Geochemistry of aliphatic-rich coals in the Cooper Basin, Australia and Taranaki Basin, New Zealand: implications for the occurrence of potentially oil-generative coals

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Abstract
Although the concentration of long-chain aliphatic constituents is a primary determinant of the oil generation potential of coals, the factors which govern their occurrence in different coals are poorly understood. In this study, Permian coals from the Cooper Basin, Australia, and the Eocene coals from the Taranaki Basin, New Zealand, were compared to determine these factors. The Taranaki Basin coals were deposited in temperate, fluvial-deltaic environments. HI values range from 236–365. Extracts have high pristane/phytane ratios and variable abundances of oleanane and other non-hopanoid terpanes. The extracts and pyrolysates contain high relative concentrations of aliphatic groups > n -C 20 . These data imply that much of this aliphatic carbon is derived directly from higher plant material. The Cooper Basin coals were deposited in high latitude bogs and contain 40–70 0nertinite. The coals have been severely degraded. Pristane/phytane ratios are low (2.15–6), but HIs are moderate (up to 243 mg g −1 OC). The extracts and pyrolysates both contain high relative concentrations of aliphatic groups; however, the distributions are different from higher plant-derived material. These data imply the bulk of the aliphatic carbon in these coals is derived from microbial biomass (both bacterial and fungal degradation products and algal input). These results show that long-chain aliphatic groups in coals can be derived directly from the higher plant material, from microbial activity in the depositional environment, or from a combination of the two.