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    20 April 2023, Volume 29 Issue 2
    Evolution of Oceanic Redox State during Early Ordovician Tremadocian Age Traced by Uranium Isotopes
    MIN Siyu, QIU Chen, LUAN Xiaocong, WU Rongchang, SHAO Qingfeng, CHEN Xi, LING Hongfei
    2023, 29(2):  147-160.  DOI: 10.16108/j.issn1006-7493.2021052
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    The oceanic redox state is one of the important environmental factors affecting evolution of animals in the ancient ocean. The Ordovician Tremadocian Stage was the‘eve’of the Great Ordovician Biodiversification Event (GOBE), during which the biodiversity was gradually increasing. However, there has been lack of researches on evolution of ocean redox state for this key interval. Studies have proved that the U isotope compositions recorded in well-preserved carbonates can effectively trace the redox state of the global ocean redox state. In this study, we conduct systematical analyses of carbon and oxygen isotope compositions and uranium isotope compositions of carbonate samples from the Xiangshuidong section in Songzi, Hubei Province. A significant positive carbon isotope excursion event—TSICE is identified at the base of the middle Tremadocian stage. The average value of  δ238U increased from -0.64‰ ±0.12‰ to -0.26‰ ±0.15‰ across the TSICE, which indicates that the redox state of the global ocean changed from significantly anoxic (mass balance model results indicating >2.56% of the seafloor covered by anoxic seawater) to much more oxygenated before and after the TSICE. This process of environmental change is consistent with the process of increase in metazoan proportion relative to microorganism proportion in reef composition. The positive drift of carbon and uranium isotope compositions may have been related to the regression and sea-surface temperature decrease, respectively, which may have been conducive to oceanic oxidation.

    Discovery of Paleogene Mudanjiang High-Mg# Andesites from Northeast China and Their Petrological Characteristics
    XIONG Qiao, ZENG Gang, ZHENG Zhichong, ZHANG Huili, ZHOU Zhongbiao, WANG Xiaojun, LIU Jianqiang, CHEN Lihui
    2023, 29(2):  161-173.  DOI: 10.16108/j.issn1006- 7493.2021109
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    Cenozoic high-Mg# andesites (HMAs) are generally distributed in the active continental margin and island-arc setting, but they are rare in the intraplate setting. In recent years, intracontinental HMAs erupting at 20.6-0.3 Ma (Neogene- Quaternary) have been found in Wuchagou of western Songliao Basin and Xunke, Menluhe and Russian Far East of northern Songliao Basin. The discovery of these intracontinental HMAs is important to understand the nature and fate of recycled crustal materials in the mantle. Here we, for the first time, report Paleogene HMAs erupting at 49.2-36.3 Ma in Mudanjiang area, eastern Songliao Basin. These volcanic rocks have SiO2 contents of 54.75-58.95 wt% and Mg# values of 45.18-51.72, falling into the scope of HMAs. They are mainly basaltic andesites and andesites belonging to subalkaline series with a small variation of the major element compositions. Based on petrographic observation and MELTS_Excel calculation, plagioclase and orthopyroxene phenocrysts were crystal phases at the earliest stage and mineral phases in the groundmass (such as orthopyroxene, clinopyroxene and titanomagnetite) appeared successively. The results of MELTS_Excel calculation indicate that the crystal phases have not been separated from the magma system and the composition of these rocks can represent the primary magma composition. The crystallizing pressures of the Mudanjiang HMAs are 169-570 MPa by using the orthopyroxene-melt barometer, suggesting a depth of 5.6-18.8 km. The crystallizing temperatures of these rocks are 1109-1181 ℃ by using the orthopyroxene-melt and melt thermometers, which are consistent with other Cenozoic HMAs (Xunke, Menluhe and Wuchagou) in northeast China (1132-1192 ℃) and are higher than island-arc andesites (950-1050 ℃). The pre-eruptive melt H2O contents vary from 0.3 to 1.0 wt% calculated by the plagioclasemelt hygrometer, which are in the range of Cenozoic HMAs in other parts of northeast China (0.3-1.4 wt%), yet tend to lower H2O than island-arc andesite (2-9 wt%). Therefore, the chemical composition, petrographic characteristics, magmatic physical properties (temperature and H2O content) and evolutionary characteristics of the Mudanjiang HMAs are similar to Cenozoic HMAs found in other areas of Northeast China, which all belong to intracontinental HMAs. The discovery of Mudanjiang HMAs suggests that these intracontinental HMA-type magmatism continued from Eocene to Pleistocene and are distributed throughout northeast China.

