Geochemistry International最新文献

{"title":"Roméite Solubility in the Fluid Immiscibility Region of the NaF–H2O System at 800°C, 200 MPa","authors":"A. F. Redkin,&nbsp;N. P. Kotova,&nbsp;Yu. B. Shapovalov,&nbsp;A. N. Nekrasov","doi":"10.1134/S0016702923700155","DOIUrl":"10.1134/S0016702923700155","url":null,"abstract":"<p>New data on roméite (CaNa)Sb₂O₆F solubility in the NaF–H₂O system of P–Q type have been obtained within a wide range of sodium fluoride concentrations (from 0 to 25 wt % NaF). The concentration of antimony, in equilibrium with roméite and fluorite, in the range of NaF concentrations from 1 to 8 mol kg^–1 H₂O (25 wt % NaF), is in the range of 0.02–0.2 mol kg^–1 H₂O. According to the data, the concentration of antimony in phases <i>L</i>₁ and <i>L</i>₂ in the region of fluid immiscibility of the NaF–H₂O system at 800°C, 200 MPa and <i>f</i>O₂ = 50 Pa, specified by the Cu₂O–CuO buffer, is 0.4 and 2.1 wt % Sb, respectively. Our experiments were the first ever to produce skeletal fluorite crystals and the intermetallic compound Pt₅Sb, which belongs the hexagonal crystal system and has the following lattice parameters (LP): <i>a</i> = <i>b</i> = 4.56(4) Å, <i>c</i> = 4.229(2) Å, and α = β = 90°, γ = 120°. Pentaplatinum antimonide was formed on the inner surface of the Pt capsules at 800°C, <i>Р</i> = 200 MPa, and <i>f</i>O₂ ≤ 10^–3.47 Pa (Cu–Cu₂O buffer) in experiments on the incongruent dissolution of roméite, which causes a sharp decrease (more than 1000 times) in antimony concentration in the solution.</p>","PeriodicalId":12781,"journal":{"name":"Geochemistry International","volume":"62 4","pages":"384 - 392"},"PeriodicalIF":0.7,"publicationDate":"2024-05-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140937937","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effect of pH, CO2, and Organic Ligand on the Kinetics of Talc and Lizardite Dissolution","authors":"O. N. Karaseva,&nbsp;L. Z. Lakshtanov,&nbsp;D. A. Khanin,&nbsp;A. S. Proskuryakova","doi":"10.1134/S0016702923700167","DOIUrl":"10.1134/S0016702923700167","url":null,"abstract":"<div><p>Natural Mg phyllosilicates are potential sources of divalent cations, which are necessary for the mineralization of CO₂ into carbonates. The influence of inorganic (<span>({text{HCO}}_{3}^{ - })</span>) and organic (oxalate and citrate) ligands on the dissolution kinetics of talc and serpentine was studied in experiments in a flow-through reactor at 25°C. The dissolution rates of natural silicates <i>r</i> (mol cm^–2 s^–1) in solutions of various composition were calculated at the stationary stage of dissolution after a rapid initial stage, which is characterized by the formation of a surface leached layer depleted in magnesium. The presence of ligands increases the dissolution rate of magnesium silicates due to the formation of surface complexes, which leads to magnesium separation from the surface and transfer into solution. The initial incongruent stage may be the most promising for the development of carbonation technologies, because the minimum removal of the network-forming elements prevents the undesirable formation of secondary minerals (for example, clays), which exclude divalent cations from the carbonation process and greatly reduce the permeability of rocks.