1998 Vol. 16, No. 2
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Display Method:
1998, 16(2): 1-4.
Abstract:
Through the simulation enperient, it is discoveped that the reaction of sulphur with U-carotene might form condensed nucleus aromatic hydrocarbons, and the reaction of sulphur or oxygen with biphenyl might form polycyclic aromatic hydrocarbons. U-carotene might be changed to condensed nucleus and polycyclic aromatic hydrocarbons in small amount while being heated. The condensed nucleus aromatic hydrocarbons originated from one single molecule, the polycyclic aromatic hydrocarbons might be changed from one single molecules, too, but they were mostly formed by two or more than two biphenyl molecules.
Through the simulation enperient, it is discoveped that the reaction of sulphur with U-carotene might form condensed nucleus aromatic hydrocarbons, and the reaction of sulphur or oxygen with biphenyl might form polycyclic aromatic hydrocarbons. U-carotene might be changed to condensed nucleus and polycyclic aromatic hydrocarbons in small amount while being heated. The condensed nucleus aromatic hydrocarbons originated from one single molecule, the polycyclic aromatic hydrocarbons might be changed from one single molecules, too, but they were mostly formed by two or more than two biphenyl molecules.
1998, 16(2): 9-13.
Abstract:
Aryl isoprenoid compounds in the aromatic fraction of sedimentary organic matter have been regarded as a biomarker that indicates a saline and strongly reducing sedimentary environment. On the basis of the detailed study on biomarker compounds in the aromatic fraction of 33 crude oils and source rocks collected from three typical terrestrial sedimentary basins in China, this paper discussed an aryl isoprenoid serial compound detected out from a Mesozoic crude oil in the Ordos basin and its geochemical significance in indicating sedimentary facies. It was proposed that this serial compound could also be an indicator to a brackish and reducing sedimentary environment.
Aryl isoprenoid compounds in the aromatic fraction of sedimentary organic matter have been regarded as a biomarker that indicates a saline and strongly reducing sedimentary environment. On the basis of the detailed study on biomarker compounds in the aromatic fraction of 33 crude oils and source rocks collected from three typical terrestrial sedimentary basins in China, this paper discussed an aryl isoprenoid serial compound detected out from a Mesozoic crude oil in the Ordos basin and its geochemical significance in indicating sedimentary facies. It was proposed that this serial compound could also be an indicator to a brackish and reducing sedimentary environment.
Iron Coated Grains and Microorganic Process in Their Formation from the Xuanlong Area,Hebei Province
1998, 16(2): 24-29.
Abstract:
Based on the detailed determination under microscope, the comparison with the texture, shape and composition of iron stromatolites, as well as on the analyses and studies of stable isotopes and organic geochemistry of oolitic ores from the Xuanlong area, the paper proposed preliminarily that ooliticores actually are coated grains by the formation of microorganisms. They can be divided into oncolites, microorganicoolites and piolites in the terms of shape. Moreover, the paper disscussed the microorganic mineralization of iron coated grains.
Based on the detailed determination under microscope, the comparison with the texture, shape and composition of iron stromatolites, as well as on the analyses and studies of stable isotopes and organic geochemistry of oolitic ores from the Xuanlong area, the paper proposed preliminarily that ooliticores actually are coated grains by the formation of microorganisms. They can be divided into oncolites, microorganicoolites and piolites in the terms of shape. Moreover, the paper disscussed the microorganic mineralization of iron coated grains.
1998, 16(2): 50-54.
Abstract:
The Tertiary gravity flow deposits in the Jingg u-Zhenyuan region, southwestern Yunnan, can be divided into three types: debris flow, grain flow and turbidity current. Debris flow deposits are mainly composed of conglomerates, which are matrix supported and poorly sorted. Their grain-size distribution frequency curves are characterized by having only one major and some secondary peaks. Grain flow deposits are also mainly composed of conglomerates, which are identified by their matrix lacking features. Clasts in these deposits were cemented by ironoxides and clay minerals, as thin film around them. Their grain-size distribution frequency curves show multimodal distribution without major peak. Turbidity current deposits are mainly composed of sandstone, siltstone and mudstone, which are characterized by their Bouma sequence. Their grain-size cumulative proba bility curves and C-M diagram reflect features of low-density flow. Development of the gravity flow in the region, asresponse to regional tectonic evolution, was controlled by collisional processes of Indian continent with Eurasian continent and post-collisional intracon-tinental deformation.
The Tertiary gravity flow deposits in the Jingg u-Zhenyuan region, southwestern Yunnan, can be divided into three types: debris flow, grain flow and turbidity current. Debris flow deposits are mainly composed of conglomerates, which are matrix supported and poorly sorted. Their grain-size distribution frequency curves are characterized by having only one major and some secondary peaks. Grain flow deposits are also mainly composed of conglomerates, which are identified by their matrix lacking features. Clasts in these deposits were cemented by ironoxides and clay minerals, as thin film around them. Their grain-size distribution frequency curves show multimodal distribution without major peak. Turbidity current deposits are mainly composed of sandstone, siltstone and mudstone, which are characterized by their Bouma sequence. Their grain-size cumulative proba bility curves and C-M diagram reflect features of low-density flow. Development of the gravity flow in the region, asresponse to regional tectonic evolution, was controlled by collisional processes of Indian continent with Eurasian continent and post-collisional intracon-tinental deformation.
1998, 16(2): 61-67.
Abstract:
The Putoupyrite ore deposit, formed in Givetian of Devonian, is a medium-scale stratiform deposit in Chengbu County of Hunan Province, China. The author reported its sedimentary environment in the present journal in 1984, and in this paper its genesis was discussed based on new data. This deposit is located in a N E deep water basin which developed in the rift system of the South China palaeocontinent margin. The ore-bearing section consists of dark siliceous rock and mar1. The ore beds are stratiform and conformably deposited in the synchronous strata. The ore is composed of only pyrite with massive and banded structures. The composition of sulfur isotope is rich in 32S, and its variation range is from -17.4‰ to -30.1‰. The ore-bearing rock and ore are rich in organic carbon, which is sapropel-humic type with higher maturity. Charateristics of the ore texture are widespread framboidal pyrite that consists of micrograined pyrite (d < 1μm) with different crystal forms and ordered or disordered structures, some framboidal pyrite appears massively with pyrite crystal in dense ores . Charateristics of REE and trace element s in the ore and hsted rocks, which conform with the mordern hydrothermal deposits of oceanic rift or rise in the pacific, suggested that their origin is the same. For this reason, the Putoupyrite deposit is a sedexore deposit and its abundant organic matter plays an important role in ore deposits.
