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Project Progress

Our work currently involves two main areas:

(1) Understanding the evolution of ancient soil profiles (paleosols) and their record of Earth’s early atmosphere and climate:

We have examined core and outcrop samples from two Paleoproterozoic weathering profiles developed on granodiorite in the Hokkalampi area of Finland. Analyses by Ph.D. student Sherry Stafford suggests that pedogenic REE fractionation, including development of Ce anomalies, took place about 2.35 Ga ago, coincident with the “Great Oxidation Event.” The Rb-Sr system records metamorphism around 1.8 Ga ago. Geochemistry and morphology of the Nuutilanvaara profile suggests formation under unsaturated, oxidized conditions; Fe and LREE depletions from the Paukkajanvaara profile suggest formation in a saturated zone. Soil textures in the Archean South Roberts Pit profile, Steep Rock region, Canada include intertexic and agglomeroplasmic fabric and cutans; rip up clasts and soft sediment deformation features are present near the unconformity. Geochemistry and Rb-Sr systematics for the profile suggest K-metasomatism occurred during greenschist metamorphism at 2.7 Ga. However, the Sm-Nd systematics yield a relatively precise age of 3.0 Ga, and document the preservation of Archean pedogenic REE fractionation.

(2) Investigations of sedimentary pyrite oxidation.

Current studies center on massive and framboidal sedimentary iron sulfides and siderite within Paleozoic coal seams and associated shale units. M.S. student Amy Wolfe developed methods for separating finely disseminated pyrite from coal and organic-rich underclay. A portion of this investigation involves NSF-supported experimental determination of Fe isotope fractionation associated with pyrite oxidation, in collaboration with Dr. David Dzombak of Carnegie Mellon University. Because preparation methods can significantly affect dissolution rates, part of this effort involved development of methods for reproducibly obtaining a restricted grain size distribution for dissolution experiments. Related work includes sequential extraction experiments to assess trace metal provenance on goethite derived from pyrite oxidation (Kairies et al., in press).