</p></div>","PeriodicalId":12781,"journal":{"name":"Geochemistry International","volume":"62 4","pages":"393 - 402"},"PeriodicalIF":0.7,"publicationDate":"2024-05-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140937990","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Deformation Microstructure, Metallic Iron, and Inclusions of Hollow Negative Crystals in Olivine from the Seymchan Pallasite: Evidence of Fe2+ Solid-State Reduction","authors":"N. R. Khisina,&nbsp;D. D. Badyukov,&nbsp;K. A. Lorenz,&nbsp;Yu. N. Palyanov,&nbsp;I. N. Kupriyanov,&nbsp;B. B. Shkursky","doi":"10.1134/S0016702923700118","DOIUrl":"10.1134/S0016702923700118","url":null,"abstract":"<p>Olivine grains from the Seymchan pallasite were studied using optical microscopy, Raman spectroscopy, and scanning electron microscopy (SEM). Olivine is characterized by the presence of hollow straight channels &lt;1 µm wide and inclusions of hollow negative crystals of prismatic habit 1–2 µm thick. The channels are oriented parallel to [001] of olivine and developed along [001] screw dislocations. The elongation axes of negative crystals are also oriented parallel to [001]. In the channels, hollow segments alternate with segments filled with metallic iron. Negative crystals are crystallographically faceted voids in olivine; the largest of them contain inclusions of metallic iron. The rectilinear configuration and crystallographic orientation of the channels correspond to the characteristics of [001] screw dislocations, which allows us to consider [001] dislocations as channel precursors. The data obtained demonstrate for the first time the evolution of [001] dislocations in olivine as a result of the shock-induced reduction of divalent iron during the interaction of olivine with the host FeNi metal. A model is proposed for the transformation of dislocations with the formation of channels and hollow negative crystals in Seymchan olivine in accordance with one of the reactions:\u0000<span>(begin{gathered} 2{text{F}}{{{text{e}}}_{{{text{host}}}}} + {{left( {{text{M}}{{{text{g}}}_{{1 - n}}}{text{F}}{{{text{e}}}_{n}}} right)}_{2}}{text{Si}}{{{text{O}}}_{4}} = 2n{{left[ {{text{FeO}}} right]}_{{{text{host}}}}} + {{left[ {n{text{Si}}{{{text{O}}}_{2}} + 2n{text{F}}{{{text{e}}}^{0}} + left( {1 - n} right){text{M}}{{{text{g}}}_{{text{2}}}}{text{Si}}{{{text{O}}}_{4}} + 2n{{v}^{{2 - }}} + 2n{{v}^{{2 + }}}} right]}_{{{text{ol}}}}}, 2{text{F}}{{{text{e}}}_{{{text{host}}}}} + {{left( {{text{M}}{{{text{g}}}_{{1 - n}}}{text{F}}{{{text{e}}}_{n}}} right)}_{2}}{text{Si}}{{{text{O}}}_{{text{4}}}} = 2n{{left[ {{text{FeO}}} right]}_{{{text{host}}}}} + {{left[ {n{text{MgSi}}{{{text{O}}}_{3}} + n{text{F}}{{{text{e}}}^{0}} + left( {1 - n} right){text{M}}{{{text{g}}}_{{text{2}}}}{text{Si}}{{{text{O}}}_{4}} + n{{v}^{{2 - }}} + n{{v}^{{2 + }}}} right]}_{{{text{ol}}}}}. end{gathered} )</span>\u0000According to the model, at <i>T</i> &gt; 1000°C the reduction process is accompanied by an increase in the concentration of Fe⁰ and associated vacancies (<span>({{v}^{{2 - }}})</span> and <span>({text{ + }}{{v}^{{2 + }}})</span>) in dislocation zones. Voids in channels and negative crystals are the products of the annihilation of anionic and cationic structural vacancies having opposite charges. Phase association formed in this solid-state transformation of olivine corresponds to either OSI (olivine → SiO₂ + 2Fe⁰) or OPI (olivine → pyroxene + Fe⁰) buffer equilibrium. The results can be used for the reconstruction of the thermal and shock histories of different types of pallasites.</p>","PeriodicalId":12781,"journal":{"name":"Geochemistry International","volume":"62 4","pages":"344 - 355"},"PeriodicalIF":0.7,"publicationDate":"2024-05-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140937641","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Features of Loparite Dissolution in Aluminosilicate Melts (Experimental Investigation)","authors":"N. I. Suk,&nbsp;A. R. Kotelnikov,&nbsp;A. A. Viryus","doi":"10.1134/S0016702923700143","DOIUrl":"10.1134/S0016702923700143","url":null,"abstract":"<p>The solubility of loparite (Na,Ce,Ca)₂(Ti,Nb)₂O₆) in aluminosilicate melts of various compositions was experimentally