Chemical Geology最新文献

{"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":"2025-12-26","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":"In-situ sulfur isotope and microscopic analyses reveal multiple pyrite genesis mechanisms in the early Ediacaran Doushantuo Formation, South China","authors":"Shiqi Cheng ,&nbsp;Lianjun Feng ,&nbsp;Guoqiang Tang ,&nbsp;Yan Liu ,&nbsp;Hao Qiu ,&nbsp;Qiuli Li ,&nbsp;Xuelei Chu ,&nbsp;Xingliang Zhang ,&nbsp;Jinhua Li","doi":"10.1016/j.chemgeo.2025.123226","DOIUrl":"10.1016/j.chemgeo.2025.123226","url":null,"abstract":"<div><div>Sedimentary pyrite constitutes an invaluable geological archive for reconstructing Earth's ancient environments, yet interpreting its origins within deep geological records is often complicated by subsequent diagenetic modification. Here, we examine four distinct pyrite morphologies (framboidal pyrites hosted in chert nodules and matrix, euhedral pyrites within calcite rims of nodules, and pyrite aggregates within surrounding matrix rocks) preserved in the Ediacaran Doushantuo Formation of South China, utilizing a combination of high-resolution electron microscopy and in-situ secondary ion mass spectrometry sulfur isotope analysis. Our microscopic observations identify well-preserved framboidal pyrites, variably altered by post-depositional processes, alongside large euhedral pyrite crystals encapsulated by calcite, and irregular pyrite aggregates. Integrated nanoscale microscopic and in situ isotopic analyses consistently demonstrate that framboidal pyrites exhibit negative δ³⁴S values, indicative of microbial sulfate reduction within the water column or at the sediment-water interface during early diagenesis. Conversely, euhedral pyrites and irregular aggregates from nodule rims and surrounding matrix yield significantly positive δ³⁴S values, consistent with thermochemical sulfate reduction during late-stage burial diagenesis. This finding contrasts with previous interpretations that attribute positive δ³⁴S values to a diminished marine sulfate reservoir within a restricted paleoceanographic setting. Our results emphasize that post-depositional thermochemical sulfate reduction processes can significantly elevate δ³⁴S values of pyrites. This study underscores the critical necessity of deconvolving diagenetic overprinting from primary signatures by integrating in-situ isotopic and microscopic analyses, thereby refining paleoenvironmental reconstructions from pyrite archives.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"702 ","pages":"Article 123226"},"PeriodicalIF":3.6,"publicationDate":"2025-12-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145823790","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":"Abundance, composition, and environmental implications of iron minerals in highly permeable sandy beaches","authors":"Yan Zhang ,&nbsp;Cheng Xing ,&nbsp;Liuqian Yu ,&nbsp;Tian Fu ,&nbsp;Shuoyu Zhang ,&nbsp;Yi Liu","doi":"10.1016/j.chemgeo.2025.123225","DOIUrl":"10.1016/j.chemgeo.2025.123225","url":null,"abstract":"<div><div>Iron minerals in sandy beaches play a crucial role in regulating chemical transport from terrestrial to marine ecosystems via coastal groundwater flow. This study investigated the abundance, composition, and distribution of iron minerals in sandy beaches (25 m long and 6 m deep; Guanghai Bay, China), assessed their role in intercepting phosphorus (P), elucidating the underlying geochemical mechanisms. We sequentially extracted 5 iron pools from sediment cores: carbonate-associated iron (Fe_Carb), easily reducible oxides (Fe_Ox1), reducible oxides (Fe_Ox2), magnetite (Fe_Mag), and silicate iron (Fe_Si). The results reveal that highly reactive iron (Fe_HR = Fe_Carb + Fe_Ox1 + Fe_Ox2 + Fe_Mag) constitutes 65 % of total iron indicating a significant enrichment in sandy aquifers compared to typical marine and river sediments (&lt;45 %) due to continuous groundwater supply and redox oscillation. Within Fe_HR, Fe_Ox2 is the most abundant form (39 %), followed by Fe_Ox1 (15 %), Fe_Carb (6 %) and Fe_Mag (5 %). The sandy