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

学术价值：鲍康如和他的同事最近在岩石记录中发现了稳定氧同位素17O在硫酸盐氧中的异常枯竭。这些神秘的信号在硫酸盐中明显很大，与世界各地的马里诺(约635迈尔斯)冰川有关。尤其是中国南部陡山沱组底部的重晶石矿物显示出不同程度的17O异常。自20世纪80年代以来，地球上许多化合物被发现具有偏离陆地分馏线的三重氧同位素组成。所有这些前人报道的异常都是正值，即17O异常富集度不同，这是由于臭氧的遗传程度不同造成的？S 17O正异常。在PI最近的出版物(《自然》2008和《科学》2009)中，他提出，新发现的异常17O消耗来自大气O2，这是平流层O2和CO2之间的交换导致O2异常17O消耗的结果。在其他变量相同的情况下，增加二氧化碳分压可以增加氧气的负17O异常的幅度。马里诺冰期末期硫酸盐~(17)O的大量亏损表明，当时可能是一个二氧化碳含量极高的大气，因此构成了对雪球地球的有力支持。假设。这一建议将集中在中国南部海滨统帽状碳酸盐岩中的17O剥离重晶石的地质背景和成因上，这里首次发现了明显的负17O异常。这项研究迫在眉睫，因为它有助于限制全球冰川后17O异常的时间和来源，这一结果将对解释重晶石-S 17O异常的意义及其环境影响至关重要。更广泛的影响：通过理解这项研究如何适应一个更广泛的新的科学问题，研究生将接受培训，获得和综合多学科数据，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进行外联工作提供了一个积极和令人兴奋的研究平台。这一结果可能最终会为大气中二氧化碳水平的升高提供一个示踪剂。

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.