globalchange  > 影响、适应和脆弱性
DOI: 10.1111/gbi.12248
Scopus记录号: 2-s2.0-85031502139
论文题名:
Oncoidal granular iron formation in the Mesoarchaean Pongola Supergroup, southern Africa: Textural and geochemical evidence for biological activity during iron deposition
作者: Smith A.J.B.; Beukes N.J.; Gutzmer J.; Czaja A.D.; Johnson C.M.; Nhleko N.
刊名: Geobiology
ISSN: 1472-4677
EISSN: 1472-4669
出版年: 2017
卷: 15, 期:6
起始页码: 731
结束页码: 749
语种: 英语
Scopus关键词: ankerite ; aragonite ; Archean ; bioactivity ; deposition ; dolomite ; geochemistry ; granular medium ; iron ; mass spectrometry ; microbial activity ; ooid ; rare earth element ; recrystallization ; texture ; KwaZulu-Natal ; Pongola ; South Africa
Scopus学科分类: Earth and Planetary Sciences: General Earth and Planetary Sciences ; Environmental Science: General Environmental Science ; Agricultural and Biological Sciences: Ecology, Evolution, Behavior and Systematic
英文摘要: We document the discovery of the first granular iron formation (GIF) of Archaean age and present textural and geochemical results that suggest these formed through microbial iron oxidation. The GIF occurs in the Nconga Formation of the ca. 3.0–2.8 Ga Pongola Supergroup in South Africa and Swaziland. It is interbedded with oxide and silicate facies micritic iron formation (MIF). There is a strong textural control on iron mineralization in the GIF not observed in the associated MIF. The GIF is marked by oncoids with chert cores surrounded by magnetite and calcite rims. These rims show laminated domal textures, similar in appearance to microstromatolites. The GIF is enriched in silica and depleted in Fe relative to the interbedded MIF. Very low Al and trace element contents in the GIF indicate that chemically precipitated chert was reworked above wave base into granules in an environment devoid of siliciclastic input. Microbially mediated iron precipitation resulted in the formation of irregular, domal rims around the chert granules. During storm surges, oncoids were transported and deposited in deeper water environments. Textural features, along with positive δ56Fe values in magnetite, suggest that iron precipitation occurred through incomplete oxidation of hydrothermal Fe2+ by iron-oxidizing bacteria. The initial Fe3+-oxyhydroxide precipitates were then post-depositionally transformed to magnetite. Comparison of the Fe isotope compositions of the oncoidal GIF with those reported for the interbedded deeper water iron formation (IF) illustrates that the Fe2+ pathways and sources for these units were distinct. It is suggested that the deeper water IF was deposited from the evolved margin of a buoyant Fe2+ aq-rich hydrothermal plume distal to its source. In contrast, oncolitic magnetite rims of chert granules were sourced from ambient Fe2+ aq-depleted shallow ocean water beyond the plume. © 2017 John Wiley & Sons Ltd
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资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/85032
Appears in Collections:影响、适应和脆弱性

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作者单位: Paleoproterozoic Mineralization Research Group, Department of Geology, University of Johannesburg, Johannesburg, South Africa; Department of Science and Technology – National Research Foundation Centre of Excellence for Integrated Mineral and Energy Resource Analysis, University of Johannesburg, Johannesburg, South Africa; Department of Geology, University of Johannesburg, Johannesburg, South Africa; Helmholtz Zentrum Dresden-Rossendorf, Helmholtz Institute Freiberg for Resource Technology, Freiberg, Germany; Department of Mineralogy, TU Bergakademie Freiberg, Freiberg, Germany; Department of Geology, University of Cincinnati, Cincinnati, OH, United States; Department of Geoscience, University of Wisconsin, Madison, WI, United States; NASA Astrobiology Institute, University of Wisconsin, Madison, WI, United States; Geological Survey and Mines Department, Mbabane, Swaziland

Recommended Citation:
Smith A.J.B.,Beukes N.J.,Gutzmer J.,et al. Oncoidal granular iron formation in the Mesoarchaean Pongola Supergroup, southern Africa: Textural and geochemical evidence for biological activity during iron deposition[J]. Geobiology,2017-01-01,15(6)
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