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    Pondering over the genesis of rocks and the evolution of lithosphere.
    Chen Guoneng
    Earth Science Frontiers    2011, 18 (1): 1-8.  
    Abstract6948)      PDF (25443KB)(74657)      

    Variation of intrinsic energy of the lithosphere results in forming and perishing of rocks. Evolution of the three kinds of rocks that constitute the lithosphere produces different tectonic effects on the earth surface, and the evolutional effects on the oceanic and continental crusts are found with complementing relationship: increasing intrinsic energy in the oceanic lithosphere leads to the birth of rocks, otherwise to the perish; and in the continental lithosphere, increasing intrinsic energy leads to the perish of rocks, otherwise to the birth. The former process creates a rocksequence in which the rocks become older from the mid oceanic ridge outwards either on a horizontal plane or on a vertical section, and the latter produces a rocksequence in which the rocks become younger from the core of a continent outwards on a horizontal plane and become younger from the MI upwards and downwards on a vertical section.

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    Earth Science Frontiers   
    Abstract6067)           
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    Earth Science Frontiers    2009, 16 (增刊): 1-.  
    Abstract5400)      PDF (42236KB)(26418)      
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    Geochemical natures of copper, nickel and PGE and their significance for the study of origin and evolution of mantlederived magmas and magmatic sulfide deposits.
    SONG Xie-Tan HU Rui-Zhong CHEN Li-Meng
    Earth Science Frontiers    2009, 16 (4): 287-305.  
    Abstract1871)      PDF (2791KB)(24971)      

    Ni, Cu and PGE are very important in the study of origin and evolution of mantle derived magmas and the formation of the related magmatic sulfide deposits, because their geochemical natures are different from other trace elements. Ni, Os, Ir and Ru are compatible elements, and Cu and Pd are incompatible in sulfur undersaturated magmas. Thus, they may be differentiated during fractional crystallization of the sulfur undersaturated basaltic magma. In contrast, all of these metals will be concentrated in sulfide liquid while sulfur saturation is reached. Particularly, minor sulfide removal will result in PGEdepletion in the basaltic magma because PGE have very high sulfide liquid/silicate melt partition coefficients. Therefore, PGE are the most sensitive tracers for sulfide segregation. Ni, Cu and PGE are also very important in the studies of key factors of the formation of magmatic sulfide deposits, which resulted from the evolution of mantle derived magmas. They are also significant for revealing fractionation of sulfide melts because Ni, Cu and PGE have different sulfide solid solution/sulfide liquid partition coefficients. In this article, the significances of Ni, Cu and PGE in the studies of origin and evolution of mantle derived magmas and the formation of magmatic sulfide deposits are presented systemically, based on the introduction of natures of these elements.

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    A study of shale gas preservation conditions for the Lower Paleozoic in Sichuan Basin and its periphery.
    Earth Science Frontiers    2012, 19 (3): 280-294.  
    Abstract7141)      PDF (86448KB)(20850)      

    The exploration of shale gas indicated an indisputable fact that there is gas in shale, but the size of the shale gas reservoir and its industrial value need further study. Compared to the high production of U.S. shale gas, shale gas has its peculiar geological characteristics in China. The shale gas preservation conditions may be the focus of the shale gas exploration in China, which is less studied in U.S. shale gas exploration. This paper studied the shale gas preservation conditions by material basis, tectonism, evolutionary history, hydrogeology, seal and its microscopic properties, gas composition, pressure coefficient and other parameters of shale in the Lower Cambrian and the Upper OrdovicianLower Silurian of the Lower Paleozoic in Sichuan Basin and its periphery. The evaluation system of shale gas preservation of south China was put forward by comprehensive analysis of various parameters.

