Table of Content

23 June 2021, Volume 35 Issue 03

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Ore Deposits

Geochemical Characteristics and Genesis of the Longwangmiao Graphite Deposit in Xixia County,North Qinling

YAN Kun, YANG Yanwei, WANG Liwei, ZHU Rongbin, LU Yunshen, ZHAO Hui

2021, 35(03):  589-598.  DOI: 10.19657/j.geoscience.1000-8527.2021.03.01

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The Longwangmiao graphite deposit in Xixia is located in the southern branch of the eastern Zhuyangguan-Liuquanpu graphite metallogenic belt in the North Qinling Mountains. The orebody occurs in the middle-deep regional metamorphic rock series of the Paleoproterozoic Qinling Group, and the original rock belongs to the terrigenous clastic rock-carbonate sandwiched basic volcanic rock sedimentary formation. The orebody is layered and quasi-layered, and the local occurrence is lenticular. The ore structure is mainly scaly, and a small amount of ore is disseminated or massive. The ore is mainly composed of calcite marble containing graphite (ribbon). The major elements are characterized by low Si, low Al, low alkali, high CaO and high LOI. The analysis of trace elements shows that large ion lithophile elements such as Rb, U, Th, La and Sm are enriched, while high field strength incompatible elements such as Ba, Nb and Ti are deficient. The Sr/Ba ratio ranged from 0.55 to 3.30, with an average of 2.07. The Rb/Sr ratio ranged from 0.02 to 1.15, with an average of 0.28. The content of ∑REE is on the high side, the differentiation degree of REE is high, the LREE is richer than HREE, and the negative anomalies of Eu and Ce are obvious, indicating that the protolith of the graphitic metamorphic rock series may have been formed in the marine tectonic environment of the passive continental margin. Comprehensive analysis shows that the Xixia Longwangmiao crystalline graphite deposit is an organic genetic regional metamorphic crystalline graphite deposit with obvious characteristics of superimposed heating metamorphism and tectonic transformation in the later stage of deposit formation.

Geochemical Characteristics and Genesis Analysis of Daheba Epimetamorphic Graphite Deposit in Wangcang, Sichuan Province

DUAN Wei, TANG Wenchun, LI Longchang, RAN Qiang, ZHANG Fei, LI Xiaosong, XU Yongsheng

2021, 35(03):  599-607.  DOI: 10.19657/j.geoscience.1000-8527.2021.03.02

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Daheba graphite deposit is a newly discovered large phanerocrystalline graphite deposit in the southern margin of Micangshan, northern Sichuan. The geological characteristics of the deposit and the geochemical characteristics of major, trace elements and rare earth elements of minerals are studied in the paper. The results show that the ore bearing strata are parametamorphic rocks. The original rock deposition of graphite ore body in Daheba mining area is under anoxic reduction environment, and the protolith is composition of carbonaceous clayey fine to silt stone and carbonaceous marlite. The characteristics of trace elements indicate that the ore body is mainly composed of terrigenous clastic sediments. The sedimentary water is mainly fresh to brackish water with low salinity and uneven mixing. The average value of ∑REE of the ore is 150×10 ^-6, which is similar to marlite; The average value of δCe is 0.91, Ce indicating weak negative anomaly; The average value of δEu is 0.67, Eu is negative anomaly and has the characteristics of coastal tidal flat facies deposition; The δ ¹³C values of the ore bearing rocks ranged from -21.4‰ to -19.0‰, with an average of -19.86‰, indicating that the main source of metallogenic carbon is organic carbon, which may be mixed with some inorganic carbon. The genetic type of the deposit is sedimentary metamorphic. The metamorphism may be multiple regional metamorphism and superimposed migmatization.

Geochemistry

A Novelty Method of REE Parameter Diagrams: A Case Study of Petrogenesis of Bairendaba-Weilasituo Dioritoids in Inner Mongolia

ZHAO Baoju, YAN Kai, XIAO Rongge

2021, 35(03):  608-624.  DOI: 10.19657/j.geoscience.1000-8527.2021.03.03

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REE parameter diagrams are important tracers for geochemical and geological studies which show potential for the rapid determination of petrogenesis and magma source. By using REE and SiO₂, LREE and LREE/HREE, δEu and LREE/HREE diagrams of dioritoids, we investigate the correlation among REE parameters taking the Bairendaba-Weilasituo dioritoids as an example. Through field petrological observation and whole-rock geochemical data, new REE parameter diagrams and REE R-type cluster analysis, this paper studied the petrogenesis and magma source. The results show that the Bairendaba-Weilasituo dioritoids have high SiO₂, Na₂O, MgO, and Al₂O₃ contents, and belong to the calc-alkaline series, indicating the mixing source of magma from both the mantle and the lower crust. The high-REE values of the Bairendaba-Weilasituo dioritoids respectively show negative correlation and positive correlation between LREE/HREE-REE and δEu-LREE/HREE, and show obviously negative Eu anomaly. They are enriched in Rb, Th, U, and K, and depleted in Nb, Ta, Sr, P, and Ti, whereas the low-REE values show absolutely contrary characteristics. We concluded that this suite of calc-alkaline dioritoids were originated from the mantle substance dominated by hybrid crust-mantle mixing magma associated with an active continental margin. The developed method can be used for estimating petrogenesis and magma source in Bairendaba-Weilasituo calc-alkaline dioritoids refe-rence materials. This empirical method shows great potential for the rapid determination of petrogenesis and magma source in large batches of samples commonly analyzed for mineral exploration and REE geochemistry studies.

