Table of Content

20 December 2022, Volume 28 Issue 6

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Geochemical Characteristics of Heavy Metal Enrichment in Soil Fe-Mn Nodules in the Karst Area of Guangxi

FENG Yifu, LIAO Qilin, JI Wenbing, REN Jingli, JI Junfeng, YANG Zhongfang, ZHUO Xiaoxiong, WANG Lei, LIU Yuanyuan

2022, 28(6):  787-798.  DOI: 10.16108/j.issn1006-7493.2021079

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The natural heavy metal contaminant is severe in the Karst area in Guangxi. In this area, the soil contains large quantities of Fe-Mn nodules. Soil Fe-Mn nodules are symbiotic products of soil formation, which is controlled by the environmental conditions. Therefore, Fe-Mn nodules is a good geological record of soil formation and development, as well as historical environmental change. Fe-Mn nodules are composed of ferromanganese oxides, which have strong capacities for heavy metal adsorption. Studying the accumulation characteristics of heavy metals in Fe-Mn nodules will improve understanding the accumulation processes of heavy metals during soil formation and provide scientific support for soil management and treatment. In this study, a series of experiments were conducted using the soil and Fe-Mn nodules from a typical Karst area in Liujiang, Guangxi. Through the determination of trace elements, the analysis shows that Fe-Mn nodules can adsorb Ni, Cu, Cd, Zn, Pb, Co, Ba, As and Cr effectively. We found concentric ring structure and regular distribution of elements in nodules by means of micro measurement methods including Raman spectrum and SEM-EDS. Combined with internal structure and elemental distribution characteristics, the formation mechanism and material source of Fe-Mn nodule was speculated. The formation of Fe-Mn nodules immobilized heavy metals and reduced heavy metal pollution in soil. However, the dissolution of Fe-Mn nodules will release large amount of heavy metals into soil especially those associated with Mn.

Classification of Heavy Metal Contamination Risk in Typical Agricultural Soils by Visible and Near Infrared Reflectance Spectroscopy

LI Quankun, ZHAO Wanfu, WEN Yubo, GUO Chao, LIU Lianwen, JI Junfeng

2022, 28(6):  799-813.  DOI: 10.16108/j.issn1006-7493.2021086

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The contamination of heavy metals in agricultural soils caused by natural or anthropogenic factors strengthens the importance of soil environmental quality survey and managements. Nevertheless, the conventional methods of sampling and analysis are time-consuming and costly. Visible and near-infrared (Vis-NIR) reflectance spectroscopy is a rapid and inexpensive alternative to measure soil physical and chemical parameters. This study explored the capacity of Vis-NIR reflectance spectroscopy models for soil heavy metal contamination risk classification. We collected 390 agricultural soils from a typical anthropogenic contaminated area (Wenling, Zhejiang) and a typical high geological background area (Hengxian, Guangxi), examining the concentrations of eight soil heavy metals (As, Cd, Cr, Cu, Hg, Ni, Pb and Zn), soil pH values, as well as soil Vis- NIR reflectance spectroscopy. Partial least square regression (PLSR) and support vector machine (SVM) algorithms were used to calibrate regression models for predicting the concentrations of soil heavy metals and pH values. Based on the predicted values of spectral models, soil heavy metal contamination risk types were classified. Results showed that, the regression prediction deviation (RPD) values of spectral models for Cd and Cu, the major pollutant elements in Wenling soils, were 1.23 and 1.19, respectively. The spectral prediction mechanism is the correlation between Cd and Cu with organic matter. The two major pollutant elements in Hengxian soils are As and Cd, which had the RPD values of 1.98 and 1.93, respectively. The spectral prediction mechanism is the correlation between As and Cd with iron oxides and clay minerals. In the high geological background soils at Hengxian, there were generally strong positive correlations between soil heavy metals and iron oxides, where spectral models gave more accurate predictions for heavy metals. The RPD values of spectral models for soil pH values were 1.76 at Wenling and 1.68 at Hengxian. Spectral classification of soil contamination risk has reliable overall accuracy (75.0%~100% at Wenling, 80.0%~100% at Hengxian). Therefore, the spectral method combining with remote sensing technology is helpful for rapid classification of heavy metal contamination risk in agricultural soils.

