Chemical Geology最新文献

{"title":"Visualising and quantifying Mg/Ca and Sr/Ca heterogeneity in the isochronous growth increments of bivalve shells (Tridacna)","authors":"Bohao Dong ,&nbsp;Niklas Hausmann ,&nbsp;Laura M. Otter ,&nbsp;Russell N. Drysdale ,&nbsp;Amy L. Prendergast","doi":"10.1016/j.chemgeo.2025.123109","DOIUrl":"10.1016/j.chemgeo.2025.123109","url":null,"abstract":"<div><div>Ultra-high (hourly to daily) and high (annual) resolution paleoenvironmental proxies derived from geological and archaeological sclerochronology archives provide us with a window into ancient times. As one of the most common and well-developed archives, bivalve shells play a very important role in reconstructing past environments and connecting palaeo-environmental records with past human behaviours. However, we still lack a basic understanding of whether bivalve shells have evenly distributed trace element abundances in shell portions that grew at the same time (i.e., isochronous growth increments). In this study, we present the first published application of laser-induced breakdown spectroscopy (LIBS) for qualitative two-dimensional elemental mapping of <em>Tridacna</em> shells. To complement the qualitative results, we also employed laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and wet-chemistry trace element analyses to acquire quantitative composition of Mg/Ca and Sr/Ca in <em>Tridacna maxima</em> shells, addressing the question of spatial heterogeneity in shell geochemistry. Our results reveal significant spatial heterogeneity in Mg/Ca and Sr/Ca ratios within contemporaneous increments, which could lead to a ± 4.3 to 5.5 °C variance in palaeo sea surface temperature reconstructions. This heterogeneous distribution may result from varying environmental exposure in different areas of a shell influencing the sensitivity and efficiency of minor and trace element incorporation in the different regions of the shell's epithelium tissue. By better understanding the natural heterogeneity of trace element uptake across isochronous growth increments, this study makes a fundamental step forward in assessing the reliability of sea surface temperature reconstructions and guiding future data acquisition strategies.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"696 ","pages":"Article 123109"},"PeriodicalIF":3.6,"publicationDate":"2025-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145327091","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 incomplete crystal-melt separation of volcanic-plutonic complex in the southern Great Xing'an Range, NE China","authors":"Beibei Pan ,&nbsp;He Huang ,&nbsp;Zhaochong Zhang","doi":"10.1016/j.chemgeo.2025.123096","DOIUrl":"10.1016/j.chemgeo.2025.123096","url":null,"abstract":"<div><div>Probing the petrogenetic link between volcanic and plutonic rocks is crucial for deciphering continental crust evolution. Reconstructing the crystal-melt separation process represents a research frontier, albeit its role in silicic mushes remains contentious. Here, we present an integrated study of the Mangtudaba volcanic-plutonic complex from the southern Great Xing'an Range in NE China, comprising bulk-rock geochemistry and in situ zircon geochemical and geochronological analyses. All lithologies, including quartz monzonite, crystal-rich trachydacite, and crystal-poor rhyolite/rhyolitic tuff, exhibit consistency in spatial distribution, zircon ages (∼138 Ma), and Hf isotopic compositions [ε_Hf(t) = +4.7 − +9.0], demonstrating their derivation from a common magma reservoir. Both petrographic and geochemical characteristics reveal that quartz monzonites represent residual cumulates after the extraction of high-silica rhyolitic melts. Integrating microstructural evidence with terminal porosity measurements (Φ, quartz monzonites: 0.2–0.3; trachydacites: 0.1–0.2), we speculate that the crystal-melt separation in Mangtudaba complex was incomplete, leaving significant pore melt (F_trap, 10–35 vol%) trapped in cumulates and unexpected cumulate fragments entrained into the extracted melts. The trachydacites displaying cumulate signatures originated from mush rejuvenation and witnessed the interruption of efficient phase separation. Zircons display distinct texture-temperature-composition spectra that record their redistribution and recrystallization history in discrete melt domains, including extracted melts, trapped interstitial melts, and hot replenishments. Regarding the separation mechanisms, compaction played a dominant role, while magma recharge facilitates phase separation only within an optimal flux range, beyond which excessive replenishments become counterproductive. This study establishes a comprehensive, quantitative model of crystal-melt separation and advances our understanding of volcanic-plutonic connections.