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    Formation and modification of deep-burial carbonate rocks and orderly distribution of multi-type reservoirs in the Tarim Basin
    FAN Tailiang, GAO Zhiqian, WU Jun
    2023, 30(4): 1-18. 
    DOI: 10.13745/j.esf.sf.2023.6.5

    Abstract ( 321 )   HTML ( 77 )   PDF (10703KB) ( 324 )  

    The deep-burial carbonate rocks in China are characterized by great burial depth, old numerical age, and complex geological evolution process. The formation and distribution of carbonate reservoirs, constrained by many factors, are one of the key scientific issues in marine oil and gas exploration. This paper summarizes the results of the team’s long-term research and reveals the main development conditions and orderly distribution of multi-type carbonate reservoirs relevant to the formation and modification of deep-burial carbonate rocks in the Tarim Basin. (1) The platform pattern, stratigraphic development and evolution, and late-stage burial and modification of the basin are all the tectono-sedimentary responses of the basin margin tectonic events. The early Paleozoic basin experienced the evolution process of geomorphic extensional differentiation and formation of small rift groups, geomorphic compression differentiation and interlayer unconformity development, paleo-uplift and large-scale unconformity, multi-stage unconformity superposition and buried modification of paleo-uplift. (2) Complex sedimentary differentiation and evolution (in terms of type and scale) during carbonate platform sedimentation can be divided into embryonic stage, construction stage, heyday stage and decomposition-extinction stage. The corresponding platform margins have undergone the construction process of gentle slope, progradation rimmed, aggradation rimmed and retrogradation steep slope. They control the distribution of sedimentary facies zones favorable for large-scale reservoir development, such as platform margin reef shoals, intraplatform shoals and early dolomitization tidal flats. (3) Multi-level unconformity and fault-fluid modification are important mechanisms for the formation of high-quality reservoirs, where multi-stage regional tectonic activities and periodic sea-level changes control the development of unconformities at different levels, while sequence boundaries dominated by sea-level fall leads to periodic outcropping of carbonate rocks to form interlayer karst and synsedimentary karst of different scales; meanwhile large-scale unconformities formed by regional tectonic movements control the large-scale carbonate outcropping and development of large-scale epigenetic karst reservoirs, as faults and fractures of different scales are not only the reservoir development zones but also the main zones of fluid activity and modification. (4) The size of unconformity and the intensity of fault activity in the Tabei-Shunbei area change gradually from north to south controlling the orderly change of reservoir type and distribution, which result in the sequential developments of, from north to south, buried hill dolomite reservoirs in the Yakla fault convex, paleo-weathered crust karst reservoirs in the main area of Tahe area, stratabound karst reservoirs in the slope area of Tahe, fault karst reservoirs in the covering area of Tahe area, and fault-controlled karst reservoirs in the Shunbei area, reflecting the gradual weakening of unconformity control on reservoirs and strengthening of fault control on reservoirs from denudation area to covering area.

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    The paleotectonic and paleogeography reconstructions of the Tarim Basin in the Neoproterozoic and prediction of favorable deep source rock areas
    HE Bizhu, JIAO Cunli, LIU Ruohan, CAO Zicheng, CAI Zhihui, LAN Mingjie, YUN Xiaorui, ZHU Ding, JIANG Zhongzheng, YANG Yujie, LI Zhenyu
    2023, 30(4): 19-42. 
    DOI: 10.13745/j.esf.sf.2022.10.18

    Abstract ( 181 )   HTML ( 18 )   PDF (15904KB) ( 315 )  

    The tectono-sedimentary development of the Neoproterozoic of the Tarim Basin is important for understanding the basin initiation process and for the regional ultra-deep/deep oil and gas exploration. Due to the deep burial and data scarcity, it is extremely difficult to research the deep buried areas of the basin, and data interpretation can be ambiguous. This study, based on comprehensive analyses of drilling data and newly reprocessed seismic reflection data collected across the basin, reveals that the Tarim Basin experienced at least three tectonic cycles during the Neoproterozoic and developed three super stratigraphic sequences and 7-9 stratigraphic sequences. The distribution of sedimentary facies of the Neoproterozoic in the basin and its margin vary greatly, constrained obviously by Neoproterozoic rift depressions. The basin developed shelf facies, glacier facies, basin facies, carbonate platform facies, tidal-flat facies, fan-delta facies, littoral and shallow sea facies, alluvial-fluvial facies, and igneous rock facies. Results on the structural architecture and spatial distribution of unconformities during the Cryogenian-Early Cambrian reveal that the tectono-sedimentary frameworks of the basin margin and deep buried area are formed in an extensional environment. The main unconformity types include angular unconformity with low-angle and monocline structures, progressive syntectonic angular unconformity, fault-controlled unconformity, and paraconformity, and they are observed in every rift depressions and at different locations. The paleotectonic and paleogeography of the basin before the deposition of the Ediacaran and the Cambrian are reconstructed based on sequence stratigraphy, Neoproterozoic fault activity, unconformity architecture, seismic stratigraphy, and wave impedance inversion property data, which show that the distribution of various sedimentary facies zones is related to the developments of rift depressions and subsidence centers and the differences of structural deformations. In response to the subduction-related outgrowth and the breakup of Rodinia, and the assembly of Gondwana, the Tarim Basin experienced three evolutionary cycles in the Neoproterozoic: initiation of deep rift depressions (900-760 Ma), development of deep rift depressions (~750-630 Ma), and rapid extensions and declining of rift depressions (630-520 Ma). Correspondingly, the Tarim block underwent subduction-related back-arc extension, continental rift, and passive continental margin transformations during the Neoproterozoic. The Ediacaran to Cambrian transition is an important period where the Tarim block transformed from continental-rift/rift-depression basins into a unified cratonic basin. This is evidenced by the unconformity between the Cambrian and the Ediacaran or pre-Ediacaran across the basin and covered by the Lower Cambrian further. Here, a new method is developed to reconstruct paleotectonic and paleogeographic history of deep buried basins based on structural and multi-attribute analyses. Besides, the favorable development areas of Lower Cambrian-Upper Cryogenian source rocks are predicted according to structural and sedimentary facies constrains, which has great significance for the evaluation of deep oil and gas resource potential in the basin.

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    Hydrocarbon accumulation and reservoir characteristics of deep marine fault-karst reservoirs in northern Tarim Basin
    YANG Debin, LU Xinbian, GAO Zhiqian, CAO Fei, WANG Yan, BAO Dian, LI Shengqing
    2023, 30(4): 43-50. 
    DOI: 10.13745/j.esf.sf.2022.10.11

    Abstract ( 152 )   HTML ( 17 )   PDF (5989KB) ( 144 )  

    The concept of “fault-karst” trap (reservoir) was proposed in 2015 on the basis of author’s experience from carbonate exploration and reservoir development in northern Tarim Basin and their understanding of reservoir/accumulation-control characteristics of fault deformation, karstification and dissolution in the fault zone. Since then fault-karst reservoir has become a new target in carbonate exploration and development in the Tarim Basin. This study further demonstrates that fault-karst reservoirs are not only significantly different from the traditional karst (buried hill) reservoirs, they may also have different genetic types and structural characteristics under different karst environments and structural settings. Fault-karst traps can be divided into three subtypes according to the dissolution conditions and fracture types, and they are characterized by fault-karst storage, deep-fault accumulation, trap structure, vertical dredging, multi-layer accumulation, and segmented reservoir formation. Fault-karst trap (reservoir) is important to oil and gas exploration and development and should be comprehensively studied.

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    Formation mechanism and distribution prediction of fine-fracture pores in the Lower Ordovician in Tahe oilfield
    ZHANG Juan, XIE Runcheng, YANG Min, GAO Zhiqian, WANG Ming, ZHANG Changjian, WANG Hong
    2023, 30(4): 51-64. 
    DOI: 10.13745/j.esf.sf.2022.10.13

    Abstract ( 203 )   HTML ( 8 )   PDF (10853KB) ( 100 )  

    The development direction of the Ordovician carbonate reservoirs in the Tahe Oilfield has gradually shifted from the seismic-reflected “bead-type” fracture/pore reservoirs to the “non-bead”-type fine-fracture/pore reservoirs. Determining the fine-fracture/pore formation mechanism and development is the key to improving tight-reservoir utilization. In this study, fine-fracture/pore characterization were carried out on core and thin sections, and the fracture genetic types, fracture parameters and filling properties of fine fractures were determined. The fracture types in the study area were classified as “tectonic fracture” and “non-tectonic fracture” according to the fracture origin, and the fractures are highly angular or vertically produced. The tectonic fractures are less filled compared to weathered fractures; whilst cavity filling is relatively high, but residual porosity can result from coarser crystals in the cavity. The formation mechanism of the fine-fracture/pore reservoirs in the study area was determined based on the analyses of pore-control factors, such as paleokarst geomorphology, local residual mound structure and fracture characteristics, combined with tectonic stress-field simulation. Fracture and pore are more developed at higher elevation in the east than in the west of the main area as highland areas are conducive to karst development. Local residual mound also influence karst development as its gentle slope allows rock and water to interact more fully which favors reservoir formation. The major faults control the formation of large caves, whilst large caves and faults control the development of fine fractures which can reach as deep as 200 m below the T74 interface. Tectonic stress fields influence the distribution of tectonic fractures, and tectonic fractures provide the dissolution channel for the formation of pores and thus indirectly controls the distribution of fine-fracture/pore reservoirs. A prediction method for fine-fracture/pore is developed based on nonlinear neural network deep learning algorithm to determine the planar distribution of fine-fracture/pores, and the prediction results agree with the single-well pore distribution data as well as the initial single-well oil production data. This research lays the technical foundation for a full utilization of fine-fracture/pore reserves in the oilfield.