Study on Ecological Risk of Heavy Metals in Water and Sediments in the Heilong River Basin

ZHENG Xu, GUAN Yiting, WU Weihua

2022, 28(6):  814-824.  DOI: 10.16108/j.issn1006-7493.2022005

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As a heavy industrial base and a commodity grain base in northeast China, the heavy metal pollution of water, sediment and soil in the Heilong River Basin is very worthy of attention. We collected the samples of river water, lake water, groundwater and riverbed sediment in the Heilong River Basin from the upstream arid area to the downstream Sanjiang Plain, and then analyzed the content of heavy metal elements, in order to reveal the water resources security and the degree of pollution risk of sediments by using different indexes. The results show that in the arid area of the upper reaches of the Heilong River Basin, the content of As in some surface water and groundwater exceeds the standard for drinking water quality (up to 7 times). Therefore, the safety of water for residents in upstream areas needs to be a concern. A comprehensive assessment of the indexes of Pcom and RI shows that the overall ecological risk of sediments in the Heilong River Basin was low. Among single heavy metal elements, Cd has moderate ecological risk in most watersheds, and three sediment samples show high ecological risk. Cd, as the main heavy metal element endangering the soil quality and human health in China, also needs to be paid special attention in the Heilong River Basin.


Enhanced Chemical Weathering in the Yukon River Basin in North America under the Background of Global Warming

NIE Haoyang, LI Shilei, CHEN Yang, WANG Hongtao

2022, 28(6):  825-837.  DOI: 10.16108/j.issn1006-7493.2022067

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The feedback of silicate weathering to climate change and tectonism may play an important role in regulating longterm climate change, quantitative evaluation of this feedback process will help us to more accurately understand how Earth’s carbon cycle works. It is generally believed that there are two weathering types called “supply-limited” and “kinetic-limited”. Global warming may accelerate chemical weathering in the basin under the “kinetic-limited” regimes, however, it remains poorly constrained. The Yukon River Basin is a typical “kinetic-limited” regime. Studying the response of Yukon River weathering to climate warming will help us to deeply understand the interaction between climate and continental weathering. Forward modeling is an important means to distinguish end-members of river weathering. This study estimates the decadal variations in chemical weathering rates in Yukon River Basin with a forward model based on a dataset of major ion composition of the riverine dissolved from 1975 to 2019. The results show that the water chemical properties of the Yukon River basin are mainly controlled by carbonate weathering and silicate weathering. The average annual CO2 consumption rates by silicate weathering and carbonate weathering are 2.1×10¹¹ mol/yr and 4.1×10¹⁰ mol/yr, respectively, which are in the middle level of the world’s large rivers. More importantly, during the same period, with a 2.2℃ temperature rise and an increase in discharge by 13.7%, the total flux of cation in the basin is increased by 35.7%. And the cation flux of silicate and carbonate weathering increased by 41% and 35% respectively, the sensitivity of cation flux/weathering rate to climate is in good agreement with the results from Iceland. Corresponding to the accelerated weathering rate, the carbon flux of silicate weathering increased by 59.6%. Although the increase of carbon sink is insignificant in terms of absolute flux compared with anthropogenic carbon emission by contemporary fossil combustion, the additional CO₂ sequestration may have an important impact on global climate during Earth’s history, given the increased rates of global silicate weathering within the tectonic scale, especially in the relatively cold high latitude area.

Identification of the Dust and Weathering Characteristics of the Soil Weathering from Basalt in Jiangsu and Anhui Provinces

