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Geological evolution from isotope proxy signals - Sulfur
Abstract
A currently emerging sulfur isotope record for Phanerozoic seawater, based on structurally substituted sulfate in stratigraphically well constrained biogenic carbonates, allows the detailed assessment of secular variations within the global sulfur cycle and the interaction between the sulfur and carbon cycles. It is superior to the evaporite-based dataset because it enables sampling of the entire biostratigraphic column. Discrete biological and environmental signals can be deciphered from a somewhat “noisy” sulfur isotope record for sedimentary biogenic pyrite. These include a maximum isotopic fractionation around −51‰ which appears to be constant throughout the entire Phanerozoic. Observable large spreads of δsulfide for any given sedimentary unit are caused by environmental parameters, such as type and availability of organic carbon or availability of sulfate. In particular, the growing importance of land plants and their impact on the amount of metabolizable organic substrate affects the sulfide sulfur isotopic composition.
... As a stable, naturally occurring isotope, sulfur is found in a variety of natural environments. Over the years, many geologists have studied and analysed it from different perspectives, especially the application of sulfur isotopes in evaporites, which primarily focuses on ascertaining the source of ore-forming materials (Liu et al. 1999;Tabakh et al. 1999;Zhang et al. 2014), studying the geological conditions of salt mineralization (Peng et al. 1999;Strauss et al. 1999;Yuan et al. 2008;Wang et al. 2013), and 34 S(‰) = ( 34 S∕ 32 S) sample − ( 34 S∕ 32 S) standard ( 34 S∕ 32 S) standard × 1000 ...
... (Kampschulte et al. 1998). This signature difference is caused by the fractionation characteristics of different minerals (Strauss 1999). Several researchers have used the sulfur isotopic values and isotopic fractionation mechanism of global marine evaporites to draw sulfur isotopic chronostratigraphic curves (Claypool et al. 1980;Cortecci et al. 1981;Kampschoole and Strauss 2004) (to avoid unnecessary duplication, the data sources of marine sulfate sulfur isotopes are given in Claypool 1980;Strauss 1997 and its references). ...
... Some studies have indicated that the fractionation of sulfur isotopes is mainly affected by inorganic reduction (thermochemical sulfate reduction, TSR), biological action (Strauss 1999;Chambers 1976;Habicht and Canfield 1997), and sulfate sources. However, TSR could occur when the geological temperature is 100-140 ℃, according to experimental results (Machel 2001). ...
The formation environment of continental evaporite—particularly the sedimentary environment closely related to continental evaporite deposits—has received significant research attention for several years. From this perspective, an intermountain basin exists in the inland area of Northwest China, known as the Kumishi basin. The elevation of this basin is relatively low, where a set of evaporite series strata developed during the late Quaternary. In this paper, we analysed the sedimentary environment of the Kumishi basin in terms of the sulfur isotopes combined with its paleosalinity characteristics. The results show that the δ³⁴SV-CDT isotopic composition ranges from 6 to 11‰. The isotopic fractionation effect of the surface salt crust is significantly lower than that of the lower halite layer owing to the influence of surrounding fresh water and other chemicals. The low sulfur isotopic value is indicative of a typical continental sedimentary environment. In addition, the bacterial sulfate reduction (BSR) indicates that the sulfate formation environment is open to sulfates, and rejects H2S. This phenomenon further indicates the weak bacterial reduction environment in the Kumishi basin. In combination with its paleosalinity characteristics, we determined that the saltwater environment influenced the changes in sulfur isotope value. This can facilitate the further understanding of the sedimentary environment of evaporites in low altitude intermountain basins.
... The sulfur isotopic characteristics of sulfate minerals in evaporite basins are mainly affected by bacterial sulfate reduction, reservoir effects, and the composition of the source. Bacterial sulfate reduction causes the resulting sulfide to be significantly enriched in the light isotope 32 S, while the residual sulfate minerals are enriched in the heavy isotope 34 S [47]. For example, the δ 34 S values of Early Triassic marine gypsum in the Sichuan Basin range from 27.8‰ to 35.9‰ [48], and the δ 34 S values of Paleogene continental gypsum in the Dongpu Depression range from 28‰ to 33‰ [49]. ...
... For example, the δ 34 S values of Early Triassic marine gypsum in the Sichuan Basin range from 27.8‰ to 35.9‰ [48], and the δ 34 S values of Paleogene continental gypsum in the Dongpu Depression range from 28‰ to 33‰ [49]. Reservoir effects can cause the δ 34 S values of postdeposition gypsum in a stratigraphic sequence to be slightly less than those of gypsum prior to deposition [47,50]. Sources of the sulfur present in evaporites include marine, terrestrial, and volcanic sources. ...
... The sulfur isotopic characteristics of sulfate minerals in evaporite basins are mainly affected by bacterial sulfate reduction, reservoir effects, and the composition of the source. Bacterial sulfate reduction causes the resulting sulfide to be significantly enriched in the light isotope 32 S, while the residual sulfate minerals are enriched in the heavy isotope 34 S [47]. For example, the δ 34 S values of Early Triassic marine gypsum in the Sichuan Basin range from 27.8% to 35.9% [48], and the δ 34 S values of Paleogene continental gypsum in the Dongpu Depression range from 28% to 33% [49]. ...
The Tethys Sea extended into the Kuqa Depression from the Paleocene to the late Eocene and provided an abundant provenance for the deposition of evaporite sequences. Until now, detailed research on the history of transgressions during the late Paleocene-early Eocene in the Kuqa Depression has been limited. Therefore, in this study, we took the upper Paleocene Talak section and the lower Eocene Xiaokuzibai section in the western part of the Depression as the research objects and analyzed the petrology, the carbon and oxygen isotopes of carbonate rocks, and the sulfur and strontium isotopes of gypsum rocks to systematically study the above issues. The δ13C, δ18O and δ34S values of the upper Paleocene evaporite sequences were determined to be between 4.2‰ and 5.7‰, between −5.2‰ and 2.4‰, and between 16.5‰ and 17.9‰, respectively. The δ13C, δ18O, δ34S, and 87Sr/86Sr values of the lower Eocene evaporite sequences were determined to be between −6.9‰ and −2.0‰, between −9.0‰ and −4.5‰, between 10.5‰ and 17.0‰, and between 0.708642 and 0.709883, respectively. The analysis results show that the evaporite sequence of the upper Paleocene was formed by transgression. The deposition of the evaporite sequence changed from continental to marine deposition, and then gradually transitioned to continental during the Early Eocene. This paper is of great significance for reconstructing the history of transgressions in the Tethys tectonic realm during this period.
... Although large temporal gaps exist in the evaporite record, their work demonstrated that the sulfur isotope ratio of seawater sulfate had undergone substantial changes over geological time and laid the groundwork for our current understanding of the Phanerozoic sulfur cycle and S-isotope stratigraphy. Further studies presented more comprehensive evaporite sulfate δ 34 S records with a thorough compilation of the evaporite data spanning the Proterozoic and the Phanerozoic (Crockford et al., 2019;Strauss, 1997Strauss, , 1999Strauss et al., 2001), which considerably extend the applications for stratigraphic correlations. ...
... Oxidation of pyrite with isotopically light sulfur can impart a δ 34 S offset of a few per mil even in sediments with low pyrite content, drawing the CAS δ 34 S toward lower values (Marenco et al., 2008). Therefore, careful sample selection and inspection, as well as cautious Fig. 2 The Phanerozoic seawater sulfate δ 34 S record. Green circles, CAS data (Gill et al., 2007;Goldberg et al., 2005;Hurtgen et al., 2009;Kah et al., 2016;Kampschulte and Strauss, 2004;Mazumdar and Strauss, 2006;Present et al., 2015;Schobben et al., 2017;Sim et al., 2015;Strauss, 1999;Thompson and Kah, 2012;Ueda et al., 1987;Wotte et al., 2012;Wu et al., 2010Wu et al., , 2014; gray circles, evaporites data (Bernasconi et al., 2017;Claypool et al., 1980;Cortecci et al., 1981;Crockford et al., 2019;Das et al., 1990;Fox and Videtich, 1997;Holser and Kaplan, 1966;Kampschulte et al., 1998;Longinelli and Flora, 2007;Orti et al., 2010;Peryt et al., 2005;Pierre and Rouchy, 1986;Rick, 1990;Sakai, 1972;Strauss, 1997Strauss, , 1999Strauss et al., 2001;Surakotra et al., 2018;Utrilla et al., 1992;Worden et al., 1997); black circles ¼ barite data (Paytan et al., 1998(Paytan et al., , 2004Yao et al., 2019, under review). Blue dash line, the modern seawater sulfate δ 34 S value of $21% Tostevin et al., 2014). in the extraction process of CAS from bulk sediment samples, are required to ensure that the recovered sulfate accurately represents only the original CAS signature. ...
... Oxidation of pyrite with isotopically light sulfur can impart a δ 34 S offset of a few per mil even in sediments with low pyrite content, drawing the CAS δ 34 S toward lower values (Marenco et al., 2008). Therefore, careful sample selection and inspection, as well as cautious Fig. 2 The Phanerozoic seawater sulfate δ 34 S record. Green circles, CAS data (Gill et al., 2007;Goldberg et al., 2005;Hurtgen et al., 2009;Kah et al., 2016;Kampschulte and Strauss, 2004;Mazumdar and Strauss, 2006;Present et al., 2015;Schobben et al., 2017;Sim et al., 2015;Strauss, 1999;Thompson and Kah, 2012;Ueda et al., 1987;Wotte et al., 2012;Wu et al., 2010Wu et al., , 2014; gray circles, evaporites data (Bernasconi et al., 2017;Claypool et al., 1980;Cortecci et al., 1981;Crockford et al., 2019;Das et al., 1990;Fox and Videtich, 1997;Holser and Kaplan, 1966;Kampschulte et al., 1998;Longinelli and Flora, 2007;Orti et al., 2010;Peryt et al., 2005;Pierre and Rouchy, 1986;Rick, 1990;Sakai, 1972;Strauss, 1997Strauss, , 1999Strauss et al., 2001;Surakotra et al., 2018;Utrilla et al., 1992;Worden et al., 1997); black circles ¼ barite data (Paytan et al., 1998(Paytan et al., , 2004Yao et al., 2019, under review). Blue dash line, the modern seawater sulfate δ 34 S value of $21% Tostevin et al., 2014). in the extraction process of CAS from bulk sediment samples, are required to ensure that the recovered sulfate accurately represents only the original CAS signature. ...
... These two signals are complementary and changes in the sulfur isotopic composition of the local water mass and/or pore waters are recorded by δ 34 S py data and the typically more global record of changes to the marine sulfate reservoir are recorded by δ 34 S CAS . Furthermore, the sulfur isotopic composition of CAS in modern biogenic carbonates and bulk micrites robustly matches that of contemporaneous seawater within ≤1‰ (Burdett et al., 1989;Kamschulte et al., 2001;Kampschulte & Strauss, 2004;Lyons et al., 2004;Strauss, 1999). ...
... In the case of CAS, the sulfate is incorporated as a trace component into carbonate minerals during their formation. Carbonate production typically occurs in shallower waters within the photic zone and the incorporation of sulfate carries little fractionation (Burdett et al., 1989;Kampschulte et al., 2001;Kampschulte & Strauss, 2004;Lyons et al., 2004;Strauss, 1999), which makes δ 34 S CAS an attractive archive of global changes in isotopic composition of the marine sulfate reservoir. However, as more data become available from multiple areas for a single event, it is becoming increasingly clear that the δ 34 S CAS does not always preserve a straightforward global record of synchronous change in all settings (e.g., see Present et al., 2019;Richardson et al., 2021). ...
New δ³⁴Spy (pyrite) and δ³⁴SCAS (carbonate‐associated sulfate) across the Llandovery‐Wenlock boundary (∼432 Ma) provide evidence for the expansion of reduced marine environments during the Ireviken Biogeochemical Event. This event consists of a major positive carbon isotope excursion, increased biotic turnover, and other major perturbations and changes within biogeochemical cycles. This interval of time has been hypothesized to coincide with an expansion of reducing marine environments that caused increased organic carbon burial and led to the Ireviken positive carbon isotope excursion (ICIE). Previous high‐resolution carbon isotope work in the Altajme core from Gotland, Sweden provides the highest resolution record of the ICIE yet documented and provides an ideal expanded stratigraphic section to study this event. Local expansion of reduced marine environments within the deeper shelf setting of the Altajme core is indicated by a positive shift in δ³⁴Spy values and increase in pyrite sulfur concentrations at the onset of the ICIE. These data are indicative of increased microbial sulfate reduction within this portion of the Baltic Basin. Combined with new δ³⁴SCAS data from this core, as well as additional data from distant basins, the new data presented here suggest a global expansion of reduced environments led to an increase in organic carbon burial and the ICIE.
... Under reduced conditions, hydrogen sulfide is produced through bacterial sulfate reduction and is eventually fixed in authigenic (sedimentary) pyrite (FeS 2 ). Pyrite production can be monitored using the sulfur isotopic composition of seawater sulfate (Strauss, 1999) because sedimentary pyrite preferentially acquires 34 S-depleted sulfur utilized by sulfatereducing bacteria. On the other hand, δ 34 S values of marine sulfates are estimated from coeval marine evaporitic sulfate (Strauss, 1999) or carbonate-associated sulfate (CAS) in biological carbonate (Kampschulte & Strauss, 2004). ...
... Pyrite production can be monitored using the sulfur isotopic composition of seawater sulfate (Strauss, 1999) because sedimentary pyrite preferentially acquires 34 S-depleted sulfur utilized by sulfatereducing bacteria. On the other hand, δ 34 S values of marine sulfates are estimated from coeval marine evaporitic sulfate (Strauss, 1999) or carbonate-associated sulfate (CAS) in biological carbonate (Kampschulte & Strauss, 2004). Direct comparison of δ 34 S values with carbon and strontium isotopes becomes possible when CAS is analyzed from the same carbonates. ...
Immediately before the extinction of the end‐Guadalupian (Middle Permian; ca. 260 Ma), a significant change to the global carbon cycle occurred in the superocean Panthalassa, as indicated by a prominent positive δ13C excursion called the Kamura event. However, the causes of this event and its connection to the major extinction of marine invertebrates remain unclear. To understand the mutual relationships between these changes, we analyzed the sulfur isotope ratio of the carbonate‐associated sulfate (CAS) and HCl‐insoluble residue, as well as the carbon isotope ratio of bulk organic matter, for the Middle‐Upper Permian carbonates of an accreted mid‐oceanic paleo‐atoll complex from Japan, where the Kamura event was first documented. We detected the following unique aspects of the stable carbon and sulfur isotope records. First, the extremely high δ13C values of carbonate (δ13Ccarb) over +5‰ during the Capitanian (late Guadalupian) were associated with large isotopic differences between carbonate and organic matter (Δ13C = δ13Ccarb ‐ δ13Corg). We infer that the Capitanian Kamura event reflected an unusually large amount of dissolved organic matter (DOC) in the expanded oxygen minimum zone (OMZ) at mid‐depth. Second, the δ34S values of CAS (δ34SCAS) were inversely correlated with the δ13Ccarb values during the Capitanian to early Wuchiapingian (early Late Permian) interval. The Capitanian trend may have appeared under increased oceanic sulfate conditions, which were accelerated by intense volcanic outgassing. Bacterial sulfate reduction with increased sulfate concentrations in seawater may have stimulated the production of pyrite that may have incorporated iron in pre‐existing iron hydroxide/oxide. This stimulated phosphorus release, which enhanced organic matter production and resulted in high δ13Ccarb. Low δ34SCAS values under high sulfate concentrations were maintained and the continuous supply of sulfate cannot by explained only by the volcanic eruption of the Emeishan Trap, which has been proposed as a cause of the extinction. The Wuchiapingian δ34SCAS–δ13Ccarb correlation, likely related to low sulfate concentration, may have been caused by the removal of oceanic sulfate through the massive evaporite deposition. This article is protected by copyright. All rights reserved.
... When all available data are considered, pyrites from the Vindhyan and Chhattisgarh basins record 34 S enrichment, ranging between 4.5‰ and 40.7‰, irrespective of the nature of pyrite (framboidal, euhedral or laminated). No pyrite from these basins has registered moderate to extreme negative δ 34 S values as observed in most sedimentary pyrites of Phanerozoic age (Strauss, 1999;Canfield & Raiswell, 1999;Canfield, 2004 and references therein). The δ 34 S values as high as ~ 40‰ are closer to or even higher than the known δ 34 S value of Proterozoic marine sulfates (Strauss, 1997;Kah et al, 2001;Gellatly and Lyons, 2005;Canfield, 2004). ...
