Chemical Geology最新文献

{"title":"Using δ65Cu and δ34S to determine the fate of copper in stream waters draining porphyry mineralization: Implications for exploration targeting","authors":"James A. Kidder ,&nbsp;Christopher E. Beckett-Brown ,&nbsp;Alexandre Voinot ,&nbsp;Zhaoping Yang ,&nbsp;Pierre Pelchat ,&nbsp;Duane C. Petts ,&nbsp;Matthew Polivchuk ,&nbsp;John B. Chapman ,&nbsp;Scott Casselman ,&nbsp;Matthew I. Leybourne","doi":"10.1016/j.chemgeo.2024.122527","DOIUrl":"10.1016/j.chemgeo.2024.122527","url":null,"abstract":"<div><div>The fate of metals, such as Cu, in stream waters draining porphyry mineralization is commonly controlled by several natural processes such as sorption, microbial processes, and ligand availability. Isotopes of Cu offer a novel approach to understanding these processes and determining metal sources within complicated mineralogical systems. Drainages at the Casino Cu-Au-Mo porphyry deposit, Yukon, Canada exhibit circumneutral (pH &gt; 5) in Casino Creek and natural acid rock drainage (pH &lt; 3.5) in Proctor Gulch with the precipitation of schwertmannite (Fe³⁺). Isotopic systems δ⁶⁵Cu and δ³⁴S_sulfate indicate different metal sources, with signatures of both hypogene and supergene mineralization. Waters from Proctor Gulch contain δ⁶⁵Cu values (&lt; −0.5 ‰) consistent with supergene Cu sources from the leached or oxide portion of the mineralization. Comparatively, drainage in the upper part of Casino Creek contains a δ⁶⁵Cu composition (&gt; 0.5 ‰) characteristic of Cu sourced from hypogene sulfide mineral oxidation. Variation in metal sources is similarly supported by aqueous δ³⁴S_sulfate values in the stream waters, which suggest mixing of S derived from a sulfide mineral phase and a much heavier sulfate mineral (e.g., gypsum or anhydrite). Isotopic fractionation of Cu in the dissolved (&lt;0.45 μm) phase presents two predominant controls on Cu dispersion. The natural acid conditions in Proctor Gulch favor the preferential co-precipitation of ⁶³Cu with schwertmannite but could be influenced by intracellular assimilation or adsorption by microbes, which also has been shown to preferentially favor ⁶³Cu. Copper isotopic fractionation results in a gradient of increasing δ⁶⁵Cu values in waters downstream. In Casino Creek, higher pH conditions favor the precipitation of Fe(OH)₃ and the preferential adsorption of ⁶⁵Cu, resulting in decreasing δ⁶⁵Cu values downstream. Copper concentrations in stream waters remain elevated (up to 4.1 μg/L) above ambient background (1.9 μg/L) levels up to 11 km downstream of the deposit. Given the abundance of surface water in many parts of northern Canada, hydrogeochemical prospecting using broad scale stream water catchment analysis is clearly a viable greenfield exploration methodology.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"673 ","pages":"Article 122527"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142815876","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":"n-Alkanes δ13C and salinity correlation in mangrove Aegiceras corniculatum leaves and surface sediments from Zhanjiang estuaries, China","authors":"Guifang Cai ,&nbsp;Zhao-Wen Zhan ,&nbsp;Zhiguang Song ,&nbsp;Yao-Ping Wang ,&nbsp;Jia Xia ,&nbsp;Ding He","doi":"10.1016/j.chemgeo.2024.122552","DOIUrl":"10.1016/j.chemgeo.2024.122552","url":null,"abstract":"<div><div>Carbon isotope ratios (δ¹³C) in plant lipid biomarkers yield insights into historical climates by reflecting plant responses to environmental stressors. Previous research has established a correlation between increased salinity and elevated δ¹³C in <em>Avicennia marina</em> leaf wax <em>n</em>-alkanes, yet it remains unclear if these isotopic signatures are universally applicable across different species and regions or consistently preserved in sedimentary records. We investigated the influence of a 30 ppt salinity gradient on <em>Aegiceras corniculatum</em> in Zhanjiang, China, examining δ¹³C values in leaf wax <em>n</em>-alkanes and adjacent sediments. Leaf wax δ¹³C values ranged from −36.7 ‰ to −31.4 ‰, while sediment <em>n</em>-alkanes ranged from −35.6 ‰ to −28.2 ‰. Sediments consistently exhibited higher δ¹³C values than leaf wax, and their total lipid and <em>n</em>-alkane δ¹³C exhibited a positive correlation with salinity, increasing by 0.06 ± 0.02 ‰ and 0.1 ± 0.04 ‰ per ppt respectively. This positive correlation may be attributed to factors such as marine material input, seasonal variations in lipid synthesis, and plant community succession. In contrast, no significant correlation with salinity was observed in <em>A. corniculatum</em>'s bulk leaf tissues or total lipids. This lack of correlation can be attributed to the unique physiological conditions and varying salt exclusion mechanisms among mangrove species, which influence water use efficiency. Accordingly, while sediment δ¹³C values can indicate past vegetation, the variability necessitates caution in using mangrove sediment δ¹³C for paleoenvironmental reconstruction.