Depositional environment and hydrocarbon source potential of the Permian Gondwana coals from the Barapukuria Basin, Northwest Bangladesh

Barapukuria Coal Basin is situated in Dinajpur district of the northwestern part of Bangladesh. A total of eight coal samples have been collected from two different locations of the basin and analyzed using organic geochemical and organic petrological methods.The extracted organic matter of the studied samples is a mixture of Type-III and Type-II kerogen as evaluated by the source rock analyzer (SRA) and PyGC pyrograms. The measured total organic carbon (TOC) ranges from 61 to 74 wt. % and the recovered extractable organic matter (EOM) varies from 27,561 to 41,389 ppm. These results suggest that the coals are ranked as good quality source rock. The hydrocarbon yield has been calculated which is also high and it ranges from 12,192 to 20,799 ppm. The organic matter is thermally mature for hydrocarbon generation considering their Tmax and measured mean vitrinite reflectance values of 431 to 435 °C and 0.72 to 0.81%Ro respectively. The hopane 22S/(22S + 22R), moretane/hopane ratio and sterane parameters are also in support of these thermal maturity assessment.The maceral composition is dominated by the inertinite group with significant amounts of vitrinite and liptinite. The more dominant odd carbon numbered n-alkanes, high Pr/Ph ratio (4–8), high Tm/Ts ratio (13–18), predominant sterane C29 (i.e., C29 > C28 > C27) and Pr/nC17 – Ph/nC18 values, GI vs TPI cross-plot and dominance of inertinite macerals group clearly demonstrate that the organic matter has been derived from terrestrial inputs and the condition of deposition was oxic (i.e., dry forest swamp) which was also supported by the absence of alginite. It is most likely that the coals were deposited within a peat-swamp flood basin environmental setting.

► The organic matter is a mixture of Type-III and Type-II kerogen. ► The hydrocarbon yield is very high and its source potential is good. ► The organic matter is thermally mature for hydrocarbon generation. ► The maceral is dominated by inertinite group followed by vitrinite and liptinite. ► The organic matter derived from terrestrial inputs while condition of deposition was oxic.