Chemical Geology最新文献

{"title":"Organic geochemical evidence links changes in marine microbes and phytoplankton to ammonite turnover in the Tethyan Middle Jurassic","authors":"Adam Zakrzewski ,&nbsp;Zoltán Kovács ,&nbsp;József Pálfy","doi":"10.1016/j.chemgeo.2025.122977","DOIUrl":"10.1016/j.chemgeo.2025.122977","url":null,"abstract":"<div><div>Carbon isotope-based chemostratigraphy is a well-established method for regional or even global correlations, especially at major stratigraphic boundaries which are often marked by global change events. However, background intervals remain less well studied and our knowledge is limited about the drivers of small-scale faunal turnovers which may be reflected in the zonal boundaries of biostratigraphic schemes. Moreover, organic geochemistry is much less used than carbon isotopes in chemostratigraphy. Here, we address these issues by a comprehensive stable isotope and organic geochemical study of three Tethyan Aalenian (Middle Jurassic) sections with good ammonite biostratigraphic control. We assess the linkages between zone-level faunal transitions and minor geochemical perturbations recorded by isotopic and biomarker indicators. A wide range of geochemical analyses (biomarkers, δ¹³C_SAT, δ¹³C_carb, δ¹⁸O_carb, and compound-specific isotope analyses (CSIA)) were performed on samples from three continuous Tethyan Aalenian–lowermost Bajocian sections in the Gerecse Mts. (Hungary) where ammonite zonal boundaries are well constrained. The organic matter is predominantly aquatic in origin with negligible terrigenous admixture. Most of the biostratigraphic boundaries coincide with minor negative Carbon Isotope Excursions in δ¹³C_SAT and phytoplankton-related CSIA. Curves of phytoplankton-related biomarker indicators, including diploptene, dehydroabietic acid methyl ester, and distribution of methylheptadecanes reveal marked changes within the phytoplankton communities at the transitions between ammonite zones and/or subzones. These biomarker results suggest that turnovers of the ammonite faunas were preceded by phytoplankton crises. Thus, biostratigraphic boundaries likely reflect minor environmental changes that first affected the primary producers, then trophic changes propagated through the entire marine food web.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"692 ","pages":"Article 122977"},"PeriodicalIF":3.6,"publicationDate":"2025-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144664935","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":"Paleoenvironmental evolution of the Eastern Paratethys: Tracing the Tethys Ocean legacy through geochemical proxies","authors":"Dan V. Palcu Rolier ,&nbsp;Zhanhong Liu ,&nbsp;Wei Wei ,&nbsp;Sergey Popov ,&nbsp;Larisa Golovina ,&nbsp;Iuliana Vasiliev ,&nbsp;Wout Krijgsman ,&nbsp;Thomas Algeo","doi":"10.1016/j.chemgeo.2025.122974","DOIUrl":"10.1016/j.chemgeo.2025.122974","url":null,"abstract":"<div><div>During the Oligocene to Miocene, the Paratethys Sea emerged as the northern offshoot of the Tethys Ocean, separated from the Mediterranean by the Alpine-Himalayan mountain range. Its history was characterized by the opening, restriction and closure of marine gateways, resulting in significant paleoenvironmental changes, including episodes of anoxia and extreme salinity fluctuations. This study investigates the paleoenvironmental evolution of the Paratethys Sea by focusing on variations in salinity and paleoventilation through advanced geochemical analyses of key sections (Belaya, Panagia, Zhelezhny Rog) in the northern Caucasus and Taman Peninsula of Russia, spanning 42 to 4 Ma. We apply a suite of geochemical proxies to reconstruct paleosalinity [e.g., using the boron/gallium (B/Ga), strontium/barium (Sr/Ba), sulfur/total organic carbon (S/TOC) ratios] and paleoredox conditions [e.g., using the organic carbon/phosphorus (C_org/P) ratio as well as trace-metal enrichment factors such as Zn_EF, V_EF, and Mo_EF]. Our results indicate that Paratethys was influenced by both global and local events, with regional factors