Cadmium Bioavailability and Influencing Factors of Soil-rice System in Nanliujiang Catchment of Guangxi

SHAO Yuxiang, YANG Zhongfang, WANG Lei, ZHUO Xiaoxiong, ZHANG Qizuan

2021, 35(03):  625-636.  DOI: 10.19657/j.geoscience.1000-8527.2021.03.04

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The alluvium soil in the Nanliujiang Catchment had the characteristics with low Cd contents in soils but high Cd contents in the rice seeds grown in there. In order to understand the distribution and transfer of Cd in the soil-rice system of the Nanliujiang Catchment, We collected rice and soil samples from different parent material in this region and analyzed the rice Cd and soil Cd, pH, Corg, N, S, Mn and oxides. Meanwhile, seven-step sequential extraction experiments were performed on some of the soil samples to find the representative bioavailability of Cd in soil-rice system. The results showed that compared with different parent soils, the Cd contents of the soils in order for the limestone soils>the upstream alluvium soils>the midstream alluvium soils>the downstream alluvium soils>the clasolite-produced soils, which was contrary to the order of Cd contents in rice seeds grown in these areas, and no significant correlation was observed between Cd contents in rice seeds and in cultivated soils (r=-0.030,p=0.84). It was revealed that total soil Cd content cannot represent bioavailable Cd content absorbed by rice. Water-soluble Cd in the soil was thought to be the main species in Cd translocation from soil to seed, according to its significant correlations between them. With the increase of soil pH, CaO, Mn, and soil organic carbon (Corg), the proportion of water-soluble Cd decreased significantly(r=0.12-0.45). This information may be of great significance for proposing effective measures to reduce the Cd contents of rice in the Nanliujiang Catchment.

Analysis of Soil Selenium Bioavailability and Its Influencing Factors Based on DGT Technology

JIANG Tianyu, YU Tao, HOU Qingye, QI Hongbin, WANG Jue, MA Xudong, YANG Zhongfang

2021, 35(03):  637-646.  DOI: 10.19657/j.geoscience.1000-8527.2021.03.05

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Se is one of the important trace elements in the environment, and the accurate evaluation of its bioavailability has always been controversial. Sixty sets of crop and root soil samples were collected in Linshui County, Guang’an City, Sichuan Province, and the Se content, physical properties, and chemical properties of crops and soil were analyzed. Results showed that the total Se content in the soil of the study area ranged from 0.15 mg/kg to 2.42 mg/kg (average=0.48 mg/kg). The total Se content of the different types of soil in the study area was considerably different and followed the order: lime soil (1.06 mg/kg)>yellow soil (0.78 mg/kg)>purple soil (0.28 mg/kg)>paddy soil (0.27 mg/kg). The organic matter and the total Fe₂O₃ (TFe₂O₃) contents of the lime and the yellow soil samples were remarkably higher than those of the other types of soil. The content of the DGT-Se in the different types of soil in the study area was evidently different. The correlation analysis showed that the soil DGT-Se was significantly related to the total Se, TFe₂O₃, S, organic matter, and Al₂O₃ contents and pH of the soil (p<0.01). The influence of its physical and chemical properties led to differences in the DGT-Se in the different types of the soil. The content of the DGT-Se in the soil of rice roots was significantly positively correlated with the Se content in rice seeds (r=0.55, n=29, p<0.01). The DGT could be used as an indicator for the bioavailability of the soil Se in the rice-root soil system. The type, physical properties, and chemical properties of the soil should be fully considered in the evaluation and the prediction of the available Se content of agricultural soils on a regional scale on the basis of the DGT technology.

Water Resources and Environmental Geology

Grain Size Characteristics and Sedimentary Dynamics of Sedimentary Column of Mangrove Wetland in Zhanjiang Bay

LUO Songying, QUAN Xiaowen, CHEN Bishan, QIU Jinkun, LIANG Jiaxin, DENG Ziyi

2021, 35(03):  647-656.  DOI: 10.19657/j.geoscience.1000-8527.2020.101

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Granularity is an important parameter for understanding the sedimentary dynamics characteristics. Mangrove wetland sediments host much sedimentary environment information during the transport and deposition processes. To unravel the vertical grain size characteristics and sedimentary dynamics of mangrove wetland in the Zhanjiang Bay and enhance wetland ecological protection, the grain size parameter characteristics, frequency distribution curve, and sedimentation rate of mangrove wetland sedimentary columns at the Nanhaidi (NHD), Dongtoushan Island (DTSD), Huguang Town (HGZ)and Guanhaichanglang (GHCL)stations were analyzed. Our work reveals the sedimentary evolution of the Zhanjiang Bay in the past century, and our results suggest that: (1)The ²¹⁰Pb_ex specific activity of NHD and DTSD columns both show a good exponential decay trend, with the deposition rate increasing with time. The average deposition rates of NHD and DTSD were 1.277 cm/a and 1.034 cm/a, respectively, but that of DTSD far exceeded that of NHD after 2011. (2)Grain-size characteristics of individual sedimentary column is markedly different, and the average grain size of NHD sedimentary column is 3.42ϕ, mainly composed of sand (67.23%)and is classified as silty sand. The mean diameter of DTSD is 5.71ϕ with sorting coefficient of 2.21. It is mainly composed of silty-sand (55.13%)and is classified as sandy-silt. HGZ is sandy-silt with mean particle size of 5.49ϕ. The GHCL is mainly composed of sand (55.85%)with average particle size of 4.18ϕ. (3)The grain size frequency distribution curves display multimodal features, implying that the deposition process was doped with the process of various sedimentary media. The NHD and GHCL particle sizes are clustered toward the sandy particle end-member, indicating strong sedimentary dynamics, whereas the sedimentary dynamics of DTSD and HGZ is considerably weaker. (4)The grain-size characteristics are influenced by the local terrestrial source, island and runoff, whilst the sedimentation process is significantly influenced by the tidal current dynamics, mangrove distribution, and human activities. In recent years, the rising sedimentation rate in the Zhanjiang Bay may have an impact on the navigation channel, and more attention should be paid to the wetland ecological environment in the bay.

