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Jurassic prototype basin reconstruction in east part of Qaidam Basin. LI Jun-Liang, XIAO Yong-Jun, WANG Da-Hua, LIN Wu Earth Science Frontiers    2016, 23 (5): 11-22.   DOI: 10.13745/j.esf.2016.05.002 Abstract （10518）      PDF（pc） （1977KB）（16836）       Knowledge map    Save The mid lower part of the Jurassic is the main source rock for mid deep buried reservoirs in the east part of Qaidam Basin. It is well accepted that “lacustrine deposits were widely distributed during the early mid Jurassic, and were still remained in the residual sags”, but this really contradicts the drilling experience. To find out the actual situation, and confirm hydrocarbon kitchen, the author carried out surface geological survey and structural modeling for the thrust belt in mountain front, and also studied activities of faults that controlled development of sags and evolution of basin range by means of balanced sections. Results indicated that there are three types of sags, namely continuing subsided sag, positive inversed sag, and negative inverted sag. Prototype basin during different epoches in the Jurassic was reconstructed according to “seven factors method”. Four separated lake basins were developed during the early mid Jurassic, they were Gaxi Yuka, Hongshan Xiaochaidan, Huobuxun, and Delingha, respectively, and then they developed into a unified basin during the late Jurassic epoches. Vertically, the early Jurassic is featured by weak elongated fault subsidence, the middle Jurassic is featured by extension downwarped swamp limnetic facies, and the late Jurassic is featured by compressiondownwarped fluvialalluvial facies. Remnant source rock in the midlower Jurassic was distributed in 4 reworked continuing subsided sags such as Gaxi, and 2 positive reversed sags such as Yuka. Related Articles | Metrics | Comments（0）

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Calculation of Carboniferous seismic interval velocity in Eastern Qaidam Basin. CENG Qiang-Meng, LIU Cheng-Lin, ZHANG Gui-Bin, MAO Zhi-Hui Earth Science Frontiers    2016, 23 (5): 176-183.   DOI: 10.13745/j.esf.2016.05.019 Abstract （9342）      PDF（pc） （1454KB）（16663）       Knowledge map    Save Seismic interval velocity is an important parameter for the Carboniferous exploration in Eastern Qaidam Basin. Interval velocity can be applied to timedepth conversion, and to reflect lithological, structural and formationpressure information. Seismic section is closely related to seismic velocity. Because of Carboniferous data shortage in Eastern Qaidam Basin, seismic velocity has long been a problem, and the velocity error in the timedepth conversion was large. To solve these problems, a new approach to calculate interval velocity was presented based on the previous work, thus improved the velocity accuracy and better understood the tectonic and geological characteristics in Eastern Qaidam Basin. Seismic stack velocity was converted into root mean square velocity based on the single well velocity analysis and multiplepicking of twodimensional seismic stack velocity, and then was converted into interval velocity using constrained Dix inversion based on the singlewell velocity trend model, at last the fitting curve of the average velocity field was done. Then, the seismic average velocity was corrected by well logging velocity as the control points, so as to establish a more reasonable interval velocity model. The new depth structure converted by the new interval velocity model is more reasonable than previous one. The new velocity model for calculating interval velocity is more accurate than the previous results, more in line with the singlewell velocity trend and is consistent with the geological cognition. Related Articles | Metrics | Comments（0）

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Genesis of altered rocks and highgrade iron ore in Gongchangling iron deposit. SHU Kai, LIU Zheng-Hong, XU Zhong-Yuan, WANG Xin-An Earth Science Frontiers    2016, 23 (5): 235-251.   DOI: 10.13745/j.esf.2016.05.024 Abstract （9320）      PDF（pc） （2629KB）（16890）       Knowledge map    Save Gongchangling iron deposit is one of the most typical BIFtype iron deposits in AnshanBenxi area, and it is the biggest producer of highgrade iron ore. Judging from the field relationship the ore is inseparately related to altered rocks.The altered rocks are characteristic of zonal distribution. In the order from highgrade iron ore outsides there are: cummingtonite rock→garnet rock→chlorite rock→weakly altered amphibolite and→amphibolite. In the weakly altered rocks, the original appearance of the primary rock is still preserved, the alteration of minerals are incomplete, the relicts of primary minerals can still be found. However， in the intensively altered rocks, the primary minerals are rarely found. The comparison on geochemistry of the altered rocks, amphibolite and magnetite quartzite indicates that the trace element characteristics of weakly altered rock, garnet rock and chlorite rock are similar to those of the amphibolites, and the trace element characteristics of cummingtonite rock are much similar with those of the lowgrade iron ores. Combined with the evidences from the microscopic characteristics, contact relationship and characteristics of major elements, we hold that the altered rocks were formed by hydrothermal interaction with amphibolites expect for cummingtonite rock. Cummingtonite rock is more likely to be formed by the hydrothermal interaction with lowgrade iron ores. According to the varying regulation of (Fe+Mg)/Si, SiO2 and Fe2OT3 showed by various altered rocks and amphibolites, there is migration of Mg, Fe and Si occurred during the hydrothermal metasomatism. The results of plottings on tectonic discrimination diagrams indicate that the protolith of these rocks are backarc basin basalts. Related Articles | Metrics | Comments（0）

