Investigation of the maturation effects on biomarker distributions in bituminous coals

•Changes in n-alkane, terpane, and sterane indices show the combined effects of maturation and depositional environment.•Pr/Ph, Pr/n-C17, and Ph/n-C18 ratios record the influence of depositional environment.•Epimerization reactions of hopanes and steranes are affected by thermal maturity and origin.•Degree of demethylation consistently depends on rank but is higher in Da Baoding coals compared to Huainan coals.•Individual PACs indices show variable trends with maturity and are sensitive to organofacies.