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

晚元古代的冰川序列是已知的， 主要的南极地区，包括北美，冈瓦纳， 大陆和波罗的海平台。 一个主要的争议涉及 这些矿床可能形成的纬度， 形成于相对高纬度地区，如二叠纪 以及现代冰川沉积物，或者它们中的许多是 离赤道近一点？ 支持低沉积的论据 许多单位的纬度已被广泛讨论 在过去的30年里，从实地观察开始， 有些杂岩含有丰富的碳酸盐 碎片，好像冰已经走过碳酸盐平台。 古地磁资料的参与既支持又攻击 这些矿床的低纬度解释。 然而，许多 旧的古地磁数据并不像它应该的那样令人信服 特别是在使用地质稳定性测试方面， 限制了获得反射磁化的时间。 最近的一个重要的例外是古地磁学的工作 在南部Elatina组的纹状沉积物上， 澳大利亚，形成于最上层的马里诺冰川期。 至少在一个大陆上，这些广泛的海平面沉积物 由分布广泛的大陆冰川形成， 赤道的几度。 如果这也适用于其他 非洲等大陆，结果将是困难的， 以任何方式解释，而不是广泛的赤道 全球范围的冰川作用。 澳大利亚的例子表明， 需要对其他地区进行类似的、严格的古地磁研究， 元古代冰川单位。 在过去的10年里，地质 对南部非洲元古代冰川序列的研究， 阐明了它们的区域地层格架和构造 设置. 古地磁研究的几个新目标现在 这些矿物变质程度极低， 进行详细的微褶皱和砾岩测试。 资金 本提案中要求支持现场采样 2004年6月和7月，这些部队在南部非洲和纳米比亚， 1993年，并支持实验室古地磁分析， 1994年上半年。

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.