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2018, Volume 25 Issue 4
15 July 2018 Previous Issue    Next Issue

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Preliminary discussion on the role of microcontinental blocks in the evolution of the Central Asian orogenic belt: taking the Xilinhaote microcontinental block as an example. SHAO Ji'an,TIAN Wei,TANG Kedong,ZHOU Xinhua 2018, 25(4): 1-10.  DOI: 10.13745/j.esf.sf.2018.4.45 Abstract ( 326 )   PDF (2171KB) ( 610 )    The old continental crustal massifs or inlaid microcontinental blocks in the Central Asia Orogenic Belt characterize a previous PaleoMongolia ocean. Discussed in this work is the Xilinhaote microcontinental block. The Xilinguole complex—basement of the microcontinental block—has experienced the Early Paleozoic tectothermal events yet still contains older Precambrian zircons. The Xilinguole microcontinental block also acted as pillar when the orogenic belt suffered strong extensional deformation and underplating in the Late Paleozoic (C2P1): while rifts occurred at north and south edges of the microcontinental block, a stable littoralneritic facies sedimentary environment was maintained inside the block. At the same time, in the event of underplating from the upper mantle, tectonic structure of the orogenic zone remained stable, as the microcontinental block further accreted vertically and consolidated through certain orogenic bimodal magmatic activity and alkalic granite emplacement associated with block remelting. It has been the purpose of this work to comprehend some of the unique regional geological phenomena that are closely related to underplating during the Late Carboniferous. Related Articles | Metrics

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The ~2.5 Ga monzogranite in the Shaolanghe area of the northern margin of the North China Craton and its geological significance. GUO Yunpeng,LIU Jianming,ZENG Qingdong,GAO Shuai,WANG Luming 2018, 25(4): 11-22.  DOI: 10.13745/j.esf.yx.2017-5-4 Abstract ( 221 )   PDF (4693KB) ( 392 )   In this study, the ~2.5 Ga late Neoarchaean monzogranites have been identified for the first time in the Shaolanghe area of the northern margin of the North China Craton (NCC). Analyses of in situ zircon UPb ages, Hf isotopic data and wholerock major and trace element contents have been performed on the monzogranites. UPb dating of magmatic zircons indicates that the monzogranites formed in 2527±25 Ma, in the late Neoarchaean. Their massive structures contain partly gneissiclike and mediumcoarse grain structures with sporadic dark inclusions. The rocks have high Na and K, low P, a A/CNK ratio of 0.800.96, and belong to the highK calcalkaline series. The monzogranites exhibit enriched light rare earth elements (LREEs) with no δEu anomalies, and are enriched in large ion lithophile elements (LILEs) (e.g., Rb, Sr and Ba), and depleted in high field strength elements (HFSEs) (e.g., Nb, Ta, P and Ti). The zircon εHf(t) value and twostage Hfdepleted mantle model age (TDM2) range from 4.0 to 4.8 and 2712 to 3221 Ma, respectively, suggesting that the monzogranites were derived from fractional crystallization after melting of the juvenile Mesoarchaean and Neoarchaean lower crust. Relating to the newly discovered greenstone belt and TTG igneous rocks of the Archean in the Shaolanghe area in recent years, this paper proposes that there exists a Precambrian basement in the Shaolanghe area, possibility in the form of an ancient microblock. The formation of the monzogranites is an important symbol of cratonization at the end of the Neoarchaean in the NCC. Although the geochemical characteristics of the monzogranites indicate their probable association with subduction, we consider such subduction or collision between arc and continent or two continents limited and at a smallscale in the late Neoarchaean, quite different from the tectonic plate system. Related Articles | Metrics

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Characteristics of the Silurian System in the middle part of the Korean Peninsula and their significance. KIM Byongsong,WANG Xunlian,KANG Jingon,LI Choljun,LI Bin,HO Cholung,KIM Myonghak 2018, 25(4): 23-31.  DOI: 10.13745/j.esf.sf.2018.4.40 Abstract ( 213 )   PDF (2345KB) ( 263 )   朝鲜半岛的志留系仅见于中朝克拉通东缘朝鲜半岛中部的平南盆地。该盆地志留系发育于谷山—新溪—遂安地区和法洞地区。谷山—新溪—遂安地区的志留系划分为碎屑碳酸盐岩组成的谷山组和碳酸盐岩为主的月阳里组，化石非常丰富，包括珊瑚类、腕足类、海百合类和腹足类等，该地区谷山组中部和月阳里组上部发育以床板珊瑚为主的生物礁。法洞地区志留系主要为碎屑岩，夹碳酸盐岩薄层，化石极少。将平南盆地志留系生物地层划分为5个组合带，自下而上依次为Striispirifer shiqianensis带、Palaeofavosites balticusCamarotoechia ubsuensis组合带、Favosites songrimensisLeptostrophia guizhouensis组合带、Parastriatopora coreanicusPleurorima granata组合带和Pentagonocyclicus monocostatusPentagonopentagonalis probus组合带。据此认为谷山组时代为兰多维列世，月阳里组时代为温洛克世—罗德洛世。 Related Articles | Metrics