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"696 ","pages":"Article 123096"},"PeriodicalIF":3.6,"publicationDate":"2025-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145315087","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":"Quantification of geothermal carbon dioxide fluxes using radiocarbon","authors":"Jocelyn C. Turnbull ,&nbsp;Tsung-Han Jimmy Yang ,&nbsp;Agnes Mazot ,&nbsp;Mus Hertoghs ,&nbsp;Isabelle Chambefort","doi":"10.1016/j.chemgeo.2025.123095","DOIUrl":"10.1016/j.chemgeo.2025.123095","url":null,"abstract":"<div><div>Volcanic-hosted active hydrothermal systems degas carbon dioxide (CO₂) into the atmosphere. Understanding the rate and variability of degassing can provide insights into geothermal system behaviour, and the response of these systems to geothermal power generation. Flux measurements from the accumulation chamber method are commonly used to quantify the natural volcanic degassing rate to the surface, but these must account for co-located CO₂ flux from soil and vegetation respiration. Uncertainty in the respiration CO₂ flux can lead to significant uncertainties in the geothermal CO₂ flux, particularly for locations where the geothermal flux is modest. We use flux estimates from accumulation chamber measurements of CO₂ and radiocarbon (¹⁴C) to partition the degassed CO₂ into geothermal and biogenic components. We demonstrate that at the Tauhara geothermal field (New Zealand), the biogenic CO₂ flux is significant and spatially variable. Further, the ¹⁴C measurements can discriminate even tiny geothermal CO₂ contributions, allowing more robust mapping of the geographic limits of natural degassing. We also examine ¹³C as an alternative partitioning method, and show that while it is generally effective, uncertainties in the end-member ∂¹³C values and the presence of both C3 and C4 plants can make interpretation complex.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"696 ","pages":"Article 123095"},"PeriodicalIF":3.6,"publicationDate":"2025-10-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145315036","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":"Tectonic thickening in stagnant to mobile lid transition facilitated the stabilization of Archean cratons","authors":"Ning Ding ,&nbsp;Chris Hawkesworth ,&nbsp;Xiao-Lei Wang ,&nbsp;Rong-Feng Ge ,&nbsp;Axel Hofmann ,&nbsp;Jun-Yong Li","doi":"10.1016/j.chemgeo.2025.123093","DOIUrl":"10.1016/j.chemgeo.2025.123093","url":null,"abstract":"<div><div>Archean cratons are the oldest domains of tectonically stable continental crust and their formation coincided with the widespread emplacement of potassic granites, which reflects reorganization of crustal composition. However, the factors influencing the shifts in crustal composition and craton stability remain controversial. In this study of ca. 3.51–3.22 Ga trondhjemite-tonalite-granodiorite (TTG) and ca. 3.11–3.10 Ga potassic granites of the eastern Kaapvaal craton, we apply a newly developed zircon oxybarometer-hygrometer and document a progressive increase of magmatic <em>f</em>O₂ values and H₂O contents from ca. 3.51 to 3.22 Ga, peaking at ca. 3.10 Ga with values higher than those of known Archean granitic rocks and similar to modern orogenic granites. Concurrent increases in magma crystallization depths and crustal thickness culminated at 3.11–3.10 Ga. These trends reflect a tectonic transition from stagnant lid (3.66–3.23 Ga) to mobile lid (3.22–3.10 Ga) in eastern Kaapvaal craton, supported by isotopic shifts from juvenile to evolved Hf-O signatures. The combination of thermodynamic and geochemical modeling demonstrates that the widespread ca. 3.11–3.10 Ga potassic granites originated from partial melting of the middle to lower crust in regions of crustal thickening. The Kaapvaal Craton is proposed to be among the earliest cratons that witnessed tectonic thickening in stagnant to mobile lid transition, which might have played a critical role in the earliest stabilization and maturation of cratons.