Pustaka Ilmiah Universitas Padjadjaran

Abstrak

Petrographycal Characteristic And Depositional Environment Of Sajau Coal Formation In Berau Basin, East Kalimantan

The coal maceral identification have been undertaken to determine the petrographic characteristics of the Sajau Formation coal in the Berau Basin, East Kalimantan and their depositional environment. The coal bearing Sajau Formation are represented by clays, carbonaceous clay, sandstones, sandy and lime clays and up to 13 coal seam. Mostly of coal is composed of fine- to coarse grained xylitic to detritic fragments with light- to dark-brown colour, mounted by dull groundmass. The Sajau coal belong to the lithotype category of matrix soft brown coals, immature stage and at low phase of coalification represents a transition from peat to lignite. The microscopic investigations revealed the coal is characterized by great maceral diversity, which dominated by huminite group, which constitute between 7–96.5 vol.% of the coal; following by liptinite macerals (mean 12,57 vol. %) and inertinite approximately 5.38 vol. %. The coal petrological properties, as well as the indices of the coal facies shown low TPI, low VI, high GI and high GWI, reveal that the coal was deposited under rheotrophic regime continuously wet limnic to limno-telmatic conditions with occasionally dry season. The coals are a result of deposition of either from the dominantly herbaceous vegetation, mixed with woody trees, forming swamp type paleomire. Presence of pyrite with framboidal structure indicated enhanced activity of sulphate-reducing bacteria, probably related to carbonate and sulphate-rich waters in the basin during peat formation. The varied palynology indicated most of coal were deposited in mire environment predominantly forest swamp. It can also be concluded that the Seam A – G coal was deposited in fluvitile to upper delta system and Seam H – M on lower delta plain environment.