     

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    The reservoir property of the Upper Paleozoic marinecontinental transitional shale and its gasbearing capacity in the Southeastern Ordos Basin.
    Earth Science Frontiers    2016, 23 (2): 147-157.   DOI: 10.13745/j.esf.2016.02.015
    Abstract7546)      PDF (1833KB)(20850)      

    The Upper Paleozoic marinecontinental transitional shale is important gasrich shale in the Ordos Basin. A series of studies have been carried out on the gas generation and resource potential, but it lacks of detailed reservoir characterization and its impact on the gas content. This constrains the shale gas exploration and exploitation. A large number of shale samples were collected from the Upper Paleozoic Benxi Formation and Shanxi Formation to investigate the geochemical and mineral composition, pore type and distribution. Field canister gas desorption and isothermal adsorption experiments were performed to measure gas content and gas bearing capacity of shale samples. The results show that the Upper Paleozoic shale contains high TOC (0.5%11%) and high thermal maturity (1.0%3.0% Ro), and its organic matter belongs to type III kerogen. These shale samples are characterized by high level of clay mineral (up to 60%) and low porosity (2%8%). Some samples are relatively microfracturedeveloped. The pore is dominated by mesopore, which accounts for over 90% of all pore surface area and volume. TOC content also has close relationship to the pore surface area and volume, suggesting the organic matter pore makes significant contribution to all pore in the shale. The canister adsorption shows the gas content varies in a wide range from 0.591 m3/t to 4.05 m3/t, isothermal adsorption measurement shows the Langmuir gas volume ranges from 0.05 m3/t to 14 m3/t, both of which were seriously impacted by the TOC content. Besides, the clay mineral content might also contribute to the gas bearing capacity of shales.

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    Timespace distribution and formation mechanism of the Mesozoic mafic dikes in Southeast China.
    Earth Science Frontiers    2011, 18 (1): 15-23.  
    Abstract6760)      PDF (14024KB)(20571)      

    Mafic dikes are found forming in different periods of the Mesozoic in Southeast China. Ages of the dikes show a spatial variation as that of the Mesozoic granites of this area, i.e. becoming younger from inland to coastal region, but the activityfastigia of mafic dikes and granites are not synchronous, and that of the former occurred relatively behind. Mafic dikes usually occurred limited in tensional cracks developed within granite bodies, seldom to perforate into the fractures in the country rocks of granite bodies. The mafic dikes generally occurred within the corresponding mafic volcanic belt that was located on the west of the intermediatedacid eruption belt of the same time, indicating that the mafic magma of eruption and intrusion should have been derived from the same source, i.e., the bottom part of the crustal magma layer or the mantle melt layer. Both reducing scales of the intermediatedacid eruption and the seaward migration of mafic eruption and intrusion belts after the Late Jurassic suggest decreasing crustal temperature of this area in the Late Mesozoic.

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    Analyses and thoughts on accumulation mechanisms of marine and lacustrine shale gas: A case study in shales of Longmaxi Formation and Daanzhai Section of Ziliujing Formation in Sichuan Basin.
    GUO Xu-Sheng, HU Dong-Feng, LI Yu-Beng, WEI Xiang-Feng, LIU Re-Bing, LIU Zhu-Jiang, YAN Ji-Gong, WANG Qiang-Bei
    Earth Science Frontiers    2016, 23 (2): 18-28.   DOI: 10.13745/j.esf.2016.02.003
    Abstract7761)      PDF (1856KB)(20527)      

    This article is dedicated to two shale gas intervals such as Longmaxi Formation and Daanzhai Section of Ziliujing Formation in the Sichuan Basin. In this study we analyzed and examined the basic conditions concerning the formation of marine and lacustrine shale gas, accumulation mechanisms and potential intervals, based on systematic experimental analysis of Longmaxi Formation in the Fuling Shale Gas Field and Daanzhai Section of Ziliujing Formation in Yuanba and Fuling areas and also based on the comparisons between six properties of shale reservoirs such as lithologies, geophysical properties, electric properties, shale gas contents, geochemical properties and brittle properties. It is considered that the differences between organic pores developed in marine and lacustrine shales are the main reasons for great differences in gas contents. Both marine and lacustrine shales have remarkable exploration prospects. Due to the differences among TOC, Ro and organic matter type, the organic pores develop better in marine shales. The intervals of organicrich mudstones or shales with streak or stripe limestones developed in shallowsemideep lacutrine are favorable facies belts for shale gas exploration. The lithofacies of grapholite shales with spicules and radiolarians deposited in deep shelf at the bottom of Longmaxi Formation are the most favorable for shale gas exploration. Furthermore, organicrich mudstones or shales are developed in shallow shelf, though the protecting conditions are destructed to a certain degree, the areas with high adsorbed gas still have potentials for shale gas exploration.

