Significance of the tuffaceous beds associated with the Bijaigarh Shale of the Kaimur Group, Vindhyan Supergroup, Central India and their correlation with tuffs in other contemporaneous Proterozoic basins

Abstract

Bijaigarh Formation is lithologically heterogeneous with grain size varying from fine to medium sand to clay. About ~1 m thick tuffaceous beds of rhyolitic to rhyodacitic nature, sandwiched between the Bijaigarh siliciclastics have been reported. We have attempted to distinguish the tuffaceous beds from the adjacent terrigenous sediments of Bijaigarh Shale on the basis of their field disposition, petrographic and geochemical characteristics. The tuffs are characterised by a relatively high content of LILE, HFSE and LREE as compared to Bijaigarh siliciclastics. They reflect their affinity to the felsic magmatic source. The geochemical signatures of the Bijaigarh tuff exhibit quite comparable characters to the contemporaneous (~1000 Ma) tuffs from other Proterozoic basins, viz., Chhattisgarh and Indravati. The extrabasinal sources for the deposition of the Bijaigarh tuff at ~1000 Ma can be inferred which can possibly be correlated with tectonothermal events of the Grenville orogeny. The integration of elemental compositions with mineralogical and textural observations makes possible the establishment of the tuffaceous beds as a stratigraphic marker in the Upper Vindhyan stratigraphy. This will have wider implications for the precise and reliable correlations of the Proterozoic basins of India.