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Percolation characteristics of Carboniferous shale gas in Eastern Qaidam Basin. GAO Dun, JIA Lou, LI Yang-Jie, XU Jing-Chun Earth Science Frontiers    2016, 23 (5): 103-112.   DOI: 10.13745/j.esf.2016.05.011 Abstract （9273）      PDF（pc） （1454KB）（16716）       Knowledge map    Save Shale gas is one kind of unconventional gas resources with rich potential resources, and it has multi scale porosity structures and a variety of seepage patterns. The study of the porosity structures and seepage law of shale gas can be used as the theoretical support for the exploration and development of shale gas. In this study, porestructure tests and methane seepage experiments were conducted on shales from the Carboniferous Hurleg and Huitoutala Formations in Eastern Qaidam Basin. Based on the mass flow model of shale gas considering gas slippage and diffusion behavior, the relationship between the apparent permeability and the average pressure was introduced. The apparent permeability of shale was measured by methane seepage experiment, and the shale gas flow characteristics affected by the slippage and the diffusion were analyzed. The results show that the shale gas seepage states include slip flow, diffusion flow and Darcy flow. The slip and diffusion behavior in the whole seepage weakens with the increase of the average pressure. Under the condition of low pressure, the lower the shale permeability, the greater the diffusion flow contribution. With the increase of permeability, the main seepage mechanism becomes slip flow. When the pressure is greater than 2 MPa, Darcy flow mainly influences the seepage, and the slip and diffusion behavior are not obvious. Darcy permeability and the macropore volume have a positive correlation, and diffusion flow contributions to the apparent permeability have certain relation with pores whose diameter smaller than 50 nm. Diffusion flow is a very important gas transport process in shales. Related Articles | Metrics | Comments（0）

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The prediction method of the tight oil reservoirs “sweet spot” in saline lacustrine basin: A case study of the upper Ganchaigou Formation in the Zhahaquan district of Qaidam Basin. TIAN Ji-Xian, CENG Xu, YI Shi-Wei, GUO Ze-Qing Earth Science Frontiers    2016, 23 (5): 193-201.   DOI: 10.13745/j.esf.2016.05.021 Abstract （9215）      PDF（pc） （2036KB）（16564）       Knowledge map    Save  Tight oil exploration in Qaidam Basin started relatively late, but with great potential. Under the influence of saline lacustrine basin, the tight oil reservoir of the upper Ganchaigou Formation in Zhahaquan district is characterized by thin single layer, distinct vertical overlap and significant lateral change, and thus the prediction of reservoir “sweet spot” has become the key and difficult point in this research. Based on the established high resolution sequence stratigraphic framework and the application of phase inversion, of strata slicing and of quantitative seismic sedimentology techniques, the seismic sedimentology study was conducted on the sand bodies composed of four parasequence sets in the upper Ganchaigou Formation, Zhahaquan district with the guidance of seismic sedimentology, which plays an important role in the deposition system research and thin layer sandstone prediction. Furthermore, combined with drilling and logging data, typical strata slices were precisely interpreted, as well as calibrated, and the distribution and evolution of thin beach bar sand bodies was predicted. This research suggests that shoreshallow lacustrine facies was dominated in the study area, where beach bar sand bodies were widely distributed. Also, on the basis of controlling factors analyses on tight oil reservoir performance, gamma inversion technique was proposed for prediction of reservoir “sweet spot”, and the favorable exploration area was determined. In addition, the prediction results tallied with the actual drilling situations, which effectively guided tight oil exploration in the study area and can be applied to prediction of reservoirs with comparable geologic characteristics in the future. Related Articles | Metrics | Comments（0）