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    Early Paleozoic orogeny in the Himalayas: Evidences from the zircon U - Pb chronology and Hf isotope compositions of the Palung granitic gneiss in Nepal.
    Earth Science Frontiers    2016, 23 (2): 190-205.   DOI: 10.13745/j.esf.2016.02.019
    Abstract7806)      PDF (2216KB)(20156)      

    The Palung granitic gneiss in Nepal is a part of the Kathmandu thrust sheet of which the major mineral compositions are: quartz, plagioclase, Kfeldspar, microcline and muscovite. Zircons from the granitic gneiss have corerim structures with inherited detrital cores and magmatic rims showing concentric oscillatory zoning. LAICPMS zircon UPb dating results of the rims gave weighted mean ages of 485.5±1.4 Ma and 455.1±3.1 Ma, hinting that the protolith of the gneiss was the early Paleozoic granite recording two episodes of magmatism. The εHf(t) values range from -8.7 to -3.5 and the calculated TCDM(twostage model age) vary from 2.01 Ga to 1.69 Ga. Combined with the petrological characteristics and compared with Hf isotope compositions of the metapelites and orthogneisses in the Greater Himalayan Complex(GHC)and the metasedimentary rocks in the Lesser Himalayan sequence(LHS), we propose that the source of granite was possibly generated from the partial melting of the metapelite in the GHC. Zircon UPb ages of the Palung granitic gneiss and the published geochronological results of the CambrianOrdovician granites/granitic gneisses demonstrate that the early Paleozoic orogeny was existed in the Himalayas. The early Paleozoic tectonic events preserved in the Himalayas are well compared with the contemporaneous ones in Lhasa terrane, Qiangtang terrane and BaoshanTengchong terrane located in the southeast of the Tibetan Plateau. Integrating the results from previous studies, we suggest that it is resulted from the Andeantype orogeny formed through the subduction of the protoTethys Ocean lithosphere along the northern margin of the Gondwana, rather than the PanAfrican orogeny which was related with the continentcontinent collision during the Gondwana assembly.

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    Analyses on the shale gas exploration prospect of the Niutitang Formation in northeastern Guizhou Area.
    LENG Ji-Gao, GONG Da-Jian, LI Fei, LI Feng
    Earth Science Frontiers    2016, 23 (2): 29-38.   DOI: 10.13745/j.esf.2016.02.004
    Abstract8655)      PDF (2359KB)(19955)      

    The shale gas resources are rich in the northeastern Guizhou area, especially in the Niutitang Formation. Based on the former failed drilling wells, combined with abundant analytical data of outcrops and cores, this study systematically investigated the geological characters of the Niutitang Formation in the northeastern Guizhou area and further implemented the resource potential in the study area. The following understandings are obtained. The kerogen types of organic matter are mainly of typeⅠand typeⅡ1, of the Niutitang Formation in the northeastern Guizhou area. The TOC content is high, with an average value of 3.52%. The average value of Ro is 3.58%, which reflects that the source rock has entered high maturation stage. The reservoirs are characterized by low porosityultralow permeability and high specific surface area. The results show that the brittle and clay minerals are averaged at 64.2% and 19.6%, respectively. The high siliceous contents and great brittleness is favorable for reservoir alteration. The recoverable resource of shale gas is estimated at 0.12 billion cubic meters. Areas including Cen gong, Yanhe, Xiushan, Dejiang, Kaili, etc. can be selected for further exploration and evaluation in the northeastern Guizhou area.