beach exhibits a low Fe_Ox1/Fe_Ox ratio of 28 % (where Fe_Ox = Fe_Ox1 + Fe_Ox2), attributed to its higher permeability and more oxidizing conditions compared to typical mangroves and salt marshes (where ratios can reach 60 %). Reducing conditions intensified seaward and downward in the sandy beach facilitating the sediment organic carbon mediated transformation of Fe(III) to Fe(II) phases. More importantly, Fe_Ox2 acts as the primary phase storing P in the saturated zone and serves as a key mineral barrier intercepting land-derived P. This study provides a comprehensive investigation of iron mineral pools, highlighting the enrichment of Fe_HR and identifying Fe_Ox2 as the dominant and functionally significant phase in highly permeable sandy beaches.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"702 ","pages":"Article 123225"},"PeriodicalIF":3.6,"publicationDate":"2025-12-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145823498","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":"Low-δ18O magmas at Batur, Indonesia: Evidence for slab-window melting beneath arc volcanoes","authors":"Guo-Rong Tang ,&nbsp;Wei Dan ,&nbsp;Adi Maulana ,&nbsp;Jian Wang ,&nbsp;Xiu-Zheng Zhang ,&nbsp;Xin Ma ,&nbsp;Qiang Wang ,&nbsp;Xi-Jun Liu ,&nbsp;Gong-Jian Tang","doi":"10.1016/j.chemgeo.2025.123224","DOIUrl":"10.1016/j.chemgeo.2025.123224","url":null,"abstract":"<div><div>Low-δ¹⁸O magmas (δ¹⁸O &lt; +5.5 ‰) record the assimilation of rocks that underwent high-temperature hydrothermal alteration. This study presents an integrated analysis of oxygen isotopes and major elements of olivines, along with whole-rock geochemistry and Sr–Nd–Hf isotopes for basaltic andesites and andesites from the Quaternary Agung and Batur volcanoes in Bali, Indonesia. Agung and Batur lavas exhibit similar trace element and Sr–Nd–Hf isotopic signatures but differ in their olivine oxygen isotopic compositions. Olivine phenocrysts from Agung lavas show δ¹⁸O values ranging from +4.65 ‰ to +5.38 ‰, with an average of +5.08 ± 0.21 ‰ (2SD, <em>n</em> = 20). Olivines from Batur lavas exhibit lower δ¹⁸O values (+3.70 ‰ to +5.15 ‰), with an average of +4.50 ± 0.14 ‰ (2SD, <em>n</em> = 120), and most are distinctly below the mantle olivine values. The low δ¹⁸O values observed in both Agung and Batur olivines are unlikely to result from assimilation of pre-existing hydrothermally altered crustal or <em>syn</em>-magmatic rocks. Instead, they provide evidence for the assimilation of recycled altered oceanic crustal materials. We propose that these assimilated oceanic crustal materials could have been derived from the partial melting of low-δ¹⁸O lower oceanic crust, possibly induced by hot asthenospheric flow through a slab window. This study highlights that slab windows may facilitate not only the formation of rear-arc ultrapotassic lavas but also significantly influence magmatism at the volcanic front.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"702 ","pages":"Article 123224"},"PeriodicalIF":3.6,"publicationDate":"2025-12-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145823499","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":"Geochemical signatures of mud and core gases from the Milun Fault Scientific Drilling (MiDAS), Taiwan: Implications for fluid pathways and crustal degassing","authors":"Ching-Chou Fu ,&nbsp;Kuo-Hang Chen ,&nbsp;Kuo-Wei Wu ,&nbsp;Pei-Ling Wang ,&nbsp;Ai-Ti Chen ,&nbsp;Vivek Walia ,&nbsp;Kuo-Fong Ma","doi":"10.1016/j.chemgeo.2025.123223","DOIUrl":"10.1016/j.chemgeo.2025.123223","url":null,"abstract":"<div><div>We investigated the fluid processes within the Milun Fault Zone (MFZ), eastern Taiwan, by combining continuous monitoring of dissolved gases in drilling mud and gases extracted from cores with the compositional and isotopic analyzers during the Milun Fault Scientific Drilling (MiDAS) project. Although atmospheric inputs dominate the background signal, distinct multi-gas anomalies of CH₄, C₂H₆, CO₂, H₂, He, and Rn occur at the discrete depths (∼440 m, 470–488 m, and ∼ 520 m). These anomalies coincide with