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The zircon U Pb geochronology and the geochemistry of magmatic rocks and their constraints on the mineralization of Jiawula Pb Zn Ag deposit, Inner Mongolia, China. DAI Meng, YAN Guang-Sheng, LIU Cui, DENG Jin-Fu Earth Science Frontiers    2016, 23 (5): 266-280.   DOI: 10.13745/j.esf.2016.05.026 Abstract （9200）      PDF（pc） （7056KB）（16781）       Knowledge map    Save The petrogenicmetallogenic events developed in Jiawula PbZnAg deposit and their relationships have been highly controversial. This paper reports the SHRIMP zircon U Pb geochronology of the Jiawula oreforming quartzporphyry(JQP) and the late metallogenic dioriticporphyrite(JDP), and their geochemical characteristics. JQP was formed at about 129±4.8 Ma and JDP at about 124±2.5 Ma. Therefore, it is reseanable to consider that the Jiawula Pb Zn Ag mineralization should be occurred during 129124 Ma, i.e. the end of Early Cretaceous. The JQP rocks show high Si, K and low Ca, and belong to subalkaline series in the TAS diagram, to CA series in the diagram of SiO2TFeO/MgO, and to high potassium calc alkalic series in the diagram of SiO2 K2O, enriched in LILE, depleted in HFSE, and having low Sr and high Yb concentrations. The JQP rocks show high Si, K and low Ca, and belong to subalkaline series in the TAS diagram and to TH series in the diagram of SiO2 TFeO/MgO, enriched in LILE, depleted in HFSE, and having low Sr and high Yb concentrations. The geochemical characteristics indicate that the JQP rocks are formed in continental volcanic arc setting with magma derived from crustal melting and the JDP rocks are formed in active continental margin arc setting with magma derived from mantle melting. So this paper suggests that the JQP, JDP magmatism and Pb Zn Ag mineralization in Jiawula all are the products of transformation of MongoliaOkhotsk Ocean from subduction to continenl continent collision at Early Cretaceous time. The Pb Zn Ag deposit in Jiawula should be formed by the post supereruption metallogenesis. Related Articles | Metrics | Comments（0）

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MA Yin-Sheng, LIU Cheng-Lin Earth Science Frontiers    2016, 23 (5): 0-0.   Abstract （9149）      PDF（pc） （492KB）（16748）       Knowledge map    Save Related Articles | Metrics | Comments（0）

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A study of Carboniferous stratigraphic distribution and controlling factors in the eastern section of North Qaidam. CHENG Rong, XIAO Yong-Jun, LIN Hui-Chi, LIU Zhong-Quan, WANG Da-Hua Earth Science Frontiers    2016, 23 (5): 75-85.   DOI: 10.13745/j.esf.2016.05.008 Abstract （9116）      PDF（pc） （2023KB）（16537）       Knowledge map    Save Carboniferous is another favourable hydrocarbon source rocks in the eastern section of North Qaidam, besides the Jurassic. There are some conflicts between the drilling data and the previous view that Carboniferous deposited in broad basin and the residue stratum distributed in some of the present sag. The author made full use of the achievement data such as field geological investigation, drilling, seismic, electrical, etc. By using the methods of the outcrops, drilling calibration, seismic facies and velocity spectrum recognition, we traced and interpreted the top and bottom interface of the Carboniferous. The distribution of Carboniferous residual stratum of the eastern section of North Qaidam has been redetermined. According to the balanced section, the characteristics of basin tectonic evolution were analyzed and its impact on the Carboniferous strata distribution were explored. The results show that there was a complete transgressive sedimentary cycle in Carboniferous of the eastern section of Qaidam. Residual stratum is mainly distributed in the western section of Gaqiu sag and eastern section of Ounan sag, Huobuxun sag and Delinha sag. There is almost no Carboniferous residual in the western section of GaxiYuqia sag，MahaiDahonggou salient, Dachaidan sag and HongshanXiaochaidan sag. The Carboniferous residual strata distribution is controlled by the tectonic movement in the later period of IndoChinese epoch. Affected by the YanshanianHimalayan tectonic movement, there were strong separation in the distribution of Carboniferous residual stratum. Related Articles | Metrics | Comments（0）