... Clark et al, 2004) with a mean value of +42.3‰ (Sarkar et al., 2010). These values are not only enriched by about 10-15‰ more than the contemporary (Mesoproterozoic) marine sulfate (Kah et al, 2001(Kah et al, , 2004Gellatly and Lyons, 2005), but also have exceptionally small variation compared to other Proterozoic barite deposits of the world (Clark et al., 2004;Strauss, 1999;Kah et al., 2001;Kah et al, 2004;Gellatly & Lyons, 2005). The maximum pyrite δ 34 S value of ~+40‰ is not very different from this sulphate value. ...
... When all available data are considered, pyrites from the Vindhyan and Chhattisgarh basins record 34 S enrichment, ranging between 4.5‰ and 40.7‰, irrespective of the nature of pyrite (framboidal, euhedral or laminated). No pyrite from these basins has registered moderate to extreme negative δ 34 S values as observed in most sedimentary pyrites of Phanerozoic age (Strauss, 1999;Canfield & Raiswell, 1999;Canfield, 2004 and references therein). The δ 34 S values as high as ~ 40‰ are closer to or even higher than the known δ 34 S value of Proterozoic marine sulfates (Strauss, 1997;Kah et al, 2001;Gellatly and Lyons, 2005;Canfield, 2004). ...
... Clark et al, 2004) with a mean value of +42.3‰ (Sarkar et al., 2010). These values are not only enriched by about 10-15‰ more than the contemporary (Mesoproterozoic) marine sulfate (Kah et al, 2001(Kah et al, , 2004Gellatly and Lyons, 2005), but also have exceptionally small variation compared to other Proterozoic barite deposits of the world (Clark et al., 2004;Strauss, 1999;Kah et al., 2001;Kah et al, 2004;Gellatly & Lyons, 2005). The maximum pyrite δ 34 S value of ~+40‰ is not very different from this sulphate value. ...
Oxygenation of atmosphere had a profound role in the evolution of life from primitive anoxygenic heterotrophic life forms to oxygenic photoautotrophs and eventually to multicellular organized plant and animal kingdom. Plethora of geological and geochemical evidences particularly the occurrences of pyritiferous- and uraniferous-reduced paleoplacers, distribution of BIF through ages, Fe-depleted reduced paleosols and more importantly the mass-independent multiple sulphur isotope fractionation prior to 2.4 Ga great oxidation event (GOE) collectively suggest an oxygen-deficient atmosphere during the Archean. Recent research from paleosols older than 2.4 Ga and coeval marine sediments using REE-distribution pattern, redox-sensitive trace elements and fractionation of their isotopes indicates more than one attempt of pre-GOE oxygenation. More case studies from well-preserved paleosols and marine sedimentary sinks for trace metals from the Archean would bridge the gap in the record from pre-GOE to GOE oxygenation history. Peninsular India with nearly continuous stratigraphic successions from Paleoarchean to Paleoproterozoic time interval may be potential to study the pre-GOE to GOE transition of the atmosphere.
... The sulfur isotopic composition (δ 34 S) of the global ocean reservoir has varied throughout Earth history due to changes in sulfur fluxes (and their isotopic compositions) into and out of the marine sulfate reservoir. These isotopic data as preserved in the rock record are used to document regional to global changes in seawater δ 34 S and reconstruct global sulfur cycling, as well as for chemostratigraphic studies to correlate stratigraphic sections within and between basins (e.g., Gill et al., 2011;Gomes et al., 2016;Hurtgen et al., 2006;Jones and Fike, 2013;Kampschulte and Strauss, 2004;Marenco et al., 2008b;Newton et al., 2004;Owens et al., 2013;Strauss, 1999;Thompson and Kah, 2012;Wotte et al., 2012b;Wotte and Strauss, 2015) Understanding the relative and absolute magnitude of δ 34 S variation is particularly important for studies that model the global sulfur cycle and atmospheric oxygen (O 2 ) levels using isotope mass balance (Berner, 2006). Other studies model the size of the ocean sulfate reservoir using the magnitude (and inferred rate) of δ 34 S variation from a single stratigraphic section (Kah et al., 2004;Thompson and Kah, 2012) as well as the magnitude and duration of δ 34 S excursions in the rock record (Gill et al., 2011). ...
... Carbonate-associated sulfate (CAS), sulfate incorporated into the carbonate mineral lattice, can preserve δ 34 S trends in deep time similar to other δ 34 S seawater proxies (Kampschulte and Strauss, 2004;Rennie et al., 2018;Strauss, 2004Strauss, , 1999. CAS is becoming regularly used for δ 34 S stratigraphy and reconstructing high-resolution records of δ 34 S seawater because carbonate successions typically have superior temporal resolution, and for Phanerozoic successions with previously published biostratigraphic age control, the ages of these units are well calibrated in comparison to non-fossil bearing Precambrian successions (Fike et al., 2006;Fike and Grotzinger, 2008;Gill et al., 2011;Gomes et al., 2016;Kampschulte and Strauss, 2004;Owens et al., 2013;Strauss, 2004;Wotte et al., 2012b;Wotte and Strauss, 2015;Young et al., 2016). ...
... Sulfur in marine sediments mainly originated from the reduction of sulfate in seawater. During sulfate reduction, the sulfur isotopic composition of sulfide and phosphorite depends on isotope fractionation (Strauss, 1999). The 32 SeO bonds are broken more easily than 34 SeO bonds are, and 32 S preferentially entered into SeS bonds (Harrison and Thode, 1958). ...
... The 32 SeO bonds are broken more easily than 34 SeO bonds are, and 32 S preferentially entered into SeS bonds (Harrison and Thode, 1958). Thus, under restricted sulfur concentrations, along with the process of sulfate reduction, more 34 S combined as SeS bonds along with the decreased 32 S, resulting to high δ 34 S in S 2and higher δ 34 S in SO 4 2- (Strauss, 1999). Research has shown that δ 34 S in apatite in the Doushantuo Formation ranged from +34.2 to +42.4‰ (Chu et al., 1995;Shi, 2005), which was higher than the δ 34 S of contemporary seawater (+30‰) (Chu et al., 1995). ...
... Strauss, 1993). The results have highlighted both links and disconnects between these two isotopic records (Utrilla et al., 1992;Strauss, 1999;Kampschulte and Strauss, 2004;Bottrell and Newton, 2006;Turchyn et al., 2009;Wu et al., 2014). ...
... To prepare samples for sulfur isotope analysis samples (both barites from CAS extractions and evaporite minerals) were boiled at 100°C in Thode solution (HI, H 3 PO 2 and HCl; Thode et al., 1961;Pepkowitz and Crockford et al. Chemical Geology xxx (xxxx) Bao et al., 2008Bao et al., , 2009Bao et al., , 2012Burke et al., 2018;Cameron, 1983;Chu et al., 2007;Claypool et al., 1980;Cortecci et al., 1981;Cowie and Johnston, 2016;Crockford et al., 2016Crockford et al., , 2017Crockford et al., , 2018Das et al., 1990;Deb et al., 1991;Fike and Grotzinger, 2008;Fox and Videtich, 1997;Gellatly and Lyons, 2005;Gill et al., 2007;Goldberg et al., 2005;Grinenko et al., 1989;Guo et al., 2009;Halverson and Hurtgen, 2007;Holser and Kaplan, 1966;Hough et al., 2006;Hurtgen et al., 2002Hurtgen et al., , 2004Hurtgen et al., , 2005Hurtgen et al., , 2009Johnston et al., 2005b;Kah et al., 2004Kah et al., , 2016Kampschulte and Strauss, 2004;Kampschulte et al., 1998;Kesler and Jones, 1980;Killingsworth et al., 2013Killingsworth et al., , 2018Krupenik et al., 2011;Li et al., 2015;Longinelli and Flora, 2007;Luo et al., 2015;Markovic et al., 2016;Masterson et al., 2016;Mazumdar and Strauss, 2006;Master et al., 1993;Misi and Veizer, 1998;Ortí et al., 2010;Palmer et al., 2004;Paytan et al., 1998;Peng et al., 2011;Peryt et al., 2010;Pierre and Rouchy, 1986;Planavsky et al., 2012;Present et al., 2015;Rennie et al., 2018;Reuschel et al., 2012;Rick, 1990;Ries et al., 2009;Sakai, 1972;Schobben et al., 2017;Schröder et al., 2008;Shi et al., 2018;Shields et al., 2004;Sim et al., 2015;Strauss, 1993Strauss, , 1999Strauss et al., 2001;Surakotra et al., 2018;Thompson and Kah, 2012;Tostevin et al., 2014Tostevin et al., , 2017Schrag, 2004, 2006;Turchyn et al., 2009;Ueda et al., 1987;Ueda et al., 1991;Utrilla et al., 1992;Velikoslavinsky et al., 2003;Worden et al., 1997;Wotte et al., 2012;Wu et al., 2010Wu et al., , 2014Wu et al., , 2015Yang et al., 2018;Yao et al., 2018 and new data from this study. Please refer to individual studies for associated errors on analysis and refer to the Methods section of this paper for errors on newly generated data. ...
The Proterozoic Eon spans Earth's middle age during which many important transitions occurred. These transitions include the oxygenation of the atmosphere, emergence of eukaryotic organisms and growth of continents. Since the sulfur and oxygen cycles are intricately linked to most surface biogeochemical processes, these transitions should be recorded in changes to the isotopic composition of marine and terrestrial sulfate minerals. Here we present oxygen (∆ ¹⁷ O, δ ¹⁸ O) and sulfur (∆ ³³ S, δ ³⁴ S) isotope records of Proterozoic sulfate from currently available data together with new measurements of 313 samples from 33 different formations bearing Earth's earliest unambiguous evaporites at 2.4 Ga through to Ediacaran aged deposits. This record depicts distinct intervals with respect to the expression of sulfate isotopes that are not completely captured by established intervals in the geologic timescale. The most salient pattern is the muted ∆ ¹⁷ O signatures across the GOE, late Proterozoic and Ediacaran with values that are only slightly more negative than modern marine sulfate, contrasting with highly negative values across the mid-Proterozoic and Cryogenian. We combine these results with estimates of atmospheric composition to produce a gross primary production (GPP) curve for the Proterozoic. Through these results we argue that changes in GPP across Earth history likely help account for many of the changes in the Proterozoic Earth surface environment such as rising atmospheric oxygen, large fluctuations in the size of the marine sulfate reservoir and variations in the isotopic composition of sedimentary sulfate.
... Subsequent studies have further characterized multiple S isotope signatures in microbial experiments ( Johnston and others, 2007;Sim and others, 2011;Sim and others 2012) and improved our understanding of the influence of rate (Leavitt and others, 2013), sulfate concentration (Bradley and others, 2015), and enzyme effects (Leavitt and others, 2015) in the ultimate expression of multiple S isotope biosignatures. Due to the overwhelming importance of MSR in the historical S isotope record (for example, Strauss, 1999), multiple S isotope studies have also tried to interpret these mass-dependent 33 S/ 32 S signatures in proxy records ( Johnston and others, 2008;Wu and others, 2010;Wu and others, 2015;Sim and others, 2015;Masterson and others, 2016). The variability in the 33 S/ 32 S record is clearly connected to microbial metabolism, but the proper quantification of the connection between laboratory calibrations of microbial signatures depends on placing those isotopic observations into a diagenetic context; recall that most geologic sedimentary records began their life as marine sediments. ...
... As it is common for the isotopic offset between pore water sulfate and free sulfide (or pyrite) to exceed this presumed limit, oxidative sulfur cycling was frequently invoked to explain environmental measurements exceeding this value (Habicht and Canfield, 1997;Habicht and others, 1998). Not only did this carry consequences for studying S cycling in modern systems, it also carried implications for interpreting S cycling through geological proxy records (for example, BaSO 4 , CaSO 4 , and sedimentary pyrite) (Canfield and Teske, 1996;Strauss, 1999;Canfield, 2001;Canfield, 2004;Canfield and Farquhar, 2009). Despite the lack of laboratory evidence that sulfur isotope fractionations could exceed ϳ46 permil, theoretical metabolic models suggested that such was possible (Brunner and Bernasconi, 2005;Johnston and others, 2007;Johnston, 2011). ...
Recent studies targeting the metabolic, physiological, and biochemical controls of sulfur isotope fractionation in microbial systems have drawn linkages between results from culture experiments and the sulfur isotope signatures observed in natural environments. Several of those studies have used newer techniques to explore the minor isotope (³³S and ³⁶S) variability in those systems, and also have attempted to place them in an ecophysiological context. Sparingly few have incorporated this newfound understanding of minor isotope behavior into natural systems (sediment pore waters, water columns) and none of them have refined existing isotope-dependent reaction-transport models to explicitly include ³³S. In this study, we construct a three-isotope (³²S, ³³S, and ³⁴S) reaction-transport model of pore water sulfate for a well-characterized sedimentary system within the California-Mexico Margin (Alfonso Basin). An additional goal is placing recent laboratory culture work into a natural, physical context. The model first reproduces the measured bulk geochemical characteristics of the pore water profiles of [SO4²], [CH4], dissolved inorganic carbon ([DIC]), and [Ca²]—and predicts bulk (non-isotope-specific but depth-dependent) rates of sulfate reduction. Next, the model uses those depth-dependent bulk rates, in combination with empirically calibrated fractionation factors, to explain the minor isotope characteristics (³⁴S and ³³S values) of the 0 to 40 cm pore water SO4². The down core, isotopic evolution of pore water sulfate requires a large fractionation associated with sulfate reduction (³⁴SR 70 5) that appears to be independent of bulk rate, but in line with low temperature thermodynamic predictions. The minor isotope characteristics (³³SR 0.5130) are also independent of rate and fall within the range expected from microbial calibrations, but differ from minor isotope predictions of thermodynamic equilibrium. The high value of ³⁴SR raises key questions in relating the physiological state of marine microorganisms relative to their laboratory counterparts, as well as point toward exceedingly low metabolic rates in natural marine sediments.
... The sulfur isotope composition of pyrite in Gaositai chromitite falls within the range of gabbro and peridotite from the Troodos ophiolite. The positive δ 34 S values of pyrite in Gaositai chromitite, different from other ophiolite rocks, resemble sulfides found in sediment-hosted or hydrothermal systems, suggesting a possible mixing with modern seawater (Strauss, 1999). ...
The Gaositai mafic-ultramafic complex in the North China Craton hosts a significant chromitite deposit that displays morphological and geochemical characteristics that deviate from the usual characteristics of typical high-Cr and low-Al podiform chromitites. Field observations and microscopic studies reveal notable variations in texture, layering, mineralogy, and geochemical composition, challenging conventional features of stratiform chromitite deposits. Zircon U-Pb ages indicate that chromitite is most likely Carboniferous-Permian in age (330-275 Ma), but also contains numerous inherited zircons with concordant ages as old as 2544 Ma, reflecting a complex geological evolution. Post-formation metasomatic or metamorphic imprints can be evident by concordant zircon ~ 247 Ma. Variable zircon εHf(t) values (-15 to +9.6) and depleted mantle model ages (432 to 2819 Ma) attest the presence of heterogeneous or reworked source materials.
The PGE and trace element characteristics of the Gaositai chromitite are comparable to the geochemical features of Bushveld and Great Dyke deposits. Pyrite, millerite, norsethite, galena, and PGM (mainly Os-Ir alloys) inclusions are ubiquitous in chromite. Galena inclusions with homogenous Pb-isotopic ratios (206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb) suggest a mixed sources of lead. In contrast, pyrite inclusions display significant variations in δ34SV-CDT values (-0.11 ‰ to 18.31‰) indicative of a crustal origin of sulfur. Bulk-rock Re-Os isotope data of 0.1264-0.1294 shows 187Os/188Os ratios similar to abyssal peridotites, implying a potential connection between chromitite and the host ultramafic rocks. Highly disparate mantle model ages (55 to 2141 Ma) and re-depletion ages (28 to 692 Ma) suggest disturbance of the Re-Os isotopic system during post-formational metasomatic or metamorphic events. These variations may, alternatively, reflect heterogeneity by subduction components. The obtained results do not support the Alaskan-type genesis of the host complex, but point towards an atypical stratiform type.