studied at <i>T</i> = 1200 and 1000°C and <i>P</i> = 2 kbar under dry conditions and in the presence of 10 wt % H₂O in a high gas pressure vessel with a duration of 1 day. The starting material was previously melted artificial glasses of malignite, urtite and eutectic albite–nepheline compositions, as well as natural loparite from the Lovozero massif. The dependence of the loparite solubility on the composition of the aluminosilicate melt (Ca/(Na + K), (Na + K)/Al) has been revealed. Partition coefficients of a number of elements (Ti, Nb, Sr, REE) between silicate melt and loparite crystals (<i>K</i>_<i>i</i> = <span>({{C_{i}^{{{text{melt}}}}} mathord{left/ {vphantom {{C_{i}^{{{text{melt}}}}} {C_{i}^{{{text{lop}}}}}}} right. kern-0em} {C_{i}^{{{text{lop}}}}}})</span>) were estimated.</p>","PeriodicalId":12781,"journal":{"name":"Geochemistry International","volume":"62 4","pages":"372 - 383"},"PeriodicalIF":0.7,"publicationDate":"2024-05-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140937956","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geochronology and Geochemistry of Mesozoic Granites in the North Qilian Shan: Implications for Petrogenesis and Tectonic Setting","authors":"Tao Yang,&nbsp;Zhi-yuan Sun,&nbsp;Ming-liang Wang,&nbsp;Xiao-qiang Zhu,&nbsp;Jing-yu Zhao","doi":"10.1134/S0016702924700320","DOIUrl":"10.1134/S0016702924700320","url":null,"abstract":"<p>This paper documents the zircon U–Pb ages, whole-rock geochemistry, and Sr–Nd–Pb isotopes of the Mesozoic granites in the central part of the North Qilian Orogenic Belt to provide information on the tectonic evolution and crustal accretion process of the Qilian Orogenic Belt. Zircon U–Pb dating yields an age of 215.3 ± 3.1 Ma, indicating that the Beidaban monzogranites formed from Late Triassic. They are characterized by high contents of SiO₂, Al₂O₃, and K₂O; are slightly peraluminous (A/CNK = 1.08–1.15); and have mineralogical assemblages of primary biotite and ilmenite, illustrating that they are shoshonitic and peraluminous S-type granite. The Beidaban monzogranites have initial (⁸⁷Sr/⁸⁶Sr)_i values ranging from 0.71456 to 0.71867 and εNd(t) values ranging from –12.9 to –8.5 with two-stage Nd model ages of 1.69–2.04 Ga, suggesting that they originated from partial melting of the Paleo-Mesoproterozoic (Longshoushan Group) continental crustal metasedimentary rocks. Initial Pb isotopic compositions (²⁰⁶Pb/²⁰⁴Pb = 19.44–21.80; ²⁰⁷Pb/²⁰⁴Pb = 15.76–15.89; ²⁰⁸Pb/²⁰⁴Pb = 39.62–41.26) and geochemical features such as high Th/Ta (9.3–67.4, 37.4 on average) and Rb/Nb (12.5–17.1) are consistent with recycled crustal components. Combined with previous geochronological and geochemical data, we suggest that the Mesozoic granites probably formed in a post-collisional tectonic setting and that the North Qilian Orogen Belt experienced comprehensive intracontinental orogenesis after the closure of the Qilian ocean.</p>","PeriodicalId":12781,"journal":{"name":"Geochemistry International","volume":"62 7","pages":"696 - 713"},"PeriodicalIF":0.7,"publicationDate":"2024-05-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140835782","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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, Monazite (U–Pb–Th) Geochronology, and P-T Pseudosection Modelling of Two-Pyroxene Mafic Granulite from Sonapahar, Shillong Meghalaya Gneissic Complex, India: Implication for Tectono-Metamorphic Evolution and Global Pan-African Correlation","authors":"Bikash Mahanta,&nbsp;Divya Prakash,&nbsp;Manish Kumar,&nbsp;Saurabh Singh,&nbsp;Rajeev Kumar Pandey,&nbsp;Chandra Kant Singh,&nbsp;Suparna Tewari","doi":"10.1134/S0016702924700319","DOIUrl":"10.1134/S0016702924700319","url":null,"abstract":"<p>Granulites