Geological study of the tertiary sediments and coal deposits of the makum coal field upper Assam India

Abstract

The entire area of the Makum Coal-field is covered by sedimentary rocks, belonging to the tertiary age. The sediments along with the coal seams are sandwiched between the Haflong-Disang and the Margherita thrusts, trending more or less in a N.N.E. - S.S.W. direction. Bounded by the two thrusts, the Barail, Surma and Tipam Series occur in the Makum Coal-field in the form of a syncline. Of the Barail Series, only the Baragolai and the Tikak Parbat Stages are represented. Bulk of the Barail Series is derived from the granitic igneous complexes while the Surma and Tipam Series are formed by the detritus, primarily derived from Metamorphic area. Turbidity current played an active role in the depositional environment during the time of sedimen-tation of the Barail Series. On the contrary, Surma and Tipam Series were deposited by the tractive currents. Chemical compositions show that the coal belongs to Lignitous rank and are quotabnormal coalquot. The coals are highly rich in sulphur content. Carbon-hydrogen and volatile-calorific value show that the coals belong to the Lignitous rank and are abnormal. The rank as determined with the help of the carbon content places the coals in sub-bituminous to bitu-minous No.1 (fat) rank, and are perhydrous. In the coal, organic sulphur always predominates. However, pyritic sulphur becomes appreciably high in the roofs, partings and floors of the coal seams. Petrographically, the coals of the different coal seams do not differ conspicuously. The reflec-tance of vitrinite is markedly higher along the viscinity in the Haflong-Disang Thrust, particularly in the western part of the coal-field. Inert index and strength index, determined from the petrographical study show the stability factor within the caking coal. The micro-hardness is appre-ciably higher along the bedding plane than in the direction perpendicular to it. Though in the initial stage of metamorphism, bacteria and fungi played their role, lateral pressure due to the earthmovement played an active part in raising the rank of the