Geobiology最新文献

{"title":"Understanding Ferruginous Versus Euxinic Conditions by Simulating Microbial Conditions in Meromictic Lakes","authors":"Vanessa M. Hawkins,&nbsp;Cody S. Sheik,&nbsp;Sergei Katsev","doi":"10.1111/gbi.70037","DOIUrl":"https://doi.org/10.1111/gbi.70037","url":null,"abstract":"<p>Ferruginous (iron-rich) conditions have been prominent in oceans throughout the Earth's geologic history but now are reliably found only in a handful of permanently stratified lakes. Microbially mediated iron reduction in such anoxic environments competes with sulfate reduction, which promotes euxinic (sulfide-rich) conditions. Besides the shared demand for organic compounds, the competition is fostered by the produced hydrogen sulfide, which may reduce iron oxides abiotically or co-precipitate with dissolved iron as iron sulfides. Understanding why some environments develop ferruginous rather than euxinic conditions (or vice versa), as well as the attendant effects on methanogenic fermentation, is key to understanding both modern and ancient anoxic ecosystems. Here, we reproduce biogeochemical distributions in multiple anoxic, low-sulfate, meromictic lakes around the world using a biomass-explicit reaction-transport model with a fixed set of metabolism-specific microbial parameters. The results suggest that sulfate reduction and methanogenesis are ubiquitous even in iron-rich systems, and are reflected in microbial surveys. Ferruginous conditions typically develop for surface sulfate concentrations below ≃100 μM. Interestingly, there seems to be a dearth of stably stratified water bodies where sulfate concentrations can persist in the medium-sulfate range of several hundred μM. Rather, when sulfur burial into the sediments becomes iron limited, sulfate tends to accumulate in the water column to much higher (mM) concentrations. A similar mechanism could be suggested to have operated in the variably sulfidic and ferruginous water columns of early oceans. Model simulations also reveal the previously underappreciated role of physical transport in shaping biogeochemical distributions, as minor variations in mixing rates can lead to large variations in microbial abundances. Model applicability across multiple lakes points to an encouraging possibility that geochemical patterns in complex biogeochemical systems may be described from a small number of thermodynamic and kinetic principles using a minimum of fitting parameters.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"23 5","pages":""},"PeriodicalIF":3.4,"publicationDate":"2025-10-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/gbi.70037","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145317800","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":"Biogeochemistry of an Iron- and Manganese-Rich Stratified Lake: Tasik Biru, Malaysia, as a Modern Model Habitat for the Ancient Ocean","authors":"Muammar Mansor,&nbsp;Andreas Kappler,&nbsp;Tomás Israel Grijalva Rodríguez,&nbsp;Samuel Lihan,&nbsp;Sergei Katsev","doi":"10.1111/gbi.70036","DOIUrl":"10.1111/gbi.70036","url":null,"abstract":"<p>Tasik Biru is a ~70 m-deep tropical lake in Malaysia, originating from a water-filled open pit mine. We investigated the biogeochemistry and microbial community of the lake as a modern model habitat to the stratified ancient ocean. We found that a sharp redoxcline exists at around 50 m depth, related to the decrease of O₂ and pH (7.2–6.8) going down into the monimolimnion. Despite being relatively sulfate-rich (~320 μM), only a slight decrease of sulfate (to ~240 μM) was observed coupled with an increase of dissolved sulfide to 4 μM, attributed to microbial sulfate reduction in the monimolimnion. Comparatively, dissolved Fe and total Mn rose to ~50 μM in the anoxic layer with an unusual 1:1 concentration ratio. Other nutrients (PO₄³⁻, Si) and trace metal(loid)s (As, Mo, Sb, Co, U, and V) depth profiles increased or decreased across the chemocline, indicating controls via cycling of redox-sensitive elements. Microbial community analysis based on 16S rRNA amplicon sequencing reflects various metabolisms, from aerobic metabolisms in the mixolimnion to putative nitrite-dependent methane oxidation (e.g., by <i>Methylomirabilis</i>) at the chemocline, to sulfate reduction, methanogenesis, and fermentation in the monimolimnion. Tasik Biru is not in steady-state, and its anoxic water is predicted to shift from being Fe/Mn-rich to sulfide-rich, perhaps lending it as a model habitat to investigate biogeochemical changes from the metal-rich Archean to the Proterozoic oceans with expanding zones of sulfide-rich margins. An overview of the current biogeochemical cycles in the lake is presented, and open questions regarding partial sulfate consumption, methane, and Mn cycling and mineralogical distribution are highlighted to guide future studies.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"23 5","pages":""},"PeriodicalIF":3.4,"publicationDate":"2025-10-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12515063/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145273150","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":"Unlocking the Secrets of Saline Lakes: How Environmental and Microbial Interactions Shape Protodolomite Formation","authors":"Yang Li,&nbsp;Xuan Qiu,&nbsp;Deng Liu,&nbsp;Hongmei Wang,&nbsp;Xiaoyan Liu,&nbsp;Weiqi Wang,&nbsp;Ting Chen,&nbsp;Haochao Zhangsun,&nbsp;Xinyu Cai,&nbsp;Shengping Jin,&nbsp;Guangquan Yu","doi":"10.1111/gbi.70035","DOIUrl":"10.1111/gbi.70035","url":null,"abstract":"<div>\u0000 \u0000 <p>Protodolomite formation in saline lakes remains enigmatic, despite favorable conditions for dolomite precipitation. To unravel this mystery, sediment samples were collected from two saline lakes in northeastern Inner Mongolia: Jibuhulangtu Nuur (JBHLT) and Dabusan Nuur (DBS). These samples were subjected to comprehensive analysis, including mineral composition detection, measurement of physicochemical variables, analysis of extracellular polymeric substances (EPS), and 16S rRNA sequencing. Results showed that protodolomite was exclusively observed in JBHLT, even though both lakes were supersaturated with respect to dolomite. Microbial communities in JBHLT were dominated by <i>Gammaproteobacteria</i> and <i>Desulfuromonadia</i>. Polysaccharide in EPS extracted from sediments was significantly enriched in JBHLT and positively correlated with microbial alpha diversity. pH was found to be the main factor significantly impacting microbial community composition, diversity, and functions. In DBS, increased pH led to the dominance of <i>Halanaerobiaeota</i>, while decreased microbial diversity and polysaccharide contents. The interplay of pH, microbial community structure, and sediment EPS content concurrently impacts protodolomite formation. Our findings highlight the interaction between environmental conditions and microbial communities and their consequence in terms of protodolomite mineralization.</p>\u0000 </div>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"23 5","pages":""},"PeriodicalIF":3.4,"publicationDate":"2025-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145205014","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":"A Flourishing Planktonic Microbial Community in an Interglacial Offshore Environment: Silicified Microfossils From the Cryogenian Datangpo Formation, South China","authors":"Qing Ouyang,&nbsp;Chuanming Zhou,&nbsp;Xianguo Lang,&nbsp;Yuangao Qu,&nbsp;Hongyi Shi,&nbsp;Yunpeng Sun,&nbsp;Zhe Chen","doi":"10.1111/gbi.70034","DOIUrl":"https://doi.org/10.1111/gbi.70034","url":null,"abstract":"<div>\u0000 \u0000 <p>The Cryogenian global glaciations profoundly shaped the evolution of Earth's ecosystem. An active Cryogenian biosphere accompanied by key evolutionary innovations has been indicated by geochemical and phylogenetic studies, although fossil records from Cryogenian strata are limited. In this study, we report a silicified microfossil assemblage from the Cryogenian Datangpo Formation in an interglacial offshore setting of the Yangtze block, South China. The Datangpo assemblage majorly comprises coccoidal microfossils classified into three morphological types, with minor components of fragmented filamentous forms. Morphological and structural observations combined with Raman spectroscopic analysis indicate that this microfossil assemblage may represent a planktonic microbial community dominated by cyanobacteria. The exceptionally silicified taphonomic window in the Datangpo microfossil assemblage provides a snapshot of primary producers in an offshore environment between the two Cryogenian global glaciations.</p>\u0000 </div>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"23 5","pages":""},"PeriodicalIF":3.4,"publicationDate":"2025-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145146668","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":"Bioturbation Shapes Marine Biogeochemical Cycling Following the End-Permian Mass Extinction in Northern Pangea","authors":"Brian Beaty,&nbsp;William J. Foster,&nbsp;Valentin Zuchuat,&nbsp;Spencer R. Moller,&nbsp;Stella Z. Buchwald,&nbsp;Hannah Brooks,&nbsp;Sofia Rauzi,&nbsp;Terry Isson,&nbsp;Sverre Planke,&nbsp;Francisco J. Rodríguez-Tovar,&nbsp;Kim Senger,&nbsp;Noah Planavsky,&nbsp;Lidya Tarhan","doi":"10.1111/gbi.70032","DOIUrl":"10.1111/gbi.70032","url":null,"abstract":"<div>\u0000 \u0000 <p>During the end-Permian mass extinction, a global decline in seafloor sediment mixing and burrowing (bioturbation) provides critical