Geochimica et Cosmochimica Acta最新文献

{"title":"Sedimentary thallium isotopes as a proxy for reconstructing global oceanic oxygenation during millennial-scale events","authors":"Fang Qian ,&nbsp;Yi Wang ,&nbsp;Kassandra M. Costa ,&nbsp;Sune G. Nielsen","doi":"10.1016/j.gca.2025.12.049","DOIUrl":"10.1016/j.gca.2025.12.049","url":null,"abstract":"<div><div>The thallium isotopic composition (ε²⁰⁵Tl) of seawater is a promising proxy for global oceanic redox conditions due to its strong association with manganese oxide burial. Previous studies have linked ε²⁰⁵Tl variability to global oceanic oxygen during the last deglaciation, but these reconstructions were limited to a single core from the Arabian Sea oxygen minimum zone, leaving uncertainties about the proxy's broader spatial applicability. Here, we present a new sedimentary ε²⁰⁵Tl record from ODP Site 1017E in the Southern California Margin oxygen minimum zone spanning the past 32 ka. The ε²⁰⁵Tl record suggests that global oxygen content was lower during the Last Glacial Maximum (∼23–19 ka) relative to the Holocene, with oxygenation during the Heinrich Stadial 1 (∼18–14.7 ka) and the Younger Dryas (∼12.9–11.7 ka), and deoxygenation during the Bølling-Allerød (∼14.7–12.9 ka). These trends mirror ε²⁰⁵Tl records from the Arabian Sea, reinforcing the robustness of Tl isotopes as a global ocean oxygen proxy. We further investigate how the Mn cycle modulates transient ε²⁰⁵Tl variability during the last deglaciation. The results show that short-lived changes in Mn oxide burial, driven by oxygen fluctuations, disrupt steady-state Tl cycling and produce millennial-scale ε²⁰⁵Tl variations. By connecting the Mn and Tl cycle, we present a semi-quantitative model of mean oceanic oxygen content over the last deglaciation highlighting the potential of ε²⁰⁵Tl as a paleo-oxygen proxy. However, an improved understanding of the marine Mn budget and its response to glacial-interglacial cycles is required before true quantitative reconstructions of average ocean oxygen contents with Tl isotopes are possible.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"416 ","pages":"Pages 319-333"},"PeriodicalIF":5.0,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145813958","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":"Transport of Pt and Pd in hydrous sodium silicate melt: A study from X-ray absorption spectroscopy","authors":"Qi Chen ,&nbsp;Jacob Huffaker ,&nbsp;Matt Newville ,&nbsp;Antonio Lanzirotti ,&nbsp;Craig C. Lundstrom","doi":"10.1016/j.gca.2025.12.061","DOIUrl":"10.1016/j.gca.2025.12.061","url":null,"abstract":"<div><div>The molecular-level speciation of Platinum (Pt) and Palladium (Pd) in silicate melt remains an essential issue in understanding the geochemical behavior of these elements in planetary magmas. However, this speciation is poorly understood, particularly in hydrous silicate melts. Here, we present experiments to determine the Pt and Pd speciation in H₂O-rich alkali silicate melts using Synchrotron-based X-ray absorption spectroscopy (XAS). All experiments were conducted in a rapid-quench cold seal system at 750 °C, 100 MPa for 72 h. Chlorine (Cl) contents and oxygen fugacity (<em>f</em>O₂) were varied. The <em>f</em>O₂, controlled by either (1) the intrinsic hydrogen fugacity of the autoclave, or (2) a double-capsule assembly, ranged from Ni-NiO (NNO) + 0.5 to Mn₃O₄-Mn₂O₃. The Pt concentrations in the glass were determined by laser ablation ICP-MS and further evaluated by X-ray fluorescence. Quenched glasses contained Pt or Pd nuggets, leading to heterogeneous distributions that were addressed through combining these two methods. The solubility of Pt in the hydrous peralkaline melt varies from ∼220 ppm under the most oxidizing conditions to &lt;10 ppm at NNO + 0.5.