Chemical Geology最新文献

{"title":"Origin of K-bentonites near the Ediacaran-Cambrian boundary in South China","authors":"Zongling Zhang ,&nbsp;Mingzhong Zhou ,&nbsp;Li Zhou ,&nbsp;Di Zhang ,&nbsp;Xixi Xue ,&nbsp;Zhuo Wu ,&nbsp;Zhongfa Zhou ,&nbsp;Enlin Yang ,&nbsp;Qing Wang ,&nbsp;Jack Longman ,&nbsp;Haifeng Fan","doi":"10.1016/j.chemgeo.2025.122984","DOIUrl":"10.1016/j.chemgeo.2025.122984","url":null,"abstract":"<div><div>Understanding the origin of volcanic material at times of environmental change and evolutionary development may help aid investigation of causal linkages between the changes and volcanic activity. One such episode of environmental change of interest is the Ediacaran-Cambrian boundary (ECB), which follows the emergence of the Ediacaran fauna, and precedes the Cambrian explosion. Owing to recent developments in geochronology, a number of K-bentonites of ECB age have been identified in strata from South China, but systematic research on their origin has not been performed. Here, we carried out mineralogical, whole-rock, and zircon geochemical studies on ECB-age K-bentonites from the middle Zhujiaqing Formation at Meishucun and the topmost Liuchapo Formation at Pingyin in South China to investigate the origin of the K-bentonites. Whole-rock major- and trace-element data, and trace-element data of volcanic zircons in the K-bentonites indicate the source magmas are felsic, whilst Hf-isotope compositions of the volcanic zircons indicate the primary source magmas likely originated from the depleted mantle, with a minor contribution of ancient crustal material. Whole-rock data and trace-element data of volcanic zircons in the K-bentonites further indicate the source volcanoes were located in a subduction-related tectonic setting. By combining our findings with previous studies of Gondwanan tectonics, we suggest the source volcanoes were most probably located in a magmatic arc setting formed by subduction of the Proto-Tethys oceanic crust towards the Iran terrane in the northwestern margin of Gondwana. Thus, the K-bentonites represent episodes of intense felsic explosive volcanism along the northwestern margin of Gondwana during the Ediacaran-Cambrian transition and have likely been transported 1000 km to the studied sites. Large-scale felsic explosive volcanism played an important role in influencing the atmospheric and oceanic environments throughout Earth's history, and the volcanic activity documented here is contemporaneous with eruptions elsewhere in the world. The tight temporal link between this activity and the dramatic environmental fluctuations and the turnover of early life evolution during the Ediacaran-Cambrian transition, leads us to propose that volcanism may have played a role in the environmental and evolutionary events of the ECB.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"693 ","pages":"Article 122984"},"PeriodicalIF":3.6,"publicationDate":"2025-07-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144757685","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":"Compositional evolution of the Archean subaerial crust revisited using machine learning constraints","authors":"Junteng Lyu,&nbsp;Ziyi Guo,&nbsp;Ming Tang","doi":"10.1016/j.chemgeo.2025.122986","DOIUrl":"10.1016/j.chemgeo.2025.122986","url":null,"abstract":"<div><div>The composition of the Archean subaerial crust, whether mafic or felsic, remains debated due to tectonic uncertainties and proxy limitations. Here, we employ Random Forest Regression algorithm-based machine learning model to analyze multi-element geochemical data from terrigenous fine-grained sedimentary rocks to reconstruct the MgO content in the subaerial crust. The model is trained using major oxides (TiO₂ and Al₂O₃) and trace elements (Sc, Cr, Co, Ni, Cu, Zn, Y, Zr, Nb and REEs) of simulated mixture samples from Archean craton igneous rocks and post-Archean igneous rocks. The validity of this model is demonstrated by using various modern samples to predict MgO content in the modern subaerial crust, whose MgO content has been well constrained. We also demonstrate that the accuracy of the predictions is not sensitive to tectonic settings. We then use this model to reconstruct the chemical evolution of the subaerial crust over Earth's history and