Detrital Zircon U-Pb Geochronology of the Neoproterozoic and Cretaceous Sandstones of Central India: Implications for Pre-Cambrian Erosional History and the Ediacaran Closure Age of the Vindhyan Basin

The Vindhyan basin, one of the largest Proterozoic basins in the world, hosts a thick sedimentary sequence which is referred to as the 'Vindhyan Supergroup'. The Vindhyan Supergroup is subdivided into the Lower Vindhyan and the Upper Vindhyan succession. The closure age of the Vindhyan basin is the subject of controversy as there is a lack of convergence between the geochronology and biochronology of the Upper Vindhyan sequence. Detrital zircon geochronology suggests an Early Neoproterozoic to Late Mesoproterozoic (~1000 Ma) age for the closure of the Vindhyan basin whereas palaeobiological data provide evidence of an Ediacaran-Cambrian age.

This study presents new U-Pb detrital zircon geochronology of the Upper Vindhyan succession, from which the first discovery of iconic Ediacaran fossil Dickinsonia has been made from the Indian subcontinent. The synthesis of new data on detrital zircon geochronology of samples from the Dickinsonia bearing Bhimbetka sandstone and younger Cretaceous sandstones from Jabalpur, Central India, combined with existing palaeobiological evidence, has been presented to address the issue of lack of convergence between geochronology and biochronology. The age-spectra of the Upper Bhander Sandstone shows the dominance of detrital zircon population between 1500-1900 Ma, a subordinate cluster of 2400-2600 Ma, and a single youngest zircon grain of ca. 770 Ma. The finding of a single zircon of ca. 770 Ma age, together with the recent discovery of Dickinsonia, supports the premise that Vindhyan deposition extended up to the Ediacaran. The Cretaceous sandstones of the Jabalpur and Lameta formations have yielded ~550 Ma and ~700-800 Ma zircon ages. Except for the youngest Vindhyan sediments, no rocks of the Late Neoproterozoic-Early Cambrian age have so far been reported from Central India, which can be correlated with these zircon ages. Similar age spectra of the Upper Vindhyan samples and the Cretaceous sandstones indicate that the proximal Vindhyan sandstones could have supplied detritus to these younger sandstones.