Grain Size Features of Surface Sediments from Populus Euphratica Echo Dunes in the Brikum Desert

KONG Xiao, LAI Fengbing, CHEN Shujiang, ZHU Xuan

2021, 35(03):  657-664.  DOI: 10.19657/j.geoscience.1000-8527.2020.057

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To determine the types of surface sediments, the sedimentary environment stability, and the surface wind power, we studied the surface grain size characteristics of the populus euphratica echo dunes, which were common in the Brikum Desert. About 195 surface sediment samples were collected from six sites, and analyzed via grain size-standard deviation, Sahu genetic discrimination, and the related statistical analysis methods. The results show that: (1) Grain size composition of the surface sediment samples is dominantly sand and silt, and the grain size decreases from north to south and from east to west; (2) Average grain sizes are in the range of very fine or fine sand. About 71.79% of the sediment samples were well sorted, and 97.94% of the samples are near-symmetrically distributed, and all the samples have a medium peak state; (3) Particle size-standard deviation curves of the six sampling sites all show a multi-peak distribution, indicative of an unstable deposition environment; (4) Discriminant values of the surface sediments from the six sites range from -7.277 to -5.912, suggestive of aeolian deposition products.

Temporal and Spatial Distribution of Evapotranspiration in the Sanjiangyuan Region

GAN Haihong, JIN Xiaomei, ZHANG Xucai, ZHU Xiaoqian

2021, 35(03):  665-674.  DOI: 10.19657/j.geoscience.1000-8527.2020.075

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Located in the southern Qinghai Province in China, the Sanjiangyuan region contains the headwaters of the three great rivers of Yangtze, Yellow and Lancang. The Sanjiangyuan region is the highest natural wetland and the largest nature reserve in China, with fragile eco-environment. Groundwater evapotranspiration (ET) assessment is important for evaluating the water cycle and water resource in the region, which is crucial for eco-environmental protection. Based on MODIS data with moderate resolution in this study, the regional ET of the Sanjiangyuan region was estimated for the period of 2001-2017 with the Surface Energy Balance System. The Sen+Mann-Kendall method was used to analyze the temporal-spatial variation trends, and the influencing factors were discussed. The results show that in the Sanjiangyuan region: (1) ET increased from 2001 to 2017; (2) the areas (from highest to lowest annual average ET) are the Lancang River, Yellow River, and the Yangtze River headwaters; (3) over 62.62% of the region has a major ET increasing trend, while 28.03% of the region has a minor increasing trend, and areas with significant ET decrease barely exist; (4) ET variation is positively correlated with precipitation and air temperature, with the correlation coefficients of 0.80 and 0.89, respectively; (5) variation of ET is positively correlated with NDVI and soil moisture.

Hydrogeological Features and Groundwater Enrichment Model of Paleogene Zhujiagou Formation in Lower Chaiwen River Valley, Shandong Province

LI Bo, WU Xuan, ZHANG Yifei, XU Congcong, LIU Chunwei, GUAN Qin, LUO Fei

2021, 35(03):  675-681.  DOI: 10.19657/j.geoscience.1000-8527.2020.041

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The Paleogene Zhujiagou Formation in south-central Shandong comprises a molassic sequence dominated by calcareous breccia, and has markedly varying water-yield properties caused by faults. Based on the regional hydrogeological survey in lower Chaiwen River valley, the aquifer characteristics, water-yield properties, and groundwater hydrochemical characteristics are analyzed. The results show that the Zhujiagou Formation comprises calcareous cemented calcirudite, and karst is developed above 90 m depth with single-well yield of 100-300 m³/d, locally reaching >300 m ³/d. Groundwater in the fissured or karst aquifers in the southern Wenkou Basin are similar, indicating close interactions between the two. The Gibbs map demonstrates that the groundwater hydrochemical features are dominated by rock-weathering, and evaporation and concentration. The ions in the groundwater are mainly sourced from rock dissolution and anthropogenic pollution. Based on drill-hole data analysis, the groundwater enrichment model is a fracture-type calcirudite karst-fissure water storage one, and we consider that fractured clastic rocks can be used as an emergency water exploration target.

Characteristics and Formation Mechanism of Strontium-rich Groundwater in Malian River Drainage Basin, Southern Ordos Basin

LI Haixue, CHENG Xuxue, MA Yuekun, LIU Weipo, ZHOU Bin

2021, 35(03):  682-692.  DOI: 10.19657/j.geoscience.1000-8527.2020.037

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The Malian River drainage basin is located at the loess plateau in the southern Ordos Basin, in which the groundwater can be divided into the loess phreatic water, bedrock phreatic water and bedrock confined water based on the storage medium and burial conditions. Using 295 sets of groundwater hydrochemical data collected from 2015 to 2018, we analyze the Sr²⁺ concentration level, vertical and downstream distribution characteristics in the groundwater, and study the source and enrichment cause of Sr²⁺ in groundwater through factor correlation analysis. The results indicate that the groundwater Sr enrichment in the Malian River drainage basin is distinct, with the average Sr concentrations in the loess phreatic water, bedrock phreatic water, and bedrock confined water being 1.14 mg/l, 1.39 mg/l, and 5.24 mg/l, respectively. The Sr enrichment is mainly led by the water-rock interaction of Sr-bearing minerals. Major sources of Sr²⁺ in the loess phreatic water, bedrock phreatic water, and bedrock confined water are leaching from the carbonates and aluminosilicates, carbonates and sulfates, and carbonate minerals, respectively. The Sr²⁺ concentration in groundwater gradually increases along the flow direction, but varies with depth in different areas.

