Chemical Geology最新文献

{"title":"Cryogenic cave carbonates: New insights from alpine ice caves","authors":"Christoph Spötl,&nbsp;Gabriella Koltai","doi":"10.1016/j.chemgeo.2025.122808","DOIUrl":"10.1016/j.chemgeo.2025.122808","url":null,"abstract":"<div><div>Cryogenic cave carbonates (CCC) are speleothems that form under freezing conditions and provide crucial insights into past cold environments and cryogenic processes. Traditionally, CCC have been classified into two categories: fine-grained CCC (hereafter CCC-f) and coarse-grained CCC (hereafter CCC-c), primarily based on particle size and stable isotopic composition. However, recent observations from alpine ice caves in Austria suggest the existence of an intermediate class, termed CCC-i, characterized by small grain sizes (&lt;1 mm) and stable isotope values that overlap with CCC-c. This study documents the occurrence, morphology, and stable isotopic composition of CCC-i found in seven ice caves, providing insights into their formation mechanism. CCC-i are associated with small pools in ice and form in a cave climate that is transitional between the fully heterothermic regime close to the entrance and the homothermic regime of the inner cave passages characterized by high thermal stability. The stable isotopic signatures of CCC-i indicate a Rayleigh-type fractionation process similar to CCC-c but at a smaller spatial and temporal scale. This study highlights the paleoclimatic significance of CCC-i, as they may improve reconstructions of past cave glaciations. However, the ongoing retreat of cave ice due to climate warming threatens the preservation of CCC deposits, emphasizing the urgency of further research.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"685 ","pages":"Article 122808"},"PeriodicalIF":3.6,"publicationDate":"2025-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143873022","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 pattern of chemoautotrophic mussels from cold seeps and hydrothermal vents: Implications for fluid and trophic type","authors":"Zice Jia ,&nbsp;Zhaoshan Zhong ,&nbsp;Xudong Wang ,&nbsp;Hongfei Lai ,&nbsp;Hongyu Zhang ,&nbsp;Na Cui ,&nbsp;Zenggui Kuang ,&nbsp;Minxiao Wang ,&nbsp;Chaolun Li","doi":"10.1016/j.chemgeo.2025.122799","DOIUrl":"10.1016/j.chemgeo.2025.122799","url":null,"abstract":"<div><div>Hydrothermal vents and cold seeps occur in tectonically active areas and along continental margins. They harbor diverse chemoautotrophic organisms, providing valuable insights into fluid types and trophic dynamics. Interestingly, certain mussel species can inhabit both ecosystems, deriving energy from the aerobic oxidation of methane (AeOM) or sulfur oxidation. However, the geochemical fingerprinting of methanotrophic mussels in hydrothermal vents areas remains largely unexplored, especially compared with cold seeps. In this study, stable isotopes (δ¹³C, δ¹⁵N, and δ³⁴S) and rare earth elements (REEs) in <em>Gigantidas platifrons</em> collected from hydrothermal vents at Iheya North Knoll in the Okinawa Trough and the cold seep at Site F in the South China Sea were examined. The δ¹³C values demonstrate carbon fixation via AeOM in both environments. The average δ¹³C_tissue values of seep <em>G. platifrons</em> (−75.4‰, <em>n</em> = 28) is similar to δ¹³C_methane. However, the average δ¹³C_tissue of hydrothermal <em>G. platifrons</em> (−25.8‰, <em>n</em> = 13) exhibits enhanced fractionation compared with δ¹³C_methane, potentially because of the abundance of methanotrophs. The δ³⁴S and δ¹⁵N values of mussels indicate two different sulfur and nitrogen sources. In both environments, <em>G. platifrons</em> consistently exhibits positive lanthanum (La) anomalies because it serves as an enzyme co-element in AeOM. Seep mussels have more positive La/La^⁎ ratios compared with hydrothermal mussels, indicating an increased number of methanotrophs on their gills. Positive europium (Eu) anomalies exist in hydrothermal mussels and are influenced by ascending hydrothermal fluids. Four REE pattern fingerprints are summarized, highlighting the potential of stable isotopes and REEs as powerful analytical proxies for studying the complex interactions between fluid sources, microbial symbiosis, and trophic structures near hydrothermal vents and cold seeps.