the fracture zones, organic carbon-rich horizons, and the fault gouge core, delineating structurally controlled fluid pathways. Core δ¹³C_CO₂ values (−10 ‰ to −15 ‰) indicate organic degradation and methanogenesis as major sources of shallow CO₂, while clustered CH₄-C₂H₆ anomalies with He and Rn reflect episodic inflow of deep fluids along the fault conduits. Integration of the mud gas and core gas datasets demonstrated that the mud gas monitoring captured transient inflows and fracture controlled variability, whereas the core gases preserved in situ compositions and the isotopic fingerprints. Meanwhile, the data reveal the structural heterogeneity of the MFZ, providing geochemical confirmation of location near 520 m and the key horizons for long term hydrogeochemical monitoring. These findings highlight the potential of multi-parameter gas geochemistry to probe crustal fluid migration and its implications for fault activity and earthquake precursors.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"702 ","pages":"Article 123223"},"PeriodicalIF":3.6,"publicationDate":"2025-12-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145823503","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":"Biomineralization induced by Shigella dysenteriae JS3: The mechanism, and the differences between biotic and abiotic whewellite and struvite","authors":"Na Guo ,&nbsp;Jizheng Qiao ,&nbsp;Shuhua Zhang ,&nbsp;Shengzhe Gao ,&nbsp;Yanhong Zhao ,&nbsp;Chao Han ,&nbsp;Hui Zhao ,&nbsp;Yanyang Zhao ,&nbsp;Xiao Gao ,&nbsp;Ruirui Meng ,&nbsp;Bin Cao ,&nbsp;Yu Li ,&nbsp;Hao Dong ,&nbsp;Jie Li ,&nbsp;Maurice E. Tucker ,&nbsp;Huaxiao Yan ,&nbsp;Zuozhen Han","doi":"10.1016/j.chemgeo.2025.123221","DOIUrl":"10.1016/j.chemgeo.2025.123221","url":null,"abstract":"<div><div>Whewellite and struvite have been successfully biomineralized; however, the underlying mechanisms and the distinctions between the biotic and abiotic minerals remain scarcely documented. Here, <em>Shigella dysenteriae</em> was used to induce whewellite and struvite precipitation. Concurrently, the biomineralization mechanism and the distinguishing characteristics of the biominerals, which set them apart from abiotic minerals, were investigated. JS3 bacteria are capable of producing alkaline phosphatase and ammonia, thereby generating an alkaline environment (pH 8.7). Under the influence of calcium (Ca²⁺), magnesium (Mg²⁺), and oxalate (C₂O₄²⁻) ions, the contents of aromatic protein-like, tryptophan-like, fulvic acid-like, and humic acid-like substances within bacterial extracellular polymeric substances increased. Ca²⁺ facilitated the precipitation of Mg²⁺, whereas C₂O₄²⁻ exhibited an antagonistic effect. Whewellite and struvite exhibited preferentially oriented growth. The biotic forms of whewellite displayed significantly more negative δ¹³C values (−15.7 ‰ to −22.9 ‰) and δ¹⁸O values (−15.0 ‰ to −7.2 ‰) compared to their abiotic counterparts, which showed δ¹³C and δ¹⁸O values of −11.1 ‰ and − 4.8 ‰, respectively. Similarly, biotic struvite demonstrated more negative δ¹⁸O values (−7.3 ‰ to −8.5 ‰) than abiotic struvite (−4.4 ‰). Biominerals tend to display a high degree of habit diversity and contain more complex functional groups derived from organic components such as lipids, proteins, and hydrocarbons. C–N–C, C–NH₂, N–C=O, C–O–PO₃, P<img>O, C–PO₃, and S<img>S can serve as potential indicators for distinguishing biogenic minerals. This study helps to further understand the biomineralization mechanisms underlying the formation of human urinary tract stones and to distinguish between biotic and abiotic minerals in nature.