Geochimica et Cosmochimica Acta最新文献

{"title":"Oxygen and hydrogen isotope compositions in dentine collagen correlate strongly with oxygen isotope compositions of enamel carbonate","authors":"L.M. Reynard,&nbsp;M.J. Kohn","doi":"10.1016/j.gca.2025.05.009","DOIUrl":"10.1016/j.gca.2025.05.009","url":null,"abstract":"<div><div>The isotopic composition of tooth and bone has long been exploited in ecological, environmental, and archaeological studies. Increasingly, hydrogen and oxygen isotopes in collagen are used as tracers of environment and diet. However, the isotopic relationship between hydrogen and oxygen in collagen and oxygen in tooth enamel is poorly described. A new investigation of varied wild large herbivores shows that δ¹⁸O and δ²H in collagen are both strongly correlated to δ¹⁸O in tooth enamel carbonate (r² = 0.96 and r² = 0.86, respectively), with a δ¹⁸O collagen vs. δ¹⁸O carbonate slope ∼ 0.8 and a δ²H collagen vs. δ¹⁸O carbonate slope ∼ 6. Given that enamel carbonate δ¹⁸O generally reflects environmental water isotopic composition, δ²H and δ¹⁸O in collagen also reflect isotopic compositions in environmental water and may be used analogously to tooth enamel for environmental or dietary studies.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"400 ","pages":"Pages 204-213"},"PeriodicalIF":4.5,"publicationDate":"2025-05-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144133759","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":"Compound class carbon isotope characterization of organic matter sources, transport, and degradation in sediments of large river-influenced coastal oceans","authors":"Fuqiang Wang ,&nbsp;Shuwen Sun ,&nbsp;Weikun Xu ,&nbsp;Wenjing Fu ,&nbsp;Honghua Shi ,&nbsp;Meixun Zhao","doi":"10.1016/j.gca.2025.05.008","DOIUrl":"10.1016/j.gca.2025.05.008","url":null,"abstract":"&lt;div&gt;&lt;div&gt;The Yangtze River Estuary and the adjacent inner shelf are significant areas for both the burial and degradation of terrestrial organic matter (OM). However, the impact of hydrodynamics on the degradation of different types of organic compound classes has not been fully elucidated. This study measured dual carbon isotopes (δ&lt;sup&gt;13&lt;/sup&gt;C, Δ&lt;sup&gt;14&lt;/sup&gt;C) of organic compound classes [total hydrolysable amino acids (THAAs), total lipids, humic acids (HAs) and acid-base insoluble OM] in both surface and core sediment samples to evaluate the influences of hydrodynamic processes on the fates of organic compound classes in the Yangtze River Estuary and the adjacent inner shelf. In surface sediments, the δ&lt;sup&gt;13&lt;/sup&gt;C (−28.6 ± 0.6 ‰ in lipids; −21.8 ± 0.5 ‰ in THAAs) and Δ&lt;sup&gt;14&lt;/sup&gt;C (−598 ± 41 ‰ in lipids; −143 ± 47 ‰ in THAAs) values of lipids and THAAs from the mobile-muds are lower than those from the offshore areas (δ&lt;sup&gt;13&lt;/sup&gt;C: −27.9 ± 0.4 ‰ in lipids; −20.9 ± 0.8 ‰ in THAAs; Δ&lt;sup&gt;14&lt;/sup&gt;C: −559 ± 20 ‰ in lipids; −64 ± 7 ‰ in THAAs), indicating replenishment of marine source may be the primary factor contributing to the rejuvenation of lipids and THAAs during seaward transport. In contrast, both HAs and acid-base insoluble OM have higher Δ&lt;sup&gt;14&lt;/sup&gt;C values in mobile muds (−298 ± 28 ‰ and −322 ± 21 ‰, respectively) than those in offshore areas (−443 ± 14 ‰ and −533 ± 30 ‰, respectively), suggesting significant aging even for the refractory OM during transport processes. The three end-member model of organic compound classes shows that lipids and THAAs in mobile-muds have higher marine source than offshore areas, while HAs show opposite change. These results indicate organic compound classes undergo different transport and degradation mechanisms during seaward transport, then affecting the contributions of marine and terrestrial sources to marine sediments. The different correlations between Δ&lt;sup&gt;14&lt;/sup&gt;C values of labile (THAAs) and refractory (HAs and acid-base insoluble OM) OM with specific mineral surface