Groundwater Renewability Study Based on Tritium (³H) in the Middle and Lower Watershed of Anyang River

HUANG Xiangui, PING Jianhua, YU Yan, ZHU Yaqiang, ZHANG Min

2021, 35(03):  693-702.  DOI: 10.19657/j.geoscience.1000-8527.2020.066

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Groundwater renewable ability in the middle and lower watershed of Anyang River are studied by analyzing the tritium concentration of water, groundwater age and mean annual renewal rate (MARR). The MGMTP is employed to reconstruct the ³H concentration of atmospheric precipitation in the study area (1953-2016), whilst the groundwater age and MARR of phreatic water and springs are assessed via Lumped Parameter Modelling (LPM) and the method developed by Le Gal La Shalle et al., respectively. The results indicate that: (1) Phreatic water and springs received atmospheric precipitation recharge over the past 20 years, and the recharge and flow condition of the unconfined groundwater extended widely due to the regional hydrogeological control. (2) The mean residence time of the Xiaonanhai spring is 23 years, associated with 3.6% of MARR and its flux has been attenuating. (3) Unconfined groundwater in the empennage of the Anyang River alluvial/proluvial fan and recharge area has considerable renewable capacity, as it received direct recharge from infiltrated atmospheric precipitation and surface water leakage. Groundwater from the middle zone of the fan to the Beijing-Hongkong-Macao highway is 40-60 years old, and is largely sourced from modern atmospheric precipitation. Nevertheless, that in frontal belt of the fan has very low renewable capacity due to its mixing nature between modern groundwater and older input, with average age not younger than 60 years. (4) Deep confined groundwater in both the eroded hills and alluvial and flood plain is very old and has thus low renewability. This indicates that protection of the Xiaonanhai spring should be increased, and considerable achievement should be obtained in short period of time. The underground water depression cone in the Anyang city urban area has been substantially shrunk by the water supply from the Middle-Route of South to North Water Transfer Project, and the restriction on groundwater exploitation.

Hydrogeochemical Characteristics and Genesis of Zhuhe Hot Springs in Zhaojue, Sichuan Province

LU Li, CHEN Yudao, DAI Junge, WANG Zhe, ZOU Shengzhang, FAN Lianjie, LIN Yongsheng, ZHOU Changsong

2021, 35(03):  703-710.  DOI: 10.19657/j.geoscience.1000-8527.2021.061

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Zhaojue, a national-level poverty-stricken county in Sichuan Province, is located in the extended Ganzi-Xinlong-Litang geothermal field. Revealing the geothermal heat cycling mechanism of Ganzi-Xinlong-Litang geothermal field in western Sichuan would help to alleviate local poverty and rationally develop and utilize geothermal resources. In this study, the Zhuhe hot springs in Zhaojue were analyzed for their hydrochemistry and H-O stable isotopes. The results show that the Zhuhe hot springs are HCO₃-Na-type, whilst the temperature of the supply area is about 14.71 ℃, and the supply elevation is 3,345-3,560 m. The mixing model and the silicon-enthalpy model were used to estimate the proportion of cold water mixing in large hot springs, which yielded 77.00% and 75.95%, respectively. Similar estimation yielded 81.00% and 78.61%, respectively, for small hot springs. The depths of heat storage cycle were estimated to be 3,426.38-3,766.81 m. Formation of the Zhuhe hot springs are likely controlled by the Mufoshan and Zhuhe faults. During the deep geothermal circulation, the spring water likely mixed with shallow cold water and reacted with the wallrocks. The exposed surface formed the medium-low temperature geothermal resource centered on “large hot spring and small hot spring”.

Fe/Ag Catalytic Ozonation for the Degradation of Phenol

HOU Ying, XU Jinming, LI Ping, MAO Junyan, ZHANG Yuanhao, SU Junjie, CHEN Nan, HU Weiwu

2021, 35(03):  711-719.  DOI: 10.19657/j.geoscience.1000-8527.2020.061

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To study the effect of bimetallic catalysts on the removal of organic pollutants, the simulated phenol wastewater was subjected to Fe/Ag catalytic ozonation treatment. The catalyst was characterized by various characterization methods (SEM, BET and XRD), and the degradation effects due to the different catalyst types and dosages and initial pH were evaluated. The results show that compared with Fe, the specific surface area of Fe/Ag is reduced by 22.8%. In the reaction system of Fe/Ag/O₃ and phenol-containing wastewater, the reaction follows the mechanism of direct action of ozone and the free radicals (·OH, ·O₂, H₂O₂). Fe/Ag and ozone show good synergistic effects in the reaction. The phenol and COD removal rate were, respectively, 18.4% and 29.4% higher than that of ozone oxidation alone (initial phenol concentration=300 mg/L, catalysts dosage=1.00 g, and initial solution pH=6.3).

Experimental Study on Mechanism of Heavy Rainfall-induced Loess-mudstone Landslides in Tianshui Area,Gansu

HAN Shuai, SUN Ping, LI Rongjian, ZHANG Jin, LI Xiaobin, ZHU Enzhen

2021, 35(03):  720-731.  DOI: 10.19657/j.geoscience.1000-8527.2020.024

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Rainfall-induced loess-mudstone landslide disasters are common every year in the Tianshui area (Gansu Province), causing significant loss of life and property. Based on field geological survey, engineering geological drilling, and rock and soil mechanics analyses, and through laboratory large-scale physical modelling experiment, we explore the dynamic deformation process of heavy rainfall-induced landslides (which are characterized by loess-mudstone bimodal structure), and reveal the failure mode and mechanism for this type of landslide. The results show that the slope deformation is mainly manifested as sliding damage under heavy rainfall. The role of water is mainly on increasing the soil weight and pore water pressure, and decreasing the soil strength, effective stress, and sliding resistance of the structural surface. Meanwhile, the failure mode of landslide is mainly manifested by slope shoulder erosion→microcrack growth and interconnection→local failure→overall sliding failure. Our findings are important for early-stage landslide recognition and provide scientific basis for landslide-related disaster prevention in the region.

