Trace-element behavior and redox facies in core shales of Upper Pennsylvanian Kansas-type cyclothems

Algeo, Thomas J.; Maynard, J. Barry

doi:10.1016/j.chemgeo.2003.12.009

Cited by 1,348 publications

(751 citation statements)

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“…From a mechanistic perspective, this approach builds from clear evidence that the burial in sediments of many redox sensitive metals in anoxic settings scales strongly with carbon flux to the sediments (18,41,42). We hold that this approach allows for a more realistic depiction of perturbations to seawater metal inventories as a function of seafloor redox dynamics by smoothly decreasing globally averaged burial rates as larger regions of the seafloor become anoxic (Cr) or sulfidic (Mo).…”

Section: Interpreting the Enrichment Record: Model For Global Mass Bamentioning

confidence: 99%

Proterozoic ocean redox and biogeochemical stasis

Reinhard

Planavsky

Robbins

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

447

407

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The partial pressure of oxygen in Earth's atmosphere has increased dramatically through time, and this increase is thought to have occurred in two rapid steps at both ends of the Proterozoic Eon (∼2.5-0.543 Ga). However, the trajectory and mechanisms of Earth's oxygenation are still poorly constrained, and little is known regarding attendant changes in ocean ventilation and seafloor redox. We have a particularly poor understanding of ocean chemistry during the mid-Proterozoic (∼1.8-0.8 Ga). Given the coupling between redoxsensitive trace element cycles and planktonic productivity, various models for mid-Proterozoic ocean chemistry imply different effects on the biogeochemical cycling of major and trace nutrients, with potential ecological constraints on emerging eukaryotic life. Here, we exploit the differing redox behavior of molybdenum and chromium to provide constraints on seafloor redox evolution by coupling a large database of sedimentary metal enrichments to a mass balance model that includes spatially variant metal burial rates. We find that the metal enrichment record implies a Proterozoic deep ocean characterized by pervasive anoxia relative to the Phanerozoic (at least ∼30-40% of modern seafloor area) but a relatively small extent of euxinic (anoxic and sulfidic) seafloor (less than ∼1-10% of modern seafloor area). Our model suggests that the oceanic Mo reservoir is extremely sensitive to perturbations in the extent of sulfidic seafloor and that the record of Mo and chromium enrichments through time is consistent with the possibility of a Mo-N colimited marine biosphere during many periods of Earth's history.paleoceanography | geobiology

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Section: Interpreting the Enrichment Record: Model For Global Mass Bamentioning

confidence: 99%

Proterozoic ocean redox and biogeochemical stasis

Reinhard

Planavsky

Robbins

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

447

407

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“…The trace element molybdenum, preserved in black shales, can be a useful redox proxy of the ancient ocean (Algeo and Maynard, 2004;Dahl et al, 2011;Scott et al, 2008;Scott and Lyons, 2012;Tribovillard et al, 2006). In the modern oxygenated ocean, Mo is the most abundant transition metal (∼105 nM) (Collier, 1985;Lyons et al, 2009) and exists primarily as molybdate (MoO 4 2− ), with a residence time of ∼0.8 Myr (Emerson and Huested, 1991;Morford and Emerson, 1999).…”

Section: Molybdenum Geochemistrymentioning

confidence: 99%

“…Mo concentrations and TOC contents exhibit co-variation in modern euxinic marine sediments as well as in many ancient black shales Algeo and Maynard, 2004;Holland, 1984;Robl and Barron, 1988). It has been demonstrated that sedimentary Mo/TOC ratios can be a useful paleohydrographic proxy to assess the degree of watermass restriction, but only under anoxic conditions Algeo and Rowe, 2012).…”

Section: Molybdenum Geochemistrymentioning

confidence: 99%

Marine redox variations and nitrogen cycle of the early Cambrian southern margin of the Yangtze Platform, South China: Evidence from nitrogen and organic carbon isotopes

Wang

Struck

Guo

et al. 2015

Precambrian Research

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“…In anoxic marine settings, U(VI) is reduced to insoluble U(IV), and subsequently adsorbed or precipitated as UO 2 (s), U 3 O 7 or U 3 O 8 in the anoxic sediments (Klinkhammer and Palmer, 1991;McManus et al, 2005). Thus, variations of U concentrations in anoxic facies like black shales can reflect changes in redox conditions (Algeo and Maynard, 2004;Tribovillard et al, 2012). Since Th is only present as relatively insoluble Th(IV) in seawater, there is no authigenic uptake of Th under changing redox conditions.…”

mentioning

confidence: 99%

Uranium isotope fractionation during coprecipitation with aragonite and calcite

Chen

Romaniello

Herrmann

et al. 2016

Geochimica et Cosmochimica Acta

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Natural variations in 238 U/ 235 U of marine carbonates might provide a useful way of constraining redox conditions of ancient environments. In order to evaluate the reliability of this proxy, we conducted aragonite and calcite coprecipitation experiments at pH ~7.5 and ~ 8.5 to study possible U isotope fractionation during incorporation into these minerals.Small but significant U isotope fractionation was observed in aragonite experiments at pH ~ 8.5, with heavier U in the solid phase. 238 U/ 235 U of dissolved U in these experiments can be fit by Rayleigh fractionation curves with fractionation factors of 1.00007+0.00002/-0.00003, 1.00005 ± 0.00001, and 1.00003 ± 0.00001. In contrast, no resolvable U isotope fractionation was observed in an aragonite experiment at pH ~7.5 or in calcite experiments at either pH. Equilibrium isotope fractionation among different aqueous U species is the most likely explanation for these findings. Certain charged U species are preferentially incorporated into calcium carbonate relative to the uncharged U species Ca 2 UO 2 (CO 3 ) 3 (aq), which we hypothesize has a lighter equilibrium U isotope composition than most of the charged species. According to this hypothesis, the magnitude of U isotope fractionation should scale with the fraction of dissolved U that is present as Ca 2 UO 2 (CO 3 ) 3 (aq). This expectation is confirmed by equilibrium speciation modeling of our experiments. Theoretical calculation of the U isotope fractionation factors between different U species could further test this hypothesis and our proposed fractionation mechanism.ii These findings suggest that U isotope variations in ancient carbonates could be controlled by changes in the aqueous speciation of seawater U, particularly changes in seawater pH, P CO2 , [Ca], or [Mg] concentrations. In general, these effects are likely to be small (<0.13 ‰), but are nevertheless potentially significant because of the small natural range of variation of 238 U/ 235 U.

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Trace-element behavior and redox facies in core shales of Upper Pennsylvanian Kansas-type cyclothems

Cited by 1,348 publications

References 100 publications

Proterozoic ocean redox and biogeochemical stasis

Proterozoic ocean redox and biogeochemical stasis

Marine redox variations and nitrogen cycle of the early Cambrian southern margin of the Yangtze Platform, South China: Evidence from nitrogen and organic carbon isotopes

Uranium isotope fractionation during coprecipitation with aragonite and calcite

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