areas (SSA) also indicate different transport and degradation mechanisms of organic compound classes in surface sediments, and causing rejuvenation of THAAs and gradually aging of HAs and acid-base insoluble OM during seaward transport. In core QT1 samples, the younger &lt;sup&gt;14&lt;/sup&gt;C ages and large variations in the accumulation rates of labile THAAs since 2003 indicate that the construction of the TGD probably altered the hydrodynamic and depositional environment in these areas, and causing the degradation of THAAs in the sediment cores. In contrast, acid-base insoluble OM have stable &lt;sup&gt;14&lt;/sup&gt;C ages and accumulation rates in cores TQ1 and QT3, suggesting minor impacts from human activities and physical processes. These carbon isotopic results suggest that labile and refractory OM respond differently to hydrodynamics, with refractory OM playing a key role in the burial of terrestrial carbon in marine sediments.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"400 ","pages":"Pages 190-203"},"PeriodicalIF":4.5,"publicationDate":"2025-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144083377","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":"Noble gases in CO chondrites: Primordial components, effects of parent body thermal alteration, and cosmic ray exposure ages","authors":"Lisa Maria Eckart ,&nbsp;Henner Busemann ,&nbsp;Daniela Krietsch ,&nbsp;Cornelia A.K. Mertens ,&nbsp;Colin Maden ,&nbsp;Conel M.O’D. Alexander ,&nbsp;Kevin Righter","doi":"10.1016/j.gca.2025.04.021","DOIUrl":"10.1016/j.gca.2025.04.021","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Carbonaceous chondrites of the Ornans type (COs) include some of the most primitive meteorites known to date, yet most of them show evidence of having experienced mild degrees of thermal alteration in their parent asteroid. Previous studies on aqueously altered CM, CR, and CY chondrites have shown that the noble gases trapped in various components with distinct susceptibility to alteration can be used to assess the extent of parent body processing. In this study, we investigated the noble gas compositions of 51 CO chondrites ranging from petrologic type 3.0 to 3.8, three suspected Mighei-type chondrites (CMs; MIL 090073, DOM 10121, DOM 10299) initially classified as COs, and DOM 10900 with intermediate properties between CMs and COs. The COs show a noble gas mixture typical for carbonaceous chondrites, deriving from primordial carriers such as presolar grains, phase Q, and the carrier of the Ar-rich/V component, which has been observed in anhydrous chondrites, and occasionally air. Additionally, the newly identified W component could be present, which is highly susceptible to water. Combining our results with CO noble gas data from the literature, we show that the &lt;sup&gt;20&lt;/sup&gt;Ne&lt;sub&gt;tr&lt;/sub&gt;/&lt;sup&gt;132&lt;/sup&gt;Xe&lt;sub&gt;corr&lt;/sub&gt; ratios correlate best (decrease) with the degree of thermal alteration, likely related to the abundance of presolar diamonds, and may thus serve as tool to subclassify thermally altered chondrites. Based on its &lt;sup&gt;20&lt;/sup&gt;Ne&lt;sub&gt;tr&lt;/sub&gt;/&lt;sup&gt;132&lt;/sup&gt;Xe&lt;sub&gt;corr&lt;/sub&gt; ratio, DOM 10847 (paired with DOM 08006) is the most primitive CO, followed by NWA 13464 and Y-74135. The &lt;sup&gt;20&lt;/sup&gt;Ne&lt;sub&gt;tr&lt;/sub&gt;/&lt;sup&gt;132&lt;/sup&gt;Xe&lt;sub&gt;corr&lt;/sub&gt; subclassification tool, however, may not be applicable for intergroup comparisons as the stability of the responsible carriers are sensitive to the chemical environment of the parent body. The abundances of heavy noble gases in bulk CO samples are much higher compared to CO etch residues (remaining after demineralization of a bulk meteorite) from the literature, indicating that other carrier(s) than insoluble organic matter must contribute significantly to the heavy noble gas inventory, which is/are susceptible to thermal alteration. DaG 331 was subclassified in this work to be a CO3.1 using the method by &lt;span&gt;&lt;span&gt;Grossman and Brearley (2005)&lt;/span&gt;&lt;/span&gt; and the trend line defined by &lt;span&gt;&lt;span&gt;Davidson et al. (2019)&lt;/span&gt;&lt;/span&gt;.