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    Ordovician palaeokarst caves in the Tahe oilfield: Burial age of cave fills and its implication for hydrocarbon reservoirs
    CHEN Xuan, LIU Wanghan, BAO Dian, ZHANG Liping, CHEN Lixiong, YANG Min, ZHANG Juan, LI Yingju, LI Guangye, JIA Yufeng
    2023, 30(4): 65-75. 
    DOI: 10.13745/j.esf.sf.2022.10.12

    Abstract ( 140 )   HTML ( 9 )   PDF (8853KB) ( 81 )  

    The burial age of cave fills can provide valuable insights into the formation of ancient caves and the cave filling order and cave reservoir development. The Ordovician palaeokarst caves in the Tahe oilfield are significantly impacted by cave filling, but the burial age of cave fills and its implication for the hydrocarbon reservoir development in the oil field have not been systematically analyzed. Here we present findings on the cave deposits based on analyses of the geologic setting of the oil field as well as core, well-logging, burial history and productivity data. We found the layered, gray-green calcareous sandstone and argillaceous siltstone were deposited via transport filling in the Early Hercynian and fracture-associated, gray-green argillaceous siltstones via seepage filling in the same era; whilst well-rounded/sorted, multicolor conglomerate fills, with complex rock composition and sandy matrix, were deposited in the Late Caledonian by transport filling. Meanwhile, poorly-sorted collapse breccias, chemically homogeneous, mixed with grey-green mudstone via seepage filling, were deposited in the Early Hercynian during early burial; whilst fractured, calcite/oil-bearing collapse breccias, mainly on cave roof, without seepage filling, were deposited in the late burial stage. The reservoir controlling factors of fracture/cavity reservoirs of karst caves were very complex, where cave fills deposited in the early burial stage via transport, seepage and collapse filling were mostly mudstones, with poor reservoir quality; whereas secondary fractures formed during late burial from collapse settlement without mud fill greatly improved reservoir quality, and the upper/top parts of karst caves were favorable for reservoir development. This research provided a valuable reference for the understanding of karst cave formation and exploration of high-quality hydrocarbon reservoirs.

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    Sedimentary characteristics of Ordovician carbonate intraclastic shoals of the Yingshan Formation, Tazhong-Shuntuoguole area, Tarim Basin
    YAN Wei, FAN Tailiang, ZHANG Guangxue, GAO Zhiqian, LI Yifan, ZHANG Guoqing, LI Fuyuan, SUN Ming, LÜ Yaoyao
    2023, 30(4): 76-87. 
    DOI: 10.13745/j.esf.sf.2022.10.21

    Abstract ( 132 )   HTML ( 10 )   PDF (12493KB) ( 124 )  

    The Tazhong-Shuntuoguole area has been shown to have rich hydrocarbon resources as major breakthroughs in hydrocarbon exploration continue to be made in this area. To understand the regional sedimentary environment and for reservoir prediction purposes it is important, both theoretically and practically, to clarify the sedimentary characteristics of shoals. Through extensive thin section analysis we find the carbonate shoals are mainly intraclastic shoals with underdeveloped biotic reefs, and composed largely of sparry calcite cement that are partly dolomitic. The intraclastic shoals contain some ooid and algae grains, with a little bioclastics often found in micrite. Ooid gains are usually small, with radial texture, and formed in a low-energy environment; while algae grains are usually mixed with intraclast and some bioclastics indicating they are formed in a mid-high-energy environment. The Yingshan Formation can be subdivided into two third-order sequences according to well log analysis. The stacking pattern of carbonate shoals typically shows thin-layered retrogradation within the ascending semi-cycle and thick-layered aggradation within the descending semi-cycle, whilst small-scale shoals develop during the maximum flooding period. Beach-interacting sea facies often develop near the maximum flooding surface. In the Yingshan Formation, open-platform and restricted-platform intraclastic shoals are recognized. The open-platform shoals are thick and distributed as clumps along the platform margin in a thick-layered aggradational stacking pattern, whilst the restricted-platform margin shoals are thin and distributed in small clumps or strips in a similar stacking pattern.

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    A new method for identification of flow units of sandstone reservoir based on reservoir performance and its application in the Akshabulak oilfield, Kazakhstan
    WANG Jincai, FAN Zifei, ZHAO Lun, CHEN Yefei, ZHANG Angang, ZHANG Xiangzhong, GUO Xuejing, LI Yi
    2023, 30(4): 88-99. 
    DOI: 10.13745/j.esf.sf.2022.10.16

    Abstract ( 225 )   HTML ( 12 )   PDF (10019KB) ( 77 )  

    Taking an example of the massive sandstone of layer J-Ⅲ, Akshabulak oilfield, southern Turgay Basin, Kazakhstan, we propose a new method to identify flow units based on reservoir performance ratings. First, four performance ratings, “excellent”, “good”, “moderate” and “poor”, are assigned according to reservoir production profile and daily well output under similar working conditions. Then, taking the reservoir performance rating as the discriminant function, based on core analysis results, seven types of reservoir quality indicators are selected for clustering analysis. Finally, based on the quality indicator values and well-log interpretation data, the flow units are delineated into four types, “high-flow”, “relatively high-flow”, “moderate-flow” and “low-flow”, according to water flow levels, by neural network clustering. Statistical analysis results show that the reservoir-quality indicator values correlate positively with reservoir performance ratings, therefore it is reasonable to identify flow units according to performance ratings. Our study indicates that the development pattern of flow units determines the reservoir performance: when flow units of different types are developed, water tends to flow towards units with higher flow levels causing uneven flooding in the vertical direction; horizontally, areas with high-level flow units are flooded preferentially causing significant uneven advancements of waterflooding front. We propose, therefore, to control vertical waterflooding by water plugging at high-level flow units and allow planar natural waterflooding combined with water injection to achieve stable and high-efficiency reservoir development.

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    Volcanic reservoir characteristics and hydrocarbon accumulation control factors of rift depressions in southern Songliao Basin
    LI Ruilei, YANG Liying, ZHU Jianfeng, LIU Yuhu, XU Wen, LI Zhongbo, FAN Xuepei, LENG Qinglei, ZHANG Tingting
    2023, 30(4): 100-111. 
    DOI: 10.13745/j.esf.sf.2022.10.24

    Abstract ( 171 )   HTML ( 11 )   PDF (9072KB) ( 144 )  

    Intermediate-basic volcanic rocks of the Huoshiling Formation are widely developed in rift depressions in southern Songliao Basin. In this present study we investigated the volcanic rock distribution, lithology and lithofacies, volcanic structure types, reservoir space characteristics and gas accumulation characteristics through comprehensive multi-scale analysis, and then discussed the formation mechanism of effective reservoir space and the main controlling factors of hydrocarbon accumulation. We found that (1) intermediate-basic volcanic rocks are widely distributed in the basin mainly as multi-stage superimposed, connected low-amplitude mounds. The rock develops 3 types of lithofacies and 7 types of subfacies as well as a composite pore-fracture network-type reservoir space. (2) Volcanic structures control the lithology and lithofacies distribution, and determine the formation and distribution of primary pores; while tectonic movements and rock dissolution are conducive to the formation of structural fractures and secondary dissolution pores and fractures, and they are the key factors controlling the formation of high-quality reservoirs. (3) The reservoir control mechanism can be described by a quaternary model: The paleostructural setting during the accumulation period determines the direction of hydrocarbon accumulation; the favorable hydrocarbon generation center of the deep depression provides the material basis for the hydrocarbon accumulation and dynamic conditions; the multi-type, multi-scale pore-fracture development zones control the distribution of favorable reservoirs and determine the degree of oil and gas enrichment; and stable mudstone and late-stage weak tectonic activities provide better preservation conditions for the development of petroleum reservoirs.

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    Tectono-sedimentary characteristics and formation mechanism of the Lishu rift depression, Songliao Basin
    WANG Hongyu, LI Ruilei, ZHU Jianfeng, ZHANG Haoyu
    2023, 30(4): 112-127. 
    DOI: 10.13745/j.esf.sf.2022.10.23

    Abstract ( 194 )   HTML ( 12 )   PDF (10940KB) ( 108 )  

    The Lishu rift depression is a typical wedge-shaped rift lake basin in the Songliao Basin with complex tectono-sedimentary features. This paper, based on tectono-sedimentary analysis using large amounts of 3-D seismic and drilling data, reveals the tectono-sedimentary characteristics and evolution, main controlling factors and formation mechanism of the rift depression. The results provide, on the one hand, a geological basis for the reservoir prediction in this area, and on the other hand, a practical reference for the relevant, in-depth studies of other rift depressions in the Songliao Basin. The Lishu rift depression experienced three sub-rift phases under left-handed tensile stress and multi-extrusion tectonic activities in the Early Cretaceous. It evolved from a small rift sag with few small, steep secondary rifts in the early rift stage, to a lacustrine basin with wedge-shaped half graben, bound by the Sangshutai fault along its western side, in the intense rifting phase, then to the shallow lake basin in the late rifting phase. Each of the sub-rift phases exhibited varied basin configuration and palaeo-geomorphological features. In the early rifting phase, both surface uplifting and fault-block tilting occurred, resulting in various types of unconformities. In the intense rifting phase, angular conformities were more developed due to fault-block rotation and tilting. While in the late-rifting phase paraconformities dominated, reflecting regional uplifting and subsidence. During basin evolution, sedimentary systems in the basin transitioned from lake delta to braided river systems. The sequence stratigraphic framework of the intense-rifting phase was characterized by upward “gradual shrinking of low system tracts (LST) and continuing expansion of high system tracts (HST)”; whilst late-rifting sequence featured transverse continuous sediment deposition and longitudinal alluvial accumulation.

