1990 Vol. 8, No. 4
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Display Method:
1990, 8(4): 1-12.
Abstract:
The Devonian sedimentary basin of the Zhashui-Zhanhan district in southern Shaanxi Province shows well developed alluvial fan, braided stream, estuarine, tidal flat, platform margin sands, point reef, slope and basin facies. A mixed terrigeneous clastic-carbonate succession mainly comprises an intercalation of carbonate platform facies with slope-basin and basinal turbidites of very great thickness. The basin shows the following features: (1) Turbidite mineral compositions fall into the passive margin and rift basin field of Valoni ＆ Maynard' s QLF figure. (2) The sedimentary succession shows rapid and complex facies variation. (3) From east to west, facies vary from shallow to deep marine indicating that the main trend of the basin is N-S. (4) There are major abrupt facies changes between three large faults in the basin. These show right lateral slip and indicate eastward basin migration. (5) The sedimentary association of the basin shows the characteristics of continental margin rift basins. (6) Volcanic rocks are of the sub-alkaline and alkaline series. (7) The structure of the basin comprises a series of south trending thrust or reverse faults, with the intervening blocks showing complex east- west trending tight folds. Overall, the sedimentary basin is a continental margin rift depression shpwing elongate N-S orientation, and right lateral strike slip faulting. The basin developed on the northern margin of the Yangtze plate, which underwent extensional crustal thinning. The stages of basin evolution are as follows: (1) Primary stage (Z2-S) ——pre-rift arch to intracontinental rift. Mantle upwelling caused thinning of the Yangtze plate margin crust. Alkaline volcanism occurred along major faults. In the early Palaezoic, there was great lateral variation in sedimentation, with areas of differential uplift and subsidence. (2) Intensive spreading middle stage (D1-D3) ——continental rifting to faulted basin developerrient. In the early part of this stage, spreading led to large scale block subsidence, aulacogen formation, and right lateral strike slipping. The basin was filled with a great thickness of flysch, with some intercalated pyroclastics. In the later part of the stage, the Yangtze and North China plates began to move together, with continental collision taking place locally in the middle Devonian. (3) The inversion stage (C-T2)——intracontinental subduction and uplift. In this late stage, from Carboniferous to middle Triassic, the basin showed little change in sedimentary pattern, with a suite of shallow marine limestones, mudstones and sandy mudstone facies being developed. Following the middle Triassic, basin closure occurred as a result of purely intracontinental, shallow coastal deformation along a large decollement with about 120km of horizontal transport. Intracontinental subduction resulted in compression of the sedimentary basin into the east-west trending Qinling belt.
The Devonian sedimentary basin of the Zhashui-Zhanhan district in southern Shaanxi Province shows well developed alluvial fan, braided stream, estuarine, tidal flat, platform margin sands, point reef, slope and basin facies. A mixed terrigeneous clastic-carbonate succession mainly comprises an intercalation of carbonate platform facies with slope-basin and basinal turbidites of very great thickness. The basin shows the following features: (1) Turbidite mineral compositions fall into the passive margin and rift basin field of Valoni ＆ Maynard' s QLF figure. (2) The sedimentary succession shows rapid and complex facies variation. (3) From east to west, facies vary from shallow to deep marine indicating that the main trend of the basin is N-S. (4) There are major abrupt facies changes between three large faults in the basin. These show right lateral slip and indicate eastward basin migration. (5) The sedimentary association of the basin shows the characteristics of continental margin rift basins. (6) Volcanic rocks are of the sub-alkaline and alkaline series. (7) The structure of the basin comprises a series of south trending thrust or reverse faults, with the intervening blocks showing complex east- west trending tight folds. Overall, the sedimentary basin is a continental margin rift depression shpwing elongate N-S orientation, and right lateral strike slip faulting. The basin developed on the northern margin of the Yangtze plate, which underwent extensional crustal thinning. The stages of basin evolution are as follows: (1) Primary stage (Z2-S) ——pre-rift arch to intracontinental rift. Mantle upwelling caused thinning of the Yangtze plate margin crust. Alkaline volcanism occurred along major faults. In the early Palaezoic, there was great lateral variation in sedimentation, with areas of differential uplift and subsidence. (2) Intensive spreading middle stage (D1-D3) ——continental rifting to faulted basin developerrient. In the early part of this stage, spreading led to large scale block subsidence, aulacogen formation, and right lateral strike slipping. The basin was filled with a great thickness of flysch, with some intercalated pyroclastics. In the later part of the stage, the Yangtze and North China plates began to move together, with continental collision taking place locally in the middle Devonian. (3) The inversion stage (C-T2)——intracontinental subduction and uplift. In this late stage, from Carboniferous to middle Triassic, the basin showed little change in sedimentary pattern, with a suite of shallow marine limestones, mudstones and sandy mudstone facies being developed. Following the middle Triassic, basin closure occurred as a result of purely intracontinental, shallow coastal deformation along a large decollement with about 120km of horizontal transport. Intracontinental subduction resulted in compression of the sedimentary basin into the east-west trending Qinling belt.
1990, 8(4): 22-32.
Abstract:
The investigated area consists of a part of Nanpan River Basin located in the conjunction area of Yunna, Guizhou and Guanxi Provinces. A paleogeographic framework of isolated platform alternating with deep troughs occured in the area during Late permian. Volcaniclastics suits are found in deep troughs. Ten dominant lithofacies can be distinguished. Although they had undergone different depositional processes, all of them deposited in deep-water marine enviornment below wave base. Detrital compositions of tuffaceous sandstones of volcani- elastics suits from studied area are similar to detrital frame-work modes of sandstones from magmatic arc provenances and doted in undissected arc plot of the QFL, QmFLt, QpLvLs and QmPR trangular diagrames by W.R.Dickinson. By this and research on lithofacies, it is known that clastic materials derived from volcanic eruption. Volcanism existed widespreadly in the area during Late Permian. Chemical compositions of volcaniclastic rock studied are similar to the basalt of same age in this area, and different from volcanic and volcaniclastic rock in western Guizhou and Central Guangxi. Moreover, major part of the area had been under water besides a few of isolated platforms during Permian. Lithic fragments with quenching-edge and doubly graded sequences are found, no shallow benthos fossils and sediments in the volcaniclastics, no volcaniclastic on isolated platform. These evidences suggest that eruption in investigated area occured in.underwater wich offered volcaniclastic. Major volcaniclastic is fine-size, it is common that subaqueous ash-fallout do not form thin layers but raised with setting sediments, volcaniclastic sequences are widespread, G facies tuffs appear in different local sections and strata, which suggest that subaqueous eruptions be multisourece and frequent. Nanpan River Basin located in the conjunction of Ancient South China Continental Plate, Ancient Tethys Plate and Ancient Pacific Plate during Late Permian, is known as a plate margin enviornment with violent tectonism. Because abundant is volcaniclastic rock from dominantly gravity flow sedimentation, the basalts belong to tholeiite, in the investigated area with a modern marginal basin, the area was tectoniclly located in a marginal basin. The marginal basin was formed by the movement of Ancient Tethys Plate turning northeastward and underthrusing for NW tension faults being great and main passages of the eruptions. And the basin may be influncea by Ancient Pacific Plate northwestward for cale-alkaline volcanism in Central Guangxi and NE faults in the basin. From the studies of sedimentery characteristics, biologic fossils, chemical petrology and pressure compensation level of subaquenous eruption it is concluded that the ancient water-depth of the troughs in this area was most probably between 300-500m, never over 1000m, in Late Permian.
