Evidence From India of a Carbon Isotope Excursion During the Statherian PaleoProterozoic

New age constraints for the Proterozoic Aravalli–Delhi successions of India and their implications

Authors:

N. Ryan McKenzie, Nigel C. Hughes, Paul M. Myrow, Dhiraj M. Banerjee, Mihir Deb and Noah J. Planavsky

Abstract:

Proterozoic sedimentary successions of India are important archives of both the tectonic history of the Indian subcontinent and the geochemical evolution of Earth surface processes. However, the lack of firm age constraints on many of these stratigraphic units limits their current utility. Here, we present new detrital zircon age data from strata of the southern Aravalli–Delhi Orogenic Belt (ADOB) and the Rajasthan Vindhyan successions. The Alwar Group of the southern Delhi Supergroup yielded a large population of ∼1.2 Ga detrital zircon grains, which refutes the 1.9–1.7 Ga age assertion for this unit. Detrital zircon age distributions from the southern Alwar Group differ strongly from the Alwar Group of the “North Delhi Belt”, demonstrating miscorrelation between these two regions. The Jhamarkotra Formation of the Lower Aravalli Group contains a large population of 1.9–1.7 Ga detrital zircon grains. Therefore, the unit cannot be ∼2.1 Ga as traditionally assumed. Age distributions of the Aravalli and Delhi supergroups are similar to those of the lower and upper Vindhyan successions, and we postulate contiguous sediment sources for both regions, with strata of the tectonically deformed ADOB representing the distal margin equivalents of the Vindhyan successions. Additionally, a late Paleoproterozoic age for the Jhamarkotra Formation nullifies the hypothesis that the markedly positive carbonate δ13C values in this unit are linked to the 2.3–2.0 Ga Lomagundi–Jatuli positive isotope excursion. The potential of a large late Paleoproterozoic (ca. 1.7 Ga) positive δ13C excursion contrasts with the long-held view of a prolonged period of carbon isotope stasis during the so-called ‘boring billion’.