Abstract

The Cherokee basin in southeastern Kansas contains a stratigraphic section consisting mostly of Permian-Pennsylvanian alternating clastics and thin carbonates overlying carbonates of Mississippian and Cambrian-Ordovician age on a Precambrian crystalline basement. Based on a conceptual model of events of deposition, nondeposition, and erosion, a burial history model for (1) noncompaction, and a series of models for (2) compaction are computed for a borehole location in the south-central part of the basin. The models are coupled with the calculation of nonsteady-state geothermal conditions. Maximum temperatures during basin evolution of about 70 degrees C at the base of the organic-rich Pennsylvanian are predicted by our models, assuming pure heat conduction and a heat flow from the basement of 60 mW/m 2 . The maturation of organic matter as indicated by three different vitrinite reflectance (R o ) models is on the order of 0.3-0.5% R o for Pennsylvanian rocks and 0.6% R o for the Devonian-Mississippian Chattanooga Shale. Vitrinite reflectance was measured on subsurface samples from three wells. The measured values correlate in the upper part of the sequence with modeled data, but diverge slightly in the Lower Pennsylvanian and Chattanooga Shale. The differences in maturation may be a result of differing local geological conditions within the basin. The relatively high R o -depth gradient observed in one borehole may be explained by conditions in the Teeter oil field, which is a typical plains-type anticline that has been affected by fluid flow through vertical faults. Higher R o values correlate positively with the grade of sulfide mineralization in the sediment, which may be a hint of fluid impact. The high R o values relative to the shallow depth of the Mississippian and the Chattanooga Shale in the Brown well are on the order of R o values modeled for the same stratigraphic units at present-day greater depths and may reflect uplift of the Ozark dome, located farther east, affecting the eastern side of the Cherokee basin.

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