Geobiology最新文献

{"title":"The Effects of Plant–Microbe–Environment Interactions on Mineral Weathering Patterns in a Granular Basalt","authors":"Valerie R. Milici,&nbsp;Samuel Abiven,&nbsp;Hannes H. Bauser,&nbsp;Lily G. Bishop,&nbsp;Rebecca G. W. Bland,&nbsp;Jon Chorover,&nbsp;Katerina M. Dontsova,&nbsp;Kielah Dyer,&nbsp;Linus Friedman,&nbsp;Matthew J. Rusek-Peterson,&nbsp;Scott Saleska,&nbsp;Katrina M. Dlugosch","doi":"10.1111/gbi.70004","DOIUrl":"10.1111/gbi.70004","url":null,"abstract":"<div>\u0000 \u0000 <p>The importance of biota to soil formation and landscape development is widely recognized. As biotic complexity increases during early succession via colonization by soil microbes followed by vascular plants, effects of biota on mineral weathering and soil formation become more complex. Knowledge of the interactions among groups of organisms and environmental conditions will enable us to better understand landscape evolution. Here, we used experimental columns of unweathered granular basalt to investigate how early successional soil microbes, vascular plants (alfalfa; <i>Medicago sativa</i>), and soil moisture interact to affect both plant performance and mineral weathering. We found that the presence of soil microbes reduced plant growth rates, total biomass, and survival, which suggests that plants and microbes were competing for nutrients in this environment. However, we also found considerable genotype-specific variation in plant–microbial interactions, which underscores the importance of within-species genetic variation on biotic interactions. We also found that the presence of vascular plants reduced variability in pH and electrical conductivity, suggesting that plants may homogenize weathering reactions across the soil column. We also show that there is heterogeneity in the abiotic conditions in which microbes, plants, or their combination have the strongest effect on weathering, and that many of these relationships are sensitive to soil moisture. Our findings highlight the importance of interdependent effects of environmental and biotic factors on weathering during initial landscape formation.</p>\u0000 </div>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"22 6","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-11-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142694911","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Ultrastructural Perspectives on the Biology and Taphonomy of Tonian Microfossils From the Draken Formation, Spitsbergen","authors":"Alexandre Fadel,&nbsp;Kevin Lepot,&nbsp;Sylvain Bernard,&nbsp;Ahmed Addad,&nbsp;Armelle Riboulleau,&nbsp;Andrew H. Knoll","doi":"10.1111/gbi.70000","DOIUrl":"10.1111/gbi.70000","url":null,"abstract":"<p>Silicified peritidal carbonates of the Tonian Draken Formation, Spitsbergen, contain highly diverse and well-preserved microfossil assemblages dominated by filamentous microbial mats, but also including diverse benthic and/or allochthonous (possibly planktonic) microorganisms. Here, we characterize eight morphospecies in focused ion beam (FIB) ultrathin sections using transmission electron microscopy (TEM) and X-ray absorption near-edge structure (XANES) spectromicroscopy. Raman and XANES spectroscopies show the highly aromatic molecular structure of preserved organic matter. Despite this apparently poor molecular preservation, nano-quartz crystallization allowed for the preservation of various ultrastructures distinguished in TEM. In some filamentous microfossils (<i>Siphonophycus</i>) as well as in all cyanobacterial coccoids, extracellular polysaccharide sheaths appear as bands of dispersed organic nanoparticles. <i>Synodophycus</i> microfossils, made up of pluricellular colonies of coccoids, contain organic walls similar to the F-layers of pleurocapsalean cyanobacteria. In some fossils, internal content occurs as particulate organic matter, forming dense networks throughout ghosts of the intracellular space (e.g., in <i>Salome svalbardensis</i> filaments), or scarce granules (in some <i>Chroococcales</i>). In some chroococcalean microfossils (<i>Gloeodiniopsis mikros</i>, and also possibly <i>Polybessurus</i>), we find layered internal contents that are more continuous than nanoparticulate bands defining the sheaths, and with a shape that can be contracted, folded, or invaginated. We interpret these internal layers as the remains of cell envelope substructures and/or photosynthetic membranes thickened by additional cellular material. Some <i>Myxococccoides</i> show a thick (up to ~ 0.9 μm) wall ultrastructure displaying organic pillars that is best reconciled with a eukaryotic affinity. Finally, a large spheroid with ruptured wall, of uncertain affinity, displays a bi-layered envelope. Altogether, our nanoscale investigations provide unprecedented insights into the taphonomy and taxonomy of this well-preserved assemblage, which can help to assess the nature of organic microstructures in older rocks.