56-7 High-Resolution Sequence Stratigraphy and Facies Architecture of a Mixed Siliciclastic–Carbonate System: Strawn Group, Pennsylvanian of the Eastern Shelf of the Permian Basin, Texas

Abstract:

Mixed siliciclastic–carbonate systems display pronounced vertical and lateral heterogeneity from bed to basin scale. The Middle–Upper Pennsylvanian (Desmoinesian–lower Missourian) Strawn Group is an important conventional hydrocarbon reservoir on the Eastern Shelf of the Permian Basin, Texas. However, predicting facies distribution remains challenging because of its heterogeneous stratigraphic architecture and the absence of a high-resolution subsurface sequence stratigraphic framework. This complexity reflects both the mixed nature of the depositional system and cyclic sedimentation controlled by autogenic processes, including basin morphology, carbonate buildup development, and deltaic sediment supply, together with allogenic controls such as tectonic subsidence, high-frequency glacioeustatic fluctuations, and variations in sediment influx. This study establishes a stratigraphic framework for the upper Strawn Group in the KMA Field (Wichita County, Texas), where deposition was influenced by repeated interaction between the Haskell Delta–Knox–Baylor trough system and the Red River carbonate platform. The dataset integrates facies analysis of 880 ft (270 m) of core from seven wells with wireline-log correlation, ichnology, and whole-rock XRF geochemistry to characterize facies architecture, high-resolution sequence stratigraphy, and evaluate controls on mixed siliciclastic–carbonate deposition during the Late Paleozoic Ice Age glacioeustatic regime. Core description identified siliciclastic, carbonate, and mixed lithofacies together with 20 ichnotaxa. The succession contains eight to nine fourth- to fifth-order depositional sequences, approximately 11–70 ft (3–21 m) thick. Sequence boundaries are recognized by subaerial exposure features, including microkarst, paleosols, pedogenic alteration, and intertidal exposure surfaces, as well as firmgrounds assigned to the Glossifungites ichnofacies, intraclast lags, and colonization surfaces. Transgressive surfaces are commonly expressed by carbonate-cemented sandstone firmgrounds. Many sequence boundaries cut across lithostratigraphic contacts, emphasizing substantial lateral facies variability. Mixed reservoir facies, including ooid grainstones, skeletal–ooid grainstones, sandstones, and crinoid-rich sandstones, exhibit strong vertical and lateral heterogeneity governed by grain composition, sorting, cementation, and bioturbation. These deposits accumulated within a tide-influenced system of migrating mouth bars, tidal conduits, and ooid shoals that promoted repeated reworking and interfingering of siliciclastic and carbonate sediments. Continued integration of petrographic and biostratigraphic (fusulinid and conodont) data will refine depositional ages, improve recognition of key stratigraphic surfaces, and demonstrate key elements for correlating high-frequency depositional sequences between siliciclastic-dominated and carbonate-dominated domains in mixed systems

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