evidence for the collapse of marine ecosystems, likely triggered by rapid ocean warming and deoxygenation. However, the decline and subsequent recovery of bioturbation after the extinction event may not only have been a symptom of environmental change but also a driver, influencing nutrient exchange and reductant burial across the sediment–water interface and thus water column oxygen availability and seafloor habitability more broadly. Here we test this hypothesis through combined analyses of bioturbation and sedimentary geochemistry, focusing on marine siliciclastic records of the Permian–Triassic transition from Svalbard. We find that total organic carbon, total sulfur, and organic phosphorus decrease with increasing bioturbation intensity, whereas inorganic reactive phosphorus phases (authigenic and iron oxide-bound phosphorus) increase. These differences are most strongly associated with biodiffusion (particle mixing) rather than bioirrigation (solute exchange). Our findings suggest that bioturbation primarily influenced sediment chemistry by enhancing organic matter oxidation, in contrast to some modern settings where downward mixing may promote organic matter preservation within the anoxic portion of seafloor sediments. The early return of shallow-tier bioturbators in this region &lt; 200 kyr after the extinction event likely promoted a rapid restoration of efficient carbon and sulfur cycling within benthic ecosystems. In contrast, efficient phosphorus burial via sink-switching may not have resumed until deeper-tier bioturbators achieved pre-extinction levels of sediment mixing &gt; 1 Myr after the mass extinction.</p>\u0000 </div>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"23 5","pages":""},"PeriodicalIF":3.4,"publicationDate":"2025-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145084717","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":"Oxygenation and Alkalinity Drive the Lacustrine Nitrogen Isotope Record Throughout the Past 3.2 Billion Years","authors":"Diana Velazquez,&nbsp;Nathan D. Sheldon,&nbsp;Michael T. Hren,&nbsp;Jenan J. Kharbush","doi":"10.1111/gbi.70033","DOIUrl":"10.1111/gbi.70033","url":null,"abstract":"<p>The widespread, stepwise oxygenation of Earth's atmosphere in the Precambrian led to a transformation of the global carbon (C) and nitrogen (N) cycles. While the temporal evolution of these nutrient cycles has been studied extensively in marine environments, lacustrine environments are understudied. This study first examines how water column oxygen conditions impact sedimentary carbon (δ¹³C_org) and nitrogen (δ¹⁵N) isotope signals in modern lakes. Subsequently, we use these patterns to interpret past changes in the geological record of lacustrine δ¹⁵N during atmospheric oxygenation. The compiled modern lake sediment dataset reveals average (± standard deviation) δ¹⁵N values of +2.9‰ ± 3.2‰ and δ¹³C_org values of −25.99‰ ± 3.77‰, as well as thresholds in δ¹³C_org for oxic versus anoxic conditions, and in δ¹⁵N for circumneutral versus alkaline pH conditions. In contrast to the stepwise oxygenation of the atmosphere, the lacustrine δ¹⁵N record does not directly reflect major oxygenation events, but instead increases gradually in response to the evolution of new aerobic N metabolic pathways, with a notable shift in the Phanerozoic. While we found that intrasite variability at a single modern anoxic lake is expected to remain within ~5‰ for δ¹⁵N, alkaline lakes in both the ancient and modern deviate from this range. We observe δ¹⁵N &gt; +10‰ for approximately half of total ancient alkaline lake sediments and some modern lake sediments. This is consistent with previous applications of enriched δ¹⁵N as a basicity proxy. The lacustrine δ¹⁵N record aligns well with the evolution of microbial metabolic pathways in addition to providing information pertaining to environmental conditions of the depositional setting.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"23 5","pages":""},"PeriodicalIF":3.4,"publicationDate":"2025-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12444620/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145079326","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":"Mineralization Controls Informative Biomarker Preservation Associated With Soft Part Fossilization in Deep Time","authors":"Madison Tripp,&nbsp;Jasmina Wiemann,&nbsp;Luke Brosnan,&nbsp;William D. A. Rickard,&nbsp;Vivi Vajda,&nbsp;Michael Ernst Böttcher,&nbsp;Paul F. Greenwood,&nbsp;Kliti Grice","doi":"10.1111/gbi.70030","DOIUrl":"10.1111/gbi.70030","url":null,"abstract":"<p>Diagenetically mineralized fossil tissues represent invaluable paleobiological evidence of past life. Lipid biomarkers may be identified alongside fossils, yet the relationship