Geobiology最新文献

{"title":"Troubles With Tubules: How Do Iron-Mineral Chemical Gardens Differ From Iron-Mineralized Sheaths of Iron Oxidizing Bacteria?","authors":"Melanie Podbielski,&nbsp;Pamela Knoll,&nbsp;Georgia Brown,&nbsp;Sigrid Huld,&nbsp;Anna Neubeck,&nbsp;Julyan H. E. Cartwright,&nbsp;C. Ignacio Sainz-Díaz,&nbsp;Carlos Pimentel,&nbsp;Sean McMahon","doi":"10.1111/gbi.70021","DOIUrl":"https://doi.org/10.1111/gbi.70021","url":null,"abstract":"<p>Microscopic tubules and filaments composed of iron minerals occur in various rock types of all ages. Although typically lacking carbonaceous matter, many are reasonably interpreted as the remains of filamentous microorganisms coated with crystalline iron oxyhydroxides. Iron-oxidizing bacteria (IOB) acquire such a coating naturally during life. However, recent debates about purported microfossils have highlighted the potential for self-organized nonbiological mineral growth (particularly in chemical gardens) to form compositionally and morphologically similar tubules. How can biogenic and abiogenic iron-mineral tubules be differentiated? Here, we use optical and electron microscopy and Mössbauer spectroscopy to compare the composition, microtexture, and morphology of ferruginous chemical gardens and iron-mineralized sheaths of bacteria in the genus <i>Leptothrix</i>. Despite broad morphological similarity, we find that <i>Leptothrix</i> exhibits a narrower range of filament diameters and lower filament tortuosity than chemical gardens. Chemical gardens produced from a ferrous salt also tend to incorporate Fe²⁺ whereas <i>Leptothrix</i> sheaths predominantly do not. Finally, the oxyhydroxides formed in <i>Leptothrix</i> sheaths tend to be smoother and denser on the inward-facing side, rougher and sparser on the outward side, whereas for chemical garden tubules the reverse is true. Some of these differences show promise for the diagnosis of natural samples.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"23 3","pages":""},"PeriodicalIF":2.7,"publicationDate":"2025-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/gbi.70021","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143949745","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":"Cretaceous Chert-Hosted Microfossils Visualized With Synchrotron Ptychographic X-Ray Computed Tomography (PXCT)","authors":"Kelsey R. Moore,&nbsp;Theodore M. Present,&nbsp;Antoine Crémière,&nbsp;Manuel Guizar-Sicairos,&nbsp;Mirko Holler,&nbsp;Andrew Barnett,&nbsp;Kristin Bergmann,&nbsp;Joachim Amthor,&nbsp;John Grotzinger","doi":"10.1111/gbi.70019","DOIUrl":"https://doi.org/10.1111/gbi.70019","url":null,"abstract":"<p>Silicification of microfossils is an important taphonomic process that provides a record of microbial life across a range of environments throughout Earth history. However, questions remain regarding the mechanism(s) by which silica precipitated and preserved delicate organic material and detailed cellular morphologies. Constraining the different mechanisms of silica precipitation and identifying the common factors that allow for microfossil preservation is the key to understanding ancient microbial communities and fossil-preserving mechanisms. Here, we use synchrotron ptychographic X-ray computed tomography (PXCT) as a novel technique to analyze microfossils from the Cretaceous Barra Velha Formation and better characterize their diverse morphologies and preservation styles. Through this technique, we generate 2D and 3D reconstructions that illustrate the microfossils and silica-organic textures at nanometer resolution. At this resolution, we identify previously uncharacterized silica textures and organic-silica relationships that help us relate findings from modern silicifying environments and experimental work to the fossil record. Additionally, we identify primary morphological differences among the microfossils as well as preservational variability that may have been driven by physiological and/or biochemical differences between the different organisms that inhabited the Cretaceous pre-salt basin. These findings help us to better characterize the diversity and complexity of the microbiota in this ancient basin as well as taphonomic processes and biases that may have driven microfossil preservation in this and other silicifying environments throughout Earth history.