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.

知识分子的优点：Bao及其同事最近发现了岩石记录中硫酸盐氧气中稳定的氧同位素（17o）的异常耗竭。这些神秘的信号在与世界各地的冰川（约635 Myrs Old）相关的硫酸盐中明显很大。尤其是，中国南部基底杜桑图（Basal doushantuo）地层中的稀矿矿物质在17o异常中显示出可变的幅度。自1980年代以来，已经发现地球上的许多化合物具有偏离陆地分级线的三氧同位素组成。所有这些先前报道的异常都是阳性的，即，由于臭氧阳性17o异常的遗传程度不同，因此17o异常富集。在PI的最新出版物（自然2008年和Science 2009）中，他提出，新发现的异常17O耗竭来自大气O2，这是由于平流层O2＆＃8722; CO2＆＃8722; O3的化学作用，其中O3和CO2在O3和CO2之间产生了17o depletepletion o2 nomalous 17o depletepletion in O2 in o2中的交换。其他变量是相同的，增加PCO2可以增加O2负17o异常的大小。玛丽奴冰川结束时硫酸盐17o耗竭的大量表明，当时可能是极高的PCO2气氛，因此构成了对“雪球地球”的强烈支持吗？假设。该提议将集中于中国南部大麻帽碳酸盐岩的地质环境和起源，首先发现了明显的17o异常。这项研究之所以紧迫，是因为它有助于在全球冰川后的情况下限制17o异常的时机和起源，结果对于解释Barite的含义至关重要，这将是至关重要的。更广泛的影响：通过了解该研究如何适应更广泛的新科学问题，研究生将接受培训，以获取和综合多学科数据，包括现场地质学，地层学，岩石学，稳定的同位素地球化学，大气 - 双性恋相互作用和地球历史。学生将获得与国际同事在海外工作的宝贵经验，并使自己的投资组合多样化？科学合作和资助来源。该项目还提供了一个积极而令人兴奋的研究平台，用于在大型介绍课程中进行教学和招聘，并通过社区活动进行外展工作。结果最终可能会为大气中二氧化碳水平升高提供示踪剂。