compare the differences between our model and other proxies reflecting the composition of the subaerial crust. Our model results suggest that a systematic decline of MgO content in the subaerial crust (7–10 wt% to 3–4 wt%) and a shift from mafic (70–100 % komatiite-basalt) to felsic dominance (∼70–90 % TTG) of the subaerial crust in the Neoarchean period, after which the subaerial crust attained a similar composition to that of the modern subaerial crust. The results from our approach are similar to those from Ni/Co and Cr/Zn proxies, but differ from the results of Zr/TiO₂ and Al₂O₃/TiO₂ proxies. We suggest that many previously used composition proxies are sensitive to tectonic settings and applying these proxies to terrigenous sediments can lead to erroneous results on the subaerial crust composition in the Archean. In addition, we caution against the use of proxies whose correlations with MgO or SiO₂ content are highly nonlinear, which may result in large uncertainties in the projected MgO or SiO₂ content for the source rocks.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"693 ","pages":"Article 122986"},"PeriodicalIF":3.6,"publicationDate":"2025-07-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144749026","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":"Drimane-type sesquiterpanes as molecular tracers for thermal effects and geologic processes in sedimentary basins","authors":"Biqing Zhu ,&nbsp;Quanyou Liu ,&nbsp;Huiyuan Xu ,&nbsp;Dongya Zhu ,&nbsp;Weilong Peng ,&nbsp;Xiaoqi Wu ,&nbsp;Yongqi Ruan ,&nbsp;Chi Zhang","doi":"10.1016/j.chemgeo.2025.122987","DOIUrl":"10.1016/j.chemgeo.2025.122987","url":null,"abstract":"<div><div>Drimane-type sesquiterpanes exhibit exceptional thermal stability and ubiquity across organic-rich sedimentary systems, from hydrothermal vents to crude oils, positioning them as critical molecular intermediaries in biomarker transformation pathways. The systematic GC–MS analysis of multi-phase crude oils from the Tarim Basin's ultra-deep reservoirs (depth &gt; 7 km, temperature &gt; 140 °C) identifies thermally-controlled molecular transformations. Cheilanthanes, particularly C₁₉ ∼ C₂₃ homologues, exhibit greater thermal stability than hopanes. Drimane-type sesquiterpanes display source-dependent initial abundances and maturation-driven transformations: 4,4,8,8,9-pentamethyldecane (RD1) accumulates progressively, 4,4,8,9,9-pentamethyldecane (RD2) shows transient accumulation followed by depletion, while drimane (D) and homodrimane (HD) decline continuously. The transmethylation reaction under high thermal stress leads to RD1 enrichment, making it an ultra-stable end-member in the thermal maturation of C₁₅ drimane-type sesquiterpanes. Maturity indicators derived from trimethylnaphthalenes and methylphenanthrenes exhibit good correlations with thermal gradient, whereas dibenzothiophene-derived parameters demonstrate the weak correlation. In contrast, sesquiterpane-derived ratios display superior strong correlation with thermal gradient compared to aromatic hydrocarbon indices. The RD1/(RD1 + D + HD) ratio is proposed as an optimized molecular proxy for assessing thermal effects and phase behaviors in sedimentary basins. This study provides a potential tool for investigating the thermal effects of diverse geological processes, such as plate movement, earthquake slip, magmatic intrusion, and hydrothermal activity.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"693 ","pages":"Article 122987"},"PeriodicalIF":3.6,"publicationDate":"2025-07-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144722931","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":"Oxygen isotopic re-equilibration during transformation of ikaite to calcite via amorphous calcium carbonate","authors":"Anett Lázár ,&nbsp;Attila Demény ,&nbsp;István Hegyi ,&nbsp;László Előd Aradi ,&nbsp;Laurence A.J. Garvie ,&nbsp;Péter Németh","doi":"10.1016/j.chemgeo.2025.122980","DOIUrl":"10.1016/j.chemgeo.2025.122980","url":null,"abstract":"<div><div>Glendonites are calcite pseudomorphs of ikaite (CaCO₃·6H₂O), a mineral that typically forms below 4 °C. Ikaite is found in marine clastic sediments, caves and lacustrine sediments, and its presence is correlated with cold paleo-environments. However, it is uncertain