Petrology of some Permian coals of India

Abstract

In India, Permian coal deposits constitute approximately 99% of the total coal reserves of the country and occur in the Early Permian Karharbari Formation, Early Permian Barakar Formation and the Late Permian Raniganj Formation. In the present study, petrographic analyses were carried out on coals from the Pench-Kanhan Valley, Son-Mahanadi Valley and Damodar Valley Basins. The Permian coals of India show a remarkable range in vitrinite content (13–79%); seams with low vitrinite content are common. The Raniganj Formation coals contain more vitrinite than the coals of the Barakar and Karharbari Formation. Exinite (liptinite) content of many Indian coals varies from 2 to 23%. Sporinite is generally dominant over cutinite and resinite. Exinite tends to be associated with vitrinite-rich coal, and most inertiniterich coals have relatively low exinite content. Inertinite is relatively abundant (10–67%) in many Permian coals of India and consists mainly of semifusinite, inertodetrinite and fusinite. Coal-facies analysis based on petrographic parameters indicate that the Indian peats (coals) were deposited in dry and wet forest swamps. A comparison of Indian coals with some other coals of Permian age from Australia and South Africa shows broad similarities even though the coals are from different basinal settings. This suggests that palaeoclimate and floral assemblages outweighed basinal setting in determining the coal type being deposited. In India, outcrops of high-rank coals ( R o max0.85–1.30%) are largely restricted to the Damodar Valley Basin. In this basin, vertical rank gradients are higher and uplift and erosion have occurred to a greater extent than in other Gondwana basins of India. Coals of other Gondwana basins occur at shallow depth and are generally subituminous in rank ( R o max 0.40–0.65%). The oil potential of the coals of the Barakar and Raniganj formations is very good except in the Jharia basin. In this basin, the oil may have been released due to breaching of the structures.