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Influence of weathering on abundance of source rocks：A case study of Keluke Formation of Upper Carboniferous in the Shihuigou area, North Margin of Qaidam Basin. YANG Yuan-Yuan, MA Yin-Sheng, LIU Cheng-Lin, CHENG Hai-Yan Earth Science Frontiers    2016, 23 (5): 113-118.   DOI: 10.13745/j.esf.2016.05.012 Abstract （9110）      PDF（pc） （1094KB）（16711）       Knowledge map    Save Qaidam Basin is the one of the large petroliferous basins in the western China, and the hydrocarbons have been found mainly in the Mesozoic and Cenozoic strata. Recent studies have shown that the Carboniferous is one of the main source rocks in Qaidam Basin. The discovery of oil seepage and the similar characteristics of biomarkers with the carboniferous source rock show that the Qaidam Basin has large Carboniferous hydrocarbons resource potential and serves as a new strata and area for strategic breakthrough in hydrocarbons resources exploration. The number of wells that drilled into the Carboniferous strata in the Qaidam Basin is small, and the parameters of outcrop samples were used in the Carboniferous resource evaluation. Outcrop samples generally have undergone weathering, which have impact on the abundance of source rock. In this paper, through detailed comparison of outcrop and core samples to determine the factors of weathered hydrocarbon source rocks in North Margin of Qaidam Basin, and restore organic matter abundance of outcrop source rocks by weathering factor. After recovery, the outcrops of Carboniferous in the North Margin of Qaidam Basin are middlegood source rocks. Related Articles | Metrics | Comments（0）

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Carbon and oxygen isotopic compositions of Cambrian marine carbonates in Sichuan Basin, China: Implications for sedimentary evolution and potash finding. WANG Chu-Li, ZHENG Mian-Beng, ZHANG Shen, SU Kui Earth Science Frontiers    2016, 23 (5): 202-220.   DOI: 10.13745/j.esf.2016.05.022 Abstract （9098）      PDF（pc） （2700KB）（16999）       Knowledge map    Save The Cambrian evaporite basin developed in Sichuan Basin covers an area of ~200000 km2; the saltbearing areas are mainly distributed in the central part of the evaporite basin, e.g. southeastern Sichuan, northwestern Guizhou, northeastern Chongqing, and northwestern Hubei (Jiannan). The main saltbearing strata in this area are the Lower Cambrian and Middle Cambrian (second and third series), which are different in various areas. According to the characteristics of saltbearing strata and its spatial distribution, the evaporite basin is broadly divided into two gypsumhalite accumulation areas (subbasins): the southeastern Sichuan subbasin and northeastern Chongqing subbasin. The main saltbearing horizon in southeastern Sichuan is mainly the Lower Cambrian Qingxudong Formation (midupper part of the fourth stage of the Cambrian); the saltbearing horizon in northeastern Chongqing is mainly the Middle Cambrian Qinjiamiao Formation (third series). Previously, many studies on lithofacies paleogeography and potash finding hydrochemistry had been done, but lack of the study on carbon and oxygen isotope analyzes for drilling samples of Cambrian carbonate in studying the evolution of salt basin. The present study chooses Cambrian carbonate samples from the three representative drillings (Dingshan No1 well, Lin No7 well and Jianshen No1 well) to analyze the carbon and oxygen isotope composition. We hold the opinion that the δ13C negative drift is related with marine regression and biological extinction events and δ13C positive drift is mainly effected by marine transgressive events. The frequently alternation of transgression and regression in Cambrian is good for the formation of sourcereservoircaprock system in Sichuan Basin, and the formation of ancient reservoirs. Southeastern Sichuan subbasin is a closed and strongly evaporation environment in Longwanniao formation(the middle and upper part of the fourth stage), forming the depocentres of gypsumhalite accumulation areas in JiangjinLuzhou area. The δ13C value and salinity of Jianshen 1 well is higher than that of Lin 7 well. Combing with Sichuan Basin lithofacies paleogeography research, we consider that from early to midCambrian the seawater was more and more highly concentrated from southeastern Sichuan subbasin to northeastern Chongqing subbasin, which is significant for potash finding and the study on hydrocarbon forming conditions in Sichuan Basin. Related Articles | Metrics | Comments（0）

