The late proterozoic glacial era
Abstract The Late Proterozoic glacial record is reviewed on a global basis as a setting and introduction for that part of the symposium concerned with West African tillites. No unequivocal glacial deposits have yet been recorded in the interval 1.0–2.0 Ga. Late Proterozoic glacial epochs have been grouped into three main periods namely: Lower Congo (c. 0.9 Ga), Sturtian (c. 0.8 Ga) and Varangian (c. 0.65 Ga), and a possible final Late Sinian Epoch near the Precambrian-Cambrian boundary. The Ediacaran Epoch, with its metazoan fauna follows Varangian and in part at least precedes Late Sinian. The Sturtian and Varangian glacial periods each comprise at least two main glacial epochs, the tillites of which are widespread. Chronometric ages are currently disputed and the values given are for identification in the literature rather than to provide chronometric definition. Of all the glacial epochs, only those of the Varangian glacial period appear to be represented in West Africa. It has been argued that Varangian tillites were of global extent, many forming in tropical latitudes, though some authors prefer a hypothesis of polar wandering to limit glaciation to polar latitudes.