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Uhlein GJ, Caxito FA, Frei R, Uhlein A, Sial AN, Dantas EL. Microbially induced chromium isotope fractionation and trace elements behavior in lower Cambrian microbialites from the Jaíba Member, Bambuí Basin, Brazil. GEOBIOLOGY 2021; 19:125-146. [PMID: 33347697 DOI: 10.1111/gbi.12426] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/16/2020] [Revised: 10/29/2020] [Accepted: 11/29/2020] [Indexed: 06/12/2023]
Abstract
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 (δ53 Cr = -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 δ53 Cr 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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Affiliation(s)
- Gabriel J Uhlein
- Centro de Pesquisas Manoel Teixeira da Costa, Instituto de Geociências, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil
| | - Fabrício A Caxito
- Centro de Pesquisas Manoel Teixeira da Costa, Instituto de Geociências, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil
| | - Robert Frei
- Department of Geoscience and Natural Resource Management, University of Copenhagen, Copenhagen, Denmark
| | - Alexandre Uhlein
- Centro de Pesquisas Manoel Teixeira da Costa, Instituto de Geociências, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil
| | - Alcides N Sial
- Departamento de Geologia, NEG-LABISE, Universidade Federal de Pernambuco, Recife, Brazil
| | - Elton L Dantas
- Instituto de Geociências, Universidade de Brasília, Brasília, Brazil
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Abstract
Changes in stable chromium isotopes (denoted as δ53Cr) in ancient carbonate sediments are increasingly used to reconstruct the oxygenation history in Earth’s atmosphere and oceans through time. As a significant proportion of marine carbonate older than the Cambrian is microbially-mediated, the utility of δ53Cr values in ancient carbonates hinges on whether these sediments accurately capture the isotope composition of their environment. We report Cr concentrations (Cr) and δ53Cr values of modern marginal marine and non-marine microbial carbonates. These data are supported by stable C and O isotope compositions, as well as rare earth elements and yttrium (REY) concentrations. In addition, we present data on ancient analogs from Precambrian strata. Microbial carbonates from Marion Lake (Australia, δ53Cr ≈ 0.99‰) and Mono Lake (USA, ≈0.78‰) display significantly higher δ53Cr values compared with ancient microbialites from the Andrée Land Group in Greenland (720 Ma, ≈0.36‰) and the Bitter Springs Formation in Australia (800 Ma, ≈−0.12‰). The δ53Cr values are homogenous within microbialite specimens and within individual study sites. This indicates that biological parameters, such as vital effects, causing highly variable δ53Cr values in skeletal carbonates, do not induce variability in δ53Cr values in microbialites. Together with stable C and O isotope compositions and REY patterns, δ53Cr values in microbialites seem to be driven by environmental parameters such as background lithology and salinity. In support, our Cr and δ53Cr results of ancient microbial carbonates agree well with data of abiotically precipitated carbonates of the Proterozoic. If detrital contamination is carefully assessed, microbialites have the potential to record the δ53Cr values of the waters from which they precipitated. However, it remains unclear if these δ53Cr values record (paleo-) redox conditions or rather result from other physico-chemical parameters.
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Fang Z, Qin L, Liu W, Yao T, Chen X, Wei S. Absence of hexavalent chromium in marine carbonates: implications for chromium isotopes as paleoenvironment proxy. Natl Sci Rev 2020; 8:nwaa090. [PMID: 34691584 PMCID: PMC8288429 DOI: 10.1093/nsr/nwaa090] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2020] [Revised: 04/29/2020] [Accepted: 05/07/2020] [Indexed: 11/23/2022] Open
Abstract
The oxygenation of Earth's atmosphere is widely regarded to have played an important role in early-life evolution. Chromium (Cr) isotopes recorded in sedimentary rocks have been used to constrain the atmospheric oxygen level (AOL) over geological times based on the fact that a positive Cr isotopic signature is linked to the presence of Cr(VI) as a result of oxidative continental weathering. However, there is no direct evidence of the presence of Cr(VI) in sedimentary rocks yet. Carbonates are most widely distributed over geological times and were thought to have incorporated Cr(VI) directly from seawater. Here, we present results of Cr valence states in carbonates which show Cr(III) is the dominant species in all samples spanning a wide range of geological times. These findings indicate that Cr(VI) in seawater was reduced either before or after carbonate precipitation, which might have caused Cr isotopic fractionation between seawater and carbonates, or marine carbonates preferentially uptake Cr(III) from seawater. As Cr(III) can come from non-redox Cr cycling, which also can cause isotopic fractionation, we suggest that positively fractionated Cr isotopic values do not necessarily correspond to the rise in AOL.
