Geochimica et Cosmochimica Acta最新文献

{"title":"Highly siderophile element and Re-Os isotope systematics of a Neoproterozoic Iron Formation and its temporal relation to glaciation events","authors":"Tobias Prost ,&nbsp;Toni Schulz ,&nbsp;Sebastian Viehmann ,&nbsp;Detlef H.G. Walde ,&nbsp;Christian Koeberl","doi":"10.1016/j.gca.2024.09.019","DOIUrl":"10.1016/j.gca.2024.09.019","url":null,"abstract":"<div><div>The Urucum iron- and manganese formation (IF-MnF) in the Santa Cruz Formation, Brazil, was deposited in a glacially influenced, late Neoproterozoic depositional environment. It has proven to be a reliable and robust archive for the late Neoproterozoic, allowing unique insights into the composition of seawater during an interval that is characterized by dramatic changes in the Earth’s litho-, hydros-, atmo-, and biosphere, including several episodes of low-latitude glaciations. Here we present highly siderophile element data of the Urucum IF-MnF to evaluate elemental sources that affected the Neoproterozoic seawater from which the Urucum IF-MnF precipitated. High uncertainties associated with current dating attempts of this formation overlapped with the Marinoan glaciation (∼650–635 Ma) as well as the Gaskiers glaciation event (∼580 Ma). A Re-Os regression line defined by iron-, manganese-, and chert-rich samples of the Urucum formation is interpreted as an isochron, yielding a refined age estimate of 577 ± 38 Ma and an initial ¹⁸⁷Os/¹⁸⁸Os ratio of 0.122 ± 0.003. The proposed depositional age overlaps with previous published age data of the Urucum IF-MnF, but relates the Urucum IF-MnF to the Ediacaran Gaskiers glaciation and overlaps with the age of the Shuram CIE (∼567 Ma). An initial ¹⁸⁷Os/¹⁸⁸Os ratio of 0.122 ± 0.003 is interpreted to represent pristine Neoproterozoic seawater and supports strong hydrothermal input, probably related to rifting, that promoted ferruginous conditions in the Urucum seawater.</div><div>In an alternative scenario, Re-Os isotope data for the Urucum IF-MnF could also be interpreted in a multi-component mixing scenario, defined by hydrothermally influenced water masses that sourced most metals within the Urucum basin and a crustal component that entered the Urucum seawater either as detrital admixture or via riverine loads. Although none of the scenarios can be ruled out, we consider the isochron scenario as more plausible.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"384 ","pages":"Pages 140-154"},"PeriodicalIF":4.5,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0016703724005003/pdfft?md5=173e4e92ca3048f71ecd519f5300819f&pid=1-s2.0-S0016703724005003-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142311031","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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":"Origin of the Ca-phosphate inclusions in Ivory Coast and Australasian Muong-Nong-type tektites","authors":"Pierre-Marie Zanetta, Anne-Magali Seydoux-Guillaume, Pierre Rochette, Bruno Reynard, Victor Tricaud, Petanki Soro, Southone Singsoupho, Alain Nicaise Kouamelan, Obrou Monda, David Baratoux","doi":"10.1016/j.gca.2024.09.021","DOIUrl":"https://doi.org/10.1016/j.gca.2024.09.021","url":null,"abstract":"Tektites are reduced (Fe<ce:sup loc=\"post\">2+</ce:sup>) glasses formed by the quenching of molten material ejected from Earth’s surface as a result of a hypervelocity impact. The vast majority of tektites are usually homogeneous glasses, but rare samples containing mineral inclusions can provide insights about the source material, sample thermal history, and tektite formation process. Tektites from two distinct strewn fields presenting Ca-phosphate inclusions detected from anomalous magnetic susceptibility were studied: one sample from the Ivory Coast tektite (ICT) field ejected at 1.07 Ma from the Bosumtwi crater (10.5 km in size) in Ghana and two Muong Nong type samples from the Australasian tektite field (MN-AAT) ejected at 0.79 Ma from a crater possibly situated in southeast Asia. In ICT, Ca-phosphate inclusions are systematically embedded in lechatelierite (SiO<ce:inf loc=\"post\">2</ce:inf> glass). In MN-AAT Ca-phosphate are either embedded in lechatelierite or in Fe-rich glass forming schlieren. Multiscale petrographic characterization using correlative microscopy associating scanning electron microscopy, microprobe and, transmission electron microscopy reveals that rounded inclusions in ivoirite are composed of acicular Ca-phosphates (merrillite) embedded in an amorphous P-rich glass. In MN-AAT, inclusions consist mostly of single droplets of Fe-Mg rich Ca-phosphate (structurally related to apatite), but few droplets often forming an emulsion texture show a complex