exposed in high-grade regional metamorphic belts and exhumed as xenoliths in basaltic pipes are considered as window into the deep crust thus play a key role in constraining models of crustal processes and evolution. Here we present a detailed investigation of the tectono-metamorphic history of the two-pyroxene mafic granulite located in the southern region of the Sonapahar area. This involves conducting monazite chemical dating, analyzing petrological and geochemical characteristics, applying geothermobarometry, performing phase equilibria modeling, and tracing a pressure-temperature (<i>P-T</i>) path. Metamorphic <i>P-T</i> conditions estimated for the mafic granulite using conventional thermobarometer and winTWQ shows temperature in excess of 800°C and pressure of about 8.6 kbar, stand for high temperature granulite facies metamorphism. The metamorphic evolution path obtained from <i>P-T</i> pseudosection suggest a clockwise <i>P-T</i> evolution path, thus signify isothermal decompression and indicate rapid upliftment. Geochemical study of trace and rare earth elements (REE), suggest protolith is of tholeiite basalt in nature that is derived from back arc basin setting near to subduction zone. Additionally, the analyzed rock was examined using primitive mantle-normalized trace element spider diagram. The results indicate an enrichment in large-ion lithophile elements (Th, U, K, Pb) and a depletion in high field-strength elements (Nb, Ta, Ti). The presence of negative anomalies in Nb and Ti, coupled with elevated values of Th, K, and Pb, suggests the possibility of crustal contamination. Monazite chemical data from the studied rock reveals a peak metamorphism age of 521.3 ± 4.20 Ma, which corresponds to the Kuunga Orogeny in the later phase of global Pan-African collision.</p>","PeriodicalId":12781,"journal":{"name":"Geochemistry International","volume":"62 6","pages":"574 - 608"},"PeriodicalIF":0.7,"publicationDate":"2024-05-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140836003","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Sources and Evolution of Miocene–Pleistocene Alkaline Magmatism in the Northeast Part of the Arabian Plate: Evidence from Sr–Nd–Pb Isotope Data and K–Ar Geochronometry","authors":"A. V. Chugaev,&nbsp;A. V. Parfenov,&nbsp;V. A. Lebedev,&nbsp;I. V. Chernyshev,&nbsp;V. Oyan,&nbsp;Y. Özdemir,&nbsp;E. Oyan,&nbsp;Yu. V. Gol’tsman,&nbsp;I. V. Rassokhina,&nbsp;B. I. Gareev,&nbsp;G. A. Batalin,&nbsp;S. B. Pavlidis","doi":"10.1134/S0016702924020034","DOIUrl":"10.1134/S0016702924020034","url":null,"abstract":"<p>A geochronological and isotope–geochemical study of alkaline basalts from three areas of young magmatism within the northeastern part of the Arabian Plate (Southeastern Turkey), Batman, Kurtalan and Alemdağ, was carried out. The obtained isotope data have indicated that the volcanism in the studied region developed over a 5-Ma period from the end of Miocene to the middle Pleistocene during four pulses separated by breaks in magmatic activity: 6.1–4.9 Ma (Batman area, hawaiites), ~3.0 Ma (Alemdağ plateau, phase I, basalts), 2.0–1.9 Ma (Alemdağ plateau, phase II, tephrites), and 1.5–1.3 Ma (Alemdağ plateau, phase III, basalts; Kurtalan area, basalts). A comparison of spatial–temporal changes of magmatic activity evolution in the studied part of the Arabian Plate and within the largest basalt plateau of Arabian foreland, Karacadağ Plateau, located to the west, was carried out. The results of Sr–Nd–Pb isotope–geochemical studies show that the development of young basalt volcanism in the Arabian Plate was characterized at different time by the contribution of various mantle sources in magma generation under this region. Initial pulses of