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The DL deposit is a typical tabular-shaped U deposit hosted in sandstones of the Upper Cretaceous Yaojia Formation in the southwestern Songliao Basin, northeast China. Owing to its recent discovery, the origin of the deposit remains unclear. In this study, mineralogical and geochemical data were used to constrain the genesis of the DL deposit. Two sources of U were recognized: (1) pre-ore U enrichment in the Yaojia Formation during diagenesis; and (2) the provenance of the Yaojia Formation, which comprises late Permian–Early Cretaceous granitic rocks from the southern Great Xing'an Range and northern margin of the North China Craton, rather than the oils and diabase dikes in the study area. Mineralogical and geochemical characteristics indicate that organic matter (OM) in the Yaojia Formation was derived mainly from plant debris and hydrocarbons. In situ S isotope data for pyrite from the ore-bearing sandstones show that most of the pyrite has similar δ34S values (−43.8‰ to −20.6‰) to those of pyrite associated with bacterial sulfate reduction (BSR). The pyrite is often typically replaced and/or overgrown by pitchblende, which has a high P2O5 content (0.07–1.64 wt.%), indicative of a genetic relationship between BSR and U mineralization. The geological, mineralogical, and geochemical features suggest that the U mineralization in the DL deposit was mainly associated with BSR. [ABSTRACT FROM AUTHOR]

The lacustrine organic-rich shale in the Permian Lucaogou (LCG) Formation of the Jimsar Sag, Junggar Basin, is one of the main shale oil plays in China. In this paper, geological and geochemical research techniques were employed to evaluate the geochemical variability of the lacustrine shale and the production of organic matter and its preservation conditions. The LCG Formation is characterized by its complex mineral compositions and a wide range of organic matter richness and quality. The presence of high proportions of β-carotane and C29 steranes, indicates that the organic matter mainly originated from phytoplankton and aquatic algal-bacterial organisms, especially cyanobacteria. This study found that the productivity of the Lower LCG Member (P2/1) was highest, and the Middle LCG Member (P2/2) was the lowest. During the deposition of the Lower LCG Member, the lake's bottom water was predominantly a reducing environment, and the degradation of organic matter was largely a result of bacterial sulfate reduction. During the deposition of the Middle and Upper LCG members, the lake's bottom water was mainly oxidizing, and the degradation of organic matter was likely to be caused by aerobic processes. Based on a comprehensive analysis of the origin and production of organic matter, as well as its depositional environment and preservation conditions, two organic matter accumulation models were proposed to explain the distribution of the organic-rich shale. In model A, the high influx of volcanic ash released nutrients and brought abundant sulfate into the water, the accumulation of organic matter was mainly controlled by the preservation of organic matter, which was mainly controlled by BSR. In the model B, the influx of volcanic ash was small, organic matter was mainly degraded by oxygen and the accumulation of organic matter is mainly determined by the production of organic matter. [ABSTRACT FROM AUTHOR]

Mine water containing copper and zinc exceeding the permissible discharge limit has been discharged from the S mine site in South Korea. To evaluate the feasibility of applying passive treatment methods for treating water discharged from this mine, bench-scale experiments were conducted by using columns simulating successive alkalinity-producing systems (SAPS) and bioreactors. As substrate materials, limestone and spent mushroom compost (SMC) were applied, with their structures and mixing ratios varied. The efficiency of metal removal for each column was then evaluated. SAPS (column B) and bioreactors (columns C and D) exhibited Cu removal efficiencies of 99.7%, 98.0%, and 97.1%, respectively, while the limestone reactor (column A) had an average removal efficiency of 81.3%. Except for the re-dissolution events, Zn removal efficiencies were 99.5%, 97.6%, and 88.4%, respectively, while the limestone reactor had an average removal efficiency of 29.2%. Facilitated by a pH increase caused by the dissolution of limestone, the bacterial sulfate reduction (BSR) reaction was shown to be effective at removing metal in the SAPS and bioreactor columns; the process was revealed through the presence of sulfide in the effluent. When comparing bioreactors with different compost mixing ratios, columns with greater SMC ratios had higher removal efficiencies, as well as higher alkalinity, which shows the importance of SMC in metal removal. Overall, this study will be helpful in determining on-site treatment methods for Cu- and Zn-rich mine water by reusing waste materials, SMC, through bacterial metal reduction reactions, as well as considering the potential lifespan of the treatment facility. [ABSTRACT FROM AUTHOR]

Organoclastic sulfate reduction and bacterial sulfide oxidation have been suggested to explain the formation of authigenic carbonate and native sulfur replacing gypsum in the Lorca Basin, Spain. To gain more insight into the nature of this replacement, two types of sulfur-bearing carbonate (laminated and brecciated) from the late Miocene Lorca Basin were studied. Petrographic observations revealed that a sulfur-bearing laminated carbonate consists of clay-rich and dolomite-rich laminae with carbonate and native sulfur pseudomorphs after gypsum. Positive δ18Ocarbonate values in the laminae (δ18O = 2.6‰) and lipid biomarkers of halophilic archaea (e.g., extended archaeol) suggest formation under hypersaline conditions. Bacterial sulfate reduction, evidenced by biomarkers such as iso-C15, iso-C16, and iso-C17 fatty acids, produced hydrogen sulfide inducing the abiotic formation of organic sulfur compounds. Gypsum in the laminated carbonate likely dissolved due to undersaturation as evidenced by a low content of carbonate-associated sulfate (3,668 ppm) and 34S-enriched native sulfur (δ34S = 22.4‰), reflecting sulfate limitation. Such 34S-enrichment implies limited fluid flow, which probably restricted the supply of molecular oxygen required for native sulfur formation through oxidation of hydrogen sulfide. Alternatively, sulfate-reducing bacteria may have mediated native sulfur formation directly as a stress response to environmental conditions. The formation of sulfur-bearing calcite in brecciated carbonates is due to post-depositional alteration. Negative δ18O values of the calcite (δ18O = −1.5‰) and a tenfold decrease in carbonate-associated sulfate content (752 ppm) suggest gypsum dissolution and subsequent calcite precipitation from meteoric water. Relatively 34S-depleted native sulfur (δ34S = 13.1‰) leaves it ambiguous whether meteoric water influx could have supplied sufficient molecular oxygen for oxidation of hydrogen sulfide. In case of the brecciated carbonate, methanogenesis, anaerobic oxidation of methane, and bacterial sulfate reduction apparently mediated the formation of secondary minerals as indicated by 13C-depleted lipid biomarkers representative for the respective metabolisms. This study reveals that the conditions and timing of gypsum replacement are variable–taking place 1) during or shortly after gypsum deposition or 2) significantly after sedimentation–and suggests that methanogens in addition to anaerobic methanotrophic archaea and sulfate-reducing bacteria may be involved in the mineral-forming processes in the sedimentary subsurface.

Sulfur isotope in sulfides from the Paleoarchean and the Neoarchean sedimentary rocks evidence microbial sulfur metabolism in Archean sulfur cycle. However, sulfur metabolism for the Mesoarchean interval is less obvious since evidence for a large range in sulfur isotope values has not yet been observed in Mesoarchean samples. We report the results of multiple sulfur isotope measurements for sulfide minerals from ~2.8 Ga sedimentary rocks in the southeastern part of the Karelian Craton. In situ isotope analysis of sulfide grains have been performed using a femtosecond laser-ablation fluorination method. Sulfide samples studied here yielded Δ33S values between −0.3 and +2.7‰ and δ34S values between −10 and +33‰. The Δ33S dataset was interpreted to indicate the incorporation of sulfur from two coexisting sulfur pools, photolytic sulfate and photolytically derived elemental sulfur. We suggest that the relative contributions of these Δ33S different pools to the pyritic sulfur could be controlled by the metabolic activity of coexisting sulfate-reducing and sulfur-disproportionating bacteria during pyrite formation. We therefore suggest the operation of different metabolic pathways of sulfur in Mesoarchean sedimentary environments. [ABSTRACT FROM AUTHOR]