CHEN Liao, LIU Lianwen, ZHU Xiaoyu, CAI Jie, JI Junfeng

2022, 28(6):  838-848.  DOI: 10.16108/j.issn1006-7493.2021065

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It is great significance to the identification and contribution of dust in pedogenesis，because the dust affect the global biogeochemical cycle. In this study, two typical weathering profiles (Meihua village, Mingguang County, Anhui Province and Baota village, Xuyi county, Jiangsu Province) and some surface and stream sediment samples were selected from the basaltic platform of Jiangsu Anhui Province. The main minerals, clay minerals, major and trace elements, Sr and Nd isotopic compositions of the samples were analyzed systematically. The results show that the basalt is mainly composed of plagioclase and pyroxene, and the weathered bedrock is mainly composed of montmorillonite, while the soil is characterized composed of dust minerals such as quartz and illite, which are not found in bedrock and weathered bedrock. The bedrock and weathered basalt are characterized by high Mg, low Si, K and no Eu anomaly, while the soil is characterized by high Si, K, low Mg and negative Eu anomaly. Relative to soil, the bedrock and weathered bedrock have a much higher εNd and much lower ⁸⁶Sr/⁸⁷Sr value. All mineral, element and isotope evidences show that the dust can serviced as important component of soil. Calculated by the Nd isotope mixing model, it can been foundthat the contribution of dust to the soil is more than 60%. The weathering of basalt is characterized by complete montmorillonization and significant removal of Ca and Mg. In Meihuacun section, Ce negative anomaly appears in the surface soil, while Ce positive anomaly appears in the lower layer. It is also found that the content of Si and K in the soil increases due to the accretion of wind dust. Affected by relatively large elevation difference, basalt weathering products and settled wind dust are easily eroded by precipitation, resulting in thinner weathering profile, which makes basalt weathering in “supply limited” mode. This work provides new geological evidence for the weathering mechanism of basalt and the role of wind dust in the element geochemical cycle.

Surface and Subsurface Chemical Weathering in Tropical Hainan Island: Implications for Global Carbon Cycle and Seawater Sr Isotope Evolution

PENG Jingcheng, ZHENG Xu, WU Weihua

2022, 28(6):  849-860.  DOI: 10.16108/j.issn1006-7493.2021018

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The chemical weathering of tropical volcanic island/arc plays an important role in global carbon cycle and Sr isotope evolution of seawater. In this paper, a comprehensive study of river water, groundwater, rainwater, bedrock and sediment was carried out in some small basaltic and granitic watersheds in Hainan Island, China. The element contents and 87Sr/86Sr ratios of water and solid samples were analyzed. The results show that there is a certain relationship between the chemical alteration index (CIA) and ⁸⁷Sr/⁸⁶Sr, which is mainly attributed to the different stages of weathering: in the early stage dominated by biotite weathering, ⁸⁷Sr/⁸⁶Sr is relatively high. After that, plagioclase begins to be weathered and ⁸⁷Sr/⁸⁶Sr decreases gradually. In the middle weathering stage, after a large amount of plagioclases are decomposed, the weathering of various K-rich minerals is intensified, and the ⁸⁷Sr/⁸⁶Sr value rises to the highest point. In the stage of high weathering degree, the stable weathering residual materials are dominant as the decrease of K-rich minerals, and the ⁸⁷Sr/⁸⁶Sr value declines gradually. Compared with the young active volcanic islands, for example, the Lesser Antilles Islands in the Caribbean Sea and the Reunion Island in the Indian Ocean (the subsurface chemical weathering rate is 2-5 times higher than the surface weathering rate), the underground water flow and total dissolved solids (TDS) in Hainan Island are much lower due to the relatively low rainfall and the low porosity of the old inactive volcano. As a result, the subsurface chemical weathering rate of Hainan Island is lower than that of the surface weathering, only close to the Kamchatka active volcanic island in high latitude, 6%-25% of the Lesser Antilles and Reunion Islands in tropical zone, and is one of the regions with the lowest contribution of subsurface weathering in the world. The surface chemical weathering and CO₂ consumption rates of basalt area in Hainan Island are higher than those of Massif Central, France and Siberia, slightly lower than those of Hawaii and Deccan Trap, and significantly lower than those of Java and Luzon Island in Southeast Asia. Under the condition of similar temperature, runoff has an obvious control over the chemical weathering rate. The CO₂ consumption capacity of Hainan Island in the tropical region is only in a global average range due to the low annual runoff.