assemblage of apatite, magnetite, pyroxene, and spinel growing from a Pt-rich nucleus. Diffusion profile around lechatelierite domains reveals maximum temperatures greater than 2200–2400 °C in the impact plume of the Australasian tektite and the Ivory coast tektite. Heating time is of the order of seconds-tens of seconds rather than minutes as previously suggested (20 s for MN-AAT and 5 s for ICT). The number, the density, and the fact that inclusions are entirely crystallized in MN-AAT support relatively slow cooling rates (&lt;200 °C/h), in comparison with the faster cooling rates (&gt;2000 °C/h) indicated by the precipitation of amorphous P-rich glass in ICT. In both impact events, ejecta that had been heated to high temperatures did not remain in the vapor plume for an extended period of time and landed rapidly (within tens of seconds) at a relatively high temperature (&gt;1000 °C) on the Earth’s surface.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"37 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142321644","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Multi-tracer evidence of hydrology and primary production controls on dissolved organic matter composition and stability in the semi-arid aquatic continuum","authors":"Mingyu Shao ,&nbsp;Zaihua Liu ,&nbsp;Hailong Sun ,&nbsp;Haibo He ,&nbsp;Qiang Li ,&nbsp;Sibo Zeng ,&nbsp;Junyao Yan ,&nbsp;Yan Fang ,&nbsp;Qiufang He ,&nbsp;Hailong Liu ,&nbsp;Liangxing Shi ,&nbsp;Chaowei Lai","doi":"10.1016/j.gca.2024.09.015","DOIUrl":"10.1016/j.gca.2024.09.015","url":null,"abstract":"<div><p>Autochthonous dissolved organic matter (Auto-DOM) produced by a biological carbon pump using dissolved inorganic carbon (DIC) from carbonate weathering plays an important role in carbon cycling within inland waters. However, little is known regarding how environmental conditions impact the composition and fate of organic matter, especially in surface waters of the semi-arid Loess Plateau, which is enriched in DIC by significant carbonate weathering. To obtain novel insight, we combined hydrochemistry, isotopic composition (δ²H, δ¹⁸O, and δ¹³C_DIC), Rayleigh fractionation model, optical spectroscopy (absorbance and fluorescence), and Fourier transform ion cyclotron resonance mass spectrometry measurements to elucidate how primary production and hydrology impact the composition of DOM and the stability of the resulting Auto-DOM throughout the river–reservoir–wetland aquatic continuum of the Bahe River in the carbonate-mineral-rich semi-arid Loess Plateau where carbonate weathering is significant. The Rayleigh fractionation model results indicated that watershed DIC is primarily consumed through aquatic primary production rather than CO₂ degassing. Further investigation revealed that primary production and evaporation co-occurred in this watershed. With the enrichment of the stable water isotope δ²H, the relative abundances of the allochthonous compounds decreased and the relative abundances of the autochthonous substances increased, suggesting that the terrestrial signal of riverine DOM decreased while autochthonous production increased along the flow pathway. In addition, associations between optical and molecular characteristics among DOM samples from different water bodies revealed that the stability ratio (Fmax(C2/(C2 + C4))) of Auto-DOM to the ratio of carboxylic-rich alicyclic molecules showed a consistent trend, suggesting that phytoplankton-derived and biomineralized C2 compounds are potentially recalcitrant DOM in inland waters. We conclude that hydrology and primary production affect the source, composition, and, potentially, the stability of DOM in DIC-enriched surface waters of the semi-arid Loess Plateau, which may lead to a more humic-like DOM composition in inland water and export this lower bioavailability DOC to the ocean in the long term.</p></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"384 ","pages":"Pages 80-92"},"PeriodicalIF":4.5,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142274544","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Competitive dissolution of mixed carbonate solids under simulated ocean acidification","authors":"Hannah Guiney,&nbsp;Alfonso O. Mucci","doi":"10.1016/j.gca.2024.09.014","DOIUrl":"10.1016/j.gca.2024.09.014","url":null,"abstract":"<div><div>It is estimated that at least 25 % of the anthropogenic carbon dioxide (CO₂) emitted to the atmosphere since the start of the industrial revolution has been absorbed and dissolved by the oceans. The uptake of CO₂ by the oceans leads to an increase in the seawater proton concentration ([H⁺]), and decreases in seawater pH, carbonate ion concentration ([CO₃^2–]), and saturation state (Ω) with respect to calcium carbonate (CaCO₃) minerals; a process commonly referred to as “ocean acidification”. Shallow-water (&lt;200 m), high-magnesium, biogenic calcites are expected to be amongst the first to respond to ocean acidification, and it has been proposed that they will dissolve selectively and sequentially according to their solubility in seawater. In this study, we test this competitive dissolution hypothesis by reacting a mixture of biogenic and synthetic carbonates of varying Mg content with acidified, natural seawater to simulate the progressive acidification of surface-ocean waters by anthropogenic CO₂. The results of this study confirm the hypothesis that carbonates will dissolve sequentially according to their respective solubility. They also reveal that the dissolution of high Mg-calcites will proceed incongruently. The originality of this contribution rests with the demonstration that the presence of a single high Mg-calcite will generate, like in a sediment of mixed mineralogy, a continuum of transient states as lower Mg-calcites of greater stability are precipitated and dissolved. Consequently, in a semi-closed or closed system, the pH buffering of the acidified seawater solution will be progressive rather than occur in steps according to changes in the solubility of the individual carbonate phases that compose a sediment. Hence, we expect that, as the oceans take up more anthropogenic CO₂ and further acidify, the average mineralogy and composition (Mg content) of shallow-water carbonate sediments and reef structures will change over the next few centuries as the most soluble carbonate phases (high-Mg calcites) are dissolved and no longer precipitated.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"385 ","pages":"Pages 156-168"},"PeriodicalIF":4.5,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142528603","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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":"Concurrent measurement of strain and chemical reaction rates in a calcite grain pack undergoing pressure solution: Evidence for surface-reaction controlled dissolution","authors":"Harrison Lisabeth,&nbsp;Donald J. DePaolo,&nbsp;Nicholas J. Pester,&nbsp;John N. Christensen","doi":"10.1016/j.gca.2024.09.018","DOIUrl":"10.1016/j.gca.2024.09.018","url":null,"abstract":"<div><div>Pressure solution is inferred to be a significant contributor to sediment compaction and lithification, especially in carbonate sediments. For a sediment deforming primarily by pressure solution, the compaction rate should be directly related to the rate of calcite dissolution, transport along grain contacts, and calcite reprecipitation. Previous experimental work has shown that there is evidence that deformation in wet calcite grain packs is consistent with control by pressure solution, but considerable ambiguity remains regarding the rate limiting mechanism. We present the results of laboratory compaction experiments designed to directly measure calcite dissolution and precipitation rates (recrystallization rates) concurrently with strain rate to test whether measured rates are consistent with predicted rates both in absolute magnitude and time evolution. Recrystallization rates are measured using trace element chemistry (Sr/Ca, Mg/Ca) and isotopes (⁸⁷Sr/⁸⁶Sr) of fluids flowing slowly through a compacting grain pack as it is being triaxially compressed. Imaging techniques are used to characterize the grain contacts and strain effects in the post-experiment grain pack. Our data show that calcite recrystallization rates calculated from all three geochemical parameters are in approximate agreement and that the rates closely track strain rate. The geochemically inferred rates are close to predicted rates in absolute magnitude. Uncertainty in grain contact dimensions makes distinguishing between surface reaction control and diffusion control difficult. Measured reaction rates decrease faster than predicted from standard pressure solution creep flow laws. This inconsistency may indicate that calcite dissolution rates at grain contacts are more complex, and more time-dependent, than suggested by geometric models designed to predict grain contact stresses.