The Putoupyrite ore deposit, formed in Givetian of Devonian, is a medium-scale stratiform deposit in Chengbu County of Hunan Province, China. The author reported its sedimentary environment in the present journal in 1984, and in this paper its genesis was discussed based on new data. This deposit is located in a N E deep water basin which developed in the rift system of the South China palaeocontinent margin. The ore-bearing section consists of dark siliceous rock and mar1. The ore beds are stratiform and conformably deposited in the synchronous strata. The ore is composed of only pyrite with massive and banded structures. The composition of sulfur isotope is rich in 32S, and its variation range is from -17.4‰ to -30.1‰. The ore-bearing rock and ore are rich in organic carbon, which is sapropel-humic type with higher maturity. Charateristics of the ore texture are widespread framboidal pyrite that consists of micrograined pyrite (d < 1μm) with different crystal forms and ordered or disordered structures, some framboidal pyrite appears massively with pyrite crystal in dense ores . Charateristics of REE and trace element s in the ore and hsted rocks, which conform with the mordern hydrothermal deposits of oceanic rift or rise in the pacific, suggested that their origin is the same. For this reason, the Putoupyrite deposit is a sedexore deposit and its abundant organic matter plays an important role in ore deposits.
1998, 16(2): 74-81.
Abstract:
Tarim Basin, enclosed or semienclosed by the paleocontinent or islands on the south, north and east, was the vast epicontinental sea on the continental shelf in the Neodevonian- Carboniferous which formed a series of multi type and multicyclic carbonate rocks, evaporites, clastic rocks and transitional rocks. The sequence stratigraphic patterns of the Tarim Basin are different from those proposed by P. R. Vail et al. mainly on the basis of passive continental margin basins. The Neodevo nian-Carboniferous of the Tarim Basin can be divided into fives equences and subdivided into fourteen system tracts. The Sequence I was formed under the conditions of the rising of sea level and quick compensation of more terrigenous clastic materials. The SequenceⅡ formed in an environment in which the feeding of terrigenous materials changed from quick to slow. The Sequence Ⅲ formed in an environment in which the rising of sea level changed from quick to slow and the feeding of terrigenous clastic was relatively constant. The SequenceⅣ formed in an environment in which the rising rate of sea level gradually slowed down and terrigenous clastic feeding was relatively constant, and the SequenceⅤ formed in an environment of quick rising of sea level and lacking of terrigenous clastic feeding. The Neodevonian-Carboniferous deposition in the Tarim Basin occurred during a general transgression process of rising of the relative sea level by stages. The changes of the sea level in the Neodevonian～Carboniferous may be divided into five 3rnd-order cycles, of which the generation of the CycleⅠ、Ⅱ、Ⅴ were mainly controlled by the regional tectonism and the others by the eustasy.
Tarim Basin, enclosed or semienclosed by the paleocontinent or islands on the south, north and east, was the vast epicontinental sea on the continental shelf in the Neodevonian- Carboniferous which formed a series of multi type and multicyclic carbonate rocks, evaporites, clastic rocks and transitional rocks. The sequence stratigraphic patterns of the Tarim Basin are different from those proposed by P. R. Vail et al. mainly on the basis of passive continental margin basins. The Neodevo nian-Carboniferous of the Tarim Basin can be divided into fives equences and subdivided into fourteen system tracts. The Sequence I was formed under the conditions of the rising of sea level and quick compensation of more terrigenous clastic materials. The SequenceⅡ formed in an environment in which the feeding of terrigenous materials changed from quick to slow. The Sequence Ⅲ formed in an environment in which the rising of sea level changed from quick to slow and the feeding of terrigenous clastic was relatively constant. The SequenceⅣ formed in an environment in which the rising rate of sea level gradually slowed down and terrigenous clastic feeding was relatively constant, and the SequenceⅤ formed in an environment of quick rising of sea level and lacking of terrigenous clastic feeding. The Neodevonian-Carboniferous deposition in the Tarim Basin occurred during a general transgression process of rising of the relative sea level by stages. The changes of the sea level in the Neodevonian～Carboniferous may be divided into five 3rnd-order cycles, of which the generation of the CycleⅠ、Ⅱ、Ⅴ were mainly controlled by the regional tectonism and the others by the eustasy.
1998, 16(2): 87-91.
Abstract:
Anastomosed river deposits of Fuxin Formation in Tiefa basin, one of the Late Mesozoic semigraben basin, are developed in the progradational system accompanied by the process of the lake reg ression betw een alluvial fa ns inside the fault of the basin edge and lake deltas. A great quantity of geological data of drillings and pits reveal the characteristics of facies of the channel, the stream bank and the wet land in the anastomosed river deposits and debris flow deposit is a particular genetic type among channel facies. The prosperous development of the sedimentary system of the anastomosed river is the main part in the genetic stratigraphic units, and the genetic stratig raphic units are ended by the decline of the sedimentary system of the anastomosed river accompanied by a great area of peaty swamp. Important conditions of the developing of the anastomosed river are frequent activity of the fault in the basin edge, large rate of the subsidence and deposit filling in the basin and small slope of channels.
Anastomosed river deposits of Fuxin Formation in Tiefa basin, one of the Late Mesozoic semigraben basin, are developed in the progradational system accompanied by the process of the lake reg ression betw een alluvial fa ns inside the fault of the basin edge and lake deltas. A great quantity of geological data of drillings and pits reveal the characteristics of facies of the channel, the stream bank and the wet land in the anastomosed river deposits and debris flow deposit is a particular genetic type among channel facies. The prosperous development of the sedimentary system of the anastomosed river is the main part in the genetic stratigraphic units, and the genetic stratig raphic units are ended by the decline of the sedimentary system of the anastomosed river accompanied by a great area of peaty swamp. Important conditions of the developing of the anastomosed river are frequent activity of the fault in the basin edge, large rate of the subsidence and deposit filling in the basin and small slope of channels.
1998, 16(2): 97-101.
Abstract:
The solution-type secondary pore is one of the most important types of pores in clastic reservoirs. The forming mechanism of solutio n-type secondary pores is one of the problems which petroleum geologist are very much interested in. By means of analytical test data of clastic reservoirs in Northern part depression of Tuha basin and Bazhou depression of Minhe basin, the influencing factors of solution-type secondary pore-evolution of clastic reservoirs in the researching region are analysed in this paper. Through research, the author indicates that the formation and preservation of the primary effective clastic rock bodies are controlled by sedimentation and diagenesis. The out standing change of pore fluid properties in diagenetic evolution of effective clastic rock bodies is direct cause which the solution-type secondary pores are formed on a large scale.
The solution-type secondary pore is one of the most important types of pores in clastic reservoirs. The forming mechanism of solutio n-type secondary pores is one of the problems which petroleum geologist are very much interested in. By means of analytical test data of clastic reservoirs in Northern part depression of Tuha basin and Bazhou depression of Minhe basin, the influencing factors of solution-type secondary pore-evolution of clastic reservoirs in the researching region are analysed in this paper. Through research, the author indicates that the formation and preservation of the primary effective clastic rock bodies are controlled by sedimentation and diagenesis. The out standing change of pore fluid properties in diagenetic evolution of effective clastic rock bodies is direct cause which the solution-type secondary pores are formed on a large scale.
1998, 16(2): 109-112.
