Himalayan Geology, Vol. 21 (1& 2), 2000, pp. 17-29, Printed in India

Nature, Composition, Rank (Maturation ) and Depositional Environment of Siwalik Coals from Arunachal Himalaya

ANAND-PRAKASH AND TRILOCHAN SING
Birbal Sahni Institute of Palaeobotany, Lucknow 226 007, India
Wadia Institute of Himalayan Geology, Arunachal Unit, Itanagar 791 113, India.

The organic petrological studies of coal studies of coal occurring in the form of small lenses, thin streaks and pockets in the Upper Tertiary sediments of the Siwalik Group, Arunachal Himalaya have been carried out in detail. The coals are almost entirely made of vitrinite/huminite micro-constituent with minor fraction of inorganic matter. Well-preserved cellular structures exhibiting various stages of degradation of plant matter are the characteristic features of the vitrinite/huminite maceral group. Reflectance of vitrinites in oil ranges between 0.3% to 0.6% in general, indicating that these coals have attained lignite-bituminous rank. The dominance of vitrinite/huminite maceral further suggests that these coals were formed mainly by the burial of wood togs in shallow fluvial regime. Distortion of cellular structure mainly along micro folds might have been caused by the large-scale tectonic activity in the region.