PALEOCLIMATIC AND TECTONIC CONTROL ON THE ACCUMULATION OF NORTH-AMERICAN CRATONIC SEDIMENT

Variation in accumulation rate as a function of depositional latitude has been determined for North American limestone, dolostone, sandstone , gray-black shale, red shale, and evaporite rocks from tabulations by Ronov and coworkers, from data in lexicons of United States and Canad ian stratigraphy, and from isopach and tithofacies maps published in 1 975 by Cook and Bally. Phanerozoic sediment is similar to that on othe r continents, consisting of 63% terrigenous clastic facies (23% sandst one; 40% shale), 36% carbonate, and 1% chert, evaporite, and other min or rock types. Latitudinal variation in accumulation rate is influence d primarily by past positions of foreland and intracratonic basins. Ad ditional variation related to paleoclimate is recorded as strong depen dence of limestone, dolostone, red shale, and evaporite deposition on latitudes of accumulation, a relation reflecting the importance of amb ient temperature and meteoric precipitation on the formation of variou s authigenic phases. Poleward increase in dolostone/total carbonate ra tio in both hemispheres implicates the importance of syndepositional d iagenesis in the formation of most dolostone sequences. The ratio of s andstone/total terrigenous clastic sediment exhibits little variation with latitude, a constancy indicating that most sand and mud is derive d from older sediment rather than from the weathering of crystalline r ock. As a result, terrigenous lithofacies record little climatic influ ence in the proportional delivery of mechanically versus chemically de rived weathering products to basins of accumulation.