In southeastern Kansas and northeastern Oklahoma rocks of the Cherokee Group (Desmoinesian, Middle Pennsylvanian) were deposited across the Cherokee platform--a part of the Mid-Continent craton. These sediments are a clastic sequence of the coal-cycle association. Cyclothems composed of several thin, persistent lithosomes characterize the section. The sedimentary sequence indicates a depositional model of fluctuating conditions which, from a tectono-environmental viewpoint, may be regarded as an unstable shelf dominated by nonmarine and shallow-marine environments (e.g., fluvial, swamp, lagoonal, and littoral).

The Cherokee platform is flanked by other Middle Pennsylvanian tectonic features. The mildly positive Ozark dome on the east, the active Nemaha ridge on the west, and the cratonic shelf area on the north affected significantly the depositional history of the platform. The most important influence was the adjacent Arkoma basin on the south. The Arkoma basin was an actively subsiding marginal basin between the craton and the orogenic Ouachita system. Rocks of Desmoinesian age in the Arkoma basin are a clastic wedge whose principal source area was the Ouachita orogenic region. Rapid sedimentation in the Arkoma basin kept pace with subsidence. As a result, the basin floor generally was close to sea level. Hence, most of the clastic wedge consists of coarse terrigenous clastic strata, shal , and coal, and was deposited under nonmarine conditions. Desmoinesian strata of the clastic wedge are partly continuous with Cherokee platform rocks. Much of the detritus deposited on the platform (including carbonaceous matter) was derived from the south and transported across the nonmarine Arkoma basin. Although the strandline fluctuated widely, its average position was near the craton-marginal basin hingeline.

Organic geochemical aspects of the Cherokee platform sediments were influenced by the tectono-environmental setting. This influence is displayed by regional contour maps of organic geochemical properties. For example, contour maps of organic carbon, hydrocarbon, and carbon-isotope data display regional variations related to the clastic wedge on the south and more persistent marine depocenters on the shelf. Most regional geochemical variations of the Cherokee section can be related to variations in the proportion of the different rock types making up the section. However, some rock types display smaller but significant regional organic geochemical variations, which also appear to be a response to differences in the tectono-environmental setting across the platform. Perhaps the most imp rtant single aspect that controlled the organic composition of these sediments was the interplay between marine (in situ) and terrestrial (detrital) organic sources. Rate of sedimentation, rate of burial, and postdepositional effects were less important in causing observed variations.

The geochemical results support the "shelf principle" of petroleum origin. Specifically, the regional organic geochemical contour maps suggest a rational explanation

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for the distribution and compositional variations of the petroleum across the platform. In addition, material balance calculations of oil-in-place versus indigenous sediment hydrocarbons provide a quantitative insight into petroleum migration problems.

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