Chemical Geology最新文献

{"title":"Volatile solubility in fluid-saturated haplogranitic melts under graphite-buffered redox conditions","authors":"Mikaela Krona ,&nbsp;Simone Tumiati ,&nbsp;Luca Toffolo ,&nbsp;Omar Bartoli ,&nbsp;Bruna B. Carvalho ,&nbsp;Dominik Sorger ,&nbsp;Donald B. Dingwell ,&nbsp;Bernardo Cesare","doi":"10.1016/j.chemgeo.2025.123153","DOIUrl":"10.1016/j.chemgeo.2025.123153","url":null,"abstract":"<div><div>Graphite is a common accessory mineral in metasedimentary rocks and is a potential source of carbon during anatexis. Its presence constrains the composition of C-O-H fluids, and thus acts as a fluid buffer. To date, experiments on H₂O-CO₂ mixed volatile solubility have focused primarily on binary H₂O-CO₂ fluids which are not representative of graphite-buffered systems where ternary H₂O-CO₂-CH₄ mixtures occur. In this study, we have conducted solubility experiments in graphite- and fluid-saturated haplogranitic melts at 0.5 and 1 GPa, between 800 and 1000 °C. The double-capsule technique was employed to impose graphite-buffered redox conditions. Equilibration of graphite and H₂O produces a ternary C-O-H fluid, modelling the behavior of an internally-buffered graphitic system during dehydration melting. The resultant composition of the fluid phase (determined ex-situ) corresponds to a ternary H₂O-CO₂-CH₄ mixture with H₂O contents ranging from 68 to 96 mol%. The maximum CO₂ contents dissolved in the glasses range from 0.12 to 0.2 wt%, and the H₂O contents vary from 8 to 11 wt%. Although present in the C-O-H fluid, dissolved CH₄ was not detected in the glass, indicating negligible solubility. Comparison with previous experimental studies reveals that the carbon contents of the glasses are consistently lower than those previously documented in experiments equilibrated with binary H₂O-CO₂ fluids. We further observe that solubility models overestimate the CO₂ contents of the melts studied here. Since melting of metasediments can occur in various geological settings, our results emphasize the need to consider ternary C-O-H fluids in solubility models in order to address graphite-buffered anatectic systems.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"700 ","pages":"Article 123153"},"PeriodicalIF":3.6,"publicationDate":"2026-01-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145553675","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":"Geochemistry of La Fossa fumaroles (Vulcano Island, Aeolian Islands) unveils the evolving magmatic sources of the fluid before and during the 2021 unrest","authors":"C. Federico,&nbsp;A. Paonita,&nbsp;R.M.R. Di Martino,&nbsp;S. Bellomo,&nbsp;L. La Pica,&nbsp;G. Pecoraino,&nbsp;A. Gattuso,&nbsp;A.F. Pisciotta,&nbsp;F. Sortino","doi":"10.1016/j.chemgeo.2025.123168","DOIUrl":"10.1016/j.chemgeo.2025.123168","url":null,"abstract":"<div><div>La Fossa volcano (Vulcano Island, Italy) has remained quiescent since its 1888–1890 eruption, punctuated by unrest characterized by increased vapor output and seismic activity. Fumarole vapor composition, a proxy for magmatic and hydrothermal fluid mixing, responds to enhanced magmatic volatile input during unrest, potentially revealing source characteristics. Besides being a marker of the relative contribution of magmatic and hydrothermal fluids, the fumarole composition can reveal some insights, in particular, into the depth of fluid sources and their composition.</div><div>Hypotheses suggest that varying unrest phases involve different depths within the magma reservoir, influencing fluid input into the hydrothermal system and potentially inducing pressurization.</div><div>This study presents geochemical and isotopic data from La Fossa's high-temperature fumaroles (2011–2024), including the unrest starting in September 2021. The findings indicate a three-year preparatory phase preceding the 2021 unrest, suggesting the activation of different fluid pathways. The 2021 unrest mobilized previously unobserved gas or magma reservoirs. Identifying geochemical markers linked to specific magma sources can be applied to other volcanoes to decipher degassing histories and hazards. This research underscores the complexity and interconnectedness of volcanic plumbing systems, where activity in one part can influence others, influencing monitoring and interpretation in volcanic regions globally. The interplay of magmatic and hydrothermal fluids, shifts in fluid sources, and the role of degassing in triggering unrest observed at La Fossa are relevant to many active volcanoes worldwide.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"700 ","pages":"Article 123168"},"PeriodicalIF":3.6,"publicationDate":"2026-01-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145575278","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":"Formation of natural IrO2 through Os–Ir–Ru alloy oxidation","authors":"Anton Kutyrev ,&nbsp;Olga Filimonova ,&nbsp;David W. Saxey ,&nbsp;Anna Vymazalová ,&nbsp;Katy Evans ,&nbsp;Vadim S. Kamenetsky ,&nbsp;Didier Wermeille ,&nbsp;Denis Fougerouse ,&nbsp;Steven M. Reddy","doi":"10.1016/j.chemgeo.2025.123167","DOIUrl":"10.1016/j.chemgeo.2025.123167","url":null,"abstract":"<div><div>We studied a rare platinum-group element (PGE)-bearing phase occurring as inclusions in Pt<img>Fe alloys from placer deposits, previously referred to as “iridium oxide,” but lacking confirmation of actual Ir oxide. X-ray absorption spectroscopy confirms that the studied Ir<img>O phase contains genuine IrO₂, with iridium in a formal oxidation state of 4+ and an Ir<img>O bond distance of 1.95 ± 0.02 Å, matching synthetic rutile-type IrO₂. Atom probe tomography reveals that IrO₂ forms thin films along boundaries between metallic PGE-rich domains, which are separated by oxide-rich regions composed of Ca, Mn, Fe, K, and V oxides. Mass-balance constraints indicate that Rh, Ru, and Pt occur mainly as metals, while Os is partly oxidized. Formation of IrO₂ from Os–Ir–Ru alloys requires extremely oxidizing conditions, estimated at approximately fayalite–magnetite–quartz (FMQ) + 5 to +10. While such conditions could potentially develop during hydrothermal alteration, there is limited geological evidence for such high fO₂ values in natural environments. The coexistence of iridium oxide and metallic Ru contradicts thermodynamic predictions, which suggest Ru should oxidize prior to Ir. This discrepancy indicates that conventional equilibrium thermodynamics, where pressure, temperature, and chemical potential are the controlling intensive variables, may not predict natural redox behaviour. Alternative mechanisms, including kinetically controlled reactions, extremely limited length-scales of equilibrium, or a role for electrochemical work, may permit localized Ir oxidation. The results provide rare in-situ evidence for PGE oxidation and Os<img>Ir mobility within the lithosphere, with implications for PGE distribution and Os isotope systematics in mantle and crustal rocks.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"700 ","pages":"Article 123167"},"PeriodicalIF":3.6,"publicationDate":"2026-01-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145593662","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":"Critical metal inventory of alkaline lakes of Northern Tanzania: Geochemical controls on rare earth element and Sc, W, and U distribution","authors":"Timmu Kreitsmann ,&nbsp;Lukas Klose ,&nbsp;Dennis Kraemer ,&nbsp;Albano Mahecha ,&nbsp;Simona Regenspurg ,&nbsp;Franziska D.H. Wilke ,&nbsp;Michael Bau","doi":"10.1016/j.chemgeo.2025.123159","DOIUrl":"10.1016/j.chemgeo.2025.123159","url":null,"abstract":"<div><div>Alkaline lakes in the East African Rift System represent unique environments that have attracted considerable scientific attention over the years. Their significance has grown further due to their astrobiological relevance and potential economic interest. Surprisingly, only limited data are available on trace elements, and more specifically, rare earth elements and yttrium (REY) in these systems. In this study, we present a new, comprehensive dataset of REY and other trace elements from alkaline lakes and associated hot springs in northern Tanzania. Our results reveal elevated concentrations of REY, W, Sc, and U, which are attributable to the presence of strong ligands (carbonate and phosphate), complexation with humic acids, and accumulation through evaporation. Shale-normalised REY patterns in the alkaline lakes are characterised by HREY enrichment over LREY, positive Ce anomalies, and fractionated Y/Ho ratios. These patterns are controlled by the distinctive physicochemical conditions within the lakes, rather than by the composition of inflowing river or hot spring waters; i.e., the REY distribution of the source rock does not appear to control the REY distribution in the water. Enrichment of HREY is driven by strong complexation with carbonate and phosphate, along with the preferential removal of LREY through scavenging by particles. Notably, the resemblance between the shale-normalised REY patterns of alkaline lakes and those of seawater precipitates highlights the need for caution when interpreting such signatures in the geological record, when the typical negative Ce anomaly of seawater is suppressed.