The investigated area consists of a part of Nanpan River Basin located in the conjunction area of Yunna, Guizhou and Guanxi Provinces. A paleogeographic framework of isolated platform alternating with deep troughs occured in the area during Late permian. Volcaniclastics suits are found in deep troughs. Ten dominant lithofacies can be distinguished. Although they had undergone different depositional processes, all of them deposited in deep-water marine enviornment below wave base. Detrital compositions of tuffaceous sandstones of volcani- elastics suits from studied area are similar to detrital frame-work modes of sandstones from magmatic arc provenances and doted in undissected arc plot of the QFL, QmFLt, QpLvLs and QmPR trangular diagrames by W.R.Dickinson. By this and research on lithofacies, it is known that clastic materials derived from volcanic eruption. Volcanism existed widespreadly in the area during Late Permian. Chemical compositions of volcaniclastic rock studied are similar to the basalt of same age in this area, and different from volcanic and volcaniclastic rock in western Guizhou and Central Guangxi. Moreover, major part of the area had been under water besides a few of isolated platforms during Permian. Lithic fragments with quenching-edge and doubly graded sequences are found, no shallow benthos fossils and sediments in the volcaniclastics, no volcaniclastic on isolated platform. These evidences suggest that eruption in investigated area occured in.underwater wich offered volcaniclastic. Major volcaniclastic is fine-size, it is common that subaqueous ash-fallout do not form thin layers but raised with setting sediments, volcaniclastic sequences are widespread, G facies tuffs appear in different local sections and strata, which suggest that subaqueous eruptions be multisourece and frequent. Nanpan River Basin located in the conjunction of Ancient South China Continental Plate, Ancient Tethys Plate and Ancient Pacific Plate during Late Permian, is known as a plate margin enviornment with violent tectonism. Because abundant is volcaniclastic rock from dominantly gravity flow sedimentation, the basalts belong to tholeiite, in the investigated area with a modern marginal basin, the area was tectoniclly located in a marginal basin. The marginal basin was formed by the movement of Ancient Tethys Plate turning northeastward and underthrusing for NW tension faults being great and main passages of the eruptions. And the basin may be influncea by Ancient Pacific Plate northwestward for cale-alkaline volcanism in Central Guangxi and NE faults in the basin. From the studies of sedimentery characteristics, biologic fossils, chemical petrology and pressure compensation level of subaquenous eruption it is concluded that the ancient water-depth of the troughs in this area was most probably between 300-500m, never over 1000m, in Late Permian.
1990, 8(4): 41-48.
Abstract:
The historic famous city--Leshan is located in the, southwestern part of Sichuanbasin. Three rivers--Mingjiang, Daduhe and Qingyi,yiang converge here, and theworldfamous Leshan great Buddha with:、thickness of 70m is serenelly siting on the cliff bythe Ming jiang river, facing the distant city. The red sandstone from which the staiue was carved is very attractive and interesting togeologists for its large-scale cross-beddines and unique seq,uences.In this paper, the originof the red sandstone will be discussed in detail.
The historic famous city--Leshan is located in the, southwestern part of Sichuanbasin. Three rivers--Mingjiang, Daduhe and Qingyi,yiang converge here, and theworldfamous Leshan great Buddha with:、thickness of 70m is serenelly siting on the cliff bythe Ming jiang river, facing the distant city. The red sandstone from which the staiue was carved is very attractive and interesting togeologists for its large-scale cross-beddines and unique seq,uences.In this paper, the originof the red sandstone will be discussed in detail.
1990, 8(4): 59-67.
Abstract:
The Late Carboniferous in Western Tarim Basin is the typical sedimentation of epicontinental carbonate platform. It is main sediments are micrite, sparite, biomicrosparite and dolomite. The study on sedimentary environment, features of diagenesis and evolution characteristic of pores of Upper Carboniferous carbonates was carried out by Cathodoluminescence Microscope, SEM, X-diffraction analysis, TAS-plus Image Analysis System and Reflectance of Vitrinite (R ° ), based on field work and a large quantity of thin section observation. Through research, the following main conclusions are proposed: 1.The sedimentary environment of Upper Carboniferous carbonates in Bachu-Keping region can be divided into four facies from west to east. (1) Open Sea Basin Facies It Is distributed north of Kalatieke Mt. and west of Atushi- Shache County area. The most of sediments are terrigenous fine clastic rock and marl. (2) Platform Border Shoal Facies It is distributed Maigaiti County area. The most of sediments are sparite and dolomite. (3) Open Platform Facies It is distributed Bachu County-Subashi village area. The most of sediments are biomicrite and marl. (4) Coastal Shoal Facies It is distributed east of Keping County and north of Shajinzi Town area. The most of sediments are quartzose sandstone, siltstone, intramicsparite and biomicrosparite. 2. Upper Carboniferous carbonates have undergone deep compaction, Presoiution, cementation, dolomitizatiori and solution. Measurement of vitrinite reflection (R ° ) and illite crystallinity in mudstone demenstrate that diagenetic temperature is 120℃ to 160℃ Therefore in author' s opinion, this sequence is in the middle-late postdiagenetic stage, that is organic mature stage. 3. There are five kinds of cement which are formed in different period in. Upper Carboniferous carbonates: (1) . Needle isopachous ring cement. (2) . Co-axial ring cement. ( 3) . Allotriomorphic to hypautomorphic granular sparrycalcite cement. ( 4) . Sparry cyclopean ferrocalcite cement. (5) Hypautomorphic to idiomorphic dolomite cement. 4.The original sedimentary environment of carbonate is the important condition that influences the diagenesis of carbonate. The good reservoir rocks are often evolved from sparry granular carbonate and biosparite. Especially sparry granular carbonate of Xiaohaizi formation in platform border fades, because the widespread dolomitization, formed dolomhic limestone which has residual structure, that is helpful for the formation of secondary pores. Mean porosity of dolomite is 10%, So the authors suggest that this sort of rocks is the hopeful resvoir of oil.