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"685 ","pages":"Article 122799"},"PeriodicalIF":3.6,"publicationDate":"2025-04-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143868597","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":"Study of the sources and dispersion of sediments on the Sunda Shelf based on the investigation of rare earth element concentrations and Nd isotope compositions","authors":"Kaikai Wu ,&nbsp;Shengfa Liu ,&nbsp;Xuefa Shi ,&nbsp;Che Abd. Rahim Mohamed ,&nbsp;Hui Zhang ,&nbsp;Rosella Pinna-Jamme ,&nbsp;Arnaud Dapoigny ,&nbsp;Christophe Colin","doi":"10.1016/j.chemgeo.2025.122807","DOIUrl":"10.1016/j.chemgeo.2025.122807","url":null,"abstract":"<div><div>The Sunda Shelf receives substantial sediment inputs from the Tibetan Plateau and Southeast Asia's mountainous islands, impacting southern South China Sea sedimentation during Quaternary sea-level changes. Due to multiple river basins contributing to the shelf, the origin and distribution of its surface sediments remain poorly defined. Here, we analyzed major and trace element concentrations and Nd isotope compositions (¹⁴³Nd/¹⁴⁴Nd expressed in epsilon units, εNd) of sediments from rivers around the Sunda Shelf and its surface sediments, focusing on &lt;63 μm and &lt; 2 μm fractions to evaluate grain size effects on rare earth element (REE) patterns and εNd compositions and to identify sediment sources. Significant differences in UCC-normalized REE patterns between &lt;2 μm and &lt; 63 μm river sediment fractions indicate a notable grain size effect. However, εNd variations between these fractions are typically less than 1 εNd unit, suggesting minimal grain size impact on Nd isotope compositions of the detrital fractions. Surface sediments on the western Sunda Shelf derive from the Malay Peninsula, Mekong River, and northern Thai rivers based on the δEu_UCC-(Gd/Yb)_UCC diagram. εNd spatial distribution of the detrital fraction indicates nearshore sediments of the Sunda Shelf are influenced by neighboring rivers (from −15.8 to −6.6), while the central region is affected by the Mekong and northern Thai rivers (from −15.8 to −10.3). Notably, unradiogenic εNd in central shelf sediments indicates Thai river sediments were transported there via paleo-channels during low sea levels before the Gulf of Thailand fully flooded. A large eddy in the central Sunda Shelf would have conserved these relic sediments and redistributed modern sediments by sorting and transporting sediments from nearby rivers.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"685 ","pages":"Article 122807"},"PeriodicalIF":3.6,"publicationDate":"2025-04-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143869173","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":"Thallium isotope data suggest minimal recycled material within the proto-Iceland mantle plume source","authors":"J. Kaare-Rasmussen ,&nbsp;F. Horton ,&nbsp;C.M. Ostrander ,&nbsp;S.G. Nielsen","doi":"10.1016/j.chemgeo.2025.122798","DOIUrl":"10.1016/j.chemgeo.2025.122798","url":null,"abstract":"<div><div>Mantle plume isotopic compositions are useful for understanding the processes that produce heterogeneity within the mantle. Thallium (Tl) isotopic compositions are uniquely well suited for tracing pelagic sediments and low-temperature altered oceanic crust in the mantle. We measured the Tl isotopic composition of Paleocene lavas on Baffin Island, the earliest lavas associated with the Iceland mantle plume, to constrain the geochemical evolution of the mantle plume. After correcting for assimilation and degassing, these lavas have ²⁰⁵Tl/²⁰³Tl ratios indistinguishable from the inferred ratio of the upper mantle and from modern Iceland lavas. Therefore, the amount of subducted pelagic sediments or low temperature altered oceanic crust potentially within the head of the Iceland mantle plume is vanishingly small. These components cannot account for the well-documented evolution in other isotopic systems over time in the Iceland mantle plume. Thus, we evaluate other processes that could account for this evolution, including other subducted components and core-mantle interactions.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"685 ","pages":"Article 122798"},"PeriodicalIF":3.6,"publicationDate":"2025-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143855309","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Paleoenvironmental changes and nitrogen cycling of the lacustrine systems following the Toarcian Oceanic Anoxic Event in the Sichuan Basin (China): Insights from nitrogen isotopes","authors":"Yang Bai ,&nbsp;Jianfa Chen ,&nbsp;Jin Wu ,&nbsp;Wenzhe Gang ,&nbsp;Václav Suchý ,&nbsp;Cong Chen ,&nbsp;Xuemin Xu ,&nbsp;Rao Fu ,&nbsp;Jiaqi Zhang ,&nbsp;Shuaiqi Tang","doi":"10.1016/j.chemgeo.2025.122797","DOIUrl":"10.1016/j.chemgeo.2025.122797","url":null,"abstract":"<div><div>The Toarcian Oceanic Anoxic Event (T-OAE) represents a significant disturbance of the Earth's atmosphere-ocean system in the Early Jurassic, and its response in lacustrine systems has been widely studied in recent years. However, the impact of T-OAE on the subsequent environmental changes and nitrogen cycling patterns in lacustrine systems are poorly understood. This study investigated the paleoenvironmental changes following the T-OAE based on elemental geochemistry analyses of organic-rich shales from the Early