becoming increasingly significant as isolation and fragmentation progressed. Paleoventilation proxies reveal two main episodes of anoxia: the Kuma Anoxic Event, a regional event exhibiting oceanic anoxic signatures that encompassed the time of the Middle Eocene Climatic Optimum (MECO) and; the Maikop Persistent Basin Water Stratification (PBWS) event, coinciding with the Eocene-Oligocene Transition (EOT) and lasting until the Middle Miocene Climatic Optimum (MMCO), reflecting characteristics of an enclosed sea; and a weaker, less stable suboxic-anoxic episode in the late Miocene, associated with Megalake Paratethys. Paleosalinity proxies depict both transitions from marine to brackish conditions, such as the late Maikop salinity decrease and significant short-lived marine episodes, such as the MMCO-related mid-Langhian flood (14.8 Ma), the Badenian-Sarmatian Extinction Event (12.65 Ma) and the Intra-Maeotian Event (6.8 Ma). These findings emphasize the critical role of marine connectivity as a trigger of salinity and ventilation changes in the Eastern Paratethys's evolution, laying the groundwork for future studies on restricted basins.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"692 ","pages":"Article 122974"},"PeriodicalIF":3.6,"publicationDate":"2025-07-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144664932","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 isotope fractionation during natural travertine formation","authors":"Hongming Cai ,&nbsp;Jiubin Chen ,&nbsp;Zhongwei Wang ,&nbsp;Wei Yuan ,&nbsp;Zhengrong Wang ,&nbsp;Hui Henry Teng ,&nbsp;Xiangyu Zhu ,&nbsp;Chenglong Tu ,&nbsp;Congqiang Liu ,&nbsp;Jacques Schott","doi":"10.1016/j.chemgeo.2025.122973","DOIUrl":"10.1016/j.chemgeo.2025.122973","url":null,"abstract":"<div><div>Natural precipitation of travertine provides high-resolution information about paleoclimate change. Although significant progress has been made to trace paleoenvironments using metal stable isotopes in travertine precipitation, research on their systematics and fractionation is still lacking, limiting their application in paleoclimate reconstruction. In this study, Hg isotope variations in two natural travertine precipitation systems (canal and pools) under different hydrodynamic conditions, together with hydrochemical parameters and mineral phase in water and freshly-formed minerals were investigated during travertine precipitation to determine if the resulting Hg isotope signatures could be used in paleoenvironmental reconstruction. Our results clearly demonstrated significant Hg isotope fractionation during calcite precipitation, with light Hg isotopes being preferentially incorporated into the solid phase relative to the coexisting aqueous solutions in both systems. The magnitude of Hg isotope fractionation between travertine and the solution, <em>Δ</em>^<em>202</em><em>Hg</em>_{<em>travertine-water</em>}, varied between −0.87 and − 3.29 ‰ and between −2.10 and − 3.77 ‰ for the canal and the pool systems, respectively, and decreased with increasing precipitation rate and water temperature. Hg isotope fractionation was likely triggered by the transformation from organic matter-bound Hg (e.g. fulvic acid) in solution to CO₃-Hg complex on solid surface during calcite precipitation, which was controlled, to a certain extent, by both temperature and calcite precipitation kinetics. Our study implies that Hg isotope signatures in natural travertine could provide useful information for evaluating the paleoenvironmental changes.