whether the isotopic composition of glendonite preserves the low-temperature paleoclimate conditions. Here we study the ikaite to calcite transition by following the evolution of solutions containing ikaite, prepared at pH 12.1, 10.3 and 9.1, and filtered materials exposed to air. Ikaite transformation starts with the formation of 100–200 nm-sized amorphous calcium carbonate (ACC) on the surface of ikaite grains, which transforms to carbonates dominated by calcite. In Mg-free solutions, vaterite also forms, whereas low concentrations of Mg (e.g., 26 mg/l) favor aragonite formation. Our data suggest that synthetic ikaites are formed with strong ¹⁶O-enrichment relative to other carbonate species due to kinetic fractionation. The ikaite-derived carbonates formed in contact with ambient air show a minor <strong>δ</strong>^{<strong>13</strong>}<strong>C</strong> change (−3.0 ± 0.8 ‰) relative to ikaite (−4.2 ± 0.3 ‰), but their oxygen isotope compositions remain constant. In contrast, transformation in solutions results in significant oxygen isotopic changes (from 17.7 to 20.5 ‰). Calcite-water oxygen isotopic equilibrium is approached within one week at 8 °C, and one day at 15 °C. Our experiments suggest that glendonite calcites formed by ikaite dehydration during early diagenesis undergo oxygen isotope exchange with pore waters and can record temperature and water composition conditions similar to those of the ikaite formation.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"693 ","pages":"Article 122980"},"PeriodicalIF":3.6,"publicationDate":"2025-07-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144757676","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":"Recycling of continental crust into the deep mantle in orogens: Constraints from zircon U-Pb-Hf-O and whole-rock Mg-Fe isotopes of Baihua complex, North Qinling Orogen","authors":"Gang Yang ,&nbsp;Juan Zhang ,&nbsp;Hong-fu Zhang ,&nbsp;An-Ping Chen ,&nbsp;A-Bing Lin","doi":"10.1016/j.chemgeo.2025.122982","DOIUrl":"10.1016/j.chemgeo.2025.122982","url":null,"abstract":"<div><div>Mafic magmatism in the orogenic belt acts as an invaluable repository for exploring the intricate dynamics of crust-mantle interactions. It meticulously preserves measurable signatures of recycled oceanic lithosphere and subducted continental materials within the orogenic mantle domains. This study employs an integrated approach, combining zircon U-Pb-Hf-O isotopic analyses and whole-rock geochemistry to investigate the Baihua metamorphosed magmatic complex in the North Qinling orogen, with the aim of deciphering the crustal recycling mechanisms.</div><div>Zircon U-Pb dating indicates the emplacement of mafic magma occurred between 441.6 ± 2.9–428.3 ± 2.2 Ma. Amphibolites have arc-like trace element signatures, tholeiitic differentiation trends, and a dual-source origin from mantle-derived melts (ε_Hf(t): +0.10 to +12, δ¹⁸O: 5.61 ± 0.05 ‰) and inherited crustal components (ε_Hf(t): −10.9 to −8.6, δ¹⁸O: 5.75 ± 0.15 ‰), highlighting ancient crustal components in the mantle source. Their δ²⁶Mg values range from −0.28 ± 0.01 ‰ to −0.12 ± 0.01 ‰, and δ⁵⁶Fe values from 0.06 ± 0.02 ‰ to 0.31 ± 0.04 ‰, likely due to mid-lower continental crust involvement in the mantle source.</div><div>Mafic microgranular enclaves (MMEs) and host diorites also have arc-like trace element signatures but show calc-alkaline affinities. They have uniform ε_Hf(t) values (−0.1 to +5.1) and δ¹⁸O values from 4.51 ‰ to 6.77 ‰, suggesting a cognate cumulate-residual melt relationship during magma evolution. Their δ²⁶Mg values range from −0.66 ‰ to −0.17 ‰ and δ⁵⁶Fe values from 0.11 ‰ to 0.17 ‰. Light δ²⁶Mg values suggest carbonate metasomatism, and variable Fe isotope signatures are due to fractional crystallization of olivine, clinopyroxene and ilmenite.</div><div>Consequently, the ∼433 Ma mafic rock suite likely originated from lithospheric mantle metasomatized by ancient mid-lower crustal and carbonate-rich melts. These mafic rocks preserve a geochemical signature of continental crust recycled into the deep mantle.