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The experimental study of adsorption characteristics of Carboniferous shale in Eastern Qaidam. LI Xiao-Yuan, CAO Feng, YUE Gao-Fan, LI Yang-Jie Earth Science Frontiers    2016, 23 (5): 95-102.   DOI: 10.13745/j.esf.2016.05.010 Abstract （9081）      PDF（pc） （1255KB）（16899）       Knowledge map    Save The Carboniferous shale in Eastern Qaidam is a highquality source rock with great hydrocarbon potential. Adsorption is the most important form of shale gas storage. But the shale adsorption of this region had never been wellstudied and had seriously hindered the development of shale gas production. According to the law of conservation of matter and the principle of thermodynamic equilibrium, by using the gasparticle two phase adsorption analytical instrument designed by ourselves, and based on the industrial standard of highpressure isothermal determination of adsorption of coal, we carry out methane isothermal adsorption experiments for the shale sample from Shiqian 1 Well in eastern Qaidam Basin under 30 ℃, 40 ℃, 50 ℃ and 60 ℃. The LangmuirFreundlich model is used for adsorption nonlinear regression analysis. The isosteric heat equation for mathane adsorption to coal is calculated through ClausiusClapeyron equation. The experimental results show that: at a certain pressure, methane adsorption capacity of shale decreases with increasing temperature; and at a certain temperature, pressure increases, the amount of methane adsorption increases firstly and then decreases. And it is characteristic of a typical supercritical adsorption. LF model fits well to isothermal adsorption process. Through the experimental results the 4 parameters in the model are determined and the physical meaning of each parameter is clear. The relation between the calculated isosteric heat and adsorption capacity is q=-3679.7n+9779.5. The isosteric heat deceases with the increasing of adsorption capacity. Isosteric heat combined with LF model can predict the adsorption of shale gas at any temperature and pressure. The predicted results are in good agreement with experimental data. It has practical significance for the evaluation and exploitation of shale gas. Related Articles | Metrics | Comments（0）

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Characteristics of Keluke shale reservoirs in northeast margin of Qaidam Basin. CHEN Shi-Yue, LIU Jin, MA Shuai, LIU Cheng-Lin Earth Science Frontiers    2016, 23 (5): 56-65.   DOI: 10.13745/j.esf.2016.05.006 Abstract （9054）      PDF（pc） （1773KB）（16763）       Knowledge map    Save Keluke Formation in the northeast margin of Qaidam Basin was mixed deposits of clastic rock and carbonate rock in transitional facies, in which shales were well developed. The shales’ distribution was studied by observation of the outcrops, and we found that the first section of Keluke Formation was the most beneficial shale exploration target with 60 meters thick in total and 92.6 percent of the ratio shales/stata. The characteristics of mineral composition, lithofacies, reservoir space types and physical properties were studied by detailed description of cores, analysis of thinsection, physical property, Xray diffraction and electron microscopy. The results showed that the mineral composition was dominantly clastic quartz and clay minerals; the main types of lithofacies were dark lamellar siltstone with mediumsized silt, black gray banded siltstone with coarsesized silt, black gray banded siltstone with coarsesized silt and carbonate and dark lamellar siltstone with mediumsized silt, bioclasts, etc. Interlayer lamellation crack, dissolution pores, the intercrystal pores, organicmatter pores and intraparticle pores were well developed in the shales; porosity has the range of 1%3%, permeability ranges between 0.01 and 1 mD. The development of shale reservoirs was affected by the sedimentary environment, mineral composition and diageneses, and the dark lamellar siltstone with mediumsized silt and black gray banded siltstone with coarsesized silt were the good lithofacies for shale reservoirs because of their large thickness, weak cementation of carbonate, high brittleness and good reservoir properties. Related Articles | Metrics | Comments（0）