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"692 ","pages":"Article 122973"},"PeriodicalIF":3.6,"publicationDate":"2025-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144686961","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":"Speciation distribution and phase partition laws of rare alkali metals in geothermal sinter deposits in southern Tibet: Implications for the cesium mineralisation in the geothermal system","authors":"Zhiwei Shi ,&nbsp;Hongbing Tan ,&nbsp;Peixin Cong ,&nbsp;Fei Xue ,&nbsp;Hongkai Zhu ,&nbsp;Yu Zhang","doi":"10.1016/j.chemgeo.2025.122975","DOIUrl":"10.1016/j.chemgeo.2025.122975","url":null,"abstract":"<div><div>The unusually enriched cesium (Cs) and associated some other rare alkali metals in large-scale geyserites in the geothermal system of southern Tibet, China as well as other places all over the world, has great potential for exploitation. In this paper, in order to reveal the mineralisation mechanism of Cs in geyserites, the speciation distribution and solid-liquid phase partition laws of rare alkali metals in various types of sinters at Gudui were systematically issued. It was found that Rb and Cs tend to be enriched in sinters, while Li tends to stay in geothermal springs. The speciation distribution of Cs in geyserites is that it mainly accumulates in the residual and reducible fractions, with a small amount of oxidisable fraction, suggesting that Cs is adsorbed by clay minerals and Fe<img>Mn oxides, combined with organic matter reactive groups of microorganisms, and retained in the crystalline water of the silicate lattice. Therefore, it is concluded that the unusual enrichment and mineralisation of Cs in geyserites is mainly controlled by physical and chemical effects, with biological effects playing an auxiliary contributing role. If Cs mineral resources in geyserites are to be developed in the future, geyserites in the form of amorphous SiO₂ colloids should be preferentially selected and then clay minerals, Fe<img>Mn oxides and microbial exploitation of the sedimentary layers in the geothermal deposits should be also considered.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"692 ","pages":"Article 122975"},"PeriodicalIF":3.6,"publicationDate":"2025-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144702937","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":"Regulation of coupled carbon‑sulfur interactions by Spartina alterniflora via physicochemical properties and microorganism-mediated pathways in coastal wetlands","authors":"Yu-Xiang Zhu ,&nbsp;Pei-Feng Li ,&nbsp;Chun-Ying Liu ,&nbsp;Jiang-Chen Gong ,&nbsp;En-Ren Zhang ,&nbsp;Jing-Wen Hu ,&nbsp;Qian-Qian Yang ,&nbsp;Gui-Peng Yang","doi":"10.1016/j.chemgeo.2025.122976","DOIUrl":"10.1016/j.chemgeo.2025.122976","url":null,"abstract":"<div><div>The invasive species <em>Spartina alterniflora</em> has profoundly altered biogeochemical cycling in coastal wetlands across China since its introduction decades ago. This study examined its impacts on spatiotemporal patterns of carbon and sulfur storage in intertidal sediments. Through systematic field sampling and laboratory analyses, we quantified seasonal variations in vertical sediment profiles across three distinct zones in Jiaozhou Bay wetlands: <em>S. alterniflora</em>-invaded area (SAA), native <em>Suaeda glauca</em> area (SGA), and unvegetated mudflat area (MA). Key parameters included dissolved organic carbon (DOC), soil organic matter (SOM), total carbon (TC), four inorganic sulfur forms (water soluble sulfur, adsorbed sulfur, hydrochloric acid soluble sulfur, hydrochloric acid volatile sulfur), and total sulfur (TS). Our findings revealed that SAA exhibited significantly higher DOC (16–107 %) and TC (18–21 %) concentrations compared to SGA and MA. TS accumulation in SAA surpassed the other two areas by 1.4- to 1.6-fold, with particularly large fractions of water-soluble sulfur (17–32 %) and hydrochloric acid volatile sulfur (52–133 %). Notably, SOM/TS ratios in SAA were significantly lower in winter and summer (28–37 %) than in native ecosystems. These results demonstrate that <em>S. alterniflora</em> invasion fundamentally restructures coastal sediment geochemistry through coupled carbon–sulfur interactions, with implications for wetland biogeochemical functioning under biological invasions.