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"693 ","pages":"Article 122982"},"PeriodicalIF":3.6,"publicationDate":"2025-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144713190","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":"Zirconium and its isotope behavior during weathering on Hainan Island, China","authors":"Yu Jiao ,&nbsp;Lian Zhou ,&nbsp;Jing-Liang Guo ,&nbsp;Lanping Feng ,&nbsp;Jinhua Liu ,&nbsp;Daqian Zhang ,&nbsp;Jianping Wang ,&nbsp;Mulong Chen ,&nbsp;Yong Wang ,&nbsp;Zailong Hu","doi":"10.1016/j.chemgeo.2025.122979","DOIUrl":"10.1016/j.chemgeo.2025.122979","url":null,"abstract":"<div><div>Zirconium (Zr) is mobile during extreme weathering. However, the Zr stable isotope (δ^94/90Zr) behavior in the weathering profile has not been investigated, although Zr isotope has gained much attention for tracing the provenance of sediments. Here, the behavior of Zr and its isotopes during chemical weathering was investigated from basaltic (Penglai) and granitic (Qionghai) weathering profiles on Hainan Island, China. At the Penglai basaltic weathering profile, Zr was gradually removed from the near-surface horizons, transferred downwards and precipitated in deeper horizons, which likely driven by the acid environment and organic matter in the soil layer. The sequential extraction experiment shows that Zr was released from the residual phase and adsorbed into exchangeable and adsorbed phases during increasing weathering. However, Zr isotopes in the weathering samples and bedrock are consistent within uncertainty, suggesting Zr mobilization during chemical weathering does not result in pronounced Zr isotope fractionation in the whole basaltic weathering profile. At the Qionghai granitic weathering profile, the variation in Zr concentration is likely related to zircon migration, but the shift in Zr isotope composition &lt;0.10 ‰ fractionation in the weathering profile. Our results show that insignificant Zr isotope fractionation occurred during weathering in both basaltic and granitic weathering profiles. Notably, Zr isotopes of the weathering samples in the basalt are distinguishable from that of granite, implying that Zr isotope of sediments has the potential to trace their provenance.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"692 ","pages":"Article 122979"},"PeriodicalIF":3.6,"publicationDate":"2025-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144711338","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":"Conodont apatite record of marine Sr isotopic composition in the advent of the Hangenberg Event (Late Devonian)","authors":"Thomas Letulle ,&nbsp;Przemysław Lech Świś ,&nbsp;Federico Lugli ,&nbsp;Annalisa Ferretti ,&nbsp;Manuel Rigo","doi":"10.1016/j.chemgeo.2025.122981","DOIUrl":"10.1016/j.chemgeo.2025.122981","url":null,"abstract":"<div><div>The Devonian-Carboniferous boundary constitutes one of the major gaps of the Phanerozoic oceanic radiogenic Sr curve. This gap is of particular interest in the ongoing discussion to redefine the Devonian/Carboniferous boundary, as isotopic Sr stratigraphy could provide an auxiliary correlation tool. We present herein the first latest Famennian radiogenic Sr data from three monogeneric sets of conodont elements collected from the well-studied Kowala Quarry section in central Poland. The minimal alteration of this conodont dataset, supported by the good fit with published brachiopod data from coeval intervals, makes this record highly reliable. The Kowala Quarry material provides updated seawater ⁸⁷Sr/⁸⁶Sr ratio trend along the few million years preceding the Hangenberg Event. The decreasing ⁸⁷Sr/⁸⁶Sr ratios trend from the <em>Bispathodus costatus</em> (∼ 0.70832 ± 0.00003) to the <em>Siphonodella (Eosiphodella) praesulcata</em> Zone (0.70822 ± 0.00003) suggest the early Carboniferous decreasing trend started as early as the late Fammenian. Comparison with early Fammenian trends indicate seawater ⁸⁷Sr/⁸⁶Sr ratio reached a maximum during the late or middle Famennian. We attempt to correlate this new dataset to the GTS 2020 and discuss two different age models based on available biostratigraphic, radiometric and astrochronological data. Both age models suggest higher rates of ⁸⁷Sr/⁸⁶Sr ratio decrease during the <em>S. (E.) praesulcata</em> Zone. We explore the cause of this decreasing trends using one-dimensional mass balance modelling of oceanic Sr. The modelling experiments reject the hypothesis of the coeval Kola-Dniepr Large Igneous Province emplacement as the main driver of this ⁸⁷Sr/⁸⁶Sr shift. It is more likely explained by a global and sustained imbalance of oceanic Sr, which may include a combination of orogenic belt waning, increased volcanic arc activity and accretion, increased hydrothermalism, as well as a small contribution of LIP emplacement.