... The possible sulfur sources for the Naweoba and Bagh deposits include sulfur leached from basaltic igneous rocks (δ 34 S ≈ 0-1‰; Alt et al. 1993;Kusakabe et al. 1990) and seawater sulfate (δ 34 S ≈17‰; Strauss 1999). Seawater sulfate reduction can occur in the fluid discharge zone (upflow) (Woodruff and Shanks 1988), the recharge zone (Janecky and Shanks 1988), or high-temperature deep zone (Bluth and Fig. 10 Concentrations of trace elements in pyrite and chalcopyrite in a the Naweoba and b the Bagh VMS deposits Ohmoto 1988). ...
The petrography, mineralization, and geochemistry and isotope studies of sulfide ores were used to determine the genesis of the Naweoba and Bagh Volcanogenic Massive Sulfide (VMS) deposits. These deposits consist of minor stockwork, massive sulfide, and gossan zones. They are hosted by basaltic rocks in the Naweoba Block and Bagh Complex of Zhob Valley Ophiolites, respectively. The host rocks are strongly altered to chlorite and sericite. By using whole rock and pyrite in situ analyses, it is found that the Cu concentration is higher compared to Zn and Pb. Similarly, the primary mantle normalized data of Pb, Cu, Ag, Au, and Zn as well as the high Co/Ni ratios (> 1) in pyrite for both deposits indicate that these deposits have a mafic origin dominated by hydrothermal processes. The trace element signature in pyrite and chalcopyrite in these deposits suggests that mineralization formed at high to moderate temperatures. The δ34S values of pyrite (2.4–4.6‰) and chalcopyrite (2.7–5.7‰) indicate that hydrothermal fluids have derived sulfur largely from basaltic igneous rocks. The above signatures are all consistent with a Cyprus-type VMS ore deposits associated with ophiolites. Moreover, it was found that several trace elements (Ni, Co, Se, Zn, Pb, Sb, and As) show systematic variations in pyrite from Naweoba that are correlated to the stratigraphic depth and can be used as a proxy to separate deeper from shallower sulfide ores.
... For a long time, culture-derived isotope fractionation showed considerable variability with a maximum fractionation at ∼45 mUr (where 1 mUr equals 1 ‰, see Brand and Coplen (2012) for using mUr because isotope δ values are dimensionless). The data of, e.g., Kaplan and Rittenberg (1964) and Habicht and Canfield (1997), are consistent with the idea that the globally averaged isotopic difference between seawater and pyrite must be smaller than ∼45 mUr to satisfy steady-state conditions but conflict with the sedimentary isotope record preserved in iron sulfides that often show a ∼70 mUr offset relative to seawater (Goldhaber and Kaplan, 1980;Ohmoto et al., 1990;Strauss, 1997;Strauss, 1999). The discovery of microbial disproportionation of sulfur intermediates (MSD; Bak and Pfennig, 1987;Bak and Cypionka, 1987) seemed to provide an elegant explanation for the large isotope offset observed between seawater sulfate and sedimentary pyrites (Canfield and Thamdrup, 1994). ...
Experimental studies with pure and enrichment cultures have shown that microbial disproportionation of sulfur intermediates can increase the sulfur isotopic difference between dissolved sulfate and sulfide produced by microbial sulfate reduction. However, few studies have quantified the isotope effect of disproportionation in natural settings. Here we describe a conceptual model to quantify the contribution of elemental sulfur disproportionation to the isotopic difference between dissolved sulfate and sulfide. Our results show that disproportionation increases the isotopic difference between sulfate and sulfide, but the effect is less pronounced than suggested by culture experiments. The resulting isotopic difference depends on the ratio of the rate of microbial sulfate reduction to that of disproportionation. It can be shown that in natural sediments, this relationship can be expressed as a function of the isotope enrichment during disproportionation multiplied by the fraction of sulfide that escapes burial in the form of metal sulfides. This implies that in many natural sediments, the sulfur isotope effect is limited to a few permil (mUr) or less.
... Therefore, sulfur isotopic compositions of sulfate in ocean reservoirs are dominantly impressionable of continental weathering input and burial of bacterially mediated sedimentary sulfides (pyrite) export. Based on an isotope mass balance, increased weathering results in lower δ 34 S values, while increased pyrite burial causes higher δ 34 S values (Strauss, 1999;Kah et al., 2004). ...
The early Mesoproterozoic (1.6–1.4 Ga) is a critical stage for oxygenation of Earth’s surface and early eukaryote evolution. However, the relationship between both remains uncertain. Here, we provide new carbonate associated sulfate (CAS) sulfur isotopic compositions (δ34SCAS) and trace elements from the 1.6 to 1.55 billion-year old Gaoyuzhuang Formation in multiple sections within the Yanshan Basin, North China, to investigate the temporal and spatial variation of ocean redox conditions. New and collected δ34SCAS data from five sections (Pingquan, Kuancheng, Qianxi, Jixian and Gan’gou sections) reveal similar sulfur isotopic excursions, but the differences in absolute values indicate spatial heterogeneity of sulfur isotopic compositions, which may reflect
marine low-sulfate concentrations and oceanic redox tratification. The most elevated δ34SCAS values appeared at the top of the Second Member of the Gaoyuzhuang Formation, followed by distinct negative excursions at the bottom of the Third Member, suggesting a dynamic sulfur cycle and seawater redox status during this period. Combined with previous reported carbon and sulfur isotopes and some redox proxies (e.g., Ce anomalies,
manganese-rich deposit, I/(Mg + Ca) and Fe speciation), we suggest that at least two possible oxygenation events may have occurred in the Gaoyuzhuang Formation: (1) the bottom of the Second Member and (2) the bottom or middle part of the Third Member. Different sections show asynchronous timing of these events, indicating that the redox status was spatial heterogenous within the Yanshan Basin. The spatial heterogeneity may be controlled by facies and paleogeographic locations. Considering that decimeter-scale multicellular eukaryotes are preserved
in the middle part of the Third Member, we argue that oxic bottom water condition may be a critical factor for early eukaryote evolution.
... The sulfur stable isotopes (δ 34 S) in sulfates and sulfides have been proven to be a remarkable tool for studying geochemical and biogeochemical cycles in modern and ancient environments [1][2][3]. Particularly, in magmatic-hydrothermal and hydrothermal systems and the associated ore deposits, the δ 34 S values of sulfides routinely provide constraints on the source of sulfur (e.g., magmatic and biogenic) and the processes (e.g., sulfate reduction, fluid mixing, and water-rock interactions) and environmental parameters (e.g., temperature, oxygen fugacity, and pH) associated with sulfide precipitation [4][5][6]. In some peculiar magmatic-hydrothermal and hydrothermal mineral deposits, the mineralogy may be dominated by arsenides, sulfarsenides, and arsenic (As) and mercury (Hg) sulfides. ...
The stable isotope ratios of sulfur ( δ ³⁴ S relative to Vienna Cañon Diablo Troilite) in sulfates and sulfides determined by elemental analysis and isotope ratio mass spectrometry (EA/IRMS) have been proven to be a remarkable tool for studies of the (bio)geochemical sulfur cycles in modern and ancient environments. However, the use of EA/IRMS to measure δ ³⁴ S in arsenides and sulfarsenides may not be straightforward. This difficulty can lead to potential health and environmental hazards in the workplace and analytical problems such as instrument contamination, memory effects, and a non-matrix-matched standardization of δ ³⁴ S measurements with suitable reference materials. To overcome these practical and analytical challenges, we developed a procedure for sulfur isotope analysis of arsenides, which can also be safely used for EA/IRMS analysis of arsenic sulfides (i.e., realgar, orpiment, arsenopyrite, and arsenian pyrite), and mercury sulfides (cinnabar). The sulfur dioxide produced from off-line EA combustion was trapped in an aqueous barium chloride solution in a leak-free system and precipitated as barium sulfate after quantitative oxidation of hydrogen sulfite by hydrogen peroxide. The derived barium sulfate was analyzed by conventional EA/IRMS, which bracketed the δ ³⁴ S values of the samples with three international sulfate reference materials. The protocol (BaSO 4 -EA/IRMS) was validated by analyses of reference materials and laboratory standards of sulfate and sulfides and achieved accuracy and precision comparable with those of direct EA/IRMS. The δ ³⁴ S values determined by BaSO 4 -EA/IRMS in sulfides (arsenopyrite, arsenic, and mercury sulfides) samples from different origins were comparable to those obtained by EA/IRMS, and no sulfur isotope fractionations were introduced during sample preparation. We report the first sulfur isotope data of arsenides obtained by BaSO 4 -EA/IRMS.
Graphical abstract
... Based on the range of values of sulfur isotopes (− 1.7 to 5.1‰) in Garmab-e-Paein deposit (Fig. 12), there are three major sources of sulfur for this deposit: (1) δ 34 S enriched sulfide derived by the reduction of seawater sulfate, by either inorganic or organic processes (Slack and Shanks, 1989;Strauss, 1999), (2) Sulfur leached from the underlying basalts (δ 34 S = 0-1‰; Kusakabe et al., 1990;Alt et al., 1993), and (3) sedimentary bacteriogenic sulfide depleted of δ 34 S (Slack, 1993). Many massive sulfide deposits have sulfides with δ 34 S 2-5‰ (Fig. 13) consistent with derivation of most of the sulfur from underlying volcanic rocks (e.g., Seal, 2006;Badrzadeh et al., 2011). ...
The Garmab-e-Paein Cu-Ag volcanogenic massive sulfide (VMS) deposit occurs as stratiform and stratabound orebody within a specific stratigraphic horizon in a Late Cretaceous volcano-sedimentary sequence of the Sabzevar zone, northeast Iran. The host rocks to mineralization are andesitic- trachyandesitic volcanic and volcaniclastic rocks. Based on textural and mineralogical studies, the VMS mineralization is comprised of four ore facies: 1) vein-veinlets (stringer) containing chalcopyrite, pyrite and minor magnetite, 2) massive ore, dominated by pyrite and minor chalcopyrite, 3) bedded ore containing laminated pyrite, and 4) exhalite containing Fe-Mn oxide-hydroxides such as hematite, psilomelane and pyrolusite. Wall rock alteration styles are chloritic, minor silicic and
secondary argillic. There is a distinct metal zonation in the massive sulfide orebody; Au, Pb, As, and Ag contents and the Cu/Zn ratio increase vertically from the stringer to the massive facies, but decrease laterally from the stringer to the bedded facies. Zinc and Mn increase from the stringer to the bedded ore facies. Sulfur isotope values for pyrite range from -1.7 to +5.1‰, with average +1.4‰. The δ34S values of massive ore facies (-1.7 and +2.7‰) increase downward toward the stockwork (+2.2 to +4.3‰) and laterally outward toward the bedded (+5.1‰) zones. The near-zero sulfur isotope values indicate that most of the sulfur was derived from leaching of underlying host volcanic rocks by hydrothermal fluids circulating in the high temperature reaction zone. Extensive disseminations and vein-veinlets of native copper mineralization formed within the hanging wall Late Cretaceous volcanic rocks and younger Paleocene conglomerates. The native copper
mineralization is accompanied by chlorite and zeolite alteration, and both formed after formation of the Garmab-e-Paein VMS deposit during diagenesis, burial metamorphism and uplift. The deposit is now potentially economic due to the native copper mineralization. Two generations of chlorite are observed in the deposit: Chl-I is accompanied pyrite and chalcopyrite, in the VMS mineralization system, and the second Chl-II occurs along with zeolite and native copper mineralization. The EPMA results show that Chl-I is more Fe-rich than Chl-II.
... As a proxy for seawater sulphate, CAS is a trace constituent within carbonate mineral (Pingitore, Nicholas, Meitzner, & Love, 1995). The sulphur isotopic composition of CAS in bulk micrite generally matches that of contemporaneous seawater (e.g., Burdett, Arthur, & Richardson, 1989;Kampschulte, Bruckschen, & Strauss, 2001;Strauss, 1999). The two negative δ 34 S CAS excursions were associated with increases in CAS concentrations, suggesting a marine sulphate concentrations variability explanation (Gomes et al., 2016). ...
Separated mass extinction occurred at the beginning and the ending of the Late Permian, called end‐Guadalupian and end‐Permian mass extinctions, respectively. Palaeoenvironmental changes in the middle of the Late Permian could give more insights into the environmental causes for the Permian extinctions. In this contribution, we analysed carbonate carbon isotope and carbonate‐associated‐sulphate sulphur isotope compositions to constrain the carbon and sulphur cycles across the Wuchiapingian‐Changhsingian boundary (WCB) at Yanglinqiao in Zigui in the Middle Yangtze Platform. Pyrite morphology and pyrite framboids size distribution were used to analyse redox conditions variations across the WCB. Our results show that an episodic euxinia event occurred across the WCB. This anoxic/euxinic event across the WCB was a global event, and was mainly caused by the upwelling during the cooling event. Both inorganic‐ and organic‐carbon isotopic compositions show covariance of a negative shift across the WCB at Yanglinqiao and other places in South China. This carbon‐isotopic negative excursion across the WCB was a regional carbon cycle perturbation and may be linked to the light‐carbon input from the upwelling water mass. Although the seawater δ³⁴S across the WCB recorded a negative excursion in two locations in South China, it reflects the riverine input of ³²S‐enriched sulphate and represent a regional signal. These environmental anomalies such as oceanic anoxia/euxinia, global carbon cycle perturbation, cooling, end of the Emeishan large igneous province movement across the WCB may have delayed the recovery from the end‐Guadalupian mass extinction.
... The study area belongs to the typical marine monsoon climate, and its atmospheric precipitation is mainly from marine transport, and the δ 34 S isotopic value in seawater is about +20.0‰ [43]. According to Xiao's research results in neighboring Guiyang, the averaged δ 34 S isotopic value of rainwater ranged from −4.9 to +4.6‰ [44]; moreover, the sulfur in the heavy rain with positive δ 34 S value is more likely to be marine origin. ...
Surface water samples from the Maolan National Natural Reserved Park (MNNRP) were analyzed from Sept. 2013 to June 2014, for major ion concentrations (K+, Na+, Ca2+, Mg2+, Cl−, SO42−, HCO3−), δ13C-DIC and δ34S-SO42− to quantify the sources of solutes and chemical weathering. The results show that HCO3− and SO42− are the main anions in Banzhai watershed, which account for 86.2 and 10.4% of the total anion equivalent, respectively. While Ca2+ and Mg2+ account for 76.9 and 20.5%, respectively. Considerable Mg2+ in stream water indicates that it may be affected by dolomite weathering. stream water samples present the δ13C-DIC values in the range of −16.9‰~−10.8‰ (mean value was −13.9‰), which were lower than that of the groundwater. The δ34S-SO42− values ranged from −15.2‰ to 1.7‰ (mean value was −4.4‰). There was a negative correlation between HCO3− content and δ13C value, implying the result of the interaction of temperature and precipitation intensity in different seasons. The significant positive correlation between SO42− content and δ13C-DIC indicates that H2SO4 may be involved in the weathering process of carbonate rocks in small watershed scale. The content of SO42− in a school sample site was much higher than that of other sample sites for the interference from human sources. The δ34S values show that the average δ34S-SO42− in most sites is close to the δ34S isotopic values of Guizhou coal and rain, indicating that they may be affected by local coal.
... Sulfur isotopic compositions of oceanic sulfate and sedimentary pyrite reflect integrative information of multiple geological and microbial processes and can provide critical insights into details of global sulfur cycle, depositional environment, as well as microbial metabolism evolution (e.g., Strauss, 1999;Canfield, 2004;Kampschulte and Strauss, 2004;Shen and Buick, 2004). Because 32 S is preferentially reduced relative to 34 S via BSR, the δ 34 S values of biogenic pyrite are generally more negative than those of contemporaneous seawater sulfate. ...
