ABSTRACT: Coalification of Indonesian coal

Daulay, Bukin¹, and Alan Cook²
(1) MTRDC - MME, Bandung, Indonesia 
(2) Keiraville Konsultant, Australia

The important coal bearing sequences in Indonesia Tertiary basins are Paleogene (Eocene and Oligocene) intramontane and continental margin and Neogene back-deep, deltaic and continental margin basins. Paleogene coals are generally higher in rank compared with Neogene coals. In outcrop, Paleogene coals are bituminous in rank (0.60 - 0.80% Rvmax) and most, but not all, Neogene coals are sub-bituminous in rank (<0.5% Rvmax). However, in some areas, the Neogene coals are bituminous.

The coal bearing basins are young geologically, so the existence of higher rank coals near the present land surface depends upon uplift or the presence of igneous intrusions. At Ombilin (West Sumatera) for example, uplift has occurred giving higher rank coals in outcrop. Due to igneous intrusions, some Miocene coals from Bukit Asam (South Sumatera) are bituminous to anthracitic in rank (0.60 - 2.00% Rvmax). Very high lateral and vertical rank gradients occur in this area.

Some basins in Kalimantan have high vertical rank gradients that appear to be a regional phenomenon. The Miocene coals are generally low in rank (sub-bituminous) but within the fold belt that runs through Samarinda, in the structural highs, bituminous coals are found. However, rank variation can be very rapid and within a distance of less than 1 km, the rank can fall into the low rank range. The Pinang Dome (Sangatta area) appears to be an uplifted area similar in many ways to the structural highs in the fold belt near Samarinda but it has a slightly different setting. Coals found in this area are bituminous rank.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia