Geobiology最新文献

{"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}

{"title":"How to Make a Rock in 150 Days: Observations of Biofilms Promoting Rapid Beachrock Formation","authors":"Brianna M. Hibner,&nbsp;Marjorie D. Cantine,&nbsp;Elizabeth J. Trower,&nbsp;Jacqueline E. Dodd,&nbsp;Maya L. Gomes","doi":"10.1111/gbi.70009","DOIUrl":"https://doi.org/10.1111/gbi.70009","url":null,"abstract":"<div>\u0000 \u0000 <p>Beachrock is a type of carbonate-cemented rock that forms via rapid cementation in the intertidal zone. Beachrock is a valuable geological tool as an indicator of paleoshorelines and may protect shorelines from erosion. Previous studies present a range of hypotheses about the processes enabling rapid beachrock formation, which span purely physicochemical mechanisms to a significant role for microbially mediated carbonate precipitation. We designed a set of in situ field experiments to explore the rates and mechanisms of beachrock formation on Little Ambergris Cay (Turks and Caicos Islands). Our field site has evidence for rapid beachrock cementation, including the incorporation of 20th century anthropogenic detritus into beachrock. We deployed pouches of sterilized ooid sand in the upper intertidal zone and assessed the extent of cementation and biofilm development after durations of 4 days, 2.5 months, and 5 months. We observed incipient meniscus cements after only 4 days of incubation in the field, suggesting that physicochemical processes are important in driving initial cementation. After 2.5 months, we observed substantial biofilm colonization on our experimental substrates, with interwoven networks of <i>Halomicronema</i> filaments binding clusters of ooids to the nylon pouches. After 5 months, we observed incipient beachrock formation in the form of coherent aggregates of ooids up to 1 cm in diameter, bound together by both networks of microbial filaments and incipient cements. We interpret that the cyanobacteria-dominated beachrock biofilm community on Little Ambergris Cay plays an important role in beachrock formation through the physical stabilization of sediment as cementation proceeds. Together, this combination of physicochemical and microbial mechanisms enables fresh rock to form in as little as 150 days.</p>\u0000 </div>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"23 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2025-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143362586","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":"Growth of Microbial Mats on Hard Nuclei in Shallow Sandy Environments","authors":"Kendall Valentine,&nbsp;Tanja Bosak,&nbsp;Maria Kondrat'yev,&nbsp;Vanja Klepac-Ceraj,&nbsp;Ashley S. Kleinman,&nbsp;Rebecca Rubinstein,&nbsp;Giulio Mariotti","doi":"10.1111/gbi.70011","DOIUrl":"https://doi.org/10.1111/gbi.70011","url":null,"abstract":"<div>\u0000 \u0000 <p>The growth of most stromatolites is a result of interactions among the growth of microbial mats, mineral precipitation, water flow, and sediment movement. Here, we ask how oxygenic photosynthetic microbes colonize surfaces and interact with sediments in high-energy environments that contain constantly moving sand. For this, we investigate cyanobacterial growth on centimeter-scale concrete spheres in a continuously agitated wave tank. Cyanobacteria are unable to colonize moving sand, but establish biofilms on spheres within 5–6 weeks. These biofilms trap up to 0.5 g/cm² of sand on the top and 0.3 g/cm² on the sides within 25 weeks. The colonization does not depend on the size of the spheres, but instead depends on their surface roughness. Cyanobacteria easily colonize spheres with a surface roughness that matches the bed grain size (0.3 mm), but cannot colonize the initial topographic highs with a roughness of ~0.001 mm. In both cases, recesses on the surfaces of the spheres protect cyanobacteria from sandblasting. Thus, microbial biofilms can become established even in high-energy environments, if topographic highs are large enough not to be rolled around by the flow and rough enough to provide attachment loci. If cementation occurs within biofilms, the interplay among biofilm growth, sediment trapping, and cementation can lead to the upward as well as lateral growth of stromatolites. These experimental observations can explain the preferential upward growth of stromatolites on topographic highs in areas with frequently mobilized sediment grains, including modern stromatolites in the intertidal zone in Shark Bay and the subtidal zone in The Bahamas.