Thermochemical sulfate reduction (TSR) commonly occurred in the dolostone reservoirs of the Upper Permian Changxing Formation (P3c) in the Yuanba (YB) gas field, Sichuan Basin, yet controversy remains regarding the source of sulfate required for TSR. To trace the source of the sulfate, sulfur and strontium isotopic compositions were measured for three diagenetic celestite (SrSO4) samples found in the P3c dolostone reservoirs in the YB gas field. In addition, the sulfur isotopic compositions of Carbonate-associated sulfates (CAS) from the P3c carbonates and spheroidal pyrites in dolomicrites from the P/T boundary (PTB) in the YB gas field were measured for comparative studies. The results show that the sulfur isotopic compositions of celestites are significantly heavier than those of the contemporaneous seawater, and these celestites have strontium isotopic values consistent with those of the host dolostones and contemporaneous seawater. The −33.68‰ fractionation in average δ34S values between pyrites and celestites indicated that their formation was likely to be related to bacterial sulfate reduction (BSR). During the P/T extinction event that accompanied the end-Permian regression, the reflux of brine directly precipitated 34S-rich celestites in the fractures and vugs of the dolostone reservoirs due to the BSR and the evaporation of seawater. These 34S-rich celesites and associated pore fluids provide a new explanation for the source of sulfate required for the late TSR. [ABSTRACT FROM AUTHOR]

Carbonate concretions accompanied by elemental sulfur were found in an early Messinian (Late Miocene) marine succession of NW Italy. The rocks were studied with an integrated approach including sedimentological, petrographical, stable isotope (carbon, oxygen, and multiple sulfur isotopes), and lipid biomarker analyses. Unlike other examples from Messinian strata of the Mediterranean area, the studied carbonate and sulfur concretions did not derive from the diagenetic replacement of sulfate minerals. Three lithofacies were distinguished: a) laminated lithofacies representing aphotic carbonate stromatolites enclosing fossils of filamentous sulfide-oxidizing bacteria; b) brecciated lithofacies deriving from the brecciation of carbonate stromatolites by mud injections; c) sulfur-bearing lithofacies deriving from the precipitation of thin laminae of elemental sulfur at or close to the sediment-water interface. The carbon and oxygen stable isotope composition of authigenic carbonate minerals and lipid biomarkers indicate that the initial formation of the laminated lithofacies was favored by organoclastic sulfate reduction in the shallow subsurface close to the sediment-water interface, producing sulfide that sustained dense microbial mats of sulfide-oxidizing bacteria at the seafloor. Calcification of the mats and consequent formation of stromatolites were possibly favored by nitrate-driven sulfide oxidation at the seafloor. The subsequent brecciation of the stromatolites was apparently the consequence of sulfate-driven anaerobic oxidation of methane (SD-AOM) in an underlying sulfate-methane transition zone (SMTZ). Focused fluid flow from below, possibly resulting from destabilization of gas hydrates, was not only responsible for the brecciation of the stromatolites, but also for the delivery of bicarbonate ions and the consequent precipitation of additional, 13C-depleted calcite (δ13C values as low as −52‰). Along with bicarbonate, also hydrogen sulfide was produced by SD-AOM at the SMTZ and was transported upwards. The oxidation of hydrogen sulfide at or close to the seafloor promoted the formation of elemental sulfur characterized by δ34S values and Δ33S values close to coeval seawater sulfate. • Authigenic carbonate and elemental sulfur in upper Miocene (Messinian) marine sediments record spatially and temporarily separated biogeochemical processes in the shallow subsurface and at the seafloor. • Organoclastic sulfate reduction induced the formation of microbial mats dominated by sulfide-oxidizing bacteria. • Nitrate-driven sulfide oxidation led to calcification of the microbial mats and to the formation of stromatolites. • Oxidation at the seafloor of hydrogen sulfide produced by sulfate-driven anaerobic oxidation of methane favored the formation of elemental sulfur. [ABSTRACT FROM AUTHOR]

Recent studies on the genesis of sedimentary native sulfur deposits indicate diagenetic mid‐low temperature Bacterial Sulfate Reduction (BSR) as the main process, involving organic compounds (kerogen/hydrocarbons), bacterial colonies and gypsiferous rocks. In the peri‐Mediterranean area (Southern Spain, Sicily, Northern Apennines, Israel), the main sulfur accumulations are always associated with late Miocene sulfates and organic‐rich successions encompassing the Messinian salinity crisis (MSC). In particular, the Messinian successions of the Apennine‐Adriatic foreland basin system, due to a large amount of high‐resolution stratigraphic data, represent a perfect case study for understanding the diagenetic conditions controlling the development of the BSR process during sedimentary basin evolution. In this work, thermal models performed in three sub‐basins in a sector of the Northern Apennines comprised of the Sillaro and Marecchia rivers (Italy), calibrated by means of organic and inorganic geothermometers, indicate a general thermal immaturity of the studied successions attained as a result of a constant heat flow similar to the present day one (ca. 40 mW/m2) since Late Tortonian and lithostatic loads between 615 and 1,710 m depending on different sub‐basins. These results suggest that the MSC deposits experienced maximum temperatures between about 39°C and 65°C. Temperatures derived from thermal models have been used to constraint occurrence of the diagenetic BSR associated with evaporitic deposits providing thermal constraints in sulfur genesis as well as new useful thermal‐constraints for basin analysis studies. [ABSTRACT FROM AUTHOR]

Bioremediation strategies that depend on bacterial sulfate reduction for heavy metals remediation harness the reactivity of these metals with biogenic aqueous sulfide. Quantitative knowledge of the degree to which specific toxic metals are partitioned into various sulfide, oxide, or other phases is important for predicting the long-term mobility of these metals under environmental conditions. Here we report the quantitative partitioning into sedimentary biogenic sulfides of a suite of metals and metalloids associated with acid mine drainage contamination of a natural estuarine wetland for over a century.