&lt;/div&gt;&lt;div&gt;The COs show a wide range in cosmic ray exposure (CRE) ages between 0.17 ± 0.05 Ma (Isna) and 78 Ma (maximum age determined for DOM 18286 with an uncertainty of &lt; 10 %), although the majority of CRE ages are &gt; 10 Ma. DOM 18286 has the highest CRE age reported to date for a carbonaceous chondrite. We did not find any age clusters hinting at a major impact event, nor a correlation between CRE ages and the petrologic types. Strikingly, none of the 63 COs analyzed for their noble gases (including literature) contains solar wind, indicating t","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"402 ","pages":"Pages 104-133"},"PeriodicalIF":4.5,"publicationDate":"2025-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144633940","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":"The formation of the trinitites unveiled by their oxygen and silicon isotopic compositions","authors":"Nathan Asset ,&nbsp;Marc Chaussidon ,&nbsp;Christian Koeberl ,&nbsp;Johan Villeneuve ,&nbsp;François Robert","doi":"10.1016/j.gca.2025.05.011","DOIUrl":"10.1016/j.gca.2025.05.011","url":null,"abstract":"<div><div>During the world’s first nuclear explosion, in 1945, glassy melts called “trinitites”, mostly derived from the sands at the surface of the test site, formed and were deposited at or near the hypocenter. The processes of formation of this fallout remain unclear. Here, we show how the oxygen and silicon isotopic compositions of three trinitites allow to refine their formation scenario. The three samples are typical of trinitites, being composed of various crystalline phases and of glassy phases divided into three chemical groups (CaMgFe, alkali, silica) that are mixed in various proportions in the three samples. The three samples show a large range of oxygen and silicon isotopic variations (−10.9 ± 0.6 &lt; δ³⁰Si &lt; 4.2 ± 0.6 ‰, and 2.3 ± 0.4 &lt; δ¹⁸O &lt; 24.2 ± 0.5 ‰). At variance with the Hiroshima fallout deposits, no oxygen mass-independent isotopic fractionation was found in the three trinitites. The chemical and isotopic compositions of the chemical groups reveal that they result from different processes: the silica phases are molten fragments of the site material, while the CaMgFe and alkali phases are produced by the mixing of condensates and molten site material. Models show that the observed silicon isotopic variations resulted from Rayleigh distillation during condensation of the gaseous species injected into the cloud, while the variability in composition of the site materials also played an important role for controlling the oxygen isotopic compositions. From these observations, a general scenario, beginning with the vaporization of the site surface, producing a depression, is proposed. The vaporized material condensed and grew by agglomeration with other condensates and liquid materials. These agglomerates rained on the surface and quenched, forming the trinitites. This scenario is different from the formation of the Hiroshima glasses but shows some similarities to tektite formation.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"400 ","pages":"Pages 214-226"},"PeriodicalIF":4.5,"publicationDate":"2025-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144255390","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":"Tin isotope systematics in subduction zones","authors":"Xueying Wang ,&nbsp;Oliver Nebel ,&nbsp;Alexandra Churchus ,&nbsp;Peter A. Cawood","doi":"10.1016/j.gca.2025.05.004","DOIUrl":"10.1016/j.gca.2025.05.004","url":null,"abstract":"<div><div>The origin of slab components in arc lavas remains controversial with proposed sources including direct sediment melts, sediment-mantle mélanges, or crustal fluids. Stable isotope distributions of fluid-borne metals and those