The Late Carboniferous in Western Tarim Basin is the typical sedimentation of epicontinental carbonate platform. It is main sediments are micrite, sparite, biomicrosparite and dolomite. The study on sedimentary environment, features of diagenesis and evolution characteristic of pores of Upper Carboniferous carbonates was carried out by Cathodoluminescence Microscope, SEM, X-diffraction analysis, TAS-plus Image Analysis System and Reflectance of Vitrinite (R ° ), based on field work and a large quantity of thin section observation. Through research, the following main conclusions are proposed: 1.The sedimentary environment of Upper Carboniferous carbonates in Bachu-Keping region can be divided into four facies from west to east. (1) Open Sea Basin Facies It Is distributed north of Kalatieke Mt. and west of Atushi- Shache County area. The most of sediments are terrigenous fine clastic rock and marl. (2) Platform Border Shoal Facies It is distributed Maigaiti County area. The most of sediments are sparite and dolomite. (3) Open Platform Facies It is distributed Bachu County-Subashi village area. The most of sediments are biomicrite and marl. (4) Coastal Shoal Facies It is distributed east of Keping County and north of Shajinzi Town area. The most of sediments are quartzose sandstone, siltstone, intramicsparite and biomicrosparite. 2. Upper Carboniferous carbonates have undergone deep compaction, Presoiution, cementation, dolomitizatiori and solution. Measurement of vitrinite reflection (R ° ) and illite crystallinity in mudstone demenstrate that diagenetic temperature is 120℃ to 160℃ Therefore in author' s opinion, this sequence is in the middle-late postdiagenetic stage, that is organic mature stage. 3. There are five kinds of cement which are formed in different period in. Upper Carboniferous carbonates: (1) . Needle isopachous ring cement. (2) . Co-axial ring cement. ( 3) . Allotriomorphic to hypautomorphic granular sparrycalcite cement. ( 4) . Sparry cyclopean ferrocalcite cement. (5) Hypautomorphic to idiomorphic dolomite cement. 4.The original sedimentary environment of carbonate is the important condition that influences the diagenesis of carbonate. The good reservoir rocks are often evolved from sparry granular carbonate and biosparite. Especially sparry granular carbonate of Xiaohaizi formation in platform border fades, because the widespread dolomitization, formed dolomhic limestone which has residual structure, that is helpful for the formation of secondary pores. Mean porosity of dolomite is 10%, So the authors suggest that this sort of rocks is the hopeful resvoir of oil.
1990, 8(4): 77-84.
Abstract:
The manganese carbonate beds in Minle area are abundant in isotopes S, O. C, Rb and Sr by sampling and determining. The characteristics of these isotopes are, δ34S 46.6-58.59‰ (52.17‰ on an average), δ18OPDB-3.72-9.06‰ , δ13CPDB-8.19——12.98‰ 87Rbμg/ g 0.06827-0.45154, 86Srμg/ g 0.0837-0.18809, 87Rb/ 86Sr 0.42632-5.0459, 87Sr/ 86Sr 0.70935 ± 0.00016-0.75808 ± 0.00025. According to the comprehensive study of these isotopes, this paper has inquaired into the paleogeographic environments of metallogenic epoch of manganese, the paleotemperatures of metallogenic medium of manganese, the major source of the metallogenic materials of manganese, the source and nature of Mn-bearing solution, and the period of metallogenic manganese. Conclusions are drawn by the author as follows that the environments of the manganese carbonate were semi- limit- confin weak salt water tidal flat- lagoon and they did not emerge in evaporation; the paleotemperature of metallogenic medium of manganese was 35. 72 ° -40.88℃ , much higher than that of the modern seawater; the major source of manganese was the material of weathering and separation of continental crust; the Mn-bearing solution should be seawater; the period of metallogenic manganese was 728 ± 27 Ma (B.P.), belonging to Minle to Minle period of Early Sinian period. Thus, the important information and data were contributed in the metallogenic manganese period and the origin studying of Minle manganese deposit
The manganese carbonate beds in Minle area are abundant in isotopes S, O. C, Rb and Sr by sampling and determining. The characteristics of these isotopes are, δ34S 46.6-58.59‰ (52.17‰ on an average), δ18OPDB-3.72-9.06‰ , δ13CPDB-8.19——12.98‰ 87Rbμg/ g 0.06827-0.45154, 86Srμg/ g 0.0837-0.18809, 87Rb/ 86Sr 0.42632-5.0459, 87Sr/ 86Sr 0.70935 ± 0.00016-0.75808 ± 0.00025. According to the comprehensive study of these isotopes, this paper has inquaired into the paleogeographic environments of metallogenic epoch of manganese, the paleotemperatures of metallogenic medium of manganese, the major source of the metallogenic materials of manganese, the source and nature of Mn-bearing solution, and the period of metallogenic manganese. Conclusions are drawn by the author as follows that the environments of the manganese carbonate were semi- limit- confin weak salt water tidal flat- lagoon and they did not emerge in evaporation; the paleotemperature of metallogenic medium of manganese was 35. 72 ° -40.88℃ , much higher than that of the modern seawater; the major source of manganese was the material of weathering and separation of continental crust; the Mn-bearing solution should be seawater; the period of metallogenic manganese was 728 ± 27 Ma (B.P.), belonging to Minle to Minle period of Early Sinian period. Thus, the important information and data were contributed in the metallogenic manganese period and the origin studying of Minle manganese deposit
1990, 8(4): 94-103.