Abstract:
In this work the Mossbauer effect of clay minerals in Tertiary System of Qaidam Basin is discussed and the state of Fe2+ and Fe3+ in some clay minerals is also analy zed. The ratios o f Fe2+/Fe3+ in different samples are measured. According to the ratio of Fe2+/Fe3+, some sedimentary environment and facies sequence in some sections of the basin are divided. This indicates that not only the type of clay minerals containing Fe, but also sedimentary environments a nd facies sequences may be divided by Mossbauer effect of clay minerals in oil basin.
In this work the Mossbauer effect of clay minerals in Tertiary System of Qaidam Basin is discussed and the state of Fe2+ and Fe3+ in some clay minerals is also analy zed. The ratios o f Fe2+/Fe3+ in different samples are measured. According to the ratio of Fe2+/Fe3+, some sedimentary environment and facies sequence in some sections of the basin are divided. This indicates that not only the type of clay minerals containing Fe, but also sedimentary environments a nd facies sequences may be divided by Mossbauer effect of clay minerals in oil basin.
1998, 16(2): 117-123.
Abstract:
This paper gives out a method for the determination of Orientation Index of shales by X-ray diffrac-tion. Meanwhile, the relations between orientation Index and mineral compositions and physicochemical properties (density, recovery percent, expansion percent, cation exchange capacity etc.) are discussed. A new concept-Comprehensive Index of shales is introduced on the basis of Orientation Index of shales. Then, the shales of easy collapsing formations are classified into four types according to Orientation Index and Comprehensive Index of shales. This work has an important theoretical significance and applied value in oil drilling engineering for studying mechanism of wellbore stability and preventing collapse of wellbore.
This paper gives out a method for the determination of Orientation Index of shales by X-ray diffrac-tion. Meanwhile, the relations between orientation Index and mineral compositions and physicochemical properties (density, recovery percent, expansion percent, cation exchange capacity etc.) are discussed. A new concept-Comprehensive Index of shales is introduced on the basis of Orientation Index of shales. Then, the shales of easy collapsing formations are classified into four types according to Orientation Index and Comprehensive Index of shales. This work has an important theoretical significance and applied value in oil drilling engineering for studying mechanism of wellbore stability and preventing collapse of wellbore.
1998, 16(2): 129-133.
Abstract:
The main sediments of Holocene sections are clay and sand soil with mini-sand layers in North Taklimakan desert. The evolution of Holocence environment in the North of Taklimakan desert is revealed by analyzing the characteristics of granular, change of chemical composition, sporopollen composition, content of CaCO3 and mineral. The Holocene climate is a rid and changes between hot-dry and cool-dry, which is mainly controlled by global longitude wind and cyclone. The region climate change, comparing with global climate change, and the climate gradually become arid and the environment become more deterorated with the global clima te become drier in recent years.
The main sediments of Holocene sections are clay and sand soil with mini-sand layers in North Taklimakan desert. The evolution of Holocence environment in the North of Taklimakan desert is revealed by analyzing the characteristics of granular, change of chemical composition, sporopollen composition, content of CaCO3 and mineral. The Holocene climate is a rid and changes between hot-dry and cool-dry, which is mainly controlled by global longitude wind and cyclone. The region climate change, comparing with global climate change, and the climate gradually become arid and the environment become more deterorated with the global clima te become drier in recent years.
1998, 16(2): 139-144.
Abstract:
From the theory of plate tectonics, the prototype of Qilianshan small basin Jurassic is defined as pull-apart basin, and they had undergone two time rifting during Early-Mid Jurassic. The Paper takes Datong basin for example, dissects its sedimentary system, evolutinary stages and coal-accumlation. The results show that coal-formation is related to basin boundary fault and megaclast sedimentation, with small humid fan being important coal-accumlating setting, and becoming high-coal districts in the basin. Datong basin is a representative to Qilianshan small coal basin Jurassic
From the theory of plate tectonics, the prototype of Qilianshan small basin Jurassic is defined as pull-apart basin, and they had undergone two time rifting during Early-Mid Jurassic. The Paper takes Datong basin for example, dissects its sedimentary system, evolutinary stages and coal-accumlation. The results show that coal-formation is related to basin boundary fault and megaclast sedimentation, with small humid fan being important coal-accumlating setting, and becoming high-coal districts in the basin. Datong basin is a representative to Qilianshan small coal basin Jurassic
1998, 16(2): 5-8.
Abstract:
Stable isotope geochemistry provides some insight into the origin, correlation and secondary reformation of natural gases. Generally, the carbon isotope composition of methane is controlled by maturity and organic matter type of source rock, and that of C2+ gaseous components of natural gases is depended on the carbon isotopic composition of organic matter in source rock and also influenced by maturity. The bacterial gas has- 55‰ of <W13 C1 and - 30‰ of <W13 C2. The thermogenic gases, with W13 C1 from - 50‰～- 25‰, W13 C2 from - 45‰～ - 22‰ and W13 C3 from - 38‰～- 21‰, are rich in heavy isotope as the maturity increasing. The abiogenic gas, with W13 C1- 25‰, has a carbon isotope reverse distribution of C1 to C4. The measurement of chemical components and carbon isotopic composition of natural gases from Liaohe basin shows that the natural gases form this basin can be divided into three groups. The group I gases, with W13 C1 f rom- 59‰～ - 50‰ ,W13 C2 from -48‰～-36‰, W13 C3 from- 40‰～-24‰ and very low concentration of C2+ (< 1.0%), are bacterial gases. The group Ⅱ gases, with W13 C1 from -49‰～-38‰, W13 C2 from -31 to-26‰, W13 C3 from -29‰ to-26‰ and concentration of C2+>5%, are typical thermogenic gases. The group III gases, with W13 C1 from-40‰～-40‰ ,W13 C2 from-13.0‰～-6.6‰, W13 C3 from - 6.1‰～+3.3% and relative low content of C2+ (< 2%), are enigmatic. The depth of reservoirs of group III gases is relative shallow, ranging from 1270 m to 1330 m. The group III gases are considered to be secondary reformed by bacterial oxidation, according to geochemical characters and geological background.
Stable isotope geochemistry provides some insight into the origin, correlation and secondary reformation of natural gases. Generally, the carbon isotope composition of methane is controlled by maturity and organic matter type of source rock, and that of C2+ gaseous components of natural gases is depended on the carbon isotopic composition of organic matter in source rock and also influenced by maturity. The bacterial gas has- 55‰ of <W13 C1 and - 30‰ of <W13 C2. The thermogenic gases, with W13 C1 from - 50‰～- 25‰, W13 C2 from - 45‰～ - 22‰ and W13 C3 from - 38‰～- 21‰, are rich in heavy isotope as the maturity increasing. The abiogenic gas, with W13 C1- 25‰, has a carbon isotope reverse distribution of C1 to C4. The measurement of chemical components and carbon isotopic composition of natural gases from Liaohe basin shows that the natural gases form this basin can be divided into three groups. The group I gases, with W13 C1 f rom- 59‰～ - 50‰ ,W13 C2 from -48‰～-36‰, W13 C3 from- 40‰～-24‰ and very low concentration of C2+ (< 1.0%), are bacterial gases. The group Ⅱ gases, with W13 C1 from -49‰～-38‰, W13 C2 from -31 to-26‰, W13 C3 from -29‰ to-26‰ and concentration of C2+>5%, are typical thermogenic gases. The group III gases, with W13 C1 from-40‰～-40‰ ,W13 C2 from-13.0‰～-6.6‰, W13 C3 from - 6.1‰～+3.3% and relative low content of C2+ (< 2%), are enigmatic. The depth of reservoirs of group III gases is relative shallow, ranging from 1270 m to 1330 m. The group III gases are considered to be secondary reformed by bacterial oxidation, according to geochemical characters and geological background.
