Geobiology最新文献

{"title":"Contrasting morphology and growth habits of Frutexites in Late Devonian reef complexes of the Canning Basin, northwestern Australia","authors":"France Champenois,&nbsp;Annette D. George,&nbsp;Kenneth J. McNamara,&nbsp;Jeremy Shaw,&nbsp;Maria Cherdantseva","doi":"10.1111/gbi.12579","DOIUrl":"10.1111/gbi.12579","url":null,"abstract":"<p><i>Frutexites</i>-like microstructures are described from the exhumed Late Devonian reef complexes of the northern Canning Basin, Western Australia. Several high-resolution imaging techniques, including X-ray microcomputerised tomography, scanning electron microscopy and X-ray fluorescence microscopy, were used to investigate morphology and composition in two samples. Three types of <i>Frutexites</i>-like microstructures (Types I–III) have been identified. Type I, found lining an early marine cement-filled cavity in fore-reef grainstone facies, consists of dendritic structures formed primarily of coccoid bacteria with filamentous bacteria embedded in sheets of amorphous extracellular polymeric substances (EPS). These ferromanganiferous dendrites have laminated to spheroidal textures. Types II and III are from a toe-of-slope hardground. Type II grew in a crypt between two corals, is also dendritic and composed of bacilliform and filamentous bacteria embedded in an amorphous EPS sheet. The opaqueness of these ferriferous dendrites precludes more detailed description of textures. Type III grew as branching columnar microstromatolites and is composed of entwined filaments of <i>Girvanella</i>, <i>Rothpletzella</i> and <i>Wetheredella</i> with Fe-enriched outer walls that generate <i>Frutexites</i>-like microstructures. Types I and II resemble <i>Frutexites</i> sensu stricto as defined by Maslov (<i>Stromatolites</i>, Trudy Instituta geologicheskikh nauk Akademiya nauk SSR, 1960) and are the result of the consecutive growth and permineralisation of biofilms composed of mixed bacterial communities growing in cryptic habitats. Type III superficially resembles <i>Frutexites</i> sensu stricto based on macroscopic field observations, however, detailed microscopic analysis reveals that it is composed of Fe-enriched tubular walls surrounded by Mn-enriched calcite.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"22 1","pages":""},"PeriodicalIF":3.7,"publicationDate":"2023-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/gbi.12579","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138174984","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.12578","DOIUrl":"https://doi.org/10.1111/gbi.12578","url":null,"abstract":"<p>Cover</p><p>The cover image is based on the Research Article <i>White and green rust chimneys accumulate RNA in a ferruginous chemical garden</i> by Vanessa Helmbrecht et al., https://doi.org/10.1111/gbi.12572\u0000 \u0000 <figure>\u0000 <div><picture>\u0000 <source></source></picture><p></p>\u0000 </div>\u0000 </figure>\u0000 </p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"21 6","pages":"i"},"PeriodicalIF":3.7,"publicationDate":"2023-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/gbi.12578","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41229871","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":"Distinctive microfossil supports early Paleoproterozoic rise in complex cellular organisation","authors":"Erica V. Barlow,&nbsp;Christopher H. House,&nbsp;Ming-Chang Liu,&nbsp;Maxwell T. Wetherington,&nbsp;Martin J. Van Kranendonk","doi":"10.1111/gbi.12576","DOIUrl":"10.1111/gbi.12576","url":null,"abstract":"<p>The great oxidation event (GOE), ~2.4 billion years ago, caused fundamental changes to the chemistry of Earth's surface environments. However, the effect of these changes on the biosphere is unknown, due to a worldwide lack of well-preserved fossils from this time. Here, we investigate exceptionally preserved, large spherical aggregate (SA) microfossils permineralised in chert from the c. 2.4 Ga Turee Creek Group in Western Australia. Field and petrographic observations, Raman spectroscopic mapping, and in situ carbon isotopic analyses uncover insights into the morphology, habitat, reproduction and metabolism of this unusual form, whose distinctive, SA morphology has no known counterpart in the fossil record. Comparative analysis with microfossils from before the GOE reveals the large SA microfossils represent a step-up in cellular organisation. Morphological comparison to extant micro-organisms indicates the SAs have more in common with coenobial algae than coccoidal bacteria, emphasising the complexity of this microfossil form. The remarkable preservation here provides a unique window into the biosphere, revealing an increase in the complexity of life coinciding with the GOE.