RE-EVALUATION OF TASMANITES FLUORESCENCE SPECTROSCOPY AS A THERMAL PROXY IN THE DEVONIAN OHIO SHALE, HURON MEMBER, NORTHERN APPALACHIAN BASIN, USA

Fluorescence spectroscopy of sedimentary organic matter has been used since the 1960s as a thermal proxy for basin analysis. However, absence of measurement standardization has limited reproducibility and widespread application. As part of an ongoing standardization effort, our current work documents Tasmanites microfossil fluorescence properties in the Devonian Ohio Shale, Huron Member, northern Appalachian Basin, USA, using confocal laser scanning microscopy (CLSM). Building on previous work, we here expand our sample set, thermal range, and data collection protocols, to examine multiple fluorescence parameters in relation to traditional thermal proxies [solid bitumen reflectance (BR_o) and the programmed temperature pyrolysis parameters hydrogen index (HI), production index (PI) and T_max]. Tasmanites in nineteen organic-rich samples from immature to peak oil conditions (0.32-0.87% BR_o) were characterized by CLSM. Multiple fluorescence properties were considered, e.g., λ_max, Q_650/500, Q_max/500, among others, in relation to the traditional thermal proxies. In general, the results indicate poor to moderate correlation amongst the traditional thermal proxies, with linear correlation coefficients (R²) up to 0.66 (HI vs. BR_o), indicating difficulty with accurate analysis of this sample set by the traditional approaches. Thermal proxies from CLSM also showed poor to moderate correlation with traditional parameters, e.g., R² of 0.43 for λ_max vs. BR_o and 0.51 for Q_650/500 vs. BR_o, although correlations improved when diagenetic solid bitumen was removed from consideration. Similar R² values amongst traditional, and between traditional vs. CLSM thermal proxies, indicate fluorescence spectroscopy via CLSM is a valid approach to determination of thermal maturity in this sample set. Moreover, generally higher R² values between individual proxies determined via CLSM (e.g., 0.81 for λ_max vs. Q_650/500) potentially suggest greater accuracy within the dataset of values generated by CLSM. In addition to consideration of microfossil fluorescence data from CLSM as a thermal proxy, differences in fluorescence emission dependent on internal location within Tasmanites and its orientation, and the number of measurements collected will be evaluated in the context of measurement standardization.