</p>\u0000 </div>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"23 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2025-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143362587","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":"Microbially Enhanced Growth and Metal Capture by Ferromanganese Concretions in a Laboratory Experiment","authors":"Renata Majamäki,&nbsp;Joonas Wasiljeff,&nbsp;Lotta Purkamo,&nbsp;Jenni Hultman,&nbsp;Eero Asmala,&nbsp;Pirjo Yli-Hemminki,&nbsp;Kirsten S. Jørgensen,&nbsp;Karoliina Koho,&nbsp;Jukka Kuva,&nbsp;Joonas J. Virtasalo","doi":"10.1111/gbi.70010","DOIUrl":"10.1111/gbi.70010","url":null,"abstract":"<div>\u0000 \u0000 <p>The growth and metal enrichment of ferromanganese minerals on the seafloor have intrigued many studies, yet the role of microbes in the process has remained elusive. Here, we assessed the microbial influence on the growth and trace metal accumulation and release of ferromanganese concretions from the Baltic Sea using 12-week microcosm incubation experiments. We studied three concretion morphotypes: Crust, discoidal, and spheroidal, with biotic and abiotic treatments. The concretion samples were collected into bottles containing artificial brackish seawater from the Gulf of Finland, incubated in in-situ simulating conditions, and sampled at the beginning and end of the experiment. Microscale X-ray-computed tomography confirmed the local growth of up to 10 μm thick patches on the concretion surface during the 12-week incubation period, corresponding to a growth rate of 0.04 mm/year. Scanning electron microscopy of glass slides in the microcosms revealed freshly precipitated cauliflower-like grains, typical of freshly formed Fe- and Mn-hydroxides. Decreased concentrations of dissolved trace metals (Mn, Fe Co, V, Ni, Zn, and Mo) in the incubation solutions indicated the accumulation of these elements into concretions in the biotic microcosms. In contrast, the dissolution of concretions was observed in abiotic microcosms, confirming that microbial activity enhanced the ferromanganese precipitation and the associated accumulation and release of P and trace metals into the ambient solution. The microbial contribution was confirmed by a strong decrease in headspace methane concentrations in biotic microcosms, further indicating the presence of active methanotrophs in the concretion communities.</p>\u0000 </div>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"23 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2025-02-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143078262","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":"Cyanobacteria Boring Limestones in Freshwater Settings—Their Pioneering Role in Sculpturing Pebbles and Carbonate Dissolution","authors":"Andreas Wetzel,&nbsp;Jakob Zopfi,&nbsp;Alfred Uchman","doi":"10.1111/gbi.70006","DOIUrl":"10.1111/gbi.70006","url":null,"abstract":"<div>\u0000 \u0000 <p>In freshwater lakes and rivers, cyanobacteria belonging to the family Leptolyngbyaceae bore &gt; 1 mm deep into limestone pebbles by dissolving carbonate at the tip of their 3–8 μm-thick filaments. The abundance of these borings decreases downward while it is so high at the rock surface that micrometric debris is formed. Moreover, the disintegrated material on the pebbles' surface can be easily removed, for instance, when pebbles are grinding against each other due to wave or current action or when insect larvae settle and scratch loosened grains from the surface while constructing their cases. After a larvae case has been abandoned, it decays with time and the surface benath it is colonized again by boring cyanobacteria. These processes can alternate repeatedly and lead to a sculptured appearance of the pebbles, especially because insect larvae tend to colonize already existing depressions where they are better protected from predation and where they can access suspended food more easily. In the sculptures entrenched by insect larvae, larvae of byssate bivalves like <i>Dreissena polymorpha</i> may settle. When growing, these bivalves also remove loosened carbonate from the bored surface. Thus, boring cyanobacteria play a pioneering, preconditioning role in the morphological evolution of limestone (pebble) surfaces by transforming an initially hard substrate into a firm- to softground that is subsequently colonized and structured by animals. Consequently, sculptured pebbles are the product of multiphase, preconditioned bioerosion. Ultimately, the synergistic effects of these bioerosive processes result in the dissolution of carbonate leading to a maximum take-up of approximately 0.5–0.8 kg CO₂ per square meter and year, as a preliminary estimate indicates.</p>\u0000 </div>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"23 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-12-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142890713","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":"Early-Branching Cyanobacteria Grow Faster and Upregulate Superoxide Dismutase Activity Under a Simulated Early Earth Anoxic Atmosphere","authors":"Sadia S. Tamanna,&nbsp;Joanne S. Boden,&nbsp;Kimberly M. Kaiser,&nbsp;Nicola Wannicke,&nbsp;Jonas Höring,&nbsp;Patricia Sánchez-Baracaldo,&nbsp;Marcel Deponte,&nbsp;Nicole Frankenberg-Dinkel,&nbsp;Michelle M. Gehringer","doi":"10.1111/gbi.70005","DOIUrl":"10.1111/gbi.70005","url":null,"abstract":"<p>The evolution of oxygenic photosynthesis during the Archean (4–2.5 Ga) required the presence of complementary reducing pathways to maintain the cellular redox balance. While the timing of the evolution of superoxide dismutases (SODs), enzymes that convert superoxide to hydrogen peroxide and O₂, within bacteria and archaea is not resolved, the first SODs