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"23 3","pages":""},"PeriodicalIF":2.7,"publicationDate":"2025-05-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/gbi.70019","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143938810","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":"Stromatolitic Mounds in Tidal-Facies Sandstones of the Paleoarchean Moodies Group (Barberton Greenstone Belt, Eswatini)","authors":"Sebastian Reimann,&nbsp;Martin Homann,&nbsp;Deon J. Janse van Rensburg,&nbsp;Michael Wiedenbeck,&nbsp;Christian Hallmann,&nbsp;Runa Antony,&nbsp;Christoph Heubeck","doi":"10.1111/gbi.70020","DOIUrl":"https://doi.org/10.1111/gbi.70020","url":null,"abstract":"<p>Shallow-marine environments are thought to have been pivotal to the spreading, perhaps even the origin, of early life on Earth. The shallow-marine Archean sedimentary record of early life, however, is biased towards carbonates; nearshore siliciclastic environments have not received proportional attention. Here we describe densely laminated, silicified and dolomitized fossil calcareous mounds in tidal-facies sandstones of the Archean Moodies Group (ca. 3.22 Ga) in the Barberton Greenstone Belt, Eswatini. They vary between (1) cm- to dm-scale, isolated, club- to pedestal-shaped, nodular mounds on top of and within the conduits of fluid-escape structures, and (2) mm- to cm-scale, undulatory and wavily laminated structures, interbedded with well-bedded silt- and sandstones. Geochemical indicators of a possible biogenic origin were largely obliterated by local hydrothermal alteration and regional lower-greenschist-facies metamorphism: In situ SIMS δ¹³C_carb isotope analyses from several traverses across the best-preserved laminae of a mound and δ³⁴S_VCDT values from diagenetic rims of nearby detrital pyrite grains yield ambiguous isotopic evidence about biologic processing; TOC of putative laminae is too low to measure δ¹³C_org, and Raman spectroscopy of finely dispersed carbonaceous particles and of kerogenous laminae indicate mean maximum metamorphic temperature of ca. 500°C. Textural and regional evidence, however, suggests that the carbonate laminae represent metabolic products of microbial communities that took advantage of sand volcanoes from which nutrient-rich fluids erupted episodically. We base this inference on the habitable depositional setting on a wave- or current-swept photic-zone tidal platform, the stromatolitic morphologies in two and three dimensions, the occurrence of in-situ kerogen, the carbonate mineralogy, and the presence of comparable mound structures elsewhere in the Moodies Group. Although the metabolic strategies utilized by the microorganisms remain unknown, this occurrence places a novel ecologic niche in the Paleoarchean microbial colonization of coastal regions.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"23 3","pages":""},"PeriodicalIF":2.7,"publicationDate":"2025-05-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/gbi.70020","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143896891","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":"Elevated δ15N Linked to Inhibited Nitrification Coupled to Ammonia Volatilization in Sediments of Shallow Alkaline-Hypersaline Lakes","authors":"Christopher J. Tino,&nbsp;Eva E. Stüeken,&nbsp;Daniel D. Gregory,&nbsp;Timothy W. Lyons","doi":"10.1111/gbi.70018","DOIUrl":"https://doi.org/10.1111/gbi.70018","url":null,"abstract":"<p>Alkaline lakes are among the most bioproductive aquatic ecosystems on Earth. The factors that ultimately limit productivity in these systems can vary, but nitrogen (N) cycling in particular has been shown to be adversely affected by high salinity, evidently due to the inhibition of nitrifying bacteria (i.e., those that convert ammonic species to nitrogen oxides). The coastal plain of Coorong National Park in South Australia, which hosts several alkaline lakes along 130 km of coastline, provides an ideal natural laboratory for examining how fine-scale differences in the geochemistry of such environments can lead to broad variations in nitrogen cycling through time, as manifest in sedimentary δ¹⁵N. Moreover, the lakes provide a gradient of aqueous conditions that allows us to assess the effects of pH, salinity, and carbonate chemistry on the sedimentary record. We report a wide range of δ¹⁵N values (3.8‰–18.6‰) measured in the sediments (0–35 cm depth) of five lakes of the Coorong region. Additional data include