    Characteristics of Mineralizing Fluids Forming the Debao Skarn-type Deposit in Guangxi Province
    WANG Chenguang, ZHANG Dehui, LIU Xiangchong, XIAO Changhao
    2023, 29(2):  174-185.  DOI: 10.16108/j.issn1006-7493.2021047
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    The Debao skarn-type copper-tin deposit in the Youjiang Basin is the largest copper deposit in Guangxi province. Little is known about the geochemical characteristics of ore-forming fluids and the occurrence state of tin beyond its chronology and mineralogy. We constrain the characteristics and parameters of mineralizing fluids using microprobe analysis, fluid inclusion petrography and microthermometry, and geochemical modeling. Different from typical skarn-type copper deposits, the garnet in Debao belongs to the end-member of pyrope and grossular and contains a small amount of andradite. Tin occurs mainly in chalcopyrite and pyrite, and its abundance can reach up to 0.11%. The homogenization temperatures of fluid inclusions in garnet are 182- 249 ℃ with an average of 219 ℃ , and those of fluid inclusions in calcite ranges from 109 ℃ to 215 ℃ with an average of 157 ℃ . Therefore, the mineralizing fluids in the early stage of the Debao deposit were interpreted to be of low temperature and mediumlow salinity, while those in the late quartz-carbonate stage are characterized by low temperature and low salinity. Temperature decrease favors precipitation of chalcopyrite. The oxygen fugacity and sulfur fugacity of the Debao deposit constrained from equilibrium phase diagrams of Cu-S-O and Fe-S-O systems under mineralization temperatures are log fS2 >-20, and -44<log fO2 <-25, respectively. The oxygen fugacity levels of the Debao deposits were higher than those of typical tin deposits and the high log fO2 fluid environment prevents tin transport in fluids. This is probably one of reasons why cassiterite is rare in the Debao deposit.
    Lithology in the Mantle Source of Jixi Cenozoic Basalts from Northeastern China
    ZHENG Zhichong, ZENG Gang, ZHANG Huili, LIU Jianqiang, CHEN Lihui, ZHOU Zhongbiao
    2023, 29(2):  186-200.  DOI: 10.16108/j.issn1006-7493.2021063
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    Cenozoic volcanic rocks are widespread in Northeast China, mainly surrounding the Songliao Basin. In the eastern part of the basin, volcanic rocks are distributed along Fushun-Mishan and Yilan-Yitong faults, especially near the Changbai Mountain area, and these volcanic rocks are dominated by sodium basalts. The genesis of these basalts is complex based on their significantly chemical heterogeneity found in the previous studies. Therefore, Cenozoic basalts from Jixi area in the north of Fushun-Mishan fault were selected to further identify the lithology in their mantle source. These basalts show a wide range of SiO2 (44.2~49.6 wt%) and MgO (6.7~10.6 wt%) contents, and can be subdivided into basanite, trachybasalt and basalt. In the primitive-mantle normalized incompatible element diagram, they show positive anomalies of Nb and Ta and negative anomalies of Pb and Ti, which is similar to oceanic island basalts. The calculated the primary magmas compositions of these samples are rich in MgO but poor in SiO2 and CaO; moreover, they fall in the region of silica-poor pyroxenite on the projections from or towards Diopside into the plane Olivine-Quartz-Calcium Tschermak’s (CATS). The high FC3MS (FeOT/CaO-3×MgO/SiO2) values of the basalts again indicate the presence of pyroxenite in their source. Furthermore, the olivine phenocrysts from these basalts are also analyzed, and the high-Fo olivines show lower Ca and Mn contents, and higher Ni contents and Fe/Mn ratios than the low- Fo olivines. The compositions of high-Fo olivines resemble to those olivines crystallized from pyroxenite-derived melt, strongly supporting the presence of pyroxenite in the mantle source. In summary, we highlight that pyroxenitic component, produced during the crustal recycling process, plays an important role in the formation of these mantle-derived magmas in Jixi area.

