Evidence for a gradual rise of oxygen between 2.6 and 2.5Ga from Mo isotopes and Re-PGE signatures in shales

Wille, Martin; Kramers, Jan D.; Nägler, Thomas F.; Beukes, N. J.; Schröder, Stefan; Meisel, Thomas; Lacassie, Juan Pablo; Voegelin, Andrea R.

doi:10.1016/j.gca.2007.02.019

Cited by 258 publications

(163 citation statements)

References 71 publications

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“…3.5 Gyr), a simple sensitivity test of our mass-balance model demonstrates that such input flux variations should impart minimal influence on the [Re] sed record (SI). In general, our interpretation of atmosphere-ocean O 2 levels based on the Re record conforms well to that derived from the higherresolution Cr and U records (Partin et al, 2013;Reinhard et al, 2013a (Siebert et al, 2005;Anbar et al, 2007;Wille et al, 2007;Reinhard et al, 2009;Kendall et al, 2010Kendall et al, , 2015a.…”

Section: Temporal Trends In Re Concentrationssupporting

confidence: 89%

A model for the oceanic mass balance of rhenium and implications for the extent of Proterozoic ocean anoxia

Sheen

Kendall

Reinhard

et al. 2018

Geochimica et Cosmochimica Acta

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Emerging geochemical evidence suggests that the atmosphere-ocean system underwent a significant decrease in O 2 content following the Great Oxidation Event (GOE), leading to a mid-Proterozoic ocean (ca. 2.0-0.8 Ga) with oxygenated surface waters and predominantly anoxic deep waters. The extent of mid-Proterozoic seafloor anoxia has been recently estimated using mass-balance models based on molybdenum (Mo), uranium (U), and chromium (Cr) enrichments in organic-rich mudrocks (ORM). Here, we use a temporal compilation of concentrations for the redox-sensitive trace metal rhenium (Re) in ORM to provide an independent constraint on the global extent of mid-Proterozoic ocean anoxia and as a tool for more generally exploring how the marine geochemical cycle of Re has changed through time. The compilation reveals that mid-Proterozoic ORM are dominated by low Re concentrations that overall are only mildly higher than those of Archean ORM and significantly lower than many ORM deposited during the ca. 2.22-2.06 Ga Lomagundi Event and during the Phanerozoic Eon. These temporal trends are consistent with a decrease in the oceanic Re inventory in response to an expansion of anoxia after an interval of increased oxygenation during the Lomagundi Event. Mass-balance modeling of the marine Re geochemical cycle indicates that the mid-Proterozoic ORM with low Re enrichments are consistent with extensive seafloor anoxia. Beyond this agreement, these new data bring added value because Re, like the other metals, responds generally to lowoxygen conditions but has its own distinct sensitivity to the varying environmental controls. Thus, we can broaden our capacity to infer nuanced spatiotemporal patterns in ancient redox landscapes. For example, despite the still small number of data, some mid-Proterozoic ORM units have higher Re enrichments that may reflect a larger oceanic Re inventory during transient episodes of ocean oxygenation. An improved understanding of the modern oceanic Re cycle and a higher temporal resolution for the Re compilation will enable further tests of these hypotheses regarding changes in the surficial Re geochemical cycle in response to variations in atmosphere-ocean oxygenation. Nevertheless, the existing Re compilation and model results are in agreement with previous Cr, Mo, and U evidence for pervasively anoxic and ferruginous conditions in mid-Proterozoic oceans.

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Section: Temporal Trends In Re Concentrationssupporting

confidence: 89%

A model for the oceanic mass balance of rhenium and implications for the extent of Proterozoic ocean anoxia

Sheen

Kendall

Reinhard

et al. 2018

Geochimica et Cosmochimica Acta

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“…Prior to dissolution modern skeletal carbonate was cleaned with deionized water. Mo was purified using the separation procedure described in Siebert et al (2001) and Wille et al (2007), modified to suit the carbonate matrix and to make the processing of larger amounts of sample possible. Between 0.4 and 6.5 g of material were weighed into screw-top PTFE beakers.…”