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"696 ","pages":"Article 123093"},"PeriodicalIF":3.6,"publicationDate":"2025-10-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145315038","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 controls on coupled glauconite–feldspar diagenesis and its implications for fluid–rock interactions in glauconitic-rich sandstones","authors":"Jiachen Gao ,&nbsp;Benben Ma ,&nbsp;Qin Zhang ,&nbsp;Adedapo N. Awolayo","doi":"10.1016/j.chemgeo.2025.123089","DOIUrl":"10.1016/j.chemgeo.2025.123089","url":null,"abstract":"<div><div>Glauconite and K-feldspar, two abundant aluminosilicate minerals in natural glauconitic sandstones, undergo complex diagenetic dissolution in deep subsurface environments, influencing fluid chemistry and mineral reactivity. Their coupled dissolution forms a dynamic feedback system that influences fluid storage capacity and flow pathways in glauconitic sandstones, yet the mechanisms governing their interaction remain insufficiently understood. This study revisits the diagenetic processes controlling their coupled dissolution and its impact on secondary porosity evolution in deeply buried glauconitic sandstones of the Oligocene Songnan-Baodao Sag, Qiongdongnan Basin. By integrating petrography, geochemical modelling, and microstructural analysis of glauconite–feldspar interactions in varying partial pressure of CO₂ (pCO₂) and mineralogical conditions, we systematically investigate the dissolution characteristics and controlling factors of the coupled dissolution process. Geochemical modelling demonstrates that microfracture development in glauconite markedly increases its effective surface area, accelerating dissolution and enhancing accumulation of <figure><img></figure> , <figure><img></figure> , and <figure><img></figure> in pore waters, which in turn modulates K-feldspar dissolution and precipitation dynamics. The pCO₂ critically controls mineral solubility with high pCO₂ sustaining continuous K-feldspar dissolution, whereas low pCO₂ leads to rapid solution saturation, suppressing further dissolution and potentially inducing re-precipitation that may occlude porosity. Furthermore, the glauconite-to-K-feldspar mass ratio governs their coupled behaviour, low glauconite content promotes feldspar dissolution, while high glauconite abundance inhibits it. This relationship is reflected in two distinct patterns of porosity development, one characterized by dominant glauconite dissolution with limited alteration of K-feldspar, and another where K-feldspar dissolution is more pronounced while glauconite remains relatively unaltered. These findings clarify key controls on glauconite–feldspar diagenesis and provide theoretical insight for predicting porosity evolution in deeply buried glauconitic sandstone reservoirs. They also highlight the broader implications for CO₂ storage and geothermal energy systems, where mineralogical variability exerts a strong influence on fluid–rock interactions in sedimentary basins.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"696 ","pages":"Article 123089"},"PeriodicalIF":3.6,"publicationDate":"2025-10-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145315122","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 isotopic constraints on marine primary productivity across the Ordovician–Silurian transition","authors":"Jinqi Xu ,&nbsp;Ruining Hu ,&nbsp;Wenhui Wang ,&nbsp;Xueqi Song ,&nbsp;Haibo Xu ,&nbsp;Jingqiang Tan","doi":"10.1016/j.chemgeo.2025.123090","DOIUrl":"10.1016/j.chemgeo.2025.123090","url":null,"abstract":"<div><div>The Ordovician-Silurian transition (OST) witnessed the second-largest mass extinction event during the Phanerozoic. However, while the decline of animal species is well documented, research on primary productivity during the OST remains qualitative, despite its importance in regulating ecosystem growth. In this study, we explored the potential of nitrogen isotope as a potential proxy for primary productivity in the oligotrophic oceans during the OST. We present nitrogen isotope (δ¹⁵N) data from a drill core (L203 well) in South China, combined with literature data from 17 sections from different latitudes around the world. Primary productivity is calculated independently based on sedimentary carbon contents and deposition rates, using the Knies equation. The data show that on a global scale, primary productivity is strongly negatively correlated with nitrogen isotopes. Low levels of primary productivity concur with increased δ¹⁵N, which suggests a weakening of nitrogen fixation, and vice versa. Moreover, using the δ¹⁵N data constraints primary productivity, this study reveals the differential mechanisms of organic matter accumulation in the Wufeng and Lungmachi formations, with the former primarily driven by high productivity, and the latter by enhanced preservation under anoxic conditions. This study provides new theoretical support and practical examples for using nitrogen isotope constraints paleoceanographic primary productivity.