Evidence of magnetic isotope effects during thermochemical sulfate reduction

Oduro, Harry; Harms, Brian; Sintim, Herman O.; Kaufman, Alan J.; Cody, George D.; Farquhar, James

doi:10.1073/pnas.1108112108

Cited by 92 publications

(54 citation statements)

References 37 publications

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“…Controversial discussions about the unique photochemical origin of mass-independently fractionated sulfur isotopes remain Oduro et al, 2011), including propositions that mass-independent isotopic fractionation may also result from thermochemical sulfate reduction (Watanabe et al, 2009) or chemisorption reactions (Lasaga et al, 2008). However, this study will not address these views.…”

Section: Multiple Sulfur Isotope Systematics and Applications To The mentioning

confidence: 72%

Paleoarchean sulfur cycling: Multiple sulfur isotope constraints from the Barberton Greenstone Belt, South Africa

Montinaro

Strauß

Mason

et al. 2015

Precambrian Research

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a b s t r a c tMass-dependent and mass-independent sulfur isotope fractionation archived in volcanic and sedimentary rocks from the Barberton Greenstone Belt (3550-3215 Ma), South Africa, provide constraints for sulfur cycling on the early Earth. Four different sample suites were studied: komatiites and tholeiites, barite, massive and disseminated sulfide ores, and non-mineralized black shales.Variable but generally slightly positive ı 34 S values between −0.7 and +5.2‰, negative 33 S values between −0.50 and −0.09‰, and a negative correlation between ı 34 S and 33 S as well as between 33 S and 36 S for komatiites and tholeiites from the Komati Formation and from the Weltevreden Formation are outside the expected range of unfractionated juvenile sulfur. Instead, results suggest alteration of oceanic crustal rock sulfur through interactions with fluids that most likely derived their sulfur from seawater.Barite from the Mapepe Formation displays positive ı 34 S values between +3.1 and +8.1‰ and negative 33 S values between −0.77 and −0.34‰. The mass-independent sulfur isotope fractionation indicates an atmospheric sulfur source, notably photolytic sulfate, whereas the positive ı 34 S values suggest bacterial sulfate reduction of the marine sulfate reservoir.Non-mineralized black shale samples from the presumed stratigraphic equivalent of the Mapepe Formation show positive ı 34 S values between 0.0 and +1.3‰ and positive 33 S values between +0.59 and +2.45‰. These results are interpreted to result from the reduction of photolytic elemental sulfur, carrying a positive 33 S signature.Positive ı 34 S values ranging from +0.7 to +3.5‰ and slightly negative 33 S values between −0.17 and −0.12‰ characterize massive and disseminated sulfides from the Bien Venue Prospect. Results suggest unfractionated juvenile magmatic sulfur source as the primary sulfur source, but a contribution from recycled seawater sulfate, which would be indicative of submarine hydrothermal activity, cannot be ruled out.Massive and disseminated sulfides from the M'hlati prospect are distinctly different from massive and disseminated sulfide from the Bien Venue Prospect. They show negative ı 34 S values between −1.2 and −0.1‰ and positive 33 S values between +2.66 and +3.17‰, thus, displaying a sizeable mass-independent A. Montinaro et al. / Precambrian Research 267 (2015) 311-322 sulfur isotopic fractionation. Again, these samples clearly exhibit the incorporation of an atmospheric MIF-S signal. The source of sulfur for these samples has positive 33 S values, suggesting a connection with photolytic elemental sulfur. In conclusion, the sulfur isotope signatures in Paleoarchean rocks from the Barberton Greenstone Belt are diverse and indicate the incorporation of different sources of sulfur. For komatiites and tholeiites, barite and massive and possibly also disseminated sulfides from Bien Venue, multiple sulfur isotopes are related to ambient seawater sulfate and its photolytic origin, while massive and disseminated sulfides from M'hlati and non-...

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Section: Multiple Sulfur Isotope Systematics and Applications To The mentioning

confidence: 72%

Paleoarchean sulfur cycling: Multiple sulfur isotope constraints from the Barberton Greenstone Belt, South Africa

Montinaro

Strauß

Mason

et al. 2015

Precambrian Research

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“…Once produced, atmospheric models indicate that S MIF would reach the surface in the oxidized and reduced products of sulfur photochemistry only if atmospheric oxygen was below 10 −6 to 10 −5 present atmospheric levels, depending on the trace gas composition of the atmosphere (6,7,22,23). Thermal sulfate reduction has been suggested as the source of Archean S MIF (24), but recent experiments yield only anomalous fractionation of 33 S (Δ 36 S = 0), suggesting a magnetic isotope effect and in contrast to Archean S MIF (25).…”

Section: Existing Constraintsmentioning

confidence: 99%

Production, preservation, and biological processing of mass-independent sulfur isotope fractionation in the Archean surface environment