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"699 ","pages":"Article 123159"},"PeriodicalIF":3.6,"publicationDate":"2026-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145567641","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":"Tracing the volcanic sources and differentiation of flood basalts using handheld XRF","authors":"Jussi S. Heinonen ,&nbsp;Arto V. Luttinen","doi":"10.1016/j.chemgeo.2025.123147","DOIUrl":"10.1016/j.chemgeo.2025.123147","url":null,"abstract":"<div><div>Handheld (or portable) X-ray fluorescence (hXRF) technology has advanced significantly, enabling quality geochemical analysis in field conditions. We used a hXRF device (Olympus Vanta VMR-CCC-G3) to analyze major and trace elements in Jurassic continental flood basalts at Vestfjella, western Dronning Maud Land, Antarctica. Calibration was performed using basalt samples with existing laboratory XRF data. Samples were cut and polished at the research station, and multiple measurements were averaged per sample, with more detailed analysis for coarse-grained textures. Over 300 lava units were analyzed on-site. Semi-quantitative data were obtained for major and minor elements (Si, Ti, Al, Fe, Mn, Mg, Ca, K, P) and trace elements (V, Ni, Cu, Zn, Sr, Zr, Y). Co was excluded due to lack of standard data. Most elements showed rather low coefficient of within-sample variation &lt;12 % (2 s), while Cr, Rb, and Ba showed higher variability (15–25 %). Some discrepancies in light elements such as Si and Al compared to lab data were attributed to sample heterogeneity, field conditions, and degradation of the hXRF window protective film, which was corrected using time-integrated factors. Elements such as Ti, P, Zr, Y, and Ni were key in distinguishing basalt types and tracing their volcanic sources and magmatic evolution. In addition, a previously unknown ferropicritic lava unit was discovered. This study demonstrates the potential of hXRF for semi-quantitative geochemical analysis and its value in guiding field-based petrological investigations, especially in remote environments where traditional sampling is limited.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"699 ","pages":"Article 123147"},"PeriodicalIF":3.6,"publicationDate":"2026-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145575281","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":"Element mobilities during serpentinization: Insights from the Ronda Massif, Spain","authors":"Bastien Audran ,&nbsp;Marc Ulrich ,&nbsp;Yannick Branquet ,&nbsp;Guillaume Barré ,&nbsp;Georges Beaudoin ,&nbsp;Philippe Boulvais","doi":"10.1016/j.chemgeo.2025.123157","DOIUrl":"10.1016/j.chemgeo.2025.123157","url":null,"abstract":"<div><div>Serpentinization is a widespread hydrothermal alteration of ultramafic rocks, particularly peridotites, resulting in the formation of serpentinite through hydration processes. While the behavior of fluid-mobile elements (FME; e.g. B, Li, Cl, As, Sb, Pb, U, Th, Cs, Sr, Ba) during serpentinization is well documented, the mobility of other elements (e.g. base metals) remains poorly constrained. We analyzed bulk rock compositions of pairs of poorly and highly serpentinized peridotite rocks from the Ronda Massif (Spain), complemented by in situ LA-ICP-MS mineral analyses. The Loss On Ignition (LOI) content of whole rock represents a good proxy for serpentinization intensity. Ca, Al, Cu, V, and Ti are increasingly mobilized during the initial stages of pervasive serpentinization. In a second stage corresponding to total serpentinization along cm-wide, several meters-long corridors, a systematic loss in Ca, Al, Rb, Sr, REE Hf, Ti, Cu, and V was observed. In contrast, during the third stage of serpentinization corresponding to late faulting only Ca and Cu were leached. The trace element composition of serpentine minerals, including Ti, V, and Zn, is influenced by the primary mineral assemblage, particularly olivine and pyroxenes. In contrast, the mobility of Al and Ca from millimeter to meter scale is notably linked to the bastite-pyroxene and serpentine mesh texture-olivine transformation. Co, Ni, Zn, and Cr depletion in serpentine within veins is compensated by their significant incorporation into magnetite. Copper is systematically leached from serpentinized rocks, suggesting that serpentinization likely serves as a significant source for Cu-rich hydrothermal metallogenic systems hosted in ultramafic rocks.