1998, 16(2): 20-23.
Abstract:
High organosulfur coal (HO SC) is very special in that it is rich in sulfur-containing compounds (SCC) in aromatic fraction of extract. Four series of SCC, i. e., dibenzothiophene, benzonaphthrathiophene, phenanthrathiophene and benzobisbenzothiophene, have been detected in four coal samples, which were formed on restricted carbonate platform, and have varied ranks. Inspite of the similar constitutions with respect to SCC for four coal samples, their ratios between differnet series of SCC are closely related to coal rank and exact depositional environments. The results show that with increase of coal rank: (1) the relative amount of dibenzothiophene with 3-cycle structure decreases compared with other compounds with 4-, and 5-cycle structure and (2) those SCC with methy in stable positions of molecule increase. In the mean time, we also found that the amount ratio of SCC to normal aromatic hydrocarbon wth same cycles in molecule is a good indicatior of restricted extent of platform.
High organosulfur coal (HO SC) is very special in that it is rich in sulfur-containing compounds (SCC) in aromatic fraction of extract. Four series of SCC, i. e., dibenzothiophene, benzonaphthrathiophene, phenanthrathiophene and benzobisbenzothiophene, have been detected in four coal samples, which were formed on restricted carbonate platform, and have varied ranks. Inspite of the similar constitutions with respect to SCC for four coal samples, their ratios between differnet series of SCC are closely related to coal rank and exact depositional environments. The results show that with increase of coal rank: (1) the relative amount of dibenzothiophene with 3-cycle structure decreases compared with other compounds with 4-, and 5-cycle structure and (2) those SCC with methy in stable positions of molecule increase. In the mean time, we also found that the amount ratio of SCC to normal aromatic hydrocarbon wth same cycles in molecule is a good indicatior of restricted extent of platform.
1998, 16(2): 30-33,41.
Abstract:
In this paper, the evolution characteristics of gaseous products of humic coal by hydrouspy rolysis and it's geological significance are discussed, Maturehumic coal has still large hydrocarbon potential, in main stage of hydrocarbon generation, and it mainly generates oil and a little gaseous hydrocarbon. Afterm oil generation peak, the amount of gaseous hydrocarbons begins increasing rapidly because of splitting of liquid products. In geological condition, there are enormous soluble organic matter in coal. They are main source rocks of coal type gas in high evolution stage. Methane is predominant component of gaseous hydrocarbons. Gaseous non-hydrocarbons are generated in the early stage and in them, dioxide carbon is chief.
In this paper, the evolution characteristics of gaseous products of humic coal by hydrouspy rolysis and it's geological significance are discussed, Maturehumic coal has still large hydrocarbon potential, in main stage of hydrocarbon generation, and it mainly generates oil and a little gaseous hydrocarbon. Afterm oil generation peak, the amount of gaseous hydrocarbons begins increasing rapidly because of splitting of liquid products. In geological condition, there are enormous soluble organic matter in coal. They are main source rocks of coal type gas in high evolution stage. Methane is predominant component of gaseous hydrocarbons. Gaseous non-hydrocarbons are generated in the early stage and in them, dioxide carbon is chief.
1998, 16(2): 42-49.
Abstract:
According to the data of rock cores and well logging interpretations, three order base-level cycles were recognized from Da'anzhai Fo rmatio n, Lower Jurassic in Sichuan Basin, w hich consist of 41～47 short-term base-level cycles, 5 mid-term base-level cycles and 2 long-term base-level cycles from bottom to top of the formation. The short-term base-level cycles could be divided into two cycle types of nonsymmetry and symmetry, of which the former developed fining upward and the latter developed fining upward coarsening. The 5 mid-term base-level cycles were composed of several short-term base-level cycles in different stacking pattens and represented respectively the low stand progradation sequence set, lake transgressive aggradational-retrogradational sequence set, lake flood aggradational parasequence set, early highstand aggradational to weak progradational sequence set and later highstand strong pragradational sequence set. The 2 long-term base-level cycles consisted of 5 mid-term base-level cycles, and demonstrated separately the changes of the lake level rise and fall in long term during the Da'anzhai Epoch, Early Jurassic, and constituted the complete depositional sequence of lacustrine transgressive-regressive cycles. According to the high-resolution isochronostratigrapnic correlation of the turnround points of the multi-order based-level cycles, the Da'anzhai Formation high-resolution sequence stratigraphic framework can be built and it showed the relationship among the evolution of the multi-order base-level cycles and the distribution of the reservoirs, source rocks and caprocks of the formation.
According to the data of rock cores and well logging interpretations, three order base-level cycles were recognized from Da'anzhai Fo rmatio n, Lower Jurassic in Sichuan Basin, w hich consist of 41～47 short-term base-level cycles, 5 mid-term base-level cycles and 2 long-term base-level cycles from bottom to top of the formation. The short-term base-level cycles could be divided into two cycle types of nonsymmetry and symmetry, of which the former developed fining upward and the latter developed fining upward coarsening. The 5 mid-term base-level cycles were composed of several short-term base-level cycles in different stacking pattens and represented respectively the low stand progradation sequence set, lake transgressive aggradational-retrogradational sequence set, lake flood aggradational parasequence set, early highstand aggradational to weak progradational sequence set and later highstand strong pragradational sequence set. The 2 long-term base-level cycles consisted of 5 mid-term base-level cycles, and demonstrated separately the changes of the lake level rise and fall in long term during the Da'anzhai Epoch, Early Jurassic, and constituted the complete depositional sequence of lacustrine transgressive-regressive cycles. According to the high-resolution isochronostratigrapnic correlation of the turnround points of the multi-order based-level cycles, the Da'anzhai Formation high-resolution sequence stratigraphic framework can be built and it showed the relationship among the evolution of the multi-order base-level cycles and the distribution of the reservoirs, source rocks and caprocks of the formation.
1998, 16(2): 55-60,108.