Carbon and Oxygen Isotopic Composition in Shell Carbonates of Modern Land Snails in China: Distribution and Climatic Response

LUO Ling, SHEN Hua, BAO Rui, TAN Haolin, LI Chenglong, SHENG Xuefen

2022, 28(6):  861-873.  DOI: 10.16108/j.issn1006-7493.2021088

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The carbon and oxygen isotopic composition of the land snail shell can record environmental and climate information, which are important proxies for reconstructing paleoenvironment and paleoclimate. In this paper, we added the land snails’ data in Xinjiang (controlled by the westerly zone), western Sichuan (controlled by the Indian monsoon), and northeast (north end of the East Asian monsoon) under different climate conditions, analyzing the carbon and oxygen isotope composition of snail shells and combining with previous published data. The distribution and climate response of carbon and oxygen isotope composition of land snail shells in China have been evaluated. The results showed that the relationships between the carbon isotope composition of snail shells and mean annual precipitation or relative humidity are negative, whereas the relationships between the carbon isotope composition of snail shells and mean annual evaporation amount or aridity index are positive nationwide. The carbon isotope of snail shells with annual average temperature (larger than 9.5℃ ) has a negative correlation. There is no significant relationship between the oxygen isotope composition of snail shells and five climate factors, which may be caused by the different response degrees of snail shell oxygen isotope in different monsoon regions, or caused by the contrary correlations between the oxygen isotope of the snail shell and temperature in different regions. Hence the carbon isotope of snail shells can reliably record the carbon isotope variation of C3 vegetation by effective precipitation, the interpretation of the snail shell’s oxygen isotope is still unclear, and needing more studies in the future.

Geochemical Characteristics and Metallogenic Indications of Chlorite in the Caotaobei Uranium Deposit in Southern Jiangxi Province

LIU Qiang, ZHAO Kuidong, LIU Guoqi, ZHANG Di, LI Qian

2022, 28(6):  874-893.  DOI: 10.16108/j.issn1006-7493.2021013

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The Caotaobei uranium deposit is a large-scale volcanic-hosted uranium deposit in the Hecaokeng ore field in Huichang area, southern Jiangxi Province. Granites and volcanic rocks occur in the deposit, and the orebodies are mainly hosted by the cryptoexplosive breccia and shattered granites. Chlorite, a widely developed alteration mineral in the granites, volcanic rocks and ores, is taken as the research object in this paper, and its chemical compositions are analyzed by EPMA and LA-ICPMS. The results show that the chlorite in the granites and the ores is mainly iron-rich chamosite and prochlorite, while the chlorite in the volcanic rocks is mainly magnesium-rich pycnochlorite. Ionic substitution mechanisms of Fe ⇔ Mg, Tschermak (TK) and di-trioctahedral (DT) are likely important for chemical variations of the chlorite at the Caotaobei uranium deposit. Chlorite in the ores has relatively high contents of Ti, Li, Be, B, Zn, Ga, Ge, Sn, Cs, U, Rb and Ba, and shows low Th/U ratios. Crystallization temperatures of the chlorite in the ores are calculated to be 201-269℃ with an average value of 242℃, indicating the mediumlow temperatures for ore-forming fluids. The oxygen fugacity (log f O₂) of chlorite in the ores varies from -48.4 to -41.2 with an average value of -44.5; the sulfur fugacity (log f S₂) varies from -7.5 to +2.8 with an average value of -1.8. The uranium mineralization in the Caotaobei deposit was formed in an environment of low oxygen fugacity and high sulfur fugacity. 

Study on the Evolution of Groundwater Storage Variations in the Tarim River Basin Based on GRACE and GLDAS

CHEN Danhong, ZENG Xiankui, WU Jichun, GUI Dongwei, SUN Yuanyuan

2022, 28(6):  894-901.  DOI: 10.16108/j.issn1006-7493.2021012

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Located in the arid area of northwest China, the Tarim River Basin(TRB) is characterized by scarce precipitation and fragile ecology. Water resource is the key factor to maintain the social and economic development and ecological health of TRB. Here we identify the groundwater storage (GWS) variations in the Tarim River Basin from 2003 to 2019 using the Gravity Recovery and Climate Experiment (GRACE) satellite data and Global Land Data Assimilation System (GLDAS) data, and analyzes its spatial and temporal distribution. The results show that the GWS in TRB presents a decreasing trend during 2003 to 2019 , at a rate of -2.13 mm/a. The decline trend of GWS variations decrease gradually from north to south, and the GWS depletion is largest in the middle part of the southern Tianshan Mountains while the GWS increases significantly in the lower reaches of Tarim River, which was related to the emergency ecological water transport in the past decade. Besides, the GWS variations in the TRB are consistent with annual precipitation anomalies. With less precipitation, i.e., 2004, 2006-2009，GWS in the TRB decreases significantly，while increases correspondingly during rainy year. The method based on GRACE and GLDAS data has great potential applications in analyzing GWS variations for monitoring groundwater resources in the Tarim River Basin, which lacks of groundwater monitoring networks.