Failure Mechanism of the Changhe Landslide on September 14, 2019 in Tongwei, Gansu

WANG Haojie, SUN Ping, HAN Shuai, ZHANG Shuai, LI Xiaobin, WANG Tao, XIN Peng, GUO Qiang

2021, 35(03):  732-743.  DOI: 10.19657/j.geoscience.1000-8527.2020.073

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A large loess landslide occurred in Xiaozhuang Village (Tongwei, Gansu Province) at around 11:00 am on September 14, 2019. About 800×10⁴ m³ of a historical sliding mass was reactivated by rainfall, and slipped down along a weak interface. The sliding mass destroyed several roads and the Yangpo bridge. Preliminary estimation of 2,975 people in one township and two villages of Tongwei County were affected, causing a direct economic loss of 23.47 million yuan in agriculture, water conservancy, power supply, and infrastructure. Based on site investigation, unmanned aerial vehicle photography and numerical simulation, the deformation and failure characteristics of this landslide are described in detail, and the failure mechanism are preliminarily assessed. The main factor that affected the slope stability is the post-seismic interaction of rainfall and creep, and the failure process comprise five stages: pre-earthquake, earthquake damage, creep weakening, rainfall triggering and final sliding. Sinkholes and underground rivers were well developed in the slope, and represent the key control of the landslide boundary. Strong deformation and failure occurred at the trailing and leading edges of the landslide, but the deformation in the middle was relatively weak. We infer that the landslide was a traction-movement composite one controlled by topography and ground water. Understanding the conditions and mechanism of the Changhe landslide is hugely important for the early identification and risk prevention of similar landslides in the loess region of northwestern China.

Genetic Model, Outbreak Features and Prevention of Post-seismic Deep-cut Trough-type Debris Flow: An Example from Yazhagou of Jiuzhaigou, Sichuan Province

ZHANG Luming, YANG Dong, ZHOU Yong, LIU Peng

2021, 35(03):  744-752.  DOI: 10.19657/j.geoscience.1000-8527.2020.034

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Taking the Yazhagou debris flow in Jiuzhaigou earthquake area of Sichuan as an example, the outbreak features, the critical rainfall and the origin are studied in detail through geological surveys and historical data analysis. Based on the analysis of the formation cause, the corresponding prevention and control schemes are proposed. The results show that the debris flow is featured by being concealed, sudden, and destructive, with strong sediment transport capacity. The critical rainfall of debris flow outbreak is only half of that before the 12^th May Wenchuan Earthquake, and no debris flow was reported in this area since 2014, indicating that the critical rainfall has a gradual recovery trend. Short bursts of heavy rainfall, deep-cut trough-type material supply, and elevated-steep topography are the root causes of the debris flow outbreak. The debris-flow genetic model includes the components of rainfall seepage, saturated rock and soil, mountain flood impact, deep-cut trough, headward erosion, scour erosion, bank erosion collapse, suspension and rolling. Controlling of Yazhagou debris flow in the earthquake area requires the protection standard and optimization of the control structure. Effective prevention and controlling method require mainly source control supplemented with debris obstruction. Our findings provide reference for the prevention and early warning of similar debris flows across the region.

Development Characteristics of Huozigou Debris Flow at Nanwandao,Yanqing District, Beijing

SUN Yongbin, WANG Shen, GAO Lihui, WANG Ruijun, WANG Feng, DONG Shuangfa, WANG Bing, ZHANG En, LI Cunjin

2021, 35(03):  753-762.  DOI: 10.19657/j.geoscience.1000-8527.2021.024

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In this study, we investigated the Huozigou debris flow at Nanwandao(Yanqing district, Beijing). Through careful investigation and historical data statistics, the development characteristics and formation conditions of the debris flow are unraveled. Dynamic characteristics of the debris flow are studied comprehensively, and the risk area of debris flow are predicted and evaluated, and the corresponding prevention and control measures are proposed. The results show that the dynamic reserve of loose deposits in the debris-flow gully is 18.47×10⁴ m³, which contains four kinds of supply sources, including alluvial diluvial, residual deposit, artificial deposit, and landslide. The debris-flow development stage is in the decline phase. According to the dynamic analysis, the peak flow value is 52.53 m³/s for once-in-a-decade rainfall, 59.25 m³/s for once-in-a-decade rainfall, 68.13 m³/s for once-in-a-50-year rainfall, and 74.85 m³/s for once-in-a-century rainfall, with the total volume of one solid outfall being 0.77×10⁴ m³, 0.87×10⁴ m³, 1.00×10⁴ m³, and 1.10×10⁴ m³, respectively. It is a medium-sized debris flow, and the maximum danger area is 0.238,3 km². According to the evaluation and analysis, it is still possible to have medium debris flow in this gully, which poses a traffic safety threat to Nanwan village and Qiansha highway downstream. Our results provide a scientific basis for studying the mono-channel early-warning model of debris flow at Yanqing and the related disaster prevention and control.

Petrology

Northward Subduction of Subashi Ocean in Eastern Part of the West Kunlun Orogen: Evidence from Early-Middle Permian Volcanic Rocks

ZHANG Yu, TANG Mingying, CUI Xiaofeng, HE Yuliang, DONG Weidong

2021, 35(03):  763-775.  DOI: 10.19657/j.geoscience.1000-8527.2021.034

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The Karaletash Group in the southern side of the Subashi ophiolite belt is characterized by widespread distribution of felsic and intermediate-felsic volcanic rocks. In this study, we conducted LA-ICP-MS zircon U-Pb geochronology, geochemistry and zircon Lu-Hf isotope analyses on representative rock assemblages of the Karaletash Group. LA-MC-ICP zircon U-Pb dating shows that felsic cystal tuff and basalt were formed from the early-Middle Permian (284.2±1.6 Ma and 262.6±2.0 Ma). The volcanic rocks are rich in Al, Na and Fe, and are enriched in large ion lithophilic elements (LILEs, e.g., K, Rb and Ba) and depleted in high field strength elements (HFSEs, e.g., Sr, Ta, Nb and Ti). Compositions of the mafic volcanic rocks fall into the calc-alkaline-tholeiite field, with chondrite-normalized REE patterns similar to oceanic tholeiite, with Nd/Th = 8.91-13.76 and La/Nb = 0.39-2.28. The zirconε_Hf(t) value are -0.15 to 4.95, which indicates that the mafic volcanic rocks were mainly originated from the mantle with some crust material input. Compositions of the felsic volcanic rocks fall into the calc-alkaline field, with relatively negative anomalies of P and Zr, and with Nd/Th = 1.92-4.10 and La/Nb = 2.52-3.39. The zircon ε_Hf(t) value are 0.94-3.78 and 8.26-12.45, which together with two-staged Hf model ages (1.07-1.25 Ga and 0.51-0.78 Ga), indicating that the felsic volcanic rocks were mainly originated from the re-melting of ancient crust materials and juvenile crust. Geochemical characteristics of the Karaletash Group resemble rocks formed in island arc environment. The Karaletash Group and Subashi ophiolite belt were closely related in their formation ages, the spatial distribution and the geochemical characteristics of the mafic rocks. Combined with deep-water flysch of Liuhuangdaban Formation sandstone in the Subashi ophiolite belt, these rock units constitute the orogenic-trench-arc-basin system. All these indicate that the subduction of the Subashi basin was north-dipping, and that the tectonic background was probably a forearc basin.