The emergence and proliferation of metazoan lineage in the Ediacaran Period is commonly hypothesized to reflect an increase in the oxygen content of marine environments. However, recent studies suggest that the Ediacaran oceanic redox conditions were spatially heterogeneous and temporally dynamic. In this study, we report high-resolution pyrite S-isotope data (δ³⁴Spy) for a continuous Ediacaran drill core that was deposited in a very shallow setting from the Yangtze platform, South China. Combined with petrographic observations, statistics of pyrite framboid diameters, total carbon (TC), total sulfur (TS), trace element, and published data, we attempt to characterize the details of sulfur cycle as well as oceanic redox change in the shallow-water regions of the Yangtze platform during the Ediacaran. The δ³⁴Spy profile exhibits a large amplitude of variation, ranging from –13.7‰ to 41.4‰ throughout the drill core. Both global and regional changes in environment could have exerted effects on δ³⁴Spy values. For the Doushantuo Formation, distinct δ³⁴Spy records from shelf to basin may reflect spatial heterogeneity in sulfate concentrations, depositional environments, and availability of organic matter. Notably, periods of upwelling may cause oxygen-deficient zones within shallow water column and facilitate persistent burial of organic matter and pyrite in shelf regions. Subsequent exposure and weathering of these reduced carbon and sulfur may contribute to the “Shuram-Wonoka” event. The prevalence of high δ³⁴Spy values in the terminal Ediacaran (Dengying Formation) likely indicates an enhanced pyrite burial flux at a global scale, during which extensive marine anoxia might take place. In addition, enrichments of V and U in three shale intervals of the drill core support periods of oxygenation for the Ediacaran oceans.
... The isotope fractionation between coeval sulfate [carbonate associated sulfate (CAS) or that hosed in evaporites (gypsum/anhydrite)] and pyrite from the geological record has been widely used to reconstruct environmental and redox conditions in geologic time (Strauss, 1997(Strauss, , 1999(Strauss, , 2003Shen et al., 2001;Canfield, 2004;Farquhar et al., 2007;Fike and Grotzinger, 2008;Luo et al., 2010Luo et al., , 2015Johnston, 2011;Gill et al., 2011;Planavsky et al., 2012;Owens et al., 2013;Jones and Fike, 2013;Algeo et al., 2015). The increase in δ 34 S py values in marine sediments could be explained by an increase in the burial rate of pyrite during expanded anoxia causing some δ 34 S-enrichment in the marine sulfur reservoir. ...
The Ludfordian (late Silurian) records one of the largest perturbations in the Phanerozoic marine carbon cycling, the mid-Ludfordian positive δ¹³Ccarb excursion (MLCIEcarb), which occurred in the aftermath of the Lau/Kozlowskii Bioevent (LKB). There are still controversies regarding origin of the MLCIE and its possible causal link(s) with respect to the preceding LKB. Surprisingly, the isotope fractionation of carbon between inorganic and organic carbon pools during the MLCIE was not investigated in detail. To constrain better this parameter of marine C cycle, its linkage to the LKB, and local sulfur cycle, we analysed high-resolution δ¹³Ccarb, δ¹³Corg, and δ³⁴Spy records in the Prague Basin (peri-Gondwana) representing one of the most complete records of the MLCIEcarb in the world. Evaluation of these high-resolution δ¹³Corg and δ¹³Ccarb records reveals their tight coupling, which in turn indicates the photosynthetic origin of the MLCIEorg via links to primary production and changing rates of organic carbon burial. On the other hand, our data also reveal a short-term decoupling of the δ¹³Corg and δ¹³Ccarb records preceding the MLCIE which may have been related to a purported increase in atmospheric pCO2 levels or anoxic event. The peak of the Δ¹³C anomaly exactly coincides with the LKB and, therefore, for the first time suggests a tight link between the change in marine carbon cycling and the bioevent. Subsequent rapid drop of the Δ¹³C values (and by inference also atmospheric pCO2) fits well with a rapid cooling and globally documented regression reported for this time interval. Finally, the documented strong coupling of δ¹³Ccarb and δ³⁴Spy records during the MLCIE points to an intensive microbial sulfate reduction which should increase carbonate alkalinity input, thus contributing to formation of authigenic carbonates and an increase in δ¹³C values of DIC (and anticipated seawater carbonate saturation). The coupling of δ¹³Corg and δ³⁴Spy values suggests a global enhancement of organic carbon and pyrite burial likely driven by an expansion of euxinic (anoxic and sulfidic water column) conditions in the oceans. Present study of C and S isotope variations during the MLCIE reveals for the first time a tight link among carbon and sulfur cycling, global cooling, and reorganization of faunal communities and fits well with purported seawater carbonate hypersaturation at the onset and during MLCIE.
... Negative δ 34 S shifts are caused by input of light sulfur (δ 34 S ~ 0) to the surface ocean from the deep ocean rich in H 2 S, or deposits rich in sulfide, or the mantle, possibly related to either an abrupt warming, a bolide impact to the ocean, mantle plume-induced volcanism, or a combination of these (Kaiho et al., 2001(Kaiho et al., , 2006. The decrease in ocean δ 34 S in the latest Permian predate the base of the Boundary Clay, in which the δ 34 S sulphate values are close to present day ocean sulphate values of +21‰, which are remarkably uniform except near freshwater inputs (δ 34 S ~3‰) where they can drop to ~10‰ (Hannan, 1998;Strauss, 1999). The low in δ 34 S sulphate values (<10‰) at Bálvány North in the topmost Nagyvisnyó Limestone corresponds neither with the main extinction nor with the negative δ 14 C carb peak, but they do correspond with the drop in J o u r n a l P r e -p r o o f fusulinid diversity and the inferred lower salinity in bed 4. ...
The Bálvány North Permian-Triassic boundary sediments were deposited on a carbonate platform in the tropical part of the western PaleoTethys ocean. The overall elemental geochemistry of the detailed two-metre-thick section across the boundary that we studied shows that the clastic content of the sediments came from dominantly silica-rich continental sources though with some more silica-poor inputs in the uppermost Permian and lowest Triassic limestones as shown by Ni/Al and Nb/Ta ratios. These inputs bracket, but do not coincide with, the main extinctions and associated C, O and S changes. Increased aridity at the Permian-Triassic boundary with increased wind abrasion of suitable Ti-bearing heavy minerals accounts for both the high Ti/Al and Ti/Zr ratios. Various geochemical redox proxies suggest mainly oxic depositional conditions, with episodes of anoxia, but with little systematic variation across the Permian–Triassic extinction boundary. The lack of consistent element geochemical changes across the Permian-Triassic boundary occur not only in adjacent shallower-water marine sections, and in other marine sections along the SW Tethys margin such as the Salt Range sections in Pakistan, but also in deeper shelf and oceanic sections, and in non- marine African and European continental sediments. In the absence of significant changes in physical environments, chemical changes in the atmosphere and oceans, reflected in various isotopic changes, drove the Permian–Triassic extinctions.
... Pyrite in the marlstone and argillaceous limestone samples is generally euhedral and confined to laminae (Fig. 5C), or is present as large framboids (Fig. 5D), and consistent with an early diagenetic origin driven by microbial sulfate reduction (Wilkin et al., 1996(Wilkin et al., , 1997Wignall and Newton, 1998;Bond and Wignall, 2010). The low δ 34 S values of pyrite (-16.18 to -5.28‰) are also consistent with microbially mediated diagenetic sulfate reduction (Strauss, 1999). The sedimentation of the marlstone in the 3 rd Member of the Kalaatehe Formation, which hosts the Mn ores, can therefore be considered to have formed in an oxic to Notes: δ 13 Corg, δ 13 Ccarb, δ 18 Ocarb are based on the VPDB, and the δ 34 Spy is relative to VCDT suboxic water column. ...
The Upper Carboniferous Ortokarnash manganese ore deposit in the West Kunlun orogenic belt of the Xinjiang province in China is hosted in the Kalaatehe Formation. The latter is composed of three members: (1) the 1st Member is a volcanic breccia limestone, (2) the 2nd Member is a sandy limestone, and (3) the 3rd Member is a dark gray to black marlstone containing the manganese carbonate mineralization, which, in turn, is overlain by sandy and micritic limestone. This sequence represents a single transgression-regression cycle, with the manganese deposition occurring during the highstand systems tract. Geochemical features of the rare earth elements (REE+Y) in the Kalaatehe Formation suggest that both the manganese ore and associated rocks were generally deposited under an oxic water column with Post-Archean Australian Shale (PAAS)-normalized REE+Y patterns displaying characteristics of modern seawater (e.g., light REE depletion and negative Ce anomalies). The manganese ore is dominated by fine-grained rhodochrosite (MnCO3), dispersed in Mn-rich silicates (e.g., friedelite and chlorite), and trace quantities of alabandite (MnS) and pyrolusite (MnO2). The replacement of pyrolusite by rhodochrosite suggests that the initial manganese precipitates were Mn(IV)-oxides. Precipitation within an oxic water column is supported by shale-normalized REE+Y patterns from the carbonate ores that are characterized by large positive Ce (>3.0) anomalies, negative Y (~0.7) anomalies, low Y/Ho ratios (~20), and a lack of fractionation between the light and heavy rare earth elements ((Nd/Yb)PAAS ~0.9). The manganese carbonate ores are also 13C-depleted, further suggesting that the Mn(II) carbonates formed as a result of Mn(III/IV)-oxide reduction during burial diagenesis.
... Carboniferous seawater sulphate δ 34 S has been estimated to typically range from +18 to +14‰ (Strauss, 1997;Claypool et al., 1980), although values up to c. +23‰ have been reported from the Lower Carboniferous (Claypool et al., 1980;Fallick et al., 2001). High values are characteristic of the Mississippian period (Turner and Richardson, 2004), declining through the Upper Carboniferous (Strauss, 1999). In the Permian seawater sulphate δ 34 S tended to be less positive at +8 to +14‰ (Strauss, 1997). ...
The stable isotopic (δ34S, δ18O, δ2H) composition of mine waters has been examined from coal and metal mines, of varying depth, in Spain (Asturias), the UK (north Derbyshire/Yorkshire) and Poland (Bytom, Upper Silesia). δ18O and δ2H data confirm a meteoric origin for all waters. The mine waters have elevated sulphate concentrations relative to recent meteorically-derived groundwaters and have elevated SO42−/Cl− ratios relative to marine water. In the shallower mines and Markham No. 3, the dissolved sulphate δ34S is low, suggesting the sulphate is derived from the oxidation of sulphide minerals. In most of the deeper mines, the dissolved sulphate δ34S is too high (>15‰), to be derived from simple pyrite oxidation. In the deep Polish and Spanish mine waters, the source of sulphate may be evaporite mineral dissolution, but such a mechanism is problematic in the case of the Caphouse (UK) mine. Fractionation associated with sulphate reduction may have contributed to elevated dissolved sulphate δ34S. Elevated sulphate in deep coal mine waters may not always be simply derived from pyrite oxidation. The consistent observation of elevated dissolved sulphate δ34S in deep coal mines suggests a distinct genetic pathway, the origin of which as yet remains equivocal.
... Cuddapah and Chhattisgarh). These sedimentary pyrites show highly positive δ 34 S composition of >25‰ as compared to extremely negative phanerozoic δ 34 S values (Canfield and Raiswell, 1999;Strauss, 1999) suggesting an euxinic ocean with low concentration of marine sulphates (Sarkar et al., 2004). Based on TOC composition and Mo concentration of Vindhyan shales from different stratigraphic units, Singh et al. (2018) suggested that during the initial stage the Vindhyan sedimentation, the water-mass was stratified and euxinic in nature. ...
... The 34 S py values (−21.7 to −2.3‰) at Tianfengping indicate an open to semi-enclosed system (Jørgensen, 1979), assuming that the δ 34 S of coeval seawater sulfate in the Middle Permian was ~12‰ (Strauss, 1999). Sulfur isotope fractionation during sulfate reduction is negatively correlated with sulfate concentration, exhibiting a small fractionation when sulfate concentration is less than 1 mM (Canfield & Raiswell, 1999;Habicht, Gade, Thamdrup, Berg, & Canfield, 2002). ...
The formation of carbonate concretions is a cementation process which passively infills the pore spaces within sediments. They record the original environments of deposition and diagenetic conditions of the host rocks. Little is known about the precise mechanisms responsible for the precipitation of carbonate concretions. The most common host rocks are mudstones/shales, sandstones, and limestones. This study presents an example of large carbonate concretions from an unusual host rock, the black bedded cherts of the Gufeng Formation (Guadalupian) at Enshi on the northern Yangtze Platform, South China. Petrographic observations (X‐ray diffraction, optical microscopy, scanning electron microscopy) and multiple geochemical analyses (pyrite‐ and carbonate‐associated‐sulfate (CAS)‐sulfur isotopes, carbon isotopes) indicate that (a) the studied carbonate concretion are mainly composed of micritic calcite with subordinate dolomite; (b) the concretions may have been mainly formed in the bacterial sulfate reduction (BSR) zone during very early diagenesis near the sediment–water surface; (c) the paleo‐bottom water overlying the sediments during formation of the concretions was mainly euxinic; and (d) the growth of the studied concretions proceeded via a pervasive model, where later cementation phase initiated in the lower part of the concretions and progressed upward.
... The metals have been leached from hydrothermally altered zones by heated, compositionally modified seawater convicting under a steep geothermal gradient through the volcanic pile with or without a magmatic contribution for some metals (Galley, 1993;Franklin et al., 2005). Sulfur isotope compositions of sulfides (pyrite, galena, and sphalerite minerals) in both massive sulfide and stringer portions of the Barika deposit display a relatively tight cluster, ranging from −0.8 to +5.6‰ and indicating two probable sources of sulfur for the deposit: (1) seawater sulfate (δ 34 S = 17‰; Strauss, 1999) and/or (2) sulfur leached from the underlying andesites (δ 34 S = 0-1‰; Kase et al., 1990;Alt et al., 1993). The narrow range of measured δ 34 S values from the sulfide minerals is very similar to that for sulfides from Kuroko deposits in Japan, with δ 34 S of 5 ± 3‰ (Ohmoto, 1986;Shanks et al. 1995). ...
The Barika deposit is the first documented auriferous Kuroko-type volcanogenic massive sulfide (VMS) deposit in Iran. It is hosted in meta andesites of the Sanandaj-Sirjan metamorphic Zone (SSZ). The mineralization and host rocks have been metamorphosed to lower greenschist facies. The deposit has Au and Ag grades in the stratiform lens averaging 3.5 and 175 g/t, respectively, and contains 2.3 tonnes of Au and 143 tonnes of Ag. The base metal (Pb + Zn + Cu) content of the deposit is low (<1 wt%). The stratiform part of the Barika deposit is approximately 150 m long and up to 20 m thick, and consists of massive to semi-massive sulfides, some of which are banded, which are overlain by barite and siliceous exhalites. The >200 m long and up to 500 m wide stringer zone immediately stratigraphically underlies the stratiform mineralization. Veins within the stringer zone are composed of quartz, pyrite, galena, sphalerite, tetrahedrite-tennantite, and rare chalcopyrite. Stratiform mineralization is composed of pyrite, sphalerite, galena, stibnite, tetrahedrite-tennantite, several Ag-(As-Sb-Pb) sulfosalt minerals (guettardite, ferdowsiite, barikaite, stephanite, pyrargyrite, trechmannite, miargyrite, As-rich andorite, As-rich geocronite, Sb-rich seligmanite and smithite), realgar, and electrum.
Based on mineral assemblages and textures, four mineralization stages are recognized. During stage 1, pyrite, sphalerite, galena, tetrahedrite tennantite, and stibnite were deposited during synvolcanic hydrothermal activity. During stages 2 and 3, post-mineralization deformation and shearing contemporaneous with regional metamorphism modified most of the primary textures in the stratiform mineralization. Stage 2 mineralization represents Stage 1 mineralization that was remobilized during regional metamorphism, and this mineralization is characterized by gold as submicroscopic inclusions or as “invisible” gold locked in pyrite, as well as electrum in the barite mineralization. Regional metamorphism and deformation (D1) caused recrystallization of primary mineralization (mainly pyrite) and migration of submicroscopic gold via solution-precipitation creep to the grain boundaries to form microscopic electrum. Stage 3 mineralization is attendant with D2 movement along the Barika shear zone that controlled the overall geometry of the deposit and resulted in the development of ductile-brittle deformation textures and the formation of several Ag(As-Sb-Pb)-rich sulfosalt minerals and electrum. Most of the electrum grains occur together with sulfosalt minerals that fill open spaces formed during shearing. Stage 4 mineralization is marked by the formation of white, barren quartz veins and high-angle normal faults that were developed during D3 extension-related uplift.