Study on the Effects of Various Environment Temperatures and Sand Contents on Shrinkage and Cracking of Clayey Soil

LU Yi, BU Fan, CAI Tianlu, GONG Xulong, LU Hua, WAN Jiajun, WANG Zi, GU Kai

2022, 28(6):  902-910.  DOI: 10.16108/j.issn1006-7493.2021099

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In either a engineering construction or a natural environment, the processes of shrinkage and cracking of soil due to water loss are affected by multiple factors, and the interactions among the factors are very complex. Among these factors, changes in temperature conditions affect the beginning and ending of cracking, which plays a vital role. But there is little information about the influence of internal viscosity and sand ratio on crack development. In this study, a series of indoor evaporation tests are carried out under different environmental temperatures and sand content conditions. By recording the internal water loss and the development of surface cracks, the crack ratio and the geometric shape of the crack networks are quantitatively analyzed using relevant graphic analytical software, which allows to explore the influence mechanism of different temperatures and sand contents on soil shrinkage and cracking. The finding may provide some references for the evaporation and crack development of sand-clay mixture in practical engineering and environment. The results show that: (1) The existence of sandy soil led to changes in the internal structure of the soil and changes in some water conveyance channels, which prolonged the migration path of free water; (2) The existence of sand resulted in early cracking of the soil surface, which is less affected by sand contents and related to whether it contains sand or not; (3) The higher the sand content in the soil, the shallower the depth of crack development and the shorter the extension length of crack. At the same time, the width of a crack is inversely proportional to sand content; (4) Under the condition of the same sand content, the higher the environmental temperatures, the higher the water evaporation rates and the width of cracks formed on the soil surface, i.e., surface cracks, are generated in advance to a certain extent.

Genetic Mechanism of the Geothermal System in Shulu Sag, Jizhong Depression

GAO Nanan, WANG Xinwei, LIANG Haijun, DU Li, MAO Xiang, LUO Lu, WANG Tinghao

2022, 28(6):  920-932.  DOI: 10.16108/j.issn1006-7493.2021014

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Analyzing the characteristics of geological factors in a geothermal system is the basis to establish its genetic model and to evaluate the geothermal resource. Combined with previous research and regional geothermal well data, we analyze the main geological factors including “source, reservoir, migration, and cap” of the geothermal system in the Shulu Sag, Jizhong Depression with an aim to establish the genetic model of the geothermal system and to evaluate geothermal resources. The Shulu Sag is a typical Cenozoic half graben, where heat may be supplied by a low-resistance body about 20 km in the deep crust. The Guantao Formation (Fm) sandstone thermal reservoir and Ordovician karst thermal reservoir make up two sets of geothermal systems, respectively. The sandstone thermal reservoir in the Guantao Fm is stably distributed in the whole area with itsbottom boundary at depth between 1100-2000 m. The reservoir is about 200-320 m thick with 15%-35% porosity. The permeability can reach up to 1200 mD. The temperatures at its bottom boundary are mostly 57-78℃; The distribution of the Ordovician carbonate reservoir is controlled by the half-graben and the reservoir shows a monoclinal dip with its top boundary at depth of 1800 to 6000 m. The reservoir is about 100 to 550 m thick with the porosity of mostly 2 to 18% and permeability of mostly 0.5 to 50 mD. The wellhead temperatures of the thermal reservoir are about 75-92℃. The two geothermal systems are replenished by atmospheric precipitation from the Taihang Mountains to the west of the study area. Water migrated along the unconformity of the layers and the faults, then warmed by deep heat conduction and local heat convection, and finally enriched in the reservoir. The overlying loose Quaternary sediments and Minghuazhen formations fluvial clastic sediments are 300-1400 m thick with thermal conductivity of 0.9-1.8 W/(m·K), and thus can be a good cap layer. Evaluation of the geothermal resources in the Shulu Sag shows that the sandstone geothermal system of the Guantao Fm contains 244.430×10⁸ GJ and the Ordovician karst geothermal system contains 203.752×10⁸ GJ. The total amounts to 448.182×10⁸ GJ, which is equivalent to 15.296×10⁸ t standard coal. The annual geothermal resources can meet the heating area of 1.106×10⁸ m2. Therefore, the development potential is huge.

