Chemical Geology最新文献

{"title":"The impact of burial diagenesis on soil-formed minerals in paleosols using stable isotopes of phyllosilicates and carbonate clumped isotopes","authors":"Julia A. McIntosh, Neil J. Tabor, Isabel P. Montañez","doi":"10.1016/j.chemgeo.2025.122941","DOIUrl":"https://doi.org/10.1016/j.chemgeo.2025.122941","url":null,"abstract":"To understand the effects of burial diagenesis on the stable isotope geochemistry of soil-formed minerals in paleosols, paleosol samples were collected from seven cores, spanning middle- to upper-Pennsylvanian strata, across the Illinois Basin, with varied maximum burial depths of 1–3 km. Mixed-layer illite-smectite and kaolinite mixtures give δ<ce:sup loc=\"post\">2</ce:sup>H and δ<ce:sup loc=\"post\">18</ce:sup>O values of −83 ‰ to −36 ‰ and 11.9 ‰ to 21.1 ‰ (Vienna Standard Mean Ocean Water; VSMOW), respectively. After carbonates were screened petrographically for diagenetic textures using transmitted light and cathodoluminescence, measured clumped isotope Δ<ce:inf loc=\"post\">47</ce:inf> values range from 0.504 to 0.563 ‰ (I-CDES). Resulting mineral formation temperatures for phyllosilicate mineral mixtures are 28 to 66 °C (mean = 47 °C), whereas T(Δ<ce:inf loc=\"post\">47</ce:inf>) estimates for calcites are 36 to 61 °C (mean = 45 °C). Calculated δ<ce:sup loc=\"post\">18</ce:sup>O<ce:inf loc=\"post\">water</ce:inf> values from which phyllosilicate minerals and calcites precipitated under isotopic equilibrium ranges from −7.1 to −1.2 ‰ and − 1.4 to +4.9 ‰, respectively. Closed and open-system phyllosilicate-fluid exchange modeling indicates that phyllosilicate alteration occurred in the presence of a low temperature brine or meteoric water and is interpreted to occur in a layer-by-layer illitization transformation. Due to the lack of diagenetic textures and positively correlated T(Δ<ce:inf loc=\"post\">47</ce:inf>) and δ<ce:sup loc=\"post\">18</ce:sup>O<ce:inf loc=\"post\">water</ce:inf>, calcites are interpreted to have undergone solid-state bond reordering. Despite low to moderate temperatures (&lt;125 °C) and varying depths of shallow burial (1–3 km), solid-state transformation of phyllosilicates and calcites indicates paleosols had prolonged exposure to burial conditions which has implications for the use of paleosol minerals for paleoenvironmental reconstructions.","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"239 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2025-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144335531","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 variability and alteration dynamics of chromitites under greenschist metamorphism in the Kızıldağ ophiolite, southern Türkiye","authors":"Recep Melih Akmaz ,&nbsp;Ibrahim Uysal ,&nbsp;Ben-Xun Su ,&nbsp;Ahmet D. Şen ,&nbsp;Wen-Jun Hu ,&nbsp;Hans-Michael Seitz ,&nbsp;Dirk Müller ,&nbsp;Alireza Eslami","doi":"10.1016/j.chemgeo.2025.122936","DOIUrl":"10.1016/j.chemgeo.2025.122936","url":null,"abstract":"<div><div>This study presents a complete alteration sequence in chromitites from the Kızıldağ ophiolite (southern Türkiye), documenting three distinct chromite types that record processes related to Neotethyan subduction. Chromitites exhibit predominantly lenticular forms and occasionally banded textures, embedded within mantle peridotites and the mantle-crust transition zone, specifically harzburgite and dunite. Our analysis categorizes chromite grains into three groups: fresh, altered, and porous. Fresh chromites are characterized by high contents of Cr₂O₃ ranging from 42.69 to 57.08 wt% and Al₂O₃ from 12.46 to 25.34 wt%. In contrast, altered chromites, typically located along fractures or at the edges of fresh grains, show significant variability in chemical composition, with Cr₂O₃ content between 43.34 and 63.94 wt% and Al₂O₃ between 2.91 and 14.84 wt%. Porous chromites, distinguished by their porous structure, present Cr₂O₃ contents from 44.58 to 52.66 wt% and Al₂O₃ from 3.00 to 8.38 wt%. Notably, altered and porous chromites demonstrate substantial enrichments in Fe and trace elements such as Mn, Ni, Zn, Co, and Ga, indicating a shift due to metamorphic processes. The observed high Cr# (0.68–0.93) and low Mg# (0.25–0.65) values in rims of the altered and porous chromite further illustrate the metamorphic influence on chromite, with greenschist-facies conditions indicated by the Cr–Al–Fe³⁺ diagram at temperatures below 450 °C. The alteration dynamics reflect a progression that initiates with the olivine matrix and advances through reactions involving fresh chromites. This progression results in mass loss, the formation of chlorite, and the porous structures. Our findings contribute to the understanding of metamorphic alteration processes in chromitites and provide a detailed account of the geochemical trends (such as Fe/Mg exchange and trace element enrichment) that reflect greenschist-facies metamorphism. The evidence of chlorite formation and the prevalence of porous textures highlight the influence of metamorphic fluids over serpentinization, offering a model for chromite alteration in supra-subduction zones. This research elucidates the metamorphic history of chromitites in the Kızıldağ ophiolite.