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LA-ICP-MS trace element characteristics of magnetite from the Zhangjiawa iron deposit, Laiwu and constraints on metallogenic processes. CHEN Yinghua,LAN Tingguang,WANG Hong,TANG Yanwen,DAI Zhihui 2018, 25(4): 32-49.  DOI: 10.13745/j.esf.sf.2018.5.27 Abstract ( 375 )   PDF (2846KB) ( 459 )   The Zhangjiawa skarn iron deposit is located at the Laiwu area of Luxi Block, eastern North China Craton. It is genetically associated with the Early Cretaceous highMg diorite, and occurs in the contact zones between the Ordovician Majiagou Formation limestone/dolomite and diorite. In this paper, we carried out detailed analyses of major and trace elements in magnetite using electron microprobe and laser ablation ICPMS methods, aimed to reveal the geochemical features as well as evolutional trends from the magmatic to the hydrothermal magnetites and thus provide significant constraints on the genetic processes of the Zhangjiawa Fe deposit. The results showed that igneous and hydrothermal magnetites in the Zhangjiawa deposit have distinct geochemical features. Compared with the hydrothermal magnetite, the igneous magnetite was significantly enriched in siderophile elements such as Ti, V and Cr. High field strength elements such as Nb, Ta, Zr, and Hf, and moderate compatible elements of Sn, Ga, Ge and Sc, were also relatively enriched in the igneous magnetite. However, lithophile elements such as Mg, Al, Mn, Zn and Co were remarkably enriched in hydrothermal magnetite. Ti, V, Cr, Mg, Al, Mn, and Zn typically exhibited distinct behaviors between the magmatic and hydrothermal systems. Mineralization of magmatic Ti, Cr and V in magnetite was mainly controlled by temperature, partition coefficient and fO2; whereas Mg, Al, Mn and Zn commonly enrichment in hydrothermal magnetite through isomorphic replacement was primarily controlled by waterrock interaction and later stage metasomatism of chlorite and carbonate veins. In hydrothermal magnetite, cobalt content was strongly affected by sulfide in addition to waterrock interactions and postfluid metasomatism, which would decrease drastically in the presence of sulfides. Si, Ca, Na, Sr and Ba displayed highly consistent geochemical behaviors in both the magmatic and hydrothermal magnetites systems, while Ti verus Ni/Cr ratio could be used to distinguish igneous and hydrothermal magnetites. Our analysis indicate that the Zhangjiawa hydrothermal magnetites can be divided into two stages according to the petrographical evidence. The earlystage magnetite includes early primary granular magnetite and early secondary magnetites; the latestage magnetite is composed of late primary and late secondary magnetites. The primary magnetite commonly has the typical triple point structure, while the secondary magnetite is characterized as porous and commonly shows irregular, dendritic, skeletal and metasomatic relict textures. Mg, Al, Mn, Zn and Co contents continued to increase from the early to late stage as well as from the primary to secondary magnetite, possibly due to waterrock interactions and breaking down of chlorite during later alteration. Pores are common in the late stage hydrothermal magnetite, likely resulted from elevated fluidmagnetite interaction. Therefore, the trace elements in hydrothermal magnetite not only indicate the physical and chemical conditions of the oreforming fluids, but also reflect the properties of the surrounding rocks as well as waterrock interactions. Related Articles | Metrics

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New evidence for the Late Triassic synrifting in the eastern North Qiangtang depression: redefination of the stratigraphic age of volcanic rocks and conglomerates from the Jiapila Formation. LI Xueren, WANG Jian 2018, 25(4): 50-64.  DOI: 10.13745/j.esf.sf.2018.5.25 Abstract ( 297 )   PDF (5250KB) ( 318 )   The Jiapila Formation in the Tuotuo River region, North Qiangtang depression is mainly composed of volcanic rocks intercalated with conglomerates. It is very different from the regional Jiapila Formation of primarily purplishred clastic rocks in either sedimentary characteristics or stratigraphic age. In this paper, we performed magmatic and detrital zircon UPb dating of the Jiapila Formation, involving volcanic rock and conglomerate in the Nangji and Kaixin Ridge, as well as sandstone of the Bagong Formation in the Quem Co area, to accurately determine the stratigraphic age of these rocks. Zircon UPb dating from the basaltic trachyandesite in the Jiapila Formation yielded a concordant age (weighted mean 206Pb/238U age) of 216.4±1.1 Ma (n=28, MSWD=0.39). The youngest UPb age of detrital zircons from polymictic conglomerate and sandstone samples gave weight mean ages of 222.2±3.7 Ma (n=2) for the Jiapila Formation and 222.8±1.9 Ma (n=9) for the Bagong Formation, respectively. Therefore, we placed the eruption age and the maximum depositional ages for these rocks at the Late Triassic Norian. Combined with regional historical data and lithological column of the latest well with the continuous sequences, we redefined volcanic rock of the Jiapila Formation as Nadigangri Formation, and confirmed that the conglomerate was formed by the tectonic uplift in the Late Triassic. During the mid to late stage of the Late Triassic, most areas of the North Qiangtang was subjected to the uplift and erosion. In the hiatus, a layer of weathering crust on limestones was formed at the top of Xiaochaka Formation in the west, along with the formation of an exposure surface on top of the Jiezha Group in the east, as well as formation of the distinct components of conglomerates, indicating varying degree of weathering between west and east. Due to expansion of the BangongNujiang Tethys Ocean, the North Qiangtang rifted with massive volcanic eruptions, causing widescale deposit of the volcanicsedimentary sequences of the Nadigangri Formation in the east and west. Furthermore, exposure of the Nadigangri Formation matched well with the rifting basement of the Upper Triassic strata, which indicates the volcanicsedimentary event was a localized event related to rifting in the region. Related Articles | Metrics

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Geochemical characteristics and provenance implication of mixed rocks from the Pliocene Shizigou Formation in the Nanyishan structure of the western Qaidam Basin. YU Dongdong,ZHANG Yongsheng,XING Enyuan,WANG Linlin,LI Kai,HUANG Youlin 2018, 25(4): 65-75.  DOI: 10.13745/j.esf.sf.2018.6.28 Abstract ( 248 )   PDF (3307KB) ( 310 )    The Pliocene mixed rocks contain large amounts of salt minerals in the Nanyishan structure of the western Qaidam Basin, and their provenance analyses can be valuable in finding the origin of the salt minerals. Based on field observation and microscopic identification, we analyzed the geochemical characteristics of mixed rocks from the Pliocene Shizigou Formation in the Nanyishan structure. Combined with rare earth element (REE) characteristics of granites from the surrounding orogenic belts, we discussed the provenance of terrigenous clastics in mixed rocks. The results showed that the detrital, carbonate and clay minerals in mixed rocks were homogeneously mixed, and the elemental contents of the rocks were closely related to the mineral composition. Except for Ca, Na, and Sr, the mixed rocks had generally lower mineral contents than those of the upper continental crust. Considering that CaO and Na2O are affected by the formation of carbonate and halite, Ca and Na are not suitable for identifying tectonic settings. In contrast, trace elements and REE such as Sc, Th, Co, Zr and Hf, retain mostly the geochemical information of source rocks and therefore can be used to evaluate the tectonic settings of the source area for provenance analysis. The REE patterns showed good consistency, indicating the terrigenous clastics of mixed rocks have the same provenance characteristics. Together with LaThSc, ThScZr/10, La/ThHf diagrams and Al2O3/TiO2 ratio, our data suggest that the terrigenous clastics components of mixed rocks were derived from the felsic igneous rocks of continental island arc. In comparison with REE patterns in granites from the surrounding orogenic belts, we consider the Late Silurian and Late Permian granites to be the main source rocks for terrigenous clastics and salt minerals in the mixed rock. In addition, we hypothesize that the south part of the study area, Qimantag, is the main source area, and South Altyn Tagh in the west also takes part in the sedimentary source recharge. Related Articles | Metrics

