Widespread epeirogeny in Late Mississippian time uplifted elements of the Transcontinental arch and bordering regions. Late Mississippian deposition in the Mid-Continent was confined to the Anadarko, Ardmore, and Arkoma basins where maximum thicknesses of 5,000, 3,000, and 2,000 ft of sediments (respectively) accumulated. Erosional processes accompanied regional uplift and continued after the cessation of Late Mississippian deposition. Consequently, over the Mid-Continent an erosional surface was etched on a terrane of predominately carbonate paleozoic sediments and igneous Precambrian rocks.

A maximum thickness of 4,000 ft of Morrowan (Early Pennsylvanian) sediments was deposited in the Anadarko basin. From there, northward to southwestern Nebraska, Morrowan beds onlap the Late Mississippian erosional surface and truncate rocks ranging in age from Late Mississippian to Precambrian. This depositional onlap accounts for the limits and much of the thinning of the Morrowan Series from the Anadarko basin toward the north and northeast. Morrowan rocks on the order of 3,000 ft and 5,000 ft in thickness were deposited in the Ardmore and Arkoma basins, respectively. In these basins Morrowan sediments lie on Late Mississippian rocks with minor unconformity.

The post-Morrowan, pre-Atokan Wichita orogeny brought the aligned Criner Hills-Amarillo-Wichita uplift-Cimarron arch into existence through strong vertical uplift accompanied by high-angle faulting with an estimated 10,000-15,000 ft of maximum vertical displacement. Concurrently a foredeep began to form in the Arkoma basin which would subside rapidly and receive phenomenal thicknesses of Atokan rocks--12,000 ft in the western Arkoma basin and 19,500 ft in the eastern part of the basin.

Meanwhile, an area on the western margin of this developing Atokan foredeep became mildly positive, possibly in response to the strong downwarping of the foredeep. From the Criner Hills this area trends northward across the Ardmore basin and the Arbuckle uplift, and turns northeastward toward the Ozark uplift, a distance of approximately 175 mi. This belt was about 125 mi wide and it encompassed the southeastern flank of the Anadarko basin and the northwestern flank of the Arkoma basin. Morrowan rocks were eroded from this positive area with the exception of those in the Ardmore basin, those on the southeastern flank of the Anadarko basin, and those on the northwestern margin of the Arkoma basin. These rocks exhibit an angular, unconformable relation with overlying Atokan or Desmoines an beds. Elsewhere in the Arkoma basin, and in the Anadarko basin and on its shelf area, the contact of Morrowan and Atokan rocks is nonangular and probably disconformable.

In western Oklahoma, western Kansas, and southwestern Nebraska, the depositional limit of Morrowan sediments is overstepped eastward by Atokan beds, and the depositional limit of Atokan beds is in turn overstepped eastward by Desmoinesian rocks. The uninterrupted advance of these sediments eastward toward and onto the Nemaha ridge and the Cambridge arch-Central Kansas uplift is evidence that the age of these features is pre-Morrowan (Late Mississippian) rather than post-Morrowan, pre-Atokan (Wichita orogeny) as often claimed. In addition Atokan and Desmoinesian rocks of these areas do not exhibit lateral facies changes involving the influx of coarse clastic sediments

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from the east that would be expected if the Nemaha ridge and the Cambridge arch-Central Kansas uplift experienced post-Morrowan uplift.

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