The origin of 17O-depleted barite in Neoproterozoic cap carbonates in South China

华南新元古代盖碳酸盐岩贫17O重晶石成因

• 批准号: 0952057
• 负责人: Huiming Bao
• 金额: $ 26.96万
• 依托单位: Louisiana State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-07-01 至 2013-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0952057&HistoricalAwards=false
• 关键词: origin; 17O; depleted; barite; Neoproterozoic

Intellectual merit: Bao and colleagues recently discovered anomalous depletions of the stable oxygen isotope, 17O, in sulfate oxygen in the rock record. These enigmatic signals are distinctly large in sulfate associated with Marinoan (~ 635 Myrs old) glaciation around the world. Particularly, barite minerals in the basal Doushantuo Formation in South China exhibit variable magnitudes of the 17O anomaly. Since 1980s, many compounds on Earth have been found to possess triple oxygen isotope compositions that deviate from the terrestrial fractionation line. All of these previously reported anomalies are positive, i.e. the 17O is anomalously enriched, due to different degrees of inheritance of ozone?s positive 17O anomaly. In the PI's recent publications (Nature 2008 and Science 2009) he proposed that the newly discovered anomalous 17O depletion came from atmospheric O2, as a result of stratospheric O2−CO2−O3 chemistry in which the exchange between O3 and CO2 results in an anomalous 17O depletion in O2. Other variables being the same, increasing pCO2 can increase the magnitude of the negative 17O anomaly for O2. The large magnitude of sulfate 17O depletion at the end of Marinoan glaciation suggests probably an extremely high pCO2 atmosphere at that time, constituting therefore a strong support for the ?snowball Earth? hypothesis. This proposal will focus on the geological context and the origin of the 17O-depelted barite in Marinoan cap carbonates in South China where the distinctly negative 17O anomaly was first discovered. The study is urgent because it helps constrain the timing and origin of the 17O anomaly at the aftermath of a global glaciation and the result will be critical to interpreting the meaning of barite?s 17O anomalies and their environmental implications. Broader Impacts: By understanding how this study fits into a broader and new scientific problem, graduate students will be trained in acquiring and synthesizing multidisciplinary data including field geology, stratigraphy, petrography, stable isotope geochemistry, atmosphere-biosphere interactions, and Earth history. Students will gain valuable experience working overseas with international colleagues and diversify their own ?portfolio? of scientific collaboration and funding source. The project also provides an active and exciting research platform for teaching and recruiting in a large introduction course and for outreach effort through community activities. The results may ultimately provide a tracer for elevated levels of carbon dioxide in the atmosphere.

学术价值：Bao 和同事最近发现岩石记录中硫酸盐氧中稳定氧同位素 17O 的异常消耗。这些神秘的信号在与世界各地马里诺（约 635 迈尔斯）冰川作用相关的硫酸盐中明显较大。特别是华南陡山沱组基底的重晶石矿物表现出不同程度的 17O 异常。自 20 世纪 80 年代以来，地球上的许多化合物被发现具有偏离陆地分馏线的三氧同位素组成。所有这些先前报道的异常都是正异常，即 17O 异常富集，这是由于臭氧正 17O 异常有不同程度的遗传。在 PI 最近的出版物（Nature 2008 和 Science 2009）中，他提出新发现的异常 17O 损耗来自大气中的 O2，这是平流层 O2−CO2−O3 化学反应的结果，其中 O3 和 CO2 之间的交换导致O2 中 17O 异常消耗。在其他变量相同的情况下，增加 pCO2 可以增加 O2 负 17O 异常的幅度。马里诺冰川结束时硫酸盐 17O 的大量消耗表明当时可能存在极高的 pCO2 大气，因此构成了“雪球地球”的有力支持。假设。该提案将重点关注华南马里诺盖碳酸盐岩中 17O 贫重晶石的地质背景和成因，这里首次发现了明显的负 17O 异常。这项研究非常紧迫，因为它有助于限制全球冰川作用后 17O 异常的时间和起源，其结果对于解释重晶石 17O 异常的含义及其环境影响至关重要。更广泛的影响：通过了解这项研究如何适应更广泛的新科学问题，研究生将接受获取和综合多学科数据的培训，包括野外地质学、地层学、岩相学、稳定同位素地球化学、大气-生物圈相互作用和地球历史。学生将获得与国际同事一起在海外工作的宝贵经验，并使自己的“投资组合”多样化。科学合作和资金来源。该项目还提供了一个活跃且令人兴奋的研究平台，用于大型入门课程的教学和招募以及通过社区活动进行推广工作。结果可能最终为大气中二氧化碳含量升高提供示踪剂。