Abstract:
Taking the Daanzhai formation of the condensate gas reservoir in Bajiaochang gas field which in the central Sichuan Basin as an example, this paper initiates with the description of its geological characteristics summarised below: 1.The producing formation is a typical inland freshwater lacustrine sediment which consists of lacustrine carbonates and interbedded with various thicknesses of shale layers. Coquina is a main reservoir rock. The black shale is a main source rock of hydrocarbons. 2. The reservoir rock is overlow permeable and unconvertional tight rock with the inhomogeneity. Through test to the core samples, it is proved that the porosities are mainly within the range of 1.0-1.5%, and the permeabilities are less than 0.5md (0.49 × 10-4) μm2) 3. The main types of the organic matter (kerogen) in the source rock are sapropelic and mixed ones. The evolution of the organic materials is in the mature-early supermature stages. The reflectance of vitrinite (Ro) is about 0.8-1.1. 4. The gas reservoir of Daanzhai formation consists of several gas-producing layers and different fracture systems. The well interference exists distinctly in the same systems, but independence among different ones. The distribution of oil and gas in the anticline is controlled by both the diagenesis of reservoir and the structure. 5.The fluid pressure of the producing layer exceeds the hydrostatic pressure. The pressure coefficient is about 1.56-1.70, belonging to high abnormal pressure. The formation temperature is about 70-75℃. Then this paper deals with the gas sources and the possibility of being influenced by other sources, according to the components of light hydrocarbons (,C4- C7) series in the condensate, the paraffin index, the correlation of fingerprint compounds of light hydrocarbons and the carbon isotopic characteristics. Differing from the conventional point of view, a conclusion is drawn that the oil and gas are not only from the sources in Daanzhai formation, but also from that of the deeper Xiangxi group. This idea may have some significance in studying the distribution of the inhomogeneity of oil and gas, and forming mechanism of abnormal pressure, and so on. Moreover, it discusses the changes of light hydrocarbons in the condensate in regard to their content and composition.
Taking the Daanzhai formation of the condensate gas reservoir in Bajiaochang gas field which in the central Sichuan Basin as an example, this paper initiates with the description of its geological characteristics summarised below: 1.The producing formation is a typical inland freshwater lacustrine sediment which consists of lacustrine carbonates and interbedded with various thicknesses of shale layers. Coquina is a main reservoir rock. The black shale is a main source rock of hydrocarbons. 2. The reservoir rock is overlow permeable and unconvertional tight rock with the inhomogeneity. Through test to the core samples, it is proved that the porosities are mainly within the range of 1.0-1.5%, and the permeabilities are less than 0.5md (0.49 × 10-4) μm2) 3. The main types of the organic matter (kerogen) in the source rock are sapropelic and mixed ones. The evolution of the organic materials is in the mature-early supermature stages. The reflectance of vitrinite (Ro) is about 0.8-1.1. 4. The gas reservoir of Daanzhai formation consists of several gas-producing layers and different fracture systems. The well interference exists distinctly in the same systems, but independence among different ones. The distribution of oil and gas in the anticline is controlled by both the diagenesis of reservoir and the structure. 5.The fluid pressure of the producing layer exceeds the hydrostatic pressure. The pressure coefficient is about 1.56-1.70, belonging to high abnormal pressure. The formation temperature is about 70-75℃. Then this paper deals with the gas sources and the possibility of being influenced by other sources, according to the components of light hydrocarbons (,C4- C7) series in the condensate, the paraffin index, the correlation of fingerprint compounds of light hydrocarbons and the carbon isotopic characteristics. Differing from the conventional point of view, a conclusion is drawn that the oil and gas are not only from the sources in Daanzhai formation, but also from that of the deeper Xiangxi group. This idea may have some significance in studying the distribution of the inhomogeneity of oil and gas, and forming mechanism of abnormal pressure, and so on. Moreover, it discusses the changes of light hydrocarbons in the condensate in regard to their content and composition.
1990, 8(4): 115-123.
Abstract:
Coalbeds B11b and B10 from the lower Shihezi formation of Permian are a pair of adjacent coalbeds at Xiejiaji coal district in Huainan Coalfield. Both coalbeds are of same rank ( Ro= 0. 80-0. 82% ) and under the same geological conditions. However, their gas-bearingness and gas-compositions are quite different. B11b is rich in coalbed gas and heavy hydrocarbon compositions, whereas B10 is poor. According to their coal petrology and organic geochemistry, the reasons on gas- bearingness and strong coal- generated hydrocarbon are studied in this paper. 1. Under optical and fluorescence microscopy, there exist many kinds of hydrocarbon-rich macerals and microindicators in coal-generated hydrocarbon in B11b, such as bituminite-filling, resinite-filling, exudatinite, suberinite, oil drops and oil film, and micrinit.es with many shapes and occurences. Some of these macerals are also the microindicators in migration of coal-generated oil and gas. 2.The information in organic geochemistry shows that both coal beds might form in different sedimentary evironments. Their OEP parameters are roughly same, i.e. they are in the same maturity. However, the parameters, such as Pr/Ph, Pr/nC17, Ph/nC18, are quite different. These parameters show that the reducibility of B11b is stronger than that of B10. The author has considered that B11b is mainly composed of herbaceous plant and hydrophyte and form in an environment of "open waters" or "swamp water land", while B10 is maed up of wood plant and form in an environment of "forest swamp". The thermal analysis shows that B11b is of higher thermal weight-loss than B10 and greater potential in coal-generated hydrocarbon. 3.The porosity and gas-storing capacity of both the coal beds has also been studied by author. The theory and experiments have indicated that the porosity in B11bis favourable for gas storage, diffusion and migration.
Coalbeds B11b and B10 from the lower Shihezi formation of Permian are a pair of adjacent coalbeds at Xiejiaji coal district in Huainan Coalfield. Both coalbeds are of same rank ( Ro= 0. 80-0. 82% ) and under the same geological conditions. However, their gas-bearingness and gas-compositions are quite different. B11b is rich in coalbed gas and heavy hydrocarbon compositions, whereas B10 is poor. According to their coal petrology and organic geochemistry, the reasons on gas- bearingness and strong coal- generated hydrocarbon are studied in this paper. 1. Under optical and fluorescence microscopy, there exist many kinds of hydrocarbon-rich macerals and microindicators in coal-generated hydrocarbon in B11b, such as bituminite-filling, resinite-filling, exudatinite, suberinite, oil drops and oil film, and micrinit.es with many shapes and occurences. Some of these macerals are also the microindicators in migration of coal-generated oil and gas. 2.The information in organic geochemistry shows that both coal beds might form in different sedimentary evironments. Their OEP parameters are roughly same, i.e. they are in the same maturity. However, the parameters, such as Pr/Ph, Pr/nC17, Ph/nC18, are quite different. These parameters show that the reducibility of B11b is stronger than that of B10. The author has considered that B11b is mainly composed of herbaceous plant and hydrophyte and form in an environment of "open waters" or "swamp water land", while B10 is maed up of wood plant and form in an environment of "forest swamp". The thermal analysis shows that B11b is of higher thermal weight-loss than B10 and greater potential in coal-generated hydrocarbon. 3.The porosity and gas-storing capacity of both the coal beds has also been studied by author. The theory and experiments have indicated that the porosity in B11bis favourable for gas storage, diffusion and migration.
1990, 8(4): 130-137.