Jurassic Da'anzhai Member and the Middle Jurassic Lianggaoshan Formation in the Sichuan Basin. The nitrogen cycling during this period was reconstructed drawing on nitrogen isotopes (δ¹⁵N) and their correlations with water column conditions. The results indicated that during the deposition of Da'anzhai shale (i.e., T-OAE period), the lacustrine system was dominated by a temperate-humid climate, with frequent oxic-suboxic variations in the water column. The sedimentary environment of the Lianggaoshan shale was similar to that of the Da'anzhai shale, even though there was a brief arid-cold climate during the sedimentary period at the bottom of Lianggaoshan Formation. The nitrogen isotopes of kerogen (δ¹⁵N_ker) were primarily controlled by the redox conditions of water column, and the silicate-bound inorganic nitrogen isotopes (δ¹⁵N_sil) were influenced by combined factors including climate, input of terrestrial clay minerals, and the redox conditions of the bottom water column. These variations in δ¹⁵N provided foundations for reconstructing nitrogen cycling under diverse lacustrine environmental conditions. Under the suboxic water column, the occurrence of denitrification and anaerobic ammonium oxidation (anammox) in the chemocline resulted in enrichment of ¹⁵N in kerogen. The positive excursion in δ¹⁵N_sil was a cumulative effect attributed to the enhanced influx of exogenous illite under temperate-humid climatic conditions, as well as the combined influence of anammox on NH₄⁺ concentrations. In water column with elevated oxygen concentrations, biogeochemical processes, predominantly driven by nitrification, resulted in lighter δ¹⁵N_ker values, and δ¹⁵N_sil, influenced by the low concentration of NH₄⁺ in the bottom water, also exhibited a lighter isotopic signature. The similar geochemical signatures in the Da'anzhai and Lianggaoshan shales implied that the lacustrine system might be susceptible to variations in localized paleoenvironment, and was not completely consistent with the marine system.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"685 ","pages":"Article 122797"},"PeriodicalIF":3.6,"publicationDate":"2025-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143848291","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":"Archean deep melting and post-Archean metasomatism of the cratonic mantle: A garnet Lu-Hf isotope record","authors":"Kira A. Musiyachenko ,&nbsp;Matthijs A. Smit ,&nbsp;Maya G. Kopylova ,&nbsp;Andrey V. Korsakov","doi":"10.1016/j.chemgeo.2025.122796","DOIUrl":"10.1016/j.chemgeo.2025.122796","url":null,"abstract":"<div><div>Mantle xenoliths provide a direct window into the subcontinental lithospheric mantle (SCLM) beneath Archean cratons. Age constraints on the melting, metasomatism and deformation that have affected the SCLM are crucial for developing insight into continental dynamics and craton development. Obtaining constraints is nevertheless difficult. Garnet geochronology – and Lu-Hf geochronology in particular – has good prospects in this regard, because it uniquely allows dating of a rock forming mineral and petrogenetic indicator in the mantle. However, the behavior of the Lu-Hf system at mantle conditions is not yet well-understood, and stringent sample size requirements and issues relating to melt infiltration typically impede obtaining reliable garnet ages for single xenoliths. In this study, we tested the capabilities of modern Lu-Hf methods to date garnet in kimberlite-hosted mantle xenoliths that record mantle melting, metasomatism and shearing. The samples are from the Siberian, Kaapvaal and Slave cratons, and include garnet-bearing olivine pyroxenites, lherzolites and websterites, as well as orthopyroxenite with exsolved garnet, and include both sheared and granular lithologies. The analyses yielded low-dispersion Lu-Hf isochrons for single xenoliths with age uncertainties down to 0.3 % and ages up to 3.0 Ga. Garnet in equilibrium with clinopyroxene in coarse lherzolite and websterite samples records Proterozoic ages, whereas high-Cr garnet from coarse harzburgite and orthopyroxenite samples lacking clinopyroxene yields Archean ages. The age data do not reflect ‘normal’ volume diffusion-controlled chronometric closure but instead indicate strong age retention barring events of fluid or melt infiltration. Only sheared samples yielded Lu-Hf ages close to the age of kimberlite eruption. These ages highlight that deformation and metasomatism are ongoing within otherwise stable cratonic roots. Initial Hf isotope compositions obtained from the Lu-Hf isochrons approximate chondritic values in the Archean and become gradually more superchondritic with time. These results indicate that the cratonic mantle, as well as the melts that metasomatized it since the Archean, derive from a moderately depleted mantle reservoir that has existed since at least 3 Ga. Together, the new Lu-Hf data provide a new temporal framework for the petrological development of the SCLM and establish Lu-Hf garnet geochronology as prime geochronometer for dating mantle processes.