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"695 ","pages":"Article 123090"},"PeriodicalIF":3.6,"publicationDate":"2025-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145315040","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":"Paleoaltimetry of intracontinental mountains: The uplift history of the Wallowa Mountains (Eastern Oregon, USA) as constrained by triple oxygen and hydrogen isotope analysis of meteoric hydrothermal systems","authors":"Kseniya Vialichka,&nbsp;Ilya N. Bindeman","doi":"10.1016/j.chemgeo.2025.123087","DOIUrl":"10.1016/j.chemgeo.2025.123087","url":null,"abstract":"<div><div>We here report widespread low-δD and triple oxygen isotope depletions around dikes of the Columbia River Basalt Large Igneous Province (CRB), attributed to dike-groundwater interaction. CRB dikes exposed in the uplifted, currently 2–3 km-high Wallowa Mountain granites yield δD values down to −166 ‰ and δ¹⁸O down to 0–2 ‰. At the time of dike emplacement (∼16 Ma), the Wallowa area was &lt;1 km in elevation, and the dikes were first altered by reconstructed low-altitude Miocene groundwater with δ¹⁸O of −7 to −10 ‰. However, the extremely low δD value of reconstructed meteoric water (−175 ‰), comparable to modern ice caps, suggests that the Wallowas had already attained high elevations before D/H closure but after ¹⁸O/¹⁷O/¹⁶O closure. Oxygen isotope exchange persisted for ∼0.8 Ma until closure (375–175 °C), while hydrogen exchange continued for another ∼2 Ma, until 200–78 °C at ∼13 Ma. Thus, the uplift of the Wallowa block began just ∼0.8 Ma after CRB eruptions, likely driven by eclogitic root delamination. Our data track this uplift and cooling of the CRB dike-intruded Wallowa crustal block. Applying published δD lapse rates, a − 175 ‰ δD_mw value implies elevations up to 4.5 km with ice cover. The estimated 3.5 km elevation gain corresponds to rapid uplift rates of 0.12–0.35 cm/yr from 15.7 to 13.1 Ma. Afterward, uplift ceased, lithospheric cooling and erosion reduced elevation, exposing 1–2 km deep CRB dikes. These results establish altered basalt groundmass as a novel paleoclimate and paleoaltimetry proxy, when it represents the last thermal episode.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"696 ","pages":"Article 123087"},"PeriodicalIF":3.6,"publicationDate":"2025-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145315039","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":"Wildfire records in Late Permian lacustrine deposits (Gohan Formation, Korea): Implications for paleoenvironmental reconstruction","authors":"Yong Il Lee ,&nbsp;Hyosang Kwon ,&nbsp;Mun Gi Kim","doi":"10.1016/j.chemgeo.2025.123086","DOIUrl":"10.1016/j.chemgeo.2025.123086","url":null,"abstract":"<div><div>Soot-black carbon (S-BC) produced by biomass combustion typically accounts for less than 10 % of the sedimentary organic carbon in modern lacustrine deposits, but how much in ancient lacustrine deposits is not well known. Considering that records of wildfires are common in Late Permian sediments worldwide, this study focuses on the S-BC of the Late Permian Gohan Formation, a lacustrine sediment distributed in central Korea. S-BC occurs throughout the Gohan Formation sequence, and although its concentrations are low at 0.01 to 0.90 wt% (average 0.17 wt%), it accounts for 23 to 91 % (average 54 %) of TOC. The carbon isotopic composition of S-BC ranges from −25.6 to −17.1 ‰ with an average of −21.8 ‰. Variations in S-BC carbon isotopic composition throughout the sequence suggest that the paleohumidity conditions of the S-BC sources for the Gohan Formation varied considerably, some of which differed significantly from the watershed paleohumidity conditions. Excluding S-BC, more than two thirds of the sedimentary organic carbon in Gohan paleolake sediments were derived from phytoplankton, with the remainder originating from terrestrial plants. The large variations in the δ¹³C of algae (−33.0 to −16.8 ‰) suggest that the dissolved inorganic carbon pool of the Gohan paleolake was alternately affected by episodes of increased primary production and increased organic matter respiration.