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"673 ","pages":"Article 122552"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142815867","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":"Rapid bioproductivity recovery following the Marinoan glaciation: Evidence from Sr-Cr-Cd isotopes and trace elements in the Morraria do Sul cap dolostone, Brazil","authors":"Henrique Albuquerque Fernandes ,&nbsp;Paulo César Boggiani ,&nbsp;Jesper Allan Frederiksen ,&nbsp;Marcelo Da Roz Campos ,&nbsp;Vinicius Cardoso-Lucas ,&nbsp;Bernardo Tavares Freitas ,&nbsp;Robert Frei","doi":"10.1016/j.chemgeo.2024.122548","DOIUrl":"10.1016/j.chemgeo.2024.122548","url":null,"abstract":"<div><div>Early Ediacaran cap dolostones are distinctive strata deposited directly above glaciogenic rocks from the Marinoan Glaciation (650–635 Ma), one of the most dramatic ice ages in Earth's history. These cap dolostones were rapidly deposited during global synchronous deglaciation, being a superb depositional window into the immediate glaciation aftermath and suitable for investigating the icehouse-hothouse transition in this period. However, some aspects of this transition are still unclear, such as the timing of primary productivity recovery. Aiming to explore this question, we present new sedimentological, trace element, and Sr-Cr-Cd isotope data for the Puga cap dolostone in the Southern Paraguay Belt (Brazil), here termed Morraria do Sul Formation. The cap dolostone overlies diamictites, siltstones with outsized clasts, and basement rocks. It is divided into a basal dolograinstone and an upper tubestone-microbialite succession, with abundant vertical tube-like structures. The diamictites and siltstones were formed in a glaciomarine setting, within the range of ice-rafted debris. The basal dolograinstone facies of the cap dolostone was formed under high-energy post-glacial conditions, and the overlying tubestone-microbialite facies was deposited in a low-energy, well-lit environment. Rare earth elements and yttrium (REY) preserved the original seawater-like pattern, displaying true negative Ce anomalies down to 0.84, indicating oxygenated shallow waters. The cap dolostone displays relatively high ⁸⁷Sr/⁸⁶Sr ratios, up to 0.7123, above the assumed value for the Early Ediacaran seawater, suggesting the influence of meltwater plumes in a salinity-stratified setting. Authigenic Cr isotope values (δ⁵³Cr_auth) are within the range of Bulk Silicate Earth (BSE) to slightly positive in the basal dolograinstone and negatively fractionated below BSE values in the tubestone-microbialite facies, implying that microbial-influenced Cr reduction progressively increased upwards, controlling the isotopic fractionation. A rise upwards in δ¹¹⁴Cd, from −0.11 to 0.17 ‰, reveals a substantial increase in Cd-uptake by biomass, and maximum estimates for seawater δ¹¹⁴Cd show values within the range of present-day surface seawater. The data presented herein suggest that significant primary productivity recovery occurred in the immediate aftermath of the Marinoan Glaciation. This study also shows the efficiency of combined trace elements and Sr-Cr-Cd isotope analyses on reconstructing past seawater chemistry and productivity levels.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"673 ","pages":"Article 122548"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142815871","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":"Non-conservative behaviour of molybdenum in the Ganga (Hooghly) River estuary, India: Role of solute-particle interaction and sediment diagenesis","authors":"Rakesh K. Tiwari ,&nbsp;Tarun K. Dalai ,&nbsp;Rupak Samadder ,&nbsp;Waliur Rahaman ,&nbsp;Sunil K. Singh","doi":"10.1016/j.chemgeo.2024.122526","DOIUrl":"10.1016/j.chemgeo.2024.122526","url":null,"abstract":"<div><div>This study is focussed on understanding of molybdenum (Mo) cycling in the mesotidal to macrotidal estuary of the Ganga (Hooghly) River in India. Our investigation encompasses the composition of water and suspended particulate matter (SPM) samples collected in three separate periods (pre-monsoon: PrM, monsoon: M and post-monsoon: PoM) over two consecutive years, surface sediments, exchangeable phases of surface and suspended sediments, one sediment core, urban and industrial effluent waters and ground waters. The observed dissolved Mo concentrations in the estuary are in excess of those expected from conservative