Reassessing the photochemical contribution to Archean Banded Iron Formations

IF 3.6 2区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Chemical Geology Pub Date : 2025-03-28 DOI:10.1016/j.chemgeo.2025.122763

Pilar C. Vergeli , Stephen J. Romaniello , Hilairy E. Hartnett , Ariel D. Anbar

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引用次数: 0

Abstract

Banded iron formations (BIFs) are massive iron (Fe) oxide deposits that provide information about the Precambrian environment. A biological origin for BIFs is commonly invoked. Some studies have suggested on theoretical and experimental grounds that an abiotic origin of BIFs is possible, via UV photo-oxidation of dissolved Fe(II) species, but this conclusion has been disputed. Here, we provide an experimental assessment of the viability of the photochemical hypothesis under the most realistic Archean environmental conditions simulated to date. These conditions include realistic seawater salinity and carbonate buffering, and a light source that simulates the solar UV spectrum. We report the wavelength dependence of photo-oxidation rates and calculate the quantum yield for Fe³⁺ production from FeOH⁺ (

Φ

= 0.03) and from Fe²⁺(aq) (

Φ

= 0.1). Using these quantum yields in a photogeochemical model, we calculate the rate of Fe³⁺ production by photo-oxidation as 96 mg⁻¹ cm⁻² yr⁻¹. Previous studies that do not consider wavelength-dependent effects overestimate the rate of Fe deposition by almost 50 %. Nevertheless, our modeled rate is sufficient to account for the mass of Fe deposited in BIFs at all but the most extreme periods of iron deposition, in the Neoarchean, when other mechanisms such as oxidation by photosynthetically produced O₂ or photoferrotrophy must be invoked.

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光化学对太古宙带状铁构造的贡献

带状铁地层（BIFs）是块状铁（Fe）氧化物矿床，提供了有关前寒武纪环境的信息。bif的生物学起源常被提及。一些研究在理论和实验基础上提出，非生物来源的bif是可能的，通过紫外光氧化溶解的铁（II）物种，但这一结论一直存在争议。在此，我们在迄今为止模拟的最真实的太古宙环境条件下对光化学假设的可行性进行了实验评估。这些条件包括真实的海水盐度和碳酸盐缓冲，以及模拟太阳紫外线光谱的光源。我们报道了光氧化速率的波长依赖性，并计算了FeOH+ （Φ = 0.03）和Fe2+(aq) （Φ = 0.1）生产Fe3+的量子产率。在光地球化学模型中使用这些量子产率，我们计算出光氧化产生Fe3+的速率为96 mg−1 cm−2 yr−1。先前没有考虑波长依赖效应的研究高估了铁沉积速率近50%。尽管如此，我们的模型速率足以解释除新太古代最极端的铁沉积时期外的所有bif中沉积的铁质量，当其他机制如光合作用产生的O2氧化或光嗜铁作用必须被激活时。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Chemical Geology 地学-地球化学与地球物理

CiteScore

7.20

自引率

10.30%

发文量

374

审稿时长

3.6 months

期刊介绍： Chemical Geology is an international journal that publishes original research papers on isotopic and elemental geochemistry, geochronology and cosmochemistry. The Journal focuses on chemical processes in igneous, metamorphic, and sedimentary petrology, low- and high-temperature aqueous solutions, biogeochemistry, the environment and cosmochemistry. Papers that are field, experimentally, or computationally based are appropriate if they are of broad international interest. The Journal generally does not publish papers that are primarily of regional or local interest, or which are primarily focused on remediation and applied geochemistry. The Journal also welcomes innovative papers dealing with significant analytical advances that are of wide interest in the community and extend significantly beyond the scope of what would be included in the methods section of a standard research paper.