Age of the Lower Vindhyan sediments, Central India

The basic issue raised by the two simultaneous and sensational reports(1,2) in 1998 of body fossil evidence (worm tracks and small shelly fauna, respe ctively) of multicellular life in the Lower Vindhyan sediments, is the true age of the latter. Is the true age Mid-Proterozoic as believed so far, on limited geochronological data and assumed by Seilacher et al.(1)? Or is it only Early Cambrian, as was argued by Azmi(2) and supported by a single pre liminary Ar-Ar age of 617 Ma measured soon after the reports? Although both the fossil evidences are now equivocal, the basic issue remains. We report consistent Rb-Sr ages for glauconies from the Lower Vindhyan sediments (Se mri Group) near Chitrakut, which constrain the onset of the earliest Vindhy an sedimentation to not later than 1600 Ma. Considering other available chr onological constraints, the Vindhyan basin is likely to preserve a rare, ve ry long and least disturbed record of Precambrian sedimentation.