Vitrinite Reflectance of Lower Cretaceous Coal and Thermal Maturity of the Mowry Powder River Basin, Wyoming and Montana, USA Formation,
The Mowry Formation is a major source rock in the Powder River basin, and an understanding of its thermal maturity profile is critical for oil and gas exploration. Previous thermal maturity studies in the Albian/Early Cenomanian section of the Powder River Basin have been limited by small sample sizes, have drawn on vitrinite of questionable quality, or have relied on pseudo-measurements and/or inferior proxies to measured vitrinite reflectance. Consequently, the description of maturity those source rocks in the Powder River Basin has been incomplete. To help increase maturity data coverage in the basin, we provide new vitrinite reflectance measurements for over 50 locations. While not exhaustive, this dataset represents a large step forward in the understanding of thermal stress of the Lower Cretaceous section of the Powder River Basin of Wyoming and Montana. Thousands of feet of whole and slabbed cores were examined for specimens suitable for reflectance analysis. We analyzed coaly material collected from Muddy/Newcastle sandstones, where it typically occurs as local, thin, isolated, and often subtle partings of coal. This is desirable because the macerals from such occurrences are large enough to identify under the microscope; in contrast, the identities of macerals that occur in marine shales (e.g., Mowry, Skull Creek) are commonly ambiguous. A depth-maturity transform was applied to project the vitrinite reflectance to the Mowry. These new vitrinite reflectance data points have helped to both expand and refine the maturity profile of the Powder River Basin. The new data have revealed localized and previously undocumented high and low temperature anomalies.
AAPG Datapages/Search and Discovery Article #90357 ©2019 AAPG Rocky Mountain Section Meeting, Cheyenne, Wyoming, September 15-18, 2019