Introduction The Tabriz basin is an intra-mountain basin (Reichenbacher et al., 2011), which includes the Qom Red Bed Formation along with the Miocene Upper Red Formation. The lower unit of the Upper Red formation, M2mg unit, which hosts copper deposits includes an alternation of green grey sandstone and red marl with the interlayer of gypsiferous and saltiferous sediments (Sadati et al., 2013). Based on paleontological evidence, this unit is middle Miocene in age and is overlain by red sandstone, marl, shale (M3ms, M4sm) and locally up to red conglomerate (M5sc). In addition, this unit has considerable evaporitic layers, such as gypsum and salt. On the basis of field study all mineralization is distributed in the light-colored layers of the red sedimentary sequence, especially at the boundary between a red layer and a light-colored layer and is mostly restricted to within palaeo channels which consist of greenish-grey, well-sorted coarse- to very coarse-grained sandstones to microconglomerates. Both pyrite and copper-bearing minerals usually occur in the stratification of the organic matter- bearing host rocks which are mainly composed of gray sandstone. The size of organic matter varies from a few millimeters to 5-10 cm in length; almost all fragments are flattened and oriented conformably to bedding planes of host sedimentary rocks. Also, fine-grained sulfides are disseminated along the bedding planes in the sandstone. Copper precipitation in these places was possibly promoted by reduction from such organic materials. Sampling and analytical methods Investigations on mineralized samples showed that pyrite is the first sulfide mineral precipitated in the selected samples, followed by chalcopyrite, bornite, chalcocite, digenit, and covellite. The intergrown nature of sulphur-bearing minerals, along with their small grain size and their inter locking with detrital grains and calcite cement, make physical separation extremely difficult, although microdrilling techniques can achieve spatial resolutions for these samples. In the laboratory 25 to 100 µg (weight depends on the mineral analyzed) of the samples derived from microdrilling was combusted in a Eurovector 3000 elemental analyzer, yielding sulfur dioxide that was delivered to an Isoprime mass spectrometer using continuous-flow techniques, with helium as the carrier gas. Also, sulfide mineral powder was analyzed for the sulfur isotope compositions. Some samples were crushed to 40 to 60 meshes and the sulfide mineral separates were handpicked under a binocular microscope. The sulfur isotopes were analyzed at the Stable Isotope Laboratory, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing. The isotopic data are reported using the δ notation in units of per mil, relative to the Cañón Diablo troilite (CDT) standard. Organic carbon (TOC) was determined by treating powdered samples with 6 M HCl to remove the carbonate. The sample was then rinsed to remove the acid. The mass difference between the original sample and the acid-treated residue was used to determine the carbonate content. The dried sample was then combusted and the evolved CO2 was analyzed on the mass spectrometer. During the mass spectrometric analysis the sample peak height was calibrated against organic carbon standards to estimate the organic carbon content. Result and Discussion Framboidal pyrite is the most common typical byproduct of bacterial sulfate reduction (BSR), a process that occurs at temperatures from 0°C up to about 60–80°C (Donahue et al., 2008). The metabolic activity of the sulfate reducing bacteria generally depletes (or fractionates) the resulting sulfide in 34S, by up to 70% (Kalender, 2011). The availability of S content is consistent with controlling δ34Ssulfide in some portions of this study area, but not all. Total organic carbon (TOC) is above 4% for one mineralized sample of the Upper red Formation. Sulfide sulphur and organic carbon distribution shows that pyrite-rich sandstones are the copper ore precursor, and that mineralizing the processes provoked the depletion of both reduced S and organic C as a consequence of interaction with an oxidized Cu-bearing fluid. On the other hand, lowed 34S values are consistent with bacteriogenic derivation of sulphur. Conclusion Taking into account the sedimentary environment, the abundant presence of the former evaporit layers in the host rock, the presence of evaporit layers below and above the mineralized rocks, and the absence of a widespread magmatic sulfur source, it is concluded that the Cu-Co sulfides of the Nahand-Ivand deposits obtained their sulfur by either bacterial or thermochemical reduction of sedimentary sulfate. The examined samples preserved original sedimentary textures (i.e. immature organic matter and sedimentary bedding). These geological evidences point to the fact that a biological (thermochemical) sulfate reduction is unlikely. Therefore, the sulfate-reducing bacteria were responsible for pyrite formation in the examined sample. The S isotope composition of pyrite in this study is related to organic C abundance. Most of the samples show a correlation between S and C, but mineralized samples are relatively enriched in S and TOC content. References Donahue, M.A., Werne, J.P., Meile, C. and Lyons, T.W., 2008. .Modeling sulfur isotope fractionation and differential diffusion during sulfate reduction in sediments of the Cariaco Basin. Geochimica et Cosmochimica Acta, 72(9): 2287–2297. Kalender, L., 2011. Oxygen, carbon and sulphur isotope studies in the KebanPb–Zn deposits, eastern Turkey: An approach on the origin of hydrothermal fluids. Journal of African Earth Sciences, 59(4–5): 341–348. Reichenbacher, B., Alimohammadian, H., Sabouri, J., Haghfarshi, E., Faridi, M., Abbasi, S., Matzke-Karasz, R., Fellin, M., Carnevale, G., Schiller, W., Vasilyan, D. and Scharrer, S., 2011. Late Miocene stratigraphy, palaeoecology and palaeogeography of the Tabriz Basin (NW Iran, Eastern Paratethys). Palaeogeography, Palaeoclimatology, Palaeoecology, 311(1–2): 1–18. Sadati, N., Yazdi, M., Behzadi, M., Adabi, M.H. and Mokhtari, A.A, 2013. The role of organic matter in genesis of sedimentary-hosted stratiform copper deposits in Nahand-Ivand area, NW Iran. Goldschmidt Conference, Firenze Fiera Congress and Exhibition Centre, Florence, Italy.

We present the first study of a unique acidic lake formed in the Brunita open pit (La Unión mines, Cartagena, SE Spain). This pit lake exhibits chemical characteristics typical of AMD, such as low pH (pH 2.2–5.0) and high iron content (500–6400 mg/L total Fe). It also has some of the highest sulfate concentrations reported to date in pit lakes (26,000–38,400 mg/L SO 4 2 - ) and transition metals like Mn (up to 2000 mg/L), Zn (500 mg/L), or Cu (250 mg/L). In addition, we found abnormally high concentrations of salt-forming ions (e.g. 5500 mg/L Mg, 750–1300 mg/L Cl, and 300–630 mg/L Na). The resulting high salinity (58‰) at the bottom creates a meromictic lake despite the lake's low relative depth (9%), with an anoxic, reducing monimolimnion isolated from the oxygenated mixolimnion. In the monimolimnion, we observed decreased metal concentrations (e.g. Cu, Zn, Cd, Cr, Pb, Th). We hypothesize that these metals are being removed by interaction with biogenic H2S and subsequent precipitation as metal sulfides. Scanning electron microscopy shows sub-micron, spherical particles of ZnS in close association with cocci and rod-like bacteria. Analysis of the microbial community composition through 16S rRNA gene amplicon sequencing revealed different genera of sulfate-reducing bacteria (SRB) in the monimolimnion, including Desulfobacca, Desulfomonile, Desulfurispora, and Desulfosporosinus. Their apparent ability to reduce sulfate and selectively precipitate potentially toxic metals, and their resistance to this lake's extreme geochemical conditions, makes these bacteria of great interest for biotechnological applications (e.g. bioremediation and biomining). [ABSTRACT FROM AUTHOR]

Spent organic media from the vertical flow bioreactor process unit of a passive treatment system (PTS), which received acidic drainage from an abandoned coal mine for 15 years, was evaluated. The Jennings PTS (Butler County, Pennsylvania, USA) was built in 1997. The vertical flow bioreactor was one of the first constructed in the late 1990s and included a mixed spent mushroom compost (272 t) and limestone aggregate (345 t) media. The media was expected to effectively function for 14 years. After 15 years of operation, hydraulic conductivity problems resulted in its removal and replacement. Samples of the spent media were analyzed to determine total and leachable [by toxicity characteristic leaching procedure (TCLP) extraction] metal concentrations. Remaining organic matter was estimated by combustion as loss-on-ignition. Spent media total metals analyses yielded mean concentrations of 72 g/kg Fe, 37 g/kg Al, and 0.64 g/kg Mn. The TCLP results indicated that concentrations of As, Cd, Cr, and Pb were far below USA Resource Conservation and Recovery Act regulatory criteria. Total metal concentrations in the spent media were less than the mass load removals calculated, based on the water quality and quantity data. [ABSTRACT FROM AUTHOR]

[Display omitted] • In addition to OM and hydrocarbon, pyrite was also a reducing agent for U reduction. • Coffinite evolved from the early pitchblende, with changes in morphology and composition. • Adsorption-related U enrichment constitutes an important part of the deposit. • The digenetic U enrichment can provide lots of U sources for epigenetic U mineralization. Sandstone-type uranium deposits usually exhibit a range of metallogenic mechanisms. To gain insights into the nature, genetic relationships, and mineralization mechanisms of uranium and associated minerals, representative samples from the Qianjiadian uranium deposit in the Songliao Basin were investigated through detailed mineralogical, elemental geochemical, and in-situ sulfur isotopic analyses. The results provided invaluable information on the various stages of uranium mineralization. During the early diagenetic stage, uranium mineralization occurred in the local organic matter (OM)-enriched sites (TOC = 0.70 ∼ 2.05 %) in the Yaojia Formation. The paragenetic relationship revealed that uranium was firstly precipitated as pitchblende along with the biogenetic framboidal pyrite (δ34S values ranging from −44.1 ‰ to −1.8 ‰) through bacterial sulfate reduction (BSR) process. Simultaneously, organic acids generated through biodegradation of OM caused an acidic fluid condition and subsequent dissolution of feldspars, resulting in the production of kaolinite intergrowth with pitchblende. During the late diagenetic stage, the ore-forming fluid turned alkaline, leading to the conversion of pitchblende into coffinite, with elevated elements such as Si, P, Ca, Zr, and Y in the altered phase. In addition to the contribution of OM and sulfate-reducing bacteria (SRB), pyrite was confirmed as a reducing agent manifested by its replacement by uranium minerals and the Fe-oxide produced along the boundaries. The diagenetic uranium enrichment is mainly hosted in the gray sandstone that experienced reduced alteration of deep hydrocarbons, resulting in pervasive kaolinization and promotion of reduction potential. A significant amount of uranium was fixed by adsorption, as evidenced by the rare observation of independent uranium minerals, but the higher whole-rock U content (U = 133.5 ∼ 394.0 ppm) and the detection of U signal in micro-XRF analysis and EPMA data (U content in representative kaolinite ranges from bld to 0.74 wt%). Overall, the formation of sandstone-type uranium deposits is a long-term and multi-stage process. The early enriched uranium during synsedimentary-diagenetic stages is non-negligible and can even result in an appreciable amount of mineralization, further serving as an important source for the subsequent secondary enrichment. [ABSTRACT FROM AUTHOR]

