Widayat, Agus Haris, Komang Anggayana, and Isra Khoiri. 2015. “Precipitation of Calcite During the Deposition of Paleogene Sangkarewang Oil Shale, Ombilin Basin, West Sumatra, Indonesia”. Indonesian Journal on Geoscience 2 (3):185-97. https://doi.org/10.17014/ijog.2.3.185-197.