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"385 ","pages":"Pages 184-198"},"PeriodicalIF":4.5,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142528488","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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":"Effects of climate change on growth and otolith thermometry of sand whiting (Sillago ciliata)","authors":"Melissa Tan ,&nbsp;Sebastian Litchfield ,&nbsp;Karina C. Hall ,&nbsp;Lewis Adler ,&nbsp;Brendan P. Kelaher","doi":"10.1016/j.gca.2024.09.016","DOIUrl":"10.1016/j.gca.2024.09.016","url":null,"abstract":"<div><div>Increased water temperature and ocean acidification, due to climate change, is predicted to impact aquatic species’ growth, physiology and calcification rates. The present study investigated how a high-emissions scenario of future water temperature and ocean acidification could influence somatic and otolithic growth, and oxygen isotope fractionation in accreted otolith material, of an important fisheries species, sand whiting (<em>Sillago ciliata</em>) (family Sillaginidae), using an outdoor mesocosm system. The experiment included four treatments with an orthogonal combination of current [∼22 °C], and future [∼25.0 °C] predictions of water temperature and current [∼8.13] and future [∼7.83] pH. Fish somatic and otolithic growth demonstrated a positive response to warmer water temperatures, but were not significantly influenced by increased ocean acidification. Stable oxygen isotopes within otolith material (δ¹⁸O_otolith) deposited during the 3-month experimental period, micro-milled from thin-sections and analysed via Isotope Ratio Mass Spectrometry, displayed a negative relationship with water temperature and also varied between acidification treatments. Although acidification increased the intercept of the linear relationship between temperature and oxygen isotope values, the effect was not significant, and the pooled relationship was determined to be δ¹⁸O_otolith – δ¹⁸O_water = – 0.22*<em>T</em> + 34.34 (R² = 0.522, <em>p</em> &lt; 0.001). This model demonstrated a similar slope to that for inorganic aragonite and other fish species, but a noticeably higher intercept. This species-specific relationship has fundamental applications for determining water temperature estimates using δ¹⁸O_otolith values from wild-caught whiting which may elucidate dispersal and movement patterns, thus offering essential information for informed decision-making amidst a changing climate.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"385 ","pages":"Pages 169-183"},"PeriodicalIF":4.5,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142528467","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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":"Reduced partition function ratios of iron, magnesium, oxygen, and silicon isotopes in olivine: A GGA and GGA + U study","authors":"Shanqi Liu ,&nbsp;Yongbing Li ,&nbsp;Zhiming Yang ,&nbsp;Huiquan Tian ,&nbsp;Jianming Liu","doi":"10.1016/j.gca.2024.09.017","DOIUrl":"10.1016/j.gca.2024.09.017","url":null,"abstract":"<div><p>Olivine, typically occurring as a forsterite-fayalite solid solution, is a major rock-forming mineral in mafic and ultramafic igneous rocks, and it is important for understanding the genesis, evolution, and alteration of its host rocks. In this study, both GGA and GGA + U methods were employed to calculate the reduced partition function ratios of Fe, Mg, O, and Si isotopes for the forsterite-fayalite solid solution, aiming to elucidate the impacts of Fe content and Hubbard U correction on the isotope fractionation signatures of Fe, Mg, O, and Si in olivine. On the whole, the <em>β</em>_Fe-factor, <em>β</em>_Mg-factor, <em>β</em>_O-factor, and <em>β</em>_Si-factor decrease with increasing Fe content. The linear correlations between <em>β</em>-factors and bond lengths obtained from GGA + U are better compared to those from GGA. The Hubbard U correction can increase the <em>β</em>_Fe-factor. When Fe/(Fe + Mg) ≤ 1/8, ≤ 1/2, and ≤ 1/2, the effect of Hubbard U correction on <em>β</em>_Mg-factor, <em>β</em>_O-factor, and <em>β</em>_Si-factor can be considered negligible, respectively, suggesting that the <em>β</em>_Mg-factor, <em>β</em>_O-factor, and <em>β</em>_Si-factor of Fe-bearing olivine calculated using GGA + U and those of Fe-free minerals calculated using GGA can be combined to derive 10³ln<em>α</em> and trace geological processes. Furthermore, equilibrium fractionation of Fe, Mg, O, and Si isotopes between olivine and other minerals, including troilite, clinopyroxene, and garnet, were also calculated. Our results are helpful in interpreting the observed data regarding Fe, Mg, O, and Si isotopic compositions of olivine, leading to a comprehensive understanding of relevant geological processes.