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"685 ","pages":"Article 122796"},"PeriodicalIF":3.6,"publicationDate":"2025-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143848292","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 stable U-Mo-Fe isotope records of Middle Jurassic hydrogenetic ferromanganese deposits","authors":"Viona Klamt ,&nbsp;Dennis Kraemer ,&nbsp;Oscar Fernandez ,&nbsp;Ingo Horn ,&nbsp;Simon V. Hohl ,&nbsp;Stefan Weyer ,&nbsp;Sebastian Viehmann","doi":"10.1016/j.chemgeo.2025.122795","DOIUrl":"10.1016/j.chemgeo.2025.122795","url":null,"abstract":"<div><div>Ferromanganese (Fe-Mn) nodules are marine chemical sediments that represent unique archives for the reconstruction of ambient seawater conditions. This record is limited from modern to Cenozoic times due to the instability of Fe-Mn oxides during burial and subduction of the oceanic crust and overlying sediments. However, almost uncharacterized Fe-Mn nodules exist in Jurassic sedimentary strata throughout the ancient Tethyan region approximately 100 Ma older than the oldest yet-investigated Cenozoic nodules. Their reliability as geochemical archives for the reconstruction of ancient seawater is, however, poorly understood. In this study, Fe-Mn nodules from the Pyhrntal area (Austria) are geochemically and mineralogically characterized and subdivided into four types with variable amounts of carbonates (calcite, rhodochrosite), todorokite, and hematite as major phases. Shale-normalized rare earth element and yttrium systematics of all types indicate a hydrogenetic origin with characteristic positive Ce anomalies and negative Y anomalies. In-situ Fe isotope measurements of the Fe-Mn nodules display a <em>δ</em>^56/54Fe range between −0.32 and −0.02 ‰ for the Jurassic Tethyan Ocean, similar to values from modern Atlantic nodules. Stable Mo (<em>δ</em>^98/95Mo = −0.97 to −0.56 ‰) and U (<em>δ</em>^238/235U = −0.75 to −0.47 ‰) isotope compositions resemble those of modern and Cenozoic Fe-Mn nodules, suggesting that Middle Jurassic oceans were similarly well‑oxygenated as modern oceans. Our results demonstrate the reliability of fossil Fe-Mn nodules in the Pyhrntal as geochemical archives for the composition of paleo-seawater, encouraging the investigation of other ancient Fe-Mn deposits which may significantly improve and complement the picture of the redox evolution of Phanerozoic oceans.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"684 ","pages":"Article 122795"},"PeriodicalIF":3.6,"publicationDate":"2025-04-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143838718","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":"Modeling the impact of evaporites on burial fluid-rock interactions in carbonate reservoirs","authors":"Ying Xiong ,&nbsp;Xiucheng Tan ,&nbsp;Bo Liu ,&nbsp;Michael Z. Hou ,&nbsp;Kaibo Shi ,&nbsp;Shoukang Zhong ,&nbsp;Di Xiao","doi":"10.1016/j.chemgeo.2025.122793","DOIUrl":"10.1016/j.chemgeo.2025.122793","url":null,"abstract":"<div><div>Carbonate-evaporite successions can serve as important hydrocarbon reservoirs. However, the unique petrophysical properties of evaporites and various carbonate-evaporite lithological associations have impeded understanding of the complex fluid-rock interactions and diagenetic evolution of these reservoirs. Here we present numerical modeling of the diagenetic mineral-porosity evolution in various fluid‑carbonate-evaporite systems and compare them with those in carbonate only strata. The high thermal conductivity and low permeability of thick evaporites (e.g., salt and anhydrite) could result in elevated temperature in supra-salt environment and decreased temperature and overpressure in pre-salt environment. These conditions promote carbonate precipitation from in situ pore fluids in supra-salt formations and dissolution in pre-salt formations. Besides, evaporite interlayers can function as pressure and fluid seals, limiting the influence of diagenetic geochemical reactions. Mineral dissolution-precipitation primarily occurs near the first set of dense evaporite layer in the direction of fluid transport. From the perspective of porosity preservation, the cementation pattern (type and intensity) and porosity distribution are jointly controlled by carbonate-evaporite lithological associations, fluid properties, and flow paths. High-quality reservoirs may form in all three burial environments: pre-salt, inter-salt, and supra-salt strata. The results contribute to a better understanding of burial fluid-rock interactions and the mechanisms behind reservoir formation and preservation in carbonate-evaporite systems.