    Geochronology, Geochemical Characteristics and Geological Significance of the Mesoproterozoic Diabase in Qingyuan County, Liaoning Province
    SU Zumin, SUN Fengyue, ZHANG Yajing
    2023, 29(2):  201-212.  DOI: 10.16108/j.issn1006-7493.2021058
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    This study presents LA-ICP-MS Zircon U-Pb dating and whole-rock geochemical analysis of a diabase dyke in Hongtoushan area of Qingyuan County, Liaoning Province, which is located in the northeastern margin of the North China Craton, to explore tectonic evolution of the North China Craton in the Mesoproterozoic. The LA-ICP-MS magmatic zircon U-Pb dating results show an age of 1293 Ma±35 Ma for the Hongtoshan diabase , which represents the emplacement age of the diabase dyke. The diabase shows SiO2=49.42%, MgO=3.56%-5.83%, Na2O+K2O=3.95%-6.2%, indicating transitional characteristics between alkaline and sub-alkaline series. The diabase is enriched in LREE, depleted in HREE and HFSE, and has no obvious Eu anomalies. The Hongtoushan diabase belongs to intraplate basalt that was formed in an extensional setting. The magma was derived from the enriched lithospheric mantle influenced by subducted materials and was assimilated by crustal rocks. Combined with available data on the Mesoproterozoic diabase dykes in the north and northeast of the North China Craton, it is suggested that the diabase was formed during the breakup of Columbia supercontinent.
    Selective Utilization of Feldspars by Agglutinated Foraminifera
    LI Xiaosong, ZHOU Yuefei, ZHAO Hanyue, SUN Shaohua, XU Liang, XIE Qiaoqin, CHEN Tianhu
    2023, 29(2):  213-222.  DOI: 10.16108/j.issn1006-7493.2021049
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    This study used multiple analysis methods, such as scanning electron spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and particle size analysis to investigate the tests of agglutinated foraminifera, Polskiammina asiatica and Ammoglobigerina globigeriniformis, which were separated from the coastal sediments of the Dagang Bay, Taizhou, China. Results show that P. asiatica and A. globigeriniformis are similar in components, including mineral particles, organic membrane on the external surface of tests, organic lining on the internal surface of tests, organic membrane on the surface of minerals, and filaments which are used for connecting minerals. Quartz, microcline, and kaolinite are dominant minerals in the tests. Organic components in the tests are mainly acidic glycoproteins and lipids. Both foraminifera tend to select small sized particles which are within a narrow size range to construct their tests. Microcline particles in the tests are distributed mainly in the center of the tests and the outer wall. Few feldspar particles are observed in the clapboard of the chambers. The specific distribution of feldspars in the tests of foraminifer is probably by the curvatures of the tests and the chemical compositions of the feldspars. It is indicated that the specific distribution of feldspars would help the foraminifera with the stability of tests and access to energy as well as nutrient elements.
    Late Mesozoic Bansin and Range Framework and the Related Tectono-Magmatism of Southeast China
    DONG Changchun, SHU Limin, SHU Liangshu
    2023, 29(2):  223-239.  DOI: 10.16108/j.issn1006-7493.2021053
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    The Southeast China Block was located in the back margin of the Late Mesozoic Japan-Taiwan volcanic arc. The middle Jurassic-late Cretaceous extensional basins and volcanic-intrusive rock series are widely developed in the Southeast China region as a response of ancient Pacific Plate subduction toward the eastern Asia Continent leading the back-arc expansion. The types of basin include the middle Jurassic rifts, the late Jurassic-early Cretaceous volcanoclastic and lava faulted-depression basins and the late Cretaceous-Paleogene redbed faulted-depression basins. The igneous rock series consists mainly of granitoids, bimodal magmatic rocks, A-type granites, metamorphic core complexes and doming-shape plutons, which were formed in the early Cretaceous with a peak value of 140-110 Ma). The basins coexist together with coeval plutons and constituted the Early Cretaceous Southeast China Basin and Range tectonics. This study summarized the principal geological features of the Late Mesozoic Southeast China basin and range geomorphology and analyzed the petrological and geological structural marks and the constraint factors forming the Southeast China bansin and range framework. Finally we discussed the Late Mesozoic geodynamic process of the Southeast China region.
