Knowledge Resource Center for Ecological Environment in Arid Area
DOI | 10.1111/gbi.12203 |
Chromium geochemistry of the ca. 1.85 Ga Flin Flon paleosol | |
Babechuk, M. G.1,2; Kleinhanns, I. C.1; Schoenberg, R.1 | |
通讯作者 | Babechuk, M. G. |
来源期刊 | GEOBIOLOGY |
ISSN | 1472-4677 |
EISSN | 1472-4669 |
出版年 | 2017 |
卷号 | 15期号:1页码:30-50 |
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 parts per thousand delta Cr-53/52. The protolith greenstone (delta Cr-53/52: -0.23 parts per thousand), the deepest weathering horizon (delta Cr-53/52: -0.15 to -0.23 parts per thousand) and a residual corestone in the upper paleosol (delta Cr-53/52: -0.01 parts per thousand) 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 Cr-53-enriched compositions (delta Cr-53/52 values between +1.50 and +2.38 parts per thousand), 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 Cr-53 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 O-2 from Cr isotope data alone. |
类型 | Article |
语种 | 英语 |
国家 | Germany ; Ireland |
收录类别 | SCI-E |
WOS记录号 | WOS:000390195900003 |
WOS关键词 | WESTERN MOJAVE DESERT ; ISOTOPE FRACTIONATION ; HEXAVALENT CHROMIUM ; ATMOSPHERIC OXYGEN ; TRACE-ELEMENTS ; TRANSVAAL SUPERGROUP ; ULTRAMAFIC ROCKS ; IRON SPECIATION ; SOIL FORMATION ; DECCAN TRAPS |
WOS类目 | Biology ; Environmental Sciences ; Geosciences, Multidisciplinary |
WOS研究方向 | Life Sciences & Biomedicine - Other Topics ; Environmental Sciences & Ecology ; Geology |
资源类型 | 期刊论文 |
条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/199164 |
作者单位 | 1.Univ Tubingen, Dept Geosci, Tubingen, Germany; 2.Trinity Coll Dublin, Dept Geol, Dublin 2, Ireland |
推荐引用方式 GB/T 7714 | Babechuk, M. G.,Kleinhanns, I. C.,Schoenberg, R.. Chromium geochemistry of the ca. 1.85 Ga Flin Flon paleosol[J],2017,15(1):30-50. |
APA | Babechuk, M. G.,Kleinhanns, I. C.,&Schoenberg, R..(2017).Chromium geochemistry of the ca. 1.85 Ga Flin Flon paleosol.GEOBIOLOGY,15(1),30-50. |
MLA | Babechuk, M. G.,et al."Chromium geochemistry of the ca. 1.85 Ga Flin Flon paleosol".GEOBIOLOGY 15.1(2017):30-50. |
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