</div><div>By comparing the Pt L₃-edge or Pd K-edge spectra with reference standards, we show that the Pt and Pd oxidation states increase systematically with increasing <em>f</em>O₂. Under the most oxidized condition (Mn₃O₄-Mn₂O₃), Pt is bonded to O with an effective valence near 3+, i.e., a mixed Pt⁴⁺-and Pt²⁺-like environment, with a first-shell Fourier Transform peak occurring at ∼1.70 Å (phase-shift uncorrected). Pd at the same buffer is also O bonded reflecting Pd²⁺ and a Fourier Transform peak at ∼1.44 Å. A decrease in both the absorption edge and white line was observed under more reduced conditions, indicating reduction to lower valence states for both elements. At NNO + 0.5, both Pt and Pd spectra closely approach their respective metal signals. Notably, no Pt-Cl or Pd-Cl scattering is detected in any of the measured samples, despite up to 2.0 wt% Cl dissolved in the melt, demonstrating that chloride does not enter the first coordination sphere of Pt or Pd in these hydrous peralkaline melts under present experimental conditions. These results show that for S-free conditions, redox controls dominate PGE mobility in hydrous silicate melts: appreciable dissolved Pt and Pd species occur only for <em>f</em>O₂ &gt; HM; below this, metallic states dominate, promoting nuggeting and limiting long-range melt-mediated transport.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"416 ","pages":"Pages 40-53"},"PeriodicalIF":5.0,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145893634","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":"Prior calcite precipitation systematics in stalagmites with detrital inputs","authors":"Carlos Pérez-Mejías, Juan Luis Bernal-Wormull, Hai Cheng, Heather M. Stoll","doi":"10.1016/j.gca.2026.02.041","DOIUrl":"https://doi.org/10.1016/j.gca.2026.02.041","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"296 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147334705","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":"Coupling X-ray absorption spectroscopy and chemical extractions to investigate phosphorus phase partitioning in Ningxiang iron deposits","authors":"Qiang Zhou ,&nbsp;Yafang Song ,&nbsp;Kai Gan ,&nbsp;Yijun Xiong ,&nbsp;Than Dam ,&nbsp;Mengqiang Zhu ,&nbsp;Changzhi Wu ,&nbsp;Jihua Hao ,&nbsp;Simon W. Poulton ,&nbsp;Wei Li","doi":"10.1016/j.gca.2026.01.012","DOIUrl":"10.1016/j.gca.2026.01.012","url":null,"abstract":"<div><div>Phosphorus (P) is the ultimate limiting nutrient for primary productivity on geological timescales, but reconstructing ancient seawater phosphate concentrations in iron-rich sediments is complicated by post-depositional transformations that may obscure primary P signatures. Here, we investigate phosphorus phase partitioning in Late Devonian Ningxiang oolitic ironstones from South China, using a combined approach integrating sequential chemical extractions, solid-state ³¹P nuclear magnetic resonance (SSNMR), and P <em>K-edge</em> X-ray absorption near-edge structure (XANES) spectroscopy. The ironstones, composed mainly of hematite, exhibit systematically higher P contents than their siliciclastic host rocks. Our results reveal pronounced stratigraphic variability in P phases: Al/Fe-bound P dominates in the Huangjiadeng Formation, whereas authigenic Ca-phosphates (apatite and carbonate-fluorapatite) prevail in the overlying Xiejingsi Formation. This transition reflects diagenetic transformation of primary Fe-P phases under progressively reducing pore-water conditions, followed by re-precipitation as stable Ca-phosphate minerals. Spectroscopic analyses reveal that Al-bearing minerals constitute a significant, yet previously underappreciated, sink for phosphorus. This redistribution of P among Fe-, Al- and Ca-bound phases challenges the conventional use of bulk P/Fe ratios in Phanerozoic ironstones as direct proxies for paleo-seawater phosphate concentrations. Our study demonstrates that coupling XAFS and NMR spectroscopy with sequential extractions provides a powerful approach to resolve phosphorus phase partitioning and cycling in ancient marine settings.