The results of detrital zircon U–Pb geochronology suggest a maximum depositional age of 485 ± 7.2 Ma for a glacial diamictite from the Sierra del Volcán in eastern Argentina (Tandilia System). Earlier interpretations associated the deposit with the Neoproterozoic ‘snowball Earth' hypothesis. The data allow direct correlation, for the first time, between Early Palaeozoic deposits in both South America and South Africa connecting the glacial deposits from southern Bolivia to central Argentina with those in South Africa (Pakhuis Formation). On the basis of these results, a new distribution map of glacial cover, corresponding to the Hirnantian stage, can be developed.
Sampling and analytical techniques, data, a simplified map and BSE images are available at http://www.geolsoc.org.uk/SUP18384.