Marine authigenic pyrite sulfur isotope (δ34S pyr) is one of the most important proxies for reconstructing remarkable changes of Earth's surface in deep time. Recent observations of unexpectedly large δ34S pyr variations in Quaternary sediments complicate the application of this isotopic proxy, and a mechanistic understanding of such variabilities is needed. In this study, we measured multiple sulfur isotopic compositions of pyrite in well dated sediments spanning the last 7500 years from the East China Sea (ECS) inner shelf to study the mechanism how Holocene climate controls pyrite sulfur isotopic compositions. We found that variabilities of pyrite multiple sulfur isotopes, δ34S pyr and Δ33S pyr (ranging from −38.3‰ to 2.3‰ and from −0.01‰ to 0.21‰, respectively) are significantly correlated with large fluctuations of sedimentation rates (0.03–2.09 cm/yr). In tandem with box model calculations and compiled data, the large δ34S pyr variations up to 40‰ are primarily ascribed to fluctuated anaerobic oxidation of methane coupled sulfate reduction (AOM-SR). Further analyses suggest that heightened distillation of interstitial sulfate, likely propelled by high methane flux coupled with increased sedimentation rates, can produce such negatively correlated δ34S pyr -Δ33S pyr pattern and large variations in δ34S pyr. Possible changes in isotope fractionation factors caused by varied cell-specific sulfate reduction rates result in a maximum δ34S pyr variation of <20‰ and therefore play a minor role in the large variation in δ34S pyr (>40‰). The major and minor isotopic compositions of pyrite align with sulfide produced through pure sulfate reduction, indicating little evidence of additional oxidative sulfur cycling. Sedimentation rates in the ECS are controlled by the East Asian winter monsoon that influences the sediment transport capacity from longshore currents on a multicentennial timescale, and also by the coupled East Asian summer monsoon that affects the sediment availability from the Yangtze River on a millennial timescale. Holocene climate changes alter sediment supplies at the ECS and therefore play a vital role in controlling multiple sulfur isotope compositions of sedimentary pyrite in this region. This study has the potential to provide new insights into δ34S excursions in seawater sulfate that occurred during periods of notable acceleration in sedimentation rates throughout the geological history. • ∼40‰ and 0.22‰ variations in δ34S and Δ33S of pyrite were observed in Holocene sediments. • AOM-SR account for the large sulfur isotope variations. • AOM-SR were dominated by sedimentation rate. • Climate changes regulate sulfur isotopes depending on sedimentation rate. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Understanding the oil emplacement influence on diagenesis is one of the most key factors of reservoir quality prediction. The Devonian Donghe sandstones are deeply buried to 5700～6000 m, and they are important exploration target in the Tarim Basin, additional the reservoirs experienced multi-phase hydrocarbon accumulation and destruction. The Donghe sandstones contain various diagenetic minerals, which are mainly composed of calcite cement, a small amount of quartz overgrowth and pyrite, trace ankerite and ferrocalctie. The current study investigates the influence of multiple-stage oil emplacement on the diagenesis with particular attention to calcite and quartz cementation of marine clastic reservoir interval of the Donghe sandstones in the Tarim Basin. The samples in the oil leg and water leg have been collected and a series of studies were performed, including thin section petrography, scanning electron microscopy (SEM), carbon and oxygen isotopes and cathodoluminescence (CL) analysis. The δ13C V-PDB values of calcite cement from the oil leg and water leg between −4.73 and −1.21‰ and −3.81 to −0.86‰, respectively. The δ18O V-PDB values of calcite cement from the oil leg and water leg range from −15.59 to −6.61‰ and −14.97 to −7.76‰, respectively. Both of them display no obviously different in the oil leg and water leg. All of the δ13C V-PDB values in the whole interval of the Donghe sandstones show lightly depletion was explained mixing from marine carbon and carbon produced from bacterial sulfate reduction (BSR) that happens during petroleum degradation associated with sulfate reduced by hydrocarbons bacterially. Two dull-luminescence zones, trace Fe and Mn content, and high Fe accompanied by low Mn content, and orange-red- and bright-orange-yellow-luminescence zones in oil leg indicate four generations of calcite occurred, whereas two generations of calcite occurs in water leg, which are dull- and orange-red-luminescence zones. Two origins of calcite cement were clearly identified: marine biogenic carbonates and hydrocarbon-related from palaeo-reservoir BSR during uplift. The first generation of calcite cement originated from biogenic carbonate, the second and third generations of calcite cement were mixing from predate carbonate cement dissolved and re-precipitated, and calcite precipitated by BSR directly. Some quartz grains and K-feldspars were dissolved by residual organic acids that remained in the irreducible water, and following replaced by the fourth generation of calcite cement. Some calcite cement in the oil leg precipitated in a temperature higher than the homogeneous temperature of fluid inclusion, which indicates oil emplacement has no influence on calcite cementation. The quartz overgrowth postdate the first hydrocarbon accumulation and predate the second hydrocarbon accumulation, which originated from quartz grains dissolved by organic acids that produced from BSR and re-precipitated at a low temperature (<80 °C). The pyrite cement formed as the by-product of BSR in the water leg implies the palaeo-reservoir existed. The current study can promote the understanding of the influence of multiple-stage hydrocarbon accumulation on diagenesis, and it can also inspire the diagenesis process of other Paleozoic hydrocarbon reservoirs in the Tarim Basin. • Very sufficient data set from the oil leg and water leg providing insight in the impact of oil emplacement on diagenesis. • The data set supports the model of oil emplacement inhibits quartz overgrowth but calcite cementation does not retarded. • Hydrocarbon biodegradation can cause a series of diagenesis alterations. • A model of diagenesis evolution pathways involved in multiple-stage oil emplacement is established. [ABSTRACT FROM AUTHOR]

The Silurian Pelplin Formation is a part of a thick, mud-prone distal fill of the Caledonian foredeep, which stretches along the western margin of the East European Craton. The Pelplin Formation consists of organic carbon-rich mudstones that have recently been the target of intensive investigations, as they represent a potential source of shale gas. The Pelplin mudstones host numerous calcite concretions containing authigenic pyrite and barite. Mineralogical and petrographic examination (XRD, optical microscopy, cathodoluminoscopy, SEM-EDS) and stable isotope analyses (d13Corg, d13C and d18O of carbonates, d34S and d18O of barite) were carried out in order to understand the diagenetic conditions that led to precipitation of this carbonate-sulfide-sulfate paragenesis and to see if the concretions can enhance the understanding of sedimentary settings in the Baltic and Lublin basins during the Silurian. Barite formed during early diagenesis before and during the concretionary growth due to a deceleration of sedimentation during increased primary productivity. The main stages of concretionary growth took place in yet uncompacted sediments shortly after their deposition in the sulfate reduction zone. This precompactional cementation led to preferential preservation of original sedimentary structures, faunal assemblages and early-diagenetic barite, which have been mostly lost in the surrounding mudstones during burial. These components allowed for the reconstruction of important paleoenvironmental conditions in the Baltic and Lublin basins, such as depth, proximity to the detrital orogenic source and marine primary productivity. Investigation of the concretions also enabled estimation of the magnitude of mechanical compaction of the mudstones and calculation of original sedimentation rates. Moreover, it showed that biogenic methane was produced at an early-diagenetic stage, whereas thermogenic hydrocarbons migrated through the Pelplin Formation during deep burial. [ABSTRACT FROM AUTHOR]