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"22 6","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/gbi.70000","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142542352","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Redox Gradient Shapes the Chemical Composition of Peatland Microbial Communities","authors":"Vincent P. Milesi","doi":"10.1111/gbi.70001","DOIUrl":"10.1111/gbi.70001","url":null,"abstract":"<p>The response of soil carbon to climate change and anthropogenic forcing depends on the relationship between the physicochemical variables of the environment and microbial communities. In anoxic soils that store large amounts of organic carbon, it can be hypothesized that the low amount of catabolic energy available leads microbial organisms to minimize the energy costs of biosynthesis, which may shape the composition of microbial communities. To test this hypothesis, thermodynamic modeling was used to assess the link between redox gradients in the ombrotrophic peatland of the Marcell Experimental Forest (Minnesota, USA) and the chemical and taxonomic composition of microbial communities. The average amino acid composition of community-level proteins, called hereafter model proteins, was calculated from shotgun metagenomic sequencing. The carbon oxidation state of model proteins decreases linearly from −0.14 at 10 cm depth to −0.17 at 150 cm depth. Calculating equilibrium activities of model proteins for a wide range of chemical conditions allows identification of the redox potential of maximum chemical activity. Consistent with redox measurements across peat soils, this model Eh decreases logarithmically from an average value of 300 mV at 10 cm depth, close to the stability domain of goethite relative to Fe²⁺, to an average value of −200 mV at 150 cm, within the stability domain of CH₄ relative to CO₂. The correlation identified between the taxonomic abundance and the carbon oxidation state of model proteins enables predicting the evolution of taxonomic abundance as a function of model Eh. The model taxonomic abundance is consistent with the measured gene and taxonomic abundance, which evolves from aerobic bacteria at the surface including Acidobacteria, Proteobacteria, and Verrumicrobia, to anaerobes at depth dominated by Crenarchaeota. These results indicate that the thermodynamic forcing imposed by redox gradient across peat soils shapes both the chemical and taxonomic composition of microbial communities. By providing a mechanistic understanding of the relationship between microbial community and environmental conditions, this work sheds new light on the mechanisms that govern soil microbial life and opens up prospects for predicting geochemical and microbial evolution in changing environments.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"22 6","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/gbi.70001","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142542351","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Featured Cover","authors":"","doi":"10.1111/gbi.70002","DOIUrl":"https://doi.org/10.1111/gbi.70002","url":null,"abstract":"<p><b>Cover</b></p><p>The cover image is based on the Article <i>A Biofilm Channel Origin for Vermiform Microstructure in Carbonate Microbialites</i> by Yadira Ibarra et al., https://doi.org/10.1111/gbi.12623\u0000 \u0000 <figure>\u0000 <div><picture>\u0000 <source></source></picture><p></p>\u0000 </div>\u0000 </figure>\u0000 </p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"22 5","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-10-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/gbi.70002","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142525598","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A