Primary two-phase fluid inclusions in quartz of the stringer zone and barite from the stratiform mineralization homogenize between 132° and 283 °C (average ~ 200 °C). Salinities of the primary fluid inclusions range from 1.4 to 9.6 wt% NaCl eq. The sulfur isotope compositions of sulfide minerals from stratiform and stockwork mineralization in the Barika deposit range from δ34S −0.8 to +5.6‰. This relatively narrow range suggests that the sulfur in the sulfide mineralization was derived from the leaching of igneous sulfur from the underlying andesitic rocks, similar to most Japanese Kuroko VMS deposits. Temperatures of formation for Barika sulfides estimated based on sulfur isotope values for coexisting galena-sphalerite (Δ = 2–4.8‰) and galena-pyrite (Δ = −3.3 to −5.4‰) pairs range from 146 to 293 °C, and these are consistent with fluid inclusion homogenization temperatures. The primary mineralizing fluids have a calculated δ18O value of between +4.3and +6.3‰, based on the δ18O compositions of quartz from the stringer zone and assuming a temperature of 200 °C and that isotopic equilibrium was attained.
... Sulfate and oxygen isotope data in marine host rocks reflect parental seawater composition at time of deposition (e.g. Claypool et al., 1980 and references therein, Strauss, 1997Strauss, , 1999. ...
Vein mineralization observed in boreholes, quarries and outcrops of Upper Permian and Mesozoic sediments in the Thuringian Syncline, Germany, was investigated for the first time by petrography, electron microprobe analysis and stable isotope analysis. The objective was a characterization of paleo-fluid systems within this basin. Veins are mostly restricted to NW-SE trending fault systems and comprise carbonates (calcite, dolomite), minor sulfates (gypsum/anhydrite, celestite, barite), and rarely sulfides. They are variably distributed within the Late Paleozoic to Mesozoic succession. Calcite vein mineralization occurs in almost all Triassic strata, though dominating in the Lower Muschelkalk subgroup (mu). Gypsum/anhydrite veins occur in the Middle Keuper subgroup (km), Middle Muschelkalk subgroup (mm), Middle and Upper Buntsandstein subgroup (sm, so) as well as in the Upper Permian (Zechstein). Sulfate and carbonate isotope analyses indicate that most vein mineralization dominantly crystallized from intraformational fluids within the Upper Permian and Triassic sediments. Crystallization from descending meteoric waters was observed especially for calcite veins in the Lower Muschelkalk, but also for gypsum/anhydrite veins in the Upper Buntsandstein. Mineralization from ascending, carbonate-pH-buffered, warm waters was restricted to individual parts of the southern, deep reaching main border fault zone of the Thuringian Syncline. Mixing and fault crossing fluid movements are subordinate within the Thuringian Syncline. We conclude that no large scale cross-formational fluid flow occurred in Thuringian Syncline over the last millions of years.
... Biogenic sulphides are typically negative in open systems with high sulphate concentrations (e.g. Phanerozoic marine environments), where fractionations between parent sulphate and daughter sulphide, expressed as Δ 34 S SO4-H2S , is approximately 45 ± 20‰ (Sweeney and Kaplan, 1980;Strauss, 1999). As the marine sulphate reservoir is exhausted, it is possible for the δ 34 S values preserved in sedimentary pyrite to equal or exceed the δ 34 S value of coeval sulphate (Goodfellow and Jonasson, 1984;Goodfellow, 1987). ...
The Moss Ni-Mo-Zn-Pt-Pd-Re-Au hyper-enriched black shale (HEBS) showing is located in the western Richardson Mountains and is one of several in northern Yukon. The mineralization consists of a thin, stratiform semi-massive Fe-Ni-Mo-Zn sulphide horizon that occurs at the stratigraphic contact between the Road River Group and Canol Formation. This study evaluates the ambient paleoenvironmental conditions using several robust lithogeochemical proxies. Prior to HEBS formation, terrigenous clastic sedimentation predominated, whereas chemical sedimentation predominated during and immediately after HEBS formation. Rare earth element-Y data indicate that the water column was (weakly) oxygenated (Ce/Ce* SN < 1), that hydrothermal activity was absent (Eu/Eu* SN 1), and that there was a significant seawater influence on the sedimentary environment (Y/Ho > 28) throughout the deposition interval, even during HEBS mineralization. High (>10) authigenic Mo/U ratios suggest that a ferromanganese particulate shuttle delivered metals sourced from seawater to the seafloor. Negative bulk δ 34 S values (-19.3 to-23‰) in the HEBS indicate that microbially reduced seawater sulphate was the source of reduced sulphur for the mineralization. Collectively, these data signify a basinal environment that experienced varying degrees of restriction and stratification, but fresh (i.e. unfractionated) marine waters delivered metals, metalloids, and sulphur. This type of geological setting is considered critical for the formation and preservation of HEBS mineralization.
... Sulfur minerals in marine sediments accumulate on the order of years to thousands of years (Fig. 2). Thermodynamically stable minerals (e.g., pyrite) can ultimately be preserved in the rock record, where they are often used to reconstruct and interpret sulfur cycling in Earth's history (Strauss, 1999;Canfield, 2004;Hurtgen et al., 2005;Fike et al., 2006;Fike and Grotzinger, 2008;Fike and Grotzinger, 2010;Gill et al., 2011;Jones and Fike, 2013;Fike et al., 2015). Therefore, it is essential to understand the relative contributions to the bulk sediment Fe-sulfide (e.g., pyrite) record of both microbial and abiotic reactions and the time scales that each may represent. ...
Shallow-sea hydrothermal systems are ideal for studying the relative contributions to sedimentary sulfur archives from ambient sulfur-utilizing microbes and from fluxes of hydrothermally derived sulfur. Here we present data from a vent field in Palaeochori Bay, Milos, Greece using a suite of biogeochemical analytical tools that captured both spatial and temporal variability in biotic and abiotic sulfur cycling. Samples were collected along a transect from a seagrass meadow to an area of active venting. The abundance and isotopic composition of sulfide captured in situ, together with geochemistry from sedimentary porewaters and the overlying water column and solid phase sulfide minerals, record evidence of ephemeral activity of microbial sulfate reduction as well as sulfide oxidation. The sulfur and oxygen isotope composition of porewater sulfates indicate active sulfate reduction within the transition zone between the vents and seagrass, rapid recycling of biologically produced sulfide within non-vent sediments, and reoxidation of abiotic sulfide within the vent field. A phylogenetic survey of sediments also indicates the pervasive presence of a suite of putative sulfur-metabolizing bacteria, including sulfate reducers and sulfide oxidizers, many of which can utilize intermediate valence sulfur compounds. The isotopic composition of pyrite in these sediments consistently records a microbially influenced signature (δ³⁴Spy of −4.4 to −10.8‰) relative to the hydrothermal endmember (δ³⁴S ~ + 2.5‰), independent of distance from the vent source. The narrow range of pyrite δ³⁴S across sediments with a highly variable hydrothermal influence suggests that physical mixing (e.g., by storm events) homogenizes the distribution of biogenic and hydrothermal Fe-sulfides throughout the region, overprinting the spatially and temporally variable interplay between biological and hydrothermal sulfur cycling in these environments.
... The sulfur isotopic composition of the gypsum units in the Yunlong Formation in northern Simao Basin has yielded δ 34 S values ranging from 13.4‰ to 15.2‰ (V-CDT) (Wang et al., 2014b). These values are in agreement with those of the Cretaceous marine evaporites in the Khorat Basin (Strauss, 1999;Zhang et al., 2014), also suggesting a marine origin. This marine origin may be associated with the Neo-Tethyan Ocean, according to the Metcalfe's paleogeographic reconstruction (Metcalfe, 2013). ...
Potash deposits are common in the Mesozoic-Cenozoic Tethyan domain, which features the giant potash deposits in the Late Jurassic Central Asian Basin and the Late Cretaceous Khorat Basin of Thailand-Laos. Widespread evaporitic sequences from these intervals have been found in some marine and transitional basins within the Chinese continental blocks, such as the Yangtze, Simao and Tarim blocks, in which, only one small-scale potash deposit had been found in the Late Cretaceous Simao Basin. These evaporites are commonly characterized by depositional cycles that are more frequent than those of other potash basins around the world. It remains debated whether large or giant potash deposits could be formed in Chinese blocks of Tethyan domain, and if so, what mechanism was responsible for the potash formation. To address these issues, we comprehensively review the Meso-Cenozoic drift history and collision dynamics of these Chinese blocks and summarize the formation mechanism, depositional characteristics, and paleoclimate of the evaporite basins in these blocks. These blocks drifted from the Southern Hemisphere and collided and welded together in the beginning of the late Permian in the Northern Hemisphere. The collisions often commenced in the east and gradually spread to the west of these blocks, resulting in: (1) westward seawater retreat; (2) differential topographic uplift with high topography in the east and low topography in the west and (3) increasingly closed depositional environments in these basins. In addition, these collisions often exerted nearly N-S-oriented principal compressive stress, which resulted in nearly E-W-oriented extension. These forces induced a series of faulted-bounded subsidence belts with N-S-striking extensional sub-basins arranged in an E-W-oriented chain in these blocks. In this chain-like sub-basins system, as sea level rose and seawater flowed from west to east, the western sub-basins proximal to the open sea would have precipitated calcium carbonates and calcium sulfates, resulting in a high degree of concentration by the time the brines reached the distal end, i.e. eastern sub-basins. Ultimately, potash minerals were commonly deposited in the easternmost sub-basins. Based on the above model of potash formation, we predict that potash deposits may be formed in certain sub-basins in the eastern part of these basins in Chinese Tethyan blocks, which maybe lay a theoretical foundation for China's future exploration of potash deposits.
Rationale
Sulfur isotopes have been widely used to solve some key scientific questions, especially in the last two decades with advanced instruments and analytical schemes. Different sulfur speciation and multiple isotopes analyzed in laboratories worldwide and in situ microanalysis have also been reported in many articles. However, methods of sampling to measurements are multifarious, and occasionally some inaccuracies are present in published papers. Vague methods may mislead newcomers to the field, puzzle readers, or lead to incorrect data‐based correlations.
Methods
We have reviewed multiple methods on sulfur isotopic analyses from the perspectives of sampling, laboratory work, and instrumental analysis in order to help reduce operational inhomogeneity and ensure the fidelity of sulfur isotopic data. We do not deem our proposed solutions as the ultimate standard methods but as a lead‐in to the overall introduction and summary of the current methods used.
Results
It has been shown that external contamination and transformation of different sulfur species should be avoided during the sampling, pretreatment, storage, and chemical treatment processes. Conversion rates and sulfur isotopic fractionations during sulfur extraction, purification, and conversion processes must be verified by researchers using standard or known samples. The unification of absence of isotopic fractionation is needed during all steps, and long‐term monitoring of standard samples is recommended.
Conclusion
This review compiles more details on different methods in sampling, laboratory operation, and measurement of sulfur isotopes, which is beneficial for researchers' better practice in laboratories. Microanalyses and molecular studies are the frontier techniques that compare the bulk sample with the elemental analysis/continuous flow–gas source stable isotope ratio mass spectrometry method, but the latter is widely used. The development of sulfur isotopic measurements will lead to the innovation in scientific issues with sulfur proxies.
Organic‐rich shale in saline lacustrine basins holds significant importance as a source rock for conventional hydrocarbon exploration and has emerged as a prominent target for unconventional hydrocarbon exploration and development in recent years. Based on saline lacustrine basins, this paper provides a summary of the organic matter enrichment mechanisms in saline lacustrine basins, considering sedimentary characteristics, biological activities, factors for the organic matter enrichment and consumption, and hydrocarbon generation. The implications for these factors are discussed in relation to the distribution prediction of high‐quality lacustrine shale district settings and the exploration and development of shale oil. Saline lacustrine basins undergo distinct evolutionary stages, each corresponding to different sedimentary stages involving carbonate minerals, sulphate minerals, and alkaline minerals. Moreover, these basins exhibit diverse biological types and experience extensive biological activities. The prosperity of organisms and the accumulation of sedimentary organic matter are ensured by halophilic organisms. Organic matter enrichment in saline lacustrine basins is influenced by two main aspects: the primary productivity of organic matter, which is promoted by the proliferation of halophilic organisms, and the efficient preservation of organic matter facilitated by the strong reducing environment resulting from promoted water salinity stratification. The organic matter consumption in saline lacustrine basins involves bacterial sulphate reduction (BSR) in the early stages, thermochemical sulphate reduction (TSR) in the late stages, and dilution of salt minerals with higher depositional rates. of the presence of salt beds and saline minerals positively influences hydrocarbon generation and expulsion in organic‐rich shale within saline lacustrine deposition. Consequently, continental saline lacustrine basins in China offer favourable conditions for the formation of organic‐rich shale and present broad prospects for the exploration of shale oil and gas resources.
The newly discovered stratiform Mn-carbonate ore from the Zhuwuluke deposit occurs within the fine-grained clastic rocks-carbonate of the Lower Carboniferous Talong Group. Here we utilize petrographical, mineralogical and geological data to shed light on the ore-forming materials sources and metallogenic mechanism of the manganese carbonate mineralization. The ore minerals are composed mainly of Fe-rhodochrosite, rhodochrosite, Ca-rhodochrosite, and kutnahorite. The positive Eu anomalies (average 3.03) of Mn-carbonate ores and Mn-bearing limestones reveal a hydrothermal source. The MoEF (from 2.09 to 196.18) and UEF (from 0.74 to 3.60) values of most Mn-bearing limestone and wall rock sample suggest that they were deposited in reducing conditions where sulfide was restricted to the pore waters. The higher UEF values of Mn-carbonate ores (mean 24.19) and incomplete separation of Fe from Mn suggest that they were deposited under rapid oxidation conditions. The negative S isotope compositions of pyrite (δ³⁴Spy) and Mn-bearing carbonates (average –10.16‰ and –7.17‰, respectively) indicate the microbially mediated diagenetic sulfate reduction (BSR) and a relatively sufficient supply of sulfate in hemipelagic conditions. The C isotope compositions of Mn-bearing carbonates (δ¹³Ccarb, average –10.92‰) and its negative correlation with Mn content suggest that the initial Mn precipitated as Mn (oxyhydr)oxides, followed by reduction during burial diagenesis. Apart from that, paragenetic relationships indicate some Mn-carbonates were formed during authigenesis. We suggest that the high contents of Fe in Mn-carbonates were due to rapid oxidation conditions and relatively enough sulfate supply. The redox conditions and relatively stable sedimentary environment during the Early Carboniferous collectively facilitate the formation of manganese carbonate deposit.
The sulfur isotopic composition of marine sediments and sedimentary rocks reveals a wealth of information about sulfur cycling on different spatial and temporal scales. Sulfate minerals such as gypsum/anhydrite, barite or carbonate‐associated sulfate provide a temporal record of seawater evolution that reflects secular changes in the global sulfur cycle. Dissolved porewater sulfate and sulfide, but more so sedimentary iron sulfides and/or organic sulfur reveal details about the diagenetic evolution of marine sediments. Mass‐independent sulfur isotope anomalies have proven to be a prime recorder for the atmospheric oxygen abundance in the first half of Earth's history.
Extraterrestrial materials consist of samples from the moon, Mars, Vesta and a variety of smaller bodies such as asteroidsAsteroids and comets. These planetary samples have been used to deduce the evolution of our solar system. A major difference between extraterrestrial and terrestrial materials is the existence of primordial isotopic heterogeneities in the early solar systemSolar system. These heterogeneities are not observed on Earth, because they have become obliterated during high-temperature processes over geologic time. Nevertheless, isotopes have been used as a genetic link between meteorites and the Earth (i.e. Clayton in Treatise on geochemistry, Elsevier, Amsterdam, 2004).
