AN OVERVIEW OF CHEMICAL-PROPERTIES OF MARINE-INFLUENCED OLIGOCENE COAL FROM THE NORTHEASTERN PART OF THE ASSAM-ARAKAN BASIN, INDIA

The Oligocene coals from the northeastern part of the Assam-Arakan bas in show a gradual decrease in the content of moisture, volatile matter and oxygen with corresponding increase in carbon content and calorifi c value from the Foreland Shelf to the deeper part of the geosyncline, reflecting the coalification trends in this basin. It has been sugges ted that the oxygen was replaced by organic sulphur, thereby lowering the oxygen content in the coals, The coals are perhydrous in nature wi th a high sulphur content. The high volatile content, perhydrous natur e and high sulphur content in the Oligocene coals, as well as the pres ence of streaky facies and a very fine clastics unit, indicate that th ey were probably deposited in a marine-influenced deltaic and lagoonal environment. The plots of carbon versus hydrogen on Seyler's coal ban d follow a trend which differs from that of Seyler's band of Carbonife rous bright coals. The coalification of the Oligocene coals represents the lignitic stage, in the case of the Foreland Shelf, and near subbi tuminous stage in the deeper geosynclinal part of the basin, A more in tense, and probably sudden, dynamic process was involved in bringing a bout higher coalification in Oligocene coal of the geosynclinal facies than in Foreland Shelf area. This is possibly due to intense mountain -building forces acting from the southeastern direction of the basin.