Anggayana, Komang, Agus Haris Widayat, and Sri Widodo. 2014. “Depositional Environment of the Sangkarewang Oil Shale, Ombilin Basin, Indonesia”. Journal of Engineering and Technological Sciences 46 (4):420-35. https://doi.org/10.5614/j.eng.technol.sci.2014.46.4.6.