Sinistral Ductile Shear and Magmatic Migration Pattern in the Late Mesozoic Yishu Fault Zone

LI Sheng, NI Jinlong, ZHANG Shangkun, SHEN Ying

2021, 35(03):  776-786.  DOI: 10.19657/j.geoscience.1000-8527.2021.060

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Magma intrusion in the Yishu fault zone (YFZ) is closely related to fault activity, and the magmatic geochronology in the Yishu fault zone is of major significance for revealing the tectonic setting of the YFZ. Petrological and LA-ICP MS zircon U-Pb geochronological analyses were conducted on the Fulaishan syenite (in Juxian) in the Yishu fault zone, as well as the Guanfang quartz syenite (in Junan) and the intruding diorite porphyrite dykes. The sinistral ductile shearing of the Late Mesozoic YFZ was first recognized. Zircon U-Pb dating yielded (125.1±1.7) Ma (Fulaishan pluton), (125.6±2.0) Ma (Guanfang pluton), and (122.8±2.1) Ma (ductile-deformed diorite porphyrite dyke). The 125 Ma magmatic age obtained is consistent with the rapid exhumation (122-128 Ma) of the Wulian metamorphic core complex (MCC) and the rapid sedimentation in the Zhucheng fault-bounded basin on the eastern side of the YFZ. This indicates that the YFZ was in a period of intense lithospheric thinning and destruction. The 122.8 Ma age of the diorite porphyrite dike is consistent with the crystallization age of the post-Wulian MCC (e.g., Shichang and Fangzi plutons), indicating that the extension of the YFZ was significantly weakened during this period. It also shows the similar timing of lithospheric thinning across the Jiaodong Peninsula. During the Late Mesozoic, magmatism on both sides of the YFZ had a counterclockwise migration pattern, which may have related to the changing direction, angle, and/or velocity of the Izanagi plate subduction beneath the Eurasian plate.

Zircon U-Pb Geochronology, Geochemical Characteristics and Geological Significance of Huangyugou Intrusion, Shanxi Province

YE Feng, DONG Guochen, REN Jianxun, GONG Jieli, LI Mengxing, WANG Quan, ZHANG Zhaoqi, ZHAO Sanbo

2021, 35(03):  787-797.  DOI: 10.19657/j.geoscience.1000-8527.2020.055

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To deepen our understanding on the destruction mechanism in the North China Craton, we report new geochronological and geochemical data on the fresh quartz monzonite porphyry from the Huangyugou intrusion in Shanxi. The Huangyugou intrusion is composed of quartz monzonite porphyry, which yielded a Late Jurassic weighted mean ²⁰⁶Pb/²³⁸U age of (149.3±0.9) Ma. The quartz monzonite porphyry samples are metaluminous and shoshonitic, enriched in large ion lithophile elements (LILEs, such as K, Sr and Eu), and depleted in high field strength elements (HFSEs, such as Nb, Ce, Zr and Ti). The rocks exhibit LREE/HREE enrichments and weak Eu anomalies. The quartz monzonite porphyry is classified as I-type and shows adakitic features, including high Al₂O₃, Sr, Ba, and Sr/Y, but low Y and MgO. Geochemical characteristics indicate that the Huangyugou intrusion was formed from partial melting of the lower crust, with mantle-derived inputs and have undergone magma mixing. The rocks may have formed under an extensional tectonic setting.

Petroleum Geology

Petroleum Exploration Domains and Favorable Directions of the Lower Marine Assemblage in Eastern Sichuan Basin

SUN Ziming, ZHANG Rongqiang, SUN Wei, HAO Yunqing, BIAN Changrong

2021, 35(03):  798-806.  DOI: 10.19657/j.geoscience.1000-8527.2021.041

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Sichuan Basin is a large superimposed petroliferous basin with great resource potential, which has experienced multi-stage extensional-compressional cycle. Few substantial gas exploration discoveries have been obtained so far in eastern Sichuan Basin while a series of natural gas exploration discoveries have been obtained in Dengying formation of the Upper Sinian system and Longwangmiao Formation of the Lower Cambrian system in recent years in the middle basin. By analysis of tectonic and sedimentary evolution, three evolutionary stages were built up from the Sinian period to the Silurian period in the eastern Sichuan basin and its adjacent areas: (1) extensional differentiation platform stage (from Sinian period to the Canglangpu phase of Early Cambrian period), (2) stable unified platform stage (from the Longwangmiao phase of Early Cambrian period to the Baota phase of the Middle Ordovician period), and (3) compressional foreland depression stage (Late Ordovician period to Silurian period). According to the comprehensive analysis of petroleum geological elements and the characteristics of hydrocarbon migration and accumulation, three hydrocarbon exploration domains are recognized, which are (1) pre-salt carbonate exploration domain (Sinian system to Gaotai Formation of the Middle Cambrian system), (2) post-salt carbonate exploration domain (Xixiangchi group of Middle-Upper Cambrian system to Baota Formation-Linxiang Formation of Middle-Upper Ordovician), and (3) tight clastic rock exploration domain (Upper Ordovician to Silurian system) from lower to upper, respectively. There exists major differences in the aspects of petroleum geological elements, characteristics of migration and accumulation of hydrocarbon, and main controlling factors, and therefore the key constraints of petroleum exploration are different in different exploration domains. By systematic evaluation of the exploration domains, it is pointed out that the carbonate platform marginal zone of the fourth member of the Dengying Formation in southeastern Sichuan basin, the carbonate shallow bank of the Cambrian Xixiangchi Group, and the large delta sand body of the Xiaoheba Formation of the Silurian system, etc. are favorable exploration directions and key breakthrough areas in the eastern Sichuan Basin.