Biofilm Channel Origin for Vermiform Microstructure in Carbonate Microbialites","authors":"Yadira Ibarra,&nbsp;Pedro J. Marenco,&nbsp;Jakob P. Centlivre,&nbsp;Brian P. Hedlund,&nbsp;Laura K. Rademacher,&nbsp;Sarah E. Greene,&nbsp;David J. Bottjer,&nbsp;Frank A. Corsetti","doi":"10.1111/gbi.12623","DOIUrl":"10.1111/gbi.12623","url":null,"abstract":"<div>\u0000 \u0000 <p>A three-dimensional tubular fabric known as “vermiform microstructure” in Phanerozoic and Neoproterozoic carbonate microbialites has been hypothesized to represent the body fossil of nonspicular keratose demosponges. If correct, this interpretation extends the sponge body fossil record and origin of animals to ~890 Ma. However, the veracity of the keratose sponge interpretation for vermiform microstructure remains in question, and the origin of the tubular fabric is enigmatic. Here we compare exceptionally well-preserved microbialite textures from the Upper Triassic to channel networks created by modern microbial biofilms. We demonstrate that anastomosing channel networks of similar size and geometries are produced by microbial biofilms in the absence of sponges, suggesting the origin for vermiform microstructure in ancient carbonates is not unique to sponges and perhaps best interpreted conservatively as likely microbial in origin. We present a taphonomic model of early biofilm lithification in seawater with anomalously high carbonate saturation necessary to preserve delicate microbial textures. This work has implications for the understanding of three-dimensional biofilm architecture that goes beyond the current micro-scale observations available from living biofilm experiments and suggests that biofilm channel networks have an extensive fossil record.</p>\u0000 </div>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"22 5","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142485606","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Physiology, Not Nutrient Availability, May Have Limited Primary Productivity After the Emergence of Oxygenic Photosynthesis","authors":"Christen L. Grettenberger,&nbsp;Dawn Y. Sumner","doi":"10.1111/gbi.12622","DOIUrl":"https://doi.org/10.1111/gbi.12622","url":null,"abstract":"<p>The evolution of oxygenic photosynthesis in Cyanobacteria was a transformative event in Earth's history. However, the scientific community disagrees over the duration of the delay between the origin of oxygenic photosynthesis and oxygenation of Earth's atmosphere, with estimates ranging from less than a hundred thousand to more than a billion years, depending on assumptions about rates of oxygen production and fluxes of reductants. Here, we propose a novel ecological hypothesis that a geologically significant delay could have been caused by biomolecular inefficiencies within proto-Cyanobacteria—ancestors of modern Cyanobacteria—that limited their maximum rates of oxygen production. Consideration of evolutionary processes and genomic data suggest to us that proto-cyanobacterial primary productivity was initially limited by photosystem instability, oxidative damage, and photoinhibition rather than nutrients or ecological competition. We propose that during the Archean era, cyanobacterial photosystems experienced protracted evolution, with biomolecular inefficiencies initially limiting primary productivity and oxygen production. Natural selection led to increases in efficiency and thus primary productivity through time. Eventually, evolutionary advances produced sufficient biomolecular efficiency that environmental factors, such as nutrient availability, limited primary productivity and shifted controls on oxygen production from physiological to environmental limitations. If correct, our novel hypothesis predicts a geologically significant interval of time between the first local oxygen production and sufficient production for oxygenation of environments. It also predicts that evolutionary rates were likely highly variable due to strong environmental selection pressures and potentially high mutation rates but low competitive interactions.