Stratigraphic architecture of the Proterozoic succession in the eastern Chattisgarth Basin, India: tectonic implications

Abstract

Abstract The basin-fill succession of the Proterozoic eastern Chattisgarth Basin comprises a sandstone–shale–conglomerate-dominated shallow marine assemblage, and an assemblage of limestone–shale–pyroclastics deposited in off-shelf–slope–base of slope environments. The proximal and distal lithologic assemblages developed as lateral equivalents, and show signatures of sea level fluctuations amenable to chronostratigraphic correlation. The stratigraphic architecture of the proximal assemblage is characterized by cyclic deposition on different scales. The largest order cyclicity is represented by alternating sandstone sequences and mudstone-dominated sequences, of the order of several tens of metres. The smallest order cyclicity is represented by metre-scale units, punctuated aggradation cycles (PAC), bounded by isochronous surfaces. The lowermost large-scale sandstone sequence, the Lohardih sandstone, unconformably overlies the highly deformed rocks of the gneissic basement complex. The sequence was deposited as alluvial fan–fan-delta complexes, controlled by basin margin faulting. The upper two sandstones, the Daihan sandstone and the Kansapathar sandstone, represent two different phases of major sand accumulation in fan- or river-deltas. Their rapid emplacement over muddy shelf deposits along erosional surfaces signaled abrupt sea level fall, and basinward migration of facies belts. Generation and accumulation of very large volumes of sand and their rapid influx into the basin, accompanied by major changes in depositional motif, and in the circulation system in the basin, collectively indicate that larger order sand-depositing cycles were caused by tectonic uplift of the cratonic basement. The smallest order cycles, the PACs, on the other hand, may be attributed to glacioeustacy, though tectonic control cannot be ruled out. The sand-deficient, mud-dominated large-scale sequences are attributed to major transgression during periods of relative tectonic quiescence, and subsidence of the cratonic hinterland. Episodic tectonic uplift and derivation of sands from similar quartzo-feldspathic sources suggest repeated rifting of the cratonic basement and expansion of the rift into a major marine basin.