Geothermal Regime of the Deep Area of the Qiongdongnan Basin, Northern Continental Margin of the South China Sea

WU Di, LI Xianglan, LIU Shaowen, ZHU Jitian, LI Xudong, XIONG Xiaofeng, YIN Hongwei

2022, 28(6):  933-942.  DOI: 10.16108/j.issn1006- 7493.2021017

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The accurate knowledge of geothermal regime of sedimentary basins holds importance for investigating basin formation dynamics and hydrocarbon potential assessment as well. The Qiongdongnan Basin is a key area of deep-water hydrocarbon exploration and development in the northern South China Sea, but the geothermal regime of the deep water area in the basin is still open. Combined the corrections of formation temperature data of 21 new drilling wells with measured rock thermal properties, the basic characteristics of the present-day geothermal field in the Qiongdongnan Basin were presented here. Our results show that the heat flow data in the study area are mainly concentrated in the range of 60-90 mW/m2, with the mean of 73.2±8.67 mW/m². Most of the geothermal gradients in the study area are concentrated in 30-50℃ / km, with an average of 39.4±4.86℃ / km. In addition, both the heat flow and the geothermal gradient show the similar trend and featured by higher in deep-water area and lower in the shallow water area. The average heat flow of the deep-water area is 16 mW/m2 higher than that in the shallow water area. The average geothermal gradient for the deep-water area is 10℃ /km higher than that in shallow water. This is mainly due to the differential extension and thinning of the lithosphere and thermal blanketing effects of the sediments. In addition, there is an anomaly high heat flow zone in the Changchang sag, with the mean of 94.5±6.4 mW/m2, which is the results of Late-Miocene magmatic intrusion and fracture activities. The results mentioned could provide new geothermal parameters for basin modeling and hydrocarbon potential assessment of the Qiongdongnan Basin.

Tectonic and Sedimentary Evidences for Oil and Gas Exploration Targets and Prospects of the Ediacaran-Cambrian Petroleum Systems in the Northern Oman Basin (Block 5)

CHEN Jie, LIANG Xiao, TONG Mingsheng, ZHANG Jianli, LIU Lang, XU Jianliang, CHENG Liang, LIU Ruolin, YANG Cheng

2022, 28(6):  943-957.  DOI: 10.16108/j.issn1006-7493.2021020

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As one of the most representative petroliferous basins worldwide with the development of ancient petroleum systems, the Ediacaran-Cambrian petroleum systems in the northern Oman Basin has typical geological features of complex tectonics in deep strata. This results in the difficulty of oil and gas exploration. Based on the study of the petroleum geology characteristics (including source rocks, oil-source correlation, structural traps, etc), combined with addressing global paleo-tectonic background during the Late Neoproterozoic-Early Paleozoic and sedimentary patterns of the Ediacaran-Cambrian transition period, this study analyzed the exploration potential and risk of the regional petroleum systems in the northern Oman Basin. Results showed that the subduction and aggregation of the South China Block (distant from the Proto-Tethys Ocean) towards to the northern edge of the Gondwana Continent in the Early Paleozoic caused the Oman (Arabia) Basin and the Sichuan (Upper Yangtze) Basin share similar tectonic and sedimentary features during the Ediacaran (Sinian)-Cambrian. The interpretation of the deep seismic profiles revealed a typical extensional structure in the Early Cambrian northern Oman Basin, temporarily termed as “North Oman intracratonic sag”. The paleogeomorphic highlands on both sides of the intracratonic sag develop potentially high-quality dolomite reservoirs, e.g., the Buah and Birba formations. The formation of intracratonic sag is conducive to the deposition of highquality source rocks such as the U/Athel and Dhahaban formations. Petroleum geology evaluation of deep strata indicated that the low assemblage of the northern Oman Basin (Block 5) has good oil and gas exploration prospects.