immobile in subduction components have the potential to trace the respective contribution of these components if placed into the context of additional magmatic differentiation and in conjunction with radiogenic isotopes. Here, we present the first high-precision double-spike tin abundances and isotope compositions in twenty-six arc rocks sampled along the Indonesian Sunda arc, a subduction zone with the highest subducted sediment volume globally. <em>δ</em>^122/118Sn_3161a in these samples ranges from 0.13‰ to 0.46‰ and we find that Sn isotope compositions in Sunda arc rocks were affected by magmatic differentiation, superimposed on additional influences from components derived from the subducting slab. A step change in <em>δ</em>^122/118Sn_3161a at 4–5wt.% MgO suggests the removal of heavier Sn isotopes, likely due to higher compatibility of isotopically heavier Sn⁴⁺ in Fe-Ti oxides along the liquid line of descent. This change of ∼0.1‰, however, is dwarfed by Sn isotope variations consistent with sediment melt contribution coupled with fluid addition from altered oceanic crust, both of which introduce lighter Sn isotopes. Sediment melt contamination increases with depth (temperature), but some exceptions at shallow sub-arc sources (depth ≤ 130 km) indicate additional melting of a mélange-style source. Our findings suggest the coexistence of mélange contributions, and deep fluid-induced melting plus partial sediment melts in the Sunda arc. Mélanges contribute only at shallow depths (≤130 km), consistent with their diapiric nature, whereas deeper levels favor fluid-fluxed melting and, at higher temperatures and pressures, partial sediment melting. This study provides insights into the complex interactions between fluids, sediments, and mantle wedge in subduction zones, highlighting the depth-dependent nature of slab contributions to arc magmatism. It also demonstrates the utility of Sn isotopes for tracing these processes and advancing our understanding of subduction zone geochemistry.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"399 ","pages":"Pages 18-34"},"PeriodicalIF":4.5,"publicationDate":"2025-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143947247","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":"Large Zn isotope variations in lower oceanic crust offer insights into oceanic crustal magma plumbing system","authors":"Wei-Qi Zhang ,&nbsp;Chuan-Zhou Liu ,&nbsp;Zong-Qi Zou ,&nbsp;Xiao-Ni Li","doi":"10.1016/j.gca.2025.05.005","DOIUrl":"10.1016/j.gca.2025.05.005","url":null,"abstract":"<div><div>Constraining mid-ocean ridge magmatic processes is crucial for understanding the geochemical evolution of magmas traversing the oceanic crust. A crucial archive for investigating these magmatic processes is the chemical composition of lower oceanic crust. This study presents Zn isotope data for primitive to highly evolved cumulates from the Mid-Atlantic Ridge (Kane) and the Southwest Indian Ridge (IODP Hole U1473A), which are compared with published mid-ocean ridge (MOR) lava data. Previous studies have indicated that high-degree magma differentiation results in small Zn isotope fractionation (&lt;0.1 ‰) in the mafic to felsic MOR lavas. Unlike the MOR lavas, significant δ⁶⁶Zn variations (0.1 − 0.5 ‰) are observed in the Kane and U1473A cumulates, which cannot be explained by crystal accumulation alone but reflect the variable incorporation of trapped melts. These trapped melts exhibit heavy δ⁶⁶Zn (&gt;0.5 ‰) and strongly fractionated trace element characteristics, indicative of extensive melt-rock interactions. Furthermore, the bulk normal mid-ocean ridge basalt (N-MORB)-type lower oceanic crust has δ⁶⁶Zn values (0.24 ± 0.11 ‰) that are close to the average N-MORB (0.26 ± 0.06 ‰), suggesting minor Zn isotope fractionation during the crustal processing of MOR lavas. It is proposed that the small δ⁶⁶Zn variations in MOR magmas result from the homogenization and dilution of reactive signals within the eruptive reservoir. In contrast, prolonged