major element abundances, carbonate δ¹³C and δ¹⁸O values, and the results of principal component analyses. Stable nitrogen isotopes and wt% sodium (Na) display positive correlation (<i>R</i>² = 0.59, <i>p</i> &lt; 0.001) across all lake systems. Principal component analyses further support the notion that salinity has historically impacted nitrogen cycling. We propose that the inhibition of nitrification at elevated salinity may lead to the accumulation of ammonic species, which, when exposed to the water column, are prone to ammonia volatilization facilitated by intervals of elevated pH. This process is accompanied by a significant isotope fractionation effect, isotopically enriching the nitrogen that remains in the lake water. This nitrogen is eventually buried in the sediments, preserving a record of these combined processes. Analogous enrichments in the rock record may provide important constraints on past chemical conditions and their associated microbial ecologies. Specifically, ancient terrestrial aquatic systems with high δ¹⁵N values attributed to denitrification and thus oxygen deficiency may warrant re-evaluation within the framework of this alternative. Constraints on pH as provided by elevated δ¹⁵N via ammonia volatilization may also inform critical aspects of closed-basin paleoenvironments and their suitability for a de novo origin of life.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"23 2","pages":""},"PeriodicalIF":2.7,"publicationDate":"2025-04-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/gbi.70018","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143770126","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":"Elevated Marine Dissolved Silica Levels Explain a Wide Range of Ediacaran–Cambrian Ediacara-Style Fossil Deposits","authors":"Lidya G. Tarhan,&nbsp;Ashleigh v. S. Hood,&nbsp;Mary L. Droser","doi":"10.1111/gbi.70017","DOIUrl":"https://doi.org/10.1111/gbi.70017","url":null,"abstract":"<div>\u0000 \u0000 <p>The processes responsible for the fossilization of the Ediacara Biota—Earth's earliest fossil record of communities of complex, multicellular organisms—have long been debated. On the basis of both geologic and experimental investigations, recent studies have proposed that early diagenetic silica cementation may have been pivotal to the moldic preservation in sandstone (“Ediacara-style preservation”) of fossil assemblages from the eponymous Ediacara Member of South Australia. However, the extent to which early silica cementation can explain other instances of Ediacara-style fossilization in units recording disparate depositional environments, paleogeographies, and geologic ages has not been previously constrained. Herein, we present new paleontological, petrographic, and geochemical data from a range of Ediacara-style fossil assemblages, encompassing a variety of Ediacaran and Cambrian macroorganism morphologies, ecologies, and taxonomic affinities, as well as sedimentary records of organic substrates and the macrofaunal interactions they record. These data indicate that the early diagenetic formation of silica cements was a widespread phenomenon in Ediacaran and Cambrian sandy seafloor environments and likely played a pivotal role in the preservation of these exceptional fossil assemblages. Moreover, the persistence of Ediacara-style fossilization linked to authigenic silica cementation into Cambrian strata provides new evidence that the end-Ediacaran disappearance of the Ediacara Biota was due to evolutionary rather than taphonomic phenomena.</p>\u0000 </div>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"23 2","pages":""},"PeriodicalIF":2.7,"publicationDate":"2025-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143761966","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":"Evaluating Serpentinization as a Source of Phosphite to Microbial Communities in Hydrothermal Vents","authors":"Joanne S. Boden,&nbsp;Sanjoy M. Som,&nbsp;William J. Brazelton,&nbsp;Rika E. Anderson,&nbsp;Eva E. Stüeken","doi":"10.1111/gbi.70016","DOIUrl":"https://doi.org/10.1111/gbi.70016","url":null,"abstract":"<p>Previous studies have documented the presence of phosphite, a reduced and highly soluble form of phosphorus, in serpentinites, which has led to the hypothesis that serpentinizing hydrothermal vents could have been an important source of bioavailable phosphorus for early microbial communities in