Facies characteristics of Talchir Formation, Jharia Basin, India: Implications for initiation of Gondwana sedimentation

A long phase of nondeposition that prevailed in peninsular India since the Late Proterozoic came into an end with the onset of Gondwana sedimentation. The Talchir Formation, the lowest unit of Gondwana Supergroup, deserves special attention for understanding the Late Paleozoic geological history in this part of the globe. Signatures of three major events have been identified in the Talchir Formation in different Gondwana basins of India: (1) intracratonic rifting, (2) Permo-Carboniferous glaciation and (3) marine incursion. But a unique model to explain the specific relation between these events is yet to be formulated. The present study reveals that the Talchir succession of Jharia Basin of eastern India bears certain evidences, which may lead to a possible solution to this problem. The lower part of the succession is represented by a glacigenic conglomerate, which underwent brecciation possibly due to hydraulic fracturing during deglaciation. Facies analysis leads to the conclusion that a thick fan deposit, presumably produced through resedimentation of preexisting unconsolidated glacial sediments, represents the rest of the Talchir succession. The presence of fragments of brecciated conglomerate within this fan deposit confirms a significant break in the sedimentation history. Three fining upward cycles can be identified within the proximal part of the fan succession. The lower and the middle cycles bear the signature of emplacement of subaqueous high-density flows and variations in facies pattern developed through progressive flow transformation. The upper cycle, however, is represented by sheet-flood and stream-flow deposits. Products of dominantly suspension fall-out over a vast area, with periodic influx of coarser material, constitute the distal fan deposit. The fan succession is unconformably overlain by a fluvial succession, which, in turn, interfingers with the fluviolacustrine deposits of the younger Barakar Formation derived from the opposite side of the basin. This indicates asymmetric pattern of basin-filling as expected in a continental extensional setting. The overall character of this succession indicates that: (1) emplacement of the intracratonic rift system was a post-glaciation event, (2) initial phase of deposition was dominated by resedimentation of the preexisting glacial debris, and (3) marine incursion probably followed deglaciation and persisted for a short time until isostatic equilibrium was attained before the rift system came into existence.