Summary
This geobiological study presents the first documented granular iron formation of Archaean age (ca. 3.0–2.8 Ga) from the Pongola Supergroup in southern Africa, with textural and isotopic evidence suggesting formation through incomplete microbial oxidation of hydrothermal Fe²⁺ by iron-oxidizing bacteria. The authors distinguish this shallow-water oncoidal magnetite deposit from coeval deeper-water iron formations based on iron isotope fractionation patterns and trace element geochemistry, proposing contrasting Fe²⁺ sources and oxidation pathways. The work contributes to understanding the role of early microbial metabolism in iron cycling during the Mesoarchaean eon.
UK applicability
This paper is primarily of scientific interest to geologists and biogeochemists studying early Earth history and the evolution of microbial iron metabolism. Its findings have no direct applicability to UK farming systems, soil health, nutrient density, or human health.
Key measures
δ⁵⁶Fe values in magnetite; textural analysis of oncoids; trace element and aluminium concentrations; iron mineralogy (magnetite, Fe³⁺-oxyhydroxide); silica and iron enrichment/depletion ratios
Outcomes reported
The study documents textural and geochemical evidence for microbial iron oxidation in the first identified Archaean-age granular iron formation from the Pongola Supergroup. Iron isotope compositions and mineralogical features were used to distinguish between distinct Fe²⁺ pathways and sources in shallow versus deeper water depositional environments.
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