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

学术价值：鲍和同事最近在岩石记录中发现了稳定氧同位素17O的异常耗尽。这些神秘的信号在世界各地与马里诺冰期（~ 635 Myrs）有关的硫酸盐中明显很大。特别是华南基底陡山沱组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地球分馏线的三氧同位素组成。所有这些先前报道的异常都是积极的，即由于不同程度的臭氧遗传，17O异常富集。正17O异常。在PI最近发表的文章（《自然》2008和《科学》2009）中，他提出，新发现的异常的17O损耗来自于大气中的O2，这是平流层的O2和co2的结果。O3化学，其中O3和CO2之间的交换导致O2中异常的17O损耗。在其他变量相同的情况下，co2分压的增加会增加O2负17O距平的幅度。在马里诺冰期结束时，大量的硫酸盐17O耗竭可能表明当时的大气中co2分压非常高，因此有力地支持了？雪球地球?假设。本文将重点研究中国南方Marinoan盖层碳酸盐岩中17O-贫重晶石的地质背景和成因，该地区首次发现明显的负17O异常。这项研究非常紧迫，因为它有助于确定17O年全球冰期后异常的时间和起源，其结果将对解释重晶石的意义至关重要。17O异常及其对环境的影响。更广泛的影响：通过了解本研究如何适应更广泛和新的科学问题，研究生将获得和综合多学科数据的训练，包括野外地质学，地层学，岩石学，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。该项目还为大型入门课程的教学和招聘以及通过社区活动的推广工作提供了一个活跃和令人兴奋的研究平台。该结果可能最终为大气中二氧化碳水平升高提供一种示踪剂。

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.