Redox fluctuations in the Early Ordovician oceans: An insight from chromium stable isotopes

D'Arcy, Joan; Gilleaudeau, Geoffrey J.; Peralta, Silvio H.; Gaucher, Claudio

doi:10.1016/j.chemgeo.2016.10.012

Cited by 40 publications

(8 citation statements)

References 83 publications

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“…Additionally, we dissolved the certified carbonate standard JLs‐1 and measured its Cr isotopic composition along with samples from each run. Measured δ 53 Cr values for JLs‐1 in our laboratory (+1.87 ± 0.02‰, 2σ; see also D’Arcy et al., 2017) are reproducible and in good agreement with published values (Bonnand et al., 2011).…”

Section: Methodssupporting

confidence: 89%

Microbially induced chromium isotope fractionation and trace elements behavior in lower Cambrian microbialites from the Jaíba Member, Bambuí Basin, Brazil

et al. 2020

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In east‐central Brazil, the Ediacaran‐Cambrian Bambuí Basin has the potential to provide a record of unique geochemical responses of Earth's ocean and atmosphere evolution during this key time interval. From this perspective, we studied an interval of the upper Bambuí Basin using sedimentologic, stratigraphic, and chemostratigraphic tools. The lower Cambrian Jaíba Member of the uppermost Serra da Saudade Formation is an interval of up to 60 m‐thick of carbonate rocks disposed into two shallowing upward trends. Inner to outer ramp and high‐energy shoal deposits are described, in which laminated microbialites are the prevailing sedimentary facies. REE + Y data suggest contamination by iron (oxy)hydroxides that are dissociated from the riverine detritic flux. Sedimentary iron enrichment may be related to the settling of iron nanoparticles in coastal environments, diagenetic iron mobilization, or both. MREE enrichment is caused by microbial degradation of organic matter in the iron reduction zone during the anoxic early‐diagenetic stage. Chromium isotopes yielded negatively fractionated values (δ53Cr = −0.69 to −0.27‰), probably resulting from biotic and abiotic reduction of dissolved Cr(VI) to light and less toxic Cr(III) within pores of microbial mats. The δ53Cr data of the Jaíba microbialite are thus a product of metabolic reactions in microbial mats and do not reflect seawater signal. The isotopic offset from seawater is feasible from molecular diffusion of Cr into pore water and reduction reactions occurring deep inside the mat, although the exact mechanism and consequences are not yet fully understood due to the poor preservation of metabolic reactions in the geological record. Our study suggests that Cr isotopes can be used to reconstruct Cr and other metals cycling within ancient microbial mats, and that caution should be taken when using past microbialites to infer seawater Cr records and redox state of the atmosphere and ocean.

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Section: Methodssupporting

confidence: 89%

Microbially induced chromium isotope fractionation and trace elements behavior in lower Cambrian microbialites from the Jaíba Member, Bambuí Basin, Brazil

et al. 2020

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“…This study inspired the wide-spread use of the Cr isotope system as a paleo-redox tracer (e.g. Cole et al, 2016;Crowe et al, 2013;D'Arcy et al, 2017;. The basis for this tracer's usage is that a threshold level of atmospheric oxygen is required to form manganese oxides which are a prerequisite for the oxidation of immobile Cr(III) hosted by rock minerals (Bartlett and James, 1979;Fendorf, 1995;.…”

Section: Research History Of the Cr Isotopic Systemmentioning

confidence: 99%

The marine biogeochemistry of chromium isotopes

Moos¹

2018

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“…Variations in 53 Cr/ 52 Cr (δ 53 Cr) are increasingly used to reconstruct redox variations in Earth's oceans and atmosphere (Frei et al, 2009;Reinhard et al, 2014;Scheiderich et al, 2015;Babechuk et al, 2016;Cole et al, 2016;Holmden et al, 2016;Paulukat et al, 2016;D'Arcy et al, 2017;Rodler et al, 2017;Canfield et al, 2018;Wei et al, 2018), as stable isotopes of chromium (Cr) are known to fractionate during redox reactions (Ellis et al, 2002;Schauble et al, 2004;Zink et al, 2010). Chromium dissolved in seawater accumulates in reducing sediments (e.g.…”

Section: Introductionmentioning

confidence: 99%

Chromium isotope cycling in the water column and sediments of the Peruvian continental margin

Bruggmann

Scholz

Klaebe

et al. 2019

Geochimica et Cosmochimica Acta

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Chromium (Cr) isotope fractionation is sensitive to redox changes and the Cr isotopic composition (δ 53 Cr) of sedimentary rocks has been used to reconstruct marine redox conditions and atmospheric oxygenation in the past. However, little is known about the behaviour of chromium isotopes across modern marine redox boundaries. We investigated Cr concentrations and δ 53 Cr variations in seawater and sediment across the Peruvian oxygen minimum zone (OMZ) to provide a better understanding of Cr cycling in the ocean. We found that seawater δ 53 Cr values ranged from 0.02 ± 0.16 ‰ to 0.59 ± 0.11 ‰ (2SD) and sediment values from 0.31 ± 0.07 to 0.92 ± 0.12 ‰. Neither Cr concentrations nor δ 53 Cr values in the water column revealed significant shifts across the oxic-anoxic boundaries. Instead, processes that operate at a local scale, such as Cr scavenging by Fe-rich particles and Cr release from reducing sediments, are identified as the main controls on Cr concentrations and isotope compositions in the water column. The δ 53 Cr values of sediments deposited in permanently anoxic waters (0.77 ± 0.19 ‰, n = 5) are significantly different from the δ 53 Cr values of sediments deposited in oxic bottom waters (0.46 ± 0.19 ‰, n = 4). This suggests that sediment Cr concentrations and δ 53 Cr values are to some extent influenced by water column redox (e.g. reductive dissolution and transport of Fe oxides) and/or early diagenetic (e.g. redistribution of Cr during phosphogenesis) processes as well as biologic activity. Our data demonstrate that local scale water column redox gradients and sediment exchange can lead to a large range of δ 53 Cr values in sediments, comparable to the range found in the entire geologic record to date.Given the increasing prominence of Cr isotope measurements in constraining atmospheric oxygenation in deep time, we argue that the processes influencing Cr cycling under different conditions and from the water column to the sediment need to be better resolved to verify the utility of such measurements as paleoenvironmental proxies.

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Redox fluctuations in the Early Ordovician oceans: An insight from chromium stable isotopes

Cited by 40 publications

References 83 publications

Microbially induced chromium isotope fractionation and trace elements behavior in lower Cambrian microbialites from the Jaíba Member, Bambuí Basin, Brazil

Microbially induced chromium isotope fractionation and trace elements behavior in lower Cambrian microbialites from the Jaíba Member, Bambuí Basin, Brazil

The marine biogeochemistry of chromium isotopes

Chromium isotope cycling in the water column and sediments of the Peruvian continental margin

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