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    Shale oil reservoir of the Palaeogene Shahejie Formation in the Dongpu Sag: Petrology and pore microstructural characteristics
    PENG Jun, SUN Ningliang, LU Kun, XU Yunlong, CHEN Faliang
    2023, 30(4): 128-141. 
    DOI: 10.13745/j.esf.sf.2022.10.15

    Abstract ( 124 )   HTML ( 6 )   PDF (8238KB) ( 194 )  

    Shale petrology and pore microstructures are key performance evaluation indicators for shale oil and gas reservoirs. In this study, the petrological and oil compositional characteristics of shale oil reservoir and reservoir lithofacies types, pore/fracture types and pore-throat distribution in the Shahejie Formation in the Dongpu Sag are investigated by core observation, thin section analysis, scanning electron microscopy, mercury injection-liquid nitrogen adsorption and microCT-guided 3D reconstruction methods. Results show that the shale oil reservoir contains mainly clay and carbonate minerals and some felsic minerals. The main lithofacies includes laminated limestone/clay stone/calcareous fine-grained mixed rocks/argillaceous fine-grained mixed rocks, and massive clay stone/dolomite. The reservoir pore space is mainly provided by a combination of intergranular/intragranular dissolution/clay mineral intergranular/organic pores. The microfractures can be divides into diagenetic and tectonic fractures, and the laminated limestone/calcareous fine-grained mixed rocks developed various high porosity pore spaces. Lithofacies and bedding structure are important factors influencing pore development and pore quality. Laminated rocks, except clay stone, possess large pore space and show good pore connectivity, relatively developed microfractures and high oil content and mobility, and laminated limestone is the most favorable lithofacies. These rocks are key shale oil exploration targets in the Dongpu Sag.

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    Application of astronomical cycles in shale oil exploration and in high-precision stratigraphic isochronous comparison of organic-rich fine-grain sedimentary rocks
    SHI Juye, JIN Zhijun, LIU Quanyou, FAN Tailiang, GAO Zhiqian, WANG Hongyu
    2023, 30(4): 142-151. 
    DOI: 10.13745/j.esf.sf.2022.10.14

    Abstract ( 161 )   HTML ( 13 )   PDF (7312KB) ( 179 )  

    There are different scales of cyclicity in the Earth’s evolution, from one day to several hundred million years. Presently, the scale of the astronomical cycles controlled by the Earth’s orbit is one of the most suitable timescales for high-precision stratigraphic comparison. Astronomical signals are more likely present in the continuous succession of organic-rich shale, where the “precise periodicity” of Milankovitch cycles makes it feasible to achieve stratigraphic isochronal correlation therefore to allow high-precision comparison of organic-rich shale. In this paper, the main source rocks of the Shahejie Formation in Dongying sag, Bohai Bay Basin, eastern China are studied, and the multi-scale isochronal correlation of continental organic-rich shale is achieved by using the astronomical cycles, which demonstrates that the sixth-order sequence division and organic-rich shale comparison can be performed with an error of less than 40000 years by using the obliquity cycle as the basic unit. According to the results, the high-production shale formation in the Dongying sag is located at 42.85-41.85 Ma near the E2-E4 long eccentricity cycles and coinciding with a high-amplitude obliquity cycle. It was hypothesized that the high-production shale is likely related to the obliquity-driven laminated shale that has high mobility and oil-bearing property. This result further demonstrates that the high-precision isochronal comparison of continental organic-rich shale using astronomical cycles can provide a high-precision chronological framework for the prediction of high-quality hydrocarbon source rocks.

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    Interbedded shale formation of the 7th member of the Yanchang Formation in the Ordos Basin: Petroleum accumulation patterns and controlling factors
    PANG Zhenglian, TAO Shizhen, ZHANG Qin, BAI Bin, LIN Senhu, ZHANG Tianshu, CHEN Yanyan, FAN Jianwei, SUN Feifei
    2023, 30(4): 152-163. 
    DOI: 10.13745/j.esf.sf.2022.10.17

    Abstract ( 217 )   HTML ( 11 )   PDF (8540KB) ( 158 )  

    Recent breakthroughs in shale petroleum exploration in China demonstrated good exploration prospects, and Chang-7 member of the Yanchang Formation in the Ordos Basin is a major exploration area. To study in more detail the petroleum distribution patterns and accumulation controlling factors in the main production interval and interbedded shale formation of Chang-7 member, we conducted multi-scale investigation by means of reservoir profiling, core and thin section observation, reservoir rock evaluation, rock pyrolysis and field emission scanning electron microscopy, combined with microprobe analysis and physical modeling of oil charge and migration. According to the results, petroleum distribution in the interbedded shale formation is highly anisotropic at the play, oil-layer and intra-layer levels. At the play level oil accumulation is mainly controlled by source rock quality and quantity; whilst within the oil layer accumulation is controlled primarily by the reservoir/source-rock assemblage and also by the reservoir rock properties, while reservoir anisotropy due to diagenetic effects is the main cause of oil saturation heterogeneity within the oil layer. Mechanistic studies further reveal the control mechanisms of different factors on oil accumulation in the interbedded shale formation. The source rock controls oil accumulation at the play level as it provides both the driving force for hydrocarbon migration and the source of hydrocarbon while short-distance secondary migration of hydrocarbon occurs before accumulation. Oil accumulation at the oil-layer level is primarily controlled by reservoir and source-rock assemblage as the migration driving force decreases with increasing distance between oil layer and source rock. Besides, the reservoir rock properties, due to their exponential relationship with migration resistance at petroleum charging, also control the petroleum accumulation at the oil-layer level and within the intra-layer space. Whilst fractures enhance migration efficiency by reducing the threshold pressure gradient in interbedded sandstone, which promotes petroleum accumulation in the shale formation.

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    Application of high-precision sequence stratigraphy in marine fine-grained sedimentary rocks: A case study of the Doushantuo Formation in northern Sichuan
    KUANG Mingzhi, LI Yifan, FAN Tailiang, ZHANG Tan, LIU Wangwei, LIU Nan
    2023, 30(4): 164-181. 
    DOI: 10.13745/j.esf.sf.2022.10.19

    Abstract ( 160 )   HTML ( 12 )   PDF (12506KB) ( 169 )  

    Establishing a high-precision sequence stratigraphic framework in marine fine-grained sedimentary rocks is important for an effective prediction of organic-rich intervals and high-quality unconventional oil/gas reservoirs which is still a challenge in unconventional oil/gas sedimentology and fine-grained sequence stratigraphy. Taking the fine-grained sedimentary rocks of the Doushantuo Formation in northern Sichuan as the research object typical sections are selected. Through detailed field investigation of outcrops and high-precision analysis of thin sections, the turbidite sequence section and fine-grained sedimentary section of the Doushantuo Formation are divided into 7 lithofacies types according to sedimentary structure and lithology: (1) massive coarse sandstone, (2) bedding sandstone, (3) sand-rich-interlayer siltstone, (4) collapse-crumpled silty mudstone, (5) grain-rhythmic silty mudstone, (6) intermittent sandy laminar mudstone, and (7) dark-laminar mudstone. The upper mixed sediments are divided into shallow-water mixed lithofacies which include fine-grained dolomite, calcareous sandstone, and spherulitic limestone, and deep-water mixed lithofacies including micrite limestone and calcareous mudstone. On this basis, six types of sedimentary facies are identified from bottom to top: slope facies, gentle-slope facies, deep-water shelf facies, shallow-water shelf facies, mixed tidal-flat facies, and mixed shelf facies. Through field outcrop observation, four third-order sequence boundaries are identified: lithofacies catastrophe surface SB1 of Doushantuo Formation sandstone and Nantuo Formation moraine; scouring contact surface SB2; and lithofacies transformation surfaces SB3 and SB4. According to lithofacies superposition style and sedimentary structural types, 56 parasequences and 18 parasequence sets are delineated; four types of parasequence styles—gravity-flow/wave-controlled gentle slope, wave-controlled shelf and mixed parasequences—are summarized; 9 system tracts are identified; and three complete third-order sequence units (SQ1-SQ3) and top transgressive system tract (TST4) are delineated. Combined with the characteristics of sedimentary facies and sequence, it is considered that the Doushantuo Formation has experienced a “steep-slope, to gentle-slope, to shelf, to mixed-platform” evolutionary process.

