Sulfur isotope fractionation in modern euxinic systems: Implications for paleoenvironmental reconstructions of paired sulfate–sulfide isotope records

Gomes, Maya; Hurtgen, Matthew T.

doi:10.1016/j.gca.2015.02.031

Cited by 105 publications

(61 citation statements)

References 69 publications

(87 reference statements)

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“…Thus, the positive shift of 2‰ for the δ 34 S CAS values of the Oker dolomite (Fig. 7) follows a change in the δ 34 SSO 4 isotopic composition of the dolomitizing fluids and reflects the involvement of BSR processes (e.g., Kampschulte & Strauss, 2004;Loyd et al, 2012;Gomes & Hurtgen, 2015). At the time of dolomitization BSR is reducing the pore water SO 4 2− concentrations, which is documented by the decreasing abundance of CAS in precipitating dolomite (Fig.…”

Section: The Role Of Bsr On the Formation Of Dolomitementioning

confidence: 92%

“…6). In contrast, Loyd et al (2012) and Gomes and Hurtgen (2015) have demonstrated that the CAS content of marine carbonate minerals, which form near the onset of the zone of sulfate reduction, is in the range of the sulfate concentration of the ambient seawater. Thus, the 1400 mg/kg and 1100-1950 mg/kg of CAS measured for the type A and type B of the Oker dolomite, respectively, suggest insignificant alteration of the pristine CAS contents, considering the estimated~15-20 mM sulfate concentration of Upper Jurassic seawater (e.g., Algeo et al, 2014).…”

Section: The Role Of Bsr On the Formation Of Dolomitementioning

confidence: 92%

“…This relationship is valid for the Miocene Monterey dolomites as well and thus it can be used as a measure for dolomite maturity ( Fig. 9A and B In marine-diagenetic environments, the CAS content and subsequently the ordering ratio of the dolomite precipitating within the zone of sulfate reduction are likely to be controlled both by the sulfate concentration of the dolomitizing fluids and the sulfate reduction rate in marine sediments (Loyd et al, 2012;Gomes & Hurtgen, 2015). Considering the relatively high sulfate concentrations (34-100 up to 590 mM) in most modern dolomite-forming environments (Warren, 2000;Deng et al, 2010) it is suggested that the precipitating (proto)dolomites contain high CAS contents (N 2000 mg/kg), which would explain their poorly ordered or almost completely disordered (ordering ratio b0.3) structure (Fig.…”

Section: Links Between the Cas Content And The Composition Structurementioning

confidence: 96%

“…Thus, the 1400 mg/kg and 1100-1950 mg/kg of CAS measured for the type A and type B of the Oker dolomite, respectively, suggest insignificant alteration of the pristine CAS contents, considering the estimated~15-20 mM sulfate concentration of Upper Jurassic seawater (e.g., Algeo et al, 2014). Certainly, the CAS content of marine carbonates is strongly dependent on parameters such as the precipitation rate, mineralogy and the amount and type of those minerals in sediments (Busenberg & Plummer, 1986;Loyd et al, 2012;Gomes & Hurtgen, 2015). The experimental work of Busenberg and Plummer (1985) has shown that incorporation of Na + and SO 4 2− ions in precipitating calcite is largely dependent on the calcite precipitation rate.…”

Section: The Role Of Bsr On the Formation Of Dolomitementioning

confidence: 99%

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The role of bacterial sulfate reduction during dolomite precipitation: Implications from Upper Jurassic platform carbonates

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Section: The Role Of Bsr On the Formation Of Dolomitementioning

confidence: 92%

Section: The Role Of Bsr On the Formation Of Dolomitementioning

confidence: 92%

Section: Links Between the Cas Content And The Composition Structurementioning

confidence: 96%

Section: The Role Of Bsr On the Formation Of Dolomitementioning

confidence: 99%

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The role of bacterial sulfate reduction during dolomite precipitation: Implications from Upper Jurassic platform carbonates

et al. 2015

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“…Recent studies of lacustrine euxinic systems indicate that >70& fractionations are achievable by both isolated and natural populations of sulfate reducers (Canfield et al, 2010;Gomes & Hurtgen, 2015). Recent studies of lacustrine euxinic systems indicate that >70& fractionations are achievable by both isolated and natural populations of sulfate reducers (Canfield et al, 2010;Gomes & Hurtgen, 2015).…”

