Chemical Geology最新文献

{"title":"Remobilization of Ni in framboidal pyrite within sulfide nodules in Early Cambrian nickeliferous black shales","authors":"Xu-Yang Liu ,&nbsp;Ya-Fei Wu ,&nbsp;Daniel D. Gregory ,&nbsp;Katy Evans ,&nbsp;Anthony E. Williams-Jones ,&nbsp;Wen Zhang ,&nbsp;Mei-Fu Zhou ,&nbsp;Jian-Wei Li","doi":"10.1016/j.chemgeo.2025.122913","DOIUrl":"10.1016/j.chemgeo.2025.122913","url":null,"abstract":"<div><div>Black shales commonly contain deposits extremely enriched in nickel (Ni), but the processes of Ni enrichment remain debated. Here we use laser ablation–multiple collector–inductively coupled plasma–mass spectrometry and transmission electron microscopy to present new micrometer- to nanometer-scale insights into the remobilization of Ni in framboidal pyrite from the Dazhuliushui Ni-Mo deposit, South China. Two types of framboidal pyrite have been identified in sulfide nodules: early Py-a with a core-rim texture in a MoSC phase and later Py-b in millerite aggregates. The Py-b microcrystals are larger and more tightly packed than Py-a microcrystals, indicating a decrease in FeS₂ supersaturation from sedimentation or early diagenesis to later diagenesis. This is consistent with the lighter S and Fe isotopic compositions of Py-a than Py-b (mean −6.99 ‰ vs. −2.13 ‰ and −0.31 ‰ vs. 0.09 ‰, respectively), produced via the preferential utilization of light S and Fe isotopes during pyrite formation within a semi-restricted basin and/or from pore water. Amorphous organic matter rich in gersdorffite nanoparticles via adsorption occurs within the interstices of Py-a cores. Gersdorffite and millerite nanoparticles within Py-a rims rapidly precipitated in response to continuous decomposition of organic matter. The Py-b is not associated with organic matter but with minor gersdorffite nano-veinlets that might form via the decay of residual organic matter during late diagenesis. These results reveal the complex remobilization processes of Ni in framboidal pyrite and highlight that nanoscale observations are necessary for fully understanding the detailed processes of metal enrichment in black shales.-</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"691 ","pages":"Article 122913"},"PeriodicalIF":3.6,"publicationDate":"2025-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144272065","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":"Beryllium-isotope signatures in ice sheet proximal marine sediments","authors":"Matthew Richard Jeromson ,&nbsp;Toshiyuki Fujioka ,&nbsp;David Fink ,&nbsp;Krista Simon ,&nbsp;Alexandra L. Post ,&nbsp;Marcello Blaxell ,&nbsp;José Tonatiuh Sánchez-Palacios ,&nbsp;T. Gabriel Enge ,&nbsp;Carly Beggs ,&nbsp;Duanne A. White","doi":"10.1016/j.chemgeo.2025.122912","DOIUrl":"10.1016/j.chemgeo.2025.122912","url":null,"abstract":"<div><div>Meteoric-¹⁰Be has become a popular proxy for assessing glacial environments and processes around Antarctica, such as meltwater discharge or ice shelf environments. Despite applications in recent paleostudies, little testing of the mechanisms driving the deposition of Be-isotopes into marine sediments has been conducted. We used chemical leach procedures to sequentially or partially extract ¹⁰Be and ⁹Be from bulk sediments to assess the possible sources and depositional processes affecting them. Additionally, we leached the reactive phase of five different grainsize splits to determine whether ¹⁰Be/⁹Be ratios normalise for grainsize effects acting upon the ¹⁰Be concentration. Reactive Be-isotopes are primarily situated in the oxide phases of sediments, with the amorphous oxide (Am-Ox) phases consisting of much higher ¹⁰Be/⁹Be ratios (∼7–10 × 10⁻⁸) than the crystalline oxides (∼1–3 × 10⁻⁸; X-Ox), indicating that the Am-Ox phase better represents authigenic oxide production and a circumpolar deep water source, which is contrary to most of the current literature. Published leach procedures targeting the reactive phase of sediment consist of ratios in between the Am-Ox and X-Ox phases (∼3–7 × 10⁻⁸), indicating that they target both phases to some degree. The fractionation of Be-isotopes in Antarctic sediment samples shows that circumpolar deep water is the primary source of ¹⁰Be, and that the “reactive” signatures from different leach steps targeting the reactive phase are not the same.