the Archean. Here, we test this hypothesis by evaluating the genomic hallmarks of phosphorus usage in microbial communities living in modern hydrothermal vents with and without influence from serpentinization. These genomic analyses are combined with results from a geochemical model that calculates phosphorus speciation during serpentinization as a function of temperature, water:rock ratio, and lithology at thermodynamic equilibrium. We find little to no genomic evidence of phosphite use in serpentinizing environments at the Voltri Massif or the Von Damm hydrothermal field at the Mid Cayman Rise, but relatively more in the Lost City hydrothermal field, Coast Range Ophiolite Microbial Observatory, The Cedars, and chimney samples from Old City hydrothermal field and Prony Bay hydrothermal field, as well as in the non-serpentinizing hydrothermal vents at Axial Seamount. Geochemical modeling shows that phosphite production is favored at ca 275°C–325°C and low water:rock ratios, which may explain previous observations of phosphite in serpentinite rocks; however, most of the initial phosphate is trapped in apatite during serpentinization, suppressing the absolute phosphite yield. As a result, phosphite from serpentinizing vents could have supported microbial growth around olivine minerals in chimney walls and suspended aggregates, but it is unlikely to have fueled substantial primary productivity in diffusely venting fluids during life's origin and evolution in the Archean unless substrates equivalent to dunites (composed of &gt; 90 wt% olivine) were more common.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"23 2","pages":""},"PeriodicalIF":2.7,"publicationDate":"2025-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/gbi.70016","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143690138","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":"Experimental Mineralisation of a Filamentous Hydrogenotrophic Methanogen in Carbonate, Phosphate, and Silicate","authors":"Sigrid Huld,&nbsp;Sean McMahon,&nbsp;Sebastian Willman,&nbsp;Anna Neubeck","doi":"10.1111/gbi.70014","DOIUrl":"https://doi.org/10.1111/gbi.70014","url":null,"abstract":"<p>Methanogenic archaea were likely among the earliest organisms to populate the Earth, perhaps contributing to the Archaean greenhouse effect; they are also widely discussed as analogues to any potential life on Mars. However, fossil evidence of archaea has been difficult to identify in the rock record, perhaps because their preservation potential is intrinsically low or because they are particularly small and difficult to identify. Here, we examined the preservation potential of a methanogen of the genus <i>Methanobacterium</i>, recently isolated from a low-temperature serpentinizing system, an environment somewhat analogous to habitats on the early Earth and Mars. Notably, this organism has a cell wall composed of peptidoglycan-like pseudomurein, which may imply a mineralisation potential similar to that of gram-positive bacteria. <i>Methanobacterium</i> cells were placed in carbonate, phosphate, and silicate solutions for up to 3 months in order to assess the relative tendency of these minerals to encrust and preserve cellular morphology. Cells readily acquired a thick, uniform coating of silica, enhancing their potential for long-term preservation while also increasing overall filament size, an effect that may aid the discovery of fossil archaea while hindering their interpretation. Phosphates precipitated from the medium in all experimental setups and even in parallel experiments set up with low-phosphate medium, suggesting a hitherto unknown biomineralisation capacity of methanogens. Carbonate precipitates did not form in close association with cells.