Basal Tuffs and Contemporaneity of the Chattisgarh and Khariar Basins Based on New Dates and Geochemistry

Time bracketing of thousands-of-meters-thick, unmetamorphosed, fossil-free sedimentary successions is a long-standing challenge in Indian Proterozoic stratigraphy. Limited geochronologic ages from either the basal or the upper part of the successions prevent workers from constraining the precise age interval for individual basin fill, leaving aside the issue of correlatability between different basin sequences. This article deals with silicic tuff units from the basal part of two areally separated Proterozoic sedimentary successions of central India, the Singhora Group of the Chattisgarh Supergroup and the Khariar Group. The Singhora tuff is enriched in large ion lithophile (Rb, Ba, Th, etc.) elements and light rare earth elements and in a discrimination diagram falls within the volcanic arc granite field. U-Th-Pb electron probe microanalyzer geochronology of monazite and zircon grains from the Singhora tuff revealed several age data clusters, namely,∼2500 ∼ 2500 ,∼2100 ∼ 2100 ,∼1800 ∼ 1800 ,∼1500 ∼ 1500 , and∼1000 Ma ∼ 1000 Ma . In contrast, the age data from the Khariar tuff fall within a narrow range of∼1455 Ma ∼ 1455 Ma . To isolate the depositional/crystallization age of the Singhora tuff from inherited provenance ages, we also dated monazite and zircon grains from stratigraphic units overlying and underlying the Singhora tuff. The∼1500-Ma ∼ 1500 - Ma age is proposed as the depositional/crystallization age for the Singhora tuff, considering its most frequent and exclusive presence within the tuffaceous unit. Comparable ages from the tuffaceous units at the basal part of areally separated basins, namely, Singhora (∼1500 Ma ∼ 1500 Ma ) and Khariar (1455 ± 47 Ma 1455 ± 47 Ma ), suggest nearly synchronous initiation of the two basins. Considering the recently reported U-Pb SHRIMP zircon age of1631 ± 5 Ma 1631 ± 5 Ma from the basal part of the Vindhyan Supergroup, the largest Proterozoic sedimentary basin of peninsular India, we presume a crustal-scale event in early Mesoproterozoic time (1600–1500 Ma) on the Indian continent.