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Discussion on distribution and occurrence mechanism of gallium in the Middle Jurassic coalbearing strata of the eastern Junggar coalfield, Xinjiang. CHEN Lei,SHAO Pei,XIONG Wuhou,QI Wenqiang,ZHANG Shijia,ZHANG Zhanxian 2018, 25(4): 76-85.  DOI: 10.13745/j.esf.yx.2017-12-23 Abstract ( 367 )   PDF (4347KB) ( 326 )   With the discovery of rare metal deposits in large coal measures, wide attention has been paid to the study of trace elements in coal. However, rare element study in the northwest China coal measures is still limited. In this paper, we selected the eastern Junggar coalfield in northeastern Xinjiang as the research object to study the distribution, occurrence and enrichment mechanism of gallium in coal, by analyzing coal quality and trace element data. The results showed: (1) gallium is obviously enriched in the Middle Jurassic coal seams in the eastern Junggar coalfield, with Ga contents averaged at 20.7847.98 μg/g in twelve coal mines, which are higher than or close to the boundary grade of gallium in coal (30 μg/g). (2) the distribution regularity of gallium in coal is  apparent: on plane, gallium content is higher around the basin rim than in the center; in the northeastern and southwestern coalfields especially, gallium content is abnormally high (partly exceeding 60 μg/g) due to effect of the Kelameili and Bogda Mountains. In contrast, in the central coal mines (ZD10740, ZD10464, ZD10407 and ZD10841), gallium contents are gradually enriched from the edge to the center. Vertically, gallium contents in most of coal mines studied decrease upward from bottom in the Middle Jurassic coal seams, whereas affected by the early Yanshan movement, ZD10740 near the Bogda Mountain showed the opposite trend. And (3) kaolinite was the main carrier of gallium in coal, and gallium also partly existed in organic matters of coal. Gallium was transported to the sedimentary basin mainly in finegrained material form (colloid or organic complex), and accumulated under wet sedimentary conditions. Related Articles | Metrics

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Origin of siliceous rocks in the MiddleUpper Ordovician Yanxi Formation, Hunan Province and Duiershi Formation, Jiangxi Province in South China. ZHENG Ning,LI Tingdong,CHENG Muwei 2018, 25(4): 86-98.  DOI: 10.13745/j.esf.yx.2017-12-19 Abstract ( 275 )   PDF (2512KB) ( 258 )   High siliceous rocks are extensively developed in the neriticbathyal environment of South China during the MiddleUpper Ordovician. These rocks are mainly distributed throughout the Yanxi and Duiershi Formations in Hunan and Jiangxi provinces, respectively, generally between the Yangtze and Cathaysian Plates in the EW strip. The stratum thickness gradually decreases from SE to NW, and the layers are mostly thin. Radiolarian Protoentactinia sp. is found in the rocks, sometimes more than 50% in sample content. Analysis results showed that biological and terrigenous Si is the main silicon source—a clear indication of rocks biochemical origin. It was found that the Al/(Al+Fe+Mn) ratio is greater than 0.45, and K2O/Na2O ratio ranges between 1.55 and 42.11. The Al2O3Ni, V, B, Cr diagram showed both discrete and linear relationships and a U/Th ratio of 0.72. Lastly, our study revealed that REE contents in central Hunan and Jiangxi provinces are relatively high, while element Ce in chert in the southeast area showed slightly negative anomaly. In the research area, ∑LREE≈∑HREE, this suggests that the areas from Hengyang to Ganzhou are affected by volcanic and hydrothermal activities. Related Articles | Metrics

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Distribution and influencing factors of rare earth elements in carbonate rocks along three continentalscale transects in eastern China. LIU Qingqing,CHI Qinghua,WANG Xueqiu,ZHOU Jian,LIU Hanliang,LIU Dongsheng,GAO Yanfang,ZHAI Daxing 2018, 25(4): 99-115.  DOI: 10.13745/j.esf.yx.2017-12-28 Abstract ( 265 )   PDF (4447KB) ( 381 )   As an important part of the lithosphere on the earth surface, the carbonate rocks chemical composition can provide useful information on their sedimentary environment and evolution of marine waters. However, previous studies paid little attention to the distribution characteristics of rare earth elements and other elements in the carbonate rocks. This study examined a total of 582 carbonate rock samples collected along three continentalscale transects in eastern China. The results show that the total concentrations of REE＋Y in the carbonate rocks ranged from 0.59×10-6 to 183×10-6 (average 24.0×10-6), with the mean of 4.80×10-6 in the pure carbonate rocks (CMC≥99％). Compared with MREE and HREE, LREE depletion was observed after PAASnormalization, with weak positive δEu anomaly and moderate negative δCe anomaly. Values of REEs and LREE/HREE in dolomite were generally lower than those in limestone. When the contents of sand and mud were similar, the distribution patterns of carbonate rocks were similar in different tectonic units during the preMesozoic era. Compared with the other eras, the Mesozoic and Mesoproterozoic carbonate rocks had relatively flat distribution patterns. This study proves that the distribution of REEs in carbonate rocks is obviously influenced by detrital material. Meanwhile, the concentrations of REE＋Y were negatively correlated with CO2-3 and positively correlated with the elements in the detrital material (Si, Ti, Rb, Cs, Th, Zr, etc) and in clay (Al, Fe, K, etc). The diagenesis and dolomitization had little effect on the distribution of REE＋Y in the pure carbonate rocks. The distribution pattern of Paleozoic pure carbonate rocks in eastern China was controlled by the marine environment, which was very similar to the pattern of current seawater. The Mesozoic pure limestone was affected by terrestrial facies or marineterrigenous facies, with a relatively flat REE＋Y distribution pattern. The δCe value was controlled by the marine environment, and the extreme positive anomaly (δCe＞1.3) was affected by the reducing environment/hydrothermal solution, which led to even more significant effect of redox conditions on the δCe than δEu. When the REEs in seawater had no obvious change since the Middle Proterozoic, and the mean value of REE＋Y partition coefficient was between 103.55 and 102.39, the LREE depletion, negative anomaly of Ce and positive anomaly of Y were mainly due to differences in the distribution coefficient. Microorganisms could enrich REEs and change the sedimentary environment, it might be the main reason for the flat REE＋Y distribution pattern in the MiddleUpper Proterozoic carbonate rocks. Related Articles | Metrics

