Indonesia's coal is of foremost significance to the economy of Indonesia, as evidenced by the country´s steam coal exports, which rank fourth in the world. The Barito Basin on the island of Borneo is one of the largest coal-producing basins in Indonesia. Coal seams in the Barito Basin and the adjacent Asem Asem Basin are found in the Eocene Tanjung and the Miocene Warukin formations. Despite of the great economic significance, detailed knowledge of the factors controlling Eocene and Miocene peat-forming depositional environments is not yet available.
Therefore, the main aim of the present thesis is to determine the depositional environment of coal seams in the Tanjung and Warukin formations based on bulk coal data (ash yield, sulphur content) and organic petrological data from a total of 169 samples, and detailed organic geochemical data from sample sub-sets (~80 samples). In addition, the potential of Eocene and Miocene coals to generate liquid hydrocarbons also investigated.
Eocene coals are from the TAJ Pit-1D mine (from base to top: seams D, C, and B), while Miocene coals are from the Tutupan (from base to top: seams T110, T210 and T300) and Jumbang mines (seam BL1). The TAJ Pit-1D and the Tutupan mine are located in the Barito Basin, while the Jumbang mine is located in the Asem Asem Basin.
Based on vitrinite reflectance, the Eocene coals are more mature (~0.56 %Rr) than Miocene coals (Tutupan: ~0.39 %Rr; Jumbang: ~0.34 %Rr).
Ash yields and sulphur contents together with biomarker data show that Eocene coal in the Tanjung Formation accumulated in rheotropic to ombrotrophic mires. Miocene coal from the Warukin Formation at the Tutupan mine accumulated in a kerapah (inland) ombrotrophic mire (seams T110 and T210) or in a rheotropic-ombrotrophic mire (seam T300). Seam BL1 in the Jumbang mine coal in the Asem Asem basin of the Warukin Formation shows an ombrotrophic basinal (coastal) mire. Local brackish influence is indicated by elevated sulphur contents (<1.5 wt.%) in a lower bench of the BL1 seam (BL1L).
While all coals are characterized by high liptinite contents (14.9-49.1 vol.%), petrographic analysis shows remarkable differences in maceral composition between Eocene and Miocene coals. Leaf-derived macerals cutinite and fluorinite are more abundant in Eocene (~6.0 vol.%) than in Miocene coal (~4.5 vol.%), but rootlet-derived suberinite dominantes in Miocene coal (Miocene: ~2.6 vol.%; Eocene: ~0.5 vol.%). The high percentage of funginite reflects high fungal activity in Miocene and Eocene mires, both in ombrotrophic and rheotropic conditions. Resinite is precent in high amounts in all coal seams.
Organic geochemical parameters (e.g. the terrestrial-aquatic ratio) record a cyclic change of mire environments during deposition of the two lower seams in the Tutupan mine (T110 and T210), which is tentatively related to Milankovich-type cycles (earth's axial precession). The di-/ triperpenoids ratio shows that gymnosperms were largley absent in the Eocene peat-forming vegetation and occurred in very low (BL1 seam) or low amounts in Miocene mires.
Resinite in Miocene coals was produced, at least partly, by dammar resin producing dipterocarpaceae. As dipterocarpaceae were not present in the palm/fern-dominated Eocene vegetation, resinite in Eocene coals must have a different source.
Resinite contents strongly control the Hydrogen Index of the coal samples, which reaches 539 mgHC/gTOC in the BL1 seam. Resins are the primary source of heavy bitumen components with high oxygen content in Miocene and Eocene coals. Pyrolysis-GC data show that the type of oil produced by Miocene and Eocene coals differs in the content of long-chain (waxy) and naphthenic compounds and reflects the differences in resin-forming plants. These data suggest that waxy oil produced from Eocene Tanjung Formation reservoirs in the Barito Basin is derived from Eocene coal, while oil in the Miocene Warukin Formation is generated from Miocene coal.