Acta Geochimica最新文献

{"title":"Formation and growth of nanophase iron particles on the surface of Mercury revealed by experimental study","authors":"Ronghua Pang,&nbsp;Yang Li,&nbsp;Chen Li,&nbsp;Pengfei Zhang,&nbsp;Zhuang Guo,&nbsp;Sizhe Zhao,&nbsp;Han Yu,&nbsp;Li Wang,&nbsp;Chenxi Zhu,&nbsp;Shuangyu Wang,&nbsp;Kairui Tai,&nbsp;Qinwei Zhang,&nbsp;Yuanyun Wen,&nbsp;Rui Li","doi":"10.1007/s11631-024-00699-x","DOIUrl":"10.1007/s11631-024-00699-x","url":null,"abstract":"<div><p>Space weathering is a primary factor in altering the composition and spectral characteristics of surface materials on airless planets. However, current research on space weathering focuses mainly on the Moon and certain types of asteroids. In particular, the impacts of meteoroids and micrometeoroids, radiation from solar wind/solar flares/cosmic rays, and thermal fatigue due to temperature variations are being studied. Space weathering produces various transformation products such as melted glass, amorphous layers, iron particles, vesicles, and solar wind water. These in turn lead to soil maturation, changes in visible and near-infrared reflectance spectra (weakening of characteristic absorption peaks, decreased reflectance, increased near-infrared slope), and alterations in magnetism (related to small iron particles), collectively termed the “lunar model” of space weathering transformation. Compared to the Moon and asteroids, Mercury has unique spatial environmental characteristics, including more intense meteoroid impacts and solar thermal radiation, as well as a weaker particle radiation environment due to the global distribution of its magnetic field. Therefore, the lunar model of space weathering may not apply to Mercury. Previous studies have extensively explored the effects of micrometeoroid impacts. Hence, this work focuses on the effects of solar-wind particle radiation in global magnetic-field distribution and on the weathering transformation of surface materials on Mercury under prolonged intense solar irradiation. Through the utilization of high-valence state, heavy ion implantation, and vacuum heating simulation experiments, this paper primarily investigates the weathering transformation characteristics of the major mineral components such as anorthite, pyroxene, and olivine on Mercury's surface and compares them to the weathering transformation model of the Moon. The experimental results indicate that ion implantation at room temperature is insufficient to generate np-Fe⁰ directly but can facilitate its formation, while prolonged exposure to solar thermal radiation on Mercury's surface can lead directly to the formation of np-Fe⁰. Therefore, intense solar thermal radiation is a crucial component of the unique space weathering transformation process on Mercury's surface.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"43 4","pages":"774 - 784"},"PeriodicalIF":1.4,"publicationDate":"2024-05-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141114281","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":"The abundance, distribution, and enrichment mechanism of harmful trace elements in coals from Guizhou, Southwestern China","authors":"Hui Hou,&nbsp;Wei Cheng,&nbsp;Ruidong Yang,&nbsp;Yan Zhang","doi":"10.1007/s11631-024-00694-2","DOIUrl":"10.1007/s11631-024-00694-2","url":null,"abstract":"<div><p>Coal seams can enrich a variety of harmful trace elements under specific geological conditions. The spatial distribution of harmful trace elements in coal is extremely uneven, and the distribution characteristics of each element content are different. The harmful elements released in the process of coal mining and utilization will cause serious harm to the environment and the human body. It is of great resource significance to study the geochemistry of coal that affects the enrichment and distribution characteristics of harmful trace elements. Based on the domestic and foreign literature on coal geochemistry in Guizhou published by previous investigators, this study counted 1097 sample data from 23 major coal-producing counties in Guizhou Province, systematically summarized the relevant research results of harmful trace elements in the coal of Guizhou, and revealed the overall distribution and enrichment characteristics of harmful trace elements in the coal of Guizhou. The results show that the average contents of