between localized, diagenetic mineral precipitation, and lipid preservation remains underexplored. Coprolites (fossilized feces) attract a unique diversity of early diagenetic minerals including carbonates and phosphates, within individual samples, mediating molecular preservation of soluble lipid biomarkers alongside exceptional morphological preservation. Analysis of a well-preserved coprolite from the Carboniferous (307 ± 0.1 Ma) Mazon Creek assemblage, USA via time of flight-secondary ion mass spectrometry (ToF-SIMS) spatial compound mapping demonstrated the association of 5α,14α,17α(H) 20<i>R</i> cholestane, a C₂₇ dietary sterane, with iron carbonate (and some pyrite) rather than phosphate minerals. Furthermore, Raman spectroscopic fingerprinting of a suite of organic-rich fossils spanning a number of biological species and preserved across the Mazon Creek site and other depositional settings was utilized to explore whether the localized preservation of steroids in carbonate phases represents a <i>lagerstätten</i>-specific or generalizable pattern. Our spectroscopic analyses demonstrate a significant positive correlation between signatures of lipid biomarkers and carbonates rather than phosphates across all soft-part samples at the Mazon Creek site and throughout Phanerozoic time and space. Early diagenetic carbonate measurably immobilizes otherwise labile lipid biomarkers and shields them against diagenetic stressors. Localized preservation identifies carbonate phases as a preferential resource for lipid-based biological information and reveals organomineral associations as a new frontier in understanding the survival of molecules in deep time.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"23 5","pages":""},"PeriodicalIF":3.4,"publicationDate":"2025-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/gbi.70030","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145084697","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 Tubotomaculum Enigma and the Rise of Benthic Life During the Opening of the Western Mediterranean Basin","authors":"Simone Bernardini,&nbsp;Anas Abbassi,&nbsp;Paola Cipollari,&nbsp;Giancarlo Della Ventura,&nbsp;Cesareo Saiz-Jimenez,&nbsp;Enrico Mugnaioli,&nbsp;Luigi Jovane,&nbsp;Armida Sodo,&nbsp;Fabio Bellatreccia,&nbsp;Mohamed N. Zaghloul,&nbsp;Domenico Cosentino","doi":"10.1111/gbi.70031","DOIUrl":"https://doi.org/10.1111/gbi.70031","url":null,"abstract":"<p>Large-scale geological processes shape microbial habitats and drive the evolution of life on Earth. During the Oligocene, convergence between Africa and Europe led to the opening of the Western Mediterranean Basin, a deep-ocean system characterized by fluid venting, oxygen depletion, and the absence of benthic fauna. In this extreme, inhospitable seafloor environment, fusiform objects known as <i>Tubotomaculum</i> formed, whose origin has long remained controversial. We show that these enigmatic mineralizations consist of nanosized, poorly crystalline, phosphorus-rich Mn-Fe compounds produced through microbial mediation. They preserve carbonaceous material together with morphological, chemical, and mineralogical biosignatures, including high Mn oxidation state (3.9 ± 0.15), cell envelopes, extracellular polymeric substances (EPS), cell-EPS partitioning of redox-sensitive Mn and Fe, cluster-assembled microbial cells, microbialite-like and branching structures, and channel networks for nutrient transport. Geochemical signatures indicate precipitation under suboxic to anoxic, non-sulfidic (post-oxic) conditions from mixed seawater–hydrothermal fluids, with exposure on the seafloor prior to burial. The fusiform architecture of these self-organized microbial populations suggests shaping by nutrient-rich bottom currents associated with venting activity. This study provides a detailed glimpse into initial benthic colonization of the nascent Western Mediterranean Basin and establishes <i>Tubotomaculum</i> as a model for investigating biomineralization and microbial adaptation in extreme environments, with implications for the search for life beyond Earth.