Neoproterozoic Paleogeography and Global Climate: Paleomagnetic and Magnetostratigraphic Constraints

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期，而且在那之后不久，后生动物群也发生了爆炸性的辐射。与此同时，一个超大陆可能随着冈瓦纳大陆的合并而分散。尽管从地球动力学演化的角度理解这些事件具有重要意义，但现有的晚元古代古地理约束相当薄弱。尽管目前提出的许多重建方法主要依赖于相同的古地磁数据库，但由于数据通常是可疑的，而且不同的研究人员选择不同的古地极来约束他们的模型，因此它们之间的差异很大。特别是澳大利亚、劳伦西亚、波罗的海和非洲的温迪安立场，最近一直是激烈辩论的主题。要解决这些问题，需要从这些大陆块体中获得新的、高质量的晚元古代岩石古地磁数据，并明确确定原始磁化强度和地质年龄。关于前寒武纪晚期冰期的时间和严重程度也存在争议。新元古代的冰川沉积物几乎在每一个现存的大陆上都有发现，这可以用全球性的冰窖状态和同步的冰川时期来解释，或者用大陆在一个凉爽但不寒冷的地球的极地地区的快速漂移来解释。对不同的冰川单元进行精确的测年是检验这两种选择的最明显的方法，但这受到有限的文迪安化石记录和一般无法直接从冰川单元确定同位素年龄的阻碍。虽然这类研究以前曾有过尝试，但许多人忽略了对这个时代的岩石至关重要的初级磁化进行地质实地测试。我们建议在四个文德大陆：东冈瓦纳（澳大利亚）、劳伦西亚、波罗的海和非洲（卡拉哈里克拉通）进行深入的沉积序列古地磁研究。我们的取样策略将强调对原始剩磁以及地层连续性和一致性的现场测试。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……”，包括磁地层学和盆地间对比。这将为温德时代提供可靠的古磁极，并为地球历史上这一关键时期提供一个校准良好的多学科地层时间标度。

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.