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"692 ","pages":"Article 122936"},"PeriodicalIF":3.6,"publicationDate":"2025-06-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144335453","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":"Tracing CO2 and helium origins of mineral spring water of the Water Circuit of Minas Gerais in southeastern Brazil","authors":"Hendryk Gemeiner ,&nbsp;Hung Kiang Chang ,&nbsp;Larissa Neris Alcara ,&nbsp;Marcelo Martins Reis ,&nbsp;Peter H. Barry ,&nbsp;Amauri Antonio Menegário","doi":"10.1016/j.chemgeo.2025.122939","DOIUrl":"10.1016/j.chemgeo.2025.122939","url":null,"abstract":"<div><div>The Water Circuit of Minas Gerais, situated in the southeastern region of the Brazilian state of Minas Gerais, has garnered significant interest since the 19th century due to the abundance of mineral springs with heightened mineral compositions and high levels of CO₂. However, despite decades of research, the origins of this natural CO₂ enrichment phenomenon in these springs remain unclear. Here, we present the first noble gas isotope data from these spring waters combined with hydrochemical data. Calcium bicarbonate waters predominate in the spa town parks of Caxambu, Águas de Contendas and Lambari, whereas sodium bicarbonate and “mixed type” is found in the Cambuquira park. All samples display high He concentrations and elevated ⁴He/²⁰Ne values with respect to atmospheric values, indicating a deep origin and the gradual accumulation of radiogenic ⁴He in the waters. Spring samples show air-corrected ³He/⁴He (R_c/R_a) values between 0.55 and 3.39 R_a, suggesting an admixture of crustal and mantle volatile contributions. A consistent ³He/⁴He decrease with increasing distance from the Caxambu shear zone is observed, indicating that the release of deep fluids is fault controlled. We suggest that major fault segments within the Caxambu shear zone serve as continuous pathways for the ascent of mantle-derived CO₂ and He, enriching the springs of the Water Circuit region. Carbon isotope data indicates a significant contribution of carbonate-derived CO₂. We combined discharge estimates with carbon concentrations to quantify a CO₂ flux of 4.26 × 10⁶ mol year⁻¹ into the surface system from all springs in the four spa parks.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"691 ","pages":"Article 122939"},"PeriodicalIF":3.6,"publicationDate":"2025-06-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144320887","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":"Post-depositional effects on chromium in black shales and implications for paleo-redox reconstructions based on chromium isotopes","authors":"Ziyao Fang ,&nbsp;Xiaoqing He ,&nbsp;Xi Yu ,&nbsp;Dandan Li ,&nbsp;Xiaolin Zhang ,&nbsp;Yanan Shen ,&nbsp;Liping Qin","doi":"10.1016/j.chemgeo.2025.122938","DOIUrl":"10.1016/j.chemgeo.2025.122938","url":null,"abstract":"<div><div>Chromium (Cr) is a redox-sensitive element, and its isotope system has been widely used as a paleo-redox proxy, providing insights into the evolution of oxygen in Earth's oceans and atmosphere. Black shales serve as an important archive for sedimentary Cr isotope data. The precise interpretation of Cr isotope records in black shales relies on a comprehensive understanding of the geochemical behavior of Cr throughout black shale formation and diagenesis. Here, we applied synchrotron-based X-ray spectroscopy, sequential leaching, and Cr isotope analysis to investigate the Cr species in sedimentary black shales from various sites and geologic periods. The results show that most of the authigenic Cr, which is the fraction of Cr precipitated from seawater, is not associated with the usual hydrogenetic phases (e.g., organic matter or iron-rich components) but rather resides in clay minerals. We further demonstrate that post-depositional diagenetic processes can induce redistribution of authigenic Cr in black shales, leading to enrichments of authigenic Cr in silicate minerals. Moreover, these processes were accompanied by significant Cr isotope fractionation, which substantially altered the Cr isotope compositions of the original phases. Similar effects can influence other trace elements, such as vanadium, in black shales. The findings imply that effectively separating authigenic and detrital fractions of these elements in black shales is unlikely. Instead, applying detrital corrections using the concentrations of typical detrital tracers (such as titanium and aluminum) after bulk isotope analysis is a more practical approach. This limitation affects the reliability of paleo-environmental interpretations derived from isotope data in black shales with high detrital contributions.