magmatic activity are associated with melting of Arabian subcontinental lithospheric mantle (SCLM). The processes of fractional crystallization combined with crustal assimilation (AFC) have played an important role in the petrogenesis of lavas as well. Later, a deep mantle source (PREMA) with a depleted isotopic composition played a leading role in the formation of basaltic magmas of increased alkalinity. The melts generated by this source were mixed with the SCLM material in various proportions at different stages of magmatism with a limited participation of AFC processes in the petrogenesis of the rocks. It was concluded that young basalt volcanism of increased alkalinity in the northeast of the Arabian Plate is not related to the collision of the Eurasian and Arabian plates genetically, but presumably manifested here as a result of the migration of the initial rift geodynamic setting from the Red Sea basin to the north along Levantine and East Anatolian transform faults due to directed convection flows in the lower part of mantle under this part of the Earth.</p>","PeriodicalId":12781,"journal":{"name":"Geochemistry International","volume":"62 2","pages":"99 - 123"},"PeriodicalIF":0.7,"publicationDate":"2024-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140567750","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Experimental Study of Pargasite NaCa2(Mg4Al)[Si6Al2O22](OH)2 Stability at T = 1000–1100°C and Pressure up to ({{P}_{{{{{text{H}}}_{{text{2}}}}{text{O}}}}}) = 5 Kbar","authors":"V. N. Deviatova,&nbsp;A. N. Nekrasov,&nbsp;G. V. Bondarenko","doi":"10.1134/S0016702924020046","DOIUrl":"10.1134/S0016702924020046","url":null,"abstract":"<p>Pargasite stability was experimentally studied in IHPV at <span>({{P}_{{{{{text{H}}}_{{text{2}}}}{text{O}}}}})</span> = 2 kbar and temperatures of 1000 to 1100^oC, with equilibrium approached from above and below. Calcic amphibole was used to experimentally model processes that occur in a volcanic chamber at pressures up to 5 kbar. The phase diagram of pargasite has been refined. It has been established that the stability of pargasite is controlled by three reactions. (1) At low water pressures of less than 1 kbar, the dehydration reaction <i>Prg</i> = <i>Fo</i> + <i>Sp</i> + <i>Di</i> + <i>Ne</i> + <i>An</i> + H₂O proceeds. (2) At water pressures higher than 1.2–1.5 kbar and a temperature of about 1100°C, the decomposition of pargasite is controlled by its incongruent melting <i>Prg</i> = <i>Fo</i> + <i>Sp</i> + {<i>Di</i> + <i>Ne</i> + <i>An</i>}^<i>L</i> + H₂O. (3) The third reaction <i>Prg</i> + <i>L</i> = <i>Fo</i> + <i>Sp</i> + <i>Di</i> + {<i>Ne</i> + <i>Pl</i>}^<i>L</i> + H₂O occurs within the same pressure range as the previous one but at lower temperatures of about ~1050°C. The reaction controls the pargasite liquidus and is caused by interaction between amphibole and coexisting melt. The liquidus of pargasite seems to most strongly depend on the activity of silica <span>({{a}_{{{text{Si}}{{{text{O}}}_{{text{2}}}}}}})</span> in the melt.</p>","PeriodicalId":12781,"journal":{"name":"Geochemistry International","volume":"62 2","pages":"140 - 154"},"PeriodicalIF":0.7,"publicationDate":"2024-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140567755","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Destinezite: A Physicochemical and Calorimetric Study","authors":"Yu. D. Gritsenko,&nbsp;L. P. Ogorodova,&nbsp;M. F. Vigasina,&nbsp;L. V. Melchakova,&nbsp;D. A. Ksenofontov,&nbsp;S. K. Dedushenko","doi":"10.1134/S0016702924030042","DOIUrl":"10.1134/S0016702924030042","url":null,"abstract":"<p>Destinezite (<span>({text{Fe}}_{{1.97}}^{{3 + }})</span>Al_0.02)(PO₄)_0.99(SO₄)_0.90(OH)_1.20⋅5.97H₂O (Czech Republic) has been studied