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    Geological characteristics of unconformities in Mesoproterozoic successions in the northern margin of North China Block and their tectonic implications.
    QU Yong-Jiang, MENG Qiang-Lin, MA Shou-Xian, LI Lin, WU Guo-Li
    Earth Science Frontiers    2010, 17 (4): 112-127.  
    Abstract7253)      PDF (3797KB)(19707)      

    There exist several depositional breaks and unconformities in the Mesoproterozoic successions in the northern margin of the North China Block. We carried out a field study of geologic characteristics and spatial distribution of five unconformities, and concluded that they resulted from different geological processes. The unconformity beneath the Dahongyu Formation is interpreted as a breakup unconformity in nature, representing the timing of transition from continental rift to passive continental margin. The unconformities beneath the Gaoyuzhuang and Yangzhuang Formations are considered as the consequence of regional eustatic fluctuations, leading to exposure of highlands in passive margin during sealevel falls and transgressive deposition on coastal regions during sealevel rise. The unconformity atop the Tieling Formation might be caused by uplift due to contractional deformation in backarc setting, whereas the uplift after deposition of Xiamaling Formation might have been attributed to a continental collision event. It is assumed that the occurrences of the unconformities in the Mesoproterozoic successions in the northern North China Block had a close bearing on the assemblage and breakup of the Columbia and Rodinia supercontinents.

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    The wholeaperture pore structure characteristics and its effect on gas content of the Longmaxi Formation shale in the southeastern Sichuan basin.
    JIANG Zhen-Hua, TANG Xiang-Lu, LI Zhuo, HUANG He-Xin, YANG Pei-Pei, YANG Xiao, LI Wei-Bing, HAO Jin
    Earth Science Frontiers    2016, 23 (2): 126-134.   DOI: 10.13745/j.esf.2016.02.013
    Abstract8634)      PDF (1616KB)(19041)      

    Since shale gas mainly occurs in shale pores, research on the pore structure characteristics is key to understand shale gas accumulation mechanism. Based on the experiments of CO2 adsorption, N2 adsorption, CH4 isothermal adsorption and high pressure mercury injection, the wholeaperture pore structure of the Longmaxi Formation shale is characterized in the Southeastern Sichuan Basin and the controlling effects of pore structure on the gas content are explained. Micropores (<2.0 nm), mesopores (2.050.0 nm) and macropores (>50.0 nm) are developed in shale samples, and the distribution characters change obviously in each sample. In the aspect of pore volume, the mesopores have the biggest contribution to the whole pore volume, taking about 40.8%. It is followed by micropores, taking about 34.7%. The macropores have the minimum proportion in the whole pore volume, only taking 24.5%. In the aspect of surface area, the micropores have an absolute advantage in the whole surface area, accounting for about 76.87%. The second is mesopores, taking about 23.05%. The macropores only provide surface area of 0.07%. The main pore volume is provided by mesopores and micropores, which controls the content of free gas. The surface area of micropores has a good positive correlation with the largest CH4 adsorption contents, and makes up the main surface area in shale samples, which controls the content of adsorbed gas. The macropores are not dominant in pore volume and surface area, and its influence on the content of adsorbed gas and free gas is relatively weak. But the macropores can be the main channels for shale gas seepage. Therefore, understanding the distribution characteristics of micropores, mesopores and macropores, especially the contribution of micropores on the enrichment of adsorbed gas and free gas, has an important guiding significance to the shale gas exploration and development.

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    Reservoir characteristics and its influence on continental shale: An example from Triassic Xujiahe Formation shale, Sichuan Basin.
    Earth Science Frontiers    2016, 23 (2): 158-166.   DOI: 10.13745/j.esf.2016.02.016
    Abstract8605)      PDF (1347KB)(18961)      

    Based on drilling data, outcrop geologic survey around the area and laboratory test results of lots of rock samples, reservoir characteristics of Triassic Xujiahe Formation shale in the Sichuan basin are analyzed. Physical properties of the shale reservoir were tested by high pressure mercury intrusion method, nitrogen isothermal adsorption, and pulse permeability method. It is thought that Xujiahe Formation shale has a center of reservoir performance, and the porosity ranges from 0.95% to 4.77% with an average of 2.73%. A series of methods including direct observation method such as core and thin section observation, field emission scanning electron microscopy (FSEM) in combination with highpressure mercury injection, nitrogen isothermal adsorption experiment research have been used to research the reservoir space characteristics of Xujiahe Formation. Nanoscale matrix pore is the dominant reservoir space in the Xujiahe Formation shale, and pore with size less than 50 nm accounted for 83.9%. Matrix pores with pore size of 2100 nm include residual primary pores, intergranular pores, dissolved pores, and organic pores that only developed in local parts. Its pointed out that TOC content, clay mineral content and thermal maturity were the main controlling factors on reservoir characteristics of Xujiahe Formation shale.