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    The gradual change in morphology and architecture of submarine channels in the Rakhine margin, Bengal Bay since the Late Miocene and its source-to-sink genesis
    ZHU Yijie, GONG Chenglin, SHAO Dali, QI Kun, CHEN Yanyan, DING Liangbo, MA Hongxia
    2023, 30(4): 182-195. 
    DOI: 10.13745/j.esf.sf.2022.10.22

    Abstract ( 105 )   HTML ( 10 )   PDF (12591KB) ( 77 )  

    Submarine channels are a frontier topic in deepwater sedimentology. Multi-stage channels usually migrate and evolve nonuniformly. Submarine channels in the Rakhine Basin, however, exhibit a gradual change in their geomorphology and architecture since the Late Miocene. The genesis of such gradual change is poorly understood. In this study we conducted 3D seismic investigation into the geomorphology, sedimentary characteristics, genesis and evolution of the Rakhine submarine channels. Architecturally, the Rakhine submarine channels show a gradual increasing of levee development and decreasing of undercutting. Specifically, Late-Miocene channels lack overbank levees, and erosion is predominant. Pliocene channels are characterized by mixed leveed and non-leveed channels and concurrence of deposition and erosion. Whilst Quaternary channels are flanked by extensive levees, and channel deposition is predominant. Morphologically, the Rakhine submarine channels display a gradual decreasing of erosion scales but a gradual increasing of sinuosity. Specifically, Late-Miocene channels exhibit large-scale undercutting, and are wide and deep, with a large cross-section but low sinuosity. Pliocene channels are characterized by moderate erosion, channel size and sinuosity. In comparison, Quaternary channels show reduced undercutting and channel size, but higher sinuosity. Such gradual change in channel morphology and architecture can be attributed to the gradual, westward migration of the Brahmaputra River sediment-routing system since the Late Miocene which led to gradual decreasing of extra-basinal sediment supply and subsequent development of gravity flows to bring the observed changes in submarine channels.

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    Spatio-temporal relationship between two kinds of deep-water sedimentation on the Ying-Qiong slope, South China Sea
    WANG Hairong, YU Chengqian, FAN Tailiang, CHAI Jingchao, WANG Hongyu, GAO Hongfang
    2023, 30(4): 196-208. 
    DOI: 10.13745/j.esf.sf.2022.10.20

    Abstract ( 170 )   HTML ( 4 )   PDF (15659KB) ( 75 )  

    Large amounts of oil and gas are discovered in recent years in the Yingqiong slope deep-water area, northwestern South China Sea, demonstrating the region’s high potential for oil and gas exploration and production. Deep-water sedimentation is often controlled by various mechanisms including gravity flow and contour current. Where and when these mechanisms operate and interact, and to what extent they affect or control sedimentary patterns, can result in different understandings of the regional sedimentary facies distribution due to spatio-temporal variability of hydrodynamic properties. This in turn can complicate the determination of sand body type and distribution and thus hinder gas and oil exploration and development in the region. Based on the seismic facies and stratigraphic superimposed pattern presented by the seismic data, this paper confirms the existence of two types of Miocene sedimentary systems on the Yingqiong slope: gravity (flow) and contour current sedimentary systems. These two systems are adjacent to each other sequentially in time and space, with the former superimposing over the latter in a stepwise pattern prograding towards the slope while the latter exhibiting a retrograde pattern. The boundary between the two systems indicates a special, diachronic “facies transition” interface, and, accordingly, the spatio-temporal relationship between the two distinct sedimentary processes (gravity flow and contour current) is restored. The stepwise progradation-retrogradation relationship between the two sedimentary systems can be attributed to three factors: the abundant supply of clastic materials from a multi-directional Middle-Miocene source system; the resulting strong gravity flow activity; and contour currents induced by deep-water circulation in the South China Sea. The magnitude of gravity flow largely controls the distribution range of the contour current sedimentary system, leading to a spatio-temporal stepwise progradation-retrogradational pattern.

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    Sedimentary architecture of the deep-water turbidite system in A oil field, Nigeria Delta, West Africa
    CHEN Fei, FAN Hongjun, FAN Ting’en, ZHANG Huilai, ZHAO Weiping, JING Yongquan
    2023, 30(4): 209-217. 
    DOI: 10.13745/j.esf.sf.2022.10.10

    Abstract ( 165 )   HTML ( 8 )   PDF (7869KB) ( 79 )  

    The deep-water turbidite system in A oil field, Nigeria, West Africa is extensively studied by seismic sedimentology method, combined with abundant core, outcrop, drilling and well-log data. Based on the obtained high-resolution stratigraphic sequence, deep-water fan types and channel depositional stages, the turbidite channel system is divided into three hierarchical stages—turbidite complex, multichannel complex (AU1-3) and single channel, and AU1 of reservoir A, Agbada group is divided into four single channels. The sedimentary evolution of the turbidity current channels is illustrated in detail. Constrained by ancient valley geography, the channel is mainly formed by vertical accretion, where it narrows upward, with thick sandstone with thin mud interlayers developing at the bottom and mud content increasing upward, as indicated by the bell/block-shaped GR well-log curves, and consistent with a strong-amplitude wavy reflection on the seismic profile. The general succession is lump-debris flow followed by multichannel and channel-levee complexes. Influenced by valley geography, the turbidite channel system mainly consists of restricted and semi-restricted channels. The ancient river valley, 5000-7000 m long, contains 3 stages of turbidite channels, and each stage (i.e., a single channel belt) is composed of 2-4 sub-stages of channel bodies. The multi-stage channels extend laterally and longitudinally to form a giant, thick sand body with a ternary structure: at the bottom is poorly sorted debris flow with relatively high clay content and low permeability; the middle part is low-sinuosity multichannel complex with low sand/land ratio and high permeability; and the top part is high-sinuosity single channels with low sand/land ratio and low permeability. This sedimentary model is supported by the time-lapse seismic data which show that water flooding are within the turbidite channel system. According to the fine staging of deep-water turbidity current channels and related time-lapse seismic features, residual-oil reservoirs are identified and a oil producing well is designed to provide a solid foundation for future research on the deep-water sedimentary system in the oil field.

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    Special Section on The India-Eurasia Collision and Its Long-Range Effect (Part 8)
    Overview of the crustal and upper-mantle structures of the Mongolian Plateau
    YANG Wencai, CHEN Zhaoxi, SHI Zhanjie
    2023, 30(4): 218-228. 
    DOI: 10.13745/j.esf.sf.2023.4.30

    Abstract ( 163 )   HTML ( 16 )   PDF (15550KB) ( 220 )  

    Geophysical survey and comprehensive geological analysis show that the crustal structure of the Mongolian Plateau is mainly formed under the effects of terrane amalgamation and closures of the Paleo-Asian and Mongolia-Okhotsk Oceans. Among them, the closure of the Paleo-Asian Ocean affected mainly the west and south of the Mongolian Plateau, causing the crustal uplift in the Altai collisional orogenic belt and the subsidence of the Ubuds-Bayanhonggol crust, and affecting the secondary uplift of the Hangai Mountain massif. In the east of the Mongolian Plateau, there was no strong collision at the closing of the ancient Mongolia-Okhotski Ocean in the Mesozoic Era, and the upper and lower Amur massifs and the Xilinhot land block completely merged together into one land block. This type of terrane amalgamation indicated slow land-to-land subduction played a major role. Of course, slow land-land subduction might also cause numerous crustal deformation and magma intrusions leading to continental accretion. The closure of the Mongolian-Okhotsk Ocean did not result in obvious shortening and thickening of the Earth’s crust, but large-scale mantle source magma intrusions occurred, which caused the crust to melt and the crystalline bedrock to cratonize rapidly. In the upper mantle beneath Mongolia, there are residual traces of a plume reflecting the thermal fluid upwelling to the uppermost mantle.

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    Aeolian deposits in the Yarlung Zangbo River basin, southern Tibetan Plateau: Spatial distribution, depositional model and environmental impact
    XIA Dunsheng, YANG Junhuai, WANG Shuyuan, LIU Xin, CHEN Zixuan, ZHAO Lai, NIU Xiaoyi, JIN Ming, GAO Fuyuan, LING Zhiyong, WANG Fei, LI Zaijun, WANG Xin, JIA Jia, YANG Shengli
    2023, 30(4): 229-244. 
    DOI: 10.13745/j.esf.sf.2022.9.7

    Abstract ( 254 )   HTML ( 12 )   PDF (8436KB) ( 574 )  

    Situated in the suture zone formed by the India-Euroasia collision, the Yarlung Zangbo River (YZR) basin in the southern Tibetan Plateau is a hotspot for Earth systems research, where Middle-Pleistocene aeolian deposits not only provide an important window into the history of climate change and atmospheric circulation in the Tibetan Plateau, but also help us to gain a deeper understanding of the link between tectonics, climate and landscapes in general. However, a systematic understanding of the distribution, depositional model, and environmental effects of aeolian sediments in this region is still lacking. Here, we construct a new atlas and a depositional model of aeolian sediments in the YZR basin based on extensive field investigation as well as laboratory analyses of typical sediment samples collected across the region, combined with existing research results. In general, aeolian sand and loess are distributed in patches and usually occur together. A close provenance relation between loess and nearby loose sediments such as sand dunes and river sands indicates that aeolian sediments cycle locally, hence they record spatial changes of regional climate; in contrast, the valley sediments not only receive dust from distant sources but also contribute dust materials to the world via upper-level westerly winds. Middle-Pleistocene aeolian dust activity in the YZR basin was controlled combinedly by tectonic movement and global climate change; whereas aeolian dust activity during the Holocene was relatively complex under the river valley environment, and regional climate change was generally influenced by the synergistic effect of the mid-latitude Westerlies and the Indian summer monsoon.