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"22 5","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/gbi.12622","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142320825","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Living to Lithified: Construction and Preservation of Silicified Biomarkers","authors":"Kalen L. Rasmussen,&nbsp;Patrick H. Thieringer,&nbsp;Sophia Nevadomski,&nbsp;Aaron M. Martinez,&nbsp;Katherine S. Dawson,&nbsp;Frank A. Corsetti,&nbsp;Xin-Yuan Zheng,&nbsp;Yiwen Lv,&nbsp;Xinyang Chen,&nbsp;Aaron J. Celestian,&nbsp;William M. Berelson,&nbsp;Nick E. Rollins,&nbsp;John R. Spear","doi":"10.1111/gbi.12620","DOIUrl":"https://doi.org/10.1111/gbi.12620","url":null,"abstract":"<div>\u0000 \u0000 <p>Whole microorganisms are rarely preserved in the fossil record but actively silicifying environments like hot springs provide an opportunity for microbial preservation, making silicifying environments critical for the study of microbial life through time on Earth and possibly other planetary bodies. Yet, the changes that biosignatures may undergo through lithification and burial remain unconstrained. At Steep Cone Geyser in Yellowstone National Park, we collected microbial material from (1) the living system across the active outflows, (2) the silicified areas adjacent to flows, and (3) lithified and buried material to assess the preservation of biosignatures and their changes across the lithification transect. Five biofabrics, built predominantly by <i>Cyanobacteria</i> <i>Geitlerinema</i>, <i>Pseudanabaenaceae</i>, and <i>Leptolyngbya</i> with some filamentous anoxygenic phototrophs contributions, were identified and tracked from the living system through the process of silicification/lithification. In the living systems, δ³⁰Si values decrease from +0.13‰ in surficial waters to −2‰ in biomat samples, indicating a kinetic isotope effect potentially induced by increased association with actively growing biofabrics. The fatty acids C_16:1 and <i>iso</i>-C_14:0 and the hydrocarbon C_17:0 were disentangled from confounding signals and determined to be reliable lipid biosignatures for living biofabric builders and tenant microorganisms. Builder and tenant microbial biosignatures were linked to specific <i>Cyanobacteria</i>, anoxygenic phototrophs, and heterotrophs, which are prominent members of the living communities. Upon lithification and burial, silicon isotopes of silicified biomass began to re-equilibrate, increasing from δ³⁰Si −2‰ in living biomats to −0.55‰ in lithified samples. Active endolithic microbial communities were identified in lithified samples and were dominated by <i>Cyanobacteria</i>, heterotrophic bacteria, and fungi. Results indicate that distinct microbial communities build and inhabit silicified biofabrics through time and that microbial biosignatures shift over the course of lithification. These findings improve our understanding of how microbial communities silicify, the biomarkers they retain, and transitionary impacts that may occur through lithification and burial.</p>\u0000 </div>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"22 5","pages":"1-30"},"PeriodicalIF":2.7,"publicationDate":"2024-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142320705","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Fossil Geyserite and Testate Amoebae in Geothermal Spring Vent Pools: Paleoecology and Variable Preservation Quality in Jurassic Sinter of Patagonia (Deseado Massif, Argentina)","authors":"Ana Julia Sagasti,&nbsp;Kathleen A. Campbell,&nbsp;Juan L. García Massini,&nbsp;Amanda Galar,&nbsp;Diego M. Guido,&nbsp;Pascale Gautret","doi":"10.1111/gbi.12621","DOIUrl":"https://doi.org/10.1111/gbi.12621","url":null,"abstract":"<p>Geyserite is a type of terrestrial siliceous hot spring deposit (sinter) formed subaerially in proximal vent areas, with near-neutral pH, alkali chloride discharge fluids characterized by initial high temperatures (~73°C to up to 100°C) that fluctuate rapidly in relation to dynamic hydrology, seasonality, wind, and other environmental parameters. We analyzed sinters at the Claudia paleogeothermal field from the Late Jurassic (~150 Ma) Deseado Massif geological province, Argentinean Patagonia. The geyserite samples—with spicular to columnar to nodular morphologies—contain abundant microfossils in monotypic assemblages that occur in three diagenetic states of preservation. The best-preserved microfossils consist of vesicle-like structures