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Carboniferous shale gas system evaluation for the Delingha depression in Qaidam Basin. LIU Cheng-Lin, ZHANG Xu, YANG Yuan-Yuan, LI Yang-Jie, ZHENG Ce Earth Science Frontiers    2016, 23 (5): 135-145.   DOI: 10.13745/j.esf.2016.05.015 Abstract （9040）      PDF（pc） （1970KB）（15506）       Knowledge map    Save As one of petroleum exploration frontier formations in Qaidam Basin, Carboniferous has great shale gas source potentialities but at a relatively immature exploration stage presently. Based on field geological survey and drilled well analyses, the distribution of Carboniferous shale for the Delingha depression in Qaidam Basin was clarified. The characteristics of organic geochemistry, porosity and permeability for Carboniferous shale samples were tested. We also made isothermal adsorption tests and seepage experiments for studying the shale accumulation conditions. Combined with basin modeling analysis of Well Decan 1, this paper evaluated Carboniferous shale gas system for the Delingha depression in Qaidam Basin. Carboniferous shale is widely distributed in the depression with various thickness and buried depth. Most shale has higher organic matter richness and organic matter types of Ⅱ2 and Ⅲ, and is at the thermal stage of maturity and high maturity. Upper Carboniferous shale has large thickness and organic matter richness than that of Lower Carboniferous. Carboniferous shale shows the reservoir characteristics of low porosity of 1.89%5.48% and low permeability of (0.1152.7)×10-7 μm2. Thick shale of overlying formations provides favorable cap condition for Carboniferous shale gas. Basin modeling indicates that from the end of the Paleogene to present is the critical moment for the Carboniferous shale gas system in the Delingha depression. Natural gas shows of Keluke Group of Upper Carboniferous indicate that Carboniferous shale gas system exists in the Delingha depression. In light of shale thickness, buried depth, TOC, thermal maturity and other geological conditions comprehensive evaluation, this paper divided the Delingha depression into two shale gas systems, i.e., Delingha shale gas system and Aibei shale gas system. Related Articles | Metrics | Comments（0）

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The characteristics of geothermal field and controlling factors in Qaidam Basin, Northwest China. LI Zong-Xing, GAO Dun, LI Wen-Fei, TUN Jian-Feng Earth Science Frontiers    2016, 23 (5): 23-32.   DOI: 10.13745/j.esf.2016.05.003 Abstract （9038）      PDF（pc） （1616KB）（15519）       Knowledge map    Save Geothermal field of petroliferous basin plays a very important role in oil and gas generation, transport and basin evolution. Qaidam Basin is an important oil and gas basin in western China, which is located in the northeast of the Himalayan tectonic domain. The study of the characteristic of geothermal field not only provides the scientific basis to intracontinental or intraplate continental dynamics and dynamics research in Qaidam Basin and its surrounding, but also is available to hydrocarbon generation, petroleum entrapment, the resources assessment, etc. Preliminary work of present geothermal field in Qaidam Basin mainly concentrated in the western basin, but a few in the northern and eastern Qaidam Basin, and the data used in the study were most obtained before the 20th century; the systematic research of present basin geothermal field is rare, and it is needed urgently to carry out the related research work. The advanced borehole temperature continuing acquisition system makes the measuring work of steady state temperature of deep well could be carried out in big scale and with high precision; using the Optical Scanning Method to test rock thermal conductivity, we obtained the batch, high precision rock thermal conductivity data, and 17 boreholes temperature profile. Studies show that the present geothermal gradient of Qaidam Basin is 28.6±4.6 ℃/km on average, that the geothermal gradient distribution is high in west and low in east and middle, and that the present terrestrial heat flow value of Qaidam Basin is 55.1±7.9 mW/m2 on average. The present terrestrial heat flow value of Qaidam Basin is higher than that of western China, such as Tarim and Junggar Basins, however, it is lower than the average regional terrestrial heat flow in China mainland, and it belongs to the warm basin as a whole. The distribution of geothermal field might be controlled by crustal structure, basin structures, etc. Related Articles | Metrics | Comments（0）

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The discovery and genetic analysis of grapeshaped hole of the Carboniferous in Eastern Qaidam Basin. BANG Bo, LIU Cheng-Lin, LI Zong-Xing, MA Yin-Sheng, CAO Jun Earth Science Frontiers    2016, 23 (5): 66-74.   DOI: 10.13745/j.esf.2016.05.007 Abstract （9026）      PDF（pc） （1985KB）（16414）       Knowledge map    Save This paper uses the principle of sedimentology, petrology and geochemistry to carry on the comparative study of the grapeshaped hole between the Carboniferous formation in the Qaidam Basin and the Dengying Formation in the Sichuan Basin. And its formation mechanism and distribution characteristics are discussed in detail. Through the analysis, it shows that grapeshaped hole between the Carboniferous formation in the eastern Qaidam Basin and the Dengying Formation in the Sichuan Basin have the similar petrologic characteristics. There are petrologic symbols such as multilamina crust, mesh drainage channel, fresh water calcite, terrigenous sand, mud, and siliceous authigenic mineral. Geochemical analysis shows that diagenetic fluid of grapeshaped crust carbonate mineral could be seawater, diagenetic fluid of carbonate fillings in grapeshaped hole could be atmospheric freshwater. It is concluded that the grapeshaped hole is the product of atmospheric water, and the early forms of the grapeshaped hole on the Carboniferous formation of the Qaidam Basin is the slot hole on the Dengying Formation of the Sichuan Basin. The evolution process is as follows: due to periodic regression, tidalflat environment of carbonate rocks is exposed by dissolution, and stitches columnar calcite cementations take place in dissolution hole during the period of transgression. When the water evaporates further, the imitating replacement happens in needle cylindrical calcite cements in seawater, and forms syngenetic dolomite. The periodic regression and transgression lead to the formation of the multiple cycles of grapeshaped holes on the profile. Related Articles | Metrics | Comments（0）