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    Sedimentary environment, provenance analysis and tectonic significance of the Upper-Cretaceous Abushan Formation in 114 Daoban, Anduo area, Qiangtang Basin
    DU Lintao, BI Wenjun, LI Yalin, ZHANG Jiawei, ZHANG Shaowen, YIN Xuwei, WANG Chengxiu
    2023, 30(4): 245-259. 
    DOI: 10.13745/j.esf.sf.2023.6.1

    Abstract ( 92 )   HTML ( 5 )   PDF (6498KB) ( 115 )  

    Late-Cretaceous continental strata of the Abushan Formation consist mainly of coarse clastic rocks and outcrop widely in the Qiangtang Basin, however, its sedimentary environment, source characteristics and tectonic setting remain unclear. In order to better understand the sedimentary evolution of the Qiangtang Basin and the early Tibetan Plateau uplift history after the Qiangtang-Lhasa collision we conducted detailed investigation into the depositional age, sedimentary environment, and source characteristics of the Abushan Formation in 114 Daoban, Anduo area. Angular unconformities were observed between the Abushan Formation and the underlying andesite and overlying Niubao Formation. Based on this observation, along with the eruption age of andesite and the depositional age of the Niubao Formation, we conclude that the Abushan Formation was deposited during the Late Cretaceous. Gravels of the Abushan Formation indicated a near-source deposition scenario as they mainly consisted of limestone and were transported over a short distance. Combined with geochemical data on sandstone detritus and heavy minerals, along with detrital zircon age spectra, we consider that the Abushan Formation was mainly sourced from Triassic-Jurassic strata in the southern Qiangtang and the central uplift zone. By comparing the stratigraphic characteristics between the Abushan Formation and its surrounding area, we suggest that the deposition of continental red clastic rock during the Late Cretaceous was related to large-scale thrusting in the Qiangtang Basin caused by continued plate convergence in the Qiangtang-Lhasa terranes.

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    Electron spin resonance dating for the Central Churia Thrust of the Nepal Himalaya
    NEUPANE Bhupati, ZHAO Junmeng, LIU Chunru, PEI Shunping, MAHARJAN Bishal, DHAKAL Sanjev
    2023, 30(4): 260-269. 
    DOI: 10.13745/j.esf.sf.2023.4.1

    Abstract ( 162 )   HTML ( 5 )   PDF (5201KB) ( 94 )  

    A temporal pattern of Quaternary fault activity of the Central Churia Thrust (CCT) in the southern Nepal Himalaya has been investigated using Electron Spin Resonance (ESR) signals of quartz grains in fault gouge samples. In order to better understand the reset process, the study of the variations in ESR signal, accumulated dose, and age in various quartz grain sizes was analysed. The results of the E1’ center (a type of signal for ESR dating) of sample CCT3 show a significant spatial variation in the bulk, coarse (200-250 μm), and fine (40-80 μm) grain-size fractions. The ESR date of Quaternary faults, coarser age of (5±0.5) ka and finer fraction mean age of (50±10) ka, demonstrates the latest extension event in the Siwalik region.

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    Receiving function imaging reveals the crustal structure of the East Kunlun fault zone and surrounding areas
    TONG Xiaofei, XU Xiao, GUO Xiaoyu, LI Chunsen, XIANG Bo, YU Jiahao, LUO Xucong, YUAN Zizhao, LIN Yanqi, SHI Hongcheng
    2023, 30(4): 270-282. 
    DOI: 10.13745/j.esf.sf.2023.4.20

    Abstract ( 119 )   HTML ( 5 )   PDF (7029KB) ( 119 )  

    Previous studies have suggested that the Tibetan Plateau continues to undergo eastward extrusion since the Miocene, and the observed sinistral strike-slip deformation in eastern Kunlun is strong evidence of such movement. To gain a better understanding of the land deformation, stress transfer, and material transport on the Tibetan Plateau, it is crucial to correctly identify the location of faults and the regional crustal structure. Geodetic and geomorphic evidence have indicated an eastward decrease of slip rate along the eastern Kunlun fault, particularly in the Roergai Basin covered with a variety of Quaternary sediments. However, due to basin’s alpine herbaceous swamp nature, it is particularly challenging to identify fault traces in the basin; as a result, the location of the eastern Kunlun fault within the Roergai Basin is unclear. In this contribution, a dense array of 167 seismic stations (spaced at ~1-km intervals) and 9 broadband stations were used to investigate the crustal structure beneath the eastern Kunlun fault in the Ruoergai Basin. Through basin-wide comparisons of discontinuities in crustal strata and Moho depth variations it was determined that the eastern Kunlun fault continues to extend eastward through the Ruoergai Basin; in addition, an inheritance relationship between the Tazang and eastern Kunlun faults was identified based on crustal structure similarities. The results of this study provide high-resolution evidence for the outward expansion of the Tibetan Plateau.

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    Geochemistry, geochronology and Hf isotopic characteristics of rare earth-bearing quartz syenite in eastern Dashuigou, East Kunlun
    WANG Tao, LI Jiqing, HAN Jie, WANG Taishan, LI Yulong, YUAN Bowu
    2023, 30(4): 283-298. 
    DOI: 10.13745/j.esf.sf.2023.2.41

    Abstract ( 167 )   HTML ( 7 )   PDF (7426KB) ( 135 )  

    The discovery of the rare metal/rare earth-bearing alkaline complex in Dagele area, middle East Kunlun was a major breakthrough in the exploration of rare metal and rare earth deposits in East Kunlun. The subsequent discovery of rare earth-bearing quartz syenite in eastern Dashuigou further expanded the scope of exploration, which is of great significance to the strategic mineral exploration and scientific research in East Kunlun. This paper reports the geochronological, geochemical, and Hf isotope studies of the quartz syenite to reveal its petrogenesis, magma source area and tectonic setting. The quartz syenite has a mean zircon (Zr) U-Pb age of (400.2±3.7) Ma corresponding to the Early Devonian. It belongs to the quasi-aluminous alkaline series, characterized by high SiO2 content (64.11%-66.20%), enriched Al2O3 (15.98%-16.19%) and alkali (Na2O+K2O, 11.31%-11.85%), especially K2O (7.24%-8.18%), and low Ti2O (0.38%-0.44%), CaO (1.13%-1.86%), and MgO (0.13%-0.22%) contents, with a A/CNK value of 0.9-0.98. It is enriched in large ion lithophile elements (Rb, K, Ba, Th), and depleted in high field strength elements (Nb, Ta, Ti, P). Results of 10000Ga/Al value (2.8-3.4), Zr content ((751.30-1034.85)×10-6 ), (Zr+Nb+Ce+Y) content ((881.49-1210.16)×10-6), Zr saturation temperature (905.76-931.41 ℃), and Y/Nb ratio (1.87-2.45), along with tectonic discrimination diagrams, indicate the quartz syenite is A2-type granitoid. Combined with regional tectonic and magmatic evolution data, it is believed the quartz syenite was formed in post-collision extension environment; while the Zr εHf(t) value (-0.76-+1.41), and the second stage (tDM2) Hf model age (1303-1435 Ma) indicate the quartz syenite is derived from partial melting of Middle-Proterozoic felsic crust during mantle-derived, high-temperature basaltic magmatic underplating.

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    The components of the subducted continental basement within the Dabieshan orogenic belt as evidenced by xenocrystic/inherited zircons from Cretaceous dykes
    XU Daliang, DENG Xin, PENG Lianhong, TIAN Yang, JIN Wei, JIN Xinbiao
    2023, 30(4): 299-316. 
    DOI: 10.13745/j.esf.sf.2023.5.1

    Abstract ( 161 )   HTML ( 9 )   PDF (7344KB) ( 164 )  

    Ancient continental basement of young orogenic belts may reveal the early evolutionary history of continental blocks. Continental basement of subduction plate in a collision orogen is generally located in the Earth’s lower crust and unlikely to be widely exposed on the Earth’s surface, however, xenocrystic/inherited zircons from shallow igneous rocks can be used to trace the content and evolution of continental crust at depth. Here we present in situ U-Pb and Hf isotope data for the newly discovered xenocrystic/inherited zircons from Late-Mesozoic dykes (140-127 Ma) in the southern Dabieshan orogen to address the critical issue about the nature, age and evolution of geologic basement of the Dabieshan orogenic belt. The xenocrystic/inherited zircons are dated to the Precambrian and show an episodic age distribution. They record a large number of multi-stage magmatic events (at 3.44-3.23 Ga, 2.99-2.82 Ga, 2.79-2.60 Ga, 2.47 Ga, 2.00 Ga, 1.82 Ga, 0.89 Ga, 0.82-0.78 Ga and 0.71-0.59 Ga) as well as six metamorphic events (at 3.28 Ga, 2.87 Ga, 2.73 Ga, 2.51 Ga, 1.98 Ga and 0.80 Ga). The Hf isotopic composition of the xenocrystic/inherited zircons shows that the southern Dabieshan orogen experienced significant continental growth in the Archean, mainly concentrated in the Paleoarchean (3.6-3.3 Ga) and Neoarchean (2.7-2.6 Ga), and underwent multi-stage reconstruction (3.4-3.2 Ga, 3.0~2.8 Ga, 2.7-2.5 Ga, 2.0-1.8 Ga, 0.9-0.6 Ga and 0.1 Ga). According to comprehensive analysis, the southern Dabie orogen should represent basement of subduction plate that was not involved in deep subduction and at least modified by multi-stage tectono-thermal events in the Paleoproterozoic and Neoproterozoic relating to the formation of the Columbia and breakup of the Rodinia supercontinents, respectively.