Abstract:
On the basis of analysis and correlation of strata in Lanzhou area, it is regarded in thisarticle that the youngest stratum under the Arming System naffed by C. C. Young andM.N.Bian in 1936 is a layer of gray-white sandy conglomerate formed in the early MioceneEpoch, basis on the evidences of vertebrate paleontology found at some places such as thenorth slope of Gaolan Mountain, Hanjinzi, Xianshuihe etc.，while the oldest stratumabove the Arming System is the sixth terrace gravel layer of Huanghe River (Yellow River)under the Wucheng loess layer at Jiuzhoutai, formed 1.488±0.11 Ma (8.P.) dated by themethod of gypsum fission trace. Arming System, therefore, was formed in the period ofMiddle Miocene-Pliocene. Arming System is fossil eolian sand face of desert in light of many features such as largelaminae, sandstone with calcareous cement, sand grainsize compared with desert sand,micro-texture of quartz sand granule including dish-shaped concavity, curved grouve,curved edge and silica deposit, etc. Th,e type of physial environment for the formation. of Anning System may be fromsemiarid steppe to arid desert steppe, and it mainly formed by the arid climate of LateTertiary according to the parameters of environment e.g. redish sand colour, calcareouscemented sandstone, calcareous nodule, and relating to other conclusions ofpaleogeography and paleoboany. There must be a paleo- anticyclone centre in the west of Lanzhou controlling wholenorth China inLate Tertiary according to:(1) the occurence of foreset laminae in ArmingSxstem are mainly from west to east (2) the wide spreading of eolian red earth of LateTertiary in the east of Lanzhou such as Baode and Jinle formations.
On the basis of analysis and correlation of strata in Lanzhou area, it is regarded in thisarticle that the youngest stratum under the Arming System naffed by C. C. Young andM.N.Bian in 1936 is a layer of gray-white sandy conglomerate formed in the early MioceneEpoch, basis on the evidences of vertebrate paleontology found at some places such as thenorth slope of Gaolan Mountain, Hanjinzi, Xianshuihe etc.，while the oldest stratumabove the Arming System is the sixth terrace gravel layer of Huanghe River (Yellow River)under the Wucheng loess layer at Jiuzhoutai, formed 1.488±0.11 Ma (8.P.) dated by themethod of gypsum fission trace. Arming System, therefore, was formed in the period ofMiddle Miocene-Pliocene. Arming System is fossil eolian sand face of desert in light of many features such as largelaminae, sandstone with calcareous cement, sand grainsize compared with desert sand,micro-texture of quartz sand granule including dish-shaped concavity, curved grouve,curved edge and silica deposit, etc. Th,e type of physial environment for the formation. of Anning System may be fromsemiarid steppe to arid desert steppe, and it mainly formed by the arid climate of LateTertiary according to the parameters of environment e.g. redish sand colour, calcareouscemented sandstone, calcareous nodule, and relating to other conclusions ofpaleogeography and paleoboany. There must be a paleo- anticyclone centre in the west of Lanzhou controlling wholenorth China inLate Tertiary according to:(1) the occurence of foreset laminae in ArmingSxstem are mainly from west to east (2) the wide spreading of eolian red earth of LateTertiary in the east of Lanzhou such as Baode and Jinle formations.
1990, 8(4): 13-21.
Abstract:
The Late Permian Heshan Formation in central Guangxi is well known for its coal-bear-ing carbonate sequences. It mainly consists of limestones and contains 6 coal seams. Detailedstudies in Heshan coalfield reveal that Ieshan Formation:was formed in the shallow watercarbonate platform environments under the warm and humid climate. The following faciesbelts and microfacies have been recognized in this sequence: Shallow sea basin fades: (1) Lime mudstone and wackestone and wackestone with the whole body stenohaline organisms; (2) Bioturbated bioclastic wackstone; (3) Bioclastic packstones (tempestites). Platform marginal organic reef facies: Sponge bafflestene and bindstone.Open platform fades:(1)Algal debris packstone with fecal pellets;(2)Forarr:-bioclastic packstone; (3) Fusulinid-organism packstone; (4) Mottling bioturbat-ed recrystallized limestone and dolomitic limestone. Tidal flat facies:(1)1.,am.nated algal debris packstone;(2).Rip- up'intraciasticrudstone;(3) Chera with siliceous gummy sheaths of blue-green algae and the siliciliedbiociasts. Peat flat fades: This fades is represented by the coal seams and the carbonaceousmudstone. Coastal lagoon facies: It is the products of the initial transgression and represented by the alumina claystone. The above facies belts and !nicrofacies are comparable to Wilson .s(1957) carbonateplatform model. 3ut the marginal area of the platform was a ramp which is characterized bythe reef recording middle to stronger wave activity and the gentle slope. Therefore, thedepositionai model of Heshan Formation can be outlined as the carbonate plafforrn with theramp margin. The coal-forming environment is believed to be the peat flat developed on the tidal flat.The Goal-forming materials were the mangrove-like plats which could grow in the brackishand sea water in the tide-influenced swamps which were similar to modern'intertidal m;tn-grove swamps in the southern Florida shelf in the United States and the Hain
The Late Permian Heshan Formation in central Guangxi is well known for its coal-bear-ing carbonate sequences. It mainly consists of limestones and contains 6 coal seams. Detailedstudies in Heshan coalfield reveal that Ieshan Formation:was formed in the shallow watercarbonate platform environments under the warm and humid climate. The following faciesbelts and microfacies have been recognized in this sequence: Shallow sea basin fades: (1) Lime mudstone and wackestone and wackestone with the whole body stenohaline organisms; (2) Bioturbated bioclastic wackstone; (3) Bioclastic packstones (tempestites). Platform marginal organic reef facies: Sponge bafflestene and bindstone.Open platform fades:(1)Algal debris packstone with fecal pellets;(2)Forarr:-bioclastic packstone; (3) Fusulinid-organism packstone; (4) Mottling bioturbat-ed recrystallized limestone and dolomitic limestone. Tidal flat facies:(1)1.,am.nated algal debris packstone;(2).Rip- up'intraciasticrudstone;(3) Chera with siliceous gummy sheaths of blue-green algae and the siliciliedbiociasts. Peat flat fades: This fades is represented by the coal seams and the carbonaceousmudstone. Coastal lagoon facies: It is the products of the initial transgression and represented by the alumina claystone. The above facies belts and !nicrofacies are comparable to Wilson .s(1957) carbonateplatform model. 3ut the marginal area of the platform was a ramp which is characterized bythe reef recording middle to stronger wave activity and the gentle slope. Therefore, thedepositionai model of Heshan Formation can be outlined as the carbonate plafforrn with theramp margin. The coal-forming environment is believed to be the peat flat developed on the tidal flat.The Goal-forming materials were the mangrove-like plats which could grow in the brackishand sea water in the tide-influenced swamps which were similar to modern'intertidal m;tn-grove swamps in the southern Florida shelf in the United States and the Hain
1990, 8(4): 33-40.
