DOI: 10.1111/gbi.12203
Scopus记录号: 2-s2.0-84978961940
论文题名: Chromium geochemistry of the ca. 1.85 Ga Flin Flon paleosol
作者: Babechuk M.G. ; Kleinhanns I.C. ; Schoenberg R.
刊名: Geobiology
ISSN: 1472-4677
EISSN: 1472-4669
出版年: 2017
卷: 15, 期: 1 起始页码: 30
结束页码: 50
语种: 英语
Scopus关键词: Archean
; chromium
; dissolution
; element mobility
; geochemistry
; greenstone
; isotopic composition
; isotopic fractionation
; nutrient enrichment
; paleosol
; pedogenesis
; protolith
; weathering profile
; Canada
; Flin Flon
; Manitoba
; chromium
; chemistry
; oxidation reduction reaction
; pH
; sediment
; Chromium Isotopes
; Geologic Sediments
; Hydrogen-Ion Concentration
; Oxidation-Reduction
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: Fractionation of stable Cr isotopes has been measured in Archaean paleosols and marine sedimentary rocks and interpreted to record the terrestrial oxidation of Cr(III) to Cr(VI), providing possible indirect evidence for the emergence of oxygenic photosynthesis. However, these fractionations occur amidst evidence from other geochemical proxies for a pervasively anoxic atmosphere. This study examined the Cr geochemistry of the ca. 1.85 Ga Flin Flon paleosol, which developed under an atmosphere unambiguously oxidising enough to quantitatively convert Fe(II) to Fe(III) during pedogenesis. The paleosol shows an extreme range in Cr isotope composition of 2.76 ‰ δ53/52Cr. The protolith greenstone (δ53/52Cr: −0.23 ‰), the deepest weathering horizon (δ53/52Cr: −0.15 to −0.23 ‰) and a residual corestone in the upper paleosol (δ53/52Cr: −0.01 ‰) all exhibit Cr isotopic compositions comparable to unaltered igneous rocks. The most significant isotopic fractionation is preserved in the areas influenced by oxidative subaerial weathering (i.e. increase in Fe(III)/Fe(II)) and the greatest loss of mobile elements. The uppermost paleosol horizon is both Cr and Mn depleted and offset to significantly 53Cr-enriched compositions (δ53/52Cr values between +1.50 and +2.38 ‰), which is not easily modelled with the oxidation of Cr(III) and loss of isotopically heavy Cr(VI). Instead, the currently preferred model for these data invokes the open-system removal of isotopically light aqueous Cr(III) during either pedogenesis or subsequent hydrothermal/metamorphic alteration. The 53Cr enrichment would then represent the preferential dissolution or complexation of isotopically light aqueous Cr(III) species (enhanced by lower pH conditions and possibly the presence of complexing ligands) and/or the residual signature from preferential adsorption of isotopically heavy Cr(III). Both scenarios would contradict the widely held assumption that only redox reactions of Cr can generate large magnitude isotopic fractionations and, if substantiated, non-redox isotope effects would complicate the conclusive fingerprinting of ancient atmospheric O2 from Cr isotope data alone. © 2016 John Wiley & Sons Ltd Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/85079
Appears in Collections: 影响、适应和脆弱性
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作者单位: Department of Geosciences, University of Tübingen, Tübingen, Germany; Department of Geology, Trinity College Dublin, Dublin 2, Ireland
Recommended Citation:
Babechuk M.G.,Kleinhanns I.C.,Schoenberg R.. Chromium geochemistry of the ca. 1.85 Ga Flin Flon paleosol[J]. Geobiology,2017-01-01,15(1)