2016
DOI: 10.1111/gbi.12203
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Chromium geochemistry of the ca. 1.85 Ga Flin Flon paleosol

Abstract: 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 oxid… Show more

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Cited by 44 publications
(36 citation statements)
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References 125 publications
(308 reference statements)
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“…The greatest depletion of Mn occurs in the most oxidized upper part of the Beaverlodge Lake paleosol where Fe(III)/Fe(II) ratios are highest (Figure c and d), in agreement with the findings in Babechuk et al. () for the Flin Flon paleosol. In both cases, oxygen was high enough to oxidize Fe(II) to Fe(III) during pedogenesis, but too low to oxidize and retain Mn as observed in modern soils.…”
Section: Discussionsupporting
confidence: 91%
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“…The greatest depletion of Mn occurs in the most oxidized upper part of the Beaverlodge Lake paleosol where Fe(III)/Fe(II) ratios are highest (Figure c and d), in agreement with the findings in Babechuk et al. () for the Flin Flon paleosol. In both cases, oxygen was high enough to oxidize Fe(II) to Fe(III) during pedogenesis, but too low to oxidize and retain Mn as observed in modern soils.…”
Section: Discussionsupporting
confidence: 91%
“…In addition, δ 53 Cr values are higher than the igneous inventory, substantially higher in the Flin Flon paleosol (0.19‰ to 2.23‰), but only marginally higher in the Beaverlodge Lake paleosol (0.02‰ to 0.12‰), which is the opposite behavior observed in modern soils replete with Mn‐oxide, thus opening up the possibility that the absence of Mn oxides in ca . 1.9 Ga soils tipped the balance toward preservation of alternate pathways by which Cr isotopes became fractionated in the studied paleosols (Babechuk et al., ).…”
Section: Discussionmentioning
confidence: 99%
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“…Sample powders were drilled from fresh samples taken either from outcrop or core. Powdered paleosol samples were weighed, ashed at 500°C, and then digested at 90°C using a series of acid dissolution steps used widely (e.g., Babechuk et al, ; D'Arcy, Babechuk, Døssing, Gaucher, & Frei, ; Frei et al, ) to prepare silicate samples for Cr isotope analysis: HF + HNO 3 , aqua regia, and finally 6N HCl. This digest protocol is considered sufficient to liberate all Cr in spinel‐free rocks (such as the ones studied here) save for the minor Cr in zircon; the similarity of the digestion procedure to other laboratories also facilitates direct comparison of isotope data.…”
Section: Methodsmentioning
confidence: 99%