Cd, Pb, Se, Cu, Mo, U, V, As, Hg, and Cr in coal of Guizhou are higher than those in Chinese coal and world coal. A variety of harmful trace elements in the coal of Guizhou have high background values, especially in Liupanshui, Xingyi and Qianbei coalfield. The enrichment of various harmful trace elements in the Late Permian coal in Guizhou is mainly related to the combined action of various geological and geochemical factors. The supply of terrigenous debris and sedimentary environment may be the basic background of the enrichment of harmful elements in western Guizhou, while low-temperature hydrothermal activity and volcanic ash deposition may be the main reasons for the enrichment of harmful elements in southwestern Guizhou.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"43 5","pages":"889 - 903"},"PeriodicalIF":1.4,"publicationDate":"2024-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140976048","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":"Fluid inclusion and H-O-S-Pb isotope systematics of the Chayong Cu-polymetallic deposit, Sanjiang Metallogenic Belt, Qinghai Province, China","authors":"Jian Wang,&nbsp;Hao Wang,&nbsp;Fengyue Sun,&nbsp;Fei Wang,&nbsp;Xiangwen Li,&nbsp;Hongju Yue","doi":"10.1007/s11631-024-00700-7","DOIUrl":"10.1007/s11631-024-00700-7","url":null,"abstract":"<div><p>The Chayong Cu-polymetallic deposit is a recently discovered Cu-polymetallic deposit hosted in the Sanjiang Metallogenic Belt within the Tibetan Plateau of China to the northeast of the North Qiangtang terrane. The ore body occurs in siltstone and is controlled by a northwest-trending fault structure. According to the associations, assemblages, and cutting relationships between ore veins, the hydrothermal mineralization period can be divided into three mineralization stages: (1) a molybdenite mineralization stage, (2) a Cu-polymetallic sulfide stage, and (3) a quartz-carbonate stage. Two types of fluid inclusions (FIs), namely, liquid and vapor-rich inclusions, are present in quartz associated with sulfide minerals. Early-stage FIs are both liquid and vapor-rich, homogenized at temperatures ranging from 364.1 to 384.2 °C, and have salinities ranging from 0.70% to 9.60% NaCl equivalent (eqv). The middle-stage FIs are also both liquid- and vapor-rich, homogenized at temperatures ranging from 272.4 to 355.6 °C, and have salinities ranging from 0.53%–17.10% NaCl eqv. The late-stage FIs are liquid, homogenized at temperatures ranging from 209.4 to 255.3 °C, and have salinities ranging from 0.35%–6.87% NaCl eqv. The samples from the deposit have δ³⁴S values of − 21.8‰ to − 19.2‰ and − 5.5‰ to − 6.0‰, suggesting that sulfur was derived from the host sediments and magmatic fluids, respectively. The metallic minerals within the deposit have ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb values of 18.439–18.458, 15.656–15.679, and 38.772–38.863, respectively, suggesting that the metals were derived from the upper crust and orogenic belts. The samples from the deposit have δ¹⁸O_W values of 2.99‰–7.99‰ and δD_W values ranging from − 84.4‰ to − 73.9‰, indicating that the ore-forming fluids were magmatic and mixed with minor amounts of meteoric water. The ore-forming fluid of the Chayong copper polymetallic deposit was a high-temperature, medium- to low-salinity H₂O–NaCl–CH₄–N₂ ± CO₂ fluid system. The early high-temperature magmatic fluid, due to boiling, decreased in temperature, and via the mixing of meteoric water, gradually evolved towards the later-stage medium- to low-temperature and low-salinity fluid, causing molybdenite mineralization and forming copper polymetallic sulfide veins and quartz carbonate veins.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"43 6","pages":"1153 - 1168"},"PeriodicalIF":1.4,"publicationDate":"2024-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141000864","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":"Metamorphic P–T conditions and ages of garnet-biotite schists in the Dahongshan Group from the southwestern Yangtze Block","authors":"Jun-xiao Ma,&nbsp;Guang-shu Yang,&nbsp;Yong-feng Yan,&nbsp;Xiao-Fei Xu,&nbsp;Yun-hua Ren,&nbsp;Hui Zhao,&nbsp;Xiao-jun Zheng,&nbsp;Yuan Qin","doi":"10.1007/s11631-024-00693-3","DOIUrl":"10.1007/s11631-024-00693-3","url":null,"abstract":"<div><p>The Dahongshan Group, situated at the southwestern margin of the Yangtze