Sedimentary Facies and Model Characteristics of Middle Upper Cambrian Xixiangchi Group in Sichuan Basin and Its Adjacent Areas

JIA Peng, HUANG Fuxi, LIN Shiguo, SONG Tao, GAO Yang, LÜ Weining, WANG Shaoyong, LIU Ce, FAN Jingjing, OUYANG Jinglin

2021, 35(03):  807-818.  DOI: 10.19657/j.geoscience.1000-8527.2021.026

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In recent years, marine carbonate oil and gas exploration in China has made important discoveries. With the exploration breakthrough of gas reservoirs in the Longwangmiao Formation in Sichuan basin, increasingly more researchers are paying attention to the Cambrian carbonate reservoirs. The Cambrian Xixiangchi Group, as a favorable reservoir, is still in the initial exploration stage, with geological research degree development still lagging. Based on previous research results, the sedimentary facies and sedimentary system mode of Xixiangchi Formation in/around the Sichuan basin were studied, and lithofacies paleogeographic maps were produced. Besides, the “three shoal belts with two sags” sedimentary model of the Xixiangchi Formation was established, and the directions and fields of natural gas exploration were proposed. We discovered that: (1) the Sichuan Basin paleogeography in the Xixiangchi period was a carbonate rimmed platform, and the sedimentary facies of (semi-)restricted platform, evaporation platform, platform margin and slope basin were developed; (2) the “three-shoal belts with two sags” sedimentary model of Xixiangchi Formation is established. One of them is the platform-margin grain shoal, which is distributed along the eastern basinal margin. The other two are intra-platform grain shoals, which are distributed on the eastern and western side of the restricted platform facies, respectively, belonging to the restricted and semi-restricted platform facies; (3) the grain shoal of restricted platform facies is controlled by sea-level fluctuation and paleo-uplift. The platform-margin grain shoal is mainly distributed along the eastern basinal margin, with its development controlled by the slope break of sedimentary paleogeomorphology. To conclude, the grain shoal of restricted platform facies and of platform margin facies are good reservoirs and important targets of natural gas exploration. The new understanding of “three shoal belts with two sags” sedimentary model and grain shoal distribution of Xixiangchi Formation is of great theoretical significance to ancient sedimentary system studies.

Comprehensive Study on Reservoir Heterogeneity of Toutunhe Formation in the Slope Area, North of Fukang Sag, Junggar Basin

YU Jingwei, NIU Zhijie, QI Liqi, SUN Xinming, LIU Ni, ZHANG Jin, CAO Song

2021, 35(03):  819-831.  DOI: 10.19657/j.geoscience.1000-8527.2020.098

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Reservoir heterogeneity of the Middle Jurassic Toutunhe Formation in the northern slope area of Fukang sag was discussed, which was favorable to guide deeper exploration of the Formation. Macro-/micro-heterogeneity and their controlling factors were determined by using substantial amount of data, such as those from drilling, well-log, core descriptions, sections, particle sizes, and constant-rate mercury injection. The results show that two types of pore structures are developed in the reservoirs of the Toutunhe Formation, leading to strong micro-heterogeneity. Reservoirs have three types of particle rhythm, two types of permeability rhythm and two types of interlayers, causing strong interbedded heterogeneity, intraformational and planar heterogeneity for many coefficients, together with strong macro-heterogeneity. Reservoirs of the Toutunhe Formation have strong heterogeneity, which are controlled by sedimentary and diagenetic environment, with the latter being the main controlling factor. Last but not least, the prime exploration target area is likely the central part of channel in the Toutunhe Formation (1^st member).

Characteristics and Formation Mechanism of Incised Valley on the Eastern Margin of Chepaizi Uplift, Junggar Basin

QIN Lei, LI Xiaogang, QIU Ziyao, LI Zhijun, XU Shaohua, LI Yiwen, CHEN Cen, WANG Jiabei, WEN Siqi

2021, 35(03):  832-840.  DOI: 10.19657/j.geoscience.1000-8527.2021.027

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Incised valleys are important research target of sequence stratigraphy, and are also favorable sites to search for hydrocarbon traps. Based on comprehensive drilling and logging, 3D seismic data and seismic plane attribute information, the sedimentary system of incised valleys is identified from the Chepaizi uplift to the Hongche fault zone, and the development characteristics and formation mechanism of the incised valleys are analyzed. The attribute map of the sum of absolute seismic amplitude shows four nearly EW-trending incised valleys in the study area, which mainly show the plane morphological characteristics of branch-and single-type. In the seismic section, the geometry is mainly V- and U-shaped, and the sediment filling patterns in the valley include two-way-up and lateral-accretion filling types. Meanwhile, seismic reflection characteristics of aggradation, progradation and superelevation are present, suggesting interactive deposition of “source accumulation” and “traceability accumulation”. Based on the analysis of Mesozoic structure and climate evolution characteristics of the Chepaizi uplift, the local incised valleys were formed in the Late Jurassic, during which the Chepaizi uplift was strongly uplifted and the relative lake level dropped sharply. The river eroded the underlying strata, forming the incised valleys. The filling stage of the valleys occurred in the Cretaceous, during which the Chepaizi uplift subsided readily and rose relative to lake level.