mixing of seawater and river water. The “excess” Mo values, observed in the mid-to-high salinity regions (4–27 ‰) for four out of the six study periods, are the highest in the monsoon samples. The bulk and exchangeable phase compositions are supportive of release of Mo from the Fe-Mn oxyhydroxide phases of the SPM and surface sediments in the estuary. Mass balance calculations indicate that Mo release from the SPM and surface sediments can account for up to 40 % of the median value of the “excess” Mo in the estuary. The compositions of the sediment core provide evidence for the mobilization of Mo and its release to porewater due to reductive dissolution of Fe-Mn oxyhydroxides. The tidally induced sediment resuspension likely facilitates the transport of porewater Mo to the overlying water. Mass balance calculations indicate that Mo loss from the sediment column can account for the bulk of the “excess” Mo in the estuary waters. This study further demonstrates that industrial effluents, urban waste waters and groundwaters do not constitute significant sources of dissolved Mo in the estuary.</div><div>The average annual Mo flux from the estuary is (∼2–3) × 10⁶ mol, of which ∼30–50 % of Mo is due to estuarine addition. More significantly, Mo contribution from the Hooghly River estuary, accounting for ∼0.7–1.0 % of the global riverine Mo flux, is ∼3–4 folds higher than its water contribution (∼0.25 %) to the global river water flux. Our study highlights the role of interactions between oxyhydroxide phases and estuarine water, diagenetic mobilization of elements in the sediment column and porewater transport in the cycling of Mo in a monsoon-dominated tropical estuary with high sediment loads. We also demonstrate that the mobilization of Mo through chemical weathering is driven by physical weathering in the catchments of the South Asian Rivers.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"673 ","pages":"Article 122526"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142815873","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":"Bimineralic calcite-aragonite rafts in the hypogeous lakes of Cova dets Ases (Mallorca): Controls on precipitation and polymorphism","authors":"A. Entrena ,&nbsp;L.F. Auqué ,&nbsp;M.J. Gimeno ,&nbsp;J.J. Fornós","doi":"10.1016/j.chemgeo.2024.122529","DOIUrl":"10.1016/j.chemgeo.2024.122529","url":null,"abstract":"<div><div>Calcite-aragonite bimineralic rafts and related waters from hypogenic lakes in the coastal cave of “Cova dets Ases”, Mallorca, have been analyzed for mineralogy and geochemistry (including stable isotopes). The main objective has been the evaluation of the factors that control the chemical and mineralogical composition of the precipitates as they are another natural example of the classical problem of aragonite vs calcite precipitation.</div><div>The hydrochemistry of the lakes in these coastal caves is mainly conditioned by the mixture of fresh and marine waters. The percentage of mixing, together with the CO₂ degasification from the lakes water, seems to play a fundamental role in the precipitation of the carbonate rafts. However, their presence in the studied lakes does not show a homogeneous distribution in space and time and no clear relation has been found between that distribution and the evolution of any of the monitored environmental variables. With respect to their mineralogy, the main factor that seems to control the dominant bimineralic composition of the rafts studied here is the Mg/Ca ratio in the waters, which means the percentage of marine component in those waters. The variations of this ratio, in combination with changes in the degasification rate and in the oversaturation with respect to calcite and aragonite will condition the presence of one or the other polymorph. Even small microenvironmental variations seem to affect the order of precipitation of these bimineralic rafts.</div><div>Another important issue in this work is that the data obtained in this natural system have been used to check the most suitable δ¹⁸O isotope fractionation equations for the paleotemperature calculations from rafts precipitated in the past under similar conditions.