Abstract The bacterial (dissimilatory) iron and sulfate reduction (BIR and BSR) are intimately linked to the biogeochemical cycling of C, Fe, and S in acid mine drainage (AMD) environments. This study examined the response of native microbial communities to the reduction of iron and sulfate in bench experimental systems. Results showed that the reduction of ferric iron and sulfate took place when the electron acceptors coexist. Existence of Fe(III) can postpone the reduction of sulfate, but can enhance the reduction rate. Cultures grown in the presence of 10 mM iron can reach the final level of sulfate bio-reduction rate (~100%) after 35 days incubation. 16 S rDNA -based microbial community analysis revealed that the three genera Anaeromusa, Acinetobacter and Bacteroides were dominated in the ferric-reducing conditions. SRB (Desulfobulbus , Desulfosporosinus and Desulfovibrio) were dominated in the sulfate reduction process. Results in this study highlighted the highly coupled nature of C, Fe, and S biogeochemical cycles in AMD and provided insights into the potential of environmental remediation by native microbial. Highlights • The potential mutual effects in C, Fe, and S biogeochemical cycle were identified. • The Fe3+and SO 4 2- reduction could take place successively using native microbial. • Ferric iron reduction can enhance the sulfate bio-reduction ratio. [ABSTRACT FROM AUTHOR]

• The ore-forming fluids were sedimentary basinal brines. • The δ34S isotope values of sulfide minerals were compatible with the BSR processes. • The reduced sulfur originated from evaporite sulfates. • On the basis of Pb isotope analysis, metals originated from crustal sources. • The ore genesis was related to the Miocene–Pliocene Zagros Orogenic events. The Kuh-e-Surmeh Zn–Pb deposit is hosted by Upper Permian carbonate platform in the Zagros Fold Belt of southwestern Iran. The orebody is characterized by massive, vein, and banded textures. It is mostly composed of sphalerite, galena, and pyrite accompanied with minor barite. Homogenization temperatures of fluid inclusions in sphalerite and barite range from 94.7° to 200.0 °C and 93.6° to 198.0 °C, respectively. Fluid salinities of sphalerite- and barite-hosted inclusions vary from 8.1 to 21.3 wt% NaCl equiv. and 10.5 to 22.6 wt% NaCl equiv. , respectively. The δ34S values of barite range from 11.2 to 11.9‰, similar to those of gypsum of the Nar Member (+10.9 to +11.7‰) in the Upper Permian sedimentary strata and different from the δ34S values of Jahani Salt Dome gypsum (+29.1 to +30.5‰), indicating that sulfur was derived from the Upper Permian evaporites. The δ34S values of galena and sphalerite range from −1.7 to −15.4‰, compatible with bacterial sulfate reduction (BSR) of the Upper Permian evaporites. The Pb isotopic compositions of galena yield 206Pb/204Pb ratios from 17.942 to 18.340, 207Pb/204Pb ratios from 15.649 to 15.744, and 208Pb/204Pb ratios from 38.186 to 38.458, indicating an upper crustal lead source. Based on ore textures, fluid inclusions, isotope data, and geochemical compositions of sulfide minerals, the Kuh-e-Surmeh sulfide mineralization is believed to have precipitated from low-temperature sedimentary basin brines and should be classified as a Mississippi Valley-type deposit in a salt diapir environment. Mineralization is the result of mixing of hypogene metalliferous fluids with more dilute, H 2 S-rich fluids during Miocene–Pliocene compression associated with the Zagros Orogeny. [ABSTRACT FROM AUTHOR]

The Carboniferous Donghe sandstone reservoir is the most important target in the Tabei Uplift of the Tarim Basin, which contains a range of hydrocarbon types, including bitumen, heavy oil, condensate oil, light oil, crude oil, and hydrocarbon gas, and has high contents of CO2 and N2. The origin of multiple phase hydrocarbons from Carboniferous reservoir rocks in the Donghetang area, Western Tabei Uplift, is documented in this paper based on integral analysis of the geochemistry, pyrolysis, and carbon isotopes of the bulk composition and light composition hydrocarbons. Oil-source correlations determined that the paleoreservoir hydrocarbons that formed from Permian to Triassic derived from the Lower Ordovician (O1) source rocks and that those of the present-day reservoir that formed in the Neogene derived from Middle-Upper Ordovician (O2-3) source rocks. During the uplift episode lasting from Permian to Triassic, the hydrocarbons in the entire paleoreservoir underwent water washing, biodegradation, and bacterial sulfate reduction (BSR), resulting in residual bitumen, heavy oil, H2S, and pyrites in the paleoreservoir. The high CO2 and N2 contents originated from volcanic degassing due to volcanic activity from Permian to Early Triassic. The present-day reservoirs underwent gas washing and evaporative fractionation due to natural gas charging that originated from oil cracking and kerogen degradation in the deeper reservoirs; this resulted in fractionation and formed condensate oil and light oil with a high wax content in the residual crude oil. Based on this research, it was concluded that the diverse hydrocarbon phases in the Donghetang area were primarily attributed to water washing, biodegradation, BSR, volcanic degassing, gas washing, and evaporative fractionation. [ABSTRACT FROM AUTHOR]

Abstract Microbialites are volumetrically abundant components in Last Glacial Maximum and deglacial reefs in the Australian Great Barrier Reef sampled by IODP Expedition 325 in 34 holes from 17 sites (M0030–M0058), along four transects on the shelf edge. Detailed radiometric datings show that four distinct reef phases developed between 28and 10 ka, displaying offlapping and then backstepping patterns. The reef boundstone facies include coralgal, coralgal-microbialite and microbialite boundstone. The microbialite consists of combinations of micrite/microspar, bioclasts, siliciclastic grains (up to 14.5%), fenestrae and encrusting epibionts. The micrite/microspar is high-magnesian calcite commonly irregularly clotted, fenestral and peloidal. Mesoscale microbialite fabrics include laminated, structureless, digitate, intraskeletal and boring-filling, and coatings on debris. Intraskeletal and boring-filling is the first fabric to develop in skeletal voids and borings. It is usually followed by structureless and laminated microbialite, locally overlain by digitate fabric. Microbialite-coated debris can occur at any stage in this succession, including in bioclastic accumulations where the scarce in situ framework builders are mainly encrusting corals. Lipid biomarkers of intermediate to high specificity for sulfate-reducing bacteria, together with δ13C values of these lipids, indicate that microbialite formation was favored by sulfate-reducing bacteria in anoxic microenvironments, probably under high nutrient levels. The microbialite in fore-reef deposits accumulated in the photic zone in water depths of a few to several tens of meters, within small spaces generated by large bioclasts and encrusting corals in the topmost centimeters of the sediment. These crusts that formed on the illuminated surface constitute a previously unrecognized style of microbialite formation in Quaternary reefs. As with the cryptic crusts described from other reef locations, its greatest development occurred during the Last Glacial Maximum and early deglaciation. Microbial carbonate formation during this interval may reflect elevated seawater carbonate saturation corresponding with relatively low levels of atmospheric CO 2. Highlights • Microbialite is a main component in LGM and deglacial reefs in NE Australian shelf. • Microbialite was mediated by bacterial sulfate reduction in anoxic micro-environments. • Microbialite-coated debris is common in fore-reef bioclastic accumulations. • Fore-reef microbialite formed in the photic zone in shallow water depths. • LGM and deglacial microbialites may reflect elevated seawater carbonate saturation. [ABSTRACT FROM AUTHOR]

