Pliocene age lignites from Lower Sajau seam, from borehole in Berau Basin, Northeast Kalimantan, Indonesia were investigated with respect to organic geochemistry by HPLC, GC and GC/MS. The analysis was conducted to drilling sequence of Kasai Coal Field, Berau Basin which has been applied to identify organic sources and maturity of organic matter. The result of normalized yields of the soluble organic matter (SOM) data indicates saturated and aromatic proportion of hydrocarbon are very low (under 10%), this was reflecting that lignite coal is still in immature stage. Moreover, biomarker hydrocarbon such as diterpenoids was not found from the sample that indicates absence of gymnosperm precursor in the paleo-peat. In contrast, there was great abundance of terpenoid biomarkers including lupane and oleanane showing domination of angiosperms indicate that angiosperm was dominated vegetation source. There also hopanoid biomarkers explaining acidic depositional environment in coal formation and microbes-affected conditions in peat formation process. Ratio of Tm/Ts shows paleomire where ratios value of Tm/Ts is in range of oxide condition.
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