Depositional History of the Chhattisgarh Basin, Central India: Constraints from New SHRIMP Zircon Ages

The Indian Shield includes the Singhbhum, Bastar, and East and West Dharwar cratons. Proterozoic sedimentary basins formed on these cratons have preserved rocks with a range of degrees of metamorphism and deformation. In the Chhattisgarh Basin, within the Bastar Craton, the ca. 2200-2500-m-thick Chhattisgarh Supergroup has been preserved in nearly pristine condition. Previous work has shown that the Sukhda Tuff, located about 2200 m from the base of the section, was formed ca. 1007 Ma. New U-Pb SHRIMP age determinations show that the Singhora Tuff, located about 100 m above the base of the basin, is not older than 1405 +/- 9 Ma. Thus, most of the Chhattisgarh Supergroup was deposited between 1400 and 1000 Ma. Age data for detrital zircons from sandstones show that, regardless of their stratigraphic position, there is a unimodal age peak near 2500 Ma, the typical age of adjacent granitic and rhyolitic basement rocks, indicating that these constituted the principal provenance of the sediments in the Chhattisgarh Basin. However, near the top of the succession, the Sarnadih Sandstone and a volcaniclastic sandstone near Sukhda Village, show a wide range of ages with peaks from ca. 1000 through 2680 Ma. The ca. 1000 Ma detrital zircons were probably derived from igneous sources similar to the Sukhda Tuff, but the zircons with other ages indicate a different source. Age data from rock units in the Central Indian Tectonic Zone to the north of the basin match this age spectrum better than any to the south of the basin and are consistent with a change in provenance direction to a northerly source late in the basin-filling cycle.