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"699 ","pages":"Article 123157"},"PeriodicalIF":3.6,"publicationDate":"2026-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145560226","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":"Driving forces of mineral recrystallization in aqueous solutions derived from kinetic modeling of isotope exchange data","authors":"Enzo Curti ,&nbsp;Jan Tits ,&nbsp;Frank Heberling","doi":"10.1016/j.chemgeo.2025.123169","DOIUrl":"10.1016/j.chemgeo.2025.123169","url":null,"abstract":"<div><div>Recrystallization in aqueous solutions is a ubiquitous process susceptible to control the entrapment and release of toxic contaminants in the subsurface. However, unraveling the underlying mechanisms and driving forces has proven to be elusive, as recrystallization frequently follows different kinetic pathways even for the same mineral, depending on its initial state and pre-treatment. To obtain a better insight, a large body of experimental data from isotope tracer experiments carried out in the past two decades on a variety of minerals (baryte, calcite, calcium-silicate hydrates, goethite, and UO₂) was reviewed and modeled, using the HOmogeneous Recrystallization (HOR) and the Continuous HOmogeneous Recrystallization (CHOR) models, both coupled to instantaneous reversible adsorption and denoted as a whole as C(HOR)-K_d models.</div><div>In the first part of this contribution, we develop the full mathematical formalism and discuss the model parameters. The second part is devoted to the review, modeling and interpretation of selected data. It is shown that the C(HOR)-K_d models successfully reproduce recrystallization data for widely different minerals, including Fe-isotope data on goethite modeled elsewhere using a different approach (“back-reaction” model). In combination with microscopic characterization data, the modeling results allow us to identify the thermodynamic driving forces controlling the recrystallization kinetics. These include: (i) the reduction of surface energy excess arising from a high density of defects (kink sites, dislocations, steps) and/or a high initial specific surface area; (ii) the spontaneous tendency to increase crystallinity (increase in crystallite size, transformation to a more stable habitus); (iii) the annealing of chemical potential gradients when foreign trace elements are incorporated as solid solution into the recrystallized solid; (iv) the annealing of electric potential gradients in redox active solids (Fe oxy-hydroxides). Our findings demonstrate that mineral recrystallization in aqueous solutions is a complex phenomenon driven by multiple mechanisms correlated to the properties of the primary solid. Accurate predictions on kinetics and extent of recrystallization are possible only after detailed characterization of the solid down to the molecular scale.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"699 ","pages":"Article 123169"},"PeriodicalIF":3.6,"publicationDate":"2026-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145583845","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":"Experimental Ge/Si partitioning during organic-mediated silica precipitation","authors":"Silvina Slagter ,&nbsp;Dan Asael ,&nbsp;Noah J. Planavsky ,&nbsp;Alida Perez-Fodich ,&nbsp;Lidya G. Tarhan","doi":"10.1016/j.chemgeo.2025.123156","DOIUrl":"10.1016/j.chemgeo.2025.123156","url":null,"abstract":"<div><div>Ediacara-style fossils represent Earth's earliest ecosystems of complex macroscopic organisms, preserved as three-dimensional casts and molds within sandstone beds. Differences in Ge/Si ratios between grains and cements in fossiliferous sandstones from the Ediacara Member of South Australia have been used to support early silica cementation as a key factor in moldic preservation. However, experimental studies tracking Ge/Si partitioning during decay-associated silicification are lacking. Here, we employ an experimental framework to further investigate the utility of Ge/Si ratios as a fossilization proxy. We conducted fossilization experiments using marine invertebrate animals, aquatic plants, and silica-rich artificial seawater to track the fate of Ge throughout the early stages of tissue silicification. We found that experimentally precipitated amorphous silica associated with decaying organisms is characterized by Ge/Si values of 0.25–2.07 μmol mol⁻¹, and displayed an overall increase during each experiment, concurrent with Ge incorporation into silica precipitating onto the experimental carcasses. These results help build a framework for using Ge/Si ratios to track fossilization processes and highlight the role of early silica precipitation in preserving soft tissues. Comparison of our experimental data with Ge/Si signatures from Ediacara fossiliferous sandstones improves our understanding of early diagenetic silicification and enables more robust reconstructions of the mechanisms responsible for the preservation of Earth's earliest animal communities.