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"23 5","pages":""},"PeriodicalIF":3.4,"publicationDate":"2025-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/gbi.70031","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145012653","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 Reassessment of the Coprostane Biomarker in the Ediacaran With Implications for Dickinsonia","authors":"Christopher Mulligan,&nbsp;David A. Gold","doi":"10.1111/gbi.70029","DOIUrl":"https://doi.org/10.1111/gbi.70029","url":null,"abstract":"<p>The discovery of cholestane in animal fossils from the Ediacaran (571–541 million years ago) has generated much excitement, but it is not the only interesting biomarker recovered. Coprostane, a geologically stable form of coprostanol, has also been found in Ediacaran rocks. This is surprising, since coprostanol is typically used in modern settings as an environmental biomarker for humans and other mammals, who produce the compound with help from bacteria in their gut. The prevailing hypothesis is that an abundance of coprostane in some Ediacaran fossils—particularly <i>Dickinsonia</i>—represents the degradation of the organism's cholesterol by bacteria in the microbial mat, comparable to what is seen in modern vertebrate corpses as they decompose. However, this hypothesis assumes coprostanol-producing bacteria were absent in the guts of Ediacaran organisms, and to date no one has tested whether such bacteria exist in modern invertebrates. In this study, we assembled 115 metagenomes to look for evidence of coprostanol-producing enzymes in invertebrate microbiomes. Ultimately, we did not find any evidence for the enzyme in any invertebrate microbiomes, supporting the hypothesis that coprostane is not a gut biomarker for Ediacaran animals. However, a reassessment of coprostane/cholestane ratios shows <i>Dickinsonia</i> was unique in coprostanol enrichment, with ratio levels comparable to waste polluted marine waters and modern vertebrate feces. While we cannot rule out the possibility of contamination, we prefer a novel interpretation of the coprostane signature in dickinsoniomorph fossils, where the elevated level of coprostanol comes from digestion of the microbial mat and concentration of the biologically inert compound. If correct, the elevated coprostanol signal provides new insights into the feeding strategy of these enigmatic animals.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"23 4","pages":""},"PeriodicalIF":3.4,"publicationDate":"2025-08-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/gbi.70029","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144869603","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":"Thallium Isotopes Suggest the Global Deep Ocean Did Not Approach Modern Oxygenation During Cambrian Age 3 Metazoan Radiation","authors":"Jean N. R. Clemente,&nbsp;Haifeng Fan,&nbsp;Chadlin M. Ostrander,&nbsp;Hongjie Zhang,&nbsp;Hanjie Wen,&nbsp;Erik A. Sperling,&nbsp;Sune G. Nielsen","doi":"10.1111/gbi.70028","DOIUrl":"https://doi.org/10.1111/gbi.70028","url":null,"abstract":"<div>\u0000 \u0000 <p>The geologically rapid appearance of most extant animal groups in the Cambrian fossil record is often linked to enhanced ocean oxygenation. However, conflicting reconstructions of the Cambrian redox landscape make it difficult to determine the extent of ocean oxygenation during this significant biotic event, particularly regarding the redox state of the global deep ocean. In this study, we present authigenic thallium isotope compositions (ε²⁰⁵Tl_auth) for two shale sequences from South China (Qingjiang and Weng'an) that span the Cambrian Stage 2–3 boundary to the appearance of the Qingjiang biota, approximately 521–518 million years ago (Ma), a timeframe that chronicles a particularly rapid interval of metazoan diversification and radiation in the broader Cambrian explosion. If this event occurred amid modern-like extents of global ocean oxygenation, we would expect a significant increase in the global extent of seafloor Mn-oxide burial to drive lower ε²⁰⁵Tl_auth values near the modern open-ocean composition of −6‱. Instead, we observe broadly stable ε²⁰⁵Tl_auth values of around −3 to −4‱ in both studied sections. The lack of any significant Tl isotope shifts in our dataset argues against a short-term global ocean oxygenation event and suggests the global deep ocean was not characterized by modern extents of oxygenation 521–518 Ma. We reinterpret contemporaneous near-modern Mo and U isotope compositions to signal a relatively minor increase in marine oxygenation, likely limited to the continental shelves. However, ε²⁰⁵Tl_auth lower than the average isotopic composition of approximately −2‱ in Ediacaran shales suggests a shift to comparatively better-oxygenated conditions sometime between ~555 Ma and 521 Ma. If diversification at this time was linked to increased ocean oxygen levels, these changes were likely more dominant in the relatively shallow-water settings of continental shelves most densely populated by Cambrian animals and were incapable of dramatically altering seawater Tl isotope mass balance through seafloor Mn-oxide burial.</p>\u0000 </div>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"23 4","pages":""},"PeriodicalIF":3.4,"publicationDate":"2025-08-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144782308","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}