Chemical Geology最新文献

{"title":"The selenium isotope composition of shallow-marine carbonates from the Bahamas: Implications for seawater paleoredox studies","authors":"Benjamin Eickmann ,&nbsp;Achim D. Herrmann ,&nbsp;Stephan König","doi":"10.1016/j.chemgeo.2025.123220","DOIUrl":"10.1016/j.chemgeo.2025.123220","url":null,"abstract":"<div><div>Selenium (Se) isotope ratios in marine carbonates are able to act as a novel geochemical proxy for reconstructing Earth's surface redox evolution, but our understanding of the Se cycling in shallow-water carbonates is currently limited. We thus explore the utility of carbonate-associated Se (CASe) as a paleoredox proxy by testing if modern carbonate δ^82/76Se values capture the coeval seawater δ^82/76Se value and evaluating the response of carbonate δ^82/76Se values to syndepositional processes. Our pilot study presents the first Se concentration and isotope ratio data for modern shallow-marine carbonates from open-marine environments on the Great Bahamas Bank (GBB). We find that the carbonate sediments deposited in fully oxygenated environments are characterized by authigenic Se enrichment with 0.149 to 0.224 μg/g Se and fractionated carbonate δ^82/76Se values (deviation of ⁸²Se/⁷⁶Se relative to NIST SRM 3149) of 1.23 to 4.79 ‰ ± 0.3 ‰ (2 s.d.) within the uppermost 50 cm. The extent of this authigenic Se enrichment is primarily driven by sulfidic conditions in the pore fluids due to ongoing microbial sulfate reduction in the carbonate sediments. The carbonate δ^82/76Se values identify two independent processes that record local processes specific to the shallow waters of the GBB. High biological productivity in the surface ocean produces two Se pools with distinct δ^82/76Se values, because the microbial reduction of Se oxyanions leads to isotopically light organic-bound Se and drives the remaining Se oxyanions to heavier δ^82/76Se values that is incorporated into the carbonates. The isotopically heavy CASe is further modified by syndepositional processes in the carbonate sediments. Our results thus suggests that Se in high-productivity surface oceans behaves as a non-conservative element, indicating that carbonate δ^82/76Se values in such environments do not necessarily record the seawater Se isotope composition. Instead, bulk carbonate δ^82/76Se values are potentially further modified during syndepositional diagenesis, which requires further assessment as a paleoredox proxy.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"702 ","pages":"Article 123220"},"PeriodicalIF":3.6,"publicationDate":"2026-02-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145823504","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":"Proterozoic highly siderophile element enrichment of the Kaapvaal cratonic Archean mantle","authors":"Nadine P. Cooper ,&nbsp;D. Graham Pearson ,&nbsp;Andreas Auer ,&nbsp;Tristan Bongartz ,&nbsp;Yannick Bussweiler ,&nbsp;Mario Fischer-Gödde ,&nbsp;Max Hellers ,&nbsp;Geoffrey Howarth ,&nbsp;Andrew J. Locock ,&nbsp;Ambre Luguet ,&nbsp;Carsten Münker ,&nbsp;Thomas Stachel ,&nbsp;Ashlea N. Wainwright ,&nbsp;Sarah Woodland ,&nbsp;James M. Scott","doi":"10.1016/j.chemgeo.2025.123201","DOIUrl":"10.1016/j.chemgeo.2025.123201","url":null,"abstract":"<div><div>The c. 86 Ma Jagersfontein kimberlite in the southern portion of the Kalahari craton in South Africa erupted a suite of refractory peridotite xenoliths with regionally anomalous rhenium+osmium (Re<img>Os) isotope systematics and highly siderophile element (HSE) abundances. A portion of this suite comprises peridotites with 2.7 to 3.0 Ga Re- depletion ¹⁸⁷Os/¹⁸⁸Os model ages, refractory major elements and HSE abundances that represent some of the most depleted and least metasomatised known components of Archean cratonic nuclei. Other peridotites in the Jagersfontein suite show enrichment in Os, Ir, Pd, Pt and, especially, Ru, as well as having more radiogenic ¹⁸⁷Os/¹⁸⁸Os. Ruthenium abundances reach up to ∼22 times “Primitive Upper Mantle” levels and correspond to samples containing microscopic laurite plus pentlandite. The more radiogenic ¹⁸⁷Os/¹⁸⁸Os in HSE-enriched samples, along with the modern mantle like Ru isotope composition (ε¹⁰⁰0.00 ± 0.12, ε¹⁰²–0.03 ± 0.16), indicate that the prominent HSE enrichment is not related to an excess of unequilibrated Late Veneer material in the mantle source. Instead, the HSE characteristics and Os isotope ratios of these peridotites are inferred to have been caused by metasomatic addition of small volumes of HSE-rich sulfide/alloy to the refractory Archean peridotites. Although there is some variation in the metasomatic characteristics, the calculated ¹⁸⁷Os/¹⁸⁸Os of the contaminant causing the strongly Ru-enriched peridotites is ∼0.116, which is equivalent to the convecting mantle composition in the early Mesoproterozoic. Unlike the erosion and Proterozoic replacement of older mantle interpreted to explain post-Archean ¹⁸⁷Os/¹⁸⁸Os mantle beneath the central Kaapvaal nucleus, the Archean mantle lithosphere beneath Jagersfontein therefore appears to have been modified by the passage of Proterozoic melts. The 2400 km² 1.9 Ga layered mafic Trompsburg Complex, less than 10 km southeast of Jagersfontein, indicates that the mantle lithosphere in the area has experienced substantive transfer of large volumes of post-Archean melt, and we suggest that the passage of those melts may have caused the mantle HSE enrichment.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"702 ","pages":"Article 123201"},"PeriodicalIF":3.6,"publicationDate":"2026-02-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145731849","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":"Global variation in Cr-spinel trace elements","authors":"Emil Akseli Koskinen Tonboe ,&nbsp;Ikuya Nishio ,&nbsp;Pedro Waterton","doi":"10.1016/j.chemgeo.2025.123227","DOIUrl":"10.1016/j.chemgeo.2025.123227","url":null,"abstract":"<div><div>The major element composition of Cr-spinel [(Mg,Fe²⁺)(Cr,Al,Fe³⁺)₂O₄] has long been used to infer the petrogenesis and tectonic setting of its host rocks. However, overlaps in major element compositions and susceptibility of Mg and Fe²⁺ to secondary alteration limit its diagnostic utility. In contrast, some trace elements may be particularly diagnostic of certain petrogenic processes or retain primary signatures even when major elements are modified, offering a complementary tool for petrogenetic interpretation. However, a comprehensive evaluation of the systematics of trace elements in Cr-spinel has not yet been undertaken.</div><div>This study compiles major and trace element data from Cr-spinel-bearing samples worldwide to assess global variability and to identify robust geochemical indicators. Based on a larger, more representative set of Mid-Ocean Ridge Basalt (MORB) spinel data we present new MORB spinel normalization values and a recommended element order for spinel multi-element plots. We document systematic variations in trace elements (Sc, Ga, V, Ni, Mn) with Cr# (Cr# = Cr/(Cr + Al) mol.), particularly in mantle-derived spinels, and show that these trends reflect mantle depletion. Melting models and regression of literature partition coefficients demonstrate that partitioning of Sc, Ga, Ni, Mn, and Ti is likely compositionally controlled.</div><div>We also show that Cr-spinels from lavas and intrusions can be distinguished based on late-stage re-equilibration with interstitial melt, evident from the low Ru and Cu contents and Sc/Ga ratios in Cr-spinels from intrusions. Our findings highlight the potential of trace element systematics in Cr-spinel as a powerful tool for reconstructing the petrogenesis of mafic-ultramafic rocks.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"702 ","pages":"Article 123227"},"PeriodicalIF":3.6,"publicationDate":"2026-02-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145845306","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":"Melt‑carbonate metasomatism in the Sulu orogen: Implications for CO2 release in the continental subduction zone","authors":"Shaoji Yang ,&nbsp;Pan Wang ,&nbsp;Haijin Xu ,&nbsp;Fan Feng","doi":"10.1016/j.chemgeo.2025.123217","DOIUrl":"10.1016/j.chemgeo.2025.123217","url":null,"abstract":"<div><div>Subduction zone carbon cycling governs the carbon budget balance between Earth's interior and surficial systems and constrains long-term climatic-environmental evolution. While extensive research has focused