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Integrated Diagenetic and Paleomagnetic Study of the Mississippian Limestone, North Central Oklahoma

Abstract

The Mississippian Limestone in Oklahoma is a petroleum exploration target in northern Oklahoma and southern Kansas, and diagenetic events are a significant factor in controlling reservoir quality. In this study, petrographic, geochemical, and paleomagnetic data were used to determine the origin and timing of diagenetic events in five unoriented cores from northern Oklahoma. Petrographic analysis indicates a complex paragenetic sequence. Early diagenetic events include silica precipitation and dolomitization. Middle diagenetic events include brecciation, silica dissolution, fracturing, dolomitization, and silica precipitation, and are interpreted as resulting from subaerial exposure. Late diagenetic features, attributed to burial and hydrothermal fluid flow, include stylolitization, dissolution, and precipitation of megaquartz, calcite, sphalerite, pyrite, and baroque dolomite. The 87Sr/86Sr isotopic data for the limestone range from co-eval to radiogenic. Samples from the two cores which are located to the north and closer to the Tri-State MVT district contain the most elevated values. Thermal demagnetization removes a low temperature viscous remanent magnetization (VRM) and a chemical remanent magnetization (CRM) from 240 - 500°C that is interpreted to reside in magnetite. Rock magnetic studies confirm the magnetite interpretation. An attempt was made to orient the cores using the VRM but it resulted in a 300° streaked distribution of declinations with shallow inclinations, and as a result, was not successful. The inclinations of the CRM in the five cores are similar (mean = - 2.5°, α95 = 1.4°, n = 270). The age of the CRM was determined by comparing the measured inclinations with the expected inclinations for the study area. This analysis indicates that the CRM was acquired in the Permian. This is consistent with the dates for mineralization in the nearby Tri-State MVT deposit and interpretations in other studies which hypothesize a Permian hydrothermal system. Burial remagnetization mechanisms such as maturation of organic matter or clay diagenesis are not likely because low organic matter and clay content. The age of the CRM and the evidence for hydrothermal alteration suggest that CRM acquisition was caused by external hydrothermal fluids.