2001 Vol. 19, No. 3
column
Display Method:
2001, 19(3): 321-326.
Abstract:
The main point of views in the paper are 1) the Middle Triassic in the studied area is very thick flysch facies with various characteristics of deep water mass flow sediments dominated by turbidites, 2) the size and thickness of the very thick flysch facies become coarse and thick upward, constituting a whole progressive sequence, 3) besides mass flow sediments, deep water drag flow sediments associated with turbidites were also found, e.g., contourites, and inner wave and inner tide sediments with diversified sedimentary structures, e.g., different types and scales of cross bedings showing water flow waves ripples on sedimentary bed surfaces with different characteristics, 4)if there are coarse sized channel sediments and regularities of vertical sequences and characteristics of ancient flows and rich facies types, the flysch facies are considered to be controlled by deep-sea fan sedimentary facies, 5) compared with the submarine fans developed on the passive and active margins of the plates the submarine fan is considered as an immature one.
The main point of views in the paper are 1) the Middle Triassic in the studied area is very thick flysch facies with various characteristics of deep water mass flow sediments dominated by turbidites, 2) the size and thickness of the very thick flysch facies become coarse and thick upward, constituting a whole progressive sequence, 3) besides mass flow sediments, deep water drag flow sediments associated with turbidites were also found, e.g., contourites, and inner wave and inner tide sediments with diversified sedimentary structures, e.g., different types and scales of cross bedings showing water flow waves ripples on sedimentary bed surfaces with different characteristics, 4)if there are coarse sized channel sediments and regularities of vertical sequences and characteristics of ancient flows and rich facies types, the flysch facies are considered to be controlled by deep-sea fan sedimentary facies, 5) compared with the submarine fans developed on the passive and active margins of the plates the submarine fan is considered as an immature one.
2001, 19(3): 333-339.
Abstract:
The geologists have different opinions about the depositional environment of Wulabo Formation,Upper Permian series in the south margin of Junggar Basin.In this article,the depositional environment of Wulabo Formation,Upper Permian Series in Bogeda piedmont depression is analyzed based on the geochemical criteria in the sediments, including the content of equivalent boron,the ratio of B/Ga,Sr/Ba and the relationship among B?Rb?Ga,sandstone grain size distribution and clay mineral association of mudstone. It is considered that the Wulabo Formation was formed under marine regression background. The bottom of the strata was formed in shallow marine environment, and the middle to upper section was formed in terrestrial environment. By studies of rock types and their combination, the texture of fragmental rock, primary sedimentary structures and their evolution sequence, sedimentary rhythm, four kinds of sedimentary facies have been recognized in the strata. They are tidal flat, coastal subaqueous fan, braided stream and alluvial fan. The tidal flat and coastal subaqueous fan facies are distributed at the bottom,and braided stream facies in the middle,alluvial fan facies on the top of Wulabo Formation. The evolution of the sedimentary facies in this area was controlled by the formation and evolution of Bogeda intercontinental rift system.
The geologists have different opinions about the depositional environment of Wulabo Formation,Upper Permian series in the south margin of Junggar Basin.In this article,the depositional environment of Wulabo Formation,Upper Permian Series in Bogeda piedmont depression is analyzed based on the geochemical criteria in the sediments, including the content of equivalent boron,the ratio of B/Ga,Sr/Ba and the relationship among B?Rb?Ga,sandstone grain size distribution and clay mineral association of mudstone. It is considered that the Wulabo Formation was formed under marine regression background. The bottom of the strata was formed in shallow marine environment, and the middle to upper section was formed in terrestrial environment. By studies of rock types and their combination, the texture of fragmental rock, primary sedimentary structures and their evolution sequence, sedimentary rhythm, four kinds of sedimentary facies have been recognized in the strata. They are tidal flat, coastal subaqueous fan, braided stream and alluvial fan. The tidal flat and coastal subaqueous fan facies are distributed at the bottom,and braided stream facies in the middle,alluvial fan facies on the top of Wulabo Formation. The evolution of the sedimentary facies in this area was controlled by the formation and evolution of Bogeda intercontinental rift system.
2001, 19(3): 345-350.
