An Alternate View on the Stratigraphic Position of the ～1-Ga Sukhda Tuff vis-a` -vis Chronostratigraphy of the Precambrians of the Central Indian Craton

摘要

There are several Proterozoic sedimentary sequences in India, some of which are metamorphosed and deformed, whereas others, such as the Puranas, are not metamorphosed and are virtually undeformed. On the basis of U-Pb SHRIMP ages of zircons from the Sukhda tuff (in the Chhattisgarh basin), recently an age bracket of approximately 1650–1000 Ma has been assigned to nearly all Purana basins in India. Putting Purana sedimentation in an approximately Mesoproterozoic age bracket warrants a few explanations regarding metamorphosed and unmetamorphosed Proterozoic sedimentary successions and their chronostratigraphic relationship. Our drill hole data indicate that the stratigraphic position of the Sukhda tuff is in the Gunderdehi Formation, much lower than what has been proposed recently. If so, sedimentation in the Chhattisgarh basin continued well beyond 1000 Ma and into the Neoproterozoic. It is obvious that an unequivocal assignment of the stratigraphic position of the Sukhda tuff is vital for calibrating the chronostratigraphy of the Precambrians of the Central Indian Craton.