International Research Fellowship Program: Iron Isotopes and the Neoproterozoic Snowball Earth

0401772 Halverson国际研究奖学金计划使美国科学家和工程师能够在国外进行三到二十四个月的研究。 该计划的奖项提供了联合研究的机会，并使用独特或互补的设施，专业知识和国外的实验条件。该奖项将支持由博士盖伦P. Halverson二十一个月的研究奖学金工作博士弗兰克Poitrasson和安妮Nederlane保罗萨巴蒂尔大学在图卢兹，法国：该项目的主要目标是评估保存在古代沉积物中的铁同位素信号的真实性，并检验Beard等人（2003年b）的预测。海水铁同位素组成的大幅波动与晚前寒武纪（约7.5亿至6亿年前）的全球（雪球）冰川相吻合。铁同位素地球化学是一个年轻的领域，还有很多工作要做，以阐明在生物和非生物系统中的铁同位素组成的自然变化的幅度和原因。 然而，最近的分析精度的提高和结果表明，从海水中沉淀的矿物中的铁同位素比值相对较大的波动意味着铁同位素分析肯定会在沉积地球化学中找到许多应用。 在晚前寒武纪冰川期间和之后立即沉积的岩石是寻找海洋铁同位素组成大偏差的理想场所。 根据霍夫曼等人（1998年）的“雪球”地球假说，整个海洋在这些冰川作用期间冻结，铁完全来自热液通量-具有独特的铁同位素信号-在溶液中积累。 这种信号应该保存在冰川时期沉积的含铁矿物中。 重要的是，富含铁的碳酸盐在冰川期结束时在世界范围内同步沉积，从而可以直接测试古代沉积岩中铁同位素特征作为海洋化学代表的可行性。 这项调查的其他好处将包括对自然发生的标本的铁同位素数据库的重大贡献，对不同铁相之间铁同位素组成的自然变化幅度的影响，以及适用于各种其他问题的分析技术的发展。国家的最先进的实验室建成的具体目的是分析铁同位素。该项目补充了哈佛大学和麻省理工学院正在进行的实地工作和地球化学分析，旨在揭示冰川和冰后期海洋的化学演变。

0401772HalversonThe International Research Fellowship Program enables U.S. scientists and engineers to conduct three to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad.This award will support a twenty-one-month research fellowship by Dr. Galen P. Halverson to work with Drs. Franck Poitrasson and Anne Nedelec at the University Paul-Sabatier in Toulouse, France.The main objectives of this project are to evaluate the fidelity of the iron-isotopic signal preserved in ancient sediments and to test the prediction of Beard et al. (2003b) that large fluctuations in the iron isotopic composition of seawater coincided with global (snowball) glaciations in the late Precambrian (~750 to 600 million years ago). The field of iron isotope geochemistry is young, and much work remains to be done to elucidate the magnitude and causes of natural variations in iron isotope composition in both biological and non-biological systems. However, recent improvements in analytical precision and results demonstrating relatively large fluctuations in iron isotope ratios in minerals precipitated from seawater mean that iron isotope analysis is certain to find many applications in sedimentary geochemistry. Rocks deposited during and immediately after the late Precambrian glaciations are an ideal place to look for large deviations in the iron isotopic composition of the ocean. According to the "snowball" Earth hypothesis of Hoffman et al. (1998), the entire ocean froze over during these glaciations, and iron derived exclusively from hydrothermal fluxes - which has a unique iron isotopic signal - accumulated in solution. This signal should be preserved in iron-bearing minerals deposited during the glaciations. Importantly, iron-rich carbonates were deposited synchronously and worldwide at the end of the glaciations, enabling a straightforward test of the viability of the iron isotopic signature in ancient sedimentary rocks as a proxy for marine chemistry. Additional benefits of this investigation will include a major contribution to the iron isotopic database on naturally occurring specimens, implications for the magnitude of natural variations in iron isotope compositions between different iron phases, and the development of analytical techniques applicable to a wide variety of other problems.This project takes advantage of a newly established, state-of-the art laboratory built with the specific intention of analyzing iron isotopes. The project complements ongoing field work and geochemical analysis at Harvard University and MIT aimed at unraveling the chemical evolution of the glacial and post-glacial oceans.