processing of trapped melts through melt-rock interactions leads to significant Zn isotope fractionation in the lower oceanic crust. Thus, the evolution of oceanic crustal magma plumbing systems is more complex than inferred from MORB alone. Despite these complexities, efficient homogenization within eruptive reservoirs results in limited Zn isotopic variations in the erupted magmas. Hence, the Zn isotopic variations in MORB, except for the highly evolved ones, are predominantly linked to the source heterogeneity. Our findings also suggest heterogeneous δ⁶⁶Zn in subducted oceanic crusts, which has implications for mantle Zn isotope heterogeneity.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"400 ","pages":"Pages 158-171"},"PeriodicalIF":4.5,"publicationDate":"2025-05-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144083378","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":"Combined Ca, Sr isotope and trace element analyses of Late Cretaceous dinosaur teeth: assessing diet versus diagenesis","authors":"Mateusz M. Michailow ,&nbsp;Federico Lugli ,&nbsp;Anna Cipriani ,&nbsp;Francesco Della Giustina ,&nbsp;Annalisa Ferretti ,&nbsp;Daniele Malferrari ,&nbsp;Denver Fowler ,&nbsp;Elizabeth Freedman Fowler ,&nbsp;Michael Weber ,&nbsp;Thomas Tütken","doi":"10.1016/j.gca.2025.05.006","DOIUrl":"10.1016/j.gca.2025.05.006","url":null,"abstract":"<div><div>The Sr and Ca isotope composition, along with trace element content in fossil teeth, provides valuable insights into biogenic and diagenetic processes. Identifying pristine biological signals is crucial for reconstructing the diet and trophic levels of extinct taxa. We present novel geochemical data from Tyrannosauridae and Ceratopsidae teeth of the Late Cretaceous, using radiogenic Sr (⁸⁷Sr/⁸⁶Sr), stable Sr (<em>δ</em>^88/86Sr), and Ca (<em>δ</em>^44/42Ca) isotopes, along with trace elements abundances to differentiate biogenic signals from diagenetic alteration.</div><div>Our results reveal potential taxon-specific diagenetic effects, likely influenced by enamel microstructure. Tyrannosaurid enamel contains lower concentrations of rare earth elements (REE) and uranium (U) than dentine, whereas ceratopsid teeth typically exhibit higher REE and U compared to both the enamel and dentine of tyrannosaurids. Enamel <em>δ</em>^44/42Ca values differ significantly between herbivorous ceratopsids and carnivorous tyrannosaurids, reflecting trophic level effects seen in modern mammals and reptiles. A positive correlation between <em>δ</em>^44/42Ca and <em>δ</em>^88/86Sr suggests partial preservation of biological fractionation along the trophic chain. Yet, the lack of negative <em>δ</em>^88/86Sr values in our dataset – typically expected in biologic tissues – suggests alteration by diagenetic processes of both stable and radiogenic Sr. While <em>δ</em>^44/42Ca in enamel likely remains a reliable dietary proxy, Sr isotope composition of our samples appears then to be significantly altered. The presence of high <em>δ</em>^88/86Sr in terrestrial fossil teeth could serve as a novel diagenetic proxy to assess habitat related ⁸⁷Sr/⁸⁶Sr values, aiding provenance and mobility studies in fossil ecosystems.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"400 ","pages":"Pages 172-189"},"PeriodicalIF":4.5,"publicationDate":"2025-05-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144133760","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":"Coprecipitation of phosphate with calcite: Molecular-scale evidence for incorporation and inclusion mechanisms","authors":"Chao Ren ,&nbsp;Yongfang Li ,&nbsp;Shaofeng Wang ,&nbsp;Jingzhao Wang ,&nbsp;Junfeng Ji ,&nbsp;Henry H. Teng ,&nbsp;Brian L. Phillips ,&nbsp;Kideok D. Kwon ,&nbsp;Wei Li","doi":"10.1016/j.gca.2025.04.032","DOIUrl":"10.1016/j.gca.2025.04.032","url":null,"abstract":"<div><div>Coprecipitation of phosphate in calcium carbonate minerals is a ubiquitous geochemical phenomenon in marine sedimentation and cave stalagmite formation, however, it