Development of the Late Paleozoic glaciations of the South American Gondwana in western Argentina
Abstract The Late Paleozoic Ice Age in the South American segment of Gondwana consisted of several glaciations, which can be grouped into two main glacial periods. The oldest of them occurred in late Early to early Late Carboniferous time and the younger in Early Permian time. Paleontological evidence in the western Argentine Precordillera supports a late Visean age for the beginning and a probable early Westphalian age for the end of the Carboniferous glacial period. In this span of time, subsidence and deposition of glacial debris took place in the western mobile belt and in Patagonia, but no sediments of that age were deposited in the eastern portion of the South American Gondwana, where subsidence started later. A Carboniferous glacial sequence is remarkably well preserved in the San Eduardo Group on the western flank of the Precordillera, where at least three distinct glaciations are recognized. This sequence can be taken as a reference section for the Carboniferous glacial deposits. Shorter than the former, and probably restricted to the Asselian Epoch, the Permian glacial period is better known. The evidence for it is well developed in eastern South American Gondwana, although a relic is also present in the Precordillera. The recognition of two glacial periods within the Late Paleozoic Ice Age is supported by the existence of a long-lasting interglacial, which seemingly began in the late Westphalian and lasted until the end of the Carboniferous Period. This major interglacial period is inferred from the total absence of glacial features in the Upper Carboniferous sequences. In spite of the existence of a mountainous belt parallel to the “Pacific” during the Carboniferous Period, the presence of marine beds and glacial drift well to the east of these ranges, suggests that it was not altitude that was the main factor in determining the formation of glaciers, but latitude plus a global change in temperature. It is argued that the ice sheets extended greatly during the Carboniferous glaciations and reached neighboring areas of the Paganzo basin in central Argentina.