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"692 ","pages":"Article 122976"},"PeriodicalIF":3.6,"publicationDate":"2025-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144672199","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 chemical stratigraphy of the sub-cratonic lithospheric mantle and its sampling by kimberlites tracked by olivine trace element content","authors":"Federico Casetta ,&nbsp;Theodoros Ntaflos ,&nbsp;Sonja Aulbach ,&nbsp;Igor Ashchepkov ,&nbsp;Luca Faccincani ,&nbsp;Rainer Abart","doi":"10.1016/j.chemgeo.2025.122969","DOIUrl":"10.1016/j.chemgeo.2025.122969","url":null,"abstract":"&lt;div&gt;&lt;div&gt;The chemical composition of olivine, the main constituent of Earth's upper mantle, is increasingly used to explore metasomatic and igneous processes in Earth's interior, the evolution of alkaline‑carbonatitic and kimberlitic melts, and their associated diamond potential. Yet, the trace element-poor nature of olivine in mantle-derived peridotites, and especially the low concentration of incompatible trace elements, is analytically challenging. In most studies of mantle peridotites, the chemical characterization of olivine is limited to low-current major element analyses by electron probe. Fuller characterization of olivine trace element compositions allow tracing the &lt;em&gt;T&lt;/em&gt;-&lt;em&gt;P&lt;/em&gt;-&lt;em&gt;f&lt;/em&gt;O&lt;sub&gt;2&lt;/sub&gt; conditions, nature and metasomatic modification of the lithospheric mantle. In this study, we define the chemical variability of olivine in peridotites sampled through an entire sub-cratonic lithospheric mantle section (spanning 70–230 km), &lt;em&gt;via&lt;/em&gt; detailed and comprehensive geochemical characterization of coarse granular to porphyroclastic/fluidal textured spinel, spinel-garnet and garnet peridotites from the Devonian Udachnaya-East kimberlite (Siberian craton). Combined with thermobarometric modelling, bulk-rock composition and major element composition of the coexisting minerals, this provides novel insights into the utility of olivine as a recorder of processes in the lithospheric mantle.&lt;/div&gt;&lt;div&gt;The high-resolution data and the integrated textural/chemical characterization of Udachnaya-East peridotites show that olivine composition is variably controlled by a combination of &lt;em&gt;T&lt;/em&gt;-&lt;em&gt;P-(fO&lt;/em&gt;&lt;sub&gt;&lt;em&gt;2&lt;/em&gt;&lt;/sub&gt;&lt;em&gt;)&lt;/em&gt; conditions, and melt-related enrichment, and faithfully discriminates between two groups of xenoliths. Refractory, coarse granular peridotites equilibrated at low-&lt;em&gt;T&lt;/em&gt; (770–1000 °C) are generally composed of olivine depleted in all trace elements. In contrast, fertile to refertilized garnet-bearing rocks equilibrated at high-&lt;em&gt;T&lt;/em&gt; (1180–1360 °C) and &lt;em&gt;P&lt;/em&gt; = 5–6 GPa are enriched in all basaltic components, and record earlier significant addition of HFSE, Fe, Ca, Al and P at the base of the Siberian lithosphere. A stand-alone group is constituted by metasomatically-derived wehrlites and dunites, which equilibrated at low-&lt;em&gt;T&lt;/em&gt; but preserve selective trace element enrichment in olivine. Olivine in fertile and strongly metasomatized peridotites can store surprisingly high amounts of all trace elements and especially Ti, Nb, Ta, Zr and Hf, with sometimes suprachondritic Nb amounts and Nb/Ta ratios. These results highlight the potential of olivine as a HFSE repository, and require its inclusion as a player in the terrestrial HFSE mass balance. Integrated to literature data, our results enable also to discuss the applicability of diagrams used for discrimination between spinel- and garnet-bearing peridotitic olivine, thus improving our knowledge of the provenance of the xenocrys","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"692 ","pages":"Article 122969"},"PeriodicalIF":3.6,"publicationDate":"2025-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144664948","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 (−8 ‰, VSMOW) Paleoproterozoic and discordant zircon: Lessons learned from using a combination of traditional bulk and in situ approaches","authors":"David Zakharov, André Navin Paul, Dylan P. Colòn, Maria Ovtcharova, Benita Putlitz, Anne-Sophie Bouvier, Afrid Abdaly