is not clear whether phosphate is incorporated into the calcite structure. In this research, we applied solid-state nuclear magnetic resonance (NMR) spectroscopy to analyze P speciation during coprecipitation with calcite. The ³¹P NMR results show three peaks with chemical shifts of 3.9, 3.0 and −1.0 ppm, indicative of at least three phosphate species in the coprecipitates. Combined with advanced ³¹P{¹H} cross-polarization (CP)/MAS, ¹H DE/MAS, ³¹P{¹H} 2-d heteronuclear correlation (HetCor) and ³¹P{¹³C} cross-polarization rotational echo double resonance (CP-REDOR) NMR experiments, the 3.9 ppm peak can be tentatively assigned to calcite structural defects as amorphous calcium phosphate (ACP)-like environments while the 3.0 ppm peak arises from a carbonated hydroxyapatite (CHap). The ³¹P NMR peak at −1.0 ppm can be assigned to structurally incorporated phosphate in the calcite crystals in the form of HPO₄²⁻. Nano secondary ion mass spectrometry (NanoSIMS) and high-resolution scanning transmission electron microscopy (HR-STEM) analysis further suggests that the incorporated HPO₄²⁻ substitutes for the structural carbonate group (CO₃²⁻) of calcite. However, the local expansion stress field generated with HPO₄²⁻ incorporation in the calcite structure prevents PO₄/CO₃ isomorphous substitution and favors the precipitation of calcium phosphates. The findings of this study not only provide deep insights into carbonate crystal chemistry but also shed light on the application of carbonate materials as potent geochemical proxies in paleoenvironmental reconstructions.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"399 ","pages":"Pages 1-17"},"PeriodicalIF":4.5,"publicationDate":"2025-05-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143922530","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":"238U/235U isotopic variations in angrites and their constituent minerals","authors":"Magdalena H. Huyskens ,&nbsp;Yuri Amelin ,&nbsp;Qing-Zhu Yin ,&nbsp;Tsuyoshi Iizuka","doi":"10.1016/j.gca.2025.04.030","DOIUrl":"10.1016/j.gca.2025.04.030","url":null,"abstract":"<div><div>Ages of angrites, a diverse and rapidly growing group of differentiated meteorites, are important for understanding the history of their parent body, which is proposed to be an archetypal first-generation planetesimal. Angrites also commonly serve as a time reference in the early Solar System chronology. Pb-isotopic ages of angrites can be determined with high precision, and the isotopic composition of uranium thus becomes a major contributor to the age accuracy and its total uncertainty budget. Two main groups of angrites, the rapidly cooled (volcanic and/or impact-generated) and plutonic angrites, were previously found to contain uranium with different ²³⁸U/²³⁵U ratios. The variations in isotopic compositions between mineral carriers of uranium within individual angrites, which are directly relevant to calculation of accurate Pb-isotopic ages, have not been studied yet. In this study, we determined the ²³⁸U/²³⁵U for whole rocks, leachate and residue of whole rocks and mineral separates for two rapidly cooled angrites D’Orbigny and Sahara 99555 and three plutonic angrites NWA 4801, NWA 4590 and Angra dos Reis. For the rapidly cooled angrites, all mineral separates as well as the whole rocks show consistent ²³⁸U/²³⁵U. Whole rock ²³⁸U/²³⁵U ratios for the plutonic angrites are distinctly lower than the ratios in the rapidly cooled angrites. In Angra dos Reis and NWA 4590, merrillite has higher ²³⁸U/²³⁵U than pyroxene, and both minerals have higher ²³⁸U/²³⁵U ratios than the respective whole rock, suggesting the presence of an unidentified mineral host of uranium with lower ²³⁸U/²³⁵U. These differences in U isotope composition could be possibly attributed to a combination of mass dependent and mass-independent isotope fractionation driven by the differences of oxidation state, and coordination in the crystals. We recalculated the existing Pb-isotopic dates when possible with the measured ²³⁸U/²³⁵U for the minerals that were used for the Pb-isotopic dating. The differences in U isotopic composition between cogenetic minerals point to the importance of ²³⁸U/²³⁵U determination in specific minerals that are used for Pb-isotopic dating for plutonic achondrites, rather than U isotopic data for bulk meteorites.