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"703 ","pages":"Article 123221"},"PeriodicalIF":3.6,"publicationDate":"2025-12-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145823502","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":"Optimization of lithium diffusion modelling in plagioclase: implications for the assessment of pre-eruptive timescales","authors":"Simone Costa ,&nbsp;Matteo Masotta ,&nbsp;Fabio Colle ,&nbsp;Pier Paolo Giacomoni ,&nbsp;Claudia D’Oriano ,&nbsp;Patrizia Landi","doi":"10.1016/j.chemgeo.2025.123222","DOIUrl":"10.1016/j.chemgeo.2025.123222","url":null,"abstract":"<div><div>Lithium diffusion chronometry in plagioclase is used to retrieve timescales of pre-eruptive processes that occur over seconds to hours. The random orientation of 2D crystal sections exposed for microanalysis can strongly affect modelling results, leading to flawed interpretations of pre-eruptive timescales. To evaluate the effect of random crystal orientation, we systematically applied and compared the results of one-dimensional (1D) and multidimensional (analytical 3D correction) Li diffusion modelling to multiple oriented sections obtained from a set of eight plagioclase crystals from Stromboli volcano (Italy). For each crystal, Li concentration profiles were acquired using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) on the section oriented parallel to (010) and on a sequence of three to four sections oriented perpendicular to (010), starting from the core-intersecting section. The diffusion model accounts for the analytical uncertainties in Li measurements and estimates the optimal timescale within a set of 1000 possible values through bootstrapping. Timescales obtained from Li concentration profiles acquired on sections perpendicular to (010) are maximum in the sections intersecting the crystal cores and decrease markedly within each crystal (by up to 93% for simple 1D modelling and up to 85% after 3D correction) with increasing distance from this section. In turn, timescales derived from sections parallel to (010) are systematically lower than those obtained for the theoretically equivalent section perpendicular to (010). This means that large underestimates of the timescales are introduced by the analysis of 2D crystal sections with relatively small offset from the core-intersecting section, also in the case of plagioclase exposing sections parallel to (010), where the offset from the core-intersecting section cannot be well evaluated on a morphological basis. The application of the analytical 3D correction to diffusion profiles in part compensates for the underestimates derived from the offset relative to the core-intersecting section. Yet, the choice of an adequate plagioclase crystal in 2D sections of natural rocks remains a major source of uncertainty, which adds to other uncertainties related to the choice of diffusion coefficients and Arrhenius parameters. The collective impact of these uncertainties is discussed based on the comparison between Li diffusion timescales in plagioclase obtained in this and previous studies on Stromboli volcano. The implemented methodology for Li diffusion modelling presented in this study allows a more robust assessment of pre-eruptive timescales and is applicable to other volcanic systems.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"704 ","pages":"Article 123222"},"PeriodicalIF":3.6,"publicationDate":"2025-12-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145823497","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 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":"2025-12-23","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":"Mercury concentration: A new window into ancient diets and trophic levels in vertebrate paleontology","authors":"Felipe M.S. Cardia ,&nbsp;José Vicente E. Bernardi ,&nbsp;Carlos Eduardo M. Oliveira ,&nbsp;Marco B. Andrade ,&nbsp;Max C. Langer ,&nbsp;Sandra A.S. Tavares ,&nbsp;Fabiano V. Iori ,&nbsp;William R. Nava ,&nbsp;Thiago S. Marinho ,&nbsp;Luiz Carlos B. Ribeiro ,&nbsp;Jurandir R. Souza ,&nbsp;Rodrigo M. Santucci","doi":"10.1016/j.chemgeo.2025.123218","DOIUrl":"10.1016/j.chemgeo.2025.123218","url":null,"abstract":"<div><div>Direct evidence about feeding habits and trophic levels of extinct species is scarce in the fossil record. Typically, such information is based on geochemistry, stomach contents, anatomy, and, whenever possible, comparison with living counterparts. Despite the challenges involved, such reconstructions are vital for