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Progress in “SourcetoSink” system research. CAO Yingchang,XU Qisong,WANG Jian 2018, 25(4): 116-131.  DOI: 10.13745/j.esf.sf.2018.5.30 Abstract ( 1924 )   PDF (5785KB) ( 1167 )   The “SourcetoSink” system concerns with various components of sedimentary systems, from source areas, through dispersal systems, thence to deposition in a number of potential sedimentary sinks. It plays an important role in recent sedimentology research. This paper overviewed literatures at home and abroad, and discussed the research advance made on the important elements in the “SourcetoSink” system and the coupling effect of the elements. Numerous studies indicated that the firstorder control on the system is the source area, while the transport and sedimentary processes are response, at different process level, to sediment supply. The effect of physical and chemical weathering, resulted from paleogeographic evolution of the source area, controls sediment supply; and the temporal and spatial attributes of sediment supply determine the transport mode and channel type. Subsequently, the geologic processes reshape sediment component and structure; and the modification effects rely on the ratio between the timescales of a perturbation in the source area and the transport response. Ultimately, sediment selectively deposits in the basins spatially differentiated accommodation spacegenerated by the sedimentary geomorphology evolution in response to source evolution, and molds the various sedimentary features. Distinguished from other studies, the “SourcetoSink” system focuses on forwardevolutionary, quantitative and dynamic research. Nevertheless, the research technique of “SourcetoSink” is still exploratory. This paper suggests that future developments should include provenance system research, multitimescale quantitative geological characterization, and dynamic analysis with multidisciplinary approach. Related Articles | Metrics

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Variations in basin architecture and accumulation of giant oil and gas fields along the passive continent margins of the South Atlantic. WEN Zhixin,WU Yadong,BIAN Haiguang,WANG Zhaoming,HE Zhengjun,SONG Chengpeng 2018, 25(4): 132-141.  DOI: 10.13745/j.esf.sf.2018.4.41 Abstract ( 278 )   PDF (4557KB) ( 388 )   In this study, based on plate tectonic evolution and using seismic and geological data, formation and evolution of prototype basins on the conjugated passive continental margins of the South Atlantic were studied, and ancient sedimentary environment and its controls on the forming conditions of large oil and gas fields were compared segmentwise according to variations in basin architecture, and finally the passive continental marginal basins were divided into “three segments” and “four types” to reveal the accumulation law of giant oil and gas fields. As our study showed, the “four types” of basins on “three segments” had gone through three prototype stages: early intracontinental rifting, intermediate intercontinental rifting, and late drifting passive continental margin. In the southern segment, thin sediments in the “rifttype” basin that formed in the drifting stage, developed into the large “rift structuralstratigraphic” oil and gas fields. In the middle segment, the “saltyriftdepressiontype” basins were filled with intercontinental rift salt rocks in the intermediate stage; and upper and lower sections are marine and lacustrine sediments from the drifting and rifting stages, respectively, possibly of highquality. Utilizing salt rock and marine shale as caprocks, the giant oil and gas fields of “presalt carbonate and postsalt turbidity sands” were developed. Finally, in the northern segment, thick marine sediments in the drifting stage in the “depressiontype” basin, affected by “narrow shelves” and “steep slopes” and controlled by the transform fault, developed into the large “deepwater turbidity fan group” oil and gas fields on the basin margin. Our study further showed in the Niger highconstructive “deltatype” basin, unique deltagravity flow sandstone reservoirs have been formed, and giant oil and gas fields are identified in the innerring rollover anticline delta sandstone, the middle mud diapir and the outerring thrust crust. Related Articles | Metrics

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Seismic prediction of Paleogene shale oil “sweet spots” and its influencing factor analysis in the Bonan subsag, Jiyang depression. PAN Renfang,CHEN Meiling,ZHANG Chaomo,PAN Jin 2018, 25(4): 142-154.  DOI: 10.13745/j.esf.sf.2018.5.26 Abstract ( 375 )   PDF (9360KB) ( 419 )   Organicrich terrestrial shales developed in the Paleogene Shahejie Formation in the Jiyang depression, Bohai Bay Basin, China. Seismic prediction of shale oil sweet spots and its influencing factor analysis shall promote studies on shale oil seismic response in the Jiyang depression. Based on seismic, drilling, logging and geochemistry data, we investigated the geophysical response characteristics of shale oil sweet spots using multiattribute regression method, and performed the influencing factor analysis. The results revealed the parameters for shale oil geological and engineering sweet spots in the lower interval of the 3rd Shahejie Formation in the BNHC seismic area, Bonan subsag, Jiyang depression. Organic richness and shale porosity were in the ranges of 3%6% and 5.0%12.5%, respectively, with Ro value between 0.81% and 0.94%. Furthermore, widespread overpressure developed in the Shahejie Formation shale reservoir with pressure coefficient between 1.3 and 1.8. And shale brittle index was more than 40% in the Shahejie Formation. Factors affecting geophysical response characteristics of shale oil geological and engineering sweet spots included rock physics parameters, poststack seismic Pimpedance and Simpedance inversion data volumes, GR response volume, amplitude, etc. These factors affect the prediction of “sweet spots” to varying degrees. Our comprehensive study results suggest that a “continuous sweet spots” seismic response mode was developed in the Shahejie Formation, and poststack acoustic inversion volume is considered to be the most important factor affecting seismic prediction of shale oil sweet spots in the Shahejie Formation. Related Articles | Metrics