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"691 ","pages":"Article 122938"},"PeriodicalIF":3.6,"publicationDate":"2025-06-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144335452","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":"Controls of sediment-bound and dissolved nutrient transport from a glacierised metasedimentary catchment in the high Arctic","authors":"Lukasz Stachnik ,&nbsp;Jon Hawkings ,&nbsp;Andrea Spolaor ,&nbsp;Katarzyna Stachniak ,&nbsp;Dariusz Ignatiuk ,&nbsp;Sławomir Sitek ,&nbsp;Krzysztof Janik ,&nbsp;Elżbieta Łepkowska ,&nbsp;Francois Burgay ,&nbsp;Marcin Daniel Syczewski ,&nbsp;Delia Segato ,&nbsp;Pablo Forjanes ,&nbsp;Liane G. Benning","doi":"10.1016/j.chemgeo.2025.122940","DOIUrl":"10.1016/j.chemgeo.2025.122940","url":null,"abstract":"<div><div>Rapid warming in polar and alpine areas is causing significant glacier mass loss and resulting in increasing freshwater delivery to the oceans. Recent research indicates that higher meltwater water runoff is likely to increase solute and sediment transport, which will include nutrients, to downstream environments. This enhanced delivery may drive a negative feedback effect on atmospheric CO₂ concentrations by stimulating primary production in fjords and near-coastal regions. Labile sediment-bound nutrient species constitute a high proportion of the total nutrient yield from glacierised catchments, but studies that investigate their source and behaviour are sparse. Here we determine sediment-bound and dissolved nutrient (Si, Fe, P) delivery from a polythermal glacier in SW Spitsbergen. Suspended sediment and dissolved samples were collected from subglacial outflows and a downstream site. Our results show high spatial variability in chemical weathering processes resulting in differences in sediment-bound nutrient concentration. Sulphide oxidation and carbonate dissolution appear more important in a channelised system underlain by rocks metamorphosed in green schist facies, and silicate mineral weathering appears more important in smaller subglacial outflows underlain by rocks undergone intense metamorphism in amphibolite facies. Sediments from the channelised outlet have two times higher content of sediment-bound highly reactive iron (∼0.29 % dry weight, hereafter d.w.) than the minor subglacial outflows. In contrast, sediment-bound amorphous silica (ASi) is almost double in the minor subglacial outflows compared to the channelised outlet (∼0.17 % d.w. vs ∼0.10 % d.w.). The yield of sediment-bound Fe and Si (2.3 and 1.3 10³ kg km⁻² yr⁻¹, respectively) was several times higher than the dissolved flux of those elements. Sediment-bound Fe yields were in the range of values noted previously for the Greenland Ice Sheet. Our data reinforces the critical role of sediment-bound nutrients on elemental cycling in glacierised basins of the high Arctic.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"691 ","pages":"Article 122940"},"PeriodicalIF":3.6,"publicationDate":"2025-06-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144330231","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":"Dating multiple fractionation trends in pegmatites – Implications for the genesis of a large lithium pegmatite province in West-Africa","authors":"Marieke Van Lichtervelde ,&nbsp;Oscar Laurent ,&nbsp;Prince Ofori Amponsah ,&nbsp;Isaac Iwan E. Williams","doi":"10.1016/j.chemgeo.2025.122935","DOIUrl":"10.1016/j.chemgeo.2025.122935","url":null,"abstract":"<div><div>The race for lithium supply for the green energy transition has brought Li pegmatites, the primary source of Li in the world, to the forefront. Their origins and mechanisms of formation are still debated, and geochemical tools to distinguish granite-related from anatectic pegmatites are still needed. In the current study, we combine two classical approaches, i.e., alkali fractionation in micas coupled to Nb-Ta-oxide geochronology, to date multiple fractionation trends in pegmatites from a large lithium pegmatite province in Ghana. We investigated distinct fractionation trends in the different pegmatites and we timeframed these trends by dating columbite-group minerals associated with primary magmatic micas. Distinct Rayleigh-type Rb/Cs fractionation paths were modeled using different starting Rb and Cs melt compositions that can be attained by direct partial melting of