Abstract:
The study areas include Guizhou, southern Sichuan, and eastern Yunnan, where abundant coal resources are preserved in Late Permian strata. The Late Permian key fauna and flora and their combinations are studied and a scheme of stratigraphic multi-subdivision for Late Permian succession are established. Typical Changxingian ammonoids such as Sinocel ites sichuanensis and Pseudotirolites qianjiangensis have been found in C12 coal seam of the Huoshaopu coal mine, Panxian County, western Guizhou, and a Changxingian Brachiopod fauna have been found in B4 marker limestone of the Yanbeihou section, Zhijin County, western Guizhou. This makes it possible to subcorrelate the Late Permian invast areas of southern China. For lithostratigraphic purposes, the upper Permian is subdivided into the Longtan Formation (Wuchiaping Formation, Middle and lower Members of Xuanwei Formation) and the Changxing Formation (Wangjiazai Formation, Dalong Formation, and upper Member of Xuanwei Formation). The Longtan Formation is subdivided into the lower Member and the upper Member. Synthetic studies suggest that the Late Permian coal-bearing sequences in study areas were mainly formed in five depositional systems, including braided river and braid delta system, alluvial plain fluvial system, deltatidal flat system, Lagoon-tidal flat system, and carbonate Platform System. The delta-tidal flat system is believed to be the most important system for the coal accumulation in western Guizhou. This system can be further divided into the fluvial-dominated upper delta plain, fluvial and tide influenced transitional delta plain, and tide-dominated lower delta plain and tidal plain environments. The overall paleogeographical units of the Late Permian in the study areas include non-marine alluvial plain dominated by fluvial channel, alluvial fan in eastern Yunnan, transitional paralic plain dominated by deltatidal flat system and lagoon-tidal flat system in westerm Guizhou and southern Sichuan, marine carbonate platform in eastern and southern Guizhou, eastern part of southern Sichuan, and southern part of eastern Yunnan, and deep water fault basin in the vicinity of Ziyun of southern Guizhou. Lithofacies paleogeographical maps of Early Longtanian stage, late Longtanian stage and Changxingian stage have been drawn based on analysis of various contour maps such as clastic and carbonate rocks ratio, thickness of sandstones, percentage of sandstones, thickness of coal seams, and thickness of strata.
The study areas include Guizhou, southern Sichuan, and eastern Yunnan, where abundant coal resources are preserved in Late Permian strata. The Late Permian key fauna and flora and their combinations are studied and a scheme of stratigraphic multi-subdivision for Late Permian succession are established. Typical Changxingian ammonoids such as Sinocel ites sichuanensis and Pseudotirolites qianjiangensis have been found in C12 coal seam of the Huoshaopu coal mine, Panxian County, western Guizhou, and a Changxingian Brachiopod fauna have been found in B4 marker limestone of the Yanbeihou section, Zhijin County, western Guizhou. This makes it possible to subcorrelate the Late Permian invast areas of southern China. For lithostratigraphic purposes, the upper Permian is subdivided into the Longtan Formation (Wuchiaping Formation, Middle and lower Members of Xuanwei Formation) and the Changxing Formation (Wangjiazai Formation, Dalong Formation, and upper Member of Xuanwei Formation). The Longtan Formation is subdivided into the lower Member and the upper Member. Synthetic studies suggest that the Late Permian coal-bearing sequences in study areas were mainly formed in five depositional systems, including braided river and braid delta system, alluvial plain fluvial system, deltatidal flat system, Lagoon-tidal flat system, and carbonate Platform System. The delta-tidal flat system is believed to be the most important system for the coal accumulation in western Guizhou. This system can be further divided into the fluvial-dominated upper delta plain, fluvial and tide influenced transitional delta plain, and tide-dominated lower delta plain and tidal plain environments. The overall paleogeographical units of the Late Permian in the study areas include non-marine alluvial plain dominated by fluvial channel, alluvial fan in eastern Yunnan, transitional paralic plain dominated by deltatidal flat system and lagoon-tidal flat system in westerm Guizhou and southern Sichuan, marine carbonate platform in eastern and southern Guizhou, eastern part of southern Sichuan, and southern part of eastern Yunnan, and deep water fault basin in the vicinity of Ziyun of southern Guizhou. Lithofacies paleogeographical maps of Early Longtanian stage, late Longtanian stage and Changxingian stage have been drawn based on analysis of various contour maps such as clastic and carbonate rocks ratio, thickness of sandstones, percentage of sandstones, thickness of coal seams, and thickness of strata.
1998, 16(2): 68-73.
Abstract:
A quantitative tow-dimensional depositional sequence model has been formulated to simulate the filling process of sedimentary basins. The system consist s of two subsystems: basin subsidence modelling and basin filling simulation, taking into account sea level change, tectonic subsidence, compaction of sediments, flexural isostatic compensation, erosion and sedimentation. Input basin subsidence rate can be derived by backst ripping technique, or be calculated by quantitative forward basin models. Geometric models, combined with diffusion models, have been used in the system to determine depositional surfaces and facies geometry. The system can be used to analysis the controlling processes of sedimentary basins and to predict sequence architecture and facies distribution within basins. The model has been alogrumthed to simulate the sedimentary filling of continental margin basins and shown that the tectonic subsidence rate variation and the amplitude of sea level change have a strong influence on the geometry and depositional style of basin fills.
A quantitative tow-dimensional depositional sequence model has been formulated to simulate the filling process of sedimentary basins. The system consist s of two subsystems: basin subsidence modelling and basin filling simulation, taking into account sea level change, tectonic subsidence, compaction of sediments, flexural isostatic compensation, erosion and sedimentation. Input basin subsidence rate can be derived by backst ripping technique, or be calculated by quantitative forward basin models. Geometric models, combined with diffusion models, have been used in the system to determine depositional surfaces and facies geometry. The system can be used to analysis the controlling processes of sedimentary basins and to predict sequence architecture and facies distribution within basins. The model has been alogrumthed to simulate the sedimentary filling of continental margin basins and shown that the tectonic subsidence rate variation and the amplitude of sea level change have a strong influence on the geometry and depositional style of basin fills.
1998, 16(2): 82-86.
Abstract:
The paper studied the ages of Kuche and Xiyu Formations on the edge of Tarim Basin by The means of magnetostratigraphy , and discussed the epoch when the mountains around and Qinghai- Tibet rapidly lifted. The results showed that Gilbert reversal polarity zone was recorded in the Kuche Formation (about 3.40～5.30 Ma), including Cochiti (3.80～3.90 Ma), Nunivak (4.05～4.20 Ma) , Sidufjall(4.32～4.47 Ma) and Thvera (4.85～5.00 Ma) normal polarity subzones. Gauss polarity zone(2.48～3.40 Ma), occurred within the lower Xiyu Formation, including Kaena(2.92～3.01 Ma) and Mammo the(3.05～3.15 Ma) reversal polarity subzones. While the upper Xiyu formation, which recorded the Reunion normal polarity subzone (2.12～2.14 Ma) and Olduvai normal polarity subzone (1.67～1.87 Ma), was deposited during the early Matuyama reversal polarity time about (1.50～2.48 Ma). The Kuche Formation, as a result, was formed during Early Pliocene(N1 2 k), 3.40～5.30 MaBP) The lower Xiyu formation was taken shape during Late Pliocene (N2 2 x , 2.48～3.40MaBP and the upper Xiyu Formation during Early Plioctocene(Q1 1), (1.50～2.48 MaBP). Interms of data above, it was deduced that the epoch, when the speedily lifting of Qinghai-Tibet and the Ginantic mountains on the edge of the Tarim basin occured, was at the early stage of Ea rlyPliocene, about 5.30 Ma.
