Upper Paleozoic Glacial Deposits of South Africa and Southern Australia
Glacial deposits of Late Carboniferous and Early Permian age have long been recognized throughout broad areas of the “Gondwana” continental masses. This paper describes some of these deposits in South Africa and southern Australia, and summarizes information from the literature on deposits of these and other regions. The following features in combination are widespread in the Paleozoic deposits and prove continental glaciation: polished and striated pavements and roches moutonnees; massive, nonsorted debris (tillite) containing abundant clay-free rock flour, abundant fresh grains of easily weathered minerals, and stones including faceted and striated blocks from both local and distant sources; and laminated, fine-grained sediments enclosing numerous drop-stones. Electron-microscopy studies have shown that surface textures of sand grains in modern sediments vary diagnostically from one environement to another. The large suite of surface textures that uniquely characterizes Quaternary glacial grains also characterizes Paleozoic ones. X-ray study shows that the clay-sized fraction of unweathered tillites and glacial shales is largely devoid of clay. Most of the well-dated Gondwana glacial deposits are of very Early Permian age. At least local glaciation occurred during the Late Carboniferous and also during the later Early Permian. Glacial stages alternated with interglacial ones. The continental glaciers of even the now-tropical Gondwana continents reached sea level for marine deposits occur with glacial drift. Ice sheets bearing continental-shield debris flowed onto each continent from the direction of present oceans. The distribution of warm-climate Early Permian deposits is as aberrant as that of glacial deposits; red beds, evaporites, thick biochemical limestones, diverse-fauna coral bioherms, and large foraminifera occur, for example, in the northernmost lands of the Atlantic sector of the Arctic. Only continental drift offers a rational solution to the problems of distribution of paleoclimatic indicators. All the glaciated lands lay in latitudes between 45° and 90° S. in the since-fragmented continent of Gondwanaland. Long-lasting sedimentary basins were produced by permanent changes in crust and mantle configuration resulting from glacial loading.