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Quantitative evaluation of hydrocarbon accumulation disparity in the fourth member of the Shahejie Formation in the Shaojia area of the Jiyang depression. IN Chengyan,ZHU Zhaoqun,LIU Kuiyuan,DONG Chunmei,REN Lihua,LI Zhipeng 2018, 25(4): 155-167.  DOI: 10.13745/j.esf.sf.2018.6.27 Abstract ( 254 )   PDF (4044KB) ( 263 )   A great number of hydrocarbon exploration targets exist in the fourth member of the Shahejie Formation, in the Shaojia area of the Jiyang depression. However, hydrocarbon exploration activities in Shaojia are limited due to hydrocarbon distribution heterogeneity and the lacking understanding of hydrocarbon accumulation. In this paper, a quantitative evaluation on hydrocarbon accumulation disparity was conducted to intuitively study the characteristics of hydrocarbon accumulation and provide guidance for exploration decision making fast and conveniently. Based on current exploration achievements, differences in hydrocarbon accumulation at different levels, including petroleum system, play and trap, were analyzed systematically and evaluated quantitatively in the study case, by improved geological evaluation methods of play and trap and mathematics approaches such as statistical mining. The results showed that there is a significant disparity in hydrocarbon accumulation in the study area, which is mainly controlled by the geological factors including source, reservoir, migration and accumulation. In general, the northern fault terrace zone, which possesses favorable accumulation conditions, could still be the main progressive exploration area; and the evaluated first class traps would be the optimized targets in further exploration. The southern gentle slope zone shows a large variation in accumulation conditions, which is of the potential to be the replacement tract by exploration enhancement. In contrast, the western fault zone possesses poor accumulation conditions of high exploration risks, but could be treated as potential areas of oil and gas regionally. The quantitative disparity evaluation conducted in this study can contribute to reducing exploration costs as well as deepening our understanding of hydrocarbon accumulation, and serve as a reference for efficient explorations in similar cases. Related Articles | Metrics

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Analysis of velocity anomalies of the Qa structure in the BZ1 exploration area, Bozhong sag. CAI Shaowu，ZHANG Xintao，ZHANG Jingsi，YU Ya，LIU Teng，LI Ying 2018, 25(4): 168-175.  DOI: 10.13745/j.esf.yx.2017-5-6 Abstract ( 252 )   PDF (2547KB) ( 220 )    The velocity anomalies occurred in two wells 1.3 km apart, drilled in the Qa structure of the BZ1 exploration area in the Bozhong sag. There was a contradiction between the depth of stratum from the time section of the 3D seismic data, and drilling depth from geological stratification. The predicted depth for well Qa3 (a new drilling well) was deeper than the geological layer depth, while the velocity of well Qa3 is lower than that of well Qa2. Thus, these two wells clearly showed anomaly in the transverse distribution of the seismic velocity. The main cause of this velocity anomaly was both sedimentary and structural. Using seismic stack velocity spectrum modeling and correction of well point depth and trend seedpoint, more accurate speed was obtained, and the resulting high precision variable speed mapping reflected the true underground structure. In the paper, single well velocity method was compared with velocity spectrum modeling corrected by single well velocity for predicting drilling depth. The latter method achieved higher precision in depth prediction by effectively reducing errors caused by velocity anomaly in the actual drilling process. Therefore, velocity model building, combined with variablevelocity mapping before drilling, should play an important role in future deployment of exploration and appraisal wells, and prediction of drilling depth. Related Articles | Metrics

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Analysis of paleoclimate evolution of the hyperthermal period in the early Paleogene: taking the Dongying depression as an example. LEI Huarui,JIANG Zaixing,ZHOU Hongke 2018, 25(4): 176-184.  DOI: 10.13745/j.esf.yx.2017-10-2 Abstract ( 332 )   PDF (2609KB) ( 327 )   There is a prolonged global hyperthermal period in the early Paleogene. Based on the analysis of fossil sporopollen assemblages, from the lower first submember of the Kongdian Formation to the lower third submember of the Shahejie Formation in the Dongying Depression, we systematically analyzed the paleoclimate evolution process of the Dongying Depression during the early Paleogene. We selected 23 kinds of fossil sporopollen species with statistical significance, and quantitatively classified these species into 5 categories (thermophilic, mesothermophilous, coldtolerant, xerophytic and hygrophytic groups) on the basis of three climate parameters: MAT, CMT and PER. According to the temperature index (TI) variation trend, the temperature evolution process of the Dongying Depression during the early Paleogene can be divided into three stages: continuous hot, warmhot alternation and continuous warm periods. Accordingly, the humidity evolution process can be divided into four stages: droughtpluvial alternation, continuous drought, second droughtpluvial alternation and continuous pluvial periods in terms of the humidity index (HI) variation. There were obvious hysteresis effects in the humidity evolution relative to temperature evolution in this prolonged hyperthermal period that went on from 53.89 to 47.48 Ma, with a total duration now estimated to be 6.41 Ma. Through identification of the specific strata corresponding to three worldwide greenhouse warming events in the Paleogene in the Dongying Depression, the pivotal effect of the ETM2 and EECO events on the hyperthermal period in the Dongying Depression is confirmed. In addition, by combining paleoclimate and lithofacies analyses, the control of paleoclimate over sedimentary system in the lacustrine basin is clarified. Related Articles | Metrics

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Sedimentary characteristics and controlling factors of the Early Ordovician platform-slope-basin in the northern margin of the Qaidam Basin. MA Shuai,CHEN Shiyue,JIA Beibei,SUN Jiaopeng,WANG Feng,ZENG Hanyu 2018, 25(4): 185-197.  DOI: 10.13745/j.esf.yx.2017-5-1 Abstract ( 244 )   PDF (2686KB) ( 329 )   Through geological field investigation and indoor experiments in the northern Qaidam Basin, the Early Ordovician platformslopebasin facies sedimentary system was studied in detail, according to geological profiles of rock combination types and characteristics of sedimentary structures of the study area. The results show that the continuing sea level rise in the study area, subduction of the northern margin of the Qaidam Basin, and continental arc collision, were the important controlling factors for the basin mountain pattern development and sedimentary filling evolution during this period. In the northern margin of the Qaidam Basin, the Early Ordovician platform margin particle shoal facies developed in the lower part of the Duoquanshan Formation, and lithology included bioclastic, oolitic and micrite limestones. The carbonate rock materials on the deep water slope are mainly different slope sediments, including fine microcrystalline mud, slumps breccia, grain flow, nodular limestone, debris flow and turbidite, brought by gravity flow transportation and sedimentation from various locations. The study area basin lies in a transition area between the carbonate and arc clastic sedimentary systems. Affected by the North Qaidam oceancontinent subduction and continental arc collision, uplifted continental arc material and crust basement provided a large amount of detrital material to the basin. As a result, arc basin deposits developed in the areas close to the edge of the island arc, supported by the gravity flow depositional system of sandy debris flow and turbidity current types. Related Articles | Metrics