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    Intelligent geoscience information mining and knowledge discovery using big data analytics: A case study of the Shangfanggou Mo (Fe) mine in Henan Province
    WANG Luofeng, WANG Gongwen, XU Wenhui, XU Senmin, HE Yaqing, WANG Chunyi, YANG Tao, ZHOU Xiaojiang, HUANG Leilei, ZUO Ling, MOU Nini, CAO Yi, LIU Zhifei, CHANG Yulin
    2023, 30(4): 317-334. 
    DOI: 10.13745/j.esf.sf.2022.2.85

    Abstract ( 310 )   HTML ( 13 )   PDF (8487KB) ( 2375 )  

    Industry 4.0 of the 21st century has given birth to smart mines. The multidisciplinary datasets of smart mines-such as geology, exploration, mining, geometallurgy, environment and survey/map datasets-constitute big data of mines, and they play an important role for the rapid advancements of geoscience in areas of geoscience digitization and application of information/Al technology in geoscience. Taking the Shangfanggou Mo (Fe) mine, a 5G+ smart mine, in Henan Province as an example, using big data of mines, this paper carried out geoscience information mining to highlight emerging engineering research with integrated multidisciplinary approach. Innovative results and geological knowledge discoveries from this study are summarized as follows: (1) According to theories on porphyry-associated skarns and mineralogical approach to minera resources prospecting, using borehole datasets and large-scale open-pit mapping and microscopic identification analysis, a 3D temporo-spatial model of the identified key minerals and predicted minerals in the study area was established, and a NE trending ore-bearing fault section and a penetration-type ore-bearing section were discovered. (2) Using UAV remote sensing and ground hyperspectral short-wave/long-wave infrared techniques, more than 20 types of key altered minerals in the study area were delineated, and a 3D multi-parameter mineral model was constructed. (3) Using geochemical techniques such as XRF and in-situ microscopy, a rock dataset with matching hyperspectral interpretation was established, and a dual-matrix mapping software for useful/harmful elements of rocks/ores in the study area was developed. In addition, mathematical modeling combining traditional geostatistics (gauss simulation, kriging interpolation) with machine learning (deep learning) was realized, and the composition of ore blends used between March-April 2021 was identified and the cause of the resulting low recovery rate was clarified. (4) Based on process mineralogy practice in the study area, multi-stage, multi-type mineral processing datasets (>1800 data on quarterly/monthly/daily processing of rock powder, mud powder, concentrate, tailings, etc.) were used to develop rock/mineral powder testing techniques and analysis methods, and the types of refractory ores and harmful minerals in the Shangfanggou Mo mine were identified. The multivariate, multi-type datasets of mines have the “5V” (volume, variety, velocity, veracity, value) characteristics of big data. The accurate management control of dynamic correlation measurement/analysis and rapid/efficient evaluation of big data of mines is conducive to intelligent mining decision-making and improvement of economic benefit (recovery rate). Among them, high-precision multi-parameter 3D modeling can be applied not only to deep mining of geological, structural, alteration and mineralization information models of rocks/ores as well as reserve/resources verification, but also to facilitating 4D control on real-time mining of fourth generation industrial 5G+ mines, such as 3D visualization of geological and mineral resources prediction/evaluation/storage expansion, virtual simulation of “year-quarter-month-day” dynamic ore blending and mining, and real-time digital twin for mine beneficiation. The research results provide a reference for in-depth geoscience research on mineral exploration and mineral resources assessment in smart mines.

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    Key factors and mechanisms affecting calcite growth and dissolution-a critical review
    DU Baisong, ZHU Guangyou, LIU Shufei, WANG Yehan, YU Bingsong, XU Kexin
    2023, 30(4): 335-351. 
    DOI: 10.13745/j.esf.sf.2023.2.42

    Abstract ( 268 )   HTML ( 19 )   PDF (3138KB) ( 201 )  

    Carbonate rocks account for ~20% of Phanerozoic sedimentary rocks while carbonate reservoirs hold at least 60% of the world’s proven hydrocarbon reserves. Calcite, as a common carbonate mineral, plays an important role in the formation of secondary pores in the shallow part of the Earth’s crust. This paper summarizes previous studies on the key factors and mechanisms affecting calcite growth and dissolution. For calcite growth, the key influencing factors include temperature, pressure, degree of supersaturation, as well as the types and ionic radius of ions in the surrounding solution, where the decrease of pressure and the increases of ionic strength and calcite surface supersaturation are beneficial for calcite growth. For calcite dissolution, the key influencing factors are temperature, pressure, p(CO2), ionic strength, pH/chemical composition of the surrounding solution, Zeta potential, and degree of calcite saturation, where Zeta potential of calcite is the main factor determining whether ions in the surrounding solution promote or inhibit dissolution. The surface micromorphology of calcite varies depending on the composition of the surrounding solution during calcite growth/dissolution, which makes it possible to reconstruct the palaeo-fluid by observing the surface morphology of calcite. This paper also analyzes in great detail the inconsistency in previous experimental results and interprets the inconsistency from a novel viewpoint. By focusing on the influencing factors of calcite dissolution, this paper seeks to find the optimal conditions for carbonate dissolution so as to provide a reliable theoretical basis for delineating high-quality carbonate reservoirs. This paper can be helpful for researchers to quickly learn about research hot-spots and latest progresses in this field.

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    Genesis of dolostone of the Yingshan Formation in Tarim Basin and Mg isotope evidence
    LI Xi, ZHU Guangyou, LI Tingting, AI Yifei, ZHANG Yan, WANG Shan, CHEN Zhiyong, TIAN Lianjie
    2023, 30(4): 352-375. 
    DOI: 10.13745/j.esf.sf.2022.10.43

    Abstract ( 228 )   HTML ( 6 )   PDF (9180KB) ( 174 )  

    The Yingshan Formation of the Middle-Lower Ordovician is a potential exploration replacement series in the Central Uplift of the Tarim Basin, however, the genesis of dolostone is still unclear, which hinders dolomite exploration in the basin. The ongoing dolomatization in the Yingshan Formation, as evidenced by the sequential, bottom-to-top developments of dolostone, dolomitic limestone and limestone, makes it feasible to study the dolostone reservoirs by Mg isotope analysis that has shown good results in tracing the source and migration pathway of dolomitic fluid. In this study, we systematically collected dolostone, dolomitic limestone and limestone from the Yingshan Formation and carried out comprehensive petrological, trace elemental and isotope (C, O, Mg) analyses. Six types of dolostone were identified in the Yingshan Formation: dolomicrite/micro-crystalline dolostone (D1), powder/fine-crystalline dolostone (D2), granular dolostone (D3), medium/coarse-crystalline dolostone (D4), dolomitic limestone (DL) and limestone (L). The δ13CV-PDB value of carbonate rock ranged between -2.10‰ to -0.37‰ (average -1.37‰), δ18OV-PDB value between -7.51‰ to -3.54‰ (average -5.41‰), and δ26Mg value between -4.03‰ to -1.28‰ (average -2.55‰), and certain degree of correlation in the vertical direction was observed between δ26Mg, Na, Sr/Ba, Mn/Fe, δ13CV-PDB, δ18OV-PDB, paleosalinity (Z) and plaeotemperature (T). Results on dolomite genesis revealed (1) the δ26Mg variation trend in the vertical direction was closely related to sedimentary cycles, where the top layer was identified as the source area of Mg-rich fluid and the layer interface as the migration channel. (2) There were four migration pathways of dolomitic fluid identified based on the Mg isotopic variation trends: L→DL→D, D1→D2, D2→D3→D4→L and D4→L/DL. (3) The formation of dolostone was mainly related to the periodic fluctuation of sea-level: with decreasing sea level, Mg-rich fluid formed in the confined water via evaporation migrated vertically downward along the high-porosity, high-permeability granular limestone to promote continuous dolomitazation, or it encountered low-porosity argillaceous limestone and failed to enter the rock lattice, thus terminating dolomitization; whereas rising sea-level destroyed the source area of Mg-rich fluid, thus weakening or interrupting dolomitization to form calcareous dolostone and limestone. (4) Multi-stage metasomatism, recrystallization and hydrothermal processes in the deep-burial stage were also conducive to the formation of dolostone. (5) Dolomitization had significant impact on the sedimentary reservoirs, where early dolomitization was conducive to the inheritance and preservation of pores while late-burial and hydrothermal dolomitization destroyed the reservoirs.

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    Lithospheric mantle metasomatized by oceanic crust-derived fluids: Li and Pb isotopic evidence from potassic volcanic rocks in the southern Qiangtang terrane, central Tibet
    LI Wenqiang, XU Wei, TIAN Shihong
    2023, 30(4): 376-388. 
    DOI: 10.13745/j.esf.sf.2023.2.61

    Abstract ( 153 )   HTML ( 4 )   PDF (4661KB) ( 129 )  

    Lithium (Li) isotopes show large isotopic fractionation during low-temperature processes and have been widely used to trace crust-mantle interactions. In order to identify the crust-derived components in the lithospheric mantle, this study reports new Li and Pb isotopic data for the Late Eocene (~38 Ma) lithospheric mantle-derived potassic volcanic rocks (trachydacites, rhyolites, etc.) from the southern Qiangtang terrane, central Tibet. The volcanic rocks have homogeneous Pb isotopic compositions (206Pb/204Pb=18.4979-18.5772; 207Pb/204Pb=15.5940-15.6107; 208Pb/204Pb=38.6710-38.7540) and variable Li isotopic compositions, with δ7Li values ranging from 5.67‰ to 10.97‰ (average 8.81‰, n=11), significantly higher compared to fresh mid-ocean ridge basalts (3.4‰±1.4‰) and global subducted sediments (2.42‰±0.18‰ (GLOSS-II)) but similar to that of altered oceanic crust (6‰-14.5‰). Combined with published Sr-Nd isotopes and mixing models for Sr-Nd-Pb-Li isotopes, we suggest that mantle metasomatism occurred in the southern Qiangtang terrane by a crustal component dominated by subducted oceanic crust-derived fluids, but we do not preclude the possible contribution of subducted carbonated melts.

