Neoproterozoic Paleogeography and Global Climate: Paleomagnetic and Magnetostratigraphic Constraints

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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.