Block, represents a geological unit characterized by relatively high-grade metamorphism in the region. This paper investigates the garnet-biotite schist from the Laochanghe Formation of the Dahongshan Group, employing an integrated approach that includes petrological analysis, phase equilibrium modeling, and zircon U–Pb dating. The schist is mainly composed of garnet, biotite, plagioclase, quartz, rutile, and ilmenite. Phase equilibrium modeling revealed the peak metamorphic conditions of 8–9 kbar and 635–675 °C. By further integrating the prograde metamorphic profile of garnet and geothermobarometric results, a clockwise <i>P–T</i> metamorphic evolution path is constructed, which includes an increase in temperature and pressure during the prograde stage. LA–ICP–MS zircon U–Pb dating and zircon Ti thermometry constrains the post-peak metamorphic age of 831.2 ± 7.2 Ma. Integrated with previously reported results, it is revealed that the southwestern margin of the Yangtze Block experienced a large-scale regional metamorphism during the Neoproterozoic (890–750 Ma), which is related to the collisional orogenic process. This may be associated with the late-stage assembly of the Rodinia supercontinent or with local compression and subduction processes during the breakup of the Rodinia supercontinent.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"43 4","pages":"707 - 718"},"PeriodicalIF":1.4,"publicationDate":"2024-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141012384","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":"Origin and geochemical characteristics of beryllium mineralization in the Zabara-Wadi El Gemal region, South Eastern Desert, Egypt","authors":"Gehad M. Saleh,&nbsp;Farrage M. Khaleal,&nbsp;Mohammed Z. El-Bialy,&nbsp;Mohamed S. Kamar,&nbsp;Mokhles K. Azer,&nbsp;Mohamed M. Omar,&nbsp;Mohamed N. El Dawy,&nbsp;Ahmed Abdelaal,&nbsp;El Saeed R. Lasheen","doi":"10.1007/s11631-024-00698-y","DOIUrl":"10.1007/s11631-024-00698-y","url":null,"abstract":"<div><p>Beryl is the commercial source of beryllium and several varieties of it are valued as a gemstone. To contribute to understanding the mechanism of beryl formation, we carried out detailed geological, petrographical, and geochemical investigations on beryl mineralization occurrences in the Zabara-Wadi El Gemal (Z-WG) region. This region is an NW–SE trending tract that includes six beryl-hosting areas. The green gem variety of beryl (emerald) is restricted to phlogopite schist, pegmatite, and quartz veins. Prismatic hexagonal emerald crystals are well-developed in phlogopite schist and pegmatite. The gem variety emerald examined is sodic and Cr-dominant. It contains high concentrations of chromophore transition elements ordering Cr (up to 1511 ppm) &gt; V (up to 242 ppm) &gt; Sc (up to 245 ppm), giving rise to its vivid green color, reflecting mafic–ultramafic source contribution. Among the investigated emeralds, the Sikait area contains the highest BeO (av. 10.76wt.%) concentration. The compositional variability of emeralds is most likely attributed to the contribution from the host rocks. This is revealed by the examined emerald mineralization, for instance; the Abu Rusheid area (one of the best areas exposing rare metal-bearing granitoids) possesses the highest average of trace and REEs concentrations. In contrast, Um Kabu emerald has the highest contents of Co (av. 20 ppm), Ni (av. 299 ppm), MgO (av. 8.2wt.%), Fe₂O₃ (av. 3.12wt.%), and CaO (avg. 3.4wt.%) relative to other areas, which may be linked to contribution of ultramafic rocks exposed there. The proposed mechanism we suggest for emerald genesis is metasomatic interaction between felsic (intrusions, that are enriched with K, Na, Be, Li, and B, with mafic–ultramafic rocks that are enriched in Cr, V, Mg, Fe, and Ca. This interaction is marked by the formation of phlogopite schist, the growth of emerald crystals, and desilicated pegmatite.