Sheik, Dmitry Zozulya, Martin Robyr","doi":"10.1016/j.chemgeo.2025.122972","DOIUrl":"https://doi.org/10.1016/j.chemgeo.2025.122972","url":null,"abstract":"Zircon has become an important archive of early Earth's history relating the surface water cycle and magmatism via its O isotope composition. However, metamictization of zircon presents a challenge when dealing with ancient detrital grains that are removed from their host rock. Here we use an extremely low-δ&lt;ce:sup loc=\"post\"&gt;18&lt;/ce:sup&gt;O zircon (−8 ‰) that is collected from an intact low-δ&lt;ce:sup loc=\"post\"&gt;18&lt;/ce:sup&gt;O host rock in order to refine our analytical approaches to O isotope and U&lt;ce:glyph name=\"sbnd\"&gt;&lt;/ce:glyph&gt;Pb determinations. The δ&lt;ce:sup loc=\"post\"&gt;18&lt;/ce:sup&gt;O of the hosting quartz is −4.2 ± 0.4 ‰, attesting to the primary nature of low δ&lt;ce:sup loc=\"post\"&gt;18&lt;/ce:sup&gt;O values from an ancient water-rock interaction that originated in the Neoarchean. Highly variable &lt;ce:sup loc=\"post\"&gt;18&lt;/ce:sup&gt;O/&lt;ce:sup loc=\"post\"&gt;16&lt;/ce:sup&gt;O of the zircon correlate positively with &lt;ce:sup loc=\"post\"&gt;16&lt;/ce:sup&gt;O&lt;ce:sup loc=\"post\"&gt;1&lt;/ce:sup&gt;H/&lt;ce:sup loc=\"post\"&gt;16&lt;/ce:sup&gt;O measured by SIMS, representing secondary hydration accompanied by O isotope exchange, from the least altered δ&lt;ce:sup loc=\"post\"&gt;18&lt;/ce:sup&gt;O = −8.0 ± 0.1 ‰ to the highly hydrated domains with δ&lt;ce:sup loc=\"post\"&gt;18&lt;/ce:sup&gt;O around +2 ‰. Previously measured near-concordant in situ U&lt;ce:glyph name=\"sbnd\"&gt;&lt;/ce:glyph&gt;Pb ages accompanied by high U (up to 0.5 wt%) present a puzzling observation of a preserved U&lt;ce:glyph name=\"sbnd\"&gt;&lt;/ce:glyph&gt;Pb system and highly disturbed O isotope compositions. Here we test the accuracy of these interpretations by combining several “gold standard” techniques including elemental X-ray mapping, bulk laser fluorination (δ&lt;ce:sup loc=\"post\"&gt;18&lt;/ce:sup&gt;O), and chemical abrasion isotope dilution thermal ionization mass spectrometry (CA-ID-TIMS) for U&lt;ce:glyph name=\"sbnd\"&gt;&lt;/ce:glyph&gt;Pb ages. The zircon bulk δ&lt;ce:sup loc=\"post\"&gt;18&lt;/ce:sup&gt;O values (−5.7 ‰ to −3.6 ‰) agree with the average values measured by SIMS, corroborating the effect of chemical removal of damaged domains by bulk that approach values in domains with low &lt;ce:sup loc=\"post\"&gt;16&lt;/ce:sup&gt;O&lt;ce:sup loc=\"post\"&gt;1&lt;/ce:sup&gt;H/&lt;ce:sup loc=\"post\"&gt;16&lt;/ce:sup&gt;O. Further, the triple O isotope compositions of zircon and quartz measured by laser fluorination have values similar to the isotope composition of the low-δ&lt;ce:sup loc=\"post\"&gt;18&lt;/ce:sup&gt;O protoliths found within the same area. The δD value of −175 ‰ measured in a bulk zircon with 2.4 wt% H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O points to a near-surface source of hydrating waters. The CA-ID-TIMS U&lt;ce:glyph name=\"sbnd\"&gt;&lt;/ce:glyph&gt;Pb dating of such highly metamict zircon is challenged by almost complete loss of the analyte during the chemical abrasion step and by U&lt;ce:glyph name=\"sbnd\"&gt;&lt;/ce:glyph&gt;Pb discordant ages. Leaching at 130–210 °C for 3–12 h produces variably discordant ages, with one zircon grain yielding concordance and the &lt;ce:sup loc=\"post\"&gt;207&lt;/ce:sup&gt;Pb&lt;ce:glyph name=\"sbnd\"&gt;&lt;/ce:glyph&gt;&lt;ce:sup loc=\"post\"&gt;206&lt;/ce:sup&gt;Pb age of 1773 ± 2 Ma","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"24 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2025-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144664934","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":"Spatially resolved X-ray imaging and molecular characterisation of sulfur and iron in organic- and sulfur-rich hydrocarbon source mudstones","authors":"Yusuf Abubakar ,&nbsp;Roy A. Wogelius ,&nbsp;Victoria S. Coker ,&nbsp;Kevin G. Taylor ,&nbsp;Nicholas P. Edwards ,&nbsp;Bart E. van