STURTIAN SERIES

division of Proterozoic rocks in south central Australia (the Proterozoic Eon lasted from 2.5 billion to 540 million years ago). The Sturtian Series, which forms the lower part of the Umberatana Group, is partly interpreted as being of glacial origin from the glacially produced pavements that have been recognized. The Sturtian begins with a boulder-laden horizon that generally overlies quartzites. Tillites, cemented glacial till deposits, occur higher up in the Sturtian sequence and include many glacial erratics seen as striated and faceted boulders of granite, gneiss, quartzite, shale, and limestone. Silty shales that may be laminated or even exhibit glacial varves also occur. The Sturtian thickens to the north and northeast of Adelaide, where it may be as much as 6,000 metres (20,000 feet) thick. Above the glacial deposits of the Sturtian lie blue-gray shales, arkoses, shaly sandstones, siltstones, and dolomites. The Sturtian Series is the most widespread unit of the Precambrian sedimentary basin in south central Australia, the Adelaide Geosyncline. In the Olary region the Sturtian is intruded by granite igneous masses, whereas in the Everard Ranges basalt flows are found with the tillites. The Sturtian Series is overlain by the Marinoan Series, which similarly includes within it a sequence of glacial deposits.