Abstract:
The ancient basin of Paleogene in Jizhong region is of the faulted depression type. In the depression exist fourteen dustpan-like sags and six uplifts. The regional structural characters of the depression are that depressions' being divided into east and west parts and its evolution history determine the features of the fluvial-lacustrine system and herein the sedimentary tilling. The sedimentary filling in Es2-3 of Jizhong Basin features the fluvial-lacustrine system being divided into two parts: the west part belongs to standard plain type rivers with complete fades sequences; the east is a lake region. The distribution of the system is not mainly controlled by the local dustpan-like sags. In addition to ordinary rivers there are short ancient rivers of mountain-foot type scattering along the periphery of the lake basin. The evolution process of the sags consists of three great cycles and six secondary transgression and regression cycles, which governs the longitudinal distribution of the sand bodies in the lake basin. The application of seismic stratigaphy to the study of sedimentary filling models in the depression offers plenty of geological information. The reservoirs so far discovered in Jizhong Basin all are sand bodies of lake sediment which fall into six types, the formation of which appears to be determined by the ancient river type and topographic features, and the distribution of which seems to be controlled by ancient rivers as well as the communicated waters. Jizhong region can be classified into four groups and six subgroups of sedimentary system tracts, thus characterizing the sedimentary filling in Es2-3 in the region.
The ancient basin of Paleogene in Jizhong region is of the faulted depression type. In the depression exist fourteen dustpan-like sags and six uplifts. The regional structural characters of the depression are that depressions' being divided into east and west parts and its evolution history determine the features of the fluvial-lacustrine system and herein the sedimentary tilling. The sedimentary filling in Es2-3 of Jizhong Basin features the fluvial-lacustrine system being divided into two parts: the west part belongs to standard plain type rivers with complete fades sequences; the east is a lake region. The distribution of the system is not mainly controlled by the local dustpan-like sags. In addition to ordinary rivers there are short ancient rivers of mountain-foot type scattering along the periphery of the lake basin. The evolution process of the sags consists of three great cycles and six secondary transgression and regression cycles, which governs the longitudinal distribution of the sand bodies in the lake basin. The application of seismic stratigaphy to the study of sedimentary filling models in the depression offers plenty of geological information. The reservoirs so far discovered in Jizhong Basin all are sand bodies of lake sediment which fall into six types, the formation of which appears to be determined by the ancient river type and topographic features, and the distribution of which seems to be controlled by ancient rivers as well as the communicated waters. Jizhong region can be classified into four groups and six subgroups of sedimentary system tracts, thus characterizing the sedimentary filling in Es2-3 in the region.
1990, 8(4): 49-58.
Abstract:
Biyang Depression developed on the Qinling folded belt in a Eogene inland faulted oil-bearing basin, in which Oligocene Hetaoyuan formation expresses a large degression sequence, with a multiple cycle character. During deep basin-shallow water and desiccated deep basin period of basin evolution, the natural environmental conditions were favourable for the growth and bloom of blue green algae. In addition, the frequent fluctuation ,of high and low lake level, especially flush flood caused periodic terrestrial clastic supply, which combined with algal mats growed on the mud flat, forming cryptoalgal laminite cycles with a different rhythm. The cryptoalgal laminite can be divided into two kinds based on their shapes: 1) horizontal laminated cryptoalgal laminite composed of couples, namely 4ark and light laminae, with horizontal texture; 2) cryptoalgal laminite with an irregular deformed laminated structure, generally wave or dome-like laminae. The dark laminae composed of cryptocrystal calcite and Fe-dolomite has a dark colour by organic matter infection, under SEM it displays a algal mat form consisted of dense algal filaments; the light laminae consists of carbonate and algal fragments and fine clastic minerals. The coarse clastic grains were trapped by algal filaments. It is a significant fabric in the light laminae. By identification, there mainly are blue green algae fossils: Lyngya, Microcoleus, Phormidium and Hydrocoleus. Through the study of sedimentary sequence and facies, it was found that the cryptoalgal laminite with special structure was formed by living activity of carbonate-building algae community and periodic sediment input under arid-semiarid paleoclimatic condition and hence lake diminishing and increasing in salinity of lake water. The reasons formed two kinds of cryptoalgal laminite may mainly be water depth, dynamics, genera and species of algae and its degree of development and so on. The most favourable sedimentary facies belts for formation of cryptoalgal laminite are mud flat, interfandeltaic bay and interunstable channel on mad flat. The special texture and mechanism of formation for cryptoalgal laminite makes itself become a good indicator to paleoenvironmental analysis of oil-bearing strata in Biyang Depression. It provides the valuable date for oil-gas exploration in the basin.
Biyang Depression developed on the Qinling folded belt in a Eogene inland faulted oil-bearing basin, in which Oligocene Hetaoyuan formation expresses a large degression sequence, with a multiple cycle character. During deep basin-shallow water and desiccated deep basin period of basin evolution, the natural environmental conditions were favourable for the growth and bloom of blue green algae. In addition, the frequent fluctuation ,of high and low lake level, especially flush flood caused periodic terrestrial clastic supply, which combined with algal mats growed on the mud flat, forming cryptoalgal laminite cycles with a different rhythm. The cryptoalgal laminite can be divided into two kinds based on their shapes: 1) horizontal laminated cryptoalgal laminite composed of couples, namely 4ark and light laminae, with horizontal texture; 2) cryptoalgal laminite with an irregular deformed laminated structure, generally wave or dome-like laminae. The dark laminae composed of cryptocrystal calcite and Fe-dolomite has a dark colour by organic matter infection, under SEM it displays a algal mat form consisted of dense algal filaments; the light laminae consists of carbonate and algal fragments and fine clastic minerals. The coarse clastic grains were trapped by algal filaments. It is a significant fabric in the light laminae. By identification, there mainly are blue green algae fossils: Lyngya, Microcoleus, Phormidium and Hydrocoleus. Through the study of sedimentary sequence and facies, it was found that the cryptoalgal laminite with special structure was formed by living activity of carbonate-building algae community and periodic sediment input under arid-semiarid paleoclimatic condition and hence lake diminishing and increasing in salinity of lake water. The reasons formed two kinds of cryptoalgal laminite may mainly be water depth, dynamics, genera and species of algae and its degree of development and so on. The most favourable sedimentary facies belts for formation of cryptoalgal laminite are mud flat, interfandeltaic bay and interunstable channel on mad flat. The special texture and mechanism of formation for cryptoalgal laminite makes itself become a good indicator to paleoenvironmental analysis of oil-bearing strata in Biyang Depression. It provides the valuable date for oil-gas exploration in the basin.