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    Modern fluvial fans: Global distribution, fan types and controlling factors
    ZHANG Yuanfu, WANG Min, ZHANG Sen, SUN Shitan, LI Xinxin, YUAN Xiaodong, HUANG Yunying, ZHANG Xiaohan
    2023, 30(4): 389-404. 
    DOI: 10.13745/j.esf.sf.2022.12.52

    Abstract ( 168 )   HTML ( 18 )   PDF (9305KB) ( 201 )  

    Fluvial fans are an important topic in sedimentology. As fan research attracts more attention in recent years, various fan terminology systems are being used in parallel, but there lacks an independent terminology system for fluvial fans. To address this issue, we constructed a sediment dataset containing sediments from 383 modern fluvial fans across the globe, with 8400 data analyzed using statistical method. For the first time, based on the dataset, we obtained the global distribution of modern fluvial fans, delineated the main fan types, and clarified the controlling factors of fan formation and development. The global distributions of fluvial fans show obvious latitudinal and geographical zonation, with 49.5% fans distributed between 30°N-50°N and 50.1% in central Asia and western China. According to the topographic and river swing conditions, fluvial fans can be divided into four types: unrestricted superposition, unrestricted swing, restricted superposition and restricted swing. Fluvial fans are mainly formed under arid and semi-arid climates, controlled by local tectonic conditions, climate and material source supply. Fluvial sedimentation is dominant in fluvial fans which show obvious heterogeneity from the apex to the end of the fan. The area of a fluvial fan is controlled by latitude, temperature, slope, catchment area, annual rainfall and apex-to-mountain distance. With more in-depth research, fluvial fans will play an increasingly important role in sedimentology, geological disaster prevention, oil exploration, and even in interplanetary sedimentology.

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    Mechanism of ice avalanche in the Sedongpu sag, Yarlung Zangbo River basin-an experimental study
    TANG Minggao, LIU Xinxin, LI Guang, ZHAO Huanle, XU Qiang, ZHU Xing, LI Weile
    2023, 30(4): 405-417. 
    DOI: 10.13745/j.esf.sf.2023.2.64

    Abstract ( 215 )   HTML ( 15 )   PDF (12433KB) ( 99 )  

    In recent years ice avalanche disasters occur frequently in the Tibetan Plateau and the mechanism of ice avalanche has attracted much attention. In this paper, the evolutionary process and controlling factors of ice avalanche in the Sedongpu sag were investigated via multi-stage imaging analysis. In the mechanistic study, shear strength tests were carried out at different temperatures on two types of ice materials: crystalline ice and ice-rock mixture. The crystalline ice sample was prepared by pressing crushed ices into a mold, and the ice-rock mixture was prepared by pressing crushed ices and slate. Imaging analysis results showed that glaciers with 30° or steeper terrain slopes were prone to ice avalanche while strong near-field earthquakes aggravated glacier deformation/fracture, and climate warming was the main reason for the frequent occurrence of ice avalanches in the Sedongpu sag. In the shear test, the shear stress-shear displacement curves for both materials revealed brittle deformation type, while for polycrystalline ice a “secondary peak” appeared under low temperature conditions, indicating refreezing phenomenon. With increasing temperature, the cohesive strength and internal friction angle of both materials decreased linearly, even at an accelerated pace; whilst at the same temperature, the cohesive strength was less and the internal friction angle was greater for ice-rock mixture than for polycrystalline ice. Thus the likely genetic mechanism of ice avalanche is that the rise of temperature leads to decrease of shear strength of the ice/rock shear sliding zone thus its anti-sliding force to trigger an ice avalanche.

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    Effect of vegetation on carbon sequestration in karst systems-a critical review
    YU Shi, PU Junbing, LIU Fan, YANG Hui
    2023, 30(4): 418-428. 
    DOI: 10.13745/j.esf.sf.2022.9.4

    Abstract ( 163 )   HTML ( 6 )   PDF (2380KB) ( 119 )  

    Vegetation-the link between atmosphere, water, soil and rock-is a key influencing factor of carbon sequestration via rock weathering. Understanding their relationship can help to better estimate the carbon flux in karst systems and assess the effect of karsification on the reduction of atmospheric CO2 emissions. This review summarizes and evaluates the latest research findings on the impact of vegetation succession on karst carbon sink, the control of vegetation on the karstification process in terms of biological effects, soil properties, climate, runoff changes and hydrogeological structure of karst systems, and the impact of vegetation on water cycle during the karstification process. Finally, future research directions are proposed, which include the vertical structure of karst critical zone, the effect of vegetation on carbon sequestration in karst watershed during different precipitation processes, the relationship between microstructure and hydrological effects, and the impact of vegetation succession on carbon sequestration in karst systems at watershed scale plus insights from human interventions.

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    Carbon dioxide storage in China: Current status, main challenges, and future outlooks
    DENG Yirong, WANG Yonghong, ZHAO Yanjie, GU Peike, XIAO Jin, ZHOU Jian, LI Zhaohui, YU Zhiqiang, PENG Ping’an
    2023, 30(4): 429-439. 
    DOI: 10.13745/j.esf.sf.2023.2.70

    Abstract ( 614 )   HTML ( 36 )   PDF (3840KB) ( 446 )  

    Excessive fossil fuel consumption and land misuse lead to continuous increasing emissions of carbon dioxide and other greenhouse gases, causing a series of environmental problems such as global warming. To effectively control carbon emissions underground carbon storage is developed and it plays an important role in China’s efforts to achieve carbon neutrality while ensuring its energy supplies. Here, we systematically summarize the technical principles and characteristics of typical terrestrial (such as CO2-EOR and CO2-ECBM) and marine carbon sequestration techniques (such as natural gas hydrate sequestration and marine sediment sequestration), and present an overview of China’s carbon emission profile and storage potential, characteristics of domestic carbon-storage pilot projects at different capacities (10000 s to million tons), gaps between China and foreign countries, and main challenges in carbon sequestration. In view of China’s carbon-storage status and goal of carbon peaking/carbon neutrality, we suggest to improve policy support, storage evaluation standards, and relevant laws and regulations, explore suitable storage sites and high-potential areas, strengthen scientific research and access to advanced technology, increase CCS/CCUS infrastructure investments and construction scales, and develop model pilot projects and industrial clusters. As Guangdong Province possesses industrial (trillion ton) carbon-storage potential ahead of carbon peaking, its coastal areas with the greatest carbon storage potential should take the lead in the industrial application of underground carbon-storage technology as well as in the developments of industrial carbon-storage clusters and trillion-ton carbon-storage industry towards achieving China’s carbon neutral target.

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    Groundwater circulation in the Ejina Plain: Insights from hydrochemical and environmental isotope studies
    XU Rongzhen, WEI Shibo, LI Chengye, CHENG Xuxue, ZHOU Xiangyu
    2023, 30(4): 440-450. 
    DOI: 10.13745/j.esf.sf.2023.2.44

    Abstract ( 112 )   HTML ( 11 )   PDF (8867KB) ( 132 )  

    The Ejina Plain has a fragile ecoenvironment and groundwater plays an important role in maintaining an ecological balance in the region. However, an in-depth understanding of groundwater circulation in the Ejina Plain is lacking due to limited knowledge of groundwater circulation in eco-hydrologically important sections. In this study, the characteristics of groundwater circulation at key aquatic interfaces are investigated through hydrochemical and environmental isotopic analyses, and the regional groundwater circulation patterns are revealed. In the desert area rainfall is strongly affected by evaporation during groundwater recharge via infiltration, while in the central part of the study area rainfall only contributes weakly to groundwater recharge. The Cretaceous phreatic water system in the northern Ejina Plain is recharged by lateral runoff flowing from north to south, and intersects the southern Quaternary groundwater system in the eastern and western Juyanhai areas; whereas stagnant Cretaceous confined water runoff has limited interaction with the overlying phreatic water system. In the central part of the plain groundwater is recharged by seepage from the Heihe River over an effective area of 30-50 m deep and 10 km wide, and groundwater recharge drives slow surface runoff on both sides of the river to flow to the Gurinai-Swan Lake district, where it meets the desert groundwater system in the east; the Heihe River has no impact on groundwater recharge/discharge in the desert area. This study deepens our understanding of groundwater circulation in the Ejina Plain and helps to guide local ecological environmental protection and restoration as well as rational development and utilization of groundwater.

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    Modeling of hydrological processes in cryospheric watersheds based on machine learning
    SONG Xuanyu, XU Min, KANG Shichang, SUN Liping
    2023, 30(4): 451-469. 
    DOI: 10.13745/j.esf.sf.2023.2.52

    Abstract ( 188 )   HTML ( 11 )   PDF (7773KB) ( 84 )  

    Machine learning models are widely used in hydrological research for their high predictive accuracy, however, their application in high-altitude cryospheric watersheds is seldom mentioned. In this study, machine learning models for two typical cryospheres, Yarkant and Shule river basins, were developed using BP neural network (BP), GRNN neural network (GRNN), RBF neural network (RBF), support vector regression (SVR), genetic optimization BP neural network (GA-BP) and double-layer long-term and short-term memory neural network (LSTM) algorithms, and model performance was evaluated using evaluation indexes NSE, RMSE and R and runoff frequency curves. The double-layer LSTM model performed much better than and similar to other models for the Yarkant and Shule River Basins, respectively; and overall the double-layer LSTM algorithm was more suitable for modeling hydrological processes in cryosphere basins. The loss function was used to evaluate the model parameterization scheme. It was found that the performance of the LSTM models was mainly affected by the optimizer, followed by the learning attenuation rate and initial learning rate for the Yarkant River Basin, and by the initial learning rate for the Shule River Basin. Model testing under abrupt changes in runoff suggested that climatic factors could have different hydrological impacts, meanwhile, precipitation and heavy precipitation R95p had the greatest impacts on the hydrological process in the study area, followed by temperature, during the entire study period.