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"692 ","pages":"Article 122981"},"PeriodicalIF":3.6,"publicationDate":"2025-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144712934","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":"Apatite composition and phase equilibrium modelling unravel F and Cl behavior during crustal anatexis in the Himalayan orogen","authors":"Min Ji ,&nbsp;Xiao-Ying Gao ,&nbsp;Cong Tu ,&nbsp;Xuan-Jin Chen","doi":"10.1016/j.chemgeo.2025.122978","DOIUrl":"10.1016/j.chemgeo.2025.122978","url":null,"abstract":"<div><div>Fluorine (F) and chlorine (Cl) are crucial in the evolution of magmatic–hydrothermal systems, but their behavior during crustal anatexis is not well understood. To address this, we combined electron probe micro-analysis of apatite in anatectic rocks and phase equilibrium modelling for partial melting of potential source rock in this study. Apatites in two types of rocks formed under different anatectic pressure–temperature–fluid conditions from the Cona area in the eastern Himalaya have contrasting major-minor element compositions. Apatites in Type I rocks, associated with fluid-present (hydration) melting under low pressures and temperatures, have systematically lower FeO, MnO, Na₂O, and F contents, lower F/Cl ratios, and higher Cl contents than those in Type II rocks, related to fluid-absent (dehydration) melting under high pressures and temperatures. Using measured apatite volatile contents and theoretically constrained exchange coefficients, we estimated F and Cl contents in coexisting melts. The results show that Type I melts consistently exhibit lower F/Cl ratios than Type II melts, which can be ascribed to the differences in anatectic conditions rather than melt evolution. Forward phase equilibrium modelling and element partitioning further show that F and Cl partition preferentially into melts, depleting the solid restites. Lower pressures and fluid addition decrease F/Cl ratios in melts, as observed in the Type I rocks. Given that rare metals (e.g., Li, Be, Ta, W, Sn) are also primarily hosted by muscovite and biotite, similar to F and Cl, in the metapelite, we also modelled their behavior during partial melting. The results indicate that high-pressure dehydration melting enriches F, Cl, and rare metals in melts, offering favorable conditions for rare metal mineralization. These findings not only improve our understanding of F and Cl behavior during crustal anatexis but also shed new light on the role of anatexis in rare metal enrichment.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"692 ","pages":"Article 122978"},"PeriodicalIF":3.6,"publicationDate":"2025-07-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144711339","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":"Organic geochemical evidence links changes in marine microbes and phytoplankton to ammonite turnover in the Tethyan Middle Jurassic","authors":"Adam Zakrzewski ,&nbsp;Zoltán Kovács ,&nbsp;József Pálfy","doi":"10.1016/j.chemgeo.2025.122977","DOIUrl":"10.1016/j.chemgeo.2025.122977","url":null,"abstract":"<div><div>Carbon isotope-based chemostratigraphy is a well-established method for regional or even global correlations, especially at major stratigraphic boundaries which are often marked by global change events. However, background intervals remain less well studied and our knowledge is limited about the drivers of small-scale faunal turnovers which may be reflected in the zonal boundaries of biostratigraphic schemes. Moreover, organic geochemistry is much less used than carbon isotopes in chemostratigraphy. Here, we address these issues by a comprehensive stable isotope and organic geochemical study of three Tethyan Aalenian (Middle Jurassic) sections with good ammonite biostratigraphic control. We assess the linkages between zone-level faunal transitions and minor geochemical perturbations recorded by isotopic and biomarker