appearing in cyanobacteria contained copper and zinc in the reaction center (CuZnSOD). Here, we analyse growth characteristics, SOD gene expression (qRT-PCR) and cellular enzyme activity in the deep branching strain, <i>Pseudanabaena</i> sp. PCC7367, previously demonstrated to release significantly more O₂ under anoxic conditions. The observed significantly higher growth rates (<i>p</i> &lt; 0.001) and protein and glycogen contents (<i>p</i> &lt; 0.05) in anoxically cultured <i>Pseudanabaena</i> PCC7367 compared to control cultures grown under present-day oxygen-rich conditions prompted the following question: Is the growth of <i>Pseudanabaena</i> sp. PCC7367 correlated to atmospheric <i>p</i>O₂ and cellular SOD activity? Expression of <i>sodB</i> (encoding FeSOD) and <i>sodC</i> (encoding CuZnSOD) strongly correlated with medium O₂ levels (<i>p</i> &lt; 0.001). Expression of <i>sodA</i> (encoding MnSOD) correlated significantly to SOD activity during the day (<i>p</i> = 0.019) when medium O₂ concentrations were the highest. The cellular SOD enzyme activity of anoxically grown cultures was significantly higher (<i>p</i> &lt; 0.001) 2 h before the onset of the dark phase compared to O₂-rich growth conditions. The expression of SOD encoding genes was significantly reduced (<i>p</i> &lt; 0.05) under anoxic conditions in stirred cultures, as were medium O₂ levels (<i>p</i> ≤ 0.001), compared to oxic-grown cultures, whereas total cellular SOD activity remained comparable. Our data suggest that increasing <i>p</i>O₂ negatively impacts the viability of early cyanobacteria, possibly by increasing photorespiration. Additionally, the increased expression of superoxide-inactivating genes during the dark phase suggests the increased replacement rates of SODs under modern-day conditions compared to those on early Earth.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"22 6","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11636452/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142811690","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":"Crystallization Pathways of Iron Formations: Insights From Magnetic Properties and High-Resolution Imaging of the 2.7 Ga Carajás Formation, Brazil","authors":"Livia Teixeira,&nbsp;Julie Carlut,&nbsp;Eric Siciliano Rego,&nbsp;Ricardo I.F. Trindade,&nbsp;Pascal Philippot","doi":"10.1111/gbi.70008","DOIUrl":"10.1111/gbi.70008","url":null,"abstract":"<p>Banded iron formations (BIFs) are chemical sedimentary rocks commonly utilized for exploring the chemistry and redox state of the Precambrian ocean. Despite their significance, many aspects regarding the crystallization pathways of iron oxides in BIFs remain loosely constrained. In this study, we combine magnetic properties characterization with high-resolution optical and electron imaging of finely laminated BIFs from the 2.7 Ga Carajás Formation, Brazil, to investigate their nature and potential for preserving ancient environmental conditions. Our findings reveal that magnetite, in the form of large 0.1–0.5 mm crystals, is the main iron oxide, with an overall averaged saturation magnetization (<i>M</i>_s) of 25 Am²/kg (corresponding to ~27 wt% of magnetite) over the studied 230 m of the sequence. Nevertheless, the non-negligible contribution of minerals with higher coercivity suggests variable proportions of hematite along the core. Additionally, we observe non-uniform behavior in magnetite grains, with distinct populations identified through low-temperature measurements of the Verwey transition. Petrographic observations indicate that the original sediment was an Fe–Si mud consisting of a ferrihydrite–silica mixture formed in the water column. This assemblage was rapidly transformed into nano-scale hematite embedded in silica as indicated by a honeycomb structure composed of Si-spherules distributed in a microscale hematite matrix. Textural relationships show that the nucleation of magnetite started during or soon after the formation of hematite, as indicated by the preservation of the Si-spherules within magnetite cores. Further magnetite overgrowth stages are characterized by inclusion-free rims, associated with continuous Si supply during the evolving diagenetic or early metamorphic stages. These findings, combined with existing literature, suggest that ferrihydrite precipitated alongside Si and organic material, later crystallizing as hematite on the seafloor. Anaerobic respiration by Fe(III)-reducing microorganisms likely contributed to early magnetite formation in a fluid-saturated, unconsolidated sediment. Subsequent low-grade metamorphism and Si mobilization led to palisade quartz precipitation and a second stage of magnetite growth likely formed at the expense of matrix hematite through thermochemical Fe(III) reduction. Low-temperature magnetic analyses revealed that the two generations of magnetite core and rim are associated with specific stoichiometry.