with radial heteropolar symmetry (~35 μm average diameter), circular apertures, smooth walls lacking ornamentation, and disk- or beret-like shapes. Comparisons with extant, morphologically similar organisms suggest an affinity with the testate amoebae of the <i>Arcella hemisphaerica–Arcella rotundata</i> complex and <i>Centropyxis aculeata</i> strain <i>discoides</i>. These species occur in active geothermal pools between 22°C and 45°C, inconsistent with the temperature of formation of modern geyserites. We propose that the testate amoebae may have colonized the geyserite during cooler phases in between spring-vent eruptive cycles to prey on biofilms. Silica precipitation through intermittent bathing and splashing of fluctuating thermal fluid discharge could have led to their entrapment and fossilization. Petrographic analysis supports cyclicity in paleovent water eruptions and later diagenesis that transformed the opal into quartz. Spatially patchy degradation and modification of the silicified microorganisms resulted in variable preservation quality of the microfossils. This contribution illustrates the importance of microscale analysis to locate early silicification and identify high-quality preservation of fossil remains in siliceous hot spring deposits, which are important in early life studies on Earth and potentially Mars.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"22 5","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/gbi.12621","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142320701","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Morphological and Microbial Diversity of Hydromagnesite Microbialites in Lake Salda: A Mars Analog Alkaline Lake","authors":"Yagmur Gunes,&nbsp;Fatih Sekerci,&nbsp;Burak Avcı,&nbsp;Thijs J. G. Ettema,&nbsp;Nurgul Balci","doi":"10.1111/gbi.12619","DOIUrl":"10.1111/gbi.12619","url":null,"abstract":"<div>\u0000 \u0000 <p>Lake Salda, a terrestrial analog for the paleolake in Jezero Crater on Mars, hosts active, subfossil, and fossil hydromagnesite microbialites, making it an ideal location to study microbialite formation and subsequent processes. Our understanding of this record is still limited by an incomplete knowledge of the macro- and mesoscale morphotypes of microbialites, along with their spatial distribution and correlation with microbial and geochemical processes that influence microbialite formation. In this study, we investigated the spatial distribution, morphotypes, mineralogy, geochemistry, and microbial diversity of the microbialites and identified six distinct zones (Zone I to Zone VI) with major microbialite build-ups in Lake Salda. Newly identified microbialites were classified based on the macro- and mesostructures. Our work shows that the lake contains stromatolites, thrombolites, stromatolitic thrombolites, dendrolites, and microbially induced sedimentary structures. At macroscale, Lake Salda microbialites exhibit hemispheres, stacked domes, and laterally linked columnar structures while minicolumns, knobs, mesoclots, laminae, and botryoidal structures are common at mesoscale. The macro- and mesoscale distribution of different microbialite types spatially correlates with microbial community composition and water depth. Deep-growing microbialites with a low abundance of Cyanobacteria (∼1%–4%) and high abundance of Firmicutes (28%–93%) exhibit steeply convex lamination, producing finger-like minicolumnar mesostructures. In contrast, shallow-growing microbialites with a low abundance of Firmicutes (0%–5%) and high abundance of Cyanobacteria (11%–37%) have well-preserved gently convex millimeter-scale lamination, resulting in cauliflower mesostructures. Palygorskite ((Mg, Al)₂Si₄O₁₀(OH)) is identified in the diatom-rich microbial layer of the deep-growing microbialites. Regardless of the microbialite types, hydromagnesite and aragonite are present in the extracellular polymeric substance (EPS)-rich zone of the shallow and deep-growing microbialites. Overall, environmental changes (e.g., water depth and, accommodation space) play a major role in the formation and spatial distribution of different microbialite morphologies at the macro- and mesoscale. Differences in the relative abundance of dominant microorganisms between mesostructured types suggest that mesomorphology may be influenced by changes in microbial diversity. Spatial variations in the microbialite morphotypes, along with the abundant presence of entombed biomass (e.g., mineralized filaments), may indicate areas that have a high potential for the preservation of biosignatures.