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Study on threedimensional fracture network models of Carboniferous shale in Eastern Qaidam Basin. ZHANG Cheng, JIA Lou, LI Yang-Jie, XU Jing-Chun Earth Science Frontiers    2016, 23 (5): 184-192.   DOI: 10.13745/j.esf.2016.05.020 Abstract （8992）      PDF（pc） （1453KB）（16071）       Knowledge map    Save Fractures provide both the gathering space and migration pathways for shale gas. They play a significant role in controlling shale gas reservoir. The occurrence, density and combination characteristics of fractures play a decisive role in determining whether the region has exploitation value for shale gas. More than one thousand fractures from thirteen outcrops in six areas of Eastern Qaidam Basin were observed in this study. Detailed statistical analyses of the fractures from three typical shale outcrops were carried out, and the corresponding discrete fracture networks were built. Three groups of fractures were determined in this area through statistical analyses and field observations (one group did not appear in part of the area). The mean and standard deviation of the orientation, length and density of each fracture group were determined, and the threedimensional fracture network models were constructed. The disk model was used in this study, which assumes that each fracture has a single disk shape in threedimensional space. An inverse modeling method was used in the modeling process. The basic principle was based on fitting the observed data of the outcrops to optimize the size and density of the fractures in the threedimensional parameters of the model in order to accurately reproduce the observed actual field data, including the number, density and length of the fractures. The study presented in this paper quantitatively measured the fractures in the shale of Eastern Qaidam Basin and provides essential data for studying the migration of oil and gas in shale. Related Articles | Metrics | Comments（0）

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Characteristics and main controlling factors of Carboniferous bitumens in Eastern Qaidam Basin. ZHANG Qian, LIU Cheng-Lin, LI Zong-Xing, DU E-Feng Earth Science Frontiers    2016, 23 (5): 167-175.   DOI: 10.13745/j.esf.2016.05.018 Abstract （8971）      PDF（pc） （1867KB）（16617）       Knowledge map    Save Carboniferous bitumen outcrops were widely exposed in Eastern Qaidam Basin, and previous studies have confirmed that Carboniferous source rocks have undergone a hydrocarbon generation process. So an indepth study of bitumen characteristics and reservoirforming model is important to guiding the petroleum exploration in this area. The paper studied the physics and geochemistry of the bitumen in this area by using the geographical method and the experimental geochemical method, which reveals that the bitumen underwent less extent of biodegradation and oxidation. In addition, the reservoirforming model of bitumen is discussed by studying geological settings and structure movement. The widely distributed Carboniferous and Jurassic source rocks are the material basis of the formation of Carboniferous bitumen, and partial favorable reservoirs provide effective reservoir space. Unconformity surfaces and faults system are wideranging in this area which not only control the oil and gas migration, but also provide an evidence for the structure destruction of oil reservoir. The three master factors above are crucial impacts on bitumen forming in this area. Related Articles | Metrics | Comments（0）