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"684 ","pages":"Article 122793"},"PeriodicalIF":3.6,"publicationDate":"2025-04-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143825677","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 sediment precipitated during acid mine drainage-seawater interaction. Implications for metal mining impacts on estuarine systems","authors":"K.L. Lecomte ,&nbsp;P.A. Yaciuk ,&nbsp;A.M. Sarmiento ,&nbsp;J. Borrego ,&nbsp;J.M. Nieto","doi":"10.1016/j.chemgeo.2025.122794","DOIUrl":"10.1016/j.chemgeo.2025.122794","url":null,"abstract":"<div><div>Metal-mining pollution impacts estuarine systems, where sediments with high available toxic metal concentrations precipitate. In the Ría de Huelva estuary (SW Spain), the metal-rich acidic water of the Tinto River (headwater pH = 2.2 and electrical conductivity -EC- = 25.8 mS cm⁻¹) interacts with saline-alkaline seawater of the Atlantic Ocean (pH = 7.87, EC = 55.2 mS cm⁻¹). This study analyses the geochemical characteristics of the dissolved and particulate fractions formed when mixing both systems. A pH-controlled test showed that about 2000 L of seawater are necessary to neutralise 1 L of Tinto River headwater. A six-step sequential extraction performed on the precipitated sediments indicated that: a) Fe, Al, Zn, Cu, ∑REE, Co, Pb, and As are highly available in soluble and adsorbed fractions; b) Fe, Al, Cu, Zn, ∑REE, Mo, and Co mostly concentrate in iron oxy-hydroxides and oxyhydroxysulfates; and c) As, V, Mo, U and Pb desorb at pH ≥ 5. Furthermore, Fe and Al precipitates play significant hydrochemical and environmental roles in the studied environment by attenuating pH changes, as sediment precipitation decreases pH and captures chemical elements. The results of this study are useful to better understand natural processes (e.g., disruption of buffers, instability of dissolved elements, sorption/desorption, co-precipitation) taking place in estuaries affected by AMD and to predict geochemical variations in the environment due to climate change (e.g., floods, extreme precipitations, sea level rise).</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"684 ","pages":"Article 122794"},"PeriodicalIF":3.6,"publicationDate":"2025-04-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143828153","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":"Laser ablation K-Ar dating of illite on oriented aggregate mounts","authors":"Cynthia Bermúdez-Chávez ,&nbsp;Teresa Pi-Puig ,&nbsp;Jesús Solé","doi":"10.1016/j.chemgeo.2025.122792","DOIUrl":"10.1016/j.chemgeo.2025.122792","url":null,"abstract":"<div><div>Illite, a clay mineral formed during diagenesis and low-grade metamorphism, can be dated using the K-Ar method to reconstruct the chronological history of sedimentary basins, fault and fold formation, and hydrothermal alterations. However, conventional K-Ar and Ar-Ar dating of illite faces challenges due to the clay's small grain size, hygroscopicity, limited availability in finer fractions, and other analytical issues. This study proposes a modified K-Ar dating approach that uses a laser ablation technique to date small amounts of oriented clay aggregate mounts separated by grain size fractions and prepared on glass discs.</div><div>Four groups of illite-bearing samples from various geological settings were analyzed, ranging in age from 350 Ma to 40 Ma. X-ray diffraction of the aggregate mounts revealed different mineral compositions, with illite proportions between 20 % and 90 %, along with kaolinite, chlorite, quartz, and feldspars in some samples. The K-Ar dating setup includes ultrahigh vacuum laser ablation of oriented clay mounts combined with LIBS spectroscopy for potassium measurement and noble gas mass spectrometry for argon quantification within the same experiment. Ages were obtained through various methods (single craters, lines, and multiple craters), making the isochron method utilizing multiple craters the most precise and accurate.</div><div>This innovative K-Ar method simplifies the dating of clay fractions by avoiding problematic issues such as drying, weighing, homogeneity, and Ar recoil during irradiation while enabling mineralogical characterization through X-ray diffraction on the same sample preparation. This approach offers new insights into the geological history recorded by clay minerals. During this work, we identified unknown issues concerning sample preparation and geochronological data, including differential clay sedimentation during drying and the associated age dispersion in clays from detrital samples.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"684 ","pages":"Article 122792"},"PeriodicalIF":3.6,"publicationDate":"2025-04-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143843575","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}