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"22 1","pages":""},"PeriodicalIF":3.7,"publicationDate":"2023-10-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/gbi.12576","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41093755","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":"Divergence time estimates for the hypoxia-inducible factor-1 alpha (HIF1α) reveal an ancient emergence of animals in low-oxygen environments","authors":"Flavia A. Belato,&nbsp;Beatriz Mello,&nbsp;Christopher J. Coates,&nbsp;Kenneth M. Halanych,&nbsp;Federico D. Brown,&nbsp;André C. Morandini,&nbsp;Juliana de Moraes Leme,&nbsp;Ricardo I. F. Trindade,&nbsp;Elisa Maria Costa-Paiva","doi":"10.1111/gbi.12577","DOIUrl":"10.1111/gbi.12577","url":null,"abstract":"<p>Unveiling the tempo and mode of animal evolution is necessary to understand the links between environmental changes and biological innovation. Although the earliest unambiguous metazoan fossils date to the late Ediacaran period, molecular clock estimates agree that the last common ancestor (LCA) of all extant animals emerged ~850 Ma, in the Tonian period, before the oldest evidence for widespread ocean oxygenation at ~635–560 Ma in the Ediacaran period. Metazoans are aerobic organisms, that is, they are dependent on oxygen to survive. In low-oxygen conditions, most animals have an evolutionarily conserved pathway for maintaining oxygen homeostasis that triggers physiological changes in gene expression via the hypoxia-inducible factor (HIFa). However, here we confirm the absence of the characteristic HIFa protein domain responsible for the oxygen sensing of HIFa in sponges and ctenophores, indicating the LCA of metazoans lacked the functional protein domain as well, and so could have maintained their transcription levels unaltered under the very low-oxygen concentrations of their environments. Using Bayesian relaxed molecular clock dating, we inferred that the ancestral gene lineage responsible for HIFa arose in the Mesoproterozoic Era, ~1273 Ma (Credibility Interval 957–1621 Ma), consistent with the idea that important genetic machinery associated with animals evolved much earlier than the LCA of animals. Our data suggest at least two duplication events in the evolutionary history of HIFa, which generated three vertebrate paralogs, products of the two successive whole-genome duplications that occurred in the vertebrate LCA. Overall, our results support the hypothesis of a pre-Tonian emergence of metazoans under low-oxygen conditions, and an increase in oxygen response elements during animal evolution.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"22 1","pages":""},"PeriodicalIF":3.7,"publicationDate":"2023-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41100438","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":"The role of clay minerals in the preservation of Precambrian organic-walled microfossils","authors":"C. R. Woltz,&nbsp;R. P. Anderson,&nbsp;N. J. Tosca,&nbsp;S. M. Porter","doi":"10.1111/gbi.12573","DOIUrl":"10.1111/gbi.12573","url":null,"abstract":"<p>Precambrian organic-walled microfossils (OWMs) are primarily preserved in mudstones and shales that are low in total organic carbon (TOC). Recent work suggests that high TOC may hinder OWM preservation, perhaps because it interferes with chemical interactions involving certain clay minerals that inhibit the decay of microorganisms. To test if clay mineralogy controls OWM preservation, and if TOC moderates the effect of clay minerals, we compared OWM preservational quality (measured by pitting on fossil surfaces and the deterioration of wall margins) to TOC, total clay, and specific clay mineral concentrations in 78 shale samples from 11 lithologic units ranging in age from ca. 1650 to 650 million years ago. We found that the probability of finding well-preserved microfossils positively correlates with total clay concentrations and confirmed that it negatively correlates with TOC concentrations. However, we found no evidence that TOC influences the effect of clay mineral concentrations on OWM preservation, supporting an independent role of both factors on preservation. Within