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"23 2","pages":""},"PeriodicalIF":2.7,"publicationDate":"2025-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/gbi.70014","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143629878","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":"An Anaerobic Microbial Community Mediates Epigenetic Native Sulfur and Carbonate Formation During Replacement of Messinian Gypsum at Monte Palco, Sicily","authors":"Simon E. Rouwendaal,&nbsp;Daniel Birgel,&nbsp;Marcello Natalicchio,&nbsp;Francesco Dela Pierre,&nbsp;Laetitia Guibourdenche,&nbsp;Thorsten Bauersachs,&nbsp;Giovanni Aloisi,&nbsp;Amanda L. Labrado,&nbsp;Benjamin Brunner,&nbsp;Jörn Peckmann","doi":"10.1111/gbi.70015","DOIUrl":"https://doi.org/10.1111/gbi.70015","url":null,"abstract":"<p>The microbially mediated replacement of sulfate-bearing evaporites by authigenic carbonate and native sulfur under anoxic conditions is poorly understood. Sulfur-bearing carbonates from the Monte Palco ridge (Sicily) replacing Messinian gypsum were therefore studied to better characterize the involved microorganisms. The lack of (1) sedimentary bedding, (2) lamination, and (3) significant water-column-derived lipid biomarkers in the secondary carbonates implies replacement after gypsum deposition (epigenesis). Allochthonous clasts from the older Calcare di Base and the younger Trubi Formation within these carbonates further evidence epigenetic formation. The sulfur-bearing carbonates are significantly ¹³C-depleted (δ¹³C as low as −51‰), identifying methane as a major carbon source. The ¹⁸O-enrichment of the carbonates (δ¹⁸O as high as 5.4‰) probably reflects precipitation from ¹⁸O-enriched fluids transported along adjacent faults or precipitation in a closed system with very little water. Native sulfur with variable ³⁴S-enrichment (δ³⁴S as high as 18.9‰), a relatively small maximum offset (12.3‰) between the sulfate source (gypsum) and native sulfur, and high δ³⁴S values of carbonate-associated sulfate (as high as 61.1‰) suggest a high conversion to native sulfur in a (semi-)closed system, with insignificant sulfate removal. Anaerobic methanotrophic archaea (ANME) apparently affiliated with the ANME-1 clade mediated secondary mineral formation as evidenced by the biomarker inventory, which contains abundant ¹³C-depleted isoprenoids including <i>sn3</i>-hydroxyarchaeol as the sole hydroxyarchaeol isomer and glycerol dibiphytanyl glycerol tetraethers (GDGTs). A series of various, tentatively identified ¹³C-depleted non-isoprenoidal dialkyl glycerol diethers (DAGEs), 10me-C₁₆ fatty acid, hydroxy C₁₆ fatty acids, and cyclopropyl-C_17:0ω7,8 fatty acid agree with sulfate-reducing bacteria participating in the anaerobic oxidation of methane. Specific conditions during gypsum replacement, unlike those at marine methane seeps, are reflected by the occurrence of ¹³C-depleted lipids such as lycopane, 9me-C₁₇ fatty acid, and novel DAGEs. As a response to a confined environment probably characterized by high sulfate concentrations, sulfidic conditions, and elevated salinity, ANMEs and sulfate-reducing bacteria apparently adapted their membrane compositions to cope with such stressors.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"23 2","pages":""},"PeriodicalIF":2.7,"publicationDate":"2025-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/gbi.70015","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143555086","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":"Microbial Cycling of Sulfur and Other Redox-Sensitive Elements in Porewaters of San Clemente Basin, California, and Cocos Ridge, Costa Rica","authors":"Daniela Osorio-Rodriguez,&nbsp;Frank J. Pavia,&nbsp;Daniel R. Utter,&nbsp;Matthew Quinan,&nbsp;Kameko Landry,&nbsp;Maya Gomes,&nbsp;Nathan D. Dalleska,&nbsp;Victoria J. Orphan,&nbsp;William M. Berelson,&nbsp;Jess F. Adkins","doi":"10.1111/gbi.70013","DOIUrl":"https://doi.org/10.1111/gbi.70013","url":null,"abstract":"<div>\u0000 \u0000 <p>The microbial recycling of organic matter in marine sediments depends upon electron acceptors that are utilized based on availability and energetic yield. Since sulfate is the most abundant oxidant once oxygen has been depleted, the sulfide produced after sulfate reduction becomes an important electron donor for autotrophic microbes. The ability of sulfide to be re-oxidized through multiple metabolic pathways and intermediates with variable oxidation states prompts investigation into which species are preferentially utilized and what are the factors that determine the fate of reduced sulfur species. Quantifying these sulfur intermediates in porewaters is a critical first step towards achieving a more complete understanding of the oxidative sulfur cycle, yet this has been accomplished in very few studies, none of which include oligotrophic sedimentary environments in the open ocean. Here we present profiles of porewater sulfur intermediates from sediments underlying oligotrophic regions of the ocean, which encompass about 75% of the ocean's surface and