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"673 ","pages":"Article 122529"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142857728","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Radiation-enhanced fluid diffusion and alteration around uraniferous inclusions in Cenomanian resinite from North Bohemia","authors":"Vladimír Strunga ,&nbsp;Vladimír Havránek ,&nbsp;Jan Lorinčík ,&nbsp;Kristína Sihelská ,&nbsp;Pavel Krist ,&nbsp;Martina Havelcová ,&nbsp;Bohuslava Čejková ,&nbsp;Jiří Mizera","doi":"10.1016/j.chemgeo.2024.122554","DOIUrl":"10.1016/j.chemgeo.2024.122554","url":null,"abstract":"<div><div>Advanced analytical methods including SEM/EDX and μ-PIXE/RBS microanalyses were used to investigate chemical alterations around uraniferous inclusions in a Cenomanian fossil resin (resinite). Studied alterations related to several types of discontinuities in resinite matrix are a model example of the phase interface between solid polymeric hydrocarbon and aqueous fluids exposed to long-term irradiation by heavy energetic ions resulting mostly from the natural decay of uranium. Computational models of ion ranges correspond well with the observed range of alterations about 35 μm from uraniferous inclusions. The major alteration is found within a 20 μm inner zone. It is characterized by distinct sulfur enrichment and an increase in the O/C ratio. No sulfur enrichment in the resinite matrix occurs apart from the uraniferous phases. Proton beam-induced alterations of the resinite were investigated and compared with the natural ones. The differences indicate the importance of aqueous fluids in the natural radiation-induced alteration process. It is concluded that radiation-enhanced mass transfer and reactions occur at solid-fluid interfaces during the long-term energy deposition by alphas, alpha recoils, and fission fragments combined. The role of thermal effects and and formation of radical species by radiolysis of aqueous fluids on a microscale is discussed.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"673 ","pages":"Article 122554"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142858009","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":"Preservation of biosignatures in Neoproterozoic phosphorites metamorphosed at temperatures >450 °C","authors":"Kenan Cao ,&nbsp;Zhenbing She ,&nbsp;Dominic Papineau ,&nbsp;Jingbo Nan ,&nbsp;Chao Chen ,&nbsp;Reza Deevsalar ,&nbsp;Ayetullah Tunc ,&nbsp;Qunfeng Xiao ,&nbsp;Kang-Jun Huang ,&nbsp;Yuanming Pan","doi":"10.1016/j.chemgeo.2024.122519","DOIUrl":"10.1016/j.chemgeo.2024.122519","url":null,"abstract":"&lt;div&gt;&lt;div&gt;There is still much controversy over whether apatite and graphite can be used as fingerprint mineral assemblages to preserve biosignatures in ancient sedimentary rocks that experienced medium- to high-grade metamorphism. Herein, we present a comprehensive analysis of graphite and associated phases from meta-phosphorites of the Huangmailing Formation in the South Dabie Orogen to assess possible preservation of biosignatures. Stratigraphic correlations and previous geochronological data suggest that the protoliths of Huangmailing Formation was deposited in the Ediacaran, and was metamorphosed during the Triassic Dabie Orogeny as documented by our apatite U&lt;img&gt;Pb dating. Microcrystalline graphite occurs both as inclusions within metamorphic minerals like apatite, and as matrix-hosted disseminations at grain boundaries of other phases. Bulk organic carbon isotopic analyses yield δ&lt;sup&gt;13&lt;/sup&gt;C values between −26.0 ‰ and − 15.2 ‰ and total organic carbon contents from 0.33 to 3.27 wt%. Raman spectra of the two types of graphites yield an average peak metamorphic temperature of 452 °C and 473 °C, consistent with the upper greenschist facies to lower amphibolite facies metamorphic conditions in the area. However, the matrix graphites show a wider range of peak temperature variations, likely containing graphitic carbon with lower crystallinity that was affected by retrograde metamorphic fluids. Notably, two prominent Raman bands at around 325 cm&lt;sup&gt;−1&lt;/sup&gt; and 395 cm&lt;sup&gt;−1&lt;/sup&gt; are observed for the graphite hosted in apatite. This, along with the presence of a peak at 2473 eV in the sulfur &lt;em&gt;K&lt;/em&gt;-edge XANES spectra of some graphite in apatite, and the co-occurrence of &lt;sup&gt;12&lt;/sup&gt;C and &lt;sup&gt;14&lt;/sup&gt;N and local association of &lt;sup&gt;32&lt;/sup&gt;S with &lt;sup&gt;12&lt;/sup&gt;C in graphite inclusions determined by TOF-SIMS, suggest the possible presence of C-S-Fe and N-bearing compounds and functional groups. TEM and EDS analysis reveal that graphite inclusions in apatite are closely associated with amorphous silica, and mainly occur as well crystallized, polygonal grains around 100 to 200 nm across and has an expanded (002) lattice spacing between 3.43 Å and 3.64 Å. This lattice expansion is attributable to the presence of heteroatoms such as S, Fe and Si, and N, in the graphene interlayers. In contrast, matrix graphites exhibit a wider range of structural and compositional variations than their counterpart as inclusion in apatite, which probably arise from interactions with metamorphic fluids or incorporation