the total clay fraction, well-preserved microfossils are more likely to occur in shales with high illite concentrations and low berthierine/chamosite concentrations; however, the magnitude of their effect on preservation is small. Therefore, there is little evidence that bulk clay chemistry is important in OWM preservation. Instead, we propose that OWM preservation is largely regulated by physical properties that isolate organic remains from microbial degradation such as food scarcity (low TOC) and low sediment permeability (high total clay content): low TOC increases the diffusive distances between potential carbon sources and heterotrophic microbes (or their degradative enzymes), while high clay concentrations reduce sediment pore space, thereby limiting the diffusion of oxidants and degradative enzymes to the sites of decay.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"21 6","pages":"708-724"},"PeriodicalIF":3.7,"publicationDate":"2023-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/gbi.12573","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41093756","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":"Sulfur disproportionating microbial communities in a dynamic, microoxic-sulfidic karst system","authors":"Heidi S. Aronson,&nbsp;Christian E. Clark,&nbsp;Douglas E. LaRowe,&nbsp;Jan P. Amend,&nbsp;Lubos Polerecky,&nbsp;Jennifer L. Macalady","doi":"10.1111/gbi.12574","DOIUrl":"10.1111/gbi.12574","url":null,"abstract":"<p>Biogeochemical sulfur cycling in sulfidic karst systems is largely driven by abiotic and biological sulfide oxidation, but the fate of elemental sulfur (S⁰) that accumulates in these systems is not well understood. The Frasassi Cave system (Italy) is intersected by a sulfidic aquifer that mixes with small quantities of oxygen-rich meteoric water, creating Proterozoic-like conditions and supporting a prolific ecosystem driven by sulfur-based chemolithoautotrophy. To better understand the cycling of S⁰ in this environment, we examined the geochemistry and microbiology of sediments underlying widespread sulfide-oxidizing mats dominated by <i>Beggiatoa</i>. Sediment populations were dominated by uncultivated relatives of sulfur cycling chemolithoautotrophs related to <i>Sulfurovum</i>, <i>Halothiobacillus</i>, <i>Thiofaba</i>, <i>Thiovirga</i>, <i>Thiobacillus</i>, and <i>Desulfocapsa</i>, as well as diverse uncultivated anaerobic heterotrophs affiliated with <i>Bacteroidota</i>, Anaerolineaceae, Lentimicrobiaceae, and Prolixibacteraceae. <i>Desulfocapsa</i> and <i>Sulfurovum</i> populations accounted for 12%–26% of sediment 16S rRNA amplicon sequences and were closely related to isolates which carry out autotrophic S⁰ disproportionation in pure culture. Gibbs energy (∆<i>G</i>_<i>r</i>) calculations revealed that S⁰ disproportionation under in situ conditions is energy yielding. Microsensor profiles through the mat-sediment interface showed that <i>Beggiatoa</i> mats consume dissolved sulfide and oxygen, but a net increase in acidity was only observed in the sediments below. Together, these findings suggest that disproportionation is an important sink for S⁰ generated by microbial sulfide oxidation in this oxygen-limited system and may contribute to the weathering of carbonate rocks and sediments in sulfur-rich environments.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"21 6","pages":"791-803"},"PeriodicalIF":3.7,"publicationDate":"2023-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/gbi.12574","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"10287098","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 diversity and authigenic siderite mediation in sediments surrounding the Kedr-1 mud volcano, Lake Baikal","authors":"Anna V. Lomakina,&nbsp;Sergei V. Bukin,&nbsp;Tatyana V. Pogodaeva,&nbsp;Alexandra V. Turchyn,&nbsp;Oleg M. Khlystov,&nbsp;Andrey V. Khabuev,&nbsp;Vyacheslav G. Ivanov,&nbsp;Aleksey A. Krylov,&nbsp;Tamara I. Zemskaya","doi":"10.1111/gbi.12575","DOIUrl":"10.1111/gbi.12575","url":null,"abstract":"<p>The gas hydrate-bearing structure—mud volcano Kedr-1 (Lake Baikal, southern basin)—is located near the coal-bearing sediments of the Tankhoy formation of Oligocene–Miocene age and can be an ideal source of gas-saturated fluid. A significant amount of siderite minerals (FeCO₃) were collected from sediments at depths ranging from 0.5 to 327 cm below the lake floor (cmblf). An important feature of these carbonate minerals is the