Critical Evaluation of Middle and Late Pennsylvanian Cyclic Sedimentation and Architecture in the Southern Anadarko Basin, Oklahoma
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Pennsylvanian cyclothems have been studied in detail in the eastern interior of the United States, but few researchers have applied quantitative stratigraphic analysis to test the concept. The Anadarko Basin contains a thick Pennsylvanian section and thus provides an ideal opportunity to qualitatively and quantitatively assess the vertical heterogeneity of the Pennsylvanian sedimentary record, and to determine the degree of stratal order and cyclicity in the lithologic succession. Two cross sections of the Middle and Late Pennsylvanian were constructed, and two wells were selected for Markov chain analysis and recurrence-frequency analysis. The study interval was evaluated at four observational and interpretive levels: rock type, lithofacies, depositional environment, and sequence stratigraphy. Rock types form mostly rhythmic associations, with highest transitional probability occurring in shale being succeeded by radioactive shale. The highest degree of order and cyclicity occurred at the sequence stratigraphic level, although recurrence interval of surfaces and systems tracts varies based on the degree of development of condensed sections. Glacial eustasy in the short eccentricity band controlled lithologic ordering and cyclicity, while accelerating basin subsidence was the dominant mechanism of sediment accommodation.
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