of fluid-deposited graphitic carbon. Our study documents the ubiquitous preservation of biological carbon as graphite inclusions in apatite from Huangmailing meta-phosphorites, likely as a result of metamorphic recrystallization of organic-bearing Ediacaran phosphorites. This suggests that the organic matter trapped in sedimentary apatite during their co-precipitation or early diagenesis was probably less modified during metamorphic recrystalliz","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"673 ","pages":"Article 122519"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142815783","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":"Redox conditions in a carbonatite-alkaline complex: Deciphering Fe- and S-XANES in melt inclusions with silicate‑carbonate immiscibility","authors":"Céline Baudouin ,&nbsp;Hugo Moreira ,&nbsp;Charles Le Losq ,&nbsp;Max Wilke ,&nbsp;Fleurice Parat","doi":"10.1016/j.chemgeo.2024.122559","DOIUrl":"10.1016/j.chemgeo.2024.122559","url":null,"abstract":"<div><div>Hanang is a volcano in the southern part of the east branch of the East African Rift (North Tanzania Divergence) and represents volcanism at the early stage of continental break-up. Hanang volcanism is characterized by CO₂-alkaline-rich magmas and silicate‑carbonate immiscibility process at crustal level. This study describes microscale iron (Fe) and Sulfur (S) K-edge X-ray absorption near edge structure (μXANES) spectroscopy measurements on nepheline-hosted melt inclusions (MI) preserved in Hanang lavas. For the first time, the μXANES method has been used on melt inclusions composed of both silicate glass and carbonate phase. Silicate glasses from Hanang display relatively high Fe³⁺/ΣFe ratio (Fe³⁺/ΣFe = 0.31, indicative of oxidized conditions) and very low S⁶⁺/ΣS ratio (S⁶⁺/ΣS = 0.05–0.07, indicative of reduced conditions). The discrepancy of the oxidation state measured from iron and sulfur and thus, the redox conditions (<em>f</em>O₂) inferred from these two values, either suggests that the oxidation state is affected by post entrapment processes, such as re-equilibration with the host-mineral or the immiscibility process with carbonate liquid, or it suggests a significantly different relation of Fe and S oxidation state to <em>f</em>O₂ in this chemical system. The Fe³⁺/ΣFe in melt inclusions yields magma redox conditions (<em>f</em>O₂) at around ∆FMQ + 1.4 for phonolitic liquid composition from evolved differentiation and immiscibility process between silicate melt and carbonatite (≤850C°). Sulfur speciation decoupling is attributed to silicate‑carbonate immiscibility, and as such, low S⁶⁺/ΣS does not provide primary redox conditions in this system. Hanang lavas at the early stage of East African Rift have one of the most oxidizing conditions, related to the presence of carbonate-rich alkaline magmatic system associated with carbonatites.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"673 ","pages":"Article 122559"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142858005","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":"Calcium carbonate formation below the groundwater table in response to tree transpiration","authors":"Julian A. Alwakeel ,&nbsp;René M. Price ,&nbsp;Leonard J. Scinto ,&nbsp;Michael S. Ross ,&nbsp;Jay P. Sah ,&nbsp;Susana L. Stoffella ,&nbsp;Fred H. Sklar ,&nbsp;Eric A. Cline","doi":"10.1016/j.chemgeo.2025.122672","DOIUrl":"10.1016/j.chemgeo.2025.122672","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Tree islands are biogeochemical hotspots that accumulate ions and nutrients in the groundwater and soil through root water uptake and evapotranspiration. These mechanisms lead to high ionic concentrations in tree island groundwater and potential supersaturation conditions with respect to calcite and aragonite. The precipitation of calcium carbonate minerals (caliche) within tree island soils may lead to cementation, providing greater soil stability. Although calcrete layers have been observed at depth in some tree island soils of the Florida Everglades, their method of formation has yet to be discerned. The main objective of this study was to determine if varying hydrologic conditions are conducive to calcium carbonate formation in Everglades tree islands. This investigation was conducted at the Loxahatchee Impoundment Landscape Assessment (LILA), a large physical model of Everglades' tree islands in Florida, USA. Eight tree islands were investigated across four mesocosms for nine years (2014–2023). For the first 4 years, all tree islands were exposed to similar hydrologic conditions as determined by an operational hydrograph with pre-determined seasonal variations in water levels. In the 5th year (2018 