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"699 ","pages":"Article 123156"},"PeriodicalIF":3.6,"publicationDate":"2026-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145575318","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 physical properties of Alexandrian Roman glass: Industrial optimization in the first world market","authors":"Pascal Richet ,&nbsp;Kai-Uwe Hess","doi":"10.1016/j.chemgeo.2025.123146","DOIUrl":"10.1016/j.chemgeo.2025.123146","url":null,"abstract":"<div><div>The viscosity and thermal expansion of samples from a well-preserved Roman glass ingot from the late 2nd-early 3rd century Embiez-Ouest 1 shipwreck have been measured over wide temperature ranges to determine how this material was originally produced and how to preserve it now. Measurements of the viscous and volume relaxation indicate that the annealing range of this glass ranges between 750 and 780 K and exemplifies the fact that relaxation kinetics depend not only on temperature but also on the structural state of the glass. As investigated by differential scanning calorimetry, a very slow cooling rate of about 0.4 K/day has been determined from the glass originally produced, which agrees with the size of up to 20 tons of the tank furnaces dug out in the Egyptian Wâdî Natrûn area. In terms of both chemical composition and properties, Embiez Ouest 1 glass is strikingly similar to modern window glasses. Relying on abundant natron and shell-bearing siliceous sands, this early successful industrial optimization relied on chemical compositions close to the eutectic of the Na₂O-CaO-SiO₂ system, which made mass production possible to such an extent that it gave rise to the first industrial world market.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"699 ","pages":"Article 123146"},"PeriodicalIF":3.6,"publicationDate":"2026-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145536000","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":"Seawater Sr isotopes in belemnites from the Upper Jurassic of southern Germany","authors":"M. López Correa ,&nbsp;M. Regelous ,&nbsp;W. Blendinger ,&nbsp;W. Werner ,&nbsp;S. Lohmeier","doi":"10.1016/j.chemgeo.2025.123152","DOIUrl":"10.1016/j.chemgeo.2025.123152","url":null,"abstract":"<div><div>The Late Jurassic seawater ⁸⁷Sr/⁸⁶Sr composition is constrained by relatively few data of well preserved and dated fossils, mainly from the Boreal realm, and data from Tethyan shelves are very limited. The previous seawater curve shows a continuous and nearly linear rise from a minimum in the Oxfordian through the Kimmeridgian and Tithonian. In order to improve the resolution of the ⁸⁷Sr/⁸⁶Sr curve with data from the Tethyan realm, 33 new ⁸⁷Sr/⁸⁶Sr data for 22 Kimmeridgian to Tithonian belemnites from the Franconian Jurassic, Germany, are supported by 52 δ¹⁸O and δ¹³C analyses of both belemnites, and the limestone matrix in which they are preserved. The stable isotope results of belemnite constituents are compatible with existing data, and all diagenetically altered parts of belemnites (apical area, microfractured, recrystallized and marginal parts of the rostrum) show isotope shifts towards matrix values. The originally aragonitic septa show very negative δ¹⁸O (−9.1 to −11.8 ‰) and δ¹³C (−2.6 to −5.3 ‰), probably due to disequilibrium fractionation, i.e., vital effects. The ⁸⁷Sr/⁸⁶Sr data of belemnite rostra, composed of unaltered low-Mg calcite (0.706888 to 0.707072) by and large overlap the previously inferred seawater ⁸⁷Sr/⁸⁶Sr curve, but provide more details, showing an apparent more stepwise increase during the Late Jurassic, with rapid increases followed by invariant ratios. Jurassic seawater ⁸⁷Sr/⁸⁶Sr was most likely uniform, but data from well preserved and dated belemnites of the same age show a small but significant variation in ⁸⁷Sr/⁸⁶Sr of up to 0.000018. This is most likely an artifact caused by unintentional sample contamination with macroscopically pristine but microfractured areas, attached matrix, or the apical zone. The stepwise increase of Late Jurassic seawater ⁸⁷Sr/⁸⁶Sr could also be an artifact caused by inaccuracies in the absolute ages assumed for Late Jurassic ammonite zone boundaries and imprecise relative ages within ammonite zones. Alternatively, changes in Jurassic seawater ⁸⁷Sr/⁸⁶Sr occurred far more rapidly (∼0.000200 per Ma) than the residence time of Sr would suggest, similar to increases previously reported for Phanerozoic anoxic events and related to the change in the flux of Sr from the continents.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"699 ","pages":"Article 123152"},"PeriodicalIF":3.6,"publicationDate":"2026-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145554263","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}