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The tectonic deformation and evolution of the Olongbluke area in Eastern Qaidam Basin. DAI Hun, LIU Cheng-Lin, XIAO Dui-Qing, MA Yin-Sheng, BANG Yuan Earth Science Frontiers    2016, 23 (5): 33-44.   DOI: 10.13745/j.esf.2016.05.004 Abstract （8948）      PDF（pc） （2446KB）（16607）       Knowledge map    Save The study of the tectonic deformation and evolution of the eastern section of North Qaidam is comparatively weak, particularly the paleotectonic stress characteristics and its transformation mechanism is not clear. In this paper, systematic observation and analysis on stressresponse structures (e.g. folds, joints, slickensides) and profile measurements were carried out in Olongbluke. Results indicate that compressive stress direction in the Caledonian was NE. There were two phase of compressional tectonic events in the late HercynianIndosinian, of which the early stress direction was SN and the late stress direction was NW. During the Early to Middle Jurassic, the stretching direction was approximately EW. Then, compressive stress direction changed into NE after the Late Jurassic. Based on balanced crosssection and the strata extension ratio of Ounan depression, the tectonic evolution of Northeast Qaidam can be divided into four stages. During Cambrian to Early Ordovician, the Ounan sag was under retroarc extensional environment and turned into retroarc extrusion, which resulted in the formation of the NW trending anticline. During the Permian to the Triassic, the whole uplifting of Olongbluke area resulted in the stratigraphic missing. Intracontinental extention within the Early to Middle Jurassic and extrusion inversion within the Cretaceous, the Olongbluke area was in an inherited uplifting and had not fully deposited. In Late Himalayan Epoch, tectonic deformation was intensified and surrounding mountain was uplifted rapidly caused by reverse faulting. Basement curled structural pattern was widely distributed within this phase. Related Articles | Metrics | Comments（0）

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Geochemical characteristics and genesis of shale gas for Carboniferous marinecontinental transitional facies coal measure strata in Eastern Qaidam Basin. CAO Jun, LIU Cheng-Lin, MA Yin-Sheng, LI Zong-Xing Earth Science Frontiers    2016, 23 (5): 158-166.   DOI: 10.13745/j.esf.2016.05.017 Abstract （8944）      PDF（pc） （1096KB）（16392）       Knowledge map    Save For the purpose of figuring out the characteristics and genesis of shale gas from the Carboniferous marinecontinental transitional facies strata in the eastern Qaidam Basin, the research was carried out by extracting the shale and shale gas from the Carboniferous Keluke group of the Well Chaiye 2, through the rockeval pyrolysis experiments and microscopic examination for the shale samples, shale gas field desorption, gas composition testing and carbon isotope analysis indoor. The research results indicate that Carboniferous marinecontinental transitional facies coal measure strata developed 4 types of organic rich sediments of dark shale, carbonaceous shale, coal and marl in the Qaidam Basin. The mean values of TOC are 3.46%, 12.34%, 77.62% and 1.89%, respectively. The kerogen is mainly of type Ⅲ and type Ⅱ2, which is at highly mature stage with the organic material to generate considerable amount of shale gas. The level of nitrogen is higher than others in the Well Chaiye 2 according to the shale field analysis of shale gas which also contains considerably small amount of Ar and He. Methane contributes the largest part of hydrocarbon gases and they are generally dry gas. The distribution percentage of methane stable carbon isotope ranges from -48.6% to -39.8%, which is between marine and continental shale gas, having a bias towards carbon. Shale gas contains thermogenic gas as its largest amount of composition and biogenic gas as the second. Related Articles | Metrics | Comments（0）

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Polycyclic aromatic hydrocarbons (PAHs) in the topsoils of typical reclaimed area in Pingshuo opencast coal mine: Status, sources and risk. YANG Ke, JIANG Jian-Jun, LIU Fei, BAI Zhong-Ke Earth Science Frontiers    2016, 23 (5): 281-290.   DOI: 10.13745/j.esf.2016.05.027 Abstract （8944）      PDF（pc） （1712KB）（16401）       Knowledge map    Save Coal mining, storage, transportation and processing process is the main source of polycyclic aromatic hydrocarbons (PAHs) pollution, but its influence on soil environmental quality of opencast coal mine reclamation area is not clear, because of the lack of the systematic survey. Pingshuo opencast coal mine reclamation area is mainly used as cultivated land. Understanding its PAHs pollution condition is important to food security and human health. Through the field survey, this study conducted an ecological risk assessment of PAHs in soils. 179 surface soil samples (020 cm) were collected by 500 m×500 m grid, then analyzed by 1 km×1 km compositional cell. Agilent high resolution gas chromatographylow resolution mass spectrometry (Agilent 6890 GC/5973i MS) were used for target detection and substitute standard 2fluorine biphenyl (2FBP) were added for recovery rate control. The total concentration of 16 EPAPAHs ranged from 213.60 to 2513.20 ng/g with a mean value of 717.09 ng/g. Individual composition of PAHs was of 52% for 34 rings, 42% for 56 ring and 6% for 2 ring respectively. A correlation analysis determined that the main pollution source is coal. According to the results of ecological risk assessment, the reuse of reclamation land as cultivated land should be paid more attention on PAHs pollution in soils. Related Articles | Metrics | Comments（0）