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Determining Paleoenvironmental Conditions of Late-Cambrian to Pennsylvanian Sediments From the Central Kansas Uplift Using Trace Element Analysis


Trace element analysis can differentiate subsurface sediments where conventional methods may be inadequate. Drill cuttings were obtained from five wells located within the Central Kansas Uplift (CKU), which is known to contain numerous hydrocarbon bearing formations, notably the Lansing-Kansas City, Cherokee Sand, and Arbuckle Group. The sample intervals studied are lithologically dominated by carbonates and contain interbedded shales and silts and some sandstones. Cyclical deposition of sediments during the Late-Cambrian to Pennsylvanian period resulted in lithologically similar deposits, therefore geochemical analysis can provide additional resolution of the stratigraphy of the interval where standard methods cannot. The objectives of this study were to identify and characterize the major facies, describe paleodepositional conditions, and establish a chemostratigraphic succession of the interval. Major and trace element content was analyzed using X-Ray Fluorescence. Results of elemental analysis of the interval showed that the defining major elements include Ca, Mg, and Si, and the minor elements of interest include Fe, Cu, Ni, Zn, and Mo. Other significant trace elements measured include Ti, K, Th, P, and S. Elevated Cu and Ni content is characteristic of high OM fluxes and is observed within the carbonate reservoir intervals, which include the Lansing-Kansas City and Arbuckle units. Increases in Zn and Mo are characteristic of sulfate-reducing conditions during deposition and anoxic or euxinic waters. Elevated Zn and Mo were also observed in the carbonate reservoir intervals. Elevated iron content was found within reservoir intervals and at the stratigraphic contact of the overlying unit. Elevated iron concentrations can be indicative of microbially mediated hydrocarbon degradation, as has been shown in numerous studies. Observations and previous studies have found “dead” oil (a degraded, immobile oil that cannot be produced) within wells from this study area. High iron concentrations support the presence microbial degradation within the reservoir units. Conditions of microbial degradation may be enhanced by paleoenvironmental conditions which support the proliferation of anoxic microbial organisms, as indicated by elevated Mo.