    Numerical Simulation of Compressional Deformation of Pre-existing Passive Salt Diapir in Keshen Area of Kuqa Depression
    WU Chao, XU Wenqiao, LI Qing, WANG Wei, CHEN Weili, YIN Hongwei, QU Yuanji
    2023, 29(2):  240-250.  DOI: 10.16108/j.issn1006-7493.2021057
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    Kuqa fold-thrust belt is a typical complex salt-bearing fold-thrust system. In this paper, based on seismic interpretation, two discrete element models are designed to explore the influence of pre-existing passive salt diapir on the structural geometry and evolution of double-detachment fold-and-thrust belts, as well as the causes behind the different salt structural deformation characteristics and mechanism of the strike segment in Keshen 5 structural area, and the slip displacement of subsalt faults are analyzed finely. The simulation results show that the pre-existing salt diaper, as the priority location of compressional structural deformation and the priority area of stress release, affects the sequence of faults in subsalt layer and the slip displacement of subsalt faults, proceeding to control the differential evolution of structures along the strike. Comparing the simulation results and structural features of Keshen 5 structural area in Kuqa depression, we suggest that the Tuzimazha anticline is the result of the subsequent compressional deformation of the pre-existing passive diapir in the salt basin. The Tuzimazha anticline absorbs most of the shortening, resulting in a significant uplift of the adjacent subsalt fragments, and a wide and gentle syncline is formed on the north side of the anticline under the influence of syntectonic deposits, which suppresses the formation of disordered faults in the syncline. The pre-existing salt diapir structure is the main controlling factor controlling the tectonic deformation in Keshen 5 area. There is no pre-existing salt diapir in the eastern part of the study area, Kumugelemu anticline and Kasangtuokai anticline are developed in turn, the amplitude of which decreases towards the basin, and the slip intensity of subsalt faults weakens towards the basin. The western part of the study area contains pre-existing passive salt diapir. Tuzimaza anticline is developed, and the activity intensity of subsalt faults under pre-existing passive salt diapir is stronger than that of adjacent faults.

    Discussion on the Main Controlling Factors of the Structure of Baikal Rift: Insights from Physical Modeling
    WANG Mengnan, LI Jianghai, LIU Chen, LIU Leixin
    2023, 29(2):  251-260.  DOI: 10.16108/j.issn1006-7493.2021059
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    Baikal Rift is located in the center of the largest continental area in the world, far away from any active plate boundary, but it is one of the most active and complex tectonic areas on earth today. The main controlling factors of its formation and evolution have been widely discussed. Yet, it is still the subject of intense debate concerning. In this paper, the process of lithospheric deformation under the background of local tension is studied by means of physical modeling. Baikal rift is located at the joint of the strong Siberian craton and the weak Sayan-Baikal fold belt. The Siberian craton is characterized by a strong lithosphere where the crust and mantle are mechanically coupled. The experimental results show that stress tends to accumulate on the craton side under the regional tension, and a deep and large fault first developed near the edge of the craton at the weak suture between the craton and orogenic belt. With the continuous extension of the lithosphere, the stress is transferred to the side of the orogenic belt, and the faults also migrate to the side of the orogenic belt, presenting an echelon arrangement. Compared with the young fold belt, the old craton has a cold and hard rigid basement, which determines the narrow and deep depression characteristics of Baikal rift and the asymmetry of its structure.
