Studies of modern sedimentary analogs to ancient rock precursors are critical to gain insight into the biogeochemical processes responsible for generating unique chemical or isotopic compositions in ancient rocks. A recent study published by the University of Wisconsin NAI Team in Geobiology provides an example of such a modern analog study in the context of Archean and Paleoproterozoic Banded Iron Formations (BIFs). Sediments downstream of the Iron Mountain acid mine drainage site in northern California were examined for their chemical and Fe isotope composition, as well as the presence and activity of iron-reducing microorganisms. The results link dissimilatory microbial iron reduction (DIR) to the generation of large quantities of aqueous (mobile) ferrous iron, and provide the first demonstration of Fe isotope fractionation in an environment where DIR has been shown by microbiological methods to be active in sediment metabolism. These findings provide insight into pathways whereby DIR could have led to the formation of isotopically-light Fe-bearing minerals in BIFs.
[Source: NAI Newsletter]
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