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"691 ","pages":"Article 122912"},"PeriodicalIF":3.6,"publicationDate":"2025-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144242391","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":"Revealing paleosalinity and paleoclimatic characteristics in Dawenkou Formation of the Paleogene in Huanggang Depression, eastern China: An integrated geochemical and palynological analysis","authors":"Wentao Chen ,&nbsp;Dawei Lv ,&nbsp;Zhenguo Ning ,&nbsp;Hao Xin ,&nbsp;Cuiyu Song ,&nbsp;Munira Raji ,&nbsp;Fanwei Meng ,&nbsp;Bin Yang ,&nbsp;Zhihui Zhang ,&nbsp;Lulu Tang","doi":"10.1016/j.chemgeo.2025.122911","DOIUrl":"10.1016/j.chemgeo.2025.122911","url":null,"abstract":"<div><div>The variations in paleosalinity and paleoclimate significantly influence the deposition and distribution of rock salt deposits. Understanding these variations is therefore essential for advancing knowledge of salt resource formation and supporting exploration efforts. In this study, we use an integrated approach combining geochemical and palynological proxies to reconstruct paleosalinity and paleoclimate during the salinization period of the Paleogene Dawenkou Formation, based on core samples from the ZK04 borehole in the Huanggang Depression, eastern China. The analysis identifies three distinct salinity phases spanning the late Eocene to early Oligocene: hyposaline water to mesosaline conditions, mesosaline to hypersaline conditions, and a return to hyposaline conditions. The intermediate hypersaline phase is particularly notable for a significant increase in both salinity and aridity, as evidenced by salinity-sensitive proxies such as the B/Ga ratio, boron excess (B_xs), corrected Sr/Ba, and sulfur-to-total organic carbon (S/TOC) ratios. Among these, the B/Ga ratio emerges as the most reliable indicator for reconstructing paleosalinity. The findings highlight the primary role of arid climatic conditions and elevated salinity in driving rock salt deposition in the Dawenkou Formation and offer valuable insights into the environmental controls on salt formation in other comparable basins worldwide.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"691 ","pages":"Article 122911"},"PeriodicalIF":3.6,"publicationDate":"2025-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144254911","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":"Precession-driven variations in phosphorus cycling facilitated Earth’s oxygenation in the early Proterozoic","authors":"Wytze K. Lenstra ,&nbsp;Margriet L. Lantink ,&nbsp;Rick Hennekam ,&nbsp;Paul R.D. Mason ,&nbsp;Gert-Jan Reichart ,&nbsp;Frederik J. Hilgen ,&nbsp;Caroline P. Slomp","doi":"10.1016/j.chemgeo.2025.122857","DOIUrl":"10.1016/j.chemgeo.2025.122857","url":null,"abstract":"<div><div>Oxygenic photosynthesis in the ocean of the early Proterozoic may have been limited by the nutrient phosphorus. If so, precession-driven variations in riverine phosphorus input may have enhanced oxygenic photosynthesis and thereby contributed to the rise of atmospheric oxygen. Here, we combine geochemical analyses of 2.46-billion-year-old deposits of the Joffre Member of the Brockman Iron Formation (Australia) and results of a reactive transport model to reconstruct pathways of organic matter degradation and phosphorus cycling in oceanic sediments over a precession cycle. Our results support a conceptual model in which increased phosphorus availability during precession maxima at southern paleolatitudes drove net oxygen production by inducing increased reductant burial in the sediment (mainly as pyrite, vivianite and magnetite). During precession minima, legacy benthic release of methane may have enhanced photolysis of atmospheric methane, thereby allowing for additional net oxygen production. Hence, precession-driven variations in coupled carbon–phosphorus–oxygen cycling may have acted as an accelerator towards the Great Oxidation Event.