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"416 ","pages":"Pages 94-109"},"PeriodicalIF":5.0,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145962646","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":"Redistribution and oxidation of lead in experimentally heated zircons","authors":"Paulina Zieja ,&nbsp;Monika A. Kusiak ,&nbsp;Pilar Montero ,&nbsp;Fernando Bea ,&nbsp;Richard Wirth ,&nbsp;Bożena Gołębiowska ,&nbsp;Aitor Cambeses","doi":"10.1016/j.gca.2026.01.016","DOIUrl":"10.1016/j.gca.2026.01.016","url":null,"abstract":"<div><div>The disturbance of the U-Pb isotopic system in zircon (ZrSiO₄) is an important factor for U-Th-Pb geochronology, therefore understanding zircon nanostructure is crucial for reliable age determination. To understand the process of Pb mobilization in zircon, heating experiments on zircon grains from two samples of the Central Iberian Zone (CIZ), a Variscan tonalite and a Cambro-Ordovician orthogneiss, were performed. Samples were heated at 1400 °C for 30, 90 and 180 days in a horizontal furnace in N₂ at 1 atm. Following the experiment, nano- and microstructural analyses were performed using Transmission Electron Microscopy (TEM). Mobilization of Pb was documented only in zircons from orthogneiss – these grains contain Pb nanospheres. Zircon grains from orthogneiss showed a significant influence of heating during the experiment on the microstructure. We observed Pb nanospheres (Pb⁰) and Pb nanoinclusions containing Pb in different oxidation states, namely Pb²⁺ and Pb⁴⁺. This is the first paper documenting nanospheres of metallic Pb existing together with Pb oxides (PbO, Pb₂O₃, Pb₃O₄ and PbO₂) in one sample. As a result of heating, Pb was oxidized and after 6 months of heating, the spheres of metallic Pb were no longer found. The formation of metallic Pb nanospheres is explained by an annealing process at elevated temperature, that caused the concentration of Pb in noncrystalline, metamict domains of zircon. This study indicates that more than one mechanism can be responsible for the formation of nanospheres. In this case, chemical elements present in zircon as inclusions react with Pb causing its oxidation.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"416 ","pages":"Pages 154-167"},"PeriodicalIF":5.0,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145995735","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":"Atomistic mechanisms of reactive oxygen species generation via O2 adsorption and activation on corundum surfaces: implications for transition metal redox","authors":"Mengning Xi,&nbsp;Chi Zhang,&nbsp;Zhiqiang Wang,&nbsp;Hanzhong Jia","doi":"10.1016/j.gca.2026.01.024","DOIUrl":"10.1016/j.gca.2026.01.024","url":null,"abstract":"<div><div>Understanding the activation of molecular oxygen and the generation of reactive oxygen species (ROS) on minerals is critical for elucidating a variety of geochemical and environmental processes, such as mineral weathering, pollutant degradation, and metal cycling. Despite their prevalence in geological systems, the atomistic mechanisms of dissolved O₂ activation at aluminum oxide interfaces remain poorly understood, even though this process is crucial for subsurface redox reactions. Herein, we combined first–principle molecular dynamics (FPMD) simulations with experimental characterizations to investigate the atomic–scale activation mechanism of molecular oxygen on corundum surfaces. Oxygen vacancies are identified as pivotal sites for O₂ activation, enabling electron transfer to form superoxide (O₂^•–) via inner–sphere adsorption on defective (001) and (012) surfaces. A comparative analysis reveals that the side–on configuration enables more efficient electron transfer from oxygen vacancies to adsorbed O₂ than the end–on configuration, with the defective (012) surface exhibiting superior activation capability relative to the (001) surface. Additionally, the reaction pathways mediated by generated O₂^•– are quantitatively characterized, including the oxidation of Mn(II) and the reduction of Cr(VI). These results elucidate the detailed dynamic processes governing molecular oxygen adsorption, activation, and ROS–mediated redox reactions at corundum–water surfaces. This work provides a mechanistic framework for understanding ROS formation and transformation on non–transition metal oxides, with implications for the geochemical cycling of transition metals controlled by mineral surfaces.