Underground hydrogen storage is a potential way to balance seasonal fluctuations in energy production from renewable energies. The risks of hydrogen storage in depleted gas fields include the conversion of hydrogen to CH4(g) and H2S(g) due to microbial activity, gas–water–rock interactions in the reservoir and cap rock, which are connected with porosity changes, and the loss of aqueous hydrogen by diffusion through the cap rock brine. These risks lead to loss of hydrogen and thus to a loss of energy. A hydrogeochemical modeling approach is developed to analyze these risks and to understand the basic hydrogeochemical mechanisms of hydrogen storage over storage times at the reservoir scale. The one-dimensional diffusive mass transport model is based on equilibrium reactions for gas–water–rock interactions and kinetic reactions for sulfate reduction and methanogenesis. The modeling code is PHREEQC (pH-REdox-EQuilibrium written in the C programming language). The parameters that influence the hydrogen loss are identified. Crucial parameters are the amount of available electron acceptors, the storage time, and the kinetic rate constants. Hydrogen storage causes a slight decrease in porosity of the reservoir rock. Loss of aqueous hydrogen by diffusion is minimal. A wide range of conditions for optimized hydrogen storage in depleted gas fields is identified. [ABSTRACT FROM AUTHOR]

Various anaerobic environments exist in the Earth's ecosystem, which can produce a great deal of organic matter each year. In anaerobic habitats, bacterial sulfate reduction may occur due to the action of sulfate-reducing bacteria. As a result, hydrogen sulfide (H2S) is formed. This paper focuses on sulfatereducing bacteria and the revision of the activity characteristics of these bacteria in the reducing environment. It discusses the metabolic process of sulfate-reducing bacteria using sulphate and organosulfur compounds as sulfur source, the mechanism of bacterial sulfate reduction and H2S formation mechanism. There are two main ways of H2S formation in sulfate-reducing bacteria, the production of metabolic sulphate and the metabolic organo-sulfur compounds (mainly cysteine). The paper, combined with the activity characteristics of sulfate-reducing bacteria and the pathway of metabolic formation of H2S, also discusses the circulation of sulfur in the environmental system of the Earth due to the action of sulfate-reducing bacteria, concerning the redox zone division in submarine sedimentary strata and landfills, the biogas formation phase of sulfate-reducing bacteria metabolism in sedimentary formations, and the bacterial sulfate reduction action in salt lakes (seawater) systems. Moreover, the production of hydrogen sulfide and the formation model of dolomite are both presented here. The findings support that sulfate-reducing bacteria are the most important biological source of H2S production. The study of the physiological characteristics of sulfate-reducing bacteria and the formation mechanism of H2S due to bacterial sulfate reduction can provide useful reference for the exploration of the laws of sulfur geochemical cycle and the rules of the ecological environment, which is essential for the protection of the natural environment and the restoration of polluted ecosystems, and can also provide a useful reference for the control of aerobic microorganisms. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract The sandstone-hosted Qianjiadian uranium deposit, hosted in the Upper Cretaceous Yaojia Formation in the Qianjiadian area, Songliao Basin, NE China, has been studied for over twenty years. However, there exists debate on whether mineralization fluid is low-temperature groundwater in favor of biogenic mineralization or diabase-related magmatic hydrothermal fluid for this deposit and other adjacent geologically linked sandstone-hosted uranium deposits (Baixingtu, Baolongshan and Huitianzhao deposits) in the North China. This study provided new data from petrographic and geochemical analyses, geochronology of uranium minerals (the EMPA chemical dating method) and petroleum hydrocarbon biomarkers in host sandstones. Two types of host sandstone were recognized. In calcareous sandstones, pitchblende coexists with colloform pyrite and poikilitic calcite cement while quartz and feldspars were extensively corroded. In non-calcareous sandstones, coffinite coexists with colloform pyrite and only feldspars were slightly corroded. This suggests that pitchblende formed in high pH (pH > ∼9) fluid, while the pH of ore-forming fluid for coffinite was lower (pH = 7–9). Besides, EMPA chemical dating revealed two stages of uranium mineralization. Stage-A occurred in 43–28 Ma with pitchblende as the only uranium mineral species. Stage-B occurred in 19–3 Ma with the formation of both pitchblende and coffinite. The uranium mineralization was biogenic under low-temperature groundwater condition and thus not from a diabase-related mafic magmatic hydrothermal fluid based on the following lines of evidence: (i) some coffinite occurs as phosphorus-rich microorganism-like microspherules structure; (ii) pyrite aggregates were generated from bacterial sulfate reduction as indicated by the δ34S values as low as −41.4‰; (iii) calcite cement in calcareous sandstone contains only single phase aqueous inclusions, and have δ13C values as low as −11.2‰, indicating that part of the carbon was derived from organic matter oxidation; (iv) the organic matter oxidation is further supported by hydrocarbons extracted from petroleum inclusions within calcite cement, showing occurrence of C 26 –C 31 17α, 21β 25-norhopanes, typically resulting from heavy biodegradation. [ABSTRACT FROM AUTHOR]

(a) Genetic model of Liuyang chrysanthemum stone; (b) the Liuyang chrysanthemum stone sample; (c) sulfur and oxygen isotope fractionation between the celestite and the host rocks of Liuyang chrysanthemum stone in microbial sulfate reduction processes. [Display omitted] • Chrysanthemum-like celestite aggregate related to complex diagenesis. • S-O isotope fractionation of celestite in microbial sulfate reduction processes. • Influence of marine sulfate through geologic time on δ34S and δ18O of celestite. Chrysanthemum stone refers to a radial and chrysanthemum–like mineral aggregate. Liuyang chrysanthemum stone, distributed in the carbonate of the Permian Chihsian Formation in South China, has become a rare natural art treasure due to its unique radial shape. The lack of effective constraints on the petrography and geochemistry of the chrysanthemum stone in Liuyang restricts the understanding of its origin. Hence, petrography analysis and Raman microprobe spectroscopy were used to study the mineral compositions and textural characteristics of the Liuyang chrysanthemum. Element and isotope geochemistry studies were conducted to discuss the sedimentary environment, material source, and formation mechanism. The Liuyang chrysanthemum stone was formed in the period of aragonite sea, and developed in dark gray limestone as a white radial mineral aggregate. The primary mineral is celestite, a minor amount of which was filled with and metasomatized by calcite. Trace element characteristics (δCe = 0.46–0.70, V/Cr = 1.28–1.51, Ni/Co = 2.14–4.89, Sr/Ba = 14.42–45.17) and carbon and oxygen isotopic compositions (δ13C V–PDB = 3.0 ‰–3.8 ‰, δ18O V–PDB = 5.2 ‰–4.8 ‰) of the host rocks indicate an aerobic marine sedimentary environment. The significant difference in sulfur isotopic compositions between the chrysanthemum stone (δ34S = 29.4 to 28.1 ‰) and the host rocks (δ34S = –29.4 to –28.1 ‰) indicates that bacterial sulfate reduction (BSR) and anerobic oxidation of methane (AOM) has occurred. Petrography, trace element and C–O–S isotope geochemistry of the Liuyang chrysanthemum stone had revealed the formation process of the chrysanthemum stone. The organic matter was decomposed by O 2 and produced CO 2 in the aerobic marine sedimentary environment. With the continuous sedimentation and the oxygen consumption, the early sedimentary carbonate and bioclastic was gradually separated from the relatively aerobic environment. An anoxic sedimentary–diagenetic environment was formed and the BSR occurred, during which SO 4 2– participated in the degradation of organic matter as an electron acceptor. The bacteria preferentially absorbed the light 32SO 4 2– in pore water to produce 32S–rich FeS 2 in the host rocks and the heavy SO 4 2– was combined with the Sr2+ released by aragonite dissolved by the accumulated CO 2 to precipitate the celestite. HCO 3 – accumulated during the AOM and the BSR resulted in the replacement of the celestite by the calcite. [ABSTRACT FROM AUTHOR]