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Affiliation(s)
- Ziyao Fang
- CAS Key Laboratory of Crust-Mantle Materials and Environments, University of Science and Technology of China, Hefei 230026, China
| | - Liping Qin
- CAS Key Laboratory of Crust-Mantle Materials and Environments, University of Science and Technology of China, Hefei 230026, China
| | - Wei Liu
- National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, China
| | - Tao Yao
- National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, China
| | - Xiaoyan Chen
- CAS Key Laboratory of Crust-Mantle Materials and Environments, University of Science and Technology of China, Hefei 230026, China
| | - Shiqiang Wei
- National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, China
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Janssen DJ, Rickli J, Quay PD, White AE, Nasemann P, Jaccard SL. Biological Control of Chromium Redox and Stable Isotope Composition in the Surface Ocean. GLOBAL BIOGEOCHEMICAL CYCLES 2020; 34:e2019GB006397. [PMID: 32713990 PMCID: PMC7375040 DOI: 10.1029/2019gb006397] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/15/2019] [Revised: 12/03/2019] [Accepted: 01/07/2020] [Indexed: 06/11/2023]
Abstract
While chromium stable isotopes (δ53Cr) have received significant attention for their utility as a tracer of oxygen availability in the distant geological past, a mechanistic understanding of modern oceanic controls on Cr and δ53Cr is still lacking. Here we present total dissolved δ53Cr, concentrations of Cr (III) and total dissolved Cr, and net community productivity (NCP) from the North Pacific. Chromium concentrations show surface depletions in waters with elevated NCP, but not in lower productivity waters. Observed Cr deficits correspond well with calculated Cr export derived from NCP and Cr:C ratios of natural phytoplankton and marine particulates. Chromium (III) concentrations are stable over the diel cycle yet correlate with NCP, with maxima found in highly productive surface waters but not in lower productivity waters, indicating biological control on Cr (III). The relationship between Cr (III) and δ53Cr suggests that δ53Cr distributions may be controlled by the removal of isotopically light Cr (III) at an isotopic enrichment factor (∆53Cr) of -1.08‰ ± 0.25 relative to total dissolved δ53Cr, in agreement with the global δ53Cr-Cr fractionation factor (-0.82‰ ± 0.05). No perturbation to δ53Cr, Cr, or Cr (III) is observed in oxygen-depleted waters (~10 μmol/kg), suggesting no strong control by O2 availability, in agreement with other recent studies. Therefore, we propose that biological productivity is the primary control on Cr and δ53Cr in the modern ocean. Consequently, δ53Cr records in marine sediments may not faithfully record oxygen availability in the Late Quaternary. Instead, our data demonstrate that δ53Cr records may be a useful tracer for biological productivity.
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Affiliation(s)
- David J. Janssen
- Institute of Geological Sciences and Oeschger Center for Climate Change ResearchUniversity of BernBernSwitzerland
| | - Jörg Rickli
- Institute of Geological Sciences and Oeschger Center for Climate Change ResearchUniversity of BernBernSwitzerland
- Institute of Geochemistry and PetrologyETH ZürichZürichSwitzerland
| | - Paul D. Quay
- School of OceanographyUniversity of WashingtonSeattleWAUSA
| | - Angelicque E. White
- School of Ocean and Earth Science and TechnologyUniversity of Hawai'i at MānoaHonoluluHIUSA
| | - Philipp Nasemann
- Institute of Geological Sciences and Oeschger Center for Climate Change ResearchUniversity of BernBernSwitzerland
| | - Samuel L. Jaccard
- Institute of Geological Sciences and Oeschger Center for Climate Change ResearchUniversity of BernBernSwitzerland
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Wu G, Zhu JM, Wang X, Johnson TM, Han G. High-Sensitivity Measurement of Cr Isotopes by Double Spike MC-ICP-MS at the 10 ng Level. Anal Chem 2019; 92:1463-1469. [DOI: 10.1021/acs.analchem.9b04704] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- Guangliang Wu
- State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences (Beijing), Beijing 100083, China
| | - Jian-Ming Zhu
- State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences (Beijing), Beijing 100083, China
- State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, CAS, Guiyang 550081, China
| | - Xiangli Wang
- Department of Marine Sciences, University of South Alabama, Mobile, Alabama 36688, United States
- Dauphin Island Sea Lab, Dauphin Island, Alabama 36528, United States
| | - Thomas M. Johnson
- Department of Geology, University of Illinois at Urbana−Champaign, 3081 Natural History Building, Urbana, Illinois 61801, United States
| | - Guilin Han
- State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences (Beijing), Beijing 100083, China
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Toma J, Holmden C, Shakotko P, Pan Y, Ootes L. Cr isotopic insights into ca. 1.9 Ga oxidative weathering of the continents using the Beaverlodge Lake paleosol, Northwest Territories, Canada. GEOBIOLOGY 2019; 17:467-489. [PMID: 31006990 DOI: 10.1111/gbi.12342] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2018] [Revised: 03/05/2019] [Accepted: 03/26/2019] [Indexed: 06/09/2023]