Section: Redox Constraints For the Gaojiashan Membermentioning

confidence: 99%

Environmental context for the terminal Ediacaran biomineralization of animals

et al. 2016

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In terminal Ediacaran strata of South China, the onset of calcareous biomineralization is preserved in the paleontological transition from Conotubus to Cloudina in repetitious limestone facies of the Dengying Formation. Both fossils have similar size, funnel-in-funnel construction, and epibenthic lifestyle, but Cloudina is biomineralized, whereas Conotubus is not. To provide environmental context for this evolutionary milestone, we conducted a high-resolution elemental and stable isotope study of the richly fossiliferous Gaojiashan Member. Coincident with the first appearance of Cloudina is a significant positive carbonate carbon isotope excursion (up to +6‰) and an increase in the abundance and (34) S composition of pyrite. In contrast, δ(34) S values of carbonate-associated sulfate remain steady throughout the succession, resulting in anomalously large (>70‰) sulfur isotope fractionations in the lower half of the member. The fractionation trend likely relates to changes in microbial communities, with sulfur disproportionation involved in the lower interval, whereas microbial sulfate reduction was the principal metabolic pathway in the upper. We speculate that the coupled paleontological and biogeochemical anomalies may have coincided with an increase in terrestrial weathering fluxes of sulfate, alkalinity, and nutrients to the depositional basin, which stimulated primary productivity, the spread of an oxygen minimum zone, and the development of euxinic conditions in subtidal and basinal environments. Enhanced production and burial of organic matter is thus directly connected to the carbon isotope anomaly, and likely promoted pyritization as the main taphonomic pathway for Conotubus and other soft-bodied Ediacara biotas. Our studies suggest that the Ediacaran confluence of ecological pressures from predation and environmental pressures from an increase in seawater alkalinity set the stage for an unprecedented geobiological response: the evolutionary novelty of animal biomineralization.

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Biogeochemical sulfur cycling during Cretaceous oceanic anoxic events: A comparison of OAE1a and OAE2

2016

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Biogeochemical sulfur cycling has varied widely over geologic time, mainly in response to changes in primary productivity and organic carbon burial, volcanism, weathering, and evaporite deposition. Several of these processes are explicitly linked to discreet (<1.2 Ma) intervals of widespread organic carbon burial, termed oceanic anoxic events (OAEs). During the Cretaceous, there is a highly distinctive ~4‰ negative excursion in the sulfur isotope composition of seawater sulfate (δ34SSO4) that is bracketed by the two most prominent OAEs (OAE1a and OAE2). This excursion lasted for ~25 Ma and has been variously attributed to enhanced volcanism, changes in weathering, evaporite burial, and/or changes in modes of organic carbon remineralization. We present new high‐resolution carbon and sulfur isotope records from carbonate‐associated sulfate and pyrite for OAE1a and OAE2. OAE1a is characterized by a monotonic decrease in δ34SSO4 values. Both negative and positive δ34SSO4 excursions are associated with OAE2. To refine hypotheses for the observed changes in biogeochemical sulfur cycling associated with these events, we use a simple sulfur isotope box model. Both empirical and modeling results indicate that δ34SSO4 variability was dominated by input fluxes during OAE1a, whereas enhanced volcanism, weathering, and pyrite burial controlled δ34SSO4 records during OAE2. Our analysis supports the conclusion that Cretaceous marine sulfate concentrations were much lower than modern concentrations and indicates that increases in marine sulfate occurred at the onset of both events. We conclude that increases in marine sulfate from low background concentrations, in conjunction with other environmental characteristics, contributed to the development of OAEs.

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Sulfur isotope fractionation in modern euxinic systems: Implications for paleoenvironmental reconstructions of paired sulfate–sulfide isotope records

Cited by 105 publications

References 69 publications

The role of bacterial sulfate reduction during dolomite precipitation: Implications from Upper Jurassic platform carbonates

The role of bacterial sulfate reduction during dolomite precipitation: Implications from Upper Jurassic platform carbonates

Environmental context for the terminal Ediacaran biomineralization of animals

Biogeochemical sulfur cycling during Cretaceous oceanic anoxic events: A comparison of OAE1a and OAE2

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