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"691 ","pages":"Article 122857"},"PeriodicalIF":3.6,"publicationDate":"2025-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144272066","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":"Trace-metal hyper-enrichment in Tremadocian black shales of the Baltic Palaeobasin linked to transgression and ultra-slow sedimentation rates","authors":"Mawo Ndiaye ,&nbsp;Sophie Graul ,&nbsp;Merlin Liiv ,&nbsp;Toivo Kallaste ,&nbsp;Thomas J. Algeo ,&nbsp;Rutt Hints","doi":"10.1016/j.chemgeo.2025.122910","DOIUrl":"10.1016/j.chemgeo.2025.122910","url":null,"abstract":"<div><div>Determining the local versus global influence on the metallogeny of redox-sensitive trace-metal-enriched black shales remains challenging despite extensive geochemical research in related topics. A set of local triggers or modifiers of syngenetic metal enrichment, still poorly understood, impedes the ability to adequately predict the potential distribution of metal resources. This study of the Lower Ordovician Türisalu Formation examines the stratigraphic trends of Mo and U isotopes in Mo-U-V hyper-enriched thin transgressive black shales and associated beds from the inner shelf of the Baltic Palaeobasin (Aseri PH012B drillcore, NE Estonia) to reveal underlying connections between isotopic fractionation, palaeoenvironmental changes, and metal enrichment processes. Twenty samples from the basal 28-cm-thick Unit I and overlying 66-cm-thick Unit II were analysed by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) and interpreted within a recently developed high-resolution chemostratigraphic framework. The tested samples yielded variable δ⁹⁸Mo (from −0.89 to +2.03 ‰) and δ²³⁸U values (from −0.27 to +0.52 ‰). Unit I, which is Mo-enriched, yielded the highest δ²³⁸U and lowest δ⁹⁸Mo values, whereas Unit II, which is U-enriched, is marked by sharply lower δ²³⁸U values. This black shale succession was deposited under a prolonged sea-level transgression. Variations in δ⁹⁸Mo and δ²³⁸U suggest that the mechanism of Mo and U sequestration changed depending on facies during the transgression. Metal enrichment was influenced by a combination of ultra-slow sedimentation rates (0.6–1.0 mm kyr⁻¹), relative sea-level changes, and shallow redox stratification maintained in part by surface heating under a super-greenhouse climate. Extremely slow sedimentation prolonged seawater-sediment interactions, facilitating diffusion-controlled uptake of U and Mo under euxinic conditions. Landward expansion of the subpycnoclinal oxygen-depleted watermass and related redox shifts from suboxic to euxinic conditions near the seafloor drove the selective hyper-enrichment of Mo, and U. Isotopic trends highlight efficient Mo sequestration in euxinic settings likely aided by recycling of Fe<img>Mn near redoxcline and U hyper-enrichment under Mo-depleted watermasses.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"690 ","pages":"Article 122910"},"PeriodicalIF":3.6,"publicationDate":"2025-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144230874","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":"Solving the sulfur isotope discrepancy in Central America","authors":"Ally Peccia ,&nbsp;Terry Plank ,&nbsp;Shuo Ding ,&nbsp;Louise Bolge ,&nbsp;Alessandro Aiuppa ,&nbsp;Salvatrice Vizzini ,&nbsp;Cecilia Tramati ,&nbsp;Zoltán Taracsák ,&nbsp;David M. Pyle ,&nbsp;Tamsin A. Mather","doi":"10.1016/j.chemgeo.2025.122901","DOIUrl":"10.1016/j.chemgeo.2025.122901","url":null,"abstract":"<div><div>Sulfur has considerable leverage on the redox budget of subducted materials due to its presence as both sulfide (S²⁻) and sulfate (S⁶⁺). Recent work has revealed a discrepancy: arc magmas have positive δ³⁴S values, while much of the S entering subduction zones should be hosted in pyrite, which is likely to have negative sulfur isotopic values. To address this discrepancy, we focus on the Central American subduction zone, where previous work has revealed positive δ³⁴S values in parental arc magmas. We report the first comprehensive study of the sedimentary S input to any subduction zone with S concentration and sulfur-isotopic measurements of ODP Site 1040 sediments. Sedimentary S input for Central America is greater than previously thought (1.71 ± 0.38 × 10⁸ mol S/yr/100 km), although insufficient to supply the S output from the arc without contributions from subducting oceanic crust. Furthermore, ~90 % of the sedimentary S input is hosted in pyrite, leading to a bulk sedimentary δ³⁴S of −19.5 ‰. In assessing the mass balance for Central America, we find that selective removal of sulfate does not provide enough S to support arc output and thus, additional S must be mobilized by the oxidation of pyrite with several per mil rock-fluid δ³⁴S fractionation to positive values. Our results agree with existing evidence that subduction zones act as efficient redox reactors, with oxidized portions of the slab (e.g., altered oceanic crust) providing the oxidizing power to supply sulfate to the arc, while a reduced and ³²S-enriched complement sinks into the deeper mantle.