Dolomite fluorescence Red/Green quotient: A potential new thermal maturity indicator

• There is strong correlation between dolomite Red/Green Quotient (Q) and equivalent vitrinite reflectance (VRoeqv.).
• This method can be a potential thermal indicator in organic lean samples.
• The data suggest that temperature is possibly one of the controlling factors in dolomite fluorescence color variations.

Geochemical and petrographic effects of burial temperature on sedimentary organic matter have long been recognized and used as various thermal maturity indicators (i.e., pyrolysis Tmax, conodont and spore coloration, vitrinite/bitumen/zooclast reflectance), and fluorescent spectrometry (i.e., λmax and Red/Green quotient).This study investigates variations in the fluorescence color spectra (in the visible light spectrum) of authigenic dolomite over a wide range of thermal maturities. Two sample sets of calcareous shales/siltstones from Eastern and Western Canada, with sparse dolomite crystals in the rock matrix were selected to examine the relationship between thermal maturity and fluorescent properties of dolomite. Results from a range of thermal maturities, from the oil window to the dry gas window, reveal a strong positive correlation between the Red/Green quotient (Q) of dolomite crystals and equivalent vitrinite reflectance (VRoeqv.) values. This can be optically described as the color shift in fluorescent properties of dolomite with increasing maturity. This strong positive correlation between Q and thermal maturity can potentially be used as an alternative thermal maturity indicator in calcareous shales with low organic content. Compilation of worldwide data is required to understand the relationship trend and conversion equations among dolomite Q and other established thermal maturity indicators.

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