indicators. A wide range of geochemical analyses (biomarkers, δ¹³C_SAT, δ¹³C_carb, δ¹⁸O_carb, and compound-specific isotope analyses (CSIA)) were performed on samples from three continuous Tethyan Aalenian–lowermost Bajocian sections in the Gerecse Mts. (Hungary) where ammonite zonal boundaries are well constrained. The organic matter is predominantly aquatic in origin with negligible terrigenous admixture. Most of the biostratigraphic boundaries coincide with minor negative Carbon Isotope Excursions in δ¹³C_SAT and phytoplankton-related CSIA. Curves of phytoplankton-related biomarker indicators, including diploptene, dehydroabietic acid methyl ester, and distribution of methylheptadecanes reveal marked changes within the phytoplankton communities at the transitions between ammonite zones and/or subzones. These biomarker results suggest that turnovers of the ammonite faunas were preceded by phytoplankton crises. Thus, biostratigraphic boundaries likely reflect minor environmental changes that first affected the primary producers, then trophic changes propagated through the entire marine food web.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"692 ","pages":"Article 122977"},"PeriodicalIF":3.6,"publicationDate":"2025-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144664935","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 evolution of the Eastern Paratethys: Tracing the Tethys Ocean legacy through geochemical proxies","authors":"Dan V. Palcu Rolier ,&nbsp;Zhanhong Liu ,&nbsp;Wei Wei ,&nbsp;Sergey Popov ,&nbsp;Larisa Golovina ,&nbsp;Iuliana Vasiliev ,&nbsp;Wout Krijgsman ,&nbsp;Thomas Algeo","doi":"10.1016/j.chemgeo.2025.122974","DOIUrl":"10.1016/j.chemgeo.2025.122974","url":null,"abstract":"<div><div>During the Oligocene to Miocene, the Paratethys Sea emerged as the northern offshoot of the Tethys Ocean, separated from the Mediterranean by the Alpine-Himalayan mountain range. Its history was characterized by the opening, restriction and closure of marine gateways, resulting in significant paleoenvironmental changes, including episodes of anoxia and extreme salinity fluctuations. This study investigates the paleoenvironmental evolution of the Paratethys Sea by focusing on variations in salinity and paleoventilation through advanced geochemical analyses of key sections (Belaya, Panagia, Zhelezhny Rog) in the northern Caucasus and Taman Peninsula of Russia, spanning 42 to 4 Ma. We apply a suite of geochemical proxies to reconstruct paleosalinity [e.g., using the boron/gallium (B/Ga), strontium/barium (Sr/Ba), sulfur/total organic carbon (S/TOC) ratios] and paleoredox conditions [e.g., using the organic carbon/phosphorus (C_org/P) ratio as well as trace-metal enrichment factors such as Zn_EF, V_EF, and Mo_EF]. Our results indicate that Paratethys was influenced by both global and local events, with regional factors becoming increasingly significant as isolation and fragmentation progressed. Paleoventilation proxies reveal two main episodes of anoxia: the Kuma Anoxic Event, a regional event exhibiting oceanic anoxic signatures that encompassed the time of the Middle Eocene Climatic Optimum (MECO) and; the Maikop Persistent Basin Water Stratification (PBWS) event, coinciding with the Eocene-Oligocene Transition (EOT) and lasting until the Middle Miocene Climatic Optimum (MMCO), reflecting characteristics of an enclosed sea; and a weaker, less stable suboxic-anoxic episode in the late Miocene, associated with Megalake Paratethys. Paleosalinity proxies depict both transitions from marine to brackish conditions, such as the late Maikop salinity decrease and significant short-lived marine episodes, such as the MMCO-related mid-Langhian flood (14.8 Ma), the Badenian-Sarmatian Extinction Event (12.65 Ma) and the Intra-Maeotian Event (6.8 Ma). These findings emphasize the critical role of marine connectivity as a trigger of salinity and ventilation changes in the Eastern Paratethys's evolution, laying the groundwork for future studies on restricted basins.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"692 ","pages":"Article 122974"},"PeriodicalIF":3.6,"publicationDate":"2025-07-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144664932","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}