The Laoshankou deposit is an iron oxide-copper-gold (IOCG)-like deposit in the northern margin of East Junggar, Central Asian Orogenic Belt (CAOB), in which pyrite is ubiquitous and present from stage II magnetite mineralization (Py1a and Py1b), stage III-A pyrite mineralization (Py2a and Py2b), to s tage III-B chalcopyrite mineralization (Py3a and Py3b). Despite of many previous studies, the source(s) of ore-forming fluids in the Laoshankou deposit are still controversial. Whether non-magmatic fluids were involved in the IOCG systems has also been highly debated in recent years. To further characterize the nature of ore-forming fluids in Paleozoic IOCG deposits in basin inversion settings, we conducted in-situ secondary ion mass spectrometry (SIMS) sulfur isotope and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) trace element analysis in a set of pyrite/chalcopyrite-bearing samples in the Laoshankou deposit. Sulfur isotope results of the sulfides in all stages (−3.5 to 2.6‰) fit in the magmatic sulfur range, indicating the contribution of magmatic sulfur. However, the weakly negative δ³⁴S values of −3.5‰ to −1.5‰ (Py3), possibly indicating the addition of organic sulfur, which can also be proved by organic-rich fluid inclusions and strata. The low Se/S (<5×10⁻⁵), the volcanogenic-like Co/Ni ratios (3.9−28, average 16), and the varying Ni contents (81−978 ppm, average 315 ppm) of Py1 indicate that its magmatic sulfur was leached from mafic volcanic rocks by heated seawater in a reducing condition at stage II. The elevated Ni (433−3736 ppm, average 1401 ppm) and Se (39−143 ppm, average 80 ppm) contents, and the Se/S (∼1.5×10⁻⁴) ratios of Py2 indicate a more oxidizing condition. We suggest that the magmatic sulfur of Py2 in stage III-A was also leached from mafic rocks by seawater, but magmatic hydrothermal fluid input cannot be excluded. The high Co/Ni (7.7−415, average 142) and low Ni/Se (0.43−3.4, average 1.7) ratios, and the low Ni contents (31−381 ppm, average 133 ppm) of Py3 show that such organic sulfur was likely leached from organic-rich sequence by relatively low-temperature and reduced fluid, with significant contribution from the felsic rocks in stage III-B. Combined with previous halogen and C-H-O isotopes results, external non-magmatic fluids can be proved in the Laoshankou deposit. Stage III-B chalcopyrite grains replaced early-stage pyrites, during which some alleged less-mobile elements (e.g., Co, and As) in the replaced pyrites were released into the Cu ore-forming fluids and formed extremely low-Co, porous/fractured, and inclusion-rich Py1b and Py2b, together with high Co-As contents in the Py3 and the Py3-chalcopyrite boundary. We propose that external seawater and organic bittern brine may have an effect on the mineralization at Laoshankou. Combined with previous researches in the Andean and East Tianshan, external fluids may play a key role for the IOCG deposits in arc-related basin inversion setting.
The Besshi Cu-rich volcanogenic massive sulfide (VMS) deposit occurring in the type area of Besshi, central Shikoku, Southwest Japan comprise tabular orebodies closely associated with mafic schist in the Cretaceous Sambagawa high P/T metamorphic belt. Pyrite, chalcopyrite, and sphalerite are the dominant sulfide minerals, together with minor amounts of pyrrhotite and bornite. The associated greenstone samples show geochemical features between N-MORB and E-MORB. The δ³⁴S values of sulfides from the greenstones and Cu ores are in the range of 2.10 to 7.11‰, indicating deposition from hydrothermal fluids with a heterogeneous metal source. Re-Os analysis of sulfides show initial (¹⁸⁷Os/¹⁸⁸Os)i ratio of 1.14± 0.86 and yield an isochron age of 147.9± 4.2 Ma, considered as the timing of sulfide deposition on the paleo-seafloor. The lithological association, geochemical features of the host greenstones and isotopic data from the sulfides indicate that the Besshi-type ores formed in a pelagic setting, and are possibly associated with hydrothermal activity related to mid ocean ridge volcanism and can be correlated to major oceanic anoxic event.
Evaporites and carbonates intercalated with volcanic beds are distributed in the Jialingjiang and Leikoupo Formations straddling the boundary of the Lower and Middle Triassic in the Sichuan Basin. High-resolution curves of 87Sr/86Sr ratios and δ34Ssulphate of marine sediments show the study section has relatively stable isotopic compositions of S and Sr except for the volcanic bed. The abrupt positive shift of 87Sr/86Sr ratios and negative shift of δ34Ssulphate occurred in the volcanic layer. The Sr isotopic curve defines a rough age range of 244 to 248 Ma. The volcanic bed is characterized by high anhydrite Th/U ratios, indicating a strong anoxic environment. The volcanic eruptions released a huge amount of CO2 and SO2, which could lower temperature first by sulphate aerosols and induce subsequent climate warming by greenhouse gases. This cooling-warming cycle has triggered the overturn of the deep anoxia seawater. The synergistic effects of degassing of gases (CO2and SO2) and overturn of the deep anoxia seawater have caused the negative shifts of δ34Ssulphate, and anoxic event during the volcanic eruption. Meanwhile, volcanic eruptions and associated acid rain could have enhanced the continental weathering, resulting in an increasing flux of radiogenic 87Sr. Furthermore, volcanic eruptions and related environmental changes could have imposed severe stress on the full recovery of the ecosystem since the End-Permian mass extinction, which is corroborated by fossil records.
Sulfur-bearing Fe-rich nanoparticles (SINPs) have been subject to increased levels of interest because of their catalytic properties and other features. However, with increasing interest in greener and sustainable practice, traditional engineered routes to SINP synthesis have become a concern owing to their high energy and resource demand as well as the use of potentially hazardous or environmentally harmful reagents. Here, we aim to bring attention to emerging and burgeoning research across a wide range of disciplines on the formation of both naturally occurring and synthetic SINPs. First, various SINP types are described, and their most important characteristics are outlined. Second, the natural mechanisms of SINP formation are evaluated and their environmental significance explained, predominantly in hydrothermal vents and lithogenic environments, in order to help inspire new approaches to engineered synthesis. Third, an appraisal of various synthetic approaches for SINP assembly is presented, with a focus on green synthesis methods. One exemplar is the use of nature-inspired biosynthesis, which has been increasingly explored for the fabrication of cost-effective and environmentally friendlier SINPs. Finally, potential future research directions leading to more sustainable SINP synthesis are put forward.
Les fragments de squelettes de vertébrés préservés sous forme de fossiles fournissent des informations paléo-environnementales uniques via leur composition isotopique et leur teneur en éléments traces. Toutefois la validité de ces informations dépend crucialement de la préservation de l’enregistrement géochimique biogénique au cours de la fossilisation. Ce travail a pour objectif de comprendre comment s’effectue l’acquisition de l’information géochimique puis sa préservation en étudiant les propriétés de fractionnement isotopique de l’apatite, constituant inorganique majeur des os et dents de vertébrés, et les mécanismes de transformations cristallochimiques impliqués par la fossilisation. Celles-ci sont sondées à l’échelle atomique à l’aide des spectroscopies ATR-FTIR et RMN du solide, leur interprétation s’appuyant sur la modélisation des spectres ATR-FTIR et le calcul ab initio (DFT) des propriétés de fractionnement isotopique à l’équilibre de l’apatite. Les transformations à l’échelle atomique observées suite à l’altération d’os actuel en solution aqueuse attestent d’un processus de dissolution partielle de l’apatite biogénique et de formation de fluor- ou hydroxy- apatite carbonatée secondaire à la surface des cristallites, selon la présence ou non de fluor en solution. Ces résultats ont ensuite été appliqués à l’étude de la transformation d’os fossiles issus des environnements karstiques de Bolt’s Farm dans le Berceau de l’Humanité (Afrique du Sud) et des environnements fluvio-lacustres volcano-sédimentaires des collines Tugen dans la vallée du Rift Grégory (Kenya). La formation de fluorapatite carbonatée est systématiquement observée, de l’hydroxyapatite carbonatée est également formée dans les fossiles de Bolt’s Farm moins fluorés, soulignant ainsi le potentiel des ossements fossiles à révéler les conditions précoces de fossilisation. Un degré maximal de transformation, aussi bien des os fossiles que des os actuels altérés, est observé à environ 60 % d’apatite secondaire, suggérant l’idée d’un rôle protecteur de cette phase contre la dissolution totale de l’apatite primaire.
Sediment samples from the Gulf of Alaska (GOA, IODP Expedition 341, Site U1417) have been analyzed to understand present and past diagenetic processes that overprint the primary sediment composition. No Sulfate-Methane Transition Zone (SMTZ) was observed at the zone of sulfate depletion, but a >200 m thick sulfate- and methane-free sediment interval occurred between the depth of sulfate depletion (~200 m) and the onset of methanogenesis (~440 m). We suggest that this apparent gap in biogeochemical processing of organic matter is caused by anaerobic oxidation of methane fueled by sulfate which is released during dissolution of barites at the upper boundary of the methane rich layer. Beneath the methanogenic zone, at ~650 m depth, pore-water sulfate concentrations increase again, indicating sulfate supply from greater depth feeding into a deep, inverse SMTZ. A likely explanation for the availability of sulfate in the deep sub-seafloor at U1417 is the existence of a deep aquifer related to plate bending fractures, which actively transports sulfate-rich water to, and potentially along, the interface between sediments and oceanic crust. Such inverse diagenetic zonations have been previously observed in marine sediments, but have not yet been linked to subduction-related plate bending. With the discovery of a deep inverse SMTZ in an intra-oceanic plate setting and the blocking of upward methane diffusion by sulfate released from authigenic barite dissolution, Site U1417 provides new insights into sub-seafloor pore-fluid and gas dynamics, and their implications for global element cycling and the deep biosphere.
The major ion balance of the ocean, particularly the concentrations of magnesium (Mg), calcium (Ca), and sulfate (SO 4 ), has evolved over the Phanerozoic (last 550 million years) in concert with changes in sea level and the partial pressure of carbon dioxide ( pCO 2 ). We review these changes, along with changes in Mg/Ca and strontium/calcium (Sr/Ca) of the ocean; how the changes were reconstructed; and the implication of the suggested changes for the overall charge balance of the ocean. We conclude that marine Mg, Ca, and SO 4 concentrations are responding to different aspects of coupled tectonic changes over the Phanerozoic and the resulting effect on sea level. We suggest a broad conceptual model for the Phanerozoic changes in Mg, Ca, and SO 4 concentrations along with the seawater ⁸⁷ Sr/ ⁸⁶ Sr and sulfur isotope composition. ▪ Marine concentrations of magnesium, sulfate, and calcium have varied over the last 550 million years in sync with changes in sea level and atmospheric carbon dioxide. ▪ Seawater chemistry and sea level both respond to supercontinent formation and breakup, age of the ocean floor, and extent of continental shelf area. ▪ Changes in plate tectonics impact the ocean's chemical balance and the carbon cycle in varied ways, resulting in cyclical changes in key climatic variables over geological time.
A combination of evidence from mineralogy, sulfur and oxygen stable isotope ratios from early diagenetic carbonate associated sulfate (CAS) and structurally substituted sulfate in phosphate (both termed CAS here), and carbon and oxygen stable isotope ratios from carbonate, describe a complex redox system and complex microbial ecosystem within the phosphate-rich interval of the Monterey Formation. δ ³⁴ S and δ ¹⁸ O of CAS are lower than Miocene seawater sulfate, as reconstructed from marine evaporite and barite minerals. Combined with mineralogical speciation modeling and mineralogical observations, isotopically low CAS isotope values suggest mixing from three isotopically characterized sulfate pools: two isotopically higher sulfate pools, one with the composition of Miocene seawater sulfate and a second isotopically evolved porewater modified by sulfate reducing microbes (SRM), and a third isotopically lower porewater sulfate pool resulting from the oxidation of H 2 S (produced by SRM) by sulfide oxidizing bacteria (SOB). High carbonate δ ¹³ C and diagenetic dolomite validates prior claims of methanogenesis. Differences in mineralogy are consistent with differences in isotope ratios (e.g. higher δ ¹³ C in dolomites), suggesting products from a vertical distribution of oxic to anoxic redox environments and associated ecosystems are preserved. These mineralogical and isotopic fluctuations repeat in various facies changes, suggesting that redox environments fluctuated over time. This interpretation is supported by prior sedimentologic analysis which interpreted that deposition of the phosphatic interval of the Monterey Formation was influenced by gravity-deposition processes promoted by tectonic activity. Gravity-deposition would serve to transport more oxygenated waters to the deep-water depositional environment and support microbially-mediated sulfide oxidation at depth, whereby H 2 S generated by SRM in the absence of sufficient iron could diffuse upward to a more oxygenated zone. Near the suboxic-oxic boundary, H 2 S oxidation would decrease porewater pH slightly and inhibit the preservation of carbonate minerals and promote precipitation of phosphate. Increasing depth in sediments generates successively more reducing conditions, promoting sulfate reduction, which may have been coupled with the anaerobic oxidation of methane and carbonate mineral precipitation. The most reducing conditions would support methanogenesis and dolomite production after consumption of the majority of sulfate.
This chapter describes the basic principles that govern the application of environmental isotopes in nitrogen and sulfur cycling studies in groundwater. The most relevant questions concerning evaluation of sources (fingerprinting) and processes that control nitrate and sulfate in the hydrosphere are addressed. The first part of this chapter will focus on nitrate studies and the second part will address sulfur cycling.
To improve understanding of the environmental influential and controlling factors of the Great Ordovician Biodiversification Event (GOBE), total organic carbon content (TOC), total sulfur content (TS), and sulfur isotope of pyrite (δ³⁴Spy) of black shale of the Jiangjunling section, in southern Anhui Province, China are analyzed. TOC and TS show positive correlation, indicating non-euxinic environment. δ³⁴Spy exhibits obvious decrease in Floian and more oscillation in the Middle Ordovician. Combined with global sulfur isotope of carbonate-associated sulfate (δ³⁴SCAS) and δ³⁴Spy data from previous researches, a marine oxygenation event is suggested by decreasing pyrite burial and increasing sulfur isotopic fractionation during the latest Tremadocian to middle Floian, which might boost GOBE. During the late Floian to Darriwilian, δ³⁴SCAS from different areas decreases in succession, while δ³⁴Spy is characterized by large oscillation, which is contributed to low sulfate concentration and sulfide reoxidation in the ocean.
The Devonian Period was characterized by major changes in both the terrestrial biosphere, e.g. the evolution of trees an seed plants and the appearance of multi–storied forests, and in the marine biosphere, e.g. an extended biotic crisis tha decimated tropical marine benthos, especially the stromatoporoid–tabulate coral reef community. Teleconnections between thes terrestrial and marine events are poorly understood, but a key may lie in the role of soils as a geochemical interface betwee the lithosphere and atmosphere/hydrosphere, and the role of land plants in mediating weathering processes at this interface.
The effectiveness of terrestrial floras in weathering was significantly enhanced as a consequence of increases in the siz and geographic extent of vascular land plants during the Devonian. In this regard, the most important palaeobotanical innovation were (1) arborescence (tree stature), which increased maximum depths of root penetration and rhizoturbation, and (2) the see habit, which freed land plants from reproductive dependence on moist lowland habitats and allowed colonization of drier uplan and primary successional areas. These developments resulted in a transient intensification of pedogenesis (soil formation and to large increases in the thickness and areal extent of soils. Enhanced chemical weathering may have led to increase riverine nutrient fluxes that promoted development of eutrophic conditions in epicontinental seaways, resulting in algal blooms widespread bottomwater anoxia, and high sedimentary organic carbon fluxes. Long–term effects included drawdown of atmospheri pCO2 and global cooling, leading to a brief Late Devonian glaciation, which set the stage for icehouse conditions during the Permo–Carboniferous.
This model provides a framework for understanding links between early land plant evolution and coeval marine anoxic and bioti events, but further testing of Devonian terrestrial–marine teleconnections is needed.
Within the epicratonic Selwyn Basin, at least three cycles can be recognized for Paleozoic time when the water column alternated from open and ventilated to closed and stratified conditions. These cycles are recorded by delta34S values in pyrite that exceed those for coeval seawater during periods of stagnation and decrease markedly during periods of greater circulation. The marked increase in delta34S values for pyrite formed in stratified seas is controlled by the high percentage of sulfate bacterially reduced to sulfide, coupled with the removal of isotopically lighter sulfur from a closed system during pyrite sedimentation. The delta34S curve for barite during this time has a shape similar to the mean evaporite curve except that it is displaced positively, particularly in Frasnian time. This pronounced increase in delta34S values for barite of Frasnian age coincides with the mixing of isotopically heavier sulfur, accumulated earlier in a stratified water column, with surface waters during a ventilation event.
Plots of the degree of pyritization vs C are used to distinguish syngenetic vs diagenetic and iron-limited vs carbon-limited conditions of pyrite formation in euxinic and semi-euxinic environments. Semi-euxinic is defined as a fluctuation situation in which low O2, non-sulphidic bottom waters (near-euxinic) alternate with strictly anoxic-sulphidic bottom waters during deposition of a sedimentary rock unit. Whether or not the deposition of organic matter was coupled with that of reactive Fe minerals was an important factor affecting the relation between pyrite sulphur and organic carbon. Examples of the two different types of euxinic-like C vs S plots for modern sediments and ancient sedimentary rocks are presented.-M.S.