Abstract
The ca. 1.9 Ga Beaverlodge Lake paleosol was studied using redox-sensitive Cr isotopes in order to determine the isotopic response to paleoweathering of a rhyodacite parent rock 500 million years after the Great Oxidation Event. Redox reactions occurring in modern weathering environments produce Cr(VI) that is enriched in heavy Cr isotopes compared to the igneous inventory. Cr(VI) species are soluble and easily leached from soils into streams and rivers, thus, leaving particle-reactive and isotopically light Cr(III) species to build up in soils. The Beaverlodge Lake paleosol and two other published weathering profiles of similar age, the Flin Flon and Schreiber Beach paleosols, are not as isotopically light as modern soils, indicating that rivers were not as isotopically heavy at that time. Considering that the global average δ53 Cr value for the oxidative weathering flux of Cr to the oceans today is just 0.27 ± 0.30‰ (1σ) based on a steady-state analysis of the modern ocean Cr cycle, the oxidative weathering flux of Cr to the oceans at ca. 1.9 Ga would have likely been shifted to lower δ53 Cr values, and possibly lower than the igneous inventory (-0.12 ± 0.10‰, 2σ). Mn oxides are the main oxidant of Cr(III) in modern soils, but there is no evidence that they formed in the studied paleosols. Cr(VI) may have formed by direct oxidation of Cr(III) using molecular oxygen or H2 O2 , but neither pathway is as efficient as Mn oxides for producing Cr(VI). The picture that emerges from this and other studies of Cr isotope variation in ca. 1.9 Ga paleosols is of atmospheric oxygen concentrations that are high enough to oxidize iron, but too low to oxidize Mn, resulting in low Cr(VI) inventories in Earth surface environments.
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Affiliation(s)
- Jonathan Toma
- Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB, Canada
| | - Chris Holmden
- Department of Geological Sciences, University of Saskatchewan, Saskatoon, SK, Canada
| | | | - Yuanming Pan
- Department of Geological Sciences, University of Saskatchewan, Saskatoon, SK, Canada
| | - Luke Ootes
- British Columbia Geological Survey, Stn Prov Govt, Victoria, BC, Canada
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Bruggmann S, Klaebe RM, Paulukat C, Frei R. Heterogeneity and incorporation of chromium isotopes in recent marine molluscs ( Mytilus). GEOBIOLOGY 2019; 17:417-435. [PMCID: PMC6618261 DOI: 10.1111/gbi.12336] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/27/2018] [Revised: 01/24/2019] [Accepted: 01/29/2019] [Indexed: 06/11/2023]
Abstract
The mollusc genus Mytilus is abundant in various modern marine environments and is an important substrate for palaeo‐proxy work. The redox‐sensitive chromium (Cr) isotope system is emerging as a proxy for changes in the oxidation state of the Earth's atmosphere and oceans. However, potential isotopic offsets between ambient sea water and modern biogenic carbonates have yet to be constrained. We measured Cr concentrations ([Cr]) and isotope variations (δ53Cr) in recent mollusc shells (Mytilus) from open and restricted marine environments and compared these to ambient sea water δ53Cr values. We found a large range in mollusc [Cr] (12–309 ppb) and δ53Cr values (−0.30 to +1.25‰) and in the offset between δ53Cr values of mollusc shells and ambient sea water (Δ53CrseawaterbulkMytilus, −0.17 to −0.91‰). Step digestions of cultivated Mytilus edulis specimens indicate that Cr is mainly concentrated in organic components of the shell (periostracum: 407 ppb, n = 2), whereas the mollusc carbonate minerals contain ≤3 ppb Cr. Analyses of individual Cr‐hosting phases (i.e., carbonate minerals and organic matrix) did not reveal significant differences in δ53Cr values, and thus, we suggest that Cr isotope fractionation may likely take place prior to rather than during biomineralisation of Mytilus shells. Heterogeneity of δ53Cr values in mollusc shells depends on sea water chemistry (e.g., salinity, food availability, faeces). The main control for δ53Cr values incorporated into shells, however, is likely vital effects (in particular shell valve closure time) since Cr can be partially or quantitatively reduced in sea water trapped between closed shell valves. The δ53Cr values recorded in Mytilus shells may thus be de‐coupled from the redox conditions of ambient sea water, introducing additional heterogeneity that needs to be better constrained before using δ53Cr values in mollusc shells for palaeo‐reconstructions.
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Affiliation(s)
- Sylvie Bruggmann
- Department of Geoscience and Natural Resource Management, Geology SectionUniversity of CopenhagenCopenhagenDenmark
| | - Robert M. Klaebe
- Department of Geoscience and Natural Resource Management, Geology SectionUniversity of CopenhagenCopenhagenDenmark
- Department of Earth SciencesUniversity of AdelaideAdelaideSouth AustraliaAustralia
| | | | - Robert Frei
- Department of Geoscience and Natural Resource Management, Geology SectionUniversity of CopenhagenCopenhagenDenmark
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