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"22 6","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11638513/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142816678","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":"The Impact of Early Diagenesis on Biosignature Preservation in Sulfate Evaporites: Insights From Messinian (Late Miocene) Gypsum","authors":"Luca Pellegrino,&nbsp;Marcello Natalicchio,&nbsp;Andrea Cotellucci,&nbsp;Andrea Genre,&nbsp;Richard W. Jordan,&nbsp;Giorgio Carnevale,&nbsp;Francesco Dela Pierre","doi":"10.1111/gbi.70007","DOIUrl":"10.1111/gbi.70007","url":null,"abstract":"<p>Due to their fast precipitation rate, sulfate evaporites represent excellent repositories of past life on Earth and potentially on other solid planets. Nevertheless, the preservation potential of biogenic remains can be compromised by extremely fast early diagenetic processes. The upper Miocene, gypsum-bearing sedimentary successions of the Mediterranean region, that formed <i>ca.</i> 6 million years ago during the Messinian salinity crisis, represent an excellent case study for investigating these diagenetic processes at the expense of organic matter and associated biominerals. Several gypsum crystals from the Northern Mediterranean were studied by means of destructive and non-destructive techniques in order to characterize their solid inclusion content and preservation state. In the same crystal, excellently preserved microfossils coexist with strongly altered biogenic remains. Altered remains are associated with authigenic minerals, especially clays. The results demonstrate that a significant fraction of organic matter and associated biominerals (notably biogenic silica) underwent early diagenetic modification. The latter was likely triggered by bottom sulfidic conditions when the growth of gypsum was interrupted. These results have significant implications for the interpretation of the Messinian Salt Giant.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"22 6","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11629073/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142798904","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 in Their Heyday: Iron-Oxidizing Bacteria Bloomed in Shallow-Marine, Subtidal Environments at ca. 1.88 Ga","authors":"Alex Kovalick,&nbsp;Andy W. Heard,&nbsp;Aleisha C. Johnson,&nbsp;Clara S. Chan,&nbsp;Luke Ootes,&nbsp;Sune G. Nielsen,&nbsp;Nicolas Dauphas,&nbsp;Bodo Weber,&nbsp;Andrey Bekker","doi":"10.1111/gbi.70003","DOIUrl":"10.1111/gbi.70003","url":null,"abstract":"<p>The majority of large iron formations (IFs) were deposited leading up to Earth's great oxidation episode (GOE). Following the GOE, IF deposition decreased for almost 500 Myr. Subsequently, around 1.88 Ga, there was widespread deposition of shallow-water granular iron formations (GIF) within a geologically short time interval, which has been linked to enhanced iron (Fe) supply to seawater from submarine hydrothermal venting associated with the emplacement of large igneous provinces. Previous studies of Fe-rich, microfossil-bearing stromatolites from the ca. 1.88 Ga Gunflint Formation on the Superior craton suggested direct microbial oxidation of seawater Fe²⁺_(aq) by microaerophilic, Fe-oxidizing bacteria (FeOB), as a driver of GIF deposition. Although Fe-rich, microfossil-bearing stromatolites are common in 1.88 Ga GIF deposits on several cratons, combined paleontological and geochemical studies have been applied only to the Gunflint Formation. Here, we present new paleontological and geochemical observations for the ca. 1.89 Ga Gibraltar Formation GIFs from the East Arm of the Great Slave Lake, Northwest Territories, Canada. Fossil morphology, Rare Earth element (REE) concentrations, and Fe isotopic compositions support Fe oxidation by FeOB at a redoxcline poised above the fair-weather wave base. Small positive Eu anomalies and positive ε_Nd (1.89 Ga) values suggest upwelling of deep, Fe-rich, hydrothermally influenced seawater. While high [Fe²⁺_(aq)] combined with low atmospheric pO₂ in the late Paleoproterozoic would have provided optimal conditions in shallow oceans for FeOB to precipitate Fe oxyhydroxide, these redox conditions were likely toxic to cyanobacteria. As long as local O₂ production by cyanobacteria was strongly diminished, FeOB would have had to rely on an atmospheric O₂ supply by diffusion to shallow seawater to oxidize Fe²⁺_(aq). Using a 1-D reaction dispersion model, we calculate [O_2(aq)] sufficient to deplete an upwelling Fe²⁺_(aq) source. Our results for GIF deposition are consistent with late Paleoproterozoic pO₂ estimates of ~1%–10% PAL and constraints for metabolic [O_2(aq)] requirements for modern FeOB. Widespread GIF deposition at ca. 1.88 Ga appears to mark a temporally restricted episode of optimal biogeochemical conditions in Earth's history when increased hydrothermal Fe²⁺_(aq) sourced from the deep oceans, in combination with low mid-Paleoproterozoic atmospheric pO₂, globally satisfied FeOB metabolic Fe²⁺_(aq) and O_2(aq) requirements in shallow-marine subtidal environments above the fair-weather wave base.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"22 6","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11621254/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142783522","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}