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Project Progress

As part of her work on the Fe isotope systematics of sulfides in sedimentary environments, graduate student Amy Wolfe has developed a method for extraction of pyrite from organic-rich rocks for Fe isotope analysis. We are collaborating with Ariel Anbar at ASU on the Fe isotope measurements by MC-ICPMS. Wolfe’s work is focusing on the isotopic behavior of Fe as a function of depositional environment and diagenesis, and will apply directly to interpretations of the marine Fe isotope record throughout the Precambrian. Our group is also collaborating with David Dzombak at Carnegie Mellon University to experimentally constrain pyrite dissolution rates and associated isotope fractionation effects as a function of morphology, sedimentary environment, and minor/trace element composition.

To understand element cycling in hyper-arid conditions analogous to those on Mars, undergraduate Justin Hynicka is examining the Sr isotope systematics of soil profiles in the Atacama Desert, Chile, in collaboration with Ron Amundson and colleagues at UC Berkeley. He has found systematic differences in the isotope behavior of salts in arid and in hyper-arid environments that reflect limited hydrous cation mobilization vs. pure atmospheric deposition. We are working with the Berkeley group to decipher the roles of in situ redistribution (as suggested by their sulfur isotope data) and changing atmospheric salt sources.

Graduate student Sherry Stafford is continuing to move her paleosol Sr/Nd isotope papers toward publication, with one in revision and another near submission. We have developed models to explain isotope systematics and redistribution in soils, with significant implications for the interpretation of trace elements (especially REE and Ce anomalies) in paleosols. This work highlights the promise and pitfalls of paleosol geochronology using radiogenic isotopes, and helps constrain the evolution of atmospheric chemistry in the Precambrian.