Zetra, Y.; Kusuma, H. S.; Riandra, F.; Sosrowidjojo, I. B.; Burhan, R. P. The Oxygenated Biomarker As an Indicator of Origin and Maturity of Miocene Brown Coal, Sangatta Coal Mines, East Kalimantan. Indonesian J. Geosci. 2018, 5, 107-116.