Microfacies and Depositional Environment of Senakin Coal, Tanjung Formation, South Borneo, Indonesia

The Tanjung Formation in South Borneo Province, Indonesia, is well-known as an extensive Eocene coal-bearing formation and is economically significant. Coal samples were collected from an open pit mine in Senakin area to study its characteristics. A combination of detailed petrographic composition and geochemical analysis has been used to reconstruct microfacies and depositional environment of the Senakin coal precursor. According to petrographic analysis, the Senakin coal is dominated by vitrinite (62â��72 vol%), with less abundant liptinite (20â��28 vol%) and inertinite (3.3â��6.5 vol%). Mineral matter is rare (2.3â��7.8% vol%) of which pyrite is the most abundant mineral. Resembling the modern tropical peats in Indonesia, this section can be derived from hemic to fibric peat types in which the sapric layer is observed at the upper part of the peat. The vertical sequence of maceral abundance in the coal seam shows that development starts from a topogenous to ombrogenous mire and back to a topogenous mire. In line with its variation of coal facies, high Tissue Preservation Index (TPI) and Gelification Index (GI) values suggest that coal samples were derived from woody plants and lower amounts of herbaceous plants. The telmatic setting was influenced by marine influx, which can be distinguished by the presence of framboidal-syngenetic pyrite. © 2023, The Author(s), under exclusive license to Springer Nature Switzerland AG.