on oceanic subduction zones, CO₂ release mechanisms in continental subduction zones remain poorly understood. The Sulu orogen, which experienced cold subduction followed by hot exhumation and extensive anatexis, provides an ideal natural laboratory for investigating carbon release processes in continental subduction zones. Petrology, mineral chemistry, and titanite geochronology were conducted to investigate a melt-metacarbonate interaction profile, where the migmatite – contact zone (calc-silicate rock) - marble system clearly records CO₂ release and migration. Petrographic and mineral chemical analysis reveal diverse metasomatic reactions between silicate melts and marble. In the innermost marble, limited melt infiltration led to olivine and phlogopite formation with CO₂ release. At the contact zone, intense metasomatic reactions produced diopside, tremolite, scapolite, and titanite, releasing substantial CO₂. The metasomatism also induced carbon migration through calcite-bearing melt/fluid, including calcite-bearing silicate melts near the migmatite, quartz + calcite ± tremolite veins and calcite veins in the contact zone, and carbon-bearing serpentine veins in the marble. Titanite U-Pb age (206 ± 0.7 Ma) and Zr-in-titanite thermometer (<em>T</em> = 792–862 °C) suggest the CO₂ release occurred at the exhumation stage. These findings demonstrate that metamorphic decarbonation occurs not only in hot subduction zones but also during hot exhumation of cold subducted slabs, providing new insights into carbon cycling in continental subduction zones and helping address carbon budget imbalance in global carbon cycling models.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"702 ","pages":"Article 123217"},"PeriodicalIF":3.6,"publicationDate":"2026-02-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145796051","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":"From bacterial to thermochemical sulfate reduction: Sulfur isotope constraints on the genesis of hyper-enriched black shales","authors":"Kyle M. Henderson ,&nbsp;James R. Clark ,&nbsp;Anthony E. Williams-Jones ,&nbsp;Ryan Sharpe ,&nbsp;Mostafa Fayek","doi":"10.1016/j.chemgeo.2025.123207","DOIUrl":"10.1016/j.chemgeo.2025.123207","url":null,"abstract":"<div><div>Hyper-enriched black shales (HEBS) are thin stratiform and stratabound sulfide-rich (∼70 vol%) units that have percentage level concentrations of metals such as Ni, Mo and Zn. In the Peel River area of Yukon, Canada, HEBS are highly enriched in Ni (∼3 wt%), Zn (∼0.2 wt%), and Mo (0.2 wt%), hosted mainly by millerite (NiS), sphalerite (ZnS) and pyrite (FeS₂). The processes that control millerite-sphalerite precipitation in HEBS are poorly constrained. Here, we report the first in-situ sulfur isotope measurements of sulfide minerals in the Peel River HEBS. Early diagenetic pyrite (δ³⁴S -31.9 ± 9.0 ‰) formed in response to open-system bacterial sulfate reduction (BSR), whereas later sphalerite (16.5 ± 5.1 ‰) and millerite (+10.0 ± 1.4 ‰) crystallized via thermochemical sulfate reduction. We have developed a three-stage model for HEBS formation. Stage 1 involves high primary productivity, a redox-stratified water column, a low sedimentation rate, and an active Fe-oxide shuttle, which promoted BSR-driven pyrite precipitation. Organic matter scavenged Ni and Zn from the water column and pore-water, producing metal-rich kerogen. Stages 2 and 3 occur during late diagenesis, with the infiltration of an acidic, oxidized, metal-poor, sulfate-bearing brine that interacted with the metal-bearing kerogen, triggering thermochemical sulfate reduction and millerite-sphalerite precipitation. Subsequent fracturing and increased fluid-flow during peak hydrocarbon generation caused acid-driven replacement of sphalerite by a second generation of millerite. This model accounts for HEBS formation in both Canada and China, demonstrating that, although late-stage fluids did not transport the metals, brines were essential to their genesis.