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

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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.