</p></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"384 ","pages":"Pages 111-127"},"PeriodicalIF":4.5,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142274546","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Comparison between Co(II) and Ni(II) cycling at goethite-water interfaces: Interplay with Fe(II)-catalyzed recrystallization","authors":"Zhen Wang ,&nbsp;Maximilian Mann ,&nbsp;Jessica L. Hamilton ,&nbsp;Jeremy L. Wykes ,&nbsp;Andrew J. Frierdich","doi":"10.1016/j.gca.2024.09.013","DOIUrl":"10.1016/j.gca.2024.09.013","url":null,"abstract":"<div><div>Cobalt (Co) and nickel (Ni) are critical metals for modern renewable energy technologies as well as essential micronutrients for terrestrial plant health and marine primary production. Both metals are commonly surface-adsorbed onto and/or structurally-incorporated into iron (oxyhydr)oxide minerals, such as goethite (α-FeOOH), that are ubiquitously present in soils and sediments at the Earth’s surface. In sub- and anoxic environments, aqueous ferrous iron (Fe(II)) generated from dissimilatory Fe(III) reduction can induce the recrystallization of goethite and subsequently influences the speciation and mobilization of associated metals, e.g., Co(III) being reduced to Co(II). While it is generally considered that divalent Co and Ni behave similarly at goethite-water interfaces, there lacks a direct comparison of their cycling through goethite in response to Fe(II)-catalyzed recrystallization. Here, under circumneutral anoxic conditions with and without addition of aqueous Fe(II), we performed batch reaction experiments on Co(II)-substituted goethite and Co(II) and Ni(II) sorption experiments on pure goethite. The redox state and coordination environment of Co associated with goethite were determined using high energy resolution fluorescence detected X-ray absorption spectroscopy at the Co K-edge, and the distribution of solid-bound Co and Ni in goethite following sorption was revealed by sequential dissolution. Our results show that substitution of Co(II) for Fe(III) in goethite has less negative feedback on Fe(II)-catalyzed recrystallization than Ni(II), which may be related to their differing structural distortions as evidenced by EXAFS. In the absence of Fe(II), aqueous Co(II) is more favourably adsorbed onto and incorporated deeper into goethite than Ni(II), suggesting that Co(II) is more structurally compatible with goethite. The presence of Fe(II) markedly enhances the structural incorporation of both Co(II) and Ni(II) as a result of goethite recrystallization, which in turn can be inhibited by the accumulation of metals at the mineral surface. Furthermore, structurally-incorporated Co(II) is more difficult to be released back into solution (i.e. sum of aqueous and extract fractions) than Ni(II) during Fe(II)-catalyzed goethite recrystallization. Overall, our work highlights the significant differences between Co(II) and Ni(II) in their cycling at goethite-water interfaces and intricate interplay with Fe(II)-catalyzed recrystallization. This improves our understanding of their mobilization and distribution in anoxic goethite-rich systems and can provide useful insights for their enrichment and extraction from natural and artificial laterites generated from the enhanced weathering of ultramafic mine tailings.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"384 ","pages":"Pages 128-139"},"PeriodicalIF":4.5,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0016703724004940/pdfft?md5=1135460db4a328bd0e30de7e3caccd6d&pid=1-s2.0-S0016703724004940-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142311030","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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":"Establishing the content in trace and minor elements of magnetite as a biosignature of magnetotactic bacteria","authors":"François P. Mathon ,&nbsp;Matthieu Amor ,&nbsp;François Guyot ,&nbsp;Nicolas Menguy ,&nbsp;Christopher T. Lefevre ,&nbsp;Vincent Busigny","doi":"10.1016/j.gca.2024.09.020","DOIUrl":"10.1016/j.gca.2024.09.020","url":null,"abstract":"<div><div>Magnetotactic bacteria (MTB) produce intracellular magnetite (Fe₃O₄) nanoparticles in a genetically controlled manner. They may represent some of the oldest biomineralizing organisms available in the geological record, but identification of their fossils remains highly debated. While organic molecules are degraded during diagenesis and metamorphic processes, MTB magnetite nanocrystals can be efficiently preserved in the rock record and are referred to as magnetofossils. Experimental work on the freshwater bacterium <em>Magnetospirillum magneticum</em> strain AMB-1 has demonstrated specific minor and trace element patterns distinct from those of abiotic magnetite, and were proposed as a tool for magnetofossil identification. These promising geochemical signatures need to be validated in diverse MTB strains to be used for paleontological reconstruction. Here, we cultivated a marine MTB (<em>Magnetovibrio blakemorei</em> strain MV-1) under various chemical conditions