Evolutionary developments among vascular land plants may have been the ultimate cause for oceanic anoxic events, biotic crises, global climate change, and geochemical and sedimentologic anomalies of Late Devonian age. The influence of vascular land plants on weathering processes and global geochemical cycles is likely to have increased substantially during the Late Devonian owing to large increases in root biomass associated with development of: 1) arborescence (tree-sized stature), which increased root penetration depths, and 2) the seed habit, which allowed colonization of drier upland areas. It is hypothesized that rapidly increasing root mass led to transient intensification of the rate of soil formation and to permanent gains in the thickness and areal extent of deeply weathered soil profiles. -from Authors
The authors discuss the origin of the Lower Paleozoic black shale facies found in rock successions that formed on continental shelves, slopes, and beyond. The authors propose a geologic-oceanographic model that interprets the general reduction in aerial extent of the black shale facies as a logical sequence of the progressive ventilation of the open ocean with dissolved oxygen.
Geologic records of isotopic changes in ocean composition present the possibility of unraveling the history of secular changes in the geochemical cycles of carbon, sulfur, and strontium. In general, the conventional interpretation of the C and S isotopic age curves, as reflecting changes in burial fluxes, is favored; however, short-term fluctuations may have been caused by these other effects. For Sr there is no clear, conventional interpretation of secular variability in oceanic isotopic composition against which to weigh the alternatives. -from Author
The biogeochemistry of sulfur and the mechanisms of sulfide/sulfate mineralization in Archean oceans have been thought by most geoscientists to have been much different from those in younger oceans. Archean oceans contained very little or no SO4²⁻, and sulfatereducing bacteria (SRB) were not active in the oceans. Fe-sulfides in the marine sediments formed directly from magmatic H2S, rather than by bacterial reduction of seawater sulfate. Bedded sulfate minerals in the marine sediments were formed by local oxidation of magmatic H2S by sulfide-oxidizing bacteria, rather than by evaporation of sulfate-rich seawater, and the massive Cu — Fe — Zn sulfide deposits associated with submarine volcanic rocks (volcanogenic massive sulfide deposits, VMSDs) were formed by magmatic H2S, rather than H2S-bearing fluids that developed from sulfate-bearing seawater through reactions with high temperature country rocks in the hydrothermal plumbing systems.
Describes and discusses the sulphur and oxygen isotopic composition of dissolved marine sulphates and then those of internal seas, using the Black Sea and Red Sea as examples. Models of the isotopic steady state of oceanic sulphate are reviewed in terms of, first, sulphur, and then oxygen isotopic composition. Finally, the isotopic composition of dissolved oceanic phosphate is discussed. -A.W.Hall
A paragenetic sequence of framboidal and euhedral pyrites is developed from a study of models defining different pathways of reaction, depending on the form of Fe and the reaction, kinetics as determined by rate of sulphate reduction (sulphide generation) and/or Fe availability. The study is based on analysis of pyrite textures, isotopic compositions and reactive iron content of the host sediment of pyritiferous carbonate concretions from a Jurassic outcrop on the NE coast of Yorkshire, England.-M.S.
The reduction of sulfate by sulfate reducing bacteria in the anoxic zone is an extremely important process during early diagenesis of marine sediments. Our data from Great Bay, NH reinforce the proposal that the rate of sulfate reduction is directly proportional to the reactivity of the organic matter or the amount of readily metabolizable organic matter present in the sediment and, hence, the source of the organic material in the anoxic zone. It appears that organic matter rich in marine organic remains is more easily degraded in the anoxic zone and that sulfate reduction rates can vary considerably in an estuarine system where many types of organic material may be deposited.
Until now, our knowledge of the sulfur isotopic composition of seawater through geologic time has depended on stable isotopic analysis of sulfate from evaporites. Owing to the sporadic occurrence of evaporites through time, the secular sulfur isotope age curve contains many gaps with little or no data. In order to fill in some of these gaps, particularly the Neogene, we have analyzed the sulfur isotopic composition of carbonate-associated sulfate in carbonate tests of planktonic foraminifera. Other investigators have shown that sulfate may occur in biogenic calcites either lattice-bound, as micro-fluid inclusions, in adsorbed phases, or as protein polysaccharides. Whatever the origin, the sulfur isotopic composition of this sulfate appears to be representative of that of the water in which the organism lived, as shown by results on recent calcareous foraminifera and macrofossils. Using this approach for study of Miocene to Recent pelagic marine sediments supplemented by new data for Miocene marine evaporites from the Gulf of Suez, we have found that theδ34S of seawater has decreased about 2.5‰ over the past 25 m.y. and that most of the decrease has occurred over the past 5 m.y., parallelling a decrease in theδ13C of dissolved oceanic bicarbonate from the same interval.Sedimentary redox models based on isotope records suggest that organic carbon and sulfide burial have both decreased over the past 5 m.y. Alternatively, an increase in weathering rates over the past 5 m.y. would not require a decrease in organic carbon or sulfide burial as long as the isotopic effect of the increased river input exceeds the isotopic effect of the burial of the reduced species. In either case, the net result would be a decrease in atmosphericpO2.
In fine-grained sediments in which the amount of reduced sulfur retained in stable phases substantially exceeds that present initially in pore waters, rates of sulfate reduction may have equaled or exceeded rates of sulfate transport, resulting in enrichment of [sup 34]S in pore waters and reduction products. Abundance and isotopic compositions of reduced sulfur compounds can be used to calculate the extent of sulfide retention and improve reconstructions of carbon-sulfur oxidation-reduction (redox) budgets. The Miocene Monterey Formation and Upper Devonian New Albany Shale represent distinct types of black shales that accumulated under different conditions of sulfate reduction. Our results suggest that the rate of sulfate reduction was controlled largely by mass transport in the Monterey and by the reduction process itself in the New Albany. Sulfide was more efficiently retained in the Monterey; thus each mole of sulfide in the New Albany represents a greater amount of sedimented organic carbon removed during sulfate reduction. 30 refs., 4 figs., 1 tab.
Statistical evaluation of 3056 δ13C measurements in carbonate rocks and fossils shows that they record a 2‰ 13C depletion from the late Proterozoic to the early Paleozoic, a 2.5‰ enrichment to the Permian, and a 1.5‰ depletion to the Cenozoic. These variations, not controlled primarily by facies or alteration phenomena, correlate negatively with the δ34S sulfate secular trend, as confirmed by collation of 1083 δ34S measurements. The correlation suggests that the biologically mediated redox fluxes of the C and S cycles have been approximately balanced through this long span of geological time, generally levelling available oxygen. Such a redox system is consistent with the controlling mechanism proposed by Garrels and Perry (1974). Consequently, the sedimentary reservoirs of Corganic as well as Sbacteriological'have varied through geological time.
The isotopic composition of biogenic calcites (e.g. belemnites, brachiopods) can be utilised as a proxy for the isotopic composition of coeval seawater. This is well established for carbon, oxygen and strontium isotopes, but has only recently been applied to 534S studies of the Mesozoic. In biogenic calcites, portions of the CO32-group can be structurally replaced by SO]-, (Structurally Substituted Sulphate), accounting for up to several thousand ppm of sulphate (e.g. Kampschulte and Strauss, 1996). However, for any meaningful interpretation of ancient isotope records it is important to know the natural 5348 variability. This can best be assessed by studying modem marine biota and dissolved sulphate from seawater. A second important aspect relates to a possible diagenetic influence on the 534S values of ancient shells as well as means to determine such alteration. The aim of this study is threefold: first, we like to compare 534S values for modem biogenic carbonates with those from dissolved seawater sulphates; second, we compare the 534S from well preserved fossils from Phanerozoic strata with those from coeval evaporites and whole-rock carbonates and, finally, we would like to discuss temporal sulphur isotopic variations during the Palaeozoic, as derived from SSS.
δ34S data are reported for 100 samples of evaporite sulphates from Germany.Normal Zechstein (Permian) evaporites give δ34S = +11.5 ± 1 %. which is expected to be the value for the Permian marine sulphate.Late evaporites within the different evaporation cycles are depleted in 34S by about 2%.. This may be due to fractionation by diffusion between the layered solutions within the evaporation basin.Muschelkalk and Keuper (both Triassic) evaporites give +20.5 and +17.5%., Malm (Upper Jura) +17.5%., Oligocene (Tertiary) ≈ +12 ± 1%.. Regarding the influx of terrestrial sulphate into the evaporation basins we suggest the marine values to be: Muschelkalk ≈ +21%. Keuper ≈ +17.5%. (?). Malm between +18 and +19%. and Oligocene between +16 and + 17%. (??).
In modern sediments, the isotopic composition of sulfur in iron sulfides appears to be controlled by sedimentation rate and by degree of contact of the basin with open seawater. A relationship is derived between delta/sup 34/S and sedimentation rate, which is then applied to data from ancient rocks. Sulfur isotopes in the Kupferschiefer seem to be controlled by the degree of contact of the basin with the open ocean rather than by rate of sedimentation. In the Devonian-Mississippian shales of the Appalachian Basin, on the other hand, there is a clear-cut correspondence between sulfur isotopes and inferred relative rates of sedimentation. Using the equation from recent sediments gives reasonable values for the relative rates of deposition of the various sedimentary units, but the absolute values seem too high by a factor of about five. There are several possible explanations for this discrepancy, but choosing among them requires further data from recent sediments. The relative curve, however, can still be used, if similar samples are compared.
Microbiological transformations of sulfur compounds discriminate to various degrees between the stable sulfur isotopes 32S and 34S. Comparatively little is known on isotopic effects associated with sulfur‐oxidizing organisms, and the interpretation of results is complicated since the sulfur pathways are poorly defined and compounds containing two or more sulfur atoms at different oxidation states may be involved. Dissimilatory reduction of sulfate, and sulfite reduction by certain assimilatory microorganisms, causes particularly marked isotopic effects, the expression of which depends on the extent of reaction and other incompletely defined environmental conditions. Models have been proposed to account for these effects based on current knowledge of the reduction pathways. Many of the trends observed during dissimilatory sulfate reduction in the laboratory can also be found in the modern environment leaving little doubt that microbiological factors play a significant role in determining sulfur isotope distributions in nature. However, unusually large isotopic effects, rarely approached in the laboratory, are often observed in nature. The reasons for this are not entirely clear, but in sediments it is possible that diffusional isotopic effects are imposed on biological effects.
The bacterial reduction of sulphate to sulphide at the sea bed is a key process in the oceanic sulphur cycle, and is responsible for the oxidation of organic matter which becomes buried below the oxic and sub-oxic zones of the sea bed. The oxic surface layer of the sea bed varies in thickness from a few millimetres in sheltered coastal areas to 1 m in pelagic sediments1,2. Below this layer, organic matter is mineralized mainly by fermenting, denitrifying, sulphate-reducing and methane-producing bacteria. Sulphate reduction is the predominant terminal step in the mineralization processes of sulphate-rich shelf sediments where the sulphate reducers inhibit the methanogens by competing with them for common substrates3–5. Sulphate reduction may therefore have a quantitatively important role in the overall oxidation of organic matter in the sea bed. Recently, concurrent measurements of oxygen uptake and sulphate reduction in a coastal sediment6 have demonstrated the importance of the sulphate-reducing bacteria in the mineralization of organic carbon. I present here the first comparative survey of aerobic and anaerobic mineralization in the sea bed based on direct rate measurements of the two processes. The results demonstrate a surprisingly high contribution from the sulphate-reducers. In coastal sediments, this specialized group of bacteria oxidized as much organic matter to CO2 as did all the aerobic organisms. Their relative contribution decreased three fold over the continental shelf from the shore to a depth of 200 m.
A brief review has been given of the process of bacterial sulfate reduction in respect to other processes in ocean sediments. In particular, rates of sulfate reduction have been discussed in the context of control mechanisms and geochemical consequences. It is concluded that besides temperature and pressure, which are cosmopolitan parameters influencing most biological processes, the rate of sulfate reduction is dependent on (1) total organic carbon preserved in sediment; (2) state of complexing of the organic matter and its availability for biogenic degradation. These two parameters are in turn influenced by (3) the environment of deposition and (4) the rate of sediment accumulation. Correlations are presented that show a direct relationship between rate of sulfate reduction and rate of sediment accumulation. The consequences of different rates of sulfate reduction on pyrite formation and isotope fractionation are discussed.
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SUMMARY A fractionation of sulphur isotopes was found in all hetabolic processes investigated except those in which elemental sulphur was the starting substrate for growth of Thiobacillus concretivorus and Chromatiurn sp. and for reduction by Saccharomyces cerevisiae. Except for polythionates formed during sulphide oxidation by T. concretivorus or Chromatiurn sp., the products of metabolism were enriched in s2S relative to the starting substrates. The magnitudes of the enrichment differed for different pro- cesses and for the same overall process carried out by different organisms. The 8% values (%,) ranged from -46.0 for sulphide from sulphate reduction by Desulfovibrio desulfuricans to + 19.0 for polythionate formed during growth on sulphide by T. comretivorus. Fractionation during sulphate reduction was inversely proportional to rate of reduction when lactate and ethanol were electron donors and directly proportional with molecular hydrogen as the electron donor. Temperature and sulphate concentration, within the normal physiological ranges of these parameters, influenced fractionation only in so far as they influenced rate of reduction. However, anomalous fractionation effects were obtained at low tempera- tures and when a resting suspension reducing sulphite was subjected to changes in temperature. The data are discussed with reference to the mechanism(s) of fractionation.
Three hundred new samples of marine evaporite sulfate, of world-wide distribution, were analyzed for δ34S, and 60 of these also for δ18O in the sulfate ion. Detailed δ34S age curves for Tertiary—Cretaceous, Permian—Pennsylvanian, Devonian, Cambrian and Proterozoic times document large variations in δ34S. A summary curve for δ18O also shows definite variations, some at different times than δ34S, and always smaller. The measured δ34S and δ18O correspond to variations in these isotopes in sulfate of the world ocean surface. The variations of δ18O are controlled by input and output fluxes of sulfur in the ocean, three of which are the same that control δ34S: deposition and erosion of sulfate, and deposition of sulfide. Erosion of sulfide differs in its effect on the S and O systems. δ18O in the sulfate does not seem to be measurably affected by equilibration with either seawater or with subsurface waters after crystallization. In principle, the simultaneous application of both δ34S and δ18O age curves should help reduce the number of assumptions in calculations of the cycles of sulfur and oxygen through geological time, and a new model involving symmetrical fluxes is introduced here to take advantage of the oxygen data. However, all previously published models as well as this one lead to anomalies, such as unreasonable calcium or oxygen depletions in the ocean—atmosphere system. In addition, most models are incapable of reproducing the sharp rises of the δ34S curve in the late Proterozoic, the Devonian and the Triassic which would be the result of unreasonably fast net sulfide deposition. This fast depletion could result from an ocean that has not always been mixed (as previously assumed in all model calculations).
The clearest records of changes in chemistry of the exogenic cycle are found in mineral inventories (NaCl, CaSO4, Ccarb, Corg, P), isotope ratios (δ34Ssft, δ13Ccarb, 87Sr/86Srcarb,87Sr/86Srapt), 87Sr/86Srapt), and trace elements (Ce/Laaptand heavy metals in black shales) vs. age. While these variations can be simplistically modelled in the long-term to confine all variations to the larger sedimentary reservoirs, there are several reasons to assert that some of the variability is internal to the smaller oceanic (and atmospheric) reservoirs, especially for short-term events. These are controlled by complex feedback loops, perhaps ultimately forced by plate-tectonic activity cycles. Many links are only speculative.
Catastrophic chemical events are characterised by sharp rises in
δ34S in the surface of the whole world ocean, and by
greater overshoots locally. Three events are recognised and named for
the formation in which they are most sharply displayed. The sharpness of
the rise in δ34S suggests that the sulphide deposition
necessary to explain it must have been accumulating residual
high-δ34S seawater for some tens of millions of years
out of contact with the surface ocean. A modified geological model is
presented: brine generated by evaporite deposition is stored in deeps of
a mediterranean basin; underneath the brine, pyrite precipitation builds
a store of brine heavy in
δ34Sso4, whose corresponding
buildup of δ38Oso4 may balance
the decrease of δ38Oso4 from
evaporite deposition. Catastrophic mixing of the brine and the surface
ocean, initiated by destruction of the storing basin, is the source of
the sharp rise in the sulphur isotope age curve detected world-wide in
evaporites. These events have important implications not only for
modelling of the chemical history of the ocean, atmosphere, and
sediments, but also for the explanation of faunal crises, and the many
aspects of geology that depend on the composition and circulation of the
oceans and their peripheral basins.