Abstract:
The gravity flow depositions were formed by the debris,sliding and turbidity flows in Late Jurassic-Early Cre-taceous in Shalagang ore afea of Jomzi basin located at southern Tibet．which consisted of the slope clastic rocks and interbeds of silicalites and limestones．8 three-order sequence stratigraphies are divided,induding two type-1 and six type-2 sequences．The framework of sequence stratigraphy are established．These sequences,with clear three-division structures,were characterized by the gravity-flow sediments of deep-water slope,developed within about40 Ma and the estimated average time of every three-order sequence was 5 Ma．Sequence l(SQl)of type 1 consisted of the gravity-flow sediments of deep-water slope．The SMST of SQ2 of type 2 was composed of the prograded and aggraded sequences of lower slope channel sandstones and conglomerates to upper slope black shales which interbeddded with sliding sandy-sediments and turbidity sandstones．The TST consisted of the retrograded black shales interbedded with turbidity fine-siltstones of the lower slope．the CS consisted of thin-bedding lamella limestones,and the HST consisted of the progradded black shales interbedded with sandy-and calcios-slide bodies and minor turbidty siltstones of the upper slope．The sliding sediments characterized the SQ3 of type 2．The SQ4 of type 2 consisted of siliceous turbidities．SQ5．SQ6 and SQ7 of type 2 were composed of sediments of terrigenous submarine fan．The SQ8 of type 1 were also composed of sediments of terrigenous submarine fan,and extending and reactivating of channel of inner fan towards basin was indicator of the sequence． As a whole．the formation of sequences was closely related to sea-level changes,type 1 or 2 boundaries and sequences were respectively created,corresponding to fast and slow falling．Based on study of sequence stragraphy,depesitional development of slope setting are divided into 4 stages： (1)Relatively steep terrigenous slope,corresonding to SQ1 and SQ2．In early time,calcious and terrigenous debris-flow sediments were accumulated in relatively steep slope toe．In late time,some parts of slope were cut by channel,and slope channel filling-sequence with debris-flow conglomerates and conglomerate-bearing sandstones was formed．(2)Reatively gentle terrigenous slope,corresponding to SQ3.with rising of sea level and deepening of water body,debris-flows lacked or slightly developed． It implied that slope was becoming gentle,but sandyslid bodied characterized slope．(3)Siliceous submarine fan,corresponding to SQ4.With continuos rising of sea level and halting of terrigenous supply,siliceous submarine fan was dominated over formal terrigenous gravety-flow sediments,and slope deepened again．(4)Terrigenous submarine fan,corresponding to S05．Similar to SQ5,SQ6,SQ7and SQ8 were also characterized by the development of terrigenous submarine fan．In the end of the forth stage,with large-size fast falling of sea-level once again,greatly-thick slope escallication which switched 500--600 Km and distributed widely along Shalagang-Jomzi-Zhongba areas and stopped the growth of submarine fan．After Late Cretaceous,Jomzi basin was gradually filled out by shallow-water sediments and disappeared．
The gravity flow depositions were formed by the debris,sliding and turbidity flows in Late Jurassic-Early Cre-taceous in Shalagang ore afea of Jomzi basin located at southern Tibet．which consisted of the slope clastic rocks and interbeds of silicalites and limestones．8 three-order sequence stratigraphies are divided,induding two type-1 and six type-2 sequences．The framework of sequence stratigraphy are established．These sequences,with clear three-division structures,were characterized by the gravity-flow sediments of deep-water slope,developed within about40 Ma and the estimated average time of every three-order sequence was 5 Ma．Sequence l(SQl)of type 1 consisted of the gravity-flow sediments of deep-water slope．The SMST of SQ2 of type 2 was composed of the prograded and aggraded sequences of lower slope channel sandstones and conglomerates to upper slope black shales which interbeddded with sliding sandy-sediments and turbidity sandstones．The TST consisted of the retrograded black shales interbedded with turbidity fine-siltstones of the lower slope．the CS consisted of thin-bedding lamella limestones,and the HST consisted of the progradded black shales interbedded with sandy-and calcios-slide bodies and minor turbidty siltstones of the upper slope．The sliding sediments characterized the SQ3 of type 2．The SQ4 of type 2 consisted of siliceous turbidities．SQ5．SQ6 and SQ7 of type 2 were composed of sediments of terrigenous submarine fan．The SQ8 of type 1 were also composed of sediments of terrigenous submarine fan,and extending and reactivating of channel of inner fan towards basin was indicator of the sequence． As a whole．the formation of sequences was closely related to sea-level changes,type 1 or 2 boundaries and sequences were respectively created,corresponding to fast and slow falling．Based on study of sequence stragraphy,depesitional development of slope setting are divided into 4 stages： (1)Relatively steep terrigenous slope,corresonding to SQ1 and SQ2．In early time,calcious and terrigenous debris-flow sediments were accumulated in relatively steep slope toe．In late time,some parts of slope were cut by channel,and slope channel filling-sequence with debris-flow conglomerates and conglomerate-bearing sandstones was formed．(2)Reatively gentle terrigenous slope,corresponding to SQ3.with rising of sea level and deepening of water body,debris-flows lacked or slightly developed． It implied that slope was becoming gentle,but sandyslid bodied characterized slope．(3)Siliceous submarine fan,corresponding to SQ4.With continuos rising of sea level and halting of terrigenous supply,siliceous submarine fan was dominated over formal terrigenous gravety-flow sediments,and slope deepened again．(4)Terrigenous submarine fan,corresponding to S05．Similar to SQ5,SQ6,SQ7and SQ8 were also characterized by the development of terrigenous submarine fan．In the end of the forth stage,with large-size fast falling of sea-level once again,greatly-thick slope escallication which switched 500--600 Km and distributed widely along Shalagang-Jomzi-Zhongba areas and stopped the growth of submarine fan．After Late Cretaceous,Jomzi basin was gradually filled out by shallow-water sediments and disappeared．
2001, 19(3): 357-362.