Sulfur (S) plays a significant role in saline environments, and sulfate (SO 4 2 − ) is an important component of the biogeochemical S-cycle since it acts as the main electron acceptor in anoxic sediments. The purpose of this paper is to evaluate the fate of S, its origin, and processes affecting sulfate outcome in the hypersaline Pétrola Lake in the Castilla-La Mancha region (High Segura Basin, SE Spain). The lake is the terminal discharge zone of an endorheic basin with considerable anthropogenic pressures. Anthropogenic activities (mainly agricultural inputs and wastewater discharge), together with bedrock leaching of sulfate and sulfide-rich sediments, increase dissolved SO 4 2 − in surface and groundwater up to 123,000 mg/L. The source and fate of sulfate in this environment was investigated coupling hydrochemistry, including hydrogen sulfide (H 2 S) microprofiles, isotopic analyses (δ 34 S, δ 18 O SO4 , δ 2 H H2O , δ 18 O H2O , and tritium), mineralogical determinations, and molecular biology tools (16S rDNA amplification and sequencing). The origin of dissolved SO 4 2 − in water is related to pyrite oxidation from Lower Cretaceous sediments, and secondary gypsum dissolution. Under the lake, dissolved SO 4 2 − decreases with depth, controlled by three main processes: (1) seasonal evaporation cycles, (2) hydrodynamic instability caused by the different density-driven groundwater flow, and (3) sulfate-reduction processes, i.e. dissimilatory bacterial sulfate reduction (BSR). These processes control the continuous recycling of sulfur in the system. Lake water and groundwater are in hydraulic connection, and a density-driven flow (DDF) is able to transport reactive organic matter and dissolved SO 4 2 − towards the underlying aquifer. Hydrochemical evolution in depth, H 2 S production (up to 0.024 nmol/cm 3 ·s) and the presence of sulfate-reducing bacteria suggest the existence of BSR processes. However, isotope techniques are insufficient to elucidate BSR processes since their isotopic effect is masked by low isotope fractionation and high SO 4 2 − concentrations. The pattern here described may be found in other saline basins worldwide. [ABSTRACT FROM AUTHOR]

The storage of natural gas in salt caverns can entail the risk of H 2 S generation, which in turn leads to gas pollution. H 2 S is generated by bacterial sulfate reduction. The bacteria use aqueous sulfate (aq) as an electron acceptor to oxidize the dissolved hydrocarbons and generate sulfide. Anhydrite is available in the rock salt surrounding the cavern and acts as a sulfate (aq) source. The stored natural gas, with its main component, methane, is in solubility equilibrium with the brine and is additionally delivered by diffusion into the brine. The generated H 2 S reaches the stored gas by outgassing from the brine. In this study, these processes are simulated by one- and three-dimensional hydrogeochemical diffusive mass transport models, which are based on equilibrium reactions for gas-water-rock interactions and kinetic reactions for sulfate reduction. Modelling results show that the greatest amount of H 2 S is generated in the brine. The amount of generated H 2 S (g) is mainly controlled by the amount of available sulfate (aq) as well as the rate of diffusion, which is coupled with the maximum operating live time of salt caverns. Additionally, the amount of generated and released H 2 S (g) is sensitive to the chosen kinetic rate constant. To ensure constant gas quality over time, the gas and the brine must be analyzed continuously and technical methods must be applied when the H 2 S (g) concentration increases. According to the modelling results, H 2 S (g) generation is inhibited by addition of dissolved ferrous iron to the brine. Dissolved ferrous iron reacts with sulfide-sulfur to form mackinawite (FeS (s) ) so that aqueous sulfide is no longer available for H 2 S (g) generation. Another method is the addition of NaOH to increase the pH of the brine. Then, higher fractions of generated sulfide-sulfur are transformed to free S 2− (aq) instead of H 2 S (g) and H 2 S (aq) . [ABSTRACT FROM AUTHOR]

Passive bioremediation of metal- and sulfate-containing acid mine drainage (AMD) has been investigated in a batch study. Multiple substrates were used in the AMD remediation using spent mushroom compost (SMC), limestone, activated sludge (AS), and woodchips (WC) under anoxic conditions suitable for bacterial sulfate reduction (BSR). Limestones used were of crushed limestone (CLS) and uncrushed limestone, provided at two different ratios in mixed substrates treatment and varied by the proportion of SMC and limestone. The SMC greatly assisted the removals of sulfate and metals and also acted as an essential carbon source for BSR. The mixed substrate composed of 40% CLS, 30% SMC, 20% AS, and 10% WC was found to be effective for metal removal. Mn, Cu, Pb, and Zn were greatly removed (89–100%) in the mixed substrates treatment, while Fe was only removed at 65%. Mn was found to be removed at a greatly higher rate than Fe, suggesting important Mn adsorption onto organic materials, that is, greater sorption affinity to the SMC. Complementary with multiple treatment media was the main mechanism assisting the AMD treatment through microbial metal reduction reactions. [ABSTRACT FROM AUTHOR]

Stratiform baryte deposits are widespread in Cambrian and Devonian strata in China and around the world. In this article, the authors studied the sulfur isotopic features and forming mechanism of the stratiform baryte deposits occurring within the Upper Devonian cherts of the Zhenning-Ziyun county, Guizhou province, located in the Southwestern margin of the Yangtze Platform. The sulfur isotopic data from 18 baryte ore samples of the Leji section of Zhenning county are presented herein with values that range from +41.9‰ to +68.4‰ (AVG = +59.9‰). The δ34S values of the baryte ore from the Mohao section of Ziyun county are stable and show a narrow range from +41.3‰ to +47.0‰ (AVG = +44.0‰). In the Luocheng section of Ziyun county, the δ34S values of the baryte ore vary from +27.6‰ to +36.4‰ (AVG = +32.7‰). The δ34S values of all samples are higher than those of the coeval seawater sulfates (+25‰). The scanning electron microscope analysis indicates that spherical, dumbbell-shaped, clavate bacterial and bacteria-like fossils were observed, as well as the irregular schistose and framboid forms of Fe oxides that occur around the surfaces of baryte grains and inter-grains. Fe oxides take irregular schistose and framboid forms. These findings imply the significant concentration of heavy sulfur related to the seawater sulfates with the action of bacterial sulfate reduction in a closed basin. In addition, the trend of the δ34S value of baryte ores is gradually decreasing from the Leji to Mohao and Luocheng sections, which suggests that Leji area is located in the deepwater area of the restricted rift basin, and in a more closed depositional environment. [ABSTRACT FROM PUBLISHER]

In this study, we evaluated the water quality status (especially, salinity problems) and hydrogeochemical processes of an alluvial aquifer in a floodplain of the Red River delta, Vietnam, based on the hydrochemical and isotopic data of groundwater samples (n = 23) from the Kien Xuong district of the Thai Binh province. Following the historical inundation by paleo-seawater during coastal progradation, the aquifer has been undergone progressive freshening and land reclamation to enable settlements and farming. The hydrochemical data of water samples showed a broad hydrochemical change, from Na-Cl through Na-HCO 3 to Ca-HCO 3 types, suggesting that groundwater was overall evolved through the freshening process accompanying cation exchange. The principal component analysis (PCA) of the hydrochemical data indicates the occurrence of three major hydrogeochemical processes occurring in an aquifer, namely: 1) progressive freshening of remaining paleo-seawater, 2) water-rock interaction (i.e., dissolution of silicates), and 3) redox process including sulfate reduction, as indicated by heavy sulfur and oxygen isotope compositions of sulfate. To quantitatively assess the hydrogeochemical processes, the end-member mixing analysis (EMMA) and the forward mixing modeling using PHREEQC code were conducted. The EMMA results show that the hydrochemical model with the two-dimensional mixing space composed of PC 1 and PC 2 best explains the mixing in the study area; therefore, we consider that the groundwater chemistry mainly evolved by mixing among three end-members (i.e., paleo-seawater, infiltrating rain, and the K-rich groundwater). The distinct depletion of sulfate in groundwater, likely due to bacterial sulfate reduction, can also be explained by EMMA. The evaluation of mass balances using geochemical modeling supports the explanation that the freshening process accompanying direct cation exchange occurs through mixing among three end-members involving the K-rich groundwater. This study shows that the multiple end-members mixing model is useful to more successfully assess complex hydrogeochemical processes occurring in a salinized aquifer under freshening, as compared to the conventional interpretation using the theoretical mixing line based on only two end-members (i.e., seawater and rainwater). [ABSTRACT FROM AUTHOR]