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    Reservoir characteristics and enrichment conditions of shale gas in the CarboniferousPermian coalbearing formations of Qinshui Basin.
    Earth Science Frontiers    2016, 23 (2): 167-175.   DOI: 10.13745/j.esf.2016.02.017
    Abstract8517)      PDF (1571KB)(18952)      

    Qinshui Basin, as one of the most important coalbearing basins in China, not only has plenty of coal and coalbed methane resources, but also has a lot of shale reservoirs. However, there is little research on the characteristics and potential evaluation of shale gas reservoirs in this basin. In this paper, we studied the characteristics of shale gas reservoirs in the Upper Paleozoic of Qinshui Basin, China. Comprehensive experimental methods, including Xray diffraction, NMR, FIBSEM, microscopic identification of thin sections and nitrogen adsorption etc. were applied to analyze the characteristics of organic geochemistry, rock and mineral composition and pores evolution of organicrich shale gas reservoirs. On this basis, the exploration and development potential of shale reservoirs in the study area is evaluated. The results show that different types of pores and micro fractures developed here, which provide enough spaces for the storage of shale gas. Mineral pores, mainly including intergranular pores and intercrystalline pores in shapes of plate, triangle or irregular are well developed, whereas only a small amount of organic pores in shapes of dot or occasional ellipse developed. Porosity has a large specific surface area, which has a range from 2.84 m2/g to 6.44 m2/g with an average of 4.26 m2/g. The average value of pore size distribution is between 3.64 nm and 10.34 nm, which means mainly mesopores developed. The appropriate ratio of mineral composition, which is composed of 57.5% of clay minerals and 41.3% of brittle minerals, is pretty good for the development of mircopores, gas absorption and fracturing. High value of TOC and Ro, caused by abnormal thermal gradient in Mesozoic, provided favorable conditions for shale gas formation and storage. On the whole, though the burial depth is shallow, there is great exploration and development potential for shale gas in the CP period in the Qinshui Basin because the organic chemical conditions, mineral composition and reservoir characteristics are quite suitable for the formation and storage of shale gas.

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    HUI Wei- Diao-Da-Feng
    Earth Science Frontiers    2013, 20 (2): 155-171.  
    Abstract6371)      PDF (14054KB)(18686)      
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    structural variations in the Central and Western North China craton and its implications for the craton destruction.
    CHEN Ling, WEI Zi-Gen, CHENG Cheng
    Earth Science Frontiers    2010, 17 (1): 212-228.  
    Abstract6513)      PDF (35123KB)(18472)      

     A better understanding of the Phanerozoic tectonic reactivation and destruction of the North China Craton (NCC) demands a detailed knowledge of the deep structural features of the region. We have migrated teleseismic P and Sreceiver functions from dense seismic array data to construct the structure images of the lithosphere and the upper mantle along three profiles that traverse the three constituent parts of the NCC. Our images reveal substantial structural differences among different parts of the craton. In contrast to the Eastern NCC where significantly thinned lithosphere (60100 km) is widespread, the Central and Western NCC are characterized by the coexistence of both preserved thick and dramatically thinned lithosphere. The thick lithosphere (>200 km) is present beneath the stable Ordos Basin and the thinned lithosphere (up to 80 km) is found in the Late Cenozoic YinchuanHetao and ShaanxiShanxi rift areas, with the sharpest change occurring over a lateral distance of ~200 km. Near the boundary between the Eastern and Central NCC, a rapid thickening of the lithosphere by 2040 km over ~100 km laterally is observed, concordant with abrupt changes in surface topography and roughly coincident with the NorthSouth Gravity Lineament. It also corresponds to sharp changes in crustal structure, mantle transition zone thickness and structure of the 660 km discontinuity. Such a shallowdeep structural concordance throughout the whole upper mantle may be indicative of different Phanerozoic lithospheric tectonics and mantle processes in the two domains. The much thinned crust and lithosphere, thick mantle transition zone and complex structure of the 660 km discontinuity in the Eastern NCC may reflect the strong influence that the deep subduction of the Pacific slab and associated processes have had on mantle dynamics and lithospheric reactivation of the region since the Mesozoic time. The presence of thinned lithosphere in the Central and Western NCC together with petrological and geochemical data suggest that lithospheric remobilization and thinning may have affected the NCC much further to the west than previously thought. The rift areas in the region, which are underlain by significantly thinned lithosphere, appear to be related to ancient mechanically weak zones. These preexisting lithospheric structures may have been repeatedly reactivated by successive tectonic events during the longterm evolution of the NCC, and particularly have been weakened and thinned by the Cenozoic IndiaEurasia collision which eventually caused rifting in these areas. On the other hand, the generally relatively thick crust and lithosphere and normaltothin mantle transition zone beneath the Central and Western NCC suggest that multiple tectonic events, including the IndiaEurasia collision, may have had a relatively weak effect on the tectonic evolution of this region compared to that of the Pacific subduction on the Eastern NCC. This is plausibly responsible for the preservation of the cratonic nucleus under the Ordos Basin and the marked lithospheric heterogeneity of the region.