1990, 8(4): 68-76.
Abstract:
The article is going on the distinguishing of dune rock, dune, seabeach sand, beachrock and some offshore deposits through comparison researches of their sedimentologic and petrologic features. The dune rock has great similarities to dune from the view of their sedimentologic features and landform distribution. Dip angle of the frontal deposit layer of the both is relatively large ( 30 ° ) .Components are mostly of middle to fine sands. The more favorable facing wind and sea, the more near by the frontal deposit layer, the dune rock is of, less source of slope wash and the cementation and sorting are better. A lot of slope wash, therefore, can be regarded as the principal marker of dune rock, by which it is distinguished from the non-marine deposits. The sedimentologieal difference is obviously obsered between beachrock and dune. The former was formed under the condition of windstorm tide and poorly sorted. The content of gravel and middle and coarse sands achievs over 80%. The beachrocks can be subdivided into marine sea-making and marine land-making. The former is mostly in the tide belt of the subsident or stable coast with a highery percentage of MgO molecule number (11.9-15.26), while the latter is mostly in the raised coast with a lower percentage (usually less than 5) .Generally, the MgO molecule number of the dune rock at 22m a.s.l. reaches 7.41%. Observations under have seveal that the cement of marine sea- making beachrock is composed mostly of rhombohedrens of high- Mg calcite and pessesses features of cementation under the current and vadose belt, whileof the marime land- making beachrock, it is composed mostly of granular and columnar calcite with low Mg and has the features of vadose cementation. Therefore distinguishing of dune rock from beachrock is not mostly according to the characteristic of the petrology but that of sedimentlolgy. The hard ground of the seabed, which is referred to in this article, is probably the cementation of calc-mucus discharged by the organism. The formation of dune on the sea floor is probably related to the ridge of tidal sands of the zone.
The article is going on the distinguishing of dune rock, dune, seabeach sand, beachrock and some offshore deposits through comparison researches of their sedimentologic and petrologic features. The dune rock has great similarities to dune from the view of their sedimentologic features and landform distribution. Dip angle of the frontal deposit layer of the both is relatively large ( 30 ° ) .Components are mostly of middle to fine sands. The more favorable facing wind and sea, the more near by the frontal deposit layer, the dune rock is of, less source of slope wash and the cementation and sorting are better. A lot of slope wash, therefore, can be regarded as the principal marker of dune rock, by which it is distinguished from the non-marine deposits. The sedimentologieal difference is obviously obsered between beachrock and dune. The former was formed under the condition of windstorm tide and poorly sorted. The content of gravel and middle and coarse sands achievs over 80%. The beachrocks can be subdivided into marine sea-making and marine land-making. The former is mostly in the tide belt of the subsident or stable coast with a highery percentage of MgO molecule number (11.9-15.26), while the latter is mostly in the raised coast with a lower percentage (usually less than 5) .Generally, the MgO molecule number of the dune rock at 22m a.s.l. reaches 7.41%. Observations under have seveal that the cement of marine sea- making beachrock is composed mostly of rhombohedrens of high- Mg calcite and pessesses features of cementation under the current and vadose belt, whileof the marime land- making beachrock, it is composed mostly of granular and columnar calcite with low Mg and has the features of vadose cementation. Therefore distinguishing of dune rock from beachrock is not mostly according to the characteristic of the petrology but that of sedimentlolgy. The hard ground of the seabed, which is referred to in this article, is probably the cementation of calc-mucus discharged by the organism. The formation of dune on the sea floor is probably related to the ridge of tidal sands of the zone.
1990, 8(4): 85-93.
Abstract:
Illite claystones (tonsteins) of Late Permian coal-bearing formation are well developed and extensively distributed in Southwestern China. Over the past decades it has been recognized that they are synsedimentary volcanic ash-falls in origin (altered tuff beds), based on the data derived from the comprehensive investigations on their stratigraphic and geographic distribution, petrograpbic types, chemical composition, accessory mineral assemblage, as wel as on their morphological characteristics. Recently, mineralogical and petrological identifications and x-ray diffraction analyses on these peculiar tonsteins further suggest that they can be classified mainly into three categories based on their clay mineral constitutions: kaolinitic, kaolinitic-illitic (transitional type), and illitie. As coal-partings in most cases, these different types of tonsteins show a distinct zonal distribution on a regional scale. Their mineral constitutions are profoundly modified by the combined effects of many factors during deuterogenic diagenesis, as indicated by the variation in volatile component percentage (Vr) of the adjacent coal seams (Vr is calculated on a combustible component basis) . Those tonsteins intercalated in coal with a Vr ranging from 10% to 12% are dominated by kaolinite. But they contain increating amount of illite at the expense of kaolinite when Vr of coal decreases from 10% to 8%. When Vr declines to less than 8% the clay minerals in these tonsteins are almost entirely illite with some sort of accompanying chloritization. It is clear that, from a regional point of view, the variation in clay mineral constitution of thses tonsteins is in response to the continual and progressive change in geological processes, during which the temperature and pressure were the dominent conditions, and the existence of a certain amount of alkali metal ions and ferrous ions in the solution is also one of the controlli ng factors.
Illite claystones (tonsteins) of Late Permian coal-bearing formation are well developed and extensively distributed in Southwestern China. Over the past decades it has been recognized that they are synsedimentary volcanic ash-falls in origin (altered tuff beds), based on the data derived from the comprehensive investigations on their stratigraphic and geographic distribution, petrograpbic types, chemical composition, accessory mineral assemblage, as wel as on their morphological characteristics. Recently, mineralogical and petrological identifications and x-ray diffraction analyses on these peculiar tonsteins further suggest that they can be classified mainly into three categories based on their clay mineral constitutions: kaolinitic, kaolinitic-illitic (transitional type), and illitie. As coal-partings in most cases, these different types of tonsteins show a distinct zonal distribution on a regional scale. Their mineral constitutions are profoundly modified by the combined effects of many factors during deuterogenic diagenesis, as indicated by the variation in volatile component percentage (Vr) of the adjacent coal seams (Vr is calculated on a combustible component basis) . Those tonsteins intercalated in coal with a Vr ranging from 10% to 12% are dominated by kaolinite. But they contain increating amount of illite at the expense of kaolinite when Vr of coal decreases from 10% to 8%. When Vr declines to less than 8% the clay minerals in these tonsteins are almost entirely illite with some sort of accompanying chloritization. It is clear that, from a regional point of view, the variation in clay mineral constitution of thses tonsteins is in response to the continual and progressive change in geological processes, during which the temperature and pressure were the dominent conditions, and the existence of a certain amount of alkali metal ions and ferrous ions in the solution is also one of the controlli ng factors.