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"702 ","pages":"Article 123207"},"PeriodicalIF":3.6,"publicationDate":"2026-02-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145785268","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Sedimentary geochemistry and paleoenvironments project phase 2 data release: An open data resource for the study of Earth's environmental history","authors":"Úna C. Farrell, Hunter C. Olson, Maya O. Thompson, Michelle L. Abshire, Oyeleye O. Adeboye, Anne-Sofie C. Ahm, Lewis J. Alcott, Thomas J. Algeo, Ross P. Anderson, Arif H. Ansari, Lucas Pinto Heckert Bastos, Kohen W. Bauer, Brian Beaty, Justin E. Birdwell, Fred T. Bowyer, Jochen J. Brocks, Tessa Brunoir, James F. Busch, Donald E. Canfield, Fabrício A. Caxito, Chao Chang, Meng Cheng, Jean N.R. Clemente, David R. Cordie, Peter W. Crockford, Huan Cui, Celeste M. Cunningham, Tais W. Dahl, Janaina Rodrigues de Paula, Carol M. Dehler, Lucas Del Mouro, Keith Dewing, Dermeval Aparecido do Carmo, Stephen Q. Dornbos, Nadja Drabon, Julie A. Dumoulin, Omabehere Innocent Ejeh, Emily Ellefson, Maya Elrick, Joseph F. Emmings, Bokanda Ekoko Eric, Hao Fang, Gabriella Fazio, Henrique A. Fernandes, Katherine L. French, Robert R. Gaines, Richard M. Gaschnig, Timothy M. Gibson, Geoffrey J. Gilleaudeau, Karin Goldberg, Zheng Gong, Amy P.I. Hagen, Galen P. Halverson, Kalev Hantsoo, Emma R. Haxen, Miles A. Henderson, João P.T.M. Hippertt, Malcolm S.W. Hodgskiss, Paul F. Hoffman, Edward C. Huang, Benjamin W. Johnson, Pavel B. Kabanov, Junyao Kang, C. Brenhin Keller, Brian Kendall, Julien Kimmig, Sara R. Kimmig, Michael A. Kipp, Andrew H. Knoll, Timmu Kreitsmann, Anurag A. Kulkarni, Alexandra Kunert, Marcus Kunzmann, Jiankang Lai, Richard O. Lease, Chao Li, Sen Li, Alex G. Lipp, Yang Liu, David K. Loydell, Xinze Lu, Katie M. Maloney, Kaarel Mänd, Alexie E.G. Millikin, N. Tanner Mills, Kento Motomura, Chiza N. Mwinde, Lyle L. Nelson, Nora M. Nieminski, Brennan O'Connell, Edel O'Sullivan, Juliana Okubo, Jaden K. Olah, Frantz Ossa Ossa, Chadlin M. Ostrander, Kärt Paiste, Camille A. Partin, Egberto Pereira, Shanan E. Peters, Tiffany Playter, Susannah M. Porter, Simon W. Poulton, Sara B. Pruss, Zhen Qiu, Daven P. Quinn, Mariano Remírez, Sebastian Richiano, Sylvain Richoz, Kathryn I. Rico, Samantha R. Ritzer, Zachary Roney, Alan D. Rooney, William C. Rose, Elias J. Rugen, Swapan K. Sahoo, Shane D. Schoepfer, Judith A. Sclafani, Nathan D. Sheldon, Yanan Shen, Graham A. Shields, Pulkit Singh, Arvind Kumar Singh, Sarah P. Slotznick, Emily F. Smith, Haijun Song, Sam C. Spinks, Richard G. Stockey, Justin V. Strauss, Eva E. Stüeken, Zongyuan Sun, Dongjie Tang, Lidya G. Tarhan, Danielle Thomson, Nicholas J. Tosca, Rosalie Tostevin, Chenyi Tu, Maoli N. Vizcaíno, Yuxuan Wang, Changle Wang, Xiaomei Wang, Lucas Veríssimo Warren, Lucy C. Webb, Philip R. Wilby, Christina R. Woltz, Rachel Wood, Yuyang Wu, Xiuqing Yang, Inessa A. Yurchenko, Junpeng Zhang, Jessica H. Whiteside, Benjamin C. Gill, Akshay K. Mehra, Kimberly V. Lau, Noah Planavsky, David T. Johnston, Erik A. Sperling","doi":"10.1016/j.chemgeo.2026.123311","DOIUrl":"https://doi.org/10.1016/j.chemgeo.2026.123311","url":null,"abstract":"","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"181 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2026-02-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146778175","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":"Clumped isotope constraints on secondary mineral formation and thermal overprinting in the Michigan Basin, Southwestern Ontario","authors":"Benjamin R. Fosu ,&nbsp;Josué J. Jautzy ,&nbsp;Duane C. Petts ,&nbsp;Ian D. Clark ,&nbsp;Tom A. Al","doi":"10.1016/j.chemgeo.2025.123189","DOIUrl":"10.1016/j.chemgeo.2025.123189","url":null,"abstract":"<div><div>Sections of Michigan Basin sediments were exposed to hydrothermal fluids during the Ordovician. Secondary calcite and dolomite occur as fracture-filling veins/vugs and replacement minerals in host Ordovician limestones – which occur at depth beneath the Bruce Nuclear site (near Tiverton) in southwestern Ontario. To provide insights on the evolution of diagenetic fluids responsible for secondary mineral growth and the effects of temperature-dependent alteration in the basin, clumped isotope geothermometry was applied to these carbonates. Ordovician calcite in veins/vugs have δ¹⁸O_C values of +20.0 to +23.4 ‰ (VSMOW) and are estimated to have formed at 65–83 °C from various waters (δ¹⁸O_w = +0.1 to +4.4 ‰) including Ordovician to modified (an evolved ¹⁸O-enriched) seawater, and mixed seawater and basinal brines at depth. Calcite veins/vugs in the lower Cambrian units formed at 74–91 °C, have lower δ¹⁸O_C values (+14.9 to +17.0 ‰) and precipitated from ¹⁸O-depleted hydrothermal brines (δ¹⁸O_w = −4.6 to −3.1 ‰). Calcite in the matrix of host limestones yielded higher apparent temperatures (T(Δ₄₇) = 49–82 °C)) that are inconsistent with precipitation from Ordovician seawater and burial diagenesis of the sediments but instead, reflect a solid-state isotope reordering due to a Late Devonian-Mississippian rift-related basinal heating. Diagenetic dolomitization in the basin occurred during shallow to intermediate burial, where dolomite primarily replaces calcite in the limestone matrix or occur as secondary infill in fractures and vugs. The clumped isotopic signature in dolomite is more resistant to low-temperature heating than calcite, whose ∆₄₇ composition reflects a 367–322 Ma regional heating event at 125–150 °C during burial, in agreement with, but more precise than previous estimates based on fluid inclusion microthermometry in secondary quartz and saddle dolomite.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"701 ","pages":"Article 123189"},"PeriodicalIF":3.6,"publicationDate":"2026-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145690050","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":"Calcium and copper isotope compositions in hydrothermally influenced sediments as proxies for hydrothermal activity on mid-ocean ridges: An example from the Carlsberg Ridge","authors":"Jian-Qiang Wang ,&nbsp;Shuang-Shuang Lyu ,&nbsp;Zhong-Yan Qiu ,&nbsp;Xi-Qiu Han ,&nbsp;Mou Li ,&nbsp;Chun-Feng Li ,&nbsp;Xue-Gang Chen","doi":"10.1016/j.chemgeo.2025.123197","DOIUrl":"10.1016/j.chemgeo.2025.123197","url":null,"abstract":"<div><div>As an essential product of hydrothermal activity, hydrothermally influenced sediments record source characteristics and geochemical signals of hydrothermal circulation. Here, we report on the chemical and isotopic compositions of a hydrothermally influenced sediment core (HiSC) and a biogenic carbonate sediment core (BcSC) collected near hydrothermal vents on the Carlsberg Ridge, northwest Indian Ocean. Episodic changes between metalliferous hydrothermal precipitates and calcareous sedimentation provide a unique opportunity to investigate the connection between calcium (Ca)-copper (Cu) isotope systems and hydrothermal activity. The δ^44/40Ca values (relative to NIST SRM915a) in HiSC ranged from 0.59 ± 0.10 ‰ (2SD) to 0.96 ± 0.09 ‰ and were controlled by the mixing between biogenic carbonates and detrital components (weathering product of host rock and/or sinking lithogenic particles). Endmember δ^44/40Ca of biogenic carbonates was 0.57 ± 0.07 ‰ (95 % confidence interval), consistent with the measured δ^44/40Ca range of BcSC (0.46 ± 0.12 ‰, 2SD, <em>n</em> = 8). Copper in HiSC showed δ⁶⁵Cu values (relative to NIST SRM976) of -0.03 ± 0.43 ‰ (2SD, <em>n</em> = 10), and was mostly supplied by hydrothermal inputs. The δ⁶⁵Cu of hydrothermal components in the sediments was calculated as −0.2 ± 0.1 ‰ (95 % confidence interval). Linking the Ca and Cu isotope systems we proposed a Ca<img>Cu index to semi-quantify the strength of hydrothermal activity of nearby vents. The hydrothermal activity was relatively strong at 9.8–11.8 ka and 7.4–7.8 ka, moderate at 9.0–9.8 ka, and weak at 7.8–9.0 ka. Modeling tests indicated that the Ca<img>Cu index is potentially a robust proxy for reconstructing hydrothermal history on mid-ocean ridges, despite practical application being limited by hydrothermal carbonate precipitation (e.g., at Lost City), secondary diagenetic alteration, and variations in endmember δ⁶⁵Cu values. Furthermore, our study indicated that isotopically light sources/processes are required to counterbalance the preferential removal of light Ca isotopes from seawater by marine sediments. Hydrothermal inputs eventually contribute Cu with positive δ⁶⁵Cu values (or even higher than the seawater value) to the ocean.