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    The transitional facies shale gas formation selection and favorable area prediction in the western Henan.
    LI Zhong-Meng, ZHANG Dong, ZHANG Gu-Ban, CI Ma-Xian-Zhang, LIU Yan-Jie, WANG Hong, HONG Chao
    Earth Science Frontiers    2016, 23 (2): 39-47.   DOI: 10.13745/j.esf.2016.02.005
    Abstract7591)      PDF (1377KB)(18121)      

    Shale gas is produced in mud shale formation with abundant organic matter. The transitional facies formation mud shale has large cumulative thickness and high hydrocarbon content. The gas accumulation potential is good in the western Henan, but the mud shale is characterized by thin single formation, multilayer and big transverse phase change. Because of the lack of large amount of gasbearing tests of the blank area, it is difficult to choose good shale gas formation. This paper takes the Upper Palaeozoic in western Henan province as a research object, makes a correlation and clustering analysis of the various parameters and air content of the mud shale, confirms that the main controlling factors of the air content of the shale are organic matter abundance, rock density, permeability, pyrite content and photoelectric absorption cross section index. A regression analysis is carried out with the air content to get a fitting equation, which has been validated to be good for the determination of fitting. Finally, the gasbearing of the transitional facies shale in the western Henan province has been determined by this method and a great number of gas data have been obtained. Comprehensive factor analysis method is proposed in this paper, making the gasbearing as a main factor, supplemented by secondary factors such as the organic matter maturity, porosity, coefficient of brittleness, thickness, burial depth and area. The reservoir benefit coefficient is calculated to choose a gasbearing horizon, and get the regional advantageous factor to predict favorable area. Use the measured and fitted data of the Upper Palaeozoic in the midwestern and western Henan province, favorable factor is calculated to predict the shale gas advantageous area of Zhuxianzhen, Gongyi and Mianchi by using the comprehensive factor analysis method.

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    Distribution characteristics and genesis of fluoride groundwater in the Hetao basin,Inner Mongolia.
    MAO Re-Yu, GUO Hua-Meng-*, GU Yong-Feng, JIANG Yu-Xiao, CAO Yong-Sheng, DIAO Wei-Guang, WANG Zhen
    Earth Science Frontiers    2016, 23 (2): 260-268.   DOI: 10.13745/j.esf.2016.02.024
    Abstract8528)      PDF (1429KB)(18115)      

    Not only high As groundwater but also high F- groundwater have been found in the Hetao basin of Inner Mongolia. Although much work has been done on high As groundwater, little is known about the distribution and genesis of high F- groundwater. Based on reviewing of previous data and hydrogeological setting, 406 groundwater samples were collected and analyzed from the Hetao Basin of Inner Mongolia. Mineral dissolution and precipitation, evaporation, competitive adsorption and desorption, and cation exchange were integrated to discuss the major mechanisms controlling the enrichment of groundwater fluoride in the plain and the piedmont areas in Hetao Basin with different hydrogeological conditions. Results show that over 59% of groundwater samples have fluoride concentration above the Chinas drinking water standards of 1.0 mg/L. Relatively more groundwater samples having fluoride concentrations greater than 1.0 mg/L in the piedmont area which is higher than those in the plain area. Highfluoride groundwater usually show high concentrations of Na+ and alkalinity and low concentration of Ca2+. In the flat plain, groundwater are normally higher in pH, HCO-3, δ18O, δD and TDS, and lower in Ca2+ and NO-3 than those in the piedmont area. The fluorite dissolution and calcite precipitation are the major factors controlling fluoride enrichment in groundwater at the piedmont area, while evaporation, cation exchange, competitive adsorption between OH-, HCO-3 and F- become the main controlling factors in groundwaters of the flat plain.