the meta-sedimentary country rocks. Columbite-group mineral dating reveals that each of these fractionation paths occurred at different ages spanning ca. 140 Myr. Moreover, our data shows that the oldest pegmatites correspond to poorly fractionated, Li-rich, Nb-Cs-Ta-Sn-poor pegmatites, whereas the youngest are the most fractionated, Cs-Ta-rich pegmatites (up to levels of the major Lithium-Cesium-Tantalum pegmatites worldwide). The proposed model of formation for this large Li-bearing province involves at least three distinct stages of partial melting and melt extraction at ca. 2170, 2080 and 2030 Ma. The produced melt batches evolved independently through fractional crystallization, the spodumene-bearing pegmatites being the least fractionated, and the “true LCT” pegmatites the most fractionated.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"691 ","pages":"Article 122935"},"PeriodicalIF":3.6,"publicationDate":"2025-06-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144289932","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":"Remobilization of Ni in framboidal pyrite within sulfide nodules in Early Cambrian nickeliferous black shales","authors":"Xu-Yang Liu ,&nbsp;Ya-Fei Wu ,&nbsp;Daniel D. Gregory ,&nbsp;Katy Evans ,&nbsp;Anthony E. Williams-Jones ,&nbsp;Wen Zhang ,&nbsp;Mei-Fu Zhou ,&nbsp;Jian-Wei Li","doi":"10.1016/j.chemgeo.2025.122913","DOIUrl":"10.1016/j.chemgeo.2025.122913","url":null,"abstract":"<div><div>Black shales commonly contain deposits extremely enriched in nickel (Ni), but the processes of Ni enrichment remain debated. Here we use laser ablation–multiple collector–inductively coupled plasma–mass spectrometry and transmission electron microscopy to present new micrometer- to nanometer-scale insights into the remobilization of Ni in framboidal pyrite from the Dazhuliushui Ni-Mo deposit, South China. Two types of framboidal pyrite have been identified in sulfide nodules: early Py-a with a core-rim texture in a MoSC phase and later Py-b in millerite aggregates. The Py-b microcrystals are larger and more tightly packed than Py-a microcrystals, indicating a decrease in FeS₂ supersaturation from sedimentation or early diagenesis to later diagenesis. This is consistent with the lighter S and Fe isotopic compositions of Py-a than Py-b (mean −6.99 ‰ vs. −2.13 ‰ and −0.31 ‰ vs. 0.09 ‰, respectively), produced via the preferential utilization of light S and Fe isotopes during pyrite formation within a semi-restricted basin and/or from pore water. Amorphous organic matter rich in gersdorffite nanoparticles via adsorption occurs within the interstices of Py-a cores. Gersdorffite and millerite nanoparticles within Py-a rims rapidly precipitated in response to continuous decomposition of organic matter. The Py-b is not associated with organic matter but with minor gersdorffite nano-veinlets that might form via the decay of residual organic matter during late diagenesis. These results reveal the complex remobilization processes of Ni in framboidal pyrite and highlight that nanoscale observations are necessary for fully understanding the detailed processes of metal enrichment in black shales.-</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"691 ","pages":"Article 122913"},"PeriodicalIF":3.6,"publicationDate":"2025-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144272065","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Beryllium-isotope signatures in ice sheet proximal marine sediments","authors":"Matthew Richard Jeromson ,&nbsp;Toshiyuki Fujioka ,&nbsp;David Fink ,&nbsp;Krista Simon ,&nbsp;Alexandra L. Post ,&nbsp;Marcello Blaxell ,&nbsp;José Tonatiuh Sánchez-Palacios ,&nbsp;T. Gabriel Enge ,&nbsp;Carly Beggs ,&nbsp;Duanne A. White","doi":"10.1016/j.chemgeo.2025.122912","DOIUrl":"10.1016/j.chemgeo.2025.122912","url":null,"abstract":"<div><div>Meteoric-¹⁰Be has become a popular proxy for assessing glacial environments and processes around Antarctica, such as meltwater discharge or ice shelf environments. Despite applications in recent paleostudies, little testing of the mechanisms driving the deposition of Be-isotopes into marine sediments has been conducted. We used chemical leach procedures to sequentially or partially extract ¹⁰Be and ⁹Be from bulk sediments to assess the possible sources and depositional processes affecting them. Additionally, we leached the reactive phase of five different grainsize splits to determine whether ¹⁰Be/⁹Be ratios normalise for grainsize effects acting upon the ¹⁰Be concentration. Reactive Be-isotopes are primarily situated in the oxide phases of sediments, with the amorphous oxide (Am-Ox) phases consisting of much higher ¹⁰Be/⁹Be ratios (∼7–10 × 10⁻⁸) than the crystalline oxides (∼1–3 × 10⁻⁸; X-Ox), indicating that the Am-Ox phase better represents authigenic oxide production and a circumpolar deep water source, which is contrary to most of the current literature. Published leach procedures targeting the reactive phase of sediment consist of ratios in between the Am-Ox and X-Ox phases (∼3–7 × 10⁻⁸), indicating that they target both phases to some degree. The fractionation of Be-isotopes in Antarctic sediment samples shows that circumpolar deep water is the primary source of ¹⁰Be, and that the “reactive” signatures from different leach steps targeting the reactive phase are not the same.