Abstract:
A lot of ice induced sedimentary structures are developed on Yellow River delta and one of them is rernarkedly ice induced heaving． Ice-induced heaving has a hill-like shape in appearance and circutar hill-like ones is often seen,and a few of them have long hill-like,irregular platform,tower-colurnn,earth pyramid and volcanic shapes with different sizes ranging from several centimeters(small ones)to a{ew decades of centimeters(1arge oes)and the largest is more than one meter in length,The surfaces of ice-induced heavings are smooth or have fission or pits like crater,and or have a lot of pea-like nodule or root-like structures．Some of ice-induced heavings have dome-like bedding within its interior,and some have complex deformation beading．Generally,ice-induced hearings develop in channel bar or point bar of course beds．Their genesis may be divisible into three types;the first is formed by dropping deposition of ice-melt water；the second is formed by vaulting resulting from the breakdown caused by ice melting；the third is formed by dropping deposition from a ice hole． The unusual hydrology,hydrodynamics and climate conditions in Yellow River make the ice beds containing(a great deal)mud-silt or the ice beds covered by mud-silt．As those ice beds melt,the mud-silt contained in the ice beds covering the ice beds will drop to the ground surface with ice melt water and form ice-induced heaving in the relevant position．If a hole develops in the ice bed and in the meantime,it is also covered by a layer of mudsilt,and when the ice bed melt,a heaving will be formed in the relevant position due to vaulting．If the ice bed formed in erosion pit in the point bar or channel bar has a hole or a crack,the mud-silt will drop into the pit with the ice melt water along the hole or crack to form a heaving． Ice-induced heavings are formed in an exposure and lower temperature(±0℃)conditions and their genesis is related to the complex interactions of ice and sand．
A lot of ice induced sedimentary structures are developed on Yellow River delta and one of them is rernarkedly ice induced heaving． Ice-induced heaving has a hill-like shape in appearance and circutar hill-like ones is often seen,and a few of them have long hill-like,irregular platform,tower-colurnn,earth pyramid and volcanic shapes with different sizes ranging from several centimeters(small ones)to a{ew decades of centimeters(1arge oes)and the largest is more than one meter in length,The surfaces of ice-induced heavings are smooth or have fission or pits like crater,and or have a lot of pea-like nodule or root-like structures．Some of ice-induced heavings have dome-like bedding within its interior,and some have complex deformation beading．Generally,ice-induced hearings develop in channel bar or point bar of course beds．Their genesis may be divisible into three types;the first is formed by dropping deposition of ice-melt water；the second is formed by vaulting resulting from the breakdown caused by ice melting；the third is formed by dropping deposition from a ice hole． The unusual hydrology,hydrodynamics and climate conditions in Yellow River make the ice beds containing(a great deal)mud-silt or the ice beds covered by mud-silt．As those ice beds melt,the mud-silt contained in the ice beds covering the ice beds will drop to the ground surface with ice melt water and form ice-induced heaving in the relevant position．If a hole develops in the ice bed and in the meantime,it is also covered by a layer of mudsilt,and when the ice bed melt,a heaving will be formed in the relevant position due to vaulting．If the ice bed formed in erosion pit in the point bar or channel bar has a hole or a crack,the mud-silt will drop into the pit with the ice melt water along the hole or crack to form a heaving． Ice-induced heavings are formed in an exposure and lower temperature(±0℃)conditions and their genesis is related to the complex interactions of ice and sand．
2001, 19(3): 368-374.