1990, 8(4): 104-114.
Abstract:
This paper centers on the study of the marker characteristics of vug seepages which are from marine carbonate of the upper Carboniferous in Tarim Basin. The results show that the liquid seepage, collected from biogenic limestone, has a higher thermal maturity, a lower pristane-to- (Pr/Ph) ratio, a slight even to odd dominance in the n-alkanes,. a high content of higher molecular weight hopanes, and a slightly higher abundance of 17α. (H) 21 β (H) -C35 hopane relative to 17α (H) 21β(H) -C34 hopane. All of those have a good correlation with extract of the surrounding rocks, which indicates that the vugs seepage was autochthonous. The paper has also studied on the geochemical characteristics of the asphalt veins in the limestone fissures of the lower Ordovician in the basin. It is proved that the biomarkers of as- phalt veins are mainly composed of 25-nor hopanes, 8, 14-secohopanes and ring-D-aromatic 8, 14- secohopanes; and the aromatics of asphalt veins have a intensive demethylized career; Phenanthren in it takes a percentage of 72.5 in phenanthrenoids. Obviously by analysing the geologic information, the asphalt was formed by the material originated from the crud oil of the deep part in the basin, underwent a higher geothermal alteration and the microbial-biodegradation and oxidation . It is obivous that the result mentioned above may provied important information for the assessment of petroleum prospect in the deep part of the basin.
This paper centers on the study of the marker characteristics of vug seepages which are from marine carbonate of the upper Carboniferous in Tarim Basin. The results show that the liquid seepage, collected from biogenic limestone, has a higher thermal maturity, a lower pristane-to- (Pr/Ph) ratio, a slight even to odd dominance in the n-alkanes,. a high content of higher molecular weight hopanes, and a slightly higher abundance of 17α. (H) 21 β (H) -C35 hopane relative to 17α (H) 21β(H) -C34 hopane. All of those have a good correlation with extract of the surrounding rocks, which indicates that the vugs seepage was autochthonous. The paper has also studied on the geochemical characteristics of the asphalt veins in the limestone fissures of the lower Ordovician in the basin. It is proved that the biomarkers of as- phalt veins are mainly composed of 25-nor hopanes, 8, 14-secohopanes and ring-D-aromatic 8, 14- secohopanes; and the aromatics of asphalt veins have a intensive demethylized career; Phenanthren in it takes a percentage of 72.5 in phenanthrenoids. Obviously by analysing the geologic information, the asphalt was formed by the material originated from the crud oil of the deep part in the basin, underwent a higher geothermal alteration and the microbial-biodegradation and oxidation . It is obivous that the result mentioned above may provied important information for the assessment of petroleum prospect in the deep part of the basin.
1990, 8(4): 124-129.
Abstract:
The method of coal- petrology- study and some new measurement technologies such as vitrinite reflectance, DTA-DSC thermal analysis and pulse element analysis , ect. As indicatores in this paper are used to distinguish and divide the evolution stage of coal and kerogen. The author attempts to demonstrate that each evolution parameter of kerogen preserved in different rocks is approximate but an equal by making comprehensive studies of organic geochemical information . from sections of two drilling-wells. The facts prove that each evolution perameter of type Ⅲ dispersed kerogen is lower one or half coal rank than that of mimic coal in the same drilling section and burial depth. The result also proves that the parameter of coal kerogen is larger than that of dispersed kerogen in shale which is larger than that of in mud stone which is larger than that of in sandstone. The samples are in the approximately strata depth of the same drilling section. The above diversity may be caused by the difference of kerogen preserving state of kerogen, thermal conductivity of source rock, coefficient of heat gather and radiation.
The method of coal- petrology- study and some new measurement technologies such as vitrinite reflectance, DTA-DSC thermal analysis and pulse element analysis , ect. As indicatores in this paper are used to distinguish and divide the evolution stage of coal and kerogen. The author attempts to demonstrate that each evolution parameter of kerogen preserved in different rocks is approximate but an equal by making comprehensive studies of organic geochemical information . from sections of two drilling-wells. The facts prove that each evolution perameter of type Ⅲ dispersed kerogen is lower one or half coal rank than that of mimic coal in the same drilling section and burial depth. The result also proves that the parameter of coal kerogen is larger than that of dispersed kerogen in shale which is larger than that of in mud stone which is larger than that of in sandstone. The samples are in the approximately strata depth of the same drilling section. The above diversity may be caused by the difference of kerogen preserving state of kerogen, thermal conductivity of source rock, coefficient of heat gather and radiation.
1990, 8(4): 138-142.
Abstract:
The method has been developed with which nitrogen is seperated by gas chromatograph and collected in a vacuum system, and isotope ratio of nitrogen are measured by mass spectrometry.The mean value of nitrogen isotope ratio of air in Lanzhou is 0.00368, with a standard deviation 0. 000053 (n= 7) , which is slightly higher than that of 15N/ 14N (0.00361) reported by Nier (1950) .The defference between the two measurements may be either due to analysing methods or may substantially reflects the natural phenomenon. While to the nitrogen Produced by 504 Factory in Lanzhou the mean value of 15N / 14Nis 0.00361, with a standard deviation 0.000050 (n = 5) . This method is an important means for geochemistry of natural gas, and through which the first batch of (δ15 N value of natural gas has been, so far obtained in China.
The method has been developed with which nitrogen is seperated by gas chromatograph and collected in a vacuum system, and isotope ratio of nitrogen are measured by mass spectrometry.The mean value of nitrogen isotope ratio of air in Lanzhou is 0.00368, with a standard deviation 0. 000053 (n= 7) , which is slightly higher than that of 15N/ 14N (0.00361) reported by Nier (1950) .The defference between the two measurements may be either due to analysing methods or may substantially reflects the natural phenomenon. While to the nitrogen Produced by 504 Factory in Lanzhou the mean value of 15N / 14Nis 0.00361, with a standard deviation 0.000050 (n = 5) . This method is an important means for geochemistry of natural gas, and through which the first batch of (δ15 N value of natural gas has been, so far obtained in China.
