Chemical Geology最新文献

{"title":"Iron and nitrate-driven anaerobic methane oxidation in methane seep sediments of the Laptev Sea","authors":"D. Purgina ,&nbsp;Yu Moiseeva ,&nbsp;B. Wild ,&nbsp;N. Guseva ,&nbsp;E. Gershelis ,&nbsp;O. Gustafsson ,&nbsp;A. Khvashevskaya ,&nbsp;S. Pakhomova ,&nbsp;V. Kholodov ,&nbsp;O. Dudarev ,&nbsp;D. Kosmach ,&nbsp;D. Chernykh ,&nbsp;T. Polivanova ,&nbsp;I. Gangnus ,&nbsp;A. Kurilenko ,&nbsp;A. Domaniuk ,&nbsp;E. Yakushev ,&nbsp;I. Semiletov","doi":"10.1016/j.chemgeo.2025.123170","DOIUrl":"10.1016/j.chemgeo.2025.123170","url":null,"abstract":"<div><div>The East Siberian Arctic Shelf (ESAS) is a significant source of atmospheric methane, and the coastal Laptev Sea near the Lena River Delta is a documented hotspot for methane seepage. While anaerobic oxidation of methane (AOM) acts as a critical biofilter, the specific pathways and electron acceptors driving this process in the unique river-influenced settings of the Arctic remain poorly understood. The Lena River delivers substantial terrigenous nutrients to this region, contributing approximately 10 % of the total riverine nitrogen and 17 % of the iron input to the Arctic Ocean. This study examines the hypothesis that these nutrient fluxes play a crucial role in regulating AOM, a key process mitigating methane emissions. We compared the geochemical conditions at active methane seep sites and background areas, with a special focus on nitrogen and iron compounds in bottom and pore waters.</div><div>Our geochemical investigation reveals three key findings: (1) Methane concentrations were substantially elevated at seep sites (up to 3118 nM) compared to background areas (as low as 5.5 nM) and showed negative correlations with nitrate (NO₃⁻) and iron (Fe) concentrations. (2) A clear decoupling of the Fe<img>Mn cycles at seep sites, which was absent in background sediments, indicates the preferential utilization of reactive iron oxides in AOM (Fe-AOM). (3) A severe depletion of bioavailable nitrogen species was observed in seep zones, where nitrate and nitrite concentrations were 5.5-fold and 2-fold lower, respectively, than in background areas, suggesting active nitrate/nitrite-dependent AOM (N-AOM).</div><div>These findings demonstrate that on the nutrient-rich, river-influenced Laptev Sea shelf, AOM is primarily driven not by canonical sulfate reduction, but by the reduction of nitrogen species and iron. This newly identified coupling between riverine nutrient fluxes and AOM pathways represents a critical, yet previously overlooked, mechanism that could significantly suppress methane emissions from climate-sensitive Arctic shelves. To our knowledge, this study provides the first comprehensive investigation of nitrogen and iron transformation mechanisms coupled with methane oxidation at the water-sediment interface in the cold seeps of the coastal Laptev Sea shelf.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"699 ","pages":"Article 123170"},"PeriodicalIF":3.6,"publicationDate":"2026-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145609523","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A surface complexation model for simulating sorption of rare earth elements onto goethite in low ionic strength (I = 0.01 M) aqueous solutions for use in groundwater flow systems","authors":"Jaxon Dii Horne ,&nbsp;Larissa P. Costa ,&nbsp;Brian Haley ,&nbsp;Karen H. Johannesson","doi":"10.1016/j.chemgeo.2025.123158","DOIUrl":"10.1016/j.chemgeo.2025.123158","url":null,"abstract":"<div><div>We conducted batch adsorption experiments to examine the adsorption behavior of the 14 naturally occurring lanthanides and yttrium (Y) onto synthetic goethite (α-FeOOH), focusing on the interactions that govern rare earth element (REE) and Y retention in natural environments. Goethite is among the most common Fe(III) oxide/oxyhydroxides in aquifer and sedimentary systems (van der Zee et al., 2003), yet few surface complexation model (SCM) has previously been developed specifically for REE sorption onto this mineral. To fill this gap, we generated adsorption edges and isotherms across a pH range of 2.5 to 10.5 and used these data to parameterize a generalized double-layer SCM. The model accounts for both strong and weak surface sites binding of free REE³⁺ (≡FeOLn²⁺) and weak carbonate complex (≡FeOLnCO₃⁺). The mass action reactions capture the adsorption trends and fractionation patterns (La-Lu) observed experimentally with log <span><math><msubsup><mi>K</mi><mi>M</mi><mo>∗</mo></msubsup></math></span> ranging from 10.01 to 9.73 for strong sites (≡(s)FeOLn²⁺), 3.81 to 3.39 for weak sites (≡(w)FeOLn²⁺), and − 0.52 to −0.33 for weak site carbonate complexation (≡(w)FeOLnCO₃⁺). These results provide the calibrated framework for predicting REE partitioning onto goethite, which is increasingly relevant as REEs driven by their widespread use in high-technology and green energy industries are recognized as emerging environmental contaminants (e.g., Kulaksiz &amp; Bau, 2013; Gwenzi et al., 2018). By quantifying how pH, carbonate speciation (Cantrell &amp; Byrne, 1987; Byrne &amp; Kim, 1990), and surface site heterogeneity govern REE adsorption, this study establishes a transferable SCM for application to groundwater, sediment, and early diagenetic environments, where Fe-oxyhydroxides control REE cycling and mobility.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"699 ","pages":"Article 123158"},"PeriodicalIF":3.6,"publicationDate":"2026-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145555406","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":"Nitrogen solubility in Fe-bearing bridgmanite and its implications for nitrogen segregation in Earth's deep magma ocean","authors":"Ko Fukuyama ,&nbsp;Hiroyuki Kagi ,&nbsp;Tetsuo Irifune ,&nbsp;Toru Shinmei ,&nbsp;Yuki Inoue ,&nbsp;Junji Yamamoto ,&nbsp;Johan Villeneuve ,&nbsp;Evelyn Füri","doi":"10.1016/j.chemgeo.2025.123154","DOIUrl":"10.1016/j.chemgeo.2025.123154","url":null,"abstract":"<div><div>Nitrogen is abundant on Earth's surface, comprising 78 vol% of the atmosphere. However, its relative abundance in the bulk silicate Earth, normalized to carbonaceous chondrites, is depleted by about one order of magnitude compared to other volatile elements. The deep Earth, particularly the lower mantle, where the behavior of nitrogen remains poorly understood, has been considered as a strong candidate for solving the so-called “missing” nitrogen problem.</div><div>Here, we experimentally investigated the effect of iron content on nitrogen solubility in bridgmanite, which constitutes 75 wt% of the lower mantle. High-pressure experiments were conducted using a multi-anvil apparatus at 28 GPa and 1400–1600 °C under redox conditions corresponding to those in the lower mantle.</div><div>Nitrogen solubility in the Fe-bearing bridgmanite increased from 2.1 ± 0.3 ppm to 6.9 ± 1.5 ppm with increasing FeO content from 1.9 wt% to 7.7 wt% at 1500 °C. Based on the temperature dependence of nitrogen solubility in MgSiO₃-bridgmanite, nitrogen solubilities in pyrolitic bridgmanite were estimated to be 9.2 ± 1.9 ppm (μg/g) at 1700 °C. The estimated nitrogen storage capacity of pyrolitic bridgmanite along a mantle geotherm is 3.6 ± 0.8 ppm in the bulk Earth, equivalent to 5.5 ± 1.2 PAN (PAN: mass of present atmospheric nitrogen). These results suggest that bridgmanite alone is insufficient to account for the “missing” nitrogen in the present-day bulk Earth, as its nitrogen storage capacity is lower than required to match chondritic volatile abundances. Instead, bridgmanite may have played a key role in segregating nitrogen into the deep mantle during the solidification of the magma ocean.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"699 ","pages":"Article 123154"},"PeriodicalIF":3.6,"publicationDate":"2026-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145553674","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":"Decoupling between silicate and phosphate mineral weathering in the granitic periglacial weathering-limited landscape of the Loch Vale watershed, Rocky Mountain National Park, Colorado, USA","authors":"Jason R. Price ,&nbsp;Suzanne Bricker ,&nbsp;Emerson Andelt ,&nbsp;James Kinnison","doi":"10.1016/j.chemgeo.2025.123150","DOIUrl":"10.1016/j.chemgeo.2025.123150","url":null,"abstract":"<div><div>The sole source of phosphorus (P⁵⁺) to natural waters and ecosystems is from bedrock chemical weathering. Phosphorus influences atmospheric CO₂ and global climate through its relationship with marine photosynthetic productivity. Solute-based watershed mass-balance methods were used to determine that bedrock fluorapatite dissolution released 48 ± 2 mol P⁵⁺ ha⁻¹ yr⁻¹ from the granitic periglacial Loch Vale watershed (LVW) in Colorado, USA during the 1984–2008 measurement period. This solute-based P⁵⁺ flux is one of the highest reported in the literature despite LVW bedrock P₂O₅ concentrations being ∼0.07 wt%. Frost-cracking in a weathering-limited landscape was responsible for enhanced fluorapatite dissolution. Extrapolating the area-normalized flux to all high-elevation crystalline and volcanic ecoregions of the Southern Rocky Mountains yields a total P⁵⁺ flux of ∼9 Gg yr⁻¹ which is comparable with the Greenland Ice Sheet.