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    Spatial distribution, sources and health risks of heavy metals in soil in Qingcheng District, Qingyuan City: Comparison of PCA and PMF model results
    NING Wenjing, XIE Xianming, YAN Liping
    2023, 30(4): 470-484. 
    DOI: 10.13745/j.esf.sf.2023.2.46

    Abstract ( 252 )   HTML ( 8 )   PDF (4825KB) ( 89 )  

    In this study we collected 122 soil samples from a typical, rapidly transforming industrial urban area in southeastern China to evaluate pollution characteristics of 9 heavy metals (As, Co, Cr, Cu, Hg, Ni, Pb, Ti, and Zn) in soil using enrichment factor (EF), geological accumulation index (Igeo), Spearman correlation analysis, potential ecological risk comprehensive index (RI), and human health risk model (HHR); combined with principal component analysis (PCA), positive matrix factorization (PMF) model and geostatistical analysis, the source of heavy metals was investigated. The results showed that As, Cu, Hg, Pb, and Zn were obviously enriched in soil, but the study area as a whole is clean from heavy metal pollution. Hierarchical clustering and grouping results of heavy metals by PCA and PMF models identified 2 and 3 source areas respectively, which helped to improve the accuracy of source analysis. According to ecological risk assessment the study area as a whole is at slight ecological risk, and Hg poses the highest ecological risk among all elements. By human health risk assessment neither adults nor children in the study area are at health risks from heavy metal pollution, including non-carcinogenic and carcinogenic risks, but we found that heavy metal pollution poses greater health risks to children and should be taken seriously.

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    Occurrences and health risks of high-nitrate groundwater in typical piedmont areas of the North China Plain
    ZHANG Guanglu, LIU Haiyan, GUO Huaming, SUN Zhanxue, WANG Zhen, WU Tonghang
    2023, 30(4): 485-503. 
    DOI: 10.13745/j.esf.sf.2023.2.53

    Abstract ( 251 )   HTML ( 12 )   PDF (9774KB) ( 135 )  

    Nitrate pollution in groundwater is a global concern, yet the distribution characteristics of high-nitrate groundwater and its health risks to different populations in the agricultural intensive piedmont alluvial fans are not fully understood. In this study, we carried out comprehensive hydrogeochemical analysis on 144 groundwater samples collected from two sets of piedmont aquifers (Beijing and Shijiazhuang areas) in the North China Plain to determine the distribution pattern, formation mechanism, and health risks of high-nitrate groundwater in the region. The regional groundwater was neutral to slightly alkaline, and 84% of the samples had nitrate concentrations exceeding the national standard (10 mg/L) for drinking water. The average nitrate concentration in groundwater was higher in Beijing than in Shijiazhuang areas, and in both areas higher in shallow than in deep aquifers. Planarly, high-nitrate groundwater was more commonly distributed in the southwestern region as compared to the eastern and northern regions. High-nitrate groundwater was mainly characterized by HCO3-Ca-Mg hydrochemical facies, controlled mainly by mineral dissolution, rock weathering, and evaporative crystallization, according to ion ratio and principal component analyses. Agricultural activities, ion exchange, and nitrification were the main causes of nitrate enrichment in groundwater. Water quality of deep groundwater was better compared to shallow groundwater, with EWQI values mostly between 1 and 2. According to health risks assessments of four population groups (infants, children, women, and men) using HHRA model, the potential non-carcinogenic risk of high-nitrate groundwater was high for infants, and shallow groundwater posed a greater health risk in both areas. Overall, the potential non-carcinogenic risks were lower in Shijiazhuang than in Beijing where high-nitrate groundwater posed a health risk to all populations. In Beijing, the high risk areas were mainly located in the southwest and central part, and the east was at relative low risk. In Shijiazhuang, the potential health risk was high in the west and low in the east, and most of the groundwater in the east was suitable for drinking by all populations. We concluded, therefore, that controlling nitrate input from shallow groundwater, selecting drinking water sources according to population groups, and providing deep groundwater to infants were crucial for ensuring safe drinking water for local residents.

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    Evaluation of ecological resilience in terrestrial ecosystems in Gansu, China-an empirical study
    MAO Long, WANG Shenglan, QIU Xiaoyi, TAO Zhuolin, FENG Yongzhong, HUANG Yinzhou
    2023, 30(4): 504-513. 
    DOI: 10.13745/j.esf.sf.2023.2.48

    Abstract ( 210 )   HTML ( 4 )   PDF (4594KB) ( 103 )  

    With the full implementation of ecosystem restoration program in China, the evaluation of ecological resilience has become an integral part of the regional restoration efforts. Due to diverse terrain conditions at provincial level it is extremely important for each province to build regional resilience models and choose suitable evaluation methods to evaluate the resilience models. Taking the example of Gansu Province which has the highest terrain diversity in the country, based on climate, vegetation and land use data for 87 counties, using Fragstats, ArcGIS and Geoda softwares, this paper evaluates ecological resilience in Gansu terrestrial ecosystems as a whole and in ecosystems of five regions with different terrain types, and discusses the difference in regional ecological resilience and its influencing factors. Gansu Province has an average resilience index score of 0.45 and is rated “average” in overall ecological resilience, where resilience indicators (ecological resilience intensity/limit, ecological resilience index) show trends of decreasing ecological resilience from the southeast to northwest. The calculated value of Moran’s I is 0.95 and obvious spatial clustering of high-high and low-low resiliency areas is detected; high-high clusters are mainly in the southeast and low-low clusters mainly in the northwest of Gansu. These results, combined with the suggestions put forward in this paper on ecosystem restoration for different terrain types, provide a frame of reference for decision-making in the regional terrestrial spatial planning and ecological restoration in Gansu.

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    Suitability evaluation of underground space development in Shenzhen: Urban geoenvironmental considerations
    SU Dong, HUANG Maolong, HAN Wenlong, LI Aiguo, WANG Enzhi, CHEN Xiangsheng
    2023, 30(4): 514-524. 
    DOI: 10.13745/j.esf.sf.2023.2.45

    Abstract ( 213 )   HTML ( 16 )   PDF (6920KB) ( 118 )  

    To assess the suitability of underground space development in Shenzhen we examined various influencing factors, such as geological environment, surface environment, economic development and geological disaster, to establish a suitability evaluation framework for shallow underground space development and utilization. Fourteen evaluation indicators under 6 categories (geoengineering, hydrogeology, geohazard risk, development status, topography and geology) were used, and the weight of each indicators was determined by scaling index and analytic hierarchy process (AHP) methods. In the final assessment, each urban area of interest was graded suitable, sub-suitable, average or poor for underground space development, and suitability maps were made which showed that the suitable and sub-suitable zones were concentrated in Futian, Nanshan and Bao’an Districts and accounted for ~80% of the total urban area. Therefore, Shenzhen has highly favorable conditions for underground space development. This assessment provided a theoretical basis for underground development planning in Shenzhen, and the suitability evaluation framework developed for Shenzhen can be applied to other cities with similar geological conditions.

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    Geological characteristics and evolution of the Schrödinger basin and adjacent areas: Insights from multi-source remote sensing data
    WANG Ying, DING Xiaozhong, HAN Kunying, CHEN Jian, LIU Jingwen, LU Tianqi, WANG Juntao, SHI Chenglong, JIN Ming, PANG Jianfeng
    2023, 30(4): 525-538. 
    DOI: 10.13745/j.esf.sf.2022.9.11

    Abstract ( 173 )   HTML ( 11 )   PDF (15870KB) ( 142 )  

    The Schrödinger basin is a typical lunar peak-ring basin formed in the Late Imbran with well-preserved, relatively complete basin structure. It is located at the transition zone between the floor and the southwestern rim of the South Pole-Aiken basin on the far side of the Moon. Insights into the geological evolution of the Schrödinger basin can help to better understand the evolution of the peak-ring basins in general. In this paper, using multi-source remote sensing data, combined with previous research results, we created an 1∶2500000 geological map of the Schrödinger basin and adjacent area and performed comprehensive geological analysis to investigate the basin’s topographic features, lithologic distribution characteristics, structural features, and evolution. Based on the state-of-art remote sensing data and newly updated crater size-frequency distribution we determined the extent of basalt units in the basin and obtained more accurate ages for the basalt units; besides, we identified additional structural features of the study area and developed a more comprehensive view on the regional geological evolution compared to previous studies. According to our analysis, the main rock types in the Schrödinger basin were ferroan anorthosite suite, ferroan norite suite, and magnesian anorthosite suite, along with sporadically distributed basalts, anorthosite, olivine-rich outcrops, and pyroclastic deposits. The absolute model ages of two mare basalt units were 3.26 and 3.36 Ga, respectively, indicating they belong to the Upper Imbrian strata. There were nine structural styles identified in the study area, among which crater-floor fractures, mascon, and volcanic vent might have gradually formed, post depositional, during gravitational equilibrium. We concluded that the formation of the Schrödinger basin could be divided into three stages: pre-impact, basin forming, and post-depositional reconstruction.

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