Bacterial sulfate reduction plays a crucial role in the mobilization of toxic substances in aquifers. However, the role of bacterial sulfate reduction on iodine mobilization in geogenic high-iodine groundwater systems has been unexplored. In this study, the enrichment of groundwater δ 34 S SO4 (15.56 to 69.31‰) and its significantly positive correlation with iodide and total iodine concentrations in deep groundwater samples of the North China Plain suggested that bacterial sulfate reduction participates in the mobilization of groundwater iodine. Similar significantly positive correlations were further observed between the concentrations of iodide and total iodine and the relative abundance of the dsrB gene by qPCR, as well as the composition and abundance of sulfate-reducing bacteria (SRB) predicted from 16S rRNA gene high-throughput sequencing data. Subsequent batch culture experiments by the SRB Desulfovibrio sp. B304 demonstrated that SRB could facilitate iodine mobilization through the enzyme-driven biotic and sulfide-driven abiotic reduction of iodate to iodide. In addition, the dehalogenation of organoiodine compounds by SRB and the reductive dissolution of iodine-bearing iron minerals by biogenic sulfide could liberate bound or adsorbed iodine into groundwater. The role of bacterial sulfate reduction in iodine mobilization revealed in this study provides new insights into our understanding of iodide enrichment in iodine-rich aquifers worldwide.

Thrombolites are widespread in the Mesoproterozoic Wumishan Formation in the North China Platform. This study shows that they mainly concentrated in subtidal carbonate facies with relatively low hydrodynamic conditions, rather than in intertidal zone as suggested previously. From the deep lower to the shallow upper subtidal facies, the thrombolites show evident changes in morphology from dominantly domal to tabular forms, likely suggestive of environmental controls on their morphogenesis and distribution. As the most important component in thrombolites, mesoclots typically consist of organic-rich micritic nuclei and organic-poor fibrous aragonite rims. Mesoclots may vary considerably in their morphology, but a type of specifically shaped mesoclots tends to concentrate predominantly in a particular group of thrombolites. The proportion of the fibrous aragonite rims in mesoclots decrease as the depositional environments become shallower, likely suggesting that the environmental changes also have controls on the internal fabrics of thrombolites. Putative filamentous bacterial colonies are well preserved in some aragonite fans in the matrix between mesoclots, invoking rapid precipitation and aragonite-supersaturated conditions in the ambient waters. It seems that a suboxic to anoxic environment, highly alkaline seawater and relatively low hydrodynamic conditions were among the important factors that facilitated the development and preservation of thrombolites in the Mesoproterozoic epeiric sea on the North China Platform.

Underground hydrogen storage is a potential way to balance seasonal fluctuations in energy production from renewable energies. The risks of hydrogen storage in depleted gas fields include the conversion of hydrogen to CH4(g) and H2S(g) due to microbial activity, gas⁻water⁻rock interactions in the reservoir and cap rock, which are connected with porosity changes, and the loss of aqueous hydrogen by diffusion through the cap rock brine. These risks lead to loss of hydrogen and thus to a loss of energy. A hydrogeochemical modeling approach is developed to analyze these risks and to understand the basic hydrogeochemical mechanisms of hydrogen storage over storage times at the reservoir scale. The one-dimensional diffusive mass transport model is based on equilibrium reactions for gas⁻water⁻rock interactions and kinetic reactions for sulfate reduction and methanogenesis. The modeling code is PHREEQC (pH-REdox-EQuilibrium written in the C programming language). The parameters that influence the hydrogen loss are identified. Crucial parameters are the amount of available electron acceptors, the storage time, and the kinetic rate constants. Hydrogen storage causes a slight decrease in porosity of the reservoir rock. Loss of aqueous hydrogen by diffusion is minimal. A wide range of conditions for optimized hydrogen storage in depleted gas fields is identified.

Climate and oceanographic changes during the Oceanic Anoxic Event 2 (OAE 2) and the Late Turonian–Coniacian Event (LTCE) are reported from a succession deposited in the central part of the Mexican Interior Basin, based on sedimentological, microfacies, mineralogical, and geochemical analysis. Typical δ13C positive excursions that characterize both the OAE 2 and the LTCE were identified. Organic-rich sediments during the initial stage of OAE 2 (before and around peak "A", late Cenomanian) and the middle stage of LTCE (around the Hitchwood event) accumulated under increasingly warm and humid conditions, as evidenced by high chemical index of alteration values. Elevated concentrations of detrital proxies coupled with high phosphorus mass-accumulation rates suggest that this scenario led to a rise in detrital and nutrients fluxes that induced eutrophication and anoxic/dysoxic bottom waters. Eutrophic-anoxic/dysoxic marine conditions are further supported by the highest TOC values, coinciding with significant enrichments in redox- and productivity-sensitive trace elements. Moreover, these conditions can also be inferred from the abundant presence of radiolarians and filaments in the OAE 2 interval, and the occurrence of opportunistic foraminifera in the LTCE interval. Oxygen-depleted bottom waters are also indicated by Mo–U systematics. The onset of the Mexican Orogen tectonic uplift and increased upwelling strengthened the transference of nutrients, enhancing organic matter burial during the initial stage of OAE 2. In the mid-OAE 2 δ13C trough interval (between peaks "A" and "B") equivalent to the Plenus Cold Event, bioturbated sediments with low TOC values accumulated during a short episode of cold climate conditions probably reflecting the southward flow of boreal water throughout the Mexican Interior Basin. The minimum δ34S py value occurring within the OAE 2 interval in the Mexican Interior Basin is lower than elsewhere because of a local increase in sulfate concentrations. • Environmental changes related to the OAE 2 and the LTCE are recognized. • Eutrophic-anoxic/dysoxic conditions developed during global warming phases. • Both regional/local and global forcing factors controlled organic matter deposition. • Local weathering enhanced marine sulfate concentrations. [ABSTRACT FROM AUTHOR]

Sulfate-reducing bacteria have long been known to promote mineral precipitation. However, the influence of electron donors (energy sources) and carbon sources on the minerals formed during sulfate reduction is less well understood. An investigation was therefore undertaken to determine how these nutrients affect sulfate reduction by the bacterium Desulfovibrio alaskensis G20 in a marine sediment pore water medium. Monohydrocalcite and a small amount of calcite formed during sulfate reduction with formate as the electron donor; Mg-phosphates and calcite precipitated when hydrogen served as the electron donor and when acetate and dissolved inorganic carbon served as carbon sources; and greigite and elemental sulfur were deposited when lactate was used as the electron donor and carbon source. The experimental results were generally consistent with geochemical modeling, suggesting that it may be possible to predict the processes and conditions during formation of these minerals in natural environments. [ABSTRACT FROM AUTHOR]

Sulfate in effluent is a challenging issue for wastewater reuse around the world. In this study, sulfur (S) removal and transformation in five batch constructed wetlands (CWs) treating secondary effluent were investigated. The results showed that the presence of the plant cattail ( Typha latifolia ) had little effect on sulfate removal, while the carbon-rich litter it generated greatly improved sulfate removal, but with limited sulfide accumulation in the pore-water. After sulfate removal, most of the S was deposited with the valence states S (-II) and S (0) on the iron-rich gravel surface, and acid volatile sulfide was the main S sink in the litter-added CWs. High-throughput pyrosequencing revealed that sulfate-reducing bacteria (i.e. Desulfobacter ) and sulfide-oxidizing bacteria (i.e. Thiobacillus ) were dominant in the litter-added CWs, which led to a sustainable S cycle between sulfate and sulfide. Overall, this study suggests that recycling plant litter and iron-rich filling material in CWs gives an opportunity to utilize the S in the wastewater as both an electron acceptor for sulfate reduction and as an electron donor for nitrate reduction coupled with sulfide oxidation. This leads to the simultaneous removal of sulfate, nitrate, and organics without discharging toxic sulfide into the receiving water body. [ABSTRACT FROM AUTHOR]