The thermal evolution of asphaltene-bound biomarkers from coals of different rank: A potential information resource during coal biodegradation

Abstract Asphaltenes from coals of different rank were oxidised using ruthenium tetroxide with the aim of investigating the changes in bound biomarker distributions as a function of increasing maturity. There is preliminary evidence for epimerization of bound hopanoid biomarkers from the biological configuration into the more stable geological configuration. The 22R↔22S epimerization in the bound 17α(H),21β(H) homohopanoids lags behind the corresponding isomerization in the maltenes between mean vitrinite reflectance ( R o ) values of ca. 0.5% to 0.7%. In general, the asphaltenes evolve towards a more thermally stable structure with decreasing amounts of aliphatic moieties and increasing amounts of lower molecular weight side chains relative to the higher molecular weight ones. Bound biomarkers in coal asphaltenes could be important sources of information particularly where free hydrocarbon biomarkers have been altered or completely lost to biodegradation which occurs during the generation of microbial gas.