Major tectonic features of the central mid-continent area are outlined and their relation to present thickness and distribution of pre-Des Moinesian strata is discussed. Cambro-Ordovician "Arbuckle group" thickens southward from zero along the Nemaha and central Kansas uplifts to nearly 7,000 ft. in southern Oklahoma. The Simpson, with maximum thickness of 3,000 ft. in southern Oklahoma, thins northward by convergence and overlap of younger units to extinction in northwestern Kansas. Viola-Fernvale thins northward from 1,500 ft. in Anadarko basin to 200 ft. in southern Kansas, and thickens to 400 ft. in Salina basin. The Sylvan-Maquoketa is limited to 2 areas, one in Oklahoma, the second in northeastern Kansas. Maximum thickness in Oklahoma is 600 ft., in Kansas about 150 ft. Distribution of Hunton resembles that of Sylvan; maximum thickness exceeds 1,5OO ft. in Oklahoma and 650 ft. in Forest City basin. Woodford-Chattanooga lies with regional unconformity on units from Precambrian through Hunton. A 600-ft. maximum is postulated for the Anadarko basin; 50-100 ft. covers eastern Oklahoma and Kansas. Mississippian limestones are widespread with 4,000 ft. in Anadarko basin, 1,600 ft. in Hugoton embayment, and zero in northern Kansas. Lower Pennsylvanian Springer is limited to a narrow belt in Anadarko and McAlester basins with maximum of 4,000 ft. near Ardmore. Overlying Morrow overlaps Springer, reaching maximum of 1,500 ft. in McAlester basin and more than 4,300 ft. in Anadarko basin. Distribution of Atoka resembles that of Morrow with 5,000 ft. maximum in the Anadarko basin and approximately 8,000 ft. in the McAlester basin. Widespread Des Moinesian sediments rest with marked unconformity on Atokan and older rocks. Epeirogenic movements were mild throughout early Paleozoic with geosynclinal development in southern Oklahoma. Eustatic changes produced major unconformities and offlap-overlap relations. Strong warping occurred in post-Hunton, pre-Chattanooga time. Major orogenic movements are post-Mississippian, pre-Des Moinesian with maximum movement in late Morrowan. Final structural development took place in late Cretaceous and early Tertiary. Throughout much of Paleozoic time, the axis of maximum deposition in southern Oklahoma paralleled the Wichita-Amarillo trend in the "Wichita embayment."

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