Lower Gondwana Sediments of Pranhita-Godavari Graben, India, As Possible Source Rocks of Hydrocarbons

The Pranhita-Godavari graben, located in the eastern Indian Peninsula, is aligned NW-SE and covers an area of nearly 40,000 sq. km. The graben exposes sediments ranging in age from Proterozoic to Lower Eocene. The oldest, the Pakhal Series, are disconformably overlain by Sullavai Series and together comprise at 1.5-2.0 km thick sequence. The Sullavai Series are unconformably overlain by approximately 6.5 km thick Gondwana sequence which is in turn, unconformably overlain by infra-trappean beds. Deccan Trap effusives contain inter-trappean beds and are unconformable with the underlying infra-trappean beds.

Genesis of hydrocarbons in non-marine sediments containing predominantly vegetal constituents is feasible. The Lower Gondwana sediments of the Pranhita-Godavari graben contain coal seams, and dispersed organic matter. Sediments of Talchir Stage are poor in organic matter content and their hydrocarbon-generating potential appears doubtful. The Barakars contain coal seams and are rich in dispersed organic matter. The carbon ratios, computed from proximate analyses of coals from various localities, indicate that the stage of maturity of organic matter varies within such limits which do not exclude the Barakar sediments from being considered as potential source rocks of hydrocarbons. The Kamthi sediments are dominantly arenaceous and contain small amounts of dispersed organic matter. Lack of relevant analytical data makes it difficult to assess their hydrocarbon-generating potential.