Neoproterozoic Paleogeography and Global Climate: Paleomagnetic and Magnetostratigraphic Constraints

Kirschvink 9418523 地球历史上的新元古代时期在许多方面都是值得注意的：不仅地球遭受了可能是最严重的冰川作用，而且此后不久，后生动物群的爆炸性辐射。 与此同时，一个超大陆可能随着冈瓦纳的合并而分散。 尽管了解这些事件在地球的动态演化方面的重要性，晚元古代古地理的现有限制是相当差的。 虽然目前提出的许多重建方法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磁极来约束他们的模型。 特别是，澳大利亚、劳伦蒂亚、波罗的海和非洲的文迪立场，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，古地磁数据的晚元古代岩石从这些大陆块，与明确的确定主磁化和地质年龄。 同样在争论中的是晚前寒武纪冰川的时间和严重性。 新元古代的冰川沉积物几乎在每一个现在的大陆上都能找到，这可以用全球冰库状态与同步冰川事件来解释，也可以用大陆快速漂移进出凉爽但不寒冷的地球的极地来解释。 精确测定各个冰川单元的年代是检验这两种说法的最明显的方法，但这受到了有限的文迪化石记录和无法直接从冰川单元确定同位素年龄的阻碍。 虽然以前曾尝试过这样的研究，但许多人忽略了对主要磁化的地质现场测试，这对这个年龄的岩石至关重要。 我们建议进行密集的古地磁研究的四个文迪大陆的沉积序列：东冈瓦纳（澳大利亚），劳伦提斯，波罗的海和非洲（喀拉哈里克拉通）。 我们的取样策略将强调对初级剩磁以及地层连续性和一致性的实地测试。 因此，该项目将扩展研究的晚元古代部分，“前寒武纪低纬度冰川......包括磁性地层学和盆间对比。 这应该提供可靠的古磁极的文迪时间，也导致一个良好的校准，多学科的地层时间尺度为这个关键的时间间隔的地球历史。

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.