extremely strong enrichment in the heavy ^<i>13</i><i>C</i> isotope, reaching values of +33.3‰ VPDB. The <i>δ</i>^<i>13</i><i>C</i> of the siderite minerals, as well as their morphology and elemental composition, and the <i>δ</i>^<i>13</i><i>C</i>_<i>DIC</i> of the co-existing pore water, differed across layers of the core, which implies at least two generations of siderite formation. Here, we leverage mineralogical and geochemical data with 16S rRNA data from the microbial communities in sediments surrounding layers containing siderite minerals. Statistical data reveal the formation of three clusters of microbial communities based on taxonomical composition, key taxa among bacteria and archaea, and environmental parameters. Diversity and richness estimators decrease with sediment depth, with several similar prevailing clades located at the bottom of the core. Most of the taxa in the deep sediments could be associated with putative metabolisms involving organotrophic fermentation (Bathyarchaeia, Caldatribacteriota, and Chloroflexota). Various groups of methanogens (<i>Methanoregulaceae</i>, <i>Methanosaetaceae</i>, and <i>Methanomassiliicoccales</i>) and methanotrophic (<i>Methanoperedenaceae</i>) archaea are present in the sediment at variable relative abundances throughout the sampled depth. Based on the physicochemical characteristics of the sediment, carbon isotope analysis of carbonate minerals and DIC, and phylogenetic analysis of individual taxa and their metabolic potential, we present several models for subsurface siderite precipitation in Lake Baikal sediments.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"21 6","pages":"770-790"},"PeriodicalIF":3.7,"publicationDate":"2023-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"10214427","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":"Evolution of iron and oxygen biogeochemical cycles during the Precambrian","authors":"Yasuto Watanabe,&nbsp;Eiichi Tajika,&nbsp;Kazumi Ozaki","doi":"10.1111/gbi.12571","DOIUrl":"10.1111/gbi.12571","url":null,"abstract":"<p>Iron (Fe) is an essential element for life, and its geochemical cycle is intimately linked to the coupled history of life and Earth's environment. The accumulated geologic records indicate that ferruginous waters existed in the Precambrian oceans not only before the first major rise of atmospheric O₂ levels (Great Oxidation Event; GOE) during the Paleoproterozoic, but also during the rest of the Proterozoic. However, the interactive evolution of the biogeochemical cycles of O₂ and Fe during the Archean–Proterozoic remains ambiguous. Here, we develop a biogeochemical model to investigate the coupled biogeochemical evolution of Fe–O₂–P–C cycles across the GOE. Our model demonstrates that the marine Fe cycle was less sensitive to changes in the production rate of O₂ before the GOE (atmospheric <i>p</i>O₂ &lt; 10⁻⁶ PAL; present atmospheric level). When the P supply rate to the ocean exceeds a certain threshold, the GOE occurs and atmospheric <i>p</i>O₂ rises to ~10⁻³–10⁻¹ PAL. After the GOE, the marine Fe(II) concentration is highly sensitive to atmospheric <i>p</i>O₂, suggesting that the marine redox landscape during the Proterozoic may have fluctuated between ferruginous conditions and anoxic non-ferruginous conditions with sulfidic water masses around continental margins. At a certain threshold value of atmospheric <i>p</i>O₂ of ~0.3% PAL, the primary oxidation pathway of Fe(II) shifts from the activity of Fe(II)-utilizing anoxygenic photoautotrophs in sunlit surface waters to abiotic process in the deep ocean. This is accompanied by a shift in the primary deposition site of Fe(III) hydroxides from the surface ocean to the deep sea, providing a plausible mechanistic explanation for the observed cessation of iron formations during the Proterozoic.