Vitrinite Reflectance Suppression Revisited

This study aims to investigate the phenomenon of vitrinite reflectance (VRo) suppression in the Devonian-Lower Mississippian New Albany Shale in the Illinois Basin, USA. Thirty-two samples from Indiana and Illinois were analyzed using organic petrography (vitrinite reflectance measurements and maceral analyses) and organic geochemistry (Rock-Eval and biomarkers) techniques. Based on VRo variations, we suggest that vitrinite reflectance suppression occurs in both locations. This conclusion is supported by vitrinite reflectance equivalent values obtained from biomarker ratios. The study documents strong negative relationships between alginite and alginite + solid bitumen content and measured VRo values, suggesting that the contribution of these macerals can be used to determine the correction to measured VRo values. No relationship between VRo and Rock-Eval Tmax was revealed. Still, a positive correlation was found between alginite and alginite + solid bitumen content versus the hydrogen index (HI), further emphasizing the role of maceral composition in assessing the thermal maturity and hydrocarbon generation potential of the New Albany Shale.