Direct dating of the Sete Lagoas cap carbonate (Bambui Group, Brazil) and implications for the Neoproterozoic glacial events

The end of the Neoproterozoic is punctuated by glacial deposition, but the chronology of these deposits is hindered presently by the paucity of geochronological data. Here, we present new radiometric dating for the basal Sete Lagoas cap carbonate deposits that overlie glacial units in the Sao Francisco craton. Six samples from aragonite-pseudomorph crystal-rich facies, showing pristine textures and constant Sr-87/Sr-86 ratios around 0.7075, yielded a Pb-Pb isochron age of 740 +/- 22 Ma, which is interpreted as the depositional age for these remarkably preserved rocks. This age can be used to infer a low-to-moderate palaeolatitude of 20-30 degrees for carbonate ( and glacial) deposition. In addition, as it overlaps the ages obtained for the oldest Neoproterozoic glacial successions, our result reinforces the idea of a long-standing 'Sturtian' interval, suggesting that this event represents either different discrete glaciations or a protracted event encompassing almost 80 Ma.