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"21 6","pages":"689-707"},"PeriodicalIF":3.7,"publicationDate":"2023-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"10309965","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":"White and green rust chimneys accumulate RNA in a ferruginous chemical garden","authors":"Vanessa Helmbrecht,&nbsp;Maximilian Weingart,&nbsp;Frieder Klein,&nbsp;Dieter Braun,&nbsp;William D. Orsi","doi":"10.1111/gbi.12572","DOIUrl":"10.1111/gbi.12572","url":null,"abstract":"<p>Mechanisms of nucleic acid accumulation were likely critical to life's emergence in the ferruginous oceans of the early Earth. How exactly prebiotic geological settings accumulated nucleic acids from dilute aqueous solutions, is poorly understood. As a possible solution to this concentration problem, we simulated the conditions of prebiotic low-temperature alkaline hydrothermal vents in co-precipitation experiments to investigate the potential of ferruginous chemical gardens to accumulate nucleic acids via sorption. The injection of an alkaline solution into an artificial ferruginous solution under anoxic conditions (O₂ &lt; 0.01% of present atmospheric levels) and at ambient temperatures, caused the precipitation of amakinite (“white rust”), which quickly converted to chloride-containing fougerite (“green rust”). RNA was only extractable from the ferruginous solution in the presence of a phosphate buffer, suggesting RNA in solution was bound to Fe²⁺ ions. During chimney formation, this iron-bound RNA rapidly accumulated in the white and green rust chimney structure from the surrounding ferruginous solution at the fastest rates in the initial white rust phase and correspondingly slower rates in the following green rust phase. This represents a new mechanism for nucleic acid accumulation in the ferruginous oceans of the early Earth, in addition to wet-dry cycles and may have helped to concentrate RNA in a dilute prebiotic ocean.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"21 6","pages":"758-769"},"PeriodicalIF":3.7,"publicationDate":"2023-08-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/gbi.12572","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"10062607","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":"Tocopherols and associated derivatives track the phytoplanktonic response to evolving pelagic redox conditions spanning Oceanic Anoxic Event 2","authors":"Gregory T. Connock,&nbsp;Xiao-Lei Liu","doi":"10.1111/gbi.12570","DOIUrl":"10.1111/gbi.12570","url":null,"abstract":"<p>Tocopherols serve a critical role as antioxidants inhibiting lipid peroxidation in photosynthetic organisms, yet are seldom used in geobiological investigations. The ubiquity of tocopherols in all photosynthetic lifeforms is often cited as an impediment to any diagnostic paleoenvironmental potential, while the inability to readily analyze these compounds via conventional methods, such as gas chromatography–mass spectrometry, further diminishes the capacity to serve as useful ‘biomarkers’. Here, we analyzed an exceptionally preserved black shale sequence from the Demerara Rise that spans Oceanic Anoxic Event 2 (OAE-2) to reexamine the significance of tocopherols and associated derivatives (i.e. tocol derivatives) in ancient sediments. Tocol derivatives were analyzed via liquid chromatography–quadrupole time-of-flight–mass spectrometry and included tocopherols, a methyltrimethyltridecylchroman, and the first reported detection of tocopherol quinones and methylphytylbenzoquinones in the geologic record. Strong correlations between tocol derivatives were observed over the studied interval. Tocol derivative concentrations and ratios, which normalized tocopherols to potential derivatives, revealed absolute and relative increases in tocopherols as exclusive features of OAE-2 that can be explained by two possible mechanisms related to tocopherol production and preservation. The development of photic zone euxinia during OAE-2 likely forced an upward migration of oxygenic photoautotrophs, increasing oxidative stress that elicited heightened tocopherol biosynthesis. However, shoaling euxinic conditions may have simultaneously acted to enhance tocopherol preservation given the relatively high lability of tocopherols in the water column. Both scenarios could produce the observed stratigraphic distribution of tocol derivatives in this study, although the elevated tocopherol concentrations that define OAE-2 at the Demerara Rise are primarily attributed to enhanced tocopherol production by shoaling phytoplanktonic communities. Thus, the occurrence of tocopherols and associated derivatives in sediments and rocks of marine origin is likely indicative of shallow-water anoxia, tracking the phytoplanktonic response to the abiotic stresses associated with vertical fluctuations in pelagic redox.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"21 6","pages":"743-757"},"PeriodicalIF":3.7,"publicationDate":"2023-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"10026306","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}