The Raniganj Coal Basin: an example of an Indian Gondwana rift

Rifling occurred in peninsular India during Permian-Triassic Gondwana sedimentation. The rocks of the Paleozoic-Mesozoic Indian Gondwana Supergroup succeed the Mesoproterozoic Vindhyan sedimentary rocks and the Indian Precambrian shield unconformably, and are renowned for their coal resources. The rocks of the Gondwana Supergroup occur mainly in trough-like depressions arranged in a more or less en echelon fashion along distinct shear/fault zones, which are parallel to ancient structural lineaments in the Indian peninsular shield. Thus, the Gondwana group of basins occurs along the three major directions: (a) Son-Narmada and Damodar-Koel Valley, running East-West, (b) Son-Mahanadi Valley, with a NW-SE trend, and (c) Rewa-Pranhita-Godavari Valley, which trends in a NNW-SSE direction. The important common structural imprints in most of the above basins are: (i) a 'half-graben' basin geometry with a strong master boundary fault on one side and a homoclinal tilt of the basin towards it (ii) a network of intrabasinal faults, one set oriented along the basin axis and which formed during the tensional stage and another, (iii) transverse to it. Basin marginal oblique faults and slips coincide with both the tensional and compressional stages and have different manifestations. Syndepositional subsidence of the basin floor through loss of support from below due to the lateral transport of sub-crustal/mantle materials caused faulting at the axial zones of the basins/sub-basins to accommodate a thick pile of sediments. Volcanic activities in the region or in adjacent areas provide further support for these inferred processes, and are confined within comparatively narrow and linear zones defined by the crustal weaknesses of considerable antiquity. All these stages have their signatures imprinted in the sediments, which have been studied in detail. This paper presents relevant data on the Raniganj Coalfield of eastern India, in order to examine whether these linear depressions are of 'rift' origin. The process of rifting was a prelude to the rafting of Gondwana continents after the early Cretaceous fragmentation of 'Gondwanaland'. Thus, the Gondwana rift valleys flanked the periphery of the peninsular Indian stable blocks, to collide ultimately with the Sino-Eurasian plate in the north. (C) 2002 Elsevier Science B.V. All rights reserved.