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Lithofacies classification of finegrained mixed sedimentary rocks in the Permian Lucaogou Formation, Jimsar sag, Junggar Basin. ZHANG Shaomin,CAO Yingchang,ZHU Rukai,XI Kelai,WANG Jian,ZHU Ning,HU Ruining 2018, 25(4): 198-209.  DOI: 10.13745/j.esf.yx.2017-5-2 Abstract ( 287 )   PDF (3031KB) ( 515 )   In this study, lithofacies types and characteristics were analyzed in detail through examination of the tight finegrained sedimentary rocks of Permian Lucaogou Formation in the Jimsar Sag, Junggar Basin by methods of core observation, thin section identification, SEM (scanning electron microscope) and physical property testing. The results show that: (1) The tight finegrained sedimentary rocks have a complex mineral composition of multiple components including terrigenous detrital, pyroclastic debris and carbonate components, representing a type of transitional diamicton. (2) Based on factors such as component, sedimentary structure and organic carbon, the mixed sedimentary rock lithofacies can be divided into two types, namely the unicomponent lithofacies and multicomponents mixed lithofacies. The former is mainly massive lithofacies and the later consists of massive, strippedlumpy and laminated lithofacies. (3) There are six major lithofacies types that can be identified in the Lucaogou Formation: massive micritic dolostone, massive silty dolarenite, massive tuffaceous siltstone, stripped tuffaceous dolostone, laminated silty/argillaceous tuffites and laminated dolomitic mudstone. Different lithofacies types have different reservoir qualities, porethroat structures and reservoir spaces. And the massive tuffaceous siltstone, stripped tuffaceous dolostone and laminated silty tuffites are the favorable lithofacies. Related Articles | Metrics

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Application of widefield electromagnetic method to biogas exploration and prediction of prospective target area in the northern Dongting Basin. SUN Chunyan,TANG Yao,ZHAO Hao,ZHANG Shiqiang,WANG Donglin,HE Huice,LING Fan,LI Jianhua,HE Yan 2018, 25(4): 210-225.  DOI: 10.13745/j.esf.sf.2018.6.26 Abstract ( 247 )   PDF (6183KB) ( 277 )   The Dongting Basin, located at the edge of the Paleozoic in Xiangxi, experienced two stages of tectonic cycles involving mainly the Mesozoic Late Cretaceous basin and the Cenozoic fault block. This rift basin is a result of the Yanshan (Mesozoic) and Himalayan (Cenozoic) movements. There are persistent sand and shale deposits on the Cretaceous in the basin, making the sedimentary facies of the Quaternary rivers and lakes geologically favorable for biogas generation. Based on the 20132015 geochemical exploration of the shallow sediments in the Dongting Basin, we have a clear understanding of the distribution of methane gas anomalies in the basin. The geochemical anomalies indicated that the Dongting Basin biogas resources, on the northern slopes of the Yuanjiang depression in the northern Dongting Basin, QingshuzuiHebazhen area, present the most likely prospective breakthroughs. In order to trace the source of methane gas leakage, and advance our understanding of geochemical anomaly and shallow biogas system research, we completed five widearea electromagnetic sounding and two mercury gas measurement profiles in the biogas prospective area discovered in 20152016. This accomplishment was aimed to reveal the Quaternary tectonic distribution and geochemical anomaly mechanism through the comparative study of integrated geophysical and geochemical profiles. It provided a scientific basis for the Dongting Basin biogas resource prospecting and target prediction as well as guidance for the selection of Quaternary gas prospecting methodology. The results showed: (1) The Quaternary system in Dongting area can satisfy the “sourcereservoircap” condition of biogas system and has biogas resource potential; (2) The sediment free methane anomaly is caused by the Quaternary gas accumulation along the fault zone or by leakage due to the sediment layer movement towards earth surface; (3) The area encompassing the northwestern Dongting Basin, southern P2 section, and the intersection of northern P2 line and P3/P4 sections, have good “selfgeneration and selfstorage” capability, and are the most promising targets in the prospective area; (4) The Sijihong area, located in the eastern prospective area of northern Dongting Lake, along the southern P6 line and near the Yuanjiang depression center, possesses favorable conditions to form the socalled “selfgeneration and selfstorage” and “lowergeneration and upperstorage” biogas deposits; (5) Shallow sedimentary geochemical exploration is conducive to the discovery of gas leakage associated with biogas, and it is also useful in evaluating underlying depositional system, reservoir development and characterization, and targeting geophysical exploration areas. The combination of geochemistry and widearea electromagnetic profile measurements provides a fast and economical means of biogas prospecting. Related Articles | Metrics

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The origin of biogenic silica in siliceous shale from WufengLongmaxi Formation in the Middle and Upper Yangtze region and its relationship with shale gas enrichment. LU Longfei,QIN Jianzhong,SHEN Baojian,Tenger,LIU Weixin,ZHANG Qingzhen 2018, 25(4): 226-236.  DOI: 10.13745/j.esf.yx.2017-5-5 Abstract ( 305 )   PDF (3162KB) ( 365 )   In order to study the origin of organic matter enriched siliceous shale from WufengLongmaxi Formations in the Middle and Upper Yangtze region, and its relationship with shale gas accumulation, rock features, mineral composition, micromorphology, structural characteristics and chemical elements were analyzed by Xray diffraction, scanning electron microscope (SEM) and energy disperse spectroscopy methods. Quartz content was found to be relatively high, mostly above 45% and 88% being the highest, while clay mineral content was relatively low in the Wufeng Formation and lower section of the Longmaxi Formation.  Abundant biological residue and debris can be seen in the siliceous shales under SEM, they acted as skeleton particles and bound tightly with the mineral matrix, resulting in a highly compact rock structure; clay mineral enriched shales, whereas, developed horizontal beddings. Under SEM, the observed circular layered growth structure and needle structures of the biogenic materials clearly showed the characteristics of radiolarian morphology. The chemical compositions of these structures were shown to be mainly consisted of silicon and oxygen elements by energy spectrum analysis, further providing proofs to their radiolarian origin. Moreover, surface distribution of elements indicated the terrigenous input and hydrothermal activity were very limited, implying silica was mainly from radiolarian skeleton. Altogether we now have sufficient evidence to support a biogenic origin for siliceous shales in the region. High soluble silica concentration is prerequisite for radiolarian enrichment, it creates an environment for algae proliferation which leads to organic matter accumulation. Biogenic silicon was also favorable for the preservation of primary inorganic and secondary organic pores. Enrichment of biogenic silica, therefore, plays an important role in shale gas accumulation in the Wufeng and Longmachi Formations. Related Articles | Metrics