</p>\u0000 </div>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"22 5","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142277636","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Oceanic and Sedimentary Microbial Sulfur Cycling Controlled by Local Organic Matter Flux During the Ediacaran Shuram Excursion in the Three Gorges Area, South China","authors":"Fumihiro Matsu'ura,&nbsp;Yusuke Sawaki,&nbsp;Tsuyoshi Komiya,&nbsp;Jian Han,&nbsp;Shigenori Maruyama,&nbsp;Takayuki Ushikubo,&nbsp;Kenji Shimizu,&nbsp;Yuichiro Ueno","doi":"10.1111/gbi.12617","DOIUrl":"10.1111/gbi.12617","url":null,"abstract":"&lt;div&gt;\u0000 \u0000 &lt;p&gt;The increased difference in the sulfur isotopic compositions of sedimentary sulfate (carbonate-associated sulfate: CAS) and sulfide (chromium-reducible sulfur: CRS) during the Ediacaran Shuram excursion is attributed to increased oceanic sulfate concentration in association with the oxidation of the global ocean and atmosphere. However, recent studies on the isotopic composition of pyrites have revealed that CRS in sediments has diverse origins of pyrites. These pyrites are formed either in the water column/shallow sediments, where the system is open with respect to sulfate, or in deep sediments, where the system is closed with respect to sulfate. The δ&lt;sup&gt;34&lt;/sup&gt;S value of sulfate in the open system is equal to that of seawater; on the contrary, the δ&lt;sup&gt;34&lt;/sup&gt;S value of sulfate in the closed system is higher than that of seawater. Therefore, obtaining the isotopic composition of pyrites formed in an open system, which most likely retain microbial sulfur isotope fractionation, is essential to reconstruct the paleo-oceanic sulfur cycle. In this study, we carried out multiple sulfur isotope analyses of CRS and mechanically separated pyrite grains (&gt;100 μm) using a fluorination method, in addition to secondary ion mass spectrometry (SIMS) analyses of in situ δ&lt;sup&gt;34&lt;/sup&gt;S values of pyrite grains in drill core samples of Member 3 of the Ediacaran Doushantuo Formation in the Three Gorges area, South China. The isotope fractionation of microbial sulfate reduction (MSR) in the limestone layers of the upper part of Member 3 was calculated to be &lt;sup&gt;34&lt;/sup&gt;&lt;i&gt;ε&lt;/i&gt; = 55.7‰ and &lt;sup&gt;33&lt;/sup&gt;&lt;i&gt;λ&lt;/i&gt; = 0.5129 from the δ&lt;sup&gt;34&lt;/sup&gt;S and Δ&lt;sup&gt;33&lt;/sup&gt;S' values of medium-sized pyrite grains ranging from 100 to 300 μm and the average δ&lt;sup&gt;34&lt;/sup&gt;S and Δ&lt;sup&gt;33&lt;/sup&gt;S' values of CAS. Model calculations revealed that the influence of sulfur disproportionation on the δ&lt;sup&gt;34&lt;/sup&gt;S values of these medium-sized pyrite grains was insignificant. In contrast, within the dolostone layers of the middle part of Member 3, isotope fractionation was determined to be &lt;sup&gt;34&lt;/sup&gt;&lt;i&gt;ε&lt;/i&gt; = 47.5‰. The &lt;sup&gt;34&lt;/sup&gt;&lt;i&gt;ε&lt;/i&gt; value in the middle part of Member 3 was calculated from the average δ&lt;sup&gt;34&lt;/sup&gt;S values of the rim of medium-sized pyrite grains and the average δ&lt;sup&gt;34&lt;/sup&gt;S values of CAS. This observation revealed an increase in microbial sulfur isotope fractionation during the Shuram excursion at the drill core site. Furthermore, our investigation revealed correlations between δ&lt;sup&gt;34&lt;/sup&gt;S&lt;sub&gt;CRS&lt;/sub&gt; values and CRS concentrations and between CRS and TOC concentrations, implying that organic matter load to sediments controlled the δ&lt;sup&gt;34&lt;/sup&gt;S&lt;sub&gt;CRS&lt;/sub&gt; values rather than oceanic sulfate concentrations. However, these CRS and TOC concentrations are local parameters that can change only at the kilometer scale with local redox conditions and the intensity of primary production. Therefore, the decreasing δ&lt;s","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"22 5","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142265664","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}