Exploring unconventional resources, particularly shale gas, necessitates comprehensive studies of shale rocks from reservoir to micro-fabrics to meet North America's energy demand. This study used clay mineralogy as an insight to the thermal maturity of the late Devonian-Mississippian Woodford Shale in Oklahoma.

The study analyzes the clay mineralogy of twelve outcrop samples from the Upper, Middle, and Lower Woodford at McAlister's Cemetery Quarry and Turner Falls Oklahoma. Illite, kaolinite, illite-smectite, quartz, and carbonate were identified as the main clay and non-clay minerals in the clay fractions of these shales. Diagenetic Illite-smectite (R1) was present in two samples, indicating a diagenetic origin for the illite. The R1 stacking order for I-S indicated that the transformation occurred within a burial temperature range of 100°C-130°C, corresponding to the immature to early generation of crude oil in these shales.