</div><div>Combining the LVW P⁵⁺ flux with the labile P⁵⁺ concentrations of outlet lake sediment provided a sediment yield rate of ∼190 tons km⁻² yr⁻¹. This value compares favorably with Southern Rocky Mountain granitic watershed cosmogenic nuclide-determined sediment yield rates reported in the literature. Thus, the primary disposition of P⁵⁺ is loss from the LVW adsorbed to sediment.</div><div>Biogeochemical models predicting P⁵⁺ fluxes routinely assume positive correlations between bedrock P⁵⁺ concentrations and terrestrial P⁵⁺ fluxes, and/or phosphate and silicate mineral weathering, with neither being true for the LVW. Because anthropogenic climate change may result in altered P⁵⁺ supplies to ecosystems and agriculture, biogeochemical models should be parameterized to include the P⁵⁺ dynamics of granitic weathering-limited periglacial landscapes.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"699 ","pages":"Article 123150"},"PeriodicalIF":3.6,"publicationDate":"2026-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145553676","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":"Vapor transport-induced Cu isotope fractionation: insights from open-system fluid cooling experiments","authors":"Dongmei Qi ,&nbsp;Chao Zhang ,&nbsp;Nuo Li ,&nbsp;Marina Lazarov","doi":"10.1016/j.chemgeo.2025.123155","DOIUrl":"10.1016/j.chemgeo.2025.123155","url":null,"abstract":"<div><div>Vapor transport is a critical mechanism for metal sequestration, enrichment, and isotope fractionation in geological systems. However, the isotopic fractionation of metals, such as copper (Cu), during open-system vapor transport has not been experimentally calibrated. To address this, we simulated vapor condensation in an open system and investigated the Cu isotope composition variation during rapid cooling and depressurization. Vapor-like fluids were produced from reactions between copper, copper chloride (CuCl) solids and H₂O, HCl solutions at 800°C and 200 MPa. Experiments were performed in argon cold seal pressure vessels (Ar-CSPVs). The cooling process induced phase separation and resulted in up to 50% fluid loss, mimicking vapor escape from a magmatic system. A reference experiment with no fluid loss exhibited negligible isotopic fractionation, with final fluid compositions matching that of the starting materials. In contrast, significant fluid loss led to the enrichment of ⁶⁵Cu in the residual fluids. Fractionations up to 2.12 ± 0.04‰ were observed between the final fluid and initial solid, most apparent for the chloride system. This systematic isotopic shift conforms to a kinetic Rayleigh fractionation model, implying that vapor removal as the main cause for Cu isotope fractionation. The expelled vapor preferentially concentrates the lighter isotope of ⁶³Cu, while vapor condensation during cooling and depressurization enriches the residual fluid in ⁶⁵Cu. These findings demonstrated that vapor escape during incipient phase transition can induce significant Cu isotope fractionation in open systems. Consequently, the use of Cu isotopes has direct implications for tracing fluid evolution pathways, identifying metal sources, and understanding metal enrichment processes in porphyry, epithermal, and other volcanic-hydrothermal systems.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"699 ","pages":"Article 123155"},"PeriodicalIF":3.6,"publicationDate":"2026-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145567770","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":"Divergent environmental controls on branched tetraethers along precipitation gradients in soils of the Tibetan Plateau","authors":"Yanwu Duan ,&nbsp;Yuling Zhou ,&nbsp;Shuo Hao ,&nbsp;Qing Sun ,&nbsp;Josef P. Werne ,&nbsp;Aifeng Zhou ,&nbsp;Lin Chen ,&nbsp;Yuanxin Li ,&nbsp;Mengjing Li ,&nbsp;Xianyong Cao ,&nbsp;Fahu Chen","doi":"10.1016/j.chemgeo.2025.123128","DOIUrl":"10.1016/j.chemgeo.2025.123128","url":null,"abstract":"<div><div>Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are widely used for terrestrial paleotemperature reconstructions, yet their environmental controls in Tibetan Plateau (TP) soils remain debated. Here, we analyze brGDGT distributions from 68 surface soil samples spanning a broad precipitation gradient across the TP and compare them with data from 1249 globally distributed soils. Our results show that soil pH is the primary control on brGDGT abundance and distribution for TP soils. However, regional environmental responses diverge, with a consistent threshold at ∼600 mm mean annual precipitation (MAP), as revealed by both 200-mm precipitation binning and silhouette coefficient-based clustering. In drier regions (MAP &lt;600 mm; Cluster A), 6-methyl brGDGTs dominate, primarily controlled by soil pH and precipitation. In wetter regions (MAP &gt;600 mm; Cluster B), 5-methyl brGDGTs, particularly Ia, become dominant, with mean annual air temperature (MAAT) emerging as the key driver. Consistent with global soils, cyclization (CBT′) and isomerization (IBT) indices closely track soil pH, while the relative abundance of isoprenoid GDGTs to brGDGTs (R_i/b and BIT indices) show promise as proxies for aridity. Although the MBT′_5ME index correlates with MAAT, substantial deviations occur—especially in drier regions—likely reflect combined influences of precipitation, vegetation cover, seasonal bias, air–soil temperature decoupling, and potential shifts in microbial community composition. Neither regional MBT_5/6 index nor global calibrations—including Bayesian (BayMBT) and machine learning-based (FROG) models—improve MAAT reconstructions, underscoring the limitations of existing approaches in the TP region. Notably, accounting for fractional abundance variations in brGDGT methylation subgroups substantially enhances temperature sensitivity. The resulting machine learning-based Support Vector Regression (SVR) model demonstrates strong predictive power and offers great potential for temperature reconstructions in both TP soils and diverse global settings. These findings help reconcile debates over the environmental controls on brGDGTs and contribute to a refined framework for paleoclimate reconstructions across the TP.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"698 ","pages":"Article 123128"},"PeriodicalIF":3.6,"publicationDate":"2025-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145434691","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":"Aluminum control on viscosity and structure of haplogranitic melts: Implications for rhyolitic melt viscosity determination","authors":"Gabriele Giuliani ,&nbsp;Laura Calabrò ,&nbsp;Veronica Stopponi ,&nbsp;Dmitry Bondar ,&nbsp;Sumith Abeykoon ,&nbsp;Claudia Romano ,&nbsp;Donald B. Dingwell ,&nbsp;Danilo Di Genova","doi":"10.1016/j.chemgeo.2025.123127","DOIUrl":"10.1016/j.chemgeo.2025.123127","url":null,"abstract":"<div><div>Accurate determination of melt viscosity near the glass transition temperature (<em>T</em>_<em>g</em>) is critical for modeling volcanic processes, but direct measurements are often compromised by nanostructuration in natural Fe–Ti-bearing systems, especially during experimental manipulation. Differential scanning calorimetry (DSC) offers an alternative method for estimating viscosity via “shift factors” (<em>K</em>), which link enthalpy to shear relaxation (and thus shear viscosity). This is possible because DSC analysis of supercooled melts requires significantly less time than micropenetration viscometry. However, the compositional sensitivity of the shift factors is still debated, particularly in highly polymerized melts.</div><div>To address this, we investigated the role of Al₂O₃ in controlling melt viscosity and network structure using five Fe–Ti-free haplogranitic compositions: the metaluminous HPG8 base melt and four systematically modified variants with nominal composition of +2, +5, −2 and −5 wt% Al₂O₃. We combine micropenetration viscometry, DSC, and Raman spectroscopy to examine the rheological and structural response to Al₂O₃ variation.</div><div>Our results reveal a non-linear viscosity dependence on Al₂O₃ content: peraluminous melts exhibit higher viscosities and <em>T</em>_<em>g</em>, while peralkaline melts are significantly more fluid. Despite these differences, melt fragility remains constant across the compositional series.