Dongen","doi":"10.1016/j.chemgeo.2025.122971","DOIUrl":"10.1016/j.chemgeo.2025.122971","url":null,"abstract":"<div><div>Sulfurisation of organic matter (OM) is a prominent preservation mechanism, however iron sulfide precipitation, particularly pyrite (FeS₂), can counteract this mechanism. There is a dearth of high-resolution, spatially-resolved spectroscopic (redox) information on sulfur and iron inventories within organic-rich rocks that would improve our understanding of prevailing environmental conditions during deposition. Here, state-of-the-art synchrotron-based X-ray absorption and fluorescence analyses of key organic- and sulfur-rich mudstones demonstrate the potential of these techniques to non-destructively map and produce detailed spectroscopic information. Detailed high-resolution analyses (μm- to mm-scale) reveal the presence of widespread sulfurised OM in the Blackstone Band of the Kimmeridge Clay Formation, in line with a persistence of euxinia over a long temporal span and low reactive iron input, facilitating the preservation of OM through sulfurisation. In contrast, the presence of sulfurised OM was transitional in the Monterey Formation, consistent with fluctuating water column redox conditions, and is less significant in the Whitby Mudstone Formation, likely due to the high reactive iron concentrations outcompeting sulfurised OM formation. Analyses of sulfur species using model compounds further indicate that the Whitby Formation is strongly enriched in inorganic reduced sulfur minerals, while both the Kimmeridge Clay and Monterey Formations are dominated by organic sulfur species. These synchrotron-based observations improve our understanding of environmental conditions during the time of deposition of these mudstones and thus show great promise in the study of organic-rich sediments, especially in allowing their depositional settings to be more accurately reconstructed.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"692 ","pages":"Article 122971"},"PeriodicalIF":3.6,"publicationDate":"2025-07-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144662036","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 structure of high-Mg alkali-bearing aluminosilicate glasses investigated in situ at ambient and high pressure by multi-angle energy dispersive X-ray diffraction and infrared microspectroscopy","authors":"Veronica Stopponi ,&nbsp;Federica Piccirilli ,&nbsp;Rostislav Hrubiak ,&nbsp;Valeria Misiti ,&nbsp;Stefano Lupi ,&nbsp;Vincenzo Stagno","doi":"10.1016/j.chemgeo.2025.122970","DOIUrl":"10.1016/j.chemgeo.2025.122970","url":null,"abstract":"<div><div>The structural properties of synthetic high-Mg alkali-bearing aluminosilicate glasses analogues of natural picritic-to-komatiitic magmas were investigated in situ by multi-angle energy dispersive X-ray diffraction at ambient pressure and 2.1 GPa and by Fourier Transform infrared spectroscopy up to 5.4 GPa upon compression and decompression. Our results reveal that the intermediate range ordering of the glass structure at 2.1 GPa is 3.14 Å, increasing to 3.19 Å when decompressed to ambient pressure. The local structure at 2.1 GPa shows T-O lengths of 1.66 Å and T-T distances of 3.19 Å, resulting in a T-O-T angle of 147°. Upon decompression, T-O lengths shorten to 1.65 Å and T-T distances increase to 3.21 Å, widening the T-O-T angle to 154°. The deconvoluted infrared spectra result in the presence of <em>Q</em>^<em>1</em>, <em>Q</em>^<em>2</em>, <em>Q</em>^<em>3</em> populations in the aluminosilicate spectral region, whose proportions remain relatively unchanged up to 5.4 GPa. The structural response of the investigated glasses to cold compression does not involve changes in polymerization, but rather a shrinking and compaction of the structure as evidenced by the <em>Q</em>^<em>n</em> species shifting to higher wavenumbers as a function of pressure. The structural properties determined by X-ray diffraction for this glass composition are discussed along with those of glasses from previous studies to highlight a compositional dependence dictated by the amount of SiO₂ and Al₂O₃.