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"701 ","pages":"Article 123197"},"PeriodicalIF":3.6,"publicationDate":"2026-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145731860","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":"Barite crystallization at the freezing point: Cryogenic mineral assemblage from cave glaciated in late Pleistocene","authors":"Stanislava Milovská ,&nbsp;Rastislav Milovský ,&nbsp;Monika Orvošová ,&nbsp;Sergii Kurylo ,&nbsp;Juraj Šurka ,&nbsp;Pavel Herich ,&nbsp;Frank Bellmann ,&nbsp;Anna Gibalová ,&nbsp;Lukáš Ackermann ,&nbsp;Lucia Kopčanová ,&nbsp;Muhammad Shahzeb","doi":"10.1016/j.chemgeo.2025.123172","DOIUrl":"10.1016/j.chemgeo.2025.123172","url":null,"abstract":"<div><div>A cryogenic mineral assemblage was investigated in a cave that experienced widespread glaciation in Late Pleistocene. Barite and opal crystallized alongside calcite during the progressive water freezing in cave chambers within thawing permafrost. Barite inclusions evolved from prismatic nuclei into complex spherulitic aggregates, occasionally shaped by now-vanished constraints on growth, presumably imposed by ice, CO₂, and possibly CO₂ clathrate. Clathrate formation at 0 °C requires pressures above 10 bar, a condition that can be met in freezing water pools through pressure buildup from volumetric expansion. Dispersed nanoparticulate silica is identified as a disordered opal variety. Stable strontium isotope ratios proved useful in constraining the provenance of the parental water and confirm its autochthonous seepage origin within the limestone massif. Geochemical modelling indicates early oversaturation and precipitation of barite and silica, often preceding calcite, suggesting that microscopic cryogenic minerals may persist even where macroscopic calcite is absent. These findings deepen our understanding of sub-zero mineral precipitation with potential implications for other terrestrial and extraterrestrial cryogenic environments.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"701 ","pages":"Article 123172"},"PeriodicalIF":3.6,"publicationDate":"2026-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145651135","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":"Inverse methods for extracting seasonality signals from ungulate tooth enamel","authors":"Alexandra L. Norwood ,&nbsp;Daniel R. Green ,&nbsp;Briana L. Pobiner ,&nbsp;J. Tyler Faith","doi":"10.1016/j.chemgeo.2025.123191","DOIUrl":"10.1016/j.chemgeo.2025.123191","url":null,"abstract":"<div><div>The variability in the isotopic composition of tooth enamel recorded in serially-sampled ungulate teeth provides a valuable archive of changes in the food and water consumed by an animal on the temporal scale of months to years. These records provide evidence of paleoseasonality and insight into animal behavior and ecology over seasonal temporal scales relevant to selection. However, interpreting these records proves difficult due to the complex nature of enamel mineralization, which variably compresses, lengthens, and dampens the input isotopic signal during growth. Despite these complications, “inverse modeling” can recover original input signals from serial chemical measurements in teeth, by modeling enamel mineralization and the incorporation of mineral content with specific isotopic compositions through time. Here we present a set of models to execute this process, which fit the enamel mineralization patterns of plains zebra (<em>Equus quagga</em>) but are parameterized to be adaptable to the growth patterns of other mammalian teeth. Through sensitivity testing and the application of the inverse model to real-world data from modern plains zebra from Ol Pejeta Conservancy in central Kenya, we show that these models recover an accurate seasonality signal from preserved enamel, particularly closer to the coronal end of the crown and over longer seasons (i.e., longer periodicities). These models are a valuable expansion of the existing toolkit for the analysis of enamel isotope data as a paleoecological proxy.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"701 ","pages":"Article 123191"},"PeriodicalIF":3.6,"publicationDate":"2026-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145689932","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}