</div><div>Calibrated DSC shift factors show no correlation with the network modifier content in peralkaline melts but instead they scale with the infinite-temperature viscosity (log₁₀<em>η</em>_∞). Peralkaline melts with log₁₀<em>η</em>_∞ &gt; −3.00 show low and constant shift factors, whereas metaluminous and peraluminous melts (log₁₀<em>η</em>_∞ &lt; −3.00) yield higher values. These findings establish benchmarks for the application of the DSC shift-factor approach to estimate melt viscosity in natural, silica-rich rhyolitic melts, especially where direct measurements are hindered, thereby improving our ability to model magma rheology and eruption dynamics.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"698 ","pages":"Article 123127"},"PeriodicalIF":3.6,"publicationDate":"2025-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145441784","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":"Isotopic insights into iron and sulfur cycling in acid sulfate soils: Implications of seasonal redox fluctuations","authors":"Sarah Conrad ,&nbsp;Katerina Rodiouchkina ,&nbsp;Federico Alvarellos ,&nbsp;Björn Öhlander ,&nbsp;Lena Alakangas","doi":"10.1016/j.chemgeo.2025.123151","DOIUrl":"10.1016/j.chemgeo.2025.123151","url":null,"abstract":"<div><div>Acid sulfate soils (AS-soils), common in coastal, estuarine, and mining-impacted areas, form under reducing conditions and can cause severe environmental degradation by releasing acidity and mobilizing heavy, trace, and toxic metals when sulfide minerals oxidize under changing hydrological conditions. AS-soils exhibit redox gradients that govern iron (Fe) and sulfur (S) cycling, affecting their mobility, mineral forms, and isotopic compositions. This study combines Fe/S ratios, δ⁵⁶Fe and δ³⁴S isotope systematics, sequential extractions, and groundwater monitoring to assess redox-driven processes in two AS-soil profiles from northern Sweden. In reduced zones, negative δ⁵⁶Fe and δ³⁴S values signal microbial Fe(III) and sulfate reduction, producing Fe(II) and sulfides. In oxidized zones, secondary Fe (oxy)hydroxides and sulfates form, inheriting isotopic signals from precursor sulfides. Groundwater δ⁵⁶Fe enrichment reflects Fe oxidation, while high δ³⁴S values (up to +45.2 ‰) indicate ongoing sulfate reduction. Groundwater Fe/S ratios (0.07–8.24) reveal redox interactions but are unreliable as sole redox indicators. Sequential extractions show that redox-sensitive pools—water-soluble, exchangeable, and organic-bound phases—exhibit strong isotope fractionation and drive short-term cycling, despite their small mass. Isotopic signals from different Fe phases within each profile likely offset each other when measured in bulk (∼0.06–0.11 ‰), diluting any clear redox-related patterns. Similarly, δ³⁴S values trace a shift from oxidized to stable sulfide-bound forms across depths and redox zones. The results emphasize the value of combining isotopic and phase-specific analyses to unravel redox heterogeneity, trace element fluxes, and identify acidification-prone zones. Environmentally, maintaining saturated conditions, encouraging reducing environments, and monitoring reactive Fe and S fractions can help limit the mobilization of heavy, trace, and toxic metals in AS-soils under shifting hydrology.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"698 ","pages":"Article 123151"},"PeriodicalIF":3.6,"publicationDate":"2025-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145531207","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":"Colloidal origin of hematite in Pleistocene iron-rich sedimentary rocks from Milos Island, Greece: An analogue for Precambrian iron shuttle","authors":"Si Sun ,&nbsp;Reiner Klemd ,&nbsp;Panagiotis Voudouris","doi":"10.1016/j.chemgeo.2025.123130","DOIUrl":"10.1016/j.chemgeo.2025.123130","url":null,"abstract":"<div><div>Banded iron formations (BIFs) are critical archives of Earth's early biogeochemical cycles, yet their genesis, especially regarding the origin of hematite and associated Fe transport mechanisms, remains intensely debated. The scarcity of unmetamorphosed Phanerozoic analogues has constrained a comprehensive understanding of BIF formation. Here, we investigate Pleistocene iron-rich sedimentary rocks from the Cape Vani sedimentary basin, Milos Island, Greece, to elucidate Fe transport processes in ancient oceans. High-resolution petrographic mineralogical, and spectroscopic analyses reveal that Fe is predominantly hosted in hematite nanoparticles (ca. 0.1–0.75 μm), which often form framboidal and irregular aggregates. Mössbauer spectroscopy indicates that the hematite has magnetic hyperfine fields (46.75–50.73 T) characteristic of medium to poor crystallinity. Raman