by thermal and electron-microprobe analyses, X-ray powder diffraction, and by IR, Raman, and Mössbauer spectroscopy. The enthalpy of formation of destinezite <span>({text{Fe}}_{2}^{{3 + }})</span>(PO₄)(SO₄)(OH)⋅6H₂O from elements ∆_f<i>H</i>⁰(298.15 K) = –4258 ± 12 kJ/mol was determined by the method of solution calorimetry in lead borate 2PbO⋅B₂O₃ melt on a Setaram (France) Calvet microcalorimeter. The value of its absolute entropy <i>S</i>⁰(298.15 K) = 462.0 J/(mol K) was estimated, the entropy of formation ∆_f<i>S</i>⁰(298.15 K) = –2054 J/(mol K), and the Gibbs energy of formation from the elements ∆_f<i>G</i>⁰(298.15 K) = –3646 kJ/mol were calculated.</p>","PeriodicalId":12781,"journal":{"name":"Geochemistry International","volume":"62 3","pages":"274 - 283"},"PeriodicalIF":0.7,"publicationDate":"2024-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140568112","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Lithological, Mineralogical, and Geochemical Features of the Lower Maeotian Sediments of the Kazantip Nature Reserve, Crimea","authors":"A. I. Antoshkina,&nbsp;L. V. Leonova,&nbsp;O. V. Valyaeva,&nbsp;Y. S. Simakova","doi":"10.1134/S0016702924030029","DOIUrl":"10.1134/S0016702924030029","url":null,"abstract":"<p>The paper presents the results of a study of carbonate and sulfate–carbonate–clayey rocks of the Lower Maeotian in the sections of the bays of Cape Kazantip using a complex of analytical methods. It is established that the greatest variation of chemical, bituminological, phase, and carbon-isotope composition is characterized by carbonate–clay and clayey rocks of the section bottom. It is proved that the initial OM was accumulated mainly under reducing conditions, but has some variations in composition; it is characterized by a low degree of its catagenetic transformation, which indicates the preservation of the primary isotopic composition. The diverse phase composition of the clay fraction is revealed: dioctahedral illite, kaolinite, chlorite, glauconite, and weakly ordered mixed-layer formations of illite/smectite type with different ratios of illite and smectite components and varying degrees of ordering. Modeling of their diffraction profiles showed that the illite/smectite structure may indicate significant depths of sediment mobilization by mud volcanoes. The isotopic composition of the ¹³С_org ranges widely from –33.72 to –19.27‰ the mode being –22.1…–24.93‰. The isotopic composition of ¹³С_org below –25.6‰ may be related to the entry of isotope-light mass of methane-oxidizing bacteria into the OM. It was revealed that variations of isotopic composition curves ¹³С_carb and ¹³С_org along the section of the studied rocks are rarely characterized by unidirectional (positive or negative) variations and have different trends along the section. Direction of the ¹³С_carb isotope composition curve with some variations has a pronounced upward trend toward heavier weighting, whereas the isotopic values of the ¹³С_org reveals reverse tendency. The results obtained prove that the revealed variations in the composition of OM and carbon isotope composition in the Lower Maeotian sections of Cape Kazantip reflect variations in the sedimentation conditions of temperature, salinity, freshwater ingression, bioproductivity fluctuations, and the influence of local gas–fluid deposition. It is proposed to use such accessory minerals as zircon, monazite, and ilmenite as an indicator of mud paleovolcanism.</p>","PeriodicalId":12781,"journal":{"name":"Geochemistry International","volume":"62 3","pages":"284 - 299"},"PeriodicalIF":0.7,"publicationDate":"2024-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140567744","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}