Insights into the processes and controls on the absolute abundance and distribution of manganese in Precambrian iron formations

Archean to early Paleoproterozoic iron formations document a transition in iron oxidation mechanisms

“…As such, Mn enrichments resulting from either Mn oxide precipitation or a Mn-oxide shuttle to the sediment-seawater interface may be linked to the presence of an oxygenated water column 11,31 . Although the sedimentary and diagenetic pathways responsible for the incorporation of Mn into IFs has recently been questioned 32 , secular trends in the relative enrichment of Mn in IFs are typically tied to marine redox conditions. Therefore, as IFs serve as robust archives of both the Fe isotope and Mn/Fe ratios in the deep time, they may be interrogated to constrain the redox state of local seawater during IF deposition.…”

Direct precipitation of siderite in ferruginous environments

“…However, the lack of an Mn-oxide flux in CL suggests that a fundamental control on precipitation governs this occurrence of Mn-siderite, with competition from nucleation inhibitors (e.g., Mg(II); Vuillemin et al, 2019) or the differential solubilities of Ca-Mn-Fe carbonates (e.g., Wittkop et al, 2020) offering potential explanations. Thus, the occurrence of Mn-rich siderite in the geologic record (e.g., Siahi et al, 2020;Swanner et al, 2020) may be interpreted to reflect passive incorporation of dissolved Mn into the crystal structure, rather than reduction of Mn-oxides.…”

“…Despite the diversity of environments in which siderite occurs, two mechanisms are generally considered to drive its formation: 1) direct precipitation from an anoxic and iron-enriched (ferruginous) fluid; and 2) as a diagenetic product derived from reduction of primary iron (oxyhydr)oxides coupled to microbial organic carbon remineralisation (Heimann et al, 2010). While dissimilatory reduction of reactive iron (oxyhydr)oxides, such as ferrihydrite, may explain the negative C-isotopic composition and textures of many lacustrine siderite occurrences (Vuillemin et al, 2019), the textures and C-isotope signatures of well-preserved Precambrian IFs are also consistent with precipitation from ferruginous seawater (Beukes et al, 1990;Siahi et al, 2020;Riding et al, 2022), perhaps under a strong hydrothermal influence (Jiang and Tosca, 2019).…”

2470 million-year-old banded iron formation reveals a climatic oscillation consistent with the Gleissberg solar cycle

“…6). In pre-GOE anoxic oceans, vanadium exists in the form of V(III), which readily hydrolyzes and precipitates as insoluble hydroxides, largely independent of microbial activity and iron cycling 40 ; Manganese holds unique depositional channels apart from co-precipitation with iron 41 ; reduced As(III) has high solubility and will not be scavenged by iron oxyhydroxides 42 . Therefore, the elemental spectra of these three elements did not preserve climatic cycle signals and exhibit little correlation with that of Fe (Supplementary Fig.…”