to test possible generalization of this new proxy. MV-1 was grown under various Fe concentrations (50, 100 and 150 μM) and redox states using either Fe(II)-ascorbate or Fe(III)-citrate as Fe sources. The chemical compositions of the growth media and extracted magnetite crystals were determined by ICP-MS analyses to quantify the partitioning of trace and minor elements between magnetite and solution. Results show that partition coefficients do not depend at first order on the Fe concentration and redox state, a crucial conclusion for potential application to natural systems. A comparison of the two strains shows that MV-1 magnetite generally contains higher concentrations of impurities than AMB-1 magnetite. However, a number of elements possess similar partition coefficients and may represent useful chemical proxies for testing the biological origin of magnetite. These consistent elements can be separated into three groups. The first group is composed of elements (Co, Mn, Pb, Sr) highly depleted in MTB magnetite relative to abiotic magnetite. The second group contains elements with similar partitioning in MTB and abiotic magnetite, including Ca and Li. This group may serve as a reference for constraining a paleo-fluid composition. The last group contains elements (Mo, Sn, Se) enriched in MTB magnetite relative to abiotic magnetite. Such enrichments might be related to biological function of those elements. Chemical patterns determined from laboratory experiments therefore represent promising chemical proxies to identify MTB magnetite in the rock record but now need to be tested in modern natural environments, where MTB and surrounding solution can be jointly collected.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"386 ","pages":"Pages 127-138"},"PeriodicalIF":4.5,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142662969","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Complex irradiation history of chondrules and matrix – A study of CR2 and some other meteorites","authors":"Uta Beyersdorf-Kuis ,&nbsp;Ulrich Ott ,&nbsp;Mario Trieloff","doi":"10.1016/j.gca.2024.09.012","DOIUrl":"10.1016/j.gca.2024.09.012","url":null,"abstract":"<div><p>Excesses of cosmic-ray produced nuclei in individual components of meteorites indicate “pre-irradiation”, either in the surface region of their parent bodies or as free-floating small particles in the early Solar System. We expand on our earlier work (Beyersdorf-Kuis et al., 2015) and report a study of cosmic-ray produced He and Ne in chondrules and “matrix” (i.e., matrix-dominated) material of several CR2 and CV meteorites as well as the highly primitive, unique, carbonaceous chondrite Acfer 094. In accordance with previous work, no evidence for pre-irradiation was found for CV3 Allende, while for CV3 Vigarano evidence for pre-irradiation is marginal at best. Also, the single chondrule from unique Acfer 094 that we studied has a cosmic ray exposure indistinguishable from the one we found for “matrix” material. Chondrules from Acfer 082 (CV) exhibit both excesses and deficits relative to “matrix”, which points to pre-irradiation of not only chondrules, but also matrix material. A similar case may be Renazzo (CR2), where, however, the identification is complicated by the presence of abundant pre-solar Ne-E. A large number of chondrules (ten) were studied from CR2 El Djouf 001, which yielded slightly variable, small but consistent, excesses relative to “matrix”, corresponding to “nominal” (i.e., irradiation by galactic cosmic rays in 4π geometry) excess ages of 1–2 Ma. Modelling suggests contributions from irradiation in the parent body regolith by solar cosmic rays (SCR) as well as galactic cosmic rays (GCR), where the latter dominates. Reevaluating the large variations previously identified in chondrules from QUE 99177, we suggest either a very different regolith history compared to that of El Djouf 001 or, more likely, pre-irradiation by, primarily, GCR in the early solar system as suggested previously. The case of solar-wind-rich NWA 852 (CR2) shows similarity to El Djouf 001 except for a much larger size of the effects. We suggest that the situation may be common among meteorites with a regolith origin. With independent information on the cosmic ray exposure age, which could be obtained by the study of cosmic-ray produced radionuclides, the individual parent body contributions may be disentangled, providing constraints on regolith dynamics.</p></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"384 ","pages":"Pages 65-79"},"PeriodicalIF":4.5,"publicationDate":"2024-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142239128","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}