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"43 6","pages":"1105 - 1122"},"PeriodicalIF":1.4,"publicationDate":"2024-05-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141014214","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":"The source of lithium in Lakkor Co Salt Lake on Qinghai-Tibet Plateau, China: evidence from hydrochemical characteristics and boron isotope","authors":"Zheng Yan Li,&nbsp;Bin Kai Li,&nbsp;Mao-Yong He,&nbsp;Xue Qin Wen,&nbsp;Jiang Di Zhou","doi":"10.1007/s11631-024-00697-z","DOIUrl":"10.1007/s11631-024-00697-z","url":null,"abstract":"<div><p>The availability of lithium resources is of great significance for the development of modern technologies, as well as for civil and military industries. The Qinghai-Tibet Plateau is a region known for its abundance of lithium-rich salt lakes. However, the specific origin of lithium in these lakes is still unknown, which hinders the advancement of the lithium resource business in this region. To research this issue, this study involved the collection of 20 samples from Lakkor Co Salt Lake on Qinghai-Tibet Plateau, encompassing samples of surface brine, cold springs, fresh lakes, and recharge rivers. The composition of anions and cations in these samples was determined. Furthermore, the analysis extensively utilized the Piper three-line diagram, Gibbs model, and ion proportion coefficient. The findings of this study indicate that as the moves from the recharge water system to salt lake, there is a transition in water type from strong carbonate to moderate carbonate and weak carbonate, as well as Na sulfate. This research based on a similar source of both lithium and boron, utilized ion correlation analysis and boron isotope study in the Lakkor Co area, and analyzed the source and transporting process of lithium. The main origin of lithium in Lakkor Co is the dissolution of lithium-rich rocks, recharge water systems, and deep hydrothermal fluids. These findings are highly significant in enhancing the foundational data of lithium-rich brine resources in the Qinghai-Tibet Plateau and are beneficial for assessing the future development of such deposits.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"43 5","pages":"933 - 946"},"PeriodicalIF":1.4,"publicationDate":"2024-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142415020","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":"Harnessing machine learning tools for water quality assessment in the Kebili shallow aquifers, Southwestern Tunisia","authors":"Zohra Kraiem,&nbsp;Kamel Zouari,&nbsp;Rim Trabelsi","doi":"10.1007/s11631-024-00689-z","DOIUrl":"10.1007/s11631-024-00689-z","url":null,"abstract":"<div><p>An integrated method that implements multivariate statistical analysis and ML methods to evaluate groundwater quality of the shallow aquifers of the Djerid and Kebili district, Southern Tunisia, was adopted. An evaluation of their suitability for irrigation and/or drinking purposes is necessary. A comprehensive hydrochemical assessment of 52 samples with entropy weighted water quality index (EWQI) was also proposed. Eleven water parameters were calculated to ascertain the potential use of those resources in irrigation and drinking. Multivariate analysis showed two main components with Dim1 (variance = 62.3%) and Dim.2 (variance = 22%), due to the bicarbonate, dissolution, and evaporation and the intrusion of drainage water. The evaluation of water quality has been carried out using EWQI model. The calculated EWQI for the Djerid and Kebili waters (i.e., 52 samples) varied between 7.5 and 152.62, indicating a range of 145.12. A mean of 79.12 was lower than the median (88.47). From the calculation of EWQI, only 14 samples are not suitable for irrigation because of their poor to extremely poor quality (26.92%). The bivariate plot showed high correlation for EWQI ~ TH (r = 0.93), EWQI ~ SAR(r = 0.87), indicating that water quality depended on those parameters. Different ML algorithms were successfully applied for the water quality classification. Our results indicated high prediction accuracy (SVM &gt; LDA &gt; ANN &gt; kNN) and perfect classification for kNN, LDA and Naive Bayes. For the purposes of developing the prediction models, the dataset was divided into two groups: training (80%) and testing (20%). To evaluate the models’ performance, RMSE, MSE, MAE and R² metrics were used. kNN (R² = 0.9359, MAE = 6.49, MSE = 79.00) and LDA (accuracy = 97.56%; kappa = 96.21%) achieved high accuracy. Moreover, linear regression indicated high correlation for both training (R² = 0.9727) and testing data (0.9890). This well confirmed the validity of LDA algorithm in predicting water quality. Cross validation showed a high accuracy (92.31%), high sensitivity (89.47%) and high specificity (95%). These findings are fundamentally important for an integrated water resource management in a larger context of sustainable development of the Kebili district.