to present), the hydrograph was altered such that two mesocosms (containing 4 tree islands) were exposed to more a constrained range in water levels varying about 0.4 m (4.4–4.8 m NGVD29; constrained) on a seasonal basis, while the other two mesocosms (also containing 4 tree islands) continued to experience the larger range in seasonal water levels of about 0.6 m (4.4–5.1 m NGVD29; unconstrained). The geochemical characteristics of groundwater and soils in LILA tree islands were investigated under the two hydrologic regimes. A combination of groundwater saturation indices, soil profiles, scanning electron microscopy, and Electron Dispersive X-ray Spectroscopy were utilized to locate and identify calcium carbonate mineral formation. Groundwaters exhibited persistent supersaturated conditions with respect to calcium carbonate minerals within tree islands subjected to the larger variation in water levels and within tree islands that contained clay. Both calcite and aragonite were found in the tree island soils. Rhombohedral calcite, aragonite needles, and calcium carbonate globules, which may be composed of crystalline or amorphous calcium carbonate, were observed in soils collected 1 m below the mean groundwater table (0.40 m), where shell surfaces, other limestone grains and silica grains served as nucleation sites. The main processes responsible for the calcium carbonate formation include evapotranspiration and seasonal flooding which leads to an accumulation of ions in the groundwater to supersaturation conditions. However, soil composition which influences hydrologic properties and the ease or inhibition of groundwater – surface water interactions also played a role in sustaining supersaturation conditions. The results of this investig","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"678 ","pages":"Article 122672"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143386342","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Terrestrial mercury anomalies across the Permian-Triassic transition in North China linked to volcanism","authors":"Peixin Zhang ,&nbsp;Minfang Yang ,&nbsp;Jing Lu ,&nbsp;Zhongfeng Jiang ,&nbsp;Lei Wang ,&nbsp;Yuanyuan Zhu ,&nbsp;Wenjing Guo ,&nbsp;Zejing Li ,&nbsp;Zhibiao Shi ,&nbsp;Pan Wang ,&nbsp;Kai Zhou ,&nbsp;Xiaotao Xu ,&nbsp;Longyi Shao ,&nbsp;Jason Hilton","doi":"10.1016/j.chemgeo.2024.122555","DOIUrl":"10.1016/j.chemgeo.2024.122555","url":null,"abstract":"<div><div>The Permian-Triassic mass extinction (PTME) is the most severe biological crisis in Earth history and is closely linked to massive contemporaneous volcanism. However, there is currently limited evidence of Mercury (Hg) enrichment directly from volcanic sources in terrestrial strata, necessitating evidence from different regions and latitudes to confirm the relationship between volcanism and changes in terrestrial environments and biotas. To explore this connection, we conducted a comprehensive analysis integrating astronomical cycles to provide a temporal framework, Hg concentrations, and Hg isotopes from terrestrial strata in the Yiyang Coalfield, located in the southern North China Plate (NCP). Our high-resolution astronomical timescale reveals that in the low latitude NCP the PTME commenced on land with the end-Permian Terrestrial Collapse (EPTC) which preceded the marine mass extinction by approximately 270 kyr and was latitudinally diachronous. The EPTC commenced in high-to-mid latitudes (75–30°S), then approximately 100–430 kyr later spread through different mid-to-low latitude regions (60–20°N) into equatorial paleolatitudes (10°N–0°). Hg isotopic results show that the initial Hg enrichment peak during the EPTC originated from terrestrial weathering and wildfire combustion rather than directly from volcanism, whereas the three subsequent Hg enrichment peaks over a 500 kyr interval following the EPTC originated directly from volcanism. This temporal coupling suggests that terrestrial ecosystems exhibited greater sensitivity and a more rapid response to global warming than marine ecosystems. Stratigraphic correlations show the early eruptive phase of the Siberian Traps Large Igneous Province (STLIP) led to gradual collapse of terrestrial ecosystems from high to low latitudes as they responded to increasingly warmer and more stressed conditions. The main eruptive phase of the STLIP, potentially augmented by contemporaneous widespread volcanism, may have ultimately led to the final collapse of terrestrial ecosystems and marine extinctions.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"673 ","pages":"Article 122555"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142858006","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}