    The Structure Formation Mechanism and Verification of “Trending Extrusion Bending Slip-Trending Translation” in Sudong Syncline
    LI Hao, QU Zhenghui, ZHU Guanyu, GUO Liang, ZHANG Bicheng, XUE Zhiwen
    2023, 29(2):  261-271.  DOI: 10.16108/j.issn1006-7493.2021042
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    The Sudong syncline is shaped like an asymmetric dumbbell. This special shape stands out on geological map and makes its genesis worthy of investigation. Based on the analysis of regional tectonic evolution background and the structural analysis of Sudong syncline, we discuss the genesis of Sudong syncline, which is further verified by combining the tectonic development characteristics of Zhuxianzhuang Coal Mine. The results show that the Sudong syncline can be divided into four deformation zones including NE limb integral deformation zone, SW limb extrusion deformation zone, SW limb extrusion deformation zone and SW limb normal deformation zone. Sudong syncline formation involved two key deformation stages. that is, deformation under the continuous SW directed compression: a Sudong Syncline characterized by interlayer bending adjustment and“X”conjugated fracture formation period (Extrusion bending stage), and the trending of strip of the southeast Sunan box syncline with the“X”type conjugate fracture translation characterized by intrusion and extrusion period (Trending Translation stage). The Coal vitrinite reflectance indicatrix in the 8# coal seam of Zhuxianzhuang Coal Mine records the direction of stress in each stage of syncline formation. The regular distribution of bedding slip in different deformation types and degrees of the 8# coal seam is a good response to the formation mechanism of“trending extrusion bending slip-trending translation”in Sudong syncline. We propose a method for calculating the along-strike fault offset which is based on the contour of coal seam floor. Using this method, the translation direction and offset of the fault in the southern Zhuxianzhuang Coal Mine were quantitatively characterized and the mechanism of the trending translation of the Sudong syncline was further verified.
    A 3D Dynamic Evaluation Method of Shallow Geothermal Energy Development Suitability Based on Integration of BIM and GIS
    YAO Lu, ZHANG Dan, WANG Bo, REN Kang
    2023, 29(2):  272-279.  DOI: 10.16108/j.issn1006-7493.2021062
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    When the ground source heat pump (GSHP) is utilized to supply energy for building HVAC system, the method of calculating the energy supply of shallow geothermal energy and the building energy consumption respectively is often used in design stage. However, this kind of method can not realize dynamic evaluation under different operating conditions. In this paper, a method based on the integration of BIM (Building Information Model) and GIS (Geography Information System) is proposed, which gives full play to the advantages of BIM in building high visualization and GIS in spatial information analysis and processing. This method integrates building components and underground spatial information, and realizes the 3D evaluation of shallow geothermal energy development suitability. The Zhu Gongshan Building of Nanjing University is taken as an example for the verification. Based on the seasonal average capacity-demand ratio index and monthly fluctuation of capacity-demand ratio, the suitability of shallow geothermal energy development and utilization in winter is analyzed dynamically. The results show that the shallow geothermal energy can meet the demand of the building in most of the time, and its suitability evaluation grade is medium. It is proved that the 3D dynamic evaluation method for the suitability of shallow geothermal energy development based on the BIM and GIS integration is feasible.
    Microstructures and Fractal Characteristics of Collapsible Loess Subjected to Water Immersion
    WANG Shenhao, XIE Wanli, CHANG Yilun, SHAN Shuai, JING Xu
    2023, 29(2):  280-288.  DOI: 10.16108/j.issn1006-7493.2021048
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    The collapsible loess in Yan′an New Area was chosen to carry out the immersion test and the microstructure images of loess with different immersion periods were obtained by scanning electron microscope. The image processing software Image Pro Plus (IPP) was used to extract the microstructure parameters of loess, and the microstructure of loess was quantitatively analyzed with the fractal theory. The results show that the collapsibility of soil decreases during the immersion process. The arrangement and form distribution of soil particles change regularly. Also, both the probability distribution index of pore area and the fractal dimension of particles showed a decreasing trend, the roundness of particles first decreased and then increased, and the alignment of particles changed in direction with the time of immersion. Furthermore, the influence of water immersion on the microstructures of loess is time-sensitive. In the initial stage, the soil is affected by softening of clay minerals and the loss of soluble salts, and the natural structure gradually becomes unstable under the disturbance of water; As the immersion continues, the skeleton structure is damaged, and the particles deflect, slip, and recombine; In the equilibrium stage, the particles form new structures and become
    denser, the large and medium pores decrease, and the soil structure gradually stabilizes. In this paper, the characteristics of loess structures under the action of flooding are studied from both macroscopic and microscopic perspectives, which provides an experimental and scientific basis for engineering problems in collapsible loess areas.