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"416 ","pages":"Pages 252-264"},"PeriodicalIF":5.0,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146015034","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 preservation of silicon isotope ratios in cherts and recrystallized sponge spicules","authors":"Yan Ye ,&nbsp;Patrick J. Frings ,&nbsp;Daniel A. Frick ,&nbsp;Friedhelm von Blanckenburg ,&nbsp;Qinglai Feng","doi":"10.1016/j.gca.2026.01.040","DOIUrl":"10.1016/j.gca.2026.01.040","url":null,"abstract":"<div><div>The early Phanerozoic has long been thought to have witnessed a decline in the ocean dissolved silicon inventory, but direct, quantitative investigations of dissolved silicon concentrations are missing. Silicon isotope fractionation by modern siliceous sponges is known to be related to ambient seawater silicon concentrations, opening a potential window onto reconstructions of silicon concentrations in geological time. However, whether the ratios of silicon stable isotopes (expressed as δ³⁰Si) in spicule silica can be preserved during the diagenetic transformations from amorphous silica to (re)crystallized quartz is unclear.</div><div>Here, we use <em>in situ</em> analyses of δ³⁰Si by femtosecond laser ablation multi-collector ICP mass spectrometry on sponge spicules and their matrix in Ediacaran-Cambrian cherts from the Yanziqiao section, South China. These cherts formed from seawater with little hydrothermal influence and span the proposed silicon inventory decline. All samples are pure cherts (SiO₂ &gt; 95%) dominated by microquartz. Under transmitted light, white spicules are easily distinguished from the darker matrix and usually exhibit monoaxial or multiaxial shape. There is only subtle difference between the δ³⁰Si of matrix and sponge spicules (the difference between their average δ³⁰Si values is within 0.4 ‰), implying alteration and homogenization of δ³⁰Si during diagenesis. <em>In situ</em> δ³⁰Si and Al/Si ratios in the matrix sometimes exhibit a positive relationship, which we explain by the influence of Al on the kinetics of silica diagenesis. Higher Al content can contribute to earlier transformation of silica phases under shallower burial and lower temperature, associated with a larger equilibrium fractionation factor and higher δ³⁰Si. Overall, the original δ³⁰Si at micrometer scales is most likely to be destroyed during diagenesis, and the reconstruction of dissolved silicon concentrations from <em>in situ</em> analyses of recrystallized spicules thus rendered unjustifiable. However, a reaction-advection–diffusion model shows that δ³⁰Si of bulk chert can still record relatively pristine information of initial sediment δ³⁰Si. Moreover, the range of <em>in situ</em> δ³⁰Si in cherts provide hints to distinguish if they are dominated by equilibrium or kinetic effects, which is important if we wish to reconstruct seawater δ³⁰Si from bulk chert δ³⁰Si.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"416 ","pages":"Pages 29-39"},"PeriodicalIF":5.0,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146071838","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":"A new pair of lunar gabbroic meteorites record magma recharge at ∼ 3.0 Ga","authors":"P.Y. Li, Y. Jiang, K. Zhao, S.Y. Liao, X.C. Che, X.R. Zhang","doi":"10.1016/j.gca.2026.02.040","DOIUrl":"https://doi.org/10.1016/j.gca.2026.02.040","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"44 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147334707","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":"Assessing the plausibility of direct constraints on ancient atmospheric P CO 2 from fluid inclusions in halite: a theoretical and experimental approach","authors":"Michael Naylor Hudgins, Justin G. Park, Alex M. Ryan, Jessika A. Rogers, Morgan F. Schaller","doi":"10.1016/j.gca.2026.02.039","DOIUrl":"https://doi.org/10.1016/j.gca.2026.02.039","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"95 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147334710","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":"Molecular inventory and comparative organic profiling of a homogenized aggregate sample from asteroid (101955) Bennu","authors":"José C. Aponte, Denise K. Buckner, Angel Mojarro, Jamie E. Elsila, Jason P. Dworkin, Daniel P. Glavin, Harold C. Connolly, Dante S. Lauretta","doi":"10.1016/j.gca.2026.02.036","DOIUrl":"https://doi.org/10.1016/j.gca.2026.02.036","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"68 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147334706","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}