U/u in marine carbonates as a tracer of precambrian paleoredox

CONDITIONS. C. Chen, F.L.H Tissot, N. Dauphas, A. Bekker, G.P. Halverson, J. Veizer Origins Lab, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, Chicago, IL (chenxicindy@uchicago.edu), Department of the Earth, Atmospheric and Planetary Sciences, MIT, Cambridge, Department of Earth Sciences, University of California Riverside, Riverside, CA, Department of Earth and Planetary Sciences, McGill University, Montreal, Quebec, Canada, Department of Earth and Environmental Sciences, University of Ottawa, Ottawa, Canada.