Halevy

2013

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

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Mass-independent fractionation of sulfur isotopes (S MIF) in Archean and Paleoproterozoic rocks provides strong evidence for an anoxic atmosphere before ∼2,400 Ma. However, the origin of this isotopic anomaly remains unclear, as does the identity of the molecules that carried it from the atmosphere to Earth's surface. Irrespective of the origin of S MIF, processes in the biogeochemical sulfur cycle modify the primary signal and strongly influence the S MIF preserved and observed in the geological record. Here, a detailed model of the marine sulfur cycle is used to propagate and distribute atmospherically derived S MIF from its delivery to the ocean to its preservation in the sediment. Bulk pyrite in most sediments carries weak S MIF because of microbial reduction of most sulfur compounds to form isotopically homogeneous sulfide. Locally, differential incorporation of sulfur compounds into pyrite leads to preservation of S MIF, which is predicted to be most highly variable in nonmarine and shallow-water settings. The Archean ocean is efficient in diluting primary atmospheric S MIF in the marine pools of sulfate and elemental sulfur with inputs from SO 2 and H 2 S, respectively. Preservation of S MIF with the observed range of magnitudes requires the S MIF production mechanism to be moderately fractionating ( ± 20-40‰). Constraints from the marine sulfur cycle allow that either elemental sulfur or organosulfur compounds (or both) carried S MIF to the surface, with opposite sign to S MIF in SO 2 and H 2 SO 4 . Optimal progress requires observations from nonmarine and shallow-water environments and experimental constraints on the reaction of photoexcited SO 2 with atmospheric hydrocarbons.W ith few exceptions, the enrichment or depletion of the rare, stable isotopes of sulfur ( 33 S, 34 S, and 36 S) relative to the abundant isotope ( 32 S) scale as the mass difference between the isotopes (1). Sulfur isotope mass-independent fractionation (S MIF) is defined as a departure from these theoretically derived and empirically observed mass laws, and denoted Δ 33 S and Δ 36 S. S MIF is observed in modern atmospheric sulfate aerosols, as well as in sulfate-bearing layers hosted in glacial ice (2, 3), but is conspicuously absent from the sedimentary record of the last 2,400 My. In contrast, older rocks of the Archean and early Paleoproterozoic eons preserve large and variable S MIF (4, 5). On the basis of experimental SO 2 photolysis and atmospheric chemistry models, the prevailing hypothesis to explain this observation is that the absence of atmospheric oxygen before ∼2,400 Ma allowed both the photochemical production of S MIF and its delivery to the surface in the reduced and oxidized products of sulfur photochemistry (4-7). Thus, S MIF is considered strong geochemical evidence for an anoxic atmosphere before ∼2,400 Ma.Although research converges on atmospheric processes as the source of S MIF, its production mechanism and the identity of its vectors to the surface remain unclear. A focus on photolysis experiments and meas...

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“…Indeed, a substantially different hypothesis was proposed wherein MAF arises during high-temperature diagenetic reactions involving the interaction of sulfur-bearing fluids with kerogen in the protolith (23,24). Although this mechanism does not appear to explain the aforementioned secular MAF trends (25), it is important to note that all Archean successions have undergone diagenetic and, in most cases, metasomatic episodes of sulfur mineralization, which complicates interpretation of isotope records (e.g., ref. 26).…”

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confidence: 99%

SQUID–SIMS is a useful approach to uncover primary signals in the Archean sulfur cycle

Fischer

Fike²,

Johnson

et al. 2014

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

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Many aspects of Earth's early sulfur cycle, from the origin of massanomalous fractionations to the degree of biological participation, remain poorly understood-in part due to complications from postdepositional diagenetic and metamorphic processes. Using a combination of scanning high-resolution magnetic superconducting quantum interference device (SQUID) microscopy and secondary ion mass spectrometry (SIMS) of sulfur isotopes ( 32 S, 33 S, and 34 S), we examined drill core samples from slope and basinal environments adjacent to a major Late Archean (∼2.6-2.5 Ga) marine carbonate platform from South Africa. Coupled with petrography, these techniques can untangle the complex history of mineralization in samples containing diverse sulfur-bearing phases. We focused on pyrite nodules, precipitated in shallow sediments. These textures record systematic spatial differences in both mass-dependent and mass-anomalous sulfur-isotopic composition over length scales of even a few hundred microns. Petrography and magnetic imaging demonstrate that mass-anomalous fractionations were acquired before burial and compaction, but also show evidence of postdepositional alteration 500 million y after deposition. Using magnetic imaging to screen for primary phases, we observed large spatial gradients in Δ 33 S (>4‰) in nodules, pointing to substantial environmental heterogeneity and dynamic mixing of sulfur pools on geologically rapid timescales. In other nodules, large systematic radial δ 34 S gradients (>20‰) were observed, from low values near their centers increasing to high values near their rims. These fractionations support hypotheses that microbial sulfate reduction was an important metabolism in organic-rich Archean environments-even in an Archean ocean basin dominated by iron chemistry. mass independent fractionation | MIF | metamorphism | metasomatism P atterns emerging from multiple sulfur-isotope ratios in sedimentary rocks have provided powerful insights into the behavior of the Archean (>2.5 Ga) sulfur cycle and the timing of the rise of atmospheric oxygen (1). Sulfur-isotope data from Archean sedimentary successions show distinct differences from those contained in younger successions-in rocks older than ∼2.32 Ga, S-bearing minerals display large deviations in isotope ratios from predicted mass-fractionation relationships, captured by the statistic (1,4,5). If this interpretation is correct, photochemical and geochemical models can use stratigraphic sulfur-isotope data to provide quantitative constraints on the oxidative power of the Archean atmosphere (e.g., O 2 mixing ratio << 10 −5 ; ref. 6), continental crust growth, volatile fluxes from the solid earth (7), seawater chemistry, and the degree of biological cycling (8).In addition to the nature of the MAF that is so conspicuous in Archean strata, questions remain about what role, if any, biology played in the early sulfur cycle. Comparative molecular biology suggests that both sulfide-based photosynthesis and dissimilatory sulfate reduction (DSR) were important ear...

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Evidence of magnetic isotope effects during thermochemical sulfate reduction

Cited by 92 publications

References 37 publications

Paleoarchean sulfur cycling: Multiple sulfur isotope constraints from the Barberton Greenstone Belt, South Africa

Paleoarchean sulfur cycling: Multiple sulfur isotope constraints from the Barberton Greenstone Belt, South Africa

Production, preservation, and biological processing of mass-independent sulfur isotope fractionation in the Archean surface environment

SQUID–SIMS is a useful approach to uncover primary signals in the Archean sulfur cycle

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