Collaborative Research: The Aftermath of a Snowball Earth

合作研究：雪球地球的后果

• 批准号: 9905495
• 负责人: Paul Hoffman
• 金额: $ 22.9万
• 依托单位: Harvard University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-09-01 至 2002-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9905495&HistoricalAwards=false
• 关键词: Collaborative; Research; Aftermath; Snowball; Earth

An investigation of the unique set of environmental conditions attending the aftermath of a Neoproterozoic "snowball" Earth will be undertaken. It is hypothesized that a series of glaciations occurred 750-570 million years ago that were so severe that the oceans froze over to the equator. These glaciations ended violently under ultra-greenhouse conditions (required to overcome the high ice albedo), brought about by the slow buildup of CO2 by subaerial volcanic outgassing in the absence of sinks for C. Intense silicate weathering must have followed deglaciation, driven by high surface temperatures, carbonic acid rain, and frost-shattered bedrock including unaltered volcanic material accumulated during the prolonged snowball period. The weathering reactions would have taken up the excess CO2 and delivered cations and bicarbonate to the oceans, driving massive and rapid precipitation of "cap" dolomites and limestones, which are widely observed overlying Neoproterozoic glacial deposits. The following studies of selected cap dolomites and limestones in Namibia, Mauritania, Australia and China will be carried out: (1) Radiogenic Sr isotopic anomalies will be sought which would record the input of riverine Sr to the surface ocean at a time when ocean mixing would have been impeded by high surface temperatures and low density glacial meltwater, (2) U-Pb dating of cap dolomites will be attempted, given evidence that the dolomites are primary and result from high Mg/Ca riverine input due to rapid weathering of mafic volcanic material; (3) Subsidence histories of cap carbonate sequences will be studied as a means of estimating the duration of snowball periods; (4) Collections of cap carbonates and associated terrigenous sediments will be made for the purpose of investigating the turnover of acritarch assemblages coincident with snowball events. These studies will be used to test the validity and our understanding of the snowball Earth hypothesis, which if true connotes the most extreme climates and climate changes in Earth history.

将对新元古代“雪球”地球后的独特环境条件进行调查。据推测，7.5 - 5.7亿年前发生了一系列严重的冰川作用，以至于海洋冻结到赤道。这些冰期在极端温室条件下剧烈结束（需要克服高冰反照率），这是由于在没有碳汇的情况下，由地面高温、碳酸酸雨和冻伤的基岩（包括在漫长的雪球期积累的未改变的火山物质）造成的二氧化碳缓慢积聚造成的。风化反应吸收了多余的二氧化碳，并将阳离子和碳酸氢盐输送到海洋中，推动了“帽状”白云岩和石灰石的大量快速降水，这些白云岩和石灰石被广泛观察到覆盖在新元古代的冰川沉积物上。将对纳米比亚、毛里塔尼亚、澳大利亚和中国选定的帽状白云岩和石灰石进行下列研究：(1)寻找放射性成因Sr同位素异常，记录在海洋混合受到高表面温度和低密度冰川融水阻碍的时期，河流Sr向海洋表面的输入；(2)考虑到白云岩是原生白云岩，是基性火山物质快速风化导致的高Mg/Ca河流输入的结果，将尝试对帽状白云岩进行U-Pb定年；(3)研究盖层碳酸盐岩层序沉降史，作为估算雪球期持续时间的手段；(4)收集盖层碳酸盐岩及其伴生陆源沉积物，以研究与雪球事件同时发生的生物群落更替。这些研究将被用来检验雪球地球假说的有效性和我们对它的理解，如果这个假说是真的，它意味着地球历史上最极端的气候和气候变化。