期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：27
页码：8193-8198
DOI：10.1073/pnas.1505515112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceCombined Fe- and Nd-isotope signatures suggest that banded iron formations (BIFs) contain a major component of continentally derived iron that was mobilized by microbial iron reduction followed by transport through an iron shuttle to the site of BIF formation in deep basin environments. This Fe source is in addition to the widely accepted submarine hydrothermal source of Fe in BIFs, and the two sources of Fe may be comparable in importance, although their proportions change over time dependent on basin-scale circulation. Banded iron formations (BIFs) record a time of extensive Fe deposition in the Precambrian oceans, but the sources and pathways for metals in BIFs remain controversial. Here, we present Fe- and Nd-isotope data that indicate two sources of Fe for the large BIF units deposited 2.5 billion y ago. High-{varepsilon}Nd and -{delta}56Fe signatures in some BIF samples record a hydrothermal component, but correlated decreases in {varepsilon}Nd- and {delta}56Fe values reflect contributions from a continental component. The continental Fe source is best explained by Fe mobilization on the continental margin by microbial dissimilatory iron reduction (DIR) and confirms for the first time, to our knowledge, a microbially driven Fe shuttle for the largest BIFs on Earth. Detailed sampling at various scales shows that the proportions of hydrothermal and continental Fe sources were invariant over periods of 100-103 y, indicating that there was no seasonal control, although Fe sources varied on longer timescales of 105-106 y, suggesting a control by marine basin circulation. These results show that Fe sources and pathways for BIFs reflect the interplay between abiologic (hydrothermal) and biologic processes, where the latter reflects DIR that operated on a basin-wide scale in the Archean.
关键词：BIF ; DIR ; iron shuttle ; Nd isotope ; Fe isotope