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Moisture content characteristics of high rank coal reservoir and its influence on adsorption capacity. LI Xiawei,LIU Dameng,CAI Yidong,YAO Yanbin,ZHANG Bairen,ZHANG Xueying 2018, 25(4): 237-244.  DOI: 10.13745/j.esf.sf.2018.4.42 Abstract ( 276 )   PDF (2091KB) ( 280 )   In order to study the effects of moisture content on adsorption capability of high rank coal reservoir, we conducted experimental investigations on eight representative coal samples collected from the YangquanShouyang block. Vitrinite reflectance, maceral composition and porosity measurements, combined with mercury injection, nuclear magnetic resonance (NMR) and methane isothermal adsorption experiments, were carried out to investigate pore size distribution, NMR T2 spectrum response, NMR porosity and adsorption capability of coal reservoir. Moisture contents in the water saturated coal samples were quantitatively characterized, and their impacts on methane adsorption capability were studied. The results showed that micropores dominate the pore structure in high rank coal; the bound water is the main source of moisture in micropores; and the bound water content shows a positive correlation with Ro,m. Moreover, among the factors affecting methane adsorption capacity, moisture content, especially bound water in micropores, plays a key role as higher bound water content corresponds to poorer methane adsorption capability. Related Articles | Metrics

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Experimental study on the shale reservoir-supercritical CO2-simulated fracturing fluid interaction and its environmental significance. XU Yongqiang,LI Zijing,GUO Jilong,CHEN Jiawei 2018, 25(4): 245-254.  DOI: 10.13745/j.esf.sf.2018.2.1 Abstract ( 207 )   PDF (3905KB) ( 232 )   Shale gas is an important unconventional source of natural gas and has become a research hot topic in recent years. However, current studies have been mainly focused on the extraction technology improvements and environmental monitoring while waterrock interaction during shale gas exploration has seldom been reported. In this work, simulated experiments were conducted on the CO2fracturing fluidshale interaction at 90 ℃ temperature and 10 MPa pressure, using selected shale rock samples. The main goal was to investigate the changes in rock mineral and flowback fluid compositions following sequential injections of hydraulic fracturing fluid and supercritical CO2. The results showed that the fracturing fluid could cause shale to erode, and the presence of supercritical CO2 could further enhance dissolution of minerals, which resulted in increase of pore size and micropore formation, making more channels available for shale gas and oil to migrate. This migration enhancement, however, may pose environmental threats and should not be ignored. As our study showed, many elements, including large amounts of Ca, Mg, Si and small amounts of Fe and Mn, were dissolved from the shale. Furthermore, under acidic environments of high temperature and pressure, volatile organic compounds (VOCs) were easily produced by the reaction system made of supercritical CO2, organic matters (in shale) and surfactants (in fracturing fluid). Moreover, VOCs remained in the stratum, and very likely leaked through the pores or faults and polluted the aquifer. Also, flowback fluid was more difficult to treat since various VOCs and elements were mixed with the high salinity solution. This study should help to understand the waterrock interactions as well as potential environmental risks during shale gas exploration. Related Articles | Metrics

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Earthquake generation: a review. DU Jianguo,WU Ketian,SUN Fengxia 2018, 25(4): 255-267.  DOI: 10.13745/j.esf.yx.2017-12-21 Abstract ( 592 )   PDF (4325KB) ( 901 )   The genetic mechanism of earthquake was discussed based on geological, geophysical and geochemical data and energy estimation. Highenergy fluids derived from the core and mantle can provide enough thermal energy for magma generation, earthquake formation and geothermal field; but rocks cannot accumulate enough strain energy to produce a strong earthquake. The strong and great earthquakes (M≥6.0) are mainly distributed in the trench, volcanic island arc and continental rift zones and other tensile structural belts in the world, such as the western Pacific Ocean trench, the eastern Indian Ocean trench, the midocean ridge, the rift valley in eastern Africa, the Mediterranean SeaBlack SeaCaspian SeaPersian Gulf tensile zone, and the Ise LakeAla KulUbud LakeSuzukur LakeLake Baikal rift valley in the eastern Eurasian continent. Fluids play an important role in the movement of mantle and crust as well as activities of earthquake and volcano. Cryptoexplosive breccias that have been found all over the world indicate the cryptoexplosion was pervasive in the geological history. Explosion occurred in the process of deep fluid upward migration towards the earth surface, resulting in earthquakes of different magnitudes and focal depths in the earth interior. Therefore, the crytoexplosion can be considered as the predominant mechanism of earthquake generation. The generation of various types of earthquakes that occurred in discontinuous and anisotropic inelastic media, such as the moderate and deepfocus earthquakes, earthquake swarm, slow earthquakes and nodipolecouple earthquakes, can be explained by the proposed model. The model can also much better explain the spatial overlap of earthquake, volcanic and geothermal zones in the world as well as formation of cryptoexplosive breccias associated ore deposits. Related Articles | Metrics

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Preliminary study of paleoearthquakes in the northern section of the Lingshan fault, Guangxi. LI Xiguang,PAN Lili,LI Bingsu,NIE Guanjun,WU Jiaobing,LU Junhong,LI Junliang,YAN Xiaomin 2018, 25(4): 268-275.  DOI: 10.13745/j.esf.yx.2017-12-25 Abstract ( 301 )   PDF (2944KB) ( 337 )    Presently paleoearthquake research in China mainly focuses on the strong seismotectonic provinces in the western and northern parts of the country. The South China Block (SCB) is located across the mediumstrong seismotectonic provinces where earthquakes of MS≥7.0 seldom occur. Traces of paleoearthquakes in SCB are hard to preserve due to high humidity, frequent rainfall and human activities in the region; as a result no detailed paleoearthquake studies are available. This research on the Lingshan paleoearthquakes, therefore, may fill the gap in the study of paleoearthquakes in South China. Based on our analysis of trenching, surface rupture and dating, it could be concluded that historically there were at least four earthquake events in the northern section of the Lingshan fault, and three of those were paleoearthquake events. They occurred around >36300, 25000, 13090 and 80 a B.P., respectively, following a trend of decreasing magnitude. The average time interval of the four earthquake events was about 12073 a and apparently longer compared with that of earthquakes occurred in the western and northern China, mainly due to relatively low tectonic activities in the Lingshan region. Related Articles | Metrics

