Microfacies and Paleomire Reconstruction of Coal in the Tanjung Formation, Barito Basin, Kandangan Area, South Kalimantan

Abstract

The occurrence of the Tanjung Formation as a coal-bearing formation that has thick coals and is laterally distributed along in Barito Basin causes it to be well-known as one of the biggest coal-producing basins in Indonesia. The genesis of Eocene coal formed in terrestrial depositional environment influenced by freshwater and marine transgression is the uniqueness of this coal and interesting to examine maceral’s characteristic and its microfacies, and the evolution of paleomire seam AGM-B3, AGM-B4, AGM-B5, and AGM-B6 in Kandangan area by organic petrography’s analysis and coal’s chemical analysis. The result of subbituminous coal’s petrography show vitrinite is the most abundant maceral ranging from 56,.6% - 80.36% vol, liptinite (15.27% - 39.45% vol), inertinite (0.55% - 15.18% vol), and mineral matter (0.18% - 4.36% vol) which is dominated by pyrite. Based on maceral’s assemblages, coal’s microfacies divided into four groups are (1) telovitrinite-rich group, (2) detrovitrinite-rich group, (3) telovitrinite-liptinite-rich group, (4) inertinite-rich group. The basal section of seam AGM-B6 is characterized by detrovitrinite-rich group while seam AGM-B3, AGM-B4, and AGM-B5 are characterized by telovitrinite-liptinite-rich group. The middle section only represented the inertinite-rich group in seam AGM-B3, and the top section of the coal seams, except AGM-B6, is typically represented by the telovitrinite-rich group. The vertical profile of paleomire evolution shows a repetition of topogenous mire changing into ombrogenous mire and then back to topogenous mire. The paleomire type developed includes wet forest swamp, forested peatlands, and intermittently dry forested swamp and the environmental conditions are telmatic. The correlation between paleomire’s type and coal maceral’s abundance in the Kandangan area reflects that the type of vegetation from woody plants that underwent high degradation, moderate gelification, and intensive oxidation processes triggered by a short dry season.