spectra further exhibit a prominent band shift ca. 650 cm⁻¹, a feature diagnostic of nanocrystalline hematite. Carbonaceous material is spatially associated with the aggregates but is absent from individual nanoparticles. The uniform sizes and morphology of the hematite particles suggest that the majority of Fe was transported as colloids. This implies a possible allochthonous origin and <em>ex situ</em> Fe-oxidation, since colloids can be transported over long distances. The aggregation and subsequent deposition of these colloids were likely facilitated by high concentrations of dissolved Si and interactions with carbonaceous materials. The prevalence of colloidally-derived hematite at Milos highlights colloidal transport as a potentially significant mechanism for iron distribution in past oceans. Consequently, the presence of hematite in ancient sediments like BIFs does not necessarily imply <em>in situ</em> Fe-oxidation or associated microbial processes. The established model for a colloidal iron shuttle capable of transporting iron across oceanic basins offers a new perspective for interpreting the genesis of BIFs and a refined understanding on the early Earth's biogeochemical cycles.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"698 ","pages":"Article 123130"},"PeriodicalIF":3.6,"publicationDate":"2025-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145448042","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":"Copper isotopic compositions of surface sediment in the Yangtze Estuary and East China Sea Shelf","authors":"Daqian Zhang ,&nbsp;Jincun Liu ,&nbsp;Lian Zhou ,&nbsp;Qian Wang ,&nbsp;Lanping Feng ,&nbsp;Jinhua Liu ,&nbsp;Yating Hu ,&nbsp;Thomas J. Algeo","doi":"10.1016/j.chemgeo.2025.123149","DOIUrl":"10.1016/j.chemgeo.2025.123149","url":null,"abstract":"<div><div>Estuaries represent an important interface between rivers and oceans within which copper (Cu) can be sequestered or isotopically fractionated. However, the geochemical behavior of Cu isotopes in estuaries and adjacent continental shelves has not been adequately considered in previous assessments of the marine Cu cycle. Here, we use bulk-sample and sequential-extraction Cu isotope data in surface sediments of the Yangtze Estuary (YE), mixing zone (MZ), and adjacent East China Sea Shelf (ECSS) to reveal mechanism(s) of Cu isotopic fractionation in estuaries and their influence on the marine Cu cycle. Our results show that Cu is present mainly in clay minerals and iron oxides, and that variations in physicochemical conditions at the land-sea interface can lead to surface-sediment Cu isotope fractionation, yielding bulk-sample δ⁶⁵Cu values ranging from −0.07 to +0.30 ‰ (relative to NIST 976). The negative correlation of δ⁶⁵Cu with Al/Si in the YE and ECSS reflect adsorption of isotopically light Cu by clay minerals. Although the relationship of δ⁶⁵Cu to Al/Si is statistically insignificant in the MZ, this zone has higher clay-mineral content and lower bulk-sample δ⁶⁵Cu values than the YE. These results reflect the redistribution and fractionation of Cu among clay minerals during re-suspension of surface sediments in the MZ. We identify two pools of Cu in the surface sediments: a labile pool (including the exchangeable, reducible, oxidizable fractions) that is extractable using weak acidic leach, and a refractory pool (residual fraction). For the reducible copper fraction (Cu_ox), negative correlations between its amount (<em>f</em> Cu_ox) and isotopic composition (δ⁶⁵Cu_ox) in the YE, MZ and ECSS reflect desorption of isotopically light Cu from iron oxides. Additionally, the Cu isotopic values of the labile pool (+0.12 ± 0.04 ‰, <em>n</em> = 12, 2SD) are consistent with missing isotopically light Cu (∼ + 0.1 ‰) in our oceanic Cu mass balance model. These considerations suggest that re-suspension of estuarine surface sediment promotes release of isotopically light Cu to seawater. Thus, partial dissolution of terrigenous substances (including clays, iron oxides and organic matter) entering the ocean through estuaries is one of the main reasons for isotopically light Cu in surface seawater. Our results provide new insights into the marine biogeochemical cycle of Cu.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"698 ","pages":"Article 123149"},"PeriodicalIF":3.6,"publicationDate":"2025-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145531300","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}