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"692 ","pages":"Article 122970"},"PeriodicalIF":3.6,"publicationDate":"2025-07-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144664936","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":"Groundwater-mediated U–Th–Pb differential migration in monazites during hydrochemical weathering","authors":"Hao-Xiang Zhang ,&nbsp;Shao-Yong Jiang ,&nbsp;Wen-Tian Li ,&nbsp;Wei Zhang ,&nbsp;Hui-Min Su","doi":"10.1016/j.chemgeo.2025.122968","DOIUrl":"10.1016/j.chemgeo.2025.122968","url":null,"abstract":"&lt;div&gt;&lt;div&gt;The influence of near-surface weathering on U–Th–Pb isotope systematics in accessory minerals remains poorly understood. Here, we investigate monazite samples (DFS225, DFS277 and DFS620) collected from the Duanfengshan (DFS) pegmatites (Hubei Province, South China), which exhibit supergene alteration driven by oxidizing groundwater. Combined optical microscopy, scanning electron microscopy (SEM), and TESCAN Integrated Mineral Analyzer (TIMA) analyses were used to characterize high-porosity textures and minor mineral inclusions (MIs) within the monazite grains. Results indicate that MIs are enriched in U and Th (e.g., U–Th–rich silicate and oxide phases) relative to host monazite and possess lower Th/U ratios. Porous domains frequently occur spatially proximate to these inclusions. Based on these observations, DFS monazites were classified into two distinct types: Type I (porous domains) and Type II (MI-bearing domains).&lt;/div&gt;&lt;div&gt;LA–ICP–MS U–Th–Pb isotope analyses revealed that Type I monazites yield U/Pb ages of 135–138 Ma, identical to published magmatic ages. In contrast, Type IIa monazites (MI-bearing) show younger U/Pb ages (125–128 Ma). Laser ablation analyses of Type IIa samples show elevated U signals coinciding with low &lt;sup&gt;206&lt;/sup&gt;Pb/&lt;sup&gt;238&lt;/sup&gt;U ratios, suggesting age resetting via incorporation of secondary U–rich phases. Type-IIb monazites (porous domains) display significant common Pb contamination (up to 81 %), resulting in imprecise intercept ages on the Tera-Wasserburg (T-W) plot with low &lt;sup&gt;207&lt;/sup&gt;Pb/&lt;sup&gt;206&lt;/sup&gt;Pb intercepts (DFS225: 0.781; DFS620: 0.719) and artefactually older common Pb-corrected U&lt;img&gt;Pb ages (142–152 Ma). These samples also exhibit elevated Cu signals and positive correlations between &lt;sup&gt;207&lt;/sup&gt;Pb/&lt;sup&gt;206&lt;/sup&gt;Pb ratios and U depletion, interpreted as evidence for late–stage U leaching coupled with external Pb infiltration. Remarkably, Th/Pb ages for both monazite types remain consistent (131–134 Ma), highlighting systematic discordance between U/Pb and Th/Pb chronometers in these weathering-affected samples. Based on U–Th–Pb isotope analyses and binary mixing-based forward modeling, we identify three distinct scenarios of differential U–Th–Pb mobility in monazite grains during groundwater leaching: (1) Unaltered monazite—no visible textural modification; proportional U&lt;img&gt;Pb loss preserves true crystallization ages (t&lt;sub&gt;U/Pb&lt;/sub&gt; = t&lt;sub&gt;True&lt;/sub&gt; &gt; t&lt;sub&gt;Th/Pb&lt;/sub&gt;), demonstrating the relative robustness of the U&lt;img&gt;Pb chronometer to hydrochemical attack. (2) Porous monazite—intense U loss yields spuriously old U/Pb ages (t&lt;sub&gt;U/Pb&lt;/sub&gt; &gt; t&lt;sub&gt;True&lt;/sub&gt; &gt; t&lt;sub&gt;Th/Pb&lt;/sub&gt;). Concurrent Pb contamination positively correlates with U loss, producing imprecise U&lt;img&gt;Pb isochrons with low &lt;sup&gt;207&lt;/sup&gt;Pb/&lt;sup&gt;206&lt;/sup&gt;Pb intercepts on Tera–Wasserburg diagrams. (3) MI-bearing monazite—secondary low-Th/U phase admixture induces preferential U/Pb disturbance (t&lt;sub&gt;T","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"692 ","pages":"Article 122968"},"PeriodicalIF":3.6,"publicationDate":"2025-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144662035","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}