a demonstrable correlation with plate interactions?
Why is deformation of the craton sometimes dominated by flexure, at other times by fracture? When the fractural mode is operating, is the continental crust in extension or compression? That is, are the downdropped basins and block uplifts characteristic of Absaroka I deposition produced by thrusts of Wind River type or are they representative of distinctly different stress/strain patterns? In either case, what are the driving forces?
Is the tectonic mode prevailing on the craton during Sauk deposition as distinct from the younger Phanerozoic as is suggested here? If so, does this indicate that there are irreversible secular changes in cratonic behavior as a product of evolving crustal thickness, or rheologic change, or whatever?
Why do sedimentary basins and intervening arches remain fixed in positions for hundreds of millions of years? Is it demonstrable that basins are
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.