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    Runout prediction of large thickbedded unstable rock: A case study of Daxiang unstable rock in Yangjiao town, Wulong county, Chongqing.
    WANG Lei, LI Bin, GAO Yang, SHU Sai-Nan
    Earth Science Frontiers    2016, 23 (2): 251-259.   DOI: 10.13745/j.esf.2016.02.023
    Abstract8499)      PDF (1842KB)(17953)      

    Highspeed long runout landslidedebris flow is one of the most destructive failure modes of large unstable rock,which can be fast launching, run long distance and cover large area, so the runout prediction research of large unstable rock has great practical significance. Taking the Daxiang unstable rock as a study case, this project aimed at predicting the dynamic characteristics of long runout landslidedebris flow. Based on geological and geomorphological survey,the development characteristics and failure pattern of Daxiang unstable rock were analyzed. The DAN3D code and the rheological parameters calibrated through the inversion analysis of Jiweishan landslide were used for the analysis of the Daxiang unstable slope. The simulation results show that (1) the movement process of rockslidedebris avalanche could be divided into four stages as launching, deflection and throwing, crash and erosion, and long range accumulation. The whole process took 220 s, and travel distance was 2500 m; (2) the volume of the sliding mass was 530×104 m3, the total volume of the accumulation was 790×104 m3, the length of the accumulation was 1680 m and average depth was 6 m, the maximum erosion depth along the path was 8 m, and the maximum velocity was 60 m/s; (3) the debris could go though Yangjiao Town and reach the Wujiang River, which implies that the Yangjiao Town is in the danger zone; and (4) the simulated prediction could be used as a reference for landslide hazard quantitative assessment.

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    Shale uniaxial compressive failure property and the affecting factors of UCS.
    YIN Shuai, DING Wen-Long-*, SUN Ya-Xiong, WANG Xin-Hua, ZHANG Min, ZHANG Ning-Ji
    Earth Science Frontiers    2016, 23 (2): 75-95.   DOI: 10.13745/j.esf.2016.02.009
    Abstract8561)      PDF (3470KB)(17908)      

    Correct understanding of the uniaxial compressive strength of shale failure characteristics and its UCS influencing factors has an important reference value in detecting shale failure mechanism, drilling and well completion, fracturing evaluation, micro crack prediction, logging interpretation and seismic response. In this paper, based on the systematic study and comprehensive analysis of the recent research results of shale uniaxial compressive characteristics and the UCS study, reviewed the shale uniaxial failure characteristics and its UCS affecting factors. The results show that, the shale inelastic deformation mechanism in uniaxial loading curve is affected by the sliding of micro cracks, the production and extension of micro cracks, and the pore collapse. The shale uniaxial compression characteristics present tensile or tensileshear fracture. The tensile fracture is easy to occur in location that has high rigidity and degree of consolidation. The shear fracture is easy to occur in location that has low rigidity and degree of consolidation. The S shape failure criterion can accurately describe the shale compressive failure strength variation from uniaxial to three axis failure. From the point of view of geology, making an induction and summary of shale UCS affecting factors, they are composition, bedding plane angle, sorting, micro fabric, organic matter content and its distribution, porosity, moisture content, and microcracks. The affecting mechanism of these factors are analyzed in detail. Among these factors, due to the complex distribution characteristics of micro cracks, the mechanism of micro cracks on shale UCS is not well understood. So, it is recommended that quantitative research of shale micro crack parameters and study of the influence mechanism of micro cracks on shale uniaxial compressional failure from the microscope scale should be strengthened in the future. This study can provide a scientific guidance for shale oil and gas exploration and development.

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