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"691 ","pages":"Article 122901"},"PeriodicalIF":3.6,"publicationDate":"2025-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144254910","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 effects of experimental heating and alteration on melt inclusions in magmatic zircon","authors":"Joseph P. Gonzalez ,&nbsp;Kouki Kitajima ,&nbsp;Tyler B. Blum ,&nbsp;Kei Shimizu ,&nbsp;Renat R. Almeev ,&nbsp;William O. Nachlas ,&nbsp;Sandra L. Kamo ,&nbsp;Alexander V. Sobolev ,&nbsp;Francois Holtz ,&nbsp;Michael J. Spicuzza ,&nbsp;Chloe Bonamici ,&nbsp;John W. Valley","doi":"10.1016/j.chemgeo.2025.122900","DOIUrl":"10.1016/j.chemgeo.2025.122900","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Melt inclusions (MIs) in zircon can preserve information on the evolution of magmas. However, MIs in plutonic zircons are typically devitrified, consisting of multiple phases that must be remelted to obtain a homogeneous glass for reconstruction of melt composition and magma processes. We undertake a systematic investigation of melt inclusions in zircons from a ∼ 3300 Ma xenolith of tonalite gneiss from the Barberton Greenstone belt, a well-studied section of cratonic lithosphere with components dating back to 3500 Ma. To better understand the influence of experimental heating on zircon and MI chemistry, multiple aliquots of zircons were heated in an internally heated pressure vessel at 0.4 GPa and temperatures ranging from 900 to 1200 °C (T&lt;sub&gt;step&lt;/sub&gt; = 100 °C). Homogeneous MIs in domains with low degrees of radiation damage and isolated from cracks in the zircon were found by examination of &gt;5000 zircons by SEM (CL, BSE). Oxygen isotopes (δ&lt;sup&gt;18&lt;/sup&gt;O), OH/O ratios, U-Pb isotopes, trace and rare earth element (TREE) concentrations in zircon, along with δ&lt;sup&gt;18&lt;/sup&gt;O, H&lt;sub&gt;2&lt;/sub&gt;O contents, and major element compositions in glassy MIs were measured by SIMS and EPMA. Investigated MIs have granitic compositions with 67 to 81 wt% SiO&lt;sub&gt;2&lt;/sub&gt;. Both heated and unheated host zircon possess statistically identical and uniform δ&lt;sup&gt;18&lt;/sup&gt;O values of 6.02 ± 0.45 ‰ (2SD), while OH/O ratios systematically decrease with increasing temperature of laboratory heating. Inclusion textures (BSE contrast homogeneity) and composition (H&lt;sub&gt;2&lt;/sub&gt;O, δ&lt;sup&gt;18&lt;/sup&gt;O) suggest that experimental heating at 1100 °C was the most successful in recovering initial MI compositions. Inclusions in lower temperature experiments either did not homogenize (900 °C) or are rarely homogenized (1000 °C), while those at higher temperature (1200 °C) are systematically dehydrated. Twenty-two hydrous MIs from the 1100 °C experiment have 3.1–11.5 wt% H&lt;sub&gt;2&lt;/sub&gt;O and an average δ&lt;sup&gt;18&lt;/sup&gt;O of 7.5 ± 0.9 ‰. Four zircons have a Δ&lt;sup&gt;18&lt;/sup&gt;O(MI-Zrn) fractionation inconsistent with equilibration at magmatic temperatures. In general, δ&lt;sup&gt;18&lt;/sup&gt;O values and TREE concentrations measured in the zircons heated at 1100 °C show consistent behavior with unannealed zircons, indicating these systems are not significantly disturbed on the μm-scale during heating experiments, and support the use of anomalous TREE concentrations/patterns as indicators of alteration. These measurements combined with Δ&lt;sup&gt;18&lt;/sup&gt;O(MI-Zrn) identify the MI-zircon pairs that are unlikely to represent the melt composition at the time of entrapment. Ti-in-zircon temperatures (αSiO&lt;sub&gt;2&lt;/sub&gt; = 1, αTiO&lt;sub&gt;2&lt;/sub&gt; = 