The paper studied the ages of Kuche and Xiyu Formations on the edge of Tarim Basin by The means of magnetostratigraphy , and discussed the epoch when the mountains around and Qinghai- Tibet rapidly lifted. The results showed that Gilbert reversal polarity zone was recorded in the Kuche Formation (about 3.40～5.30 Ma), including Cochiti (3.80～3.90 Ma), Nunivak (4.05～4.20 Ma) , Sidufjall(4.32～4.47 Ma) and Thvera (4.85～5.00 Ma) normal polarity subzones. Gauss polarity zone(2.48～3.40 Ma), occurred within the lower Xiyu Formation, including Kaena(2.92～3.01 Ma) and Mammo the(3.05～3.15 Ma) reversal polarity subzones. While the upper Xiyu formation, which recorded the Reunion normal polarity subzone (2.12～2.14 Ma) and Olduvai normal polarity subzone (1.67～1.87 Ma), was deposited during the early Matuyama reversal polarity time about (1.50～2.48 Ma). The Kuche Formation, as a result, was formed during Early Pliocene(N1 2 k), 3.40～5.30 MaBP) The lower Xiyu formation was taken shape during Late Pliocene (N2 2 x , 2.48～3.40MaBP and the upper Xiyu Formation during Early Plioctocene(Q1 1), (1.50～2.48 MaBP). Interms of data above, it was deduced that the epoch, when the speedily lifting of Qinghai-Tibet and the Ginantic mountains on the edge of the Tarim basin occured, was at the early stage of Ea rlyPliocene, about 5.30 Ma.
1998, 16(2): 92-96.
Abstract:
Lacustrine delta in QW area of Shanganning basin has a different characteristic from other traditional deltas. Subaqueous distributary channel sandbodies and mouth bars are well developed here, and mouth bar complexes locate both at the beginning and the end parts of the subaqueous distributary channels, these sandbodies build up the framework of the delta front. Sediments of subaqueous distributary channels are distinguishable from those in distributary channels of delta plain as those in thickness, depositional structures and well-logging curvesect. After reviewing the past researches on river mouth processes and comparing with some other similar studies, this paper introduces the concept of river mouth processes of differentiated fluid and different mouth bars respectively, and attempts to explain the developing mechanism of the lacustrine delta in QW area with this theory. The differentiated fluid is characterized by vertical loads and speed differentiated distribution, and mainly controlled by climate and quantities of sediments supporting. The results of river mouth processes are affected by basin structure and bottom geometry which may result in those stable moving forward or rapid downcutting of subaqueous distributary channels after the river water flew into the basin. Two different types of mouth bars can be distinguished by connecting microfacies or facies association. long drived subaqueous distributary channels and its terminal mouth bar complex together with the ordinary mouth bar complex may be the most important responses to the river mouth processes of differentiated fluid.
Lacustrine delta in QW area of Shanganning basin has a different characteristic from other traditional deltas. Subaqueous distributary channel sandbodies and mouth bars are well developed here, and mouth bar complexes locate both at the beginning and the end parts of the subaqueous distributary channels, these sandbodies build up the framework of the delta front. Sediments of subaqueous distributary channels are distinguishable from those in distributary channels of delta plain as those in thickness, depositional structures and well-logging curvesect. After reviewing the past researches on river mouth processes and comparing with some other similar studies, this paper introduces the concept of river mouth processes of differentiated fluid and different mouth bars respectively, and attempts to explain the developing mechanism of the lacustrine delta in QW area with this theory. The differentiated fluid is characterized by vertical loads and speed differentiated distribution, and mainly controlled by climate and quantities of sediments supporting. The results of river mouth processes are affected by basin structure and bottom geometry which may result in those stable moving forward or rapid downcutting of subaqueous distributary channels after the river water flew into the basin. Two different types of mouth bars can be distinguished by connecting microfacies or facies association. long drived subaqueous distributary channels and its terminal mouth bar complex together with the ordinary mouth bar complex may be the most important responses to the river mouth processes of differentiated fluid.
1998, 16(2): 102-107.
Abstract:
Qi 108 is a small oil developing block of Huanxiling oilfield in Liaohe basin. The reservoir, the third member of Shahejie Formation, consists of fan-delta deposits. Based on the theory of sequence stratigraphy and dynamic sedimentology, with the need of oil developing bed, the Lianhua reservoir of Qi 108 can be divided into three oil bed groups containning ten sandstone beds. The reservoir is recognized 11 lithofacies as follows: Gm, Sm, Ss, Smg , Sp, Sw, Sh, Sr, Fm, Ff and Fds. 12 lithofacies assemblages are composed of the 11 lithofacies, and they are: Gm→Sp→Sm→Fm, Gm→Smg→Fm, Ss→Sm→Sr→Fm; Sm→Sh→Fm, Ss→Sm→Sr→Fm; Gm→ Sm→Fm; Ff→Sr→Sm, Fm→Sw→Sh; Fds→ Sr→Sh→Fm, Fm→Fds→Sw→Sr→Ff; Sm→Sr→Fm; Ff→Sr→Fm. The lithofacies and assemblages constitute subaqueous fan-delta depositional modelling, containing 1) subaqueous major distributary channel, 2) subaque-
Qi 108 is a small oil developing block of Huanxiling oilfield in Liaohe basin. The reservoir, the third member of Shahejie Formation, consists of fan-delta deposits. Based on the theory of sequence stratigraphy and dynamic sedimentology, with the need of oil developing bed, the Lianhua reservoir of Qi 108 can be divided into three oil bed groups containning ten sandstone beds. The reservoir is recognized 11 lithofacies as follows: Gm, Sm, Ss, Smg , Sp, Sw, Sh, Sr, Fm, Ff and Fds. 12 lithofacies assemblages are composed of the 11 lithofacies, and they are: Gm→Sp→Sm→Fm, Gm→Smg→Fm, Ss→Sm→Sr→Fm; Sm→Sh→Fm, Ss→Sm→Sr→Fm; Gm→ Sm→Fm; Ff→Sr→Sm, Fm→Sw→Sh; Fds→ Sr→Sh→Fm, Fm→Fds→Sw→Sr→Ff; Sm→Sr→Fm; Ff→Sr→Fm. The lithofacies and assemblages constitute subaqueous fan-delta depositional modelling, containing 1) subaqueous major distributary channel, 2) subaque-
1998, 16(2): 113-116,123.