are characterized by low nutrient levels and productivity. Aiming at addressing uncertainties about if and how sulfide produced by the degradation of scarce sedimentary organic matter plays a role in carbon fixation in the sediment, we determine depth profiles of redox-sensitive metals and sulfate isotope compositions and integrate these datasets with 16S rRNA microbial community composition data and solid-phase sulfur concentrations. We did not find significant correlations between sulfur species or trace metals and specific sulfur cycling taxa, which suggests that microorganisms in pelagic and oxic sediments may be generalists utilizing flexible metabolisms to oxidize organic matter through different electron acceptors.</p>\u0000 </div>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"23 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2025-02-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143446821","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":"Untangling the Primary Biotic and Abiotic Controls on Oxygen, Inorganic and Organic Carbon Isotope Signals in Modern Microbialites","authors":"Robin Havas,&nbsp;Christophe Thomazo,&nbsp;Jeanne Caumartin,&nbsp;Miguel Iniesto,&nbsp;Hugo Bert,&nbsp;Didier Jézéquel,&nbsp;David Moreira,&nbsp;Rosaluz Tavera,&nbsp;Vladimir Bettencourt,&nbsp;Purificación López-García,&nbsp;Emmanuelle Vennin,&nbsp;Karim Benzerara","doi":"10.1111/gbi.70012","DOIUrl":"https://doi.org/10.1111/gbi.70012","url":null,"abstract":"<p>Microbialites are organo-sedimentary structures formed throughout most of the Earth history, over a wide range of geological contexts, and under a multitude of environmental conditions affecting their composition. The carbon and oxygen isotope records of carbonates, which are most often their main constituents, have been used as a widespread tool for paleoenvironmental reconstructions. However, the multiplicity of factors that influence microbialites formation is not always properly distinguished in their isotopic record, in both ancient and modern settings. It is therefore crucial to refine our understanding of the processes controlling microbialites isotopic signal. Here, we analyzed the carbon and oxygen isotope compositions from bulk and micro-drilled carbonates as well as bulk organic carbon isotope compositions in microbialites from four Mexican volcanic crater lakes of increasing alkalinity. The survey of four lakes allows comparing microbialite formation processes and their geochemical record within distinct physico-chemical contexts. The geochemical analyses were performed in parallel to petrographic and mineralogical characterization and interpreted in light of the known microbial community composition for microbialites of the same lakes. Combining these data, we show that the potential for isotopic biosignature preservation primarily depends on physico-chemical conditions. Carbon isotope biosignatures pointing out to an autotrophic influence on carbonate precipitation are preserved in the lowest alkalinity lakes. By contrast, higher alkalinity lakes, where microbialites are more massive, favor carbonate precipitation in isotopic equilibrium with the lake water, with secondary influence of heterotrophic organic carbon degradation. From these results, we suggest that microbialite carbonate C isotope records can be interpreted as the balance between the microbialite net primary productivity and the amount of precipitation that relates to physico-chemical forcing. The signals of microbialite oxygen isotope compositions highlight a lack of understanding in the oxygen isotope records of relatively rare carbonate phases such as hydromagnesite. Nonetheless, we show that these signals are primarily influenced by the basins' hydrology, though biological effects may also play a (minor) role. Overall, both carbon and oxygen isotopic signals may record a mixture of different local/global and biotic/abiotic phenomena, making microbialites intricate archives of their growth environment, which should thus be interpreted with cautions and in the light of their surrounding sediments.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"23 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2025-02-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/gbi.70012","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143423638","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}