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"43 6","pages":"1065 - 1086"},"PeriodicalIF":1.4,"publicationDate":"2024-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142664463","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":"Study on the spatial and temporal evolutionary characteristics of ozone concentration and the impact of human activities in China in 2019","authors":"Yongchun Wang,&nbsp;Wang Zhang,&nbsp;Yu’an Liu,&nbsp;Yazhu Wang,&nbsp;Yuting Fu,&nbsp;Zhaohui Feng,&nbsp;Lingqing Wang","doi":"10.1007/s11631-024-00695-1","DOIUrl":"10.1007/s11631-024-00695-1","url":null,"abstract":"<div><p>Ozone (O₃) pollution has a profound impact on human health, vegetation development, and the ecological environment, making it a critical focus of global academic research. In recent years, O₃ pollution in China has been on a steady rise, with ozone emerging as the sole conventional pollutant to consistently increase in concentration without any decline. This study conducted a quantitative analysis of O₃ concentrations across 367 Chinese cities in 2019, examining spatial autocorrelation and local clustering of O₃ levels, and investigated the diverse relationships between human activity factors and O₃ concentration. The seasonal fluctuation of O₃ exhibited the “M-type” pattern, with peak concentrations in winter and the lowest levels in summer. The center of O₃ pollution migrated southeastward, with the area of highest concentration progressively shifting south along the eastern coast. Moreover, O₃ concentration showed a strong positive correlation with population density, road freight volume, and industrial emissions, suggesting that human activities, vehicle emissions, and industrial operations are significant contributors to O₃ production. The results provide comprehensive information on the characteristics, causes, and occurrence mechanism of O₃ in Chinese cities that can be utilized by global government departments to formulate strategies to prevent and control O₃ pollution.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"43 5","pages":"985 - 995"},"PeriodicalIF":1.4,"publicationDate":"2024-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142415033","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":"Nitrogen isotope stratigraphy of the Early Cambrian successions in the Tarim Basin: Spatial variability of nitrogen cycling and its implication for paleo-oceanic redox conditions","authors":"Bi Zhu,&nbsp;Xuefeng Li,&nbsp;Lu Ge,&nbsp;Yongquan Chen","doi":"10.1007/s11631-024-00681-7","DOIUrl":"10.1007/s11631-024-00681-7","url":null,"abstract":"<div><p>The Early Cambrian represents a critical time period characterized by extraordinary biological innovations and dynamic redox conditions in seawaters. Nitrogen isotopic signatures of ancient sediments have the potential to elucidate the evolutionary path of marine redox states and the biogeochemical nitrogen cycle within the water column of the Early Cambrian ocean. While existing research on this topic has predominantly focused on South China, the exploration of other continental margins has been limited, leaving contradictory hypotheses untested. In this study, paired δ¹⁵N and δ¹³C_org analyses were performed on the Lower Cambrian successions from the Shiairike section (inner ramp) and Well Tadong 2 (deep shelf/basin) in the northwestern and eastern Tarim Basin, respectively. Our data from the Shiairike section reveal a discernible shift in the operation of different nitrogen cycles for the black chert-shale unit, also referred to as the black rock series in Chinese literature, of the Yurtus Formation (Fortunian stage to lower Stage 3). Oscillating δ¹⁵N values for its lower part are suggestive of alternating anaerobic assimilation of NH₄⁺ and denitrification/anammox. This is likely attributed to a shallow, unstable chemocline consistent with the upwelling and incursion of deep, anoxic waters during a major transgression. In contrast, aerobic nitrogen cycling, indicated by positive δ¹⁵N values of  &gt;2‰, dominated the upper part alongside a reduction in upwelling intensity. On the other hand, the δ¹⁵N signatures of Xishanbulake and Xidashan Formations of Well Tadong 2, which encompass a time