Abstract:
The analyses of Neogene-Quaternary sedimentary environment, depocenter distribution and geodynamic origin of structural deformation of the Tarim Basin suggest that Aheqi-West Kunlun-Altynsinistral transpression tectonics controlled the Neogene-Quaternary sedimentation and structural deformation of the Tarim basin. It accelerated the hydrocarbon maturation process, formed many new anticline and fault traps, and controlled Cenozoic hydrocarbon migration and accumulation. The secondary oil and gas accumulation in the non-structural traps and fault screened traps are favorable prospecting targets on the Bachu uplift.
The analyses of Neogene-Quaternary sedimentary environment, depocenter distribution and geodynamic origin of structural deformation of the Tarim Basin suggest that Aheqi-West Kunlun-Altynsinistral transpression tectonics controlled the Neogene-Quaternary sedimentation and structural deformation of the Tarim basin. It accelerated the hydrocarbon maturation process, formed many new anticline and fault traps, and controlled Cenozoic hydrocarbon migration and accumulation. The secondary oil and gas accumulation in the non-structural traps and fault screened traps are favorable prospecting targets on the Bachu uplift.
1998, 16(2): 124-128.
Abstract:
The phenomen n that dinosaur fossils can be preserved very well shows that dinosaurs were rapidly buried and preserved after or before their death. The strange phenomenon that a number of dinosaur fossils were unearthed in complete body frames or throngs in the Upper Cretaceceous clastics nearly around the globe indicates that this set of clastics which buried dinosaurs should belong to a kind of "event sedimentation". On the other hand, the formation of the late Upper Cretaceous have such features as: ① Together with the Eogene above, a complete Ⅱ-class sedimentary cycle was formed. Among them there was a conformable contact, and the classfication limit was determined by the distinguishing line of dinosaurs or by the appearance line of mammalia. The micropalaeobio logics show the mixing feature of Meso zoic-Cenozoic molecules. ② This set of strata overlapped on the earier layers in widespread way or in capped way; and it is of large thickness, similar features and easy correlation.③ There is an unconfomity at the bottom of the strata which can be correlated worldwide. ④ The geologic time of forming the strata is very short. ⑤ There are abnormal transgressive feature. The comprehensive analysis shows that this kind of sedimentary strata can be formed only under widespread way or capped way catastrophic flood conditions. This set of sediments are called "event sedimentation" relation to the normal sedimentation. The catastrophic flood of forming the event sedimentation may be the catastrophic seaquake worldwide, and it is caused by the planet collision. In order to explain the abnormal phenomenon that the biological distinguishing line is underlying the argillic horizon, the clastics concluding dinosaur fossils and iyidium-rich argillic horizon are considered as the different part of "event sedimentation" in this paper. A lot of transporting matter carried by the catastrophic seaquake worldwide deposited repidly in very short time, and some organism such as dinosaurs were preserved completely, then come the sedmentation of the iydumrch matter in the air. This special kind of transgression may by one of the causes of the marine organism and salt-deposit that have been argued in the inland basins.
The phenomen n that dinosaur fossils can be preserved very well shows that dinosaurs were rapidly buried and preserved after or before their death. The strange phenomenon that a number of dinosaur fossils were unearthed in complete body frames or throngs in the Upper Cretaceceous clastics nearly around the globe indicates that this set of clastics which buried dinosaurs should belong to a kind of "event sedimentation". On the other hand, the formation of the late Upper Cretaceous have such features as: ① Together with the Eogene above, a complete Ⅱ-class sedimentary cycle was formed. Among them there was a conformable contact, and the classfication limit was determined by the distinguishing line of dinosaurs or by the appearance line of mammalia. The micropalaeobio logics show the mixing feature of Meso zoic-Cenozoic molecules. ② This set of strata overlapped on the earier layers in widespread way or in capped way; and it is of large thickness, similar features and easy correlation.③ There is an unconfomity at the bottom of the strata which can be correlated worldwide. ④ The geologic time of forming the strata is very short. ⑤ There are abnormal transgressive feature. The comprehensive analysis shows that this kind of sedimentary strata can be formed only under widespread way or capped way catastrophic flood conditions. This set of sediments are called "event sedimentation" relation to the normal sedimentation. The catastrophic flood of forming the event sedimentation may be the catastrophic seaquake worldwide, and it is caused by the planet collision. In order to explain the abnormal phenomenon that the biological distinguishing line is underlying the argillic horizon, the clastics concluding dinosaur fossils and iyidium-rich argillic horizon are considered as the different part of "event sedimentation" in this paper. A lot of transporting matter carried by the catastrophic seaquake worldwide deposited repidly in very short time, and some organism such as dinosaurs were preserved completely, then come the sedmentation of the iydumrch matter in the air. This special kind of transgression may by one of the causes of the marine organism and salt-deposit that have been argued in the inland basins.
1998, 16(2): 134-138.
Abstract:
The flume study was made at Environment Research Center of Tsukuba University, Japan. The observation of the bedload transportation and the grain size analysis of samples collected along the channel from upper to downstream showed that selective sorting plays a very important part in heavy mineral concentrations. The results were as follows: 1) The sediment from superficial layer was fining downst reamward. As a result, the percentage of heavy mineral fractions increased with increasing distance off the flume inlet. The longer the distance, the higher the percentage was. The maximum reached 48% near the flume outlet, whereas the initial population was lower than 5%. 2) Heavy particles were characterized by good sorting and fine diameter size. Mean particle size ranged from 1.5 to 2.5φ. Major content was fine sand. 3) The percentage of the heavy mineral fractions changed with the variation of bedforms. Stoss side of a bar, trough and pool were traps of heavy particles. 4) According to the texture of the sediment, a bar was divided into three parts. The superficial layer of the tail was observed to contain large amount of fine and medium sand and to be rich in heavy minerals. In contrast, the head of a bar was mainly composed of gravel and coarse sand, which contains few heavy particles. The body of a bar mediated between the tail and head. 5) On transection, three layers with abundant heavy minerals were observed, but only the lag layer was continuous and signified to forming placers.
The flume study was made at Environment Research Center of Tsukuba University, Japan. The observation of the bedload transportation and the grain size analysis of samples collected along the channel from upper to downstream showed that selective sorting plays a very important part in heavy mineral concentrations. The results were as follows: 1) The sediment from superficial layer was fining downst reamward. As a result, the percentage of heavy mineral fractions increased with increasing distance off the flume inlet. The longer the distance, the higher the percentage was. The maximum reached 48% near the flume outlet, whereas the initial population was lower than 5%. 2) Heavy particles were characterized by good sorting and fine diameter size. Mean particle size ranged from 1.5 to 2.5φ. Major content was fine sand. 3) The percentage of the heavy mineral fractions changed with the variation of bedforms. Stoss side of a bar, trough and pool were traps of heavy particles. 4) According to the texture of the sediment, a bar was divided into three parts. The superficial layer of the tail was observed to contain large amount of fine and medium sand and to be rich in heavy minerals. In contrast, the head of a bar was mainly composed of gravel and coarse sand, which contains few heavy particles. The body of a bar mediated between the tail and head. 5) On transection, three layers with abundant heavy minerals were observed, but only the lag layer was continuous and signified to forming placers.
