Abstract

Vitrinite reflectance was measured on 40 grab samples from outcrops of the Woodford Shale (Upper Devonian-Lower Mississippian) collected near the Washita Valley fault in the Arbuckle Mountains in south-central Oklahoma. Samples are widely distributed over 40 km. Sample localities range from 60 m to 7.63 km normal to the Washita Valley fault trace. Vitrinite reflectance values were measured from standard kerogen concentrate pellets.

Mean random (% _e; plane-polarized light, stationary stage) reflectance values from low-gray vitrinite are 0.35-0.77% _e with a weighted average of 0.54% _e based on 14 to 98 measurements per sample with an average of 46.

Variation in vitrinite reflectance values is attributed to geologic history (e.g., tectonics), organic variables (e.g., geochemical gelification or vitrinitization of huminite; liptinite maceral and/or bitumen impregnation of vitrinite maceral), and analytical error (e.g., kerogen concentration process; number of reflectance measurements).

Implications of the data specific to the Arbuckle Mountains include: the Woodford Shale is immature to marginally mature with respect to the generation of oil; high heat flow associated with the rifting stage of the southern Oklahoma aulacogen was diminished by Early Ordovician; the Woodford Shale was never deeply buried; and frictional heating from the Washita Valley fault did not raise near-surface temperatures enough to be resolved by vitrinite reflectance measurements.