Section: Mo Purification and Mc-icpms Analysesmentioning

confidence: 99%

Molybdenum isotopic composition of modern and Carboniferous carbonates

et al. 2009

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We investigate the redox-sensitive isotope system of molybdenum (Mo) in marine carbonates to evaluate their potential as archive of the Mo isotopic composition of coeval seawater. We present Mo isotope data (δ 98/95 Mo) of modern skeletal and non-skeletal carbonates as well as a variety of precipitates from the mid and late Carboniferous. The external reproducibility is determined by repeated analyses of two commercially available carbonate standards. The resulting uncertainty of the low concentration samples is ±0.1‰ (2σ). Analysis of modern ooid sands from the Bahamas shows a consistently heavy Mo isotopic composition (δ 98/95 Mo between 2 and 2.2‰), approaching modern mean seawater values (δ 98/95 Mo = 2.3‰ ± 0.1‰ (2σ)). This suggests that isotope fractionation during Mo uptake into non-skeletal carbonate precipitates is small. In contrast, modern skeletal carbonates show variable isotopic compositions (0.1 to 2.2‰) which suggests a biologically controlled fractionation process. The varying Mo signatures found in Carboniferous cement phases point to a strong response to local changes in fluid composition from which they precipitated. Overall, we recognized three important factors to cause an offset relative to ocean water: Mo derived from skeletal components, input of detrital Mo and admixture of light, hydroxide derived Mo via diagenetic fluids. All of these factors cause a lighter Mo isotopic composition relative to seawater. Due to the apparent small isotope fractionation during Mo uptake into non-skeletal carbonates, their δ 98/95Mo closely reflects the ambient fluid composition. From these results we conclude that carbonates represent a promising new tool to characterize the water mass Mo isotopic composition of marine paleo-environments.

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“…Consequently variations in δ 98/95 Mo can be utilised as a palaeoredox proxy, and have been used to demonstrate the expansion of reducing marine conditions at a number of times throughout Earth's history (e.g. Arnold et al, 2004;Siebert et al, 2005;Wille et al, 2007;Pearce et al, 2008). A critical assumption in the application of the Mo-isotope redox proxy in this manner is that the isotope composition of Mo entering the oceans has remained more-or-less constant throughout geological history, and that the net Mo isotope composition of weathered continental material input to the oceans is similar to the mean composition of the continental crust (e.g.…”

Section: Introductionmentioning

confidence: 99%

Molybdenum isotope behaviour accompanying weathering and riverine transport in a basaltic terrain

Pearce

Burton

Strandmann

et al. 2010

Earth and Planetary Science Letters

100

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Editor: M.L. DelaneyKeywords: molybdenum (Mo) isotopes basaltic weathering riverine inputs estuarine mixingThe application of the molybdenum (Mo) isotope system as a proxy for determining changes in the redox state of the oceans is predicated on the assumption that the composition of continental input can be characterised from crustal rock types, and remains constant. However, it has recently been shown that the δ 98/95 Mo composition of global rivers varies between 0.15‰ and 2.4‰ and is therefore systematically heavier than the average composition of the continental crust (∼ 0‰ 4‰).Systematic changes in the dissolved Mo-isotope composition are also observed within river catchments, with δ 98/95 Mo values increasing from ∼ 0‰ in glacial rivers (close to the source) to ∼ 1‰ downstream, consistent with Mo-isotopes being fractionated during weathering. Analysis of other riverine phases (bedload, colloids and iron-precipitates) demonstrates that these phases preferentially incorporate light Moisotopes, and remain coupled to the dissolved load during riverine transportation. A δ 98/95 Mo profile through the Borgarfjörður estuary exhibits a predominantly conservative mixing behaviour, but suggests that the release of isotopically light Mo from the particulate and/or colloidal phases may occur in the low salinity part of the estuarine mixing zone.

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Evidence for a gradual rise of oxygen between 2.6 and 2.5Ga from Mo isotopes and Re-PGE signatures in shales

Cited by 258 publications

References 71 publications

A model for the oceanic mass balance of rhenium and implications for the extent of Proterozoic ocean anoxia

A model for the oceanic mass balance of rhenium and implications for the extent of Proterozoic ocean anoxia

Molybdenum isotopic composition of modern and Carboniferous carbonates

Molybdenum isotope behaviour accompanying weathering and riverine transport in a basaltic terrain

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