    Spatial-Temporal Evolution of Land Subsidence Based on InSAR Monitoring: A Case of Lianyungang City
    CAI Tianlu, LU Yi, LU Hua, MIN Wang
    2023, 29(2):  289-297.  DOI: 10.16108/j.issn1006-7493.2021006
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    The occurrence and development of land subsidence are closely related to human social and economic activities. With the continuous development of coastal areas, land subsidence centers have shifted from inland to port, seawall and reclamation areas, and the influencing factors have also changed from single to mixed types. The regional full coverage characteristics of InSAR monitoring can meet the changing monitoring requirements. Taking Lianyungang Area as an example, , this paper conducts multi-source data comparison and verification of land subsidence, to verify and evaluate the InSAR monitoring results. The results show good consistency and high credibility, and meet the current requirements for land subsidence monitoring accuracy. The study provides data support for the optimization and improvement of urban land subsidence monitoring technology system. 
    Hirnantian (latest Ordovician) Stratigraphy and Palaeogeography of the Western Yangtze Platform, South China
    WANG Guangxu, WEI Xin, CUI Yunong, ZHANG Xiaole, WANG Qian, ZHAN Renbin
    2023, 29(2):  298-315.  DOI: 10.16108/j.issn1006- 7493.2022051
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    Hirnantian (latest Ordovician) rocks and fossils have still not been sufficiently documented in the western Yangtze region of South China (today’s southwestern Sichuan and northeastern Yunnan provinces, Southwest China). Compilation of published and new data results in refined Hirnantian stratigraphy and palaeogeography of the region. The lower Hirnantian is typified by the dark-grey cacareous mudstone or argillaceous limestone of the Kuanyinchiao Formation yielding cool-water Transitional Benthic Fauna 1 (TBF 1). The middle Hirnantian strata, however, can be grouped into a near-shore lithofacies belt with distinctive grainstones of the upper Kuanyinchiao Formation yielding warm-water TBF 2, and a more offshore belt characterized by black shales of the basal Lungmachi Formation. A similar facies differentiation occurs in the upper Hirnantian of the region, but the near-shore sediments are in places represented by TBF 3-bearing calcareous siltstones, for which a new lithostratigraphic unit, the Weiba Formation, is proposed. On this basis, refined Hirnantian paleogeographic reconstructions of the western Yangtze Platform are presented.
    End Member Model Analysis of Sediments Grain-size from Erlongwan Maar Lake and Corresponding Environmental Implication in the Past 100 Years
    LIAO Dongxia, GUO Haiting, WU Mengmeng, PAN Shaoming
    2023, 29(2):  316-324.  DOI: 10.16108/j.issn1006-7493.2021051
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    Sediment grain size contains paleo-environmental information such as regional precipitation intensity, water level fluctuation and sediment provenance. The end-member modeling analysis can extract the end members representing different sedimentary dynamic processes. We collected two sediment cores from the center and the shore of the Erlongwan Maar Lake. 137Cs activities were measured by Coaxial High Purity Germanium Detector GMX30P-A Series, particle size was measured by the Malvern Mastersizer 2000. The parametric EMA modeling was used to analyze the grain size data of sediment cores in Erlongwan Maar Lake. Based on the results, we analyzed the sediment source and the sedimentary environment of Erlongwan Maar Lake in the past 100 years. The results indicate that the parametric EMA modeling has recognized three end members. The sediments in
    Erlongwan Maar Lake are thought to be aqueous mainly, and the eolian deposits are relatively less. From EM1 to EM3, the mode
    particle size increases successively. EM1 represents eolian deposits and fine-grained materials carried into the lake by flowing water. EM2 comes from the erosion of debris in the basin by surface runoff, which is the major component of sediments. EM1 and EM2 indicate a closed lake sedimentary environment with weak hydrodynamics, and EM3 indicates a process of strong surface runoff transport. The detrital material derived from continent is the main source of sediments. The distant clayey particles carried by the upper westerly wind and the near dust particles carried by meso-scale regional wind also contribute to the sediments. The sedimentary environment is relatively stable during recent 100 years. The sedimentation rate of the lake core is lower than that of the lakeshore. After 1963, the content of fine-grained materials increased, while the proportion of coarse-grained components decreased. This means the improvement of ecological environmental and the decrease of surface materials loss, which indicates that the establishment of Jilin Longwan National Nature Reserve plays an important role in soil and water conservation.