understanding the structure of past ecosystems. Here, we propose a novel geochemical approach in paleontology that uses total mercury concentration (THg) in fossil vertebrate tissues (bones and tooth enamel) and its bioaccumulation and biomagnification properties as geochemical indicators for the inference of feeding habits and trophic levels. Thin section and X-ray diffractometry (XRD) revealed that THg values found in bioapatite from the diverse and well-preserved fossil vertebrates of the Upper Cretaceous Bauru Group (Brazil) are not altered by diagenetic processes. The results show that each vertebrate group analyzed (e.g., fishes, turtles, amphibians, crocodylomorphs, avian, and non-avian dinosaurs) are characterized by different THg concentrations (ranging from 1.66 to 15 ng.g⁻¹ Hg). Notably, similar values were found in fossils of the same taxonomic group regardless of their geological unit of origin. More importantly, taxa with different feeding habits were positioned at different trophic levels based on the bioaccumulation and biomagnification of Hg. Reliable Hg analyses in fossils require confirming that bones are free from diagenetic contamination that may artificially elevate their Hg concentrations.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"702 ","pages":"Article 123218"},"PeriodicalIF":3.6,"publicationDate":"2025-12-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145813959","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 partitioning and isotope fractionation during crustal Anatexis: New constraints from across-grade traverses and centimeter-scale Leucosome-Restite Pairs","authors":"Juan Felipe Bustos-Moreno ,&nbsp;Gray E. Bebout ,&nbsp;Rolf L. Romer ,&nbsp;Lorenzo Magnani","doi":"10.1016/j.chemgeo.2025.123219","DOIUrl":"10.1016/j.chemgeo.2025.123219","url":null,"abstract":"<div><div>We investigated nitrogen (N) partitioning and isotope fractionation during crustal anatexis, in three metapelitic migmatite suites: the Anatectic Complex of Toledo and Tormes Dome Anatectic Region in Spain, and the Adamello Pluton Contact Aureole (APCA) in Italy. Restites have N concentrations higher than those in corresponding leucosomes and pegmatites, related to higher modal abundances of biotite in restitic domains. In general, restites and migmatites (whole-rocks consisting of both leucosome and restite) have higher δ¹⁵N values, by up to 5.3 ‰, than the leucosomes and pegmatites. During partial melting, the mobility and isotope fractionation of N are strongly influenced by the stability and breakdown of muscovite and biotite. Differences in the δ¹⁵N of restites and leucosomes are inconsistent with the expectation of minimal fractionation at high temperatures among NH₄⁺-bearing micas and feldspars in equilibrium in closed-systems. These differences may instead reflect, open-system behavior during melting and conceivably also during partial retrograde reactions (back-reaction) between partial melts and restites. Possible additional evidence for open-system behavior during melting exists for the APCA, where shifts to lower δ¹⁵N values resulting from a series of up-grade melting reactions contrast with the shifts to higher values expected for Rayleigh N loss involving N₂, NH₃, and NH₄⁺. In general, the partial melts did not inherit the isotope compositions of their source rocks, but seem to record variably lower δ¹⁵N values, challenging the assumption that granitic melts directly reflect the isotope composition of their metasedimentary sources. The results of our study of these metapelitic migmatites indicate great compatibility of N in residues of partial melting, largely in biotite, and thus implicate highly devolatilized and partially melted sedimentary rocks as important sites of long-term N storage at mid- to deep-levels of the continental crust.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"702 ","pages":"Article 123219"},"PeriodicalIF":3.6,"publicationDate":"2025-12-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145813960","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}