0.3) and rhyoliteMELTS thermometry of the unaltered MI-zircon pairs return similar temperature ranges of 762–833 °C and 750–865 °C respectively, and combined with the granitic major element compositions, suggest that zircons crystallized relatively late during melt fracti","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"690 ","pages":"Article 122900"},"PeriodicalIF":3.6,"publicationDate":"2025-06-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144220821","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":"Promises and pitfalls of source terrane prediction from inclusions in detrital zircon","authors":"Elizabeth A. Bell ,&nbsp;Heather M. Kirkpatrick ,&nbsp;T. Mark Harrison","doi":"10.1016/j.chemgeo.2025.122899","DOIUrl":"10.1016/j.chemgeo.2025.122899","url":null,"abstract":"<div><div>Understanding the relationship between the assemblage of mineral inclusions trapped by an igneous zircon suite and the composition of the host magma is complicated by processes that preclude simple relationships between, for example, the relative proportions of modal mineral inclusions (e.g., quartz, alkali feldspar, and plagioclase; QAP) and the degree of magma differentiation. However, apatite and ferromagnesian inclusion abundances can be approximately related to the SiO₂ content in some magmas, potentially allowing for broad inferences of source rock composition from detrital zircon mineral inclusion suites. This study presents mineral inclusion assemblages in igneous zircon from a wide range of magma compositions, tectono-magmatic settings, and geographic locations to better determine the correlation between major inclusion phases and source rock chemistry. We find that the relationship between apatite and whole rock SiO₂ is strongly dependent on the aluminosity (as shown by A/CNK) of the source rock, with peraluminous and metaluminous rocks showing opposite trends. For inclusion assemblages containing less than about 30–40 % apatite, discrimination of highly silicic peraluminous from mafic-intermediate metaluminous granitoid sources is possible. Metaluminous samples display a broad increase in whole rock phosphate content with increasing apatite inclusion abundance, potentially allowing estimation of lower limits on protolith phosphate abundance. The ratio of ferromagnesian to late-crystallizing inclusions exceeds 0.5 mostly for mafic-intermediate samples, with some exceptions. Inclusion phases concentrating highly incompatible trace elements exceed 5 % of the inclusion suite only in highly silicic (&gt;70 % SiO₂) granites. However, there is no discernable relationship between QAP and whole rock chemistry, with inclusion QAP from compositionally diverse magmas clustering in a similar region of the QAP diagram. Application of these observations to several first-generation sediments derived from granitoid terranes suggests that apatite abundance, the ratio of ferromagnesian to late-crystallizing silicate inclusions, and trace elements can help select between peraluminous vs. metaluminous sources and help to distinguish mafic-intermediate from highly silicic source rocks. This could have wide applicability to using the detrital zircon record to infer petrogenetic provenance.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"690 ","pages":"Article 122899"},"PeriodicalIF":3.6,"publicationDate":"2025-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144212742","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":"Boron isotope evidence for Ordovician-Silurian Transition postglacial marginal marine salinity with implications for redox conditions and biotic recovery","authors":"Jingyu Zhang ,&nbsp;Wei Wei ,&nbsp;Jun Shen ,&nbsp;Jingbo Nan ,&nbsp;Yi Zhong ,&nbsp;Xiaojie Fan ,&nbsp;Yanan Zhang ,&nbsp;Qingsong Liu ,&nbsp;Lin Chen ,&nbsp;Leslie J. Robbins ,&nbsp;Kurt O. Konhauser","doi":"10.1016/j.chemgeo.2025.122891","DOIUrl":"10.1016/j.chemgeo.2025.122891","url":null,"abstract":"<div><div>Anoxic conditions in marginal marine settings play a critical role in paleoceanographic and paleoecological studies. Understanding the mechanisms underpinning anoxia requires insights into watermass conditions in the study area. While salinity is a fundamental property of water, proxies for reconstructing