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"695 ","pages":"Article 123086"},"PeriodicalIF":3.6,"publicationDate":"2025-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145261850","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":"Spectrophotometric determination of the stability of La hydroxyl complexes at near neutral to alkaline pH from 25 to 75 °C","authors":"Kevin Padilla ,&nbsp;Hannah Juan Han ,&nbsp;Alexander P. Gysi","doi":"10.1016/j.chemgeo.2025.123067","DOIUrl":"10.1016/j.chemgeo.2025.123067","url":null,"abstract":"<div><div>The hydrolysis of rare earth elements (REE) potentially controls their mobility during fluid-rock interaction in a broad range of pH and temperature conditions. However, there is still a lack of thermodynamic data for modeling accurately the stability of REE hydroxyl complexes in hydrothermal aqueous fluids. In this study, UV–Vis spectrophotometric experiments were conducted from 25 to 75 °C in near-neutral to alkaline NaOH-bearing aqueous solutions with varying lanthanum (La) concentrations (0 to ∼0.23 mmol/kg). The color indicator <em>m</em>-cresol purple was used to determine <em>in situ</em> pH and derive the average OH⁻ ligand number (<span><math><mover><mi>n</mi><mo>→</mo></mover></math></span>) and formation constants for the La hydroxyl complexes (LaOH²⁺, La(OH)₂⁺, and La(OH)₃⁰). From 25 to 50 °C, <span><math><mover><mi>n</mi><mo>→</mo></mover></math></span> ranges between ∼1 and 2 at pH from 7.0 to 9.3. At 75 °C, <span><math><mover><mi>n</mi><mo>→</mo></mover></math></span> ranges between ∼1.5 and 3 at pH from 6.3 to 8.8. These results suggest the predominance of LaOH²⁺ and La(OH)₂⁺ complexes from 25 to 50 °C, and an increased predominance of La(OH)₃⁰ at 75 °C. The cumulative formation constants (<em>β</em>_n^°, <em>n</em> = 1 to 3) are derived for the reaction La³⁺ + <em>n</em>OH⁻ = La(OH)_<em>n</em>^3-<em>n</em>, and fitted between 25 and 250 °C by combining the UV–Vis and literature solubility data. The resulting log<em>β</em>_n^° are expressed as function of temperature (<em>T</em> in Kelvin): log<em>β</em>₁^° = −1.786 + 0.0133 <em>T</em> + 1.049·10³/<em>T</em>; log<em>β</em>₂^° = −5.797 + 0.0267 <em>T</em> + 2.713·10³/<em>T</em>; log<em>β</em>₃^° = 6.435 + 0.0223 <em>T</em> + 512.7/<em>T</em>. A comparison between these new fits and existing extrapolations using the Helgeson-Kirkham-Flowers equation of state indicates significant differences in the predicted hydrolysis of La. The latter extrapolations should therefore be updated for the hydrolysis of REE.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"696 ","pages":"Article 123067"},"PeriodicalIF":3.6,"publicationDate":"2025-10-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145277924","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":"Whole rock and pyrite geochemistry of the low-grade metamorphic sediments trace the redox conditions in the ocean during the Tonian","authors":"Yufei Hao ,&nbsp;Sifan Wu ,&nbsp;Jianghong Deng ,&nbsp;Congying Li ,&nbsp;Weidong Sun ,&nbsp;Jing Huang","doi":"10.1016/j.chemgeo.2025.123085","DOIUrl":"10.1016/j.chemgeo.2025.123085","url":null,"abstract":"<div><div>The Tonian Period captures critical co-evolutionary transitions between marine redox conditions and early life, but the sediments that have undergone low-grade metamorphism complicate investigations into contemporaneous marine redox conditions. In this study, comprehensive analysis of whole rock and pyrite chemistry in slates of the Tongtawan Formation (∼800 Ma) is conducted to reconstruct oceanic redox conditions and evaluate diagenetic/metamorphic impacts on these sediments. The size of framboidal pyrites mostly ranges from 3.33 to 7.67 μm, indicating a predominantly ferruginous deep ocean, with minor occurrences of euxinic or dysoxic conditions. However, depressed ratios of highly reactive iron to total iron (i.e., Fe_HR/Fe_T mostly &lt;0.38) in whole rock seem to indicate oxic conditions. This is attributed to the consumption of highly reactive iron due to chloritization during diagenesis/metamorphism. Pyrite morphology and diagnostic trace element ratios confirm its syngenetic to early-diagenetic origins, validating pyrite chemistry as a robust proxy for contemporaneous seawater composition. In situ LA-ICP-MS analyses document pronounced enrichments of elements (e.g., Co, Ni, Mo, and Mn) in pyrites, exceeding typical Tonian and Mesoproterozoic records. These enrichments reflect enhanced inventory in the ocean due to atmospheric and oceanic oxygenation—with Mo exhibiting the most diagnostic response—and additional fluxes from the erosion of mafic/ultramafic rocks and from hydrothermal inputs linked to the mantle plume and Rodinia breakup (e.g., Co, Ni, and Mn). This indicates Tonian oceans possessed a significantly expanded element reservoir during the Tonian, displaying enhanced oxidation levels despite largely ferruginous deep waters against a backdrop of increasing atmospheric oxygen.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"695 ","pages":"Article 123085"},"PeriodicalIF":3.6,"publicationDate":"2025-10-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145261836","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}