1998, 16(2): 145-149.
Abstract:
Based on the systematic study on the groundwater chemistry typer and their evolutional characteristics in the Shiyang river basin, the author hasthe evolution mechanism of chemical environment of the groundwater in the Shiyang river basin by the saturation index (SI) obtained through chemical simulation program. Some cognitions are reached as follows: 1. Groundwater chemistry types of the Shiyang river basin show the complete zonation, i. e, bicarbonate zone is mainly distributed in the mountainous fissure water in the upper reach and mountain front gravel area; sulfate zone is in the mountain front alluvial and fluvial plain in the middle reach; and chloride zone is in the desert and salt depression area in the lower reach. 2. In April (dry period), the calcite and dolomite are oversaturated both in the upperreach (Wuwei basin) and the lower reach(Minqing basin), but in August (rain period) the SI of the calcite and dolomite decreased obviously in Wuwei basin. In the meantime that in Minqin basin had an obviously increasing trend and both calcite and dolomite reached over saturation, implying that groundwater chemistry environment in the lower reach of the Shiyang river basin is mainly controlled by evaporation. 3. Groundwater overdraft in recent ten years has resulted in the chemistry types of the groundwater changed from bicarbonate to sulfate and even chloride in the lower reach, especially in the margin area of the desert, showing the increasing trend of mineralization and worse groundwater quality.
Based on the systematic study on the groundwater chemistry typer and their evolutional characteristics in the Shiyang river basin, the author hasthe evolution mechanism of chemical environment of the groundwater in the Shiyang river basin by the saturation index (SI) obtained through chemical simulation program. Some cognitions are reached as follows: 1. Groundwater chemistry types of the Shiyang river basin show the complete zonation, i. e, bicarbonate zone is mainly distributed in the mountainous fissure water in the upper reach and mountain front gravel area; sulfate zone is in the mountain front alluvial and fluvial plain in the middle reach; and chloride zone is in the desert and salt depression area in the lower reach. 2. In April (dry period), the calcite and dolomite are oversaturated both in the upperreach (Wuwei basin) and the lower reach(Minqing basin), but in August (rain period) the SI of the calcite and dolomite decreased obviously in Wuwei basin. In the meantime that in Minqin basin had an obviously increasing trend and both calcite and dolomite reached over saturation, implying that groundwater chemistry environment in the lower reach of the Shiyang river basin is mainly controlled by evaporation. 3. Groundwater overdraft in recent ten years has resulted in the chemistry types of the groundwater changed from bicarbonate to sulfate and even chloride in the lower reach, especially in the margin area of the desert, showing the increasing trend of mineralization and worse groundwater quality.
1998, 16(2): 150-154.
Abstract:
Fan delta sediments is widely developed in Jurassic in the depression of the SW Tarim Basin. Based on analyses of sedimentary characteristics, the paper is lonsidered that fan delta is a typical set of retro-gradinging ression lacustrine sequence. Three-layer structre of the sequence is quite clear with prefan-delta plain in the lower part, fan-delta-front in the middle part and prefandelta in the upper part. It indicates that the region be in margin of active basin in Early-Middle Jurassic, in which lake changes form shallow to deep and rate of subsidence is more rapid that rate of sedimentaion. Generally peaking, the forming of fan delta be resericted by three main condition wuioth marginal type of lake basin, distance form provanance to lake basin and palaeoclimate, so fan delta usually develop in the region of short distance form provenance to lake basin and lacking plant near foreland. It has develped a complete source-reser-voir-cap rock assemblage in Jurassic in the depression of the SW Tarim basin. Dark mudstone of lake are main hydrocarbon source rocks, fandelta foront sand bodies are good resewoirs, and gypmudrock in Upper Cretaceous and Tertiary is good cover rock It has been proved that Jurassic have good potentials for exploration of oil and gas in this region.
Fan delta sediments is widely developed in Jurassic in the depression of the SW Tarim Basin. Based on analyses of sedimentary characteristics, the paper is lonsidered that fan delta is a typical set of retro-gradinging ression lacustrine sequence. Three-layer structre of the sequence is quite clear with prefan-delta plain in the lower part, fan-delta-front in the middle part and prefandelta in the upper part. It indicates that the region be in margin of active basin in Early-Middle Jurassic, in which lake changes form shallow to deep and rate of subsidence is more rapid that rate of sedimentaion. Generally peaking, the forming of fan delta be resericted by three main condition wuioth marginal type of lake basin, distance form provanance to lake basin and palaeoclimate, so fan delta usually develop in the region of short distance form provenance to lake basin and lacking plant near foreland. It has develped a complete source-reser-voir-cap rock assemblage in Jurassic in the depression of the SW Tarim basin. Dark mudstone of lake are main hydrocarbon source rocks, fandelta foront sand bodies are good resewoirs, and gypmudrock in Upper Cretaceous and Tertiary is good cover rock It has been proved that Jurassic have good potentials for exploration of oil and gas in this region.
1998, 16(2): 155-160.
Abstract:
Anion Chlorine in inland lakes is a commonindicator highly sensitive to climatic change. The variation of the content of anion chlorime in the Late Cenozoic stratigraphy in the Linxia Basim, Gansu Province, China, demonstrates that climate changes clearly in phase (step) and periodicity. The climate was shited rapidly at about 6.3 Ma from relatively humid to very dry environments, and reached an extreme dry environment between 5.3 Ma and 4.5 Ma, with drought degree 33 times the early Quaternary. In low frequency, climate presents ca. 400 ka periodicity of dry-humid fluctuation, matching global hot-cold (cool) fluctuation in similar periodicity in the Late Miocene-Early Pliocene; w hile matching global cold-warm fluctuation in the early Quaternary. The change of moistureheat regime from the Late Pliocene to the early Quaternary may suggest that the Asian monsoon system began to form gradually since the Late Pliocene and was completely established in the esrly Quaternary. The strong whole uplift of the Tibetan plateau at ca. 3.4 Ma may be responsible for such change.
Anion Chlorine in inland lakes is a commonindicator highly sensitive to climatic change. The variation of the content of anion chlorime in the Late Cenozoic stratigraphy in the Linxia Basim, Gansu Province, China, demonstrates that climate changes clearly in phase (step) and periodicity. The climate was shited rapidly at about 6.3 Ma from relatively humid to very dry environments, and reached an extreme dry environment between 5.3 Ma and 4.5 Ma, with drought degree 33 times the early Quaternary. In low frequency, climate presents ca. 400 ka periodicity of dry-humid fluctuation, matching global hot-cold (cool) fluctuation in similar periodicity in the Late Miocene-Early Pliocene; w hile matching global cold-warm fluctuation in the early Quaternary. The change of moistureheat regime from the Late Pliocene to the early Quaternary may suggest that the Asian monsoon system began to form gradually since the Late Pliocene and was completely established in the esrly Quaternary. The strong whole uplift of the Tibetan plateau at ca. 3.4 Ma may be responsible for such change.