interval from the Cambrian Fortunian Age to Age 4, are indicative of N₂ fixation by diazotrophs as the major nitrogen source. The two studied intervals, although not time-equivalent, exhibit separated states of nitrogen cycling at least during the deposition of the Yurtus black rock series. The spatially different nitrogen cycling of the studied sections is compatible with a redox-stratified ocean during the deposition of the Yurtus black rock series. The build-up of a NO₃⁻ reservoir and aerobic nitrogen cycling in seawater was largely restricted to near-shore settings whereas anaerobic nitrogen cycling dominated by N₂ fixation served as the main nitrogen uptake pathway in off-shore settings.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"43 4","pages":"785 - 801"},"PeriodicalIF":1.4,"publicationDate":"2024-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140654053","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":"The organic geochemistry of crude oil in the Saltpond Basin (Ghana): Organic source input, depositional environment, and thermal maturity","authors":"Kojo Amoako,&nbsp;Ningning Zhong,&nbsp;Nancy Pearl Osei-Boakye,&nbsp;Ebenezer Apesegah","doi":"10.1007/s11631-024-00692-4","DOIUrl":"10.1007/s11631-024-00692-4","url":null,"abstract":"<div><p>The Saltpond Basin, situated within the South Atlantic margin of Ghana, is a significant area for petroleum exploration but has received relatively limited research attention. Previous studies have examined source rock composition, but data on crude oil organic chemistry are lacking, hindering understanding of the basin’s petroleum system and evolution. To address this gap, we analyzed biomarkers and stable carbon-isotope ratios in Saltpond Basin crude oil using gas chromatography–mass spectrometry and gas chromatography–isotope ratio mass spectrometry to elucidate organic matter source, depositional environment, and thermal maturity. Findings were compared with oils from the West African segment of the South Atlantic margin, namely the Tano Basin and the Niger Delta Basin, to identify potential correlations and gain insights into regional variations. Molecular and isotopic results unveiled a significant prevalence of organic matter derived from lower marine organisms. Patterns of organic matter deposition and preservation in Saltpond oil samples suggested a suboxic marine transitional environment, contradicting conventional understanding of terrestrial dominance in such settings. Moreover, the potential for degradation processes to obscure differentiation between terrestrial and marine organic matter origins underscores the complex nature of organic matter dynamics in transitional marine environments. Analysis of molecular thermal maturity indices suggested Saltpond oils were expelled from source rocks exhibiting thermal maturity at the early maturity stage. Correlation analysis unveiled genetic disparities among crude oils sourced from the Saltpond Basin and those from the Tano and Niger Delta Basin, primarily due to variations in source input and depositional environment conditions. Saltpond oil exhibits lower terrestrial organic input than Tano Basin’s crude oils, which also have less terrestrial input than Niger Delta Basin crude oils. Additionally, its paleodepositional environment notably differs from oils in the Tano Basin (anoxic transitional marine-lacustrine settings) and the Niger Delta Basin (suboxic–oxic terrigenous deltaic or marine or lacustrine environments). Thermal maturity range of Saltpond oil is comparable to oils in the Tano Basin but lower than oils in the Niger Delta Basin. These findings provide valuable insights into petroleum generation history and unique organic geochemical characteristics within the Saltpond Basin, essential for exploration, production, and environmental management efforts in the region. Furthermore, correlation studies provide evidence that distinct biological, geological, and paleoenvironmental conditions shaped various oil types in the West African segment of the South Atlantic margin.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"43 3","pages":"424 - 440"},"PeriodicalIF":1.4,"publicationDate":"2024-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s11631-024-00692-4.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140693106","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}