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"399 ","pages":"Pages 205-220"},"PeriodicalIF":4.5,"publicationDate":"2025-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144083379","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":"Thallium cycling and boundary exchange in a continental margin basin","authors":"Kasper P. Olesen ,&nbsp;Sune G. Nielsen ,&nbsp;Chadlin M. Ostrander ,&nbsp;Nicol Udy ,&nbsp;Donald E. Canfield","doi":"10.1016/j.gca.2025.04.005","DOIUrl":"10.1016/j.gca.2025.04.005","url":null,"abstract":"<div><div>Thallium (Tl) isotopes are a robust tracer of ancient ocean oxygenation through their link to the burial flux of deep-sea manganese oxide minerals. Yet, the details of Tl geochemistry at the continental margin remain largely unexplored, hindering quantitative application of the palaeoredox proxy. To develop our understanding of Tl diagenesis, phase dynamics, and mass transfer at the continent-ocean interface, we collected sediments from three sites in the perenially oxic Skagerrak sea as well as sediments and suspended particles from five adjacent rivers. The three Skagerrak sediment sites are biogeochemically diverse, with variable oxygen penetration (9–18 mm) and C-oxidation occurring predominantly through either sulfate, iron, or manganese reduction. Sequential extractions and porewater analyses reveal a highly homogeneous abundance and phase association pattern of Tl across all sample types and sites. Sediment and particle Tl resides almost exclusively in acid-leachable aluminous clays and residual crystalline phases. We interpret these phases to be terrigenous, except at the highly Mn-enriched site S9 where we find up to ∼45 % of Tl is authigenic. This claim is supported by Tl isotopic compositions of acid-leachable sediment (ε²⁰⁵Tl_HNO3), which average –2.5 ± 0.9‱, within uncertainty of the average upper crust value of –2.0 ± 0.5‱ and a regional riverine particle delivery value of –2.1 ± 1.2‱.</div><div>Incubations of Skagerrak sediments with added bottom water Tl reveal a fractionation factor (α) of ∼1.0007, amounting to an isotope ratio difference of ∼7‱. A comparable fractionation of 2.4 to 4.5‱ is calculated for authigenic Tl removal in the Skagerrak sediments. However, this fractionation is lower than that observed in deep sea pelagic clays and hydrogenetic Mn crusts and nodules (α ∼1.0021), yet significantly higher than expected for mature diagenetic Mn oxides like triclinic birnessite and todorokite (α ∼1.00005). Thallium cycling is largely decoupled from Mn diagenesis at our marine sites and only associates weakly with the active sedimentary Mn recycling. Rather, effluxing of dissolved Tl is observed at all sites. We employ a diagenetic reaction-transport model to quantify dissolved Tl fluxes and compare these fluxes with independent assessments of Tl mass balance based on authigenic/terrigenous Tl proportions. We find that within the oxic Skagerrak basin, sediments may be both true sources and, if Mn-enriched, true sinks of Tl, with extrapolated flux magnitudes relevant to marine Tl mass balances. Our study presents a much-needed description of Tl diagenesis in diffusive margin sediments and suggests that hitherto unrecognized sources of originally terrigenous Tl to the marine environment may occur at the continent-ocean boundary, either via the release of labile clay-bound Tl directly from riverine particles or during sediment diagenesis.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"399 ","pages":"Pages 64-81"},"PeriodicalIF":4.5,"publicationDate":"2025-05-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144083381","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}