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Project Progress

Paleosols. The Sm-Nd system has proven to be a useful chronological tool for pedogenesis in some Precambrian weathering profiles where the ages of weathering are poorly constrained, and the system can provide insight into the robustness of the REE system in the face of post-pedogenic metamorphism and alteration. Dissertation work of Sherry Stafford shows that the Sm-Nd system can record (or see through) pedogenesis in some cases, while the Rb-Sr system is sensitive to subsequent metamorphic events. However, recent results from the ultramafic Kalkkloof paleosol, S. Africa (Masters project of Katherine Walden) demonstrate that the REE can be highly mobile well after pedogenesis. This could be a general characteristic of mafic and ultramafic paleosols.

Archean Biosphere Drilling Project (ABDP): Work was initiated on Fe-bearing cherts and basalt flows from the 3.46 Ga Marble Bar greenstone belt. Results from the first samples of chert yield positive initial epsilon-Nd values, consistent with derivation of the REE from submarine hydrothermal sources. However, this is somewhat at odds with the LREE-enrichment exhibited by these samples, which suggests possible REE fractionation when the chert was precipitated. Additional work will focus on the basalt flows and microbands within the chert units.

Modern Soil Analogs: The Atacama Desert of northern Chile is one of the driest, least vegetated regions on Earth outside of Antarctica, thus making it a useful analog for both Mars and the early Earth. We are collaborating with R. Amundson and his colleagues at UC Berkeley to examine the provenance of nitrate, sulfate and carbonate that have accumulated in the Atacama soils over millions of years. Initial Sr isotope work suggests a largely lithogenic sulfate source, but with greater marine influence toward the surface. Current work is focusing on sources of Ca in both sulfate and carbonate minerals in multiple profiles.