Braided River Depositional Characteristics of the Triassic Lower Karamay Formation at Hongshanzui, Junggar Basin

WANG Jin, YU Xinghe, ZHONG Yufang, ZHOU Ming, YANG Xintao

2021, 35(03):  841-849.  DOI: 10.19657/j.geoscience.1000-8527.2021.054

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In order to unravel the sedimentary facies and characteristics of the Triassic Lower Karamay Formation in the Hongshanzui area, we integrated core and well logging, thin section, and grain-size data, and conducted various analyses on the petrological features, core sedimentary structures, lithofacies division, and vertical sequence to study the sedimentary environment and sequence. The results show that the conglomerate, coarse sandstone, and silty mudstone are the main rock types, with low maturity and large grain-size range. Eight typical lithofacies and three lithofacies assemblages were summarized. Braided river sedimentation was recognized in the Lower Karamay Formation, with its microfacies including: braided channel, mid-channel bar, overflow sand, and floodplain. Sedimentary model of the Lower Karamay Formation is featured by being source-proximal, flood-controlled with intermittent strong current. Our new model provides reference for the Lower Karamay Formation reservoir research in the district.

Seismic Prediction for Mesozoic-Cenozoic Source Rock Distribution in the Linhe Depression, Hetao Basin

WANG Quan, LIU Zhen, LI Chenxi, WANG Shaochun, SHI Yulei, WANG Zhicheng, WANG Biao, WU Han

2021, 35(03):  850-860.  DOI: 10.19657/j.geoscience.1000-8527.2021.057

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Degree of exploration in the Linhe Depression (Hetao Basin) is low, thus it is crucial to determine the source rock distribution for oil and gas exploration. However, due to the scarcity of drilling and sample analysis, early prediction of the source rock distribution is seriously limited. Therefore, distributions of main source kitchens are predicted with various organic geochemical, seismic sedimentological, and geophysical techniques. The results show two types of seismic facies, i.e. low-frequency and strong-amplitude facies, and weak-amplitude and blank facies in the Guyang Formation (2nd member) and Linhe Formation (2nd member). Low-frequency and strong-amplitude facies is widespread, corresponding to dark organic-rich mudstone.Blank facies is also widely developed, corresponding to gray-black/gray organic-poor mudstone. The most favorable semi-deep lacustrine source rocks in the Guyang Formation (2nd member) are characterized by being “multi-lacustrine”, while the semi-deep lacustrine source rock in the Linhe Formation (2nd member) is mainly distributed in the northeast. In general, the source rocks thicken toward the north, reaching 700 m thick for the Linhe Formation (2nd member). Comprehensive evaluation and analysis show that two source kitchens were developed in the Guyang Formation (2nd member), and the southwestern source kitchen is the most favorable because of their large area and thickness, and high organic matter abundance. Only one source kitchen was found in the Linhe Formation (2nd member), which is large and thick in the northeast, and has high organic matter abundance, making it the most favorable. Previous work indicated that this method can effectively predict the source kitchen distributions under few/sparse-well conditions, and provided important reference for the local hydrocarbon accumulation. The work offers a novel way for early source-rock distribution prediction in districts with low degree of exploration.

Controlling Factors of Thick Glutenite Reservoir Accumulation in Hetao Basin: A Case Study of Jihua-2X Reservoir, Linhe Sag

WANG Huilai, SUN Ruina, ZHANG Ruifeng, LIU Xiheng, LIU Jing, TIAN Sisi, XIAO Jinxia

2021, 35(03):  861-870.  DOI: 10.19657/j.geoscience.1000-8527.2021.058

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In the Meso-Cenozoic Hetao Basin, the early-stage wells have oil and gas shows but there is no substantial exploration breakthrough. The discovery of thick glutenite reservoir layer of Jihua-2X indicates good exploration prospect in the basin. To understand the hydrocarbon accumulation characteristics and delineate favorable exploration targets in the basin, we took the Jihua-2X reservoir as a research target. The major controlling factors on the accumulation of thick glutenite reservoir layers was clarified by analyzing the Jihua-2X reservoir, which is located in the eastern wing of the Jilantai tectonic belt (west of the Linhe depression). It is an inherited nose structure controlled by the Langshan branch fault. The oil-bearing sandstone is the fan delta sandbody in the Paleogene Linhe Formation and Cretaceous Guyang Formation. The Jihua-2X reservoir is well-developed and has high degree of enrichment. Matured source rocks of the Guyang Formation in the sub-sag area with high hydrocarbon expulsion power is necessary for hydrocarbon accumulation in the Jihua-2X trap. Furthermore, fan delta reservoir with high sand-strata ratio and successive nose structure, and interconnected migration pathway was likely the key for hydrocarbon accumulation in the Jihua-2X trap. Our results can provide a geological foundation for future exploration in the Hetao basin.

Hydrocarbon Accumulation Process and Exploration Potential in Linhe Depression, Hetao Basin

SHEN Hua, LIU Zhen, SHI Yuanpeng, XU Zeyang, LI Yongjun, CHEN Shuguang, WANG Huilai, WANG Zhicheng, WANG Biao, LIU Chang

2021, 35(03):  871-882.  DOI: 10.19657/j.geoscience.1000-8527.2021.056

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The Hetao basin is a small-medium continental petroliferous basin in Midwest China. A million-ton oilfield was recently discovered in the Jilantai tectonic belt in the southwestern Linhe Depression. Due to the complex geological conditions and low degree of prospecting, the reservoir dynamic evolution is yet to be well understood. The reservoirs in the Jixi uplift belt and the central fault-barrier belt are taken as the main research target. Geological and seismic data were collected from comprehensive petroleum geological analysis, whilst dynamic analysis of the reservoir was performed by the “nine histories” analysis method. Three major findings are obtained: (1) the hydrocarbon accumulation timing was late and comprises three stages, i.e. the hydrocarbon generation, fault activity, and oil filling; (2) Quaternary strike-slip tectonism affected the oil accumulation. Negative flower-like structure was not developed, and the area with strong tectonic inversion in the late period is favorable for hydrocarbon accumulation. Meanwhile, the area with intense uplift and minor negative flowery structure is favorable for oil accumulation; (3) the southwest uplift belt and the central fault-barrier belt are selected as favorable exploration zone.