Neoproterozoic Paleogeography and Global Climate: Paleomagnetic and Magnetostratigraphic Constraints

Kirschvink 9418523地球历史的新元古代时期在许多方面都是非凡的：不仅地球遭受了可能是最严重的冰川作用，而且紧随其后不久就发生了后生动物的爆炸性辐射。与此同时，随着冈瓦那的合并，一块超级大陆可能已经消散。尽管从地球动态演化的角度来理解这些事件很重要，但现有的晚元古代古地理约束条件相当差。尽管这一次提出的许多现有重建在很大程度上依赖于相同的古地磁数据库，但它们之间的差异很大，因为数据通常是可疑的，不同的工作人员选择不同的古极来约束他们的模型。特别是，澳大利亚、劳伦西亚、波罗的海和非洲的文迪安立场最近一直是激烈辩论的主题。这些问题的解决需要新的、高质量的、来自这些陆块的晚元古代岩石的古地磁数据，并明确确定原始磁化强度和地质年龄。还在争论的还有前寒武纪晚期冰川的时间和严重性。新元古代冰川沉积几乎在现在的每一块大陆上都能找到，这可以用冰期同步的全球冰库状态解释，也可以用大陆快速漂移进出凉爽但不冷的地球极地地区来解释。对各种冰川单元进行精确测年是测试这两种选择的最明显的方法，但由于文迪亚化石记录有限，而且普遍无法直接从冰川单元确定同位素年龄，这一点受到了阻碍。尽管以前曾尝试过这样的研究，但许多人忽视了对原生磁化的地质现场测试，这对这个年龄的岩石至关重要。我们建议对文迪亚四个大陆的沉积序列进行深入的古地磁研究：东冈瓦那(澳大利亚)、劳伦蒂亚、波罗的海和非洲(卡拉哈里克拉通)。我们的采样策略将强调原始剩磁的现场测试以及地层的连续性和一致性。因此，该项目将扩展研究的晚元古代部分，“前寒武纪的低纬度冰川……”，包括磁性地层学和盆地间对比。这将为文迪亚时间提供可靠的古地磁极，并为地球历史的这一关键时期提供一个经过良好校准的多学科地层学时间标尺。

Kirschvink 9418523 The Neoproterozoic interval of Earth history is remarkable in many respects: not only did the planet suffer perhaps its worst glaciation, but an explosive radiation of metazoan fauna followed shortly thereafter. At the same time, a supercontinent may have dispersed as Gondwana amalgamated. Despite the importance of understanding these events in terms of Earth's dynamic evolution, existing constraints of Late Proterozoic paleogeography are rather poor. Although the many existing reconstructions which have been proposed for this time rely largely on the same paleomagnetic database, they differ greatly because the data are commonly suspect, and different workers choose different paleopoles to constrain their models. In particular, the Vendian position of Australia, Laurentia, Baltica, and Africa, have been the subject of heated recent debate. Resolution of these problems require new, high-quality, paleomagnetic data of Late Proterozoic rocks from these continental blocks, with unambiguous determinations of primary magnetization and geological ages. Also under debate are the timing and severity of the Late Precambrian glaciations. Neoproterozoic glacial deposits are found on virtually every present continent, and this can be explained by either a global icehouse state with synchronous glacial episodes, or by rapid drift of the continents in and out of the polar regions of a cool but not frigid Earth. Precise dating of the various glacial units is the most obvious way to test the two alternatives, but this is hampered by the limited Vendian fossil record and the general inability to determine isotopic ages directly from the glacial units. Although such studies have been attempted previously, many neglected to include geological field tests on the primary magnetization, crucial for rocks of this age. We propose to conduct intensive paleomagnetic studies of sedimentary successions on four Vendian continents: East Gondwana (Australia), Laurentia, Baltica, and Africa ( Kalahari craton). Our sampling strategy will emphasize field tests for primary magnetic remanence as well as stratigraphy continuity and consistency. This project will thus extend the Late Proterozoic portion of the study, "Low-Latitude Glaciations in the Precambrian...", to include magnetostratigraphy and interbasinal correlation. This should provide reliable paleomagnetic poles for Vendian time and also lead to a well-calibrated, multidisciplinary stratigraphic timescale for this pivotal interval of Earth history.