paleosalinity and its influence on redox conditions in ancient systems are often overlooked. To illustrate this, we focus on the Yangtze Marginal Sea during the Ordovician-Silurian Transition (OST), specifically the Early Silurian postglacial anoxia. We utilized proxy records for salinity and redox conditions archived in organic-rich cherts and black shales deposited in the Yangtze Block, South China, between ca. 447.62–438.49 million years ago. Our study is the first to report the variation in bulk boron (B) isotopic (δ¹¹B) values during the OST. Analyzing paleosalinity data, such as δ¹¹B and B/gallium (Ga) along with redox indicators, such as molybdenum (Mo), uranium (U), and vanadium (V), provides constraints on the continuous vertical hydrological variability across the central Yangtze Marginal Sea. Our analysis suggests that the watermass in the study area was close in salinity to seawater during the Late Ordovician due to a well-established connection with the ocean. This was followed by a decline in salinity in the Early Silurian resulting from an influx of glacial melt water. Postglacial warming-induced freshwater input and sea-level change subsequently contributed to strong seawater stratification and elevated primary productivity. This disruption in the exchange between shallow and deep waters led to the development of anoxia in the Early Silurian Yangtze Sea, a phenomenon that has significantly impacted Earth's evolutionary history. Our study provides fresh insights into the Late Ordovician Mass Extinction event and the subsequent biotic recovery. In addition, we underscore the importance of integrating redox analyses with salinity reconstructions in explaining the mechanisms of anoxic environments.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"690 ","pages":"Article 122891"},"PeriodicalIF":3.6,"publicationDate":"2025-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144204609","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":"Variable sampling of distinct ancient mantle domains by the Iceland mantle plume over its 62 Ma eruption history","authors":"Bradley J. Peters ,&nbsp;Andrea Mundl-Petermeier ,&nbsp;Lotte M. Larsen","doi":"10.1016/j.chemgeo.2025.122882","DOIUrl":"10.1016/j.chemgeo.2025.122882","url":null,"abstract":"<div><div>Mantle plumes produce geochemically diverse lavas over their lifetime, some of which preserve compositions derived from Earth's earliest events. Most studies of plume-related lavas in this context have focused on modern ocean island basalts (OIB), primarily because these are relatively free of geochemical influences from crustal assimilation that may obscure the compositions of their mantle sources. Notwithstanding, there is no a priori reason why a mantle plume should consistently tap the same mantle domain over geological time, which means that early plume-related magmas may preserve a perspective on the early Earth that complements that of modern OIB. This study expands a previous investigation of picrites with high ³He/⁴He ratios, a likely indicator for ancient, less degassed mantle domains, with new ¹⁴²Nd/¹⁴⁴Nd (<em>n</em> = 7) and ¹⁸²W/¹⁸⁴W (<em>n</em> = 2) data that, together with literature data, comprise a detailed short-lived radiogenic isotope database for the Iceland hotspot. Heterogeneous ¹⁴²Nd/¹⁴⁴Nd ratios in lavas from different stages of the Iceland plume imply that it has tapped a variety of early-formed mantle domains, in particular that the head of the Iceland plume rapidly shifted between tapping domains with distinct histories. This behavior may reflect both the higher buoyancy flux of plume heads as well as the petrological and physical properties of these domains. Together, these data highlight the importance of developing comprehensive, high-precision short-lived radiogenic isotope datasets for all stages of plume magmatism, since the geochemical compositions of modern OIB reflect only one set of mantle domains that can be potentially tapped by mantle plumes.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"691 ","pages":"Article 122882"},"PeriodicalIF":3.6,"publicationDate":"2025-05-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144261960","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}