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Geochemical background of freshwater lake sediments: a constraint on the establishment of sediment quality guidelines in China. LI Min,CHENG Hangxin,LI Kuo 2018, 25(4): 276-284.  DOI: 10.13745/j.esf.yx.2017-5-9 Abstract ( 339 )   PDF (1977KB) ( 374 )   The National MultiPurpose Regional Geochemical Survey (NMPRGS) project has provided higher density and more systematic geochemical data of surface and deep sediment from more than 150 freshwater lakes in China. This paper builds on the information obtained from the NMPRGS project and presents the geochemical background values of lake sediments for As, Cd, Cr, Cu, Hg, Ni, Pb, Zn, TN, TP, TOC and pH for the national freshwater lakes in China. Statistics show that the heavy metal elements As, Cd, Hg and TP, TOC have been accumulating significantly in the surface sediments, indicating changes in lake sediment quality across the country caused by extensive human activities. In this paper, we also discussed the uncertainties in risk assessment using existing international sediment guidelines. Therefore, efforts should be made on establishing the sediment quality guidelines for China. Such guidelines should take full consideration of geochemical background of chemical elements in freshwater lake sediments in China, and is critical for the improvement of lake environment management and pollution prevention & control in the country. Related Articles | Metrics

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Application of longchain diol and its index as environmental indicators of coastal upwelling regions along eastern Guangdong in the northern South China Sea. MAO Shengyi,ZHU Xiaowei,JIA Guodong,WU Nengyou 2018, 25(4): 285-298.  DOI: 10.13745/j.esf.sf.2018.5.28 Abstract ( 129 )   PDF (4118KB) ( 192 )    This study examined three short columnar sediment cores from the summer upwelling region along the east coast of Guangdong, in the northern South China Sea (SCS). Through analyses of diol distribution and quantitative reconstruction of diol environmental parameters, we conducted a preliminary exploration on the sea surface temperature (SST), upwelling activity and evolution of the sedimentary environment, and their mutual interactions, over the last 80 years. The results show that the longchain diol index (LDI) was a good indicator of the annual average SST in the coastal area of eastern Guangdong, where the distribution characteristics from three sediment cores showed an overall SST increase and a similar multiyear timescale trend. In addition, LDISST and diol parameter 2 showed an excellent linear relationship (R2=0.85, n=49), with consistent overall distribution, mean multiyear variations, and El NioSouthern Oscillation (ENSO) cycles. And the majority of high/low values correlated well with ENSO warm/cold cycles or strong/weak years of the SCS summer monsoon. These results indicate that diol parameter 2 can be regarded as a representative indicator of the upwelling strength in eastern Guangdong (multiyear/singleyear timescale). 1,14diol content and ENSO index showed similar fluctuation characteristics on a multiyear timescale, indicating 1,14diol content alone can not reflect information on the multiyear variations of upwelling. Therefore, diol parameter 2 was used for the preliminary reconstruction of upwelling evolution over the last 80 years in eastern Guangdong. The upwelling strength showed an overall increasing distribution trend, with a ~2 to 5year variation cycle; the overall/multiyear distribution characteristics of the 1,15C30 (diol/diol+acyloin) ratio, on the other hand, showed opposing trend with diol parameter 2, possibly a result of resuspension and reoxidation of 1,15C30 diol source due to upwelling activities. Higher 1,15C30 ratio (≥0.82) generally reflects a strong reducing environment, which has a poor correlation with oxygen content in the water body of the upwelling region. Related Articles | Metrics

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Behavior and fate of Fe in the active bioremediation of acidic coal mine drainage. SHENG Yizhi,WANG Guangcai,LIU Ying,LI Guanghe 2018, 25(4): 299-306.  DOI: 10.13745/j.esf.sf.2018.6.1 Abstract ( 270 )   PDF (4733KB) ( 258 )   Biotic lowpH Fe(II) oxidation can be an effective component of the remediation system for acidic coal mine drainage. However, application of such system is limited because of uncertainties associated with Fe behavior and fate. By monitoring biogeochemical process at an acidic coal mine drainage site, we obtained enriched indigenous sediment microbes to explore the behavior and fate of Fe and other metals under microbialmediated condition in a chemostatic bioreactor. As the results illustrate, transformation of Fe species was the major biogeochemical process both at field site and in a bioreactor. At pH<2.7, redox reactions were more prone to produce soluble Fe(III); whereas, at 2.7<pH<4.2, insoluble Fe(III) species were preferentially produced. Under acidic conditions, no significant transformation involving other metal ions was detected in active bioreactors. The sediments generated in the reactor were mainly composed of schwertmannite and goethite, and mineralogical transformation moved towards to NaJarosite with increasing addition of acid or base. Our study helps to guide application of similar microbial processes to remediate contaminated waters and provides scientific significance for the sludge recovery and reuse effort. Related Articles | Metrics

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Distribution characteristics and genesis of highfluoride groundwater in the Niuxin Mountain, Qinhuangdao. WU Chu,WU Xiong,ZHANG Yanshuai,DONG Yanyan,ZHU Pengcheng 2018, 25(4): 307-315.  DOI: 10.13745/j.esf.yx.2017-12-29 Abstract ( 223 )   PDF (2837KB) ( 324 )   Highfluoride groundwater has been found in the Niuxin Mountain in the north Liujiang basin. The Piper, Gibbs, Alkali indices and Ion ratio diagrams were used in this study to analyze the chemical characteristics and forming mechanism of shallow groundwater in the area, and the source and enrichment of fluoride in groundwater were discussed from the perspective of mineral dissolution, precipitation and ion exchange. The results showed that the major ions include slightly alkaline Ca2+, Na+ and HCO-3, with the hydrochemical types of Ca(Na)HCO3, Ca(SO4)HCO3 and Ca(Cl)SO4; high concentration of F- is present in Ca(Na)HCO3 type water, and the chemical composition of groundwater is mainly affected by weathering. Moreover, the chemical characteristics of groundwater and the origin and distribution of fluoride are controlled by hydrogeochemical and geological factors. Calcite and gypsum are dissolved into groundwater as Ca2+ source, affecting fluorite dissolution and precipitation. The cation exchange indirectly affects the concentration of F- by changing cations concentration in groundwater, and F- adsorbed on clay minerals is replaced by OH- in the alkaline environment. Based on the new findings, we suggest that dissolution equilibrium and ionexchange are the major factors controlling fluoride concentration in groundwater runoff. References | Related Articles | Metrics