Low Latitude Glaciations in the Precambrian? Paleomagnetic Constraints from Southern Africa

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The Late Proterozoic glacial sequences are known from almost all of the major cratonic areas, including North America, the Gondwana continents, and the Baltic Platform. A major controversy involves the probable latitude of formation for these deposits--were they formed at relatively high latitudes as were those of the Permian and our modern glacial deposits, or were many of them formed much closer to the equator? Arguments supporting a low depositional latitude for many of these units have been discussed extensively for the past 30 years, beginning with the field observations that some of the diamictites had a peculiar abundance of carbonate fragments, as if the ice had marched over carbonate platforms. Paleomagnetic data have been involved to both support and attack the low-latitude interpretations of these deposits. However, much of the older paleomagnetic data is not as convincing as it should be, particularly in terms of using geological stability tests to constrain the time that the remanent magnetization was acquired. A recent and important exception to this is the paleomagnetic work on the varved sediments of the Elatina formation of South Australia, which formed during the uppermost Marinoan glaciation. At least on one continent, these extensive, sea-level deposits were formed by widespread continental glaciers which came to within a few degrees of the equator. If this is also true of other continents such as Africa, the results would be difficult to interpret in any fashion other than that of a widespread equatorial glaciation of global extent. This Australian example demonstrates the need for similar, rigorous paleomagnetic studies on other Proterozoic glacial units. During the past 10 years, geological work on Proterozoic glacial sequences in Southern Africa has clarified their regional stratigraphic framework and tectonic setting. Several new targets for paleomagnetic work are now available which are of exceptionally low metamorphic grade and lend themselves to detailed micro-fold and conglomerate tests. Funds are requested in this proposal to support the field sampling of these units in Southern Africa and Namibia during June and July of l993, and to support the laboratory paleomagnetic analyses in the first half of 1994.