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"691 ","pages":"Article 122912"},"PeriodicalIF":3.6,"publicationDate":"2025-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144242391","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Revealing paleosalinity and paleoclimatic characteristics in Dawenkou Formation of the Paleogene in Huanggang Depression, eastern China: An integrated geochemical and palynological analysis","authors":"Wentao Chen ,&nbsp;Dawei Lv ,&nbsp;Zhenguo Ning ,&nbsp;Hao Xin ,&nbsp;Cuiyu Song ,&nbsp;Munira Raji ,&nbsp;Fanwei Meng ,&nbsp;Bin Yang ,&nbsp;Zhihui Zhang ,&nbsp;Lulu Tang","doi":"10.1016/j.chemgeo.2025.122911","DOIUrl":"10.1016/j.chemgeo.2025.122911","url":null,"abstract":"<div><div>The variations in paleosalinity and paleoclimate significantly influence the deposition and distribution of rock salt deposits. Understanding these variations is therefore essential for advancing knowledge of salt resource formation and supporting exploration efforts. In this study, we use an integrated approach combining geochemical and palynological proxies to reconstruct paleosalinity and paleoclimate during the salinization period of the Paleogene Dawenkou Formation, based on core samples from the ZK04 borehole in the Huanggang Depression, eastern China. The analysis identifies three distinct salinity phases spanning the late Eocene to early Oligocene: hyposaline water to mesosaline conditions, mesosaline to hypersaline conditions, and a return to hyposaline conditions. The intermediate hypersaline phase is particularly notable for a significant increase in both salinity and aridity, as evidenced by salinity-sensitive proxies such as the B/Ga ratio, boron excess (B_xs), corrected Sr/Ba, and sulfur-to-total organic carbon (S/TOC) ratios. Among these, the B/Ga ratio emerges as the most reliable indicator for reconstructing paleosalinity. The findings highlight the primary role of arid climatic conditions and elevated salinity in driving rock salt deposition in the Dawenkou Formation and offer valuable insights into the environmental controls on salt formation in other comparable basins worldwide.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"691 ","pages":"Article 122911"},"PeriodicalIF":3.6,"publicationDate":"2025-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144254911","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Precession-driven variations in phosphorus cycling facilitated Earth’s oxygenation in the early Proterozoic","authors":"Wytze K. Lenstra ,&nbsp;Margriet L. Lantink ,&nbsp;Rick Hennekam ,&nbsp;Paul R.D. Mason ,&nbsp;Gert-Jan Reichart ,&nbsp;Frederik J. Hilgen ,&nbsp;Caroline P. Slomp","doi":"10.1016/j.chemgeo.2025.122857","DOIUrl":"10.1016/j.chemgeo.2025.122857","url":null,"abstract":"<div><div>Oxygenic photosynthesis in the ocean of the early Proterozoic may have been limited by the nutrient phosphorus. If so, precession-driven variations in riverine phosphorus input may have enhanced oxygenic photosynthesis and thereby contributed to the rise of atmospheric oxygen. Here, we combine geochemical analyses of 2.46-billion-year-old deposits of the Joffre Member of the Brockman Iron Formation (Australia) and results of a reactive transport model to reconstruct pathways of organic matter degradation and phosphorus cycling in oceanic sediments over a precession cycle. Our results support a conceptual model in which increased phosphorus availability during precession maxima at southern paleolatitudes drove net oxygen production by inducing increased reductant burial in the sediment (mainly as pyrite, vivianite and magnetite). During precession minima, legacy benthic release of methane may have enhanced photolysis of atmospheric methane, thereby allowing for additional net oxygen production. Hence, precession-driven variations in coupled carbon–phosphorus–oxygen cycling may have acted as an accelerator towards the Great Oxidation Event.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"691 ","pages":"Article 122857"},"PeriodicalIF":3.6,"publicationDate":"2025-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144272066","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}