The association of sulphate evaporites, stromatolitic carbonates and glacial sediments: examples from the Proterozoic of Australia and the Cainozoic of Antarctica

Carbonate sediments are often considered diagnostic of warm water environments, and thus the occurrence of dolomite and limestone beds within and immediately overlying many late Proterozoic glacial deposits (tillites) has long been a source of controversy. Stromatolites are also conventionally thought to be warm water indicators. We describe two examples of stromatolitic dolomite occurring, together with barite, at the top of late Proterozoic glacial sequences in the Amadeus and Ngalia Basins of central Australia. Problems of interpretation may be largely resolved after examination of published data on Antarctic lakes. Antarctic lakes of high salinity occupy enclosed glacial basins in both the Vestfold Hills, and the Taylor and Wright Dry Valleys; Lake Bonney is the most comprehensively described example. Carbonate sediments, sulphate evaporites and even stromatolites are common components of cold arid-climate lakes. The stromatolitic mats and their constructing cyanobacteria are similar to those described from warmer climates. The tundra plains and lakes, and coastal lagoons of northern Canada and Siberia are better geomorphic analogues for the Proterozoic deposits, and these too seem to contain analogous sediments, but only brief descriptions are available. We suggest that environments such as these provide modern analogues of the association of Proterozoic glacial sediments with carbonates, evaporites and stromatolites.