Organic geochemistry and petrography of Miocene ombrotrophic coals in the tropical Asem-Asem Basin (Kalimantan, Indonesia): Comparison to coeval subtropical coals in the Eastern Alps

Abstract The middle Miocene Warukin Formation in the Asem-Asem Basin (Kalimantan) contains a 20-m-thick coal seam (BL1) that is mined at Jumbang mine. seam, formed tropical peat, was studied to reconstruct peat-forming environment and compare its characteristics with those of similarly aged coals from Tutupan mine Barito ( ~ 15 Ma) subtropical Leoben Eastern Alps (Austria). Although all were ombrotrophic peatlands, comparison reveals differences biomarker maceral composition due different climate flora. study based on 22 three non–coal samples, each representing stratigraphic interval 0.2 1.0 m. samples analyzed for ash yield, carbon sulphur contents, composition. Organic geochemical parameters obtained eight obtain information vegetation. low-ash, low-sulphur BL1 deposited an basinal (coastal) mire. Locally increased contents lower bench BL1L demonstrate brackish influence near-shore environment. vegetation dominated by angiosperms including abundant dammar resin producing Dipterocarpaceae , while contribution gymnosperms negligible. seams T110 T210, which kerapah (inland) mires, have similar yields but contain higher, although still low, concentrations gymnosperm-derived diterpenoids. In addition, amounts cadinane-type biomarkers resinite suggest less dominant peats. While between Kalimantan are minor, major exist coal. These include significantly higher absence as wells leaf- rootlet-derived macerals. Apparently, fungal activity also reduced sub-tropical peat. Surprisingly, average amount oxidized plant remains