Paleoenvironment of brown coal from Sangatta Coal Mines, East Borneo, Indonesia

Organic geochemical studies on brown coal (lignite) located in Inul area were carried out, an area that is located in Sangatta coal mines, East Borneo, which is a part of the Balikpapan formation, aged as old as Middle Miocene to Late Miocene. Aliphatic hydrocarbon biomarker compounds which were identified by using the GC-MS analysis showed a presence of n-alkane (n-C₁₂-n-C₃₆) with bimodal distribution, which described the sources of organic compounds that originated from two different sources. These sources of organic compounds are phytoplankton, zooplankton and higher plants terrestrial. The Pr/Ph ratio of 1.3, the dominance of C₃₁-homohopane and a high ratio of Tm/Ts indicated that the process of peat depositions took place in an oxic environment. The existence of hopanoid contents showed that there were dominant activities of microbes and biolipids organic compounds such as bb-hopane and hop-17(21)-ene inside the samples of olean-12-ene and a-cadinene, which inidicated that they are organic compounds that came from higher plants such as Angiosperm and immature coals. The existence of 24-ethylcholestene and 5b-cholest-24-ene found in the coal samples, which are categorised as steranes, also indicated a low level of carbonization from the coal itself.