The Biogeochemical Aftermath of Neoproterozoic Ice Ages

摘要新元古代冰期的生物地球化学后果这项研究旨在严格检验著名的雪球地球假说，该假说预测，在新元古代（5.43 - 10亿年前），整个地球从两极到赤道被大陆冰川和海冰覆盖了好几次。 为了克服这种极端条件，有人认为，数百万年来，大气中的二氧化碳浓度必须上升到目前的100多倍，最终积累了足够的温室气体来温暖冰冻的地球。 一方面，神秘的碳酸盐所需的物质（覆盖着世界各地的新元古代冰川沉积物）可能来自大陆在这种充满二氧化碳的大气中的强烈风化。 或者，这些物质的来源可能来自深海，在那里硫酸盐还原菌占主导地位的水柱-类似于今天的缺氧黑海-在广泛的，但不太严重和较短的冰川时期。 测试这些端元假设的有效性将需要详细研究的帽碳酸盐岩的元素，矿物，结构和稳定同位素组成。 将分析来自纳米比亚奥塔维组（全球冰川作用的关键证据首次聚集在那里）的样本，以及来自巴西班布伊和Macaubas组的明显相当的地层样本。 厚，碳酸盐岩为主的巴西继承的区域测绘和高分辨率地层学研究将有助于评估模型，试图解释这些严重的前寒武纪气候振荡。

ABSTRACTThe Biogeochemical Aftermath of Neoproterozoic Ice AgesThe proposed research aims to critically test the celebrated Snowball Earth hypothesis, which predicts that several times in the Neoproterozoic (543-1000 million years ago), the entire planet was blanketed from the poles to equator with continental glaciers and sea ice. To overcome such extreme conditions it has been suggested that over millions of years atmospheric carbon dioxide concentration must have risen to over 100 times its present inventory, eventually building up enough greenhouse gas to warm the frozen planet. On one hand, the materials required for the enigmatic carbonates (which cap these Neoproterozoic glacial sediments worldwide) may have come from the intense weathering of the continents under such a CO2-charged atmosphere. Alternatively, the source of these materials may have derived from the deep ocean where sulfate-reducing bacteria dominated the water column - similar to the present-day anoxic Black Sea - during widespread, yet less severe and shorter glacial epochs. Testing the validity of either of these end-member hypotheses will require detailed study of the elemental, mineralogical, textural, and stable isotopic compositions of the cap carbonates. Samples from the Otavi Group in Namibia (where the critical evidence for global glaciation was first amassed), and in demonstrably equivalent strata from the Bambui and Macaubas groups of Brazil will be analyzed. Regional mapping and high-resolution stratigraphic studies of the thick, carbonate-dominated Brazilian successions will aid in the evaluation of models that seek to explain these severe oscillations of Precambrian climate.