A model of the geochemical cycles of sulfur and carbon during Phanerozoic time makes it possible to compute the masses of the major sedimentary reservoirs, their fluxes in and out of the ocean, and their isotopic compositions both forward and backward in time. The development of this model is based on an earlier study of the coupled carbon and sulfur cycles that, although conceptually correct, did not produce results reversible in time (Garrels and Lerman, 1981). The test of the validity of the new model and of the concept of coupling between the two geochemical cycles comes from results that show a reasonable good agreement between the fluctuations in size of the sulfate reservoir as predicted from sulfur isotopes and the values calculated from carbon isotopes. Large uncertainties in the estimated masses of the present-day sedimentary reservoirs (oxidized and reduced sulfur and carbon) make the conclusions of the model qualitatively useful, but they do not allow at this time a more accurate probe of the geological record for the finer causes of variation in the contents and isotopic composition of the reservoirs, such as the variations that might have been caused by changes in the global rates of continental erosion, subduction and spreading of the ocean floor, and/or additions of materials from below the crust. An important conclusion of the model, despite these caveats, is that the exogenic geochemical cycles of the carbon and sulfur can be, to a reasonably good first approximation, treated as a closed system. The dominant redox system of the exogenic cycle is the complementary sulfide-sulfate-carbonate-organic carbon relation. 13 references.
The weight ratio of organic carbon to pyrite sulfur () has been observed to fall within a relatively narrow range (2.8 ± 0.8) in most fine-grained normal marine siliciclastic sediments. Although an increasing number of exceptions to this typical ratio have been observed, it is nonetheless remarkable that so many modern and ancient marine sediments fall within a range of about a factor of two in ratios. Here we demonstrate that this demands that the three major factors that control this ratio must be quite closely coupled to each other. These factors are (1) the fraction of organic carbon that is metabolized, (2) the fraction of metabolized organic carbon that is metabolized via sulfate reduction, and (3) the fraction of reduced sulfide that is not oxidized and is buried in pyrite. A simple model is presented that has utility in demonstrating the relationships among these parameters that are necessary to produce typical normal marine sediment ratios.
The sulfur isotopic composition of stratigraphically well constrained samples from five evaporitic cycles of the German Zechstein (upper Permian) displays no systematic lateral variation and no significant temporal trend. With an average ཞS value close to 11, results confirm the previously determined sulfur isotope minimum for Phanerozoic seawater. Least radiogenic 87Sr/86Sr ratios for these sulfates define a clear temporal variation with a minimum value at 0.707008. A conclusive assessment of this temporal trend in comparison with other data sets for upper Permian seawater is not possible due to substantial differences in (bio)stratigraphic assignments.
Sulfur isotope fractionation during reduction of thiosulfate was investigated with growing batch cultures of Desulfovibrio desulfuricans CSN (DSM 9104) at 30°C. The sulfide produced was depleted in 34S by 10% as compared to total thiosulfate sulfur. The depletion was equal to that during sulfate reduction under similar conditions. The two sulfur atoms of the thiosulfate molecule were affected differently by fractionation. Sulfide produced from sulfonate sulfur was depleted by 15.4‰ sulfide produced from sulfane sulfur by 5.0‰.
Seawater was evaporated, stepwise isothermally at 23.5°C, for 73 days, up to a degree of evaporation of 138 × by H2O weight. At various stages of evaporation the precipitate was totally removed from the brine and the latter was allowed to evaporate further. The sulfur isotopic compositions of the precipitates and related brines show the following characteristics: The initial δ24S of the original seawater is +20‰. The δ34S of both precipitates and associated brines decrease gradually in the gypsum field up to the end of the halite field, where δ34Sprecipitate = + 19.09‰andδ34Sbrine = + 18.40‰. The precipitates are always enriched in 34S relative to the associated brines in these fields, but the enrichment becomes smaller towards the end of the halite field. A crossover. where the δ34S of the brines becomes higher than those of the precipitates, occurs at the beginning of the Mg-sulfate field. The δ34Sprecipitate increases from + 19.09‰ at the end of the halite field through +19.35‰ in the Mg-sulfate field to + 19.85‰ in the K-Mg-sulfate field, whereas the δ34Sbrine increased from +18.40‰, through +20.91‰ to +20.94‰, respectively. This evolution implies different values of fractionation factors (α) for the minerals precipitated at the late halite, Mg-sulfate and K-Mg-sulfate fields, other than that for gypsum (1.00165). The value of αprecipitate-residual brine would then be very slightly >1 in the late halite field and <1 in the two later fields.
Three periods of stagnation, viz. Middle Ordovician to Early Silurian, Early Devonian, and Late Devonian, have been recognized in the Selwyn Basin by extremely positive δ34S-values in pyrite. These δ34S-values in pyrite reflect almost complete bacterial sulphate reduction of sulphate to sulphide within a restricted anoxic layer of a stratified water column. W.C. Shanks and coworkers have reported a fourth anoxic event in the basin during the Early Cambrian. Each period of basin stagnation coincides with times when sedimentary ZnPb-sulphide and barite deposits formed, while intervening periods correspond with the formation of stratiform barite deposits.The stratigraphic distribution of δ34S-values for pyrite are similar across the basin, whether near to or remote from mineralization, indicating a common seawater source of S. The generally parallel tracking of isotopic curves for sphalerite and galena with pyrite indicates that this sulphide also came from the bacterial reduction of sulphate within a stratified water column. This interpretation is supported by data on hydrothermal fluids that produced ZnPb mineralization, which are near-neutral pH and range in temperature between 100° and 350°C. In such solutions, it is thermodynamically difficult to transport appreciable sulphide in the presence of Pb and Zn. Since these conditions apply to mineralizing fluids of many sedimentary-exhalative ZnPb deposits, it follows that they too were likely S-poor, requiring an external seawater source of sulphide. This source is most effectively supplied by the sulphidic bottom layers of a stratified water column. This explains the correlation between anoxic events and ZnPb sedimentary deposits, both within the Selwyn Basin and world-wide during the Phanerozoic. The latter observation also implies that the anoxic events within the Selwyn Basin were not controlled locally, but instead reflect periods of worldwide ocean stagnation.
Isotopic analysis of H2S evolved during the growth of Desulfovibrio species and Desulfotomaculum species on a defined sulphate medium at their specific optimal growth temperature indicate no noticeable intrageneric or intergeneric differences in regard to isotopic fractionation. Changes in the composition of the growth medium were reflected in minor changes in the isotopic composition of the H2S evolved and in the rate of sulphate reduction. Intergeneric differences were noted in resting cell experiments and in the organisms' ability to reduce sulphite.
The isotopic composition of sulphur has been determined for a large number of specimens representing the important geochemical phases in which sulphur is present. The most significant process that causes sulphur isotopic fractionation is the reduction of dissolved sulphate by bacteria, although other processes such as distillation of volcanic emanations, oxidation-reduction of H2S, SO2 and S during volcanism and sulphide-sulphate equilibrium under magmatie or hydrothermal conditions can be locally important.The new data are combined with earlier work in an attempt to define the range and average ratio of the various sulphur-bearing phases of the crust. The most important averages are meteorites 22.21, ocean sulphate 21.76, mafic rocks 22.16, plutonic silicic rocks 22.13, hydrothermal sulphides 22.13 and sedimentary sulphide 22.49 and post-Cambrian evaporite sulphate 21.80. A material balance calculation of the sulphur isotopes in the crust, although subject to considerable uncertainties, points to an average crustal composition of sulphur heavier than that for meteorites.No age effect is found for at least the last 2 × 109 years. Finally, a geochemical theory is described to account for the apparent distribution of sulphur isotopes in the lithosphere.
Anhydrite, gypsum and other sulfates were sampled from a wide range of origins, differing in: geological age, mineralogy, stage of evaporation, inland basin or oceanic facies, and primary or replacement crystallization. For sulfates of oceanic origin, variation with geological age is so large that it nearly masks all other factors. Tertiary, Recent and synthetic gypsum have within ±2‰ of the +20‰ of modern sea water. A large number of Late Permian samples from Germany and the United States are all in the range irrespective of mineralogy or other geological factors. Mesozoic samples are intermediate between the Permian and Tertiary levels, and Early Paleozoic sulfates have up to . These results confirm the general curve found by other workers, in which the isotopic composition of oceanic sulfate varies with time, on a worldwide scale.These variations can only be accomplished by large-scale transfer of sulfur to or from the shale reservoir. Inflow of sulfate exceeded sedimentation in the Late Paleozoic, to increase the sulfate content of the sea by 45‰ with a corresponding enrichment in 32S. In the Mesozoic, sedimentation of sulfide exceeded inflow removing the light sulfur preferentially from the sea. Review of the geochemical balance and cycle of sulfur indicates that an excess inflow of sulfate was derived from shale sulfide by an increase of either weathering or metamorphism-volcanism, along with an even larger amount of sulfur from old evaporites.Alternatively, a decrease of sulfide sedimentation is directly related to biological activity, which in turn may have been controlled by one of several geomorphic changes. The isotope evidence thus indicates substantial changes in the sulfate concentration of sea water, but is symptomatic of even more important changes in the tectonic and paleogeographical regime in the Late Paleozoic and Early Mesozoic.
Our knowledge of the isotopic composition of sedimentary sulfur and its evolution through time is based on the studies of marine evaporitic sulfate deposits and sedimentary pyrite, the latter mostly formed as a result of bacterial sulfate reduction. Traditionally, their isotope records have been utilized to model and interpret the global sulfur cycle on Earth.The significance, potential and limitations of the presently available sulfur isotope data for the Phanerozoic and the Neoproterozoic with respect to modern concepts of high-resolution isotope stratigraphy are critically evaluated. In general, the sulfate and sulfide isotope records require further systematic research, particularly in order to improve the inadequate, irregular time spacing of results.The potential of sulfur isotopic investigations of sedimentary sulfides from time boundaries is rather limited. Frequently, local depositional and/or diagenetic effects appear to dominate over potentially present global signals.
Data have been obtained, from our own chemical analyses and from the literature, for the concentrations of organic carbon (C) and pyrite sulfur (S) in over 600 samples of Cambrian to recent normal marine shales. (Normal marine refers to deposition in oxygenated bottom water as evidenced by the presence of benthic fossils and/or indicators of bioturbation). All samples were selected to minimize 1.(1) loss of C and/or S due to weathering at the outcrop (by emphasizing the use of drill core material)2.(2) analytical errors and non-diagenetic effects (by avoiding sediments low in C or S content such as sandstones)3.(3) Fe limitation of pyrite formation (by avoiding limestones, cherts, and euxinic shales)4.(4) metamorphic loss of C, relative to S (by avoiding rocks obviously subjected to, even low-grade, metamorphism).Our results indicate that (1) there is generally a good positive linear correlation between organic C and pyrite S for normal marine shales of all ages and (2) the mean ratio for normal marine shales has varied over time. Devonian to Tertiary shales exhibit mean weight ratios (1.8 ± 0.5) somewhat lower than Quaternary sediments (). This we believe is due to preferential C loss (relative to S) during biogenic methanogenesis plus diagenetic heating. Distinctly lower mean C/S values for the Cambrian and Ordovician (0.5 ± 0.1) cannot be explained solely in terms of diagenetic C loss and, instead, must represent low original ratios. The low original ratios, we suggest, were due mainly to the absence of bacterially refractory organic matter added to the marine environment by rivers at that time, because the major source of such material, vascular land plants, had not yet evolved. This, along with a possibly lower degree of bioturbation, contributed to enhanced pyrite formation and preservation and, thus, lower early Paleozoic ratios.
The fractionation of sulphur isotopes in the reduction of sulphate and of sulphite by the bacteria Desulphovibrio desulphuricans has been studied over a wide range of lactate concentration, temperature, electron donor, pH and conditions of growth using resting cell suspensions and cell free extracts of the bacteria. Isotope effects from 5.1 to 23.7%. were found for sulphate reduction and 1.7 to 25.5%. for sulphite reduction, favouring the lighter sulphur isotope (32S). These results are discussed in terms of a reaction mechanism involving several consecutive steps, favouring a small or large isotope effect, competing for control of the rate. Also sulphur isotope distribution patterns reported for various types of marine environment and marine sediment are discussed in terms of these isotope effects.
Sulfur isotopic compositions of Precambrian sulfates, both new and previously measured, are summarized and critically evaluated in relation to a seawater sulfate sulfur isotope age curve.A fragmentary Archaean record with δ-values near 0%. suggests a mantle-dominated sulfur signature for seawater in the early history of the earth. Slightly higher δ34S-values between +10 and +18%. characterize Palaeoproterozoic seawater, with evidence coming mainly from trace sulfate data. More continuous records for the Meso- and Neoproterozoic indicate a fairly constant average isotopic composition close to +20%, followed by a pronounced increase in δ34S to values around +30%. at the Precambrian/Cambrian transition.A negative correlation between the δ34Ssulfate and δ13Ccarbonate curves is indicated at least for the Neoproterozoic. This would suggest the operation of an exogenic cycle comparable to that in the Phanerozoic for at least the past 1000 Ma.
Different generations of sedimentary pyrite from the Mid-Proterozoic Newland Formation, USA, have been analysed for their sulfur isotopic compositions. The results indicate bacterial sulfate reduction as the pyrite forming process. The δ34S values for early diagenetic pyrite, around −14%., are in contrast to dominantly more positive values for many other Middle Proterozoic units. A progressive reduction of sulfate availability during diagenesis can be recognized by an increase in 34S content (Rayleigh Distillation) as well as through detailed petrographic observations. Contemporaneous seawater had a sulfur isotopic ratio between +14 and +18%. as measured from sedimentary barite within the unit.
Sulphur isotope abundances of thirty-nine specimens of seventeen meteorites are reported. The results show again the remarkable constancy of the sulphur isotope ratios for meteorites of all types. However, differences in the S32/S34 ratios of 0.4%. would appear to be significant. The S32/S34 ratio for meteorites is discussed as a possible base level from which fractionation in the earth's crust began. The value is compared with estimates of average values found for terrestrial samples including some recent results of igneous intrusives.A large suite of sea water samples collected from widely separated points in three oceans at various depths have also been investigated and the S32/S34 ratios reported. The results show that the sulphate in the three oceans is exceedingly uniform in isotope ratio, with an enrichment of 20.1%. ± 0.3 in S34 over that of the meteoritic standard. Sulphur isotope ratios of sulphur in a sea shell, sulphides in shallow ocean sediments, sulphate in rain water and in present-day formation of gypsum evaporites from the sea, have been measured and are compared to the sea water level. The geochemical sulphate cycle is discussed in the light of these results.
The sulphur isotopic composition of ocean water sulphate was determined, using the SF6 method, for samples from various depths of the Geosecs Stations II and 3 and for a single Pacific Ocean surface sample. The total spread in values obtained is less than that found in previous studies and is consistent with the experimental precision except for one Geosecs II sample which has an unusually low δ34S value. The mean value, + 20.99%., is markedly different from the hitherto accepted value of +20.0%.. The difference is attributed to the greater accuracy obtained when SF6 rather than SO2 is used as the sample gas for sulphur isotope analysis.
THE sulphur cycle has evolved over the course of the Earth's history1,2. The early Earth's surface environment was reducing, containing little atmospheric oxygen3, and with seawater sulphate concentrations estimated at less than a few per cent of those found today. The accumulation of sulphate in the ocean to much higher concentrations was probably coincident with the initial accumulation of oxygen in the atmosphere and the consequent oxidative weathering of sulphide minerals on land4,5. Past changes in sulphate concentrations in ancient oceans have previously been assessed by comparing the systematics of sulphur isotope fractionation by sulphate-reducing bacteria6-9 with the isotopic composition of sedimentary sulphides1,2,5,10,11. But such interpretations have proven equivocal: the generally small 34S depletions in Archaean sulphides (deposited ~2.5-3.8 billion years ago) have been separately argued to result both from rapid sulphate reduction in a sulphate-rich ocean5,12, and from sulphide formation in a sulphate-poor ocean1,2,11. Here we report large 34S depletions of 20-25%, observed during rapid sulphate reduction by sulphate-reducing bacteria in modern photosynthetic cyano-bacterial mats from Solar Lake, Sinai. We conclude that high sulphate concentrations give rise to highly 34S-depleted sulphides, and thus that appreciable concentrations of seawater sulphate did not accumulate until the initial accumulation of oxygen into the atmosphere in post-Archaean times.