Abstract:
Changdi region is situated in the eastern part of Zhanhua sag in Jiyang depression．It belongs to one part of the Zhuangxi-Gudong buried hill belt in Structure．with area an about 160 km2．Based on the synthetical analysis the geologieal,log,seismic and chemical analysis data,the authors believe 5 types of sedimentary system were developed in this area in Paleogene,that is,subsurface fan,beach and dam,fan delta,turbidity current and braided river. Subsurface fan can be divided 3 types of sub-facieses,i,e,root-fan,middle-fan and fan edge by core and conglomerate distribution and etc．the middle-fan can be divided 3 micro-facies-braided channel．space between channel and front-edge zone．In the braided channel,sediment grain is coatse．And it shows positive rhythm,SP curve with box type and atc．Surface of scour can be seen at the bottom of the channel． Beach and bar system were formed at the edge of lake．shallow platform and etc．They can be divided into 2 types,i．e．,terrigenous debris type and carbonate rock type．The terrigenous debris type was distributed mainly over the west edge of the study area．and carbonate rock type was distributed mainly in the middle part．About the fan delta system．there were prodelta and delta front in the area．The delta front subfaces consists of embranchment channel,channel mouth bar and etc．Judged by distribution of the sedimentary system,during the third member of Shahejie formation,researching area belongs to subsurface fan system．From the early stage to metaphase,the sediment range were widened gradually．In the later period,the range of lake and size of subsurface fan diminished．During the second member and the early stage of the first member of the Shahejie Formation,this area belonged to beach and bar system．In the third member of Dongying Formation,the study area belonged to fan delta system,and it stretched gradually from southeast to north．duing the later period,the southeast part developed the fan delta plain．The delta front subfaces consisted of embranchment channel,channel mouth bar and etc． During the second member and the first member of the Dongying Formation,this area belonged to braided river system as a whole．There were a series of channel bar deposits． It was thought by synthetically analyzing the regularity of vertical evolution of sedimentary system was stinct．During the third and second member of the Shahejie Formation．the type of sedimentary system was subsurface fan near bank,the sediments came from Changdi lower upheaval．During the first member of the Shahejie Formation．it belonged to beach and bar system,while later period of the member,it was deep lake．From the third member of the Dongying Formation to the second and first member。the sediment system was fan delta,braided river,sediments mostly came from the Kendong—Qingtuozi upheaval．
Changdi region is situated in the eastern part of Zhanhua sag in Jiyang depression．It belongs to one part of the Zhuangxi-Gudong buried hill belt in Structure．with area an about 160 km2．Based on the synthetical analysis the geologieal,log,seismic and chemical analysis data,the authors believe 5 types of sedimentary system were developed in this area in Paleogene,that is,subsurface fan,beach and dam,fan delta,turbidity current and braided river. Subsurface fan can be divided 3 types of sub-facieses,i,e,root-fan,middle-fan and fan edge by core and conglomerate distribution and etc．the middle-fan can be divided 3 micro-facies-braided channel．space between channel and front-edge zone．In the braided channel,sediment grain is coatse．And it shows positive rhythm,SP curve with box type and atc．Surface of scour can be seen at the bottom of the channel． Beach and bar system were formed at the edge of lake．shallow platform and etc．They can be divided into 2 types,i．e．,terrigenous debris type and carbonate rock type．The terrigenous debris type was distributed mainly over the west edge of the study area．and carbonate rock type was distributed mainly in the middle part．About the fan delta system．there were prodelta and delta front in the area．The delta front subfaces consists of embranchment channel,channel mouth bar and etc．Judged by distribution of the sedimentary system,during the third member of Shahejie formation,researching area belongs to subsurface fan system．From the early stage to metaphase,the sediment range were widened gradually．In the later period,the range of lake and size of subsurface fan diminished．During the second member and the early stage of the first member of the Shahejie Formation,this area belonged to beach and bar system．In the third member of Dongying Formation,the study area belonged to fan delta system,and it stretched gradually from southeast to north．duing the later period,the southeast part developed the fan delta plain．The delta front subfaces consisted of embranchment channel,channel mouth bar and etc． During the second member and the first member of the Dongying Formation,this area belonged to braided river system as a whole．There were a series of channel bar deposits． It was thought by synthetically analyzing the regularity of vertical evolution of sedimentary system was stinct．During the third and second member of the Shahejie Formation．the type of sedimentary system was subsurface fan near bank,the sediments came from Changdi lower upheaval．During the first member of the Shahejie Formation．it belonged to beach and bar system,while later period of the member,it was deep lake．From the third member of the Dongying Formation to the second and first member。the sediment system was fan delta,braided river,sediments mostly came from the Kendong—Qingtuozi upheaval．
2001, 19(3): 381-385,432.
Abstract:
Juye coalfield is a Permo carboniferous coalfield,located at the southwest part of the Shandong Province.With the guidance of the sequence stratigraphic theory and the methodology,based on the analysis of cores and well logs,the authors carry out the detailed study on the feature of the depositional system and its constitute of the Permian in the study area our.study shows that the Lower Permain is a set of sediments dominanted by deltaic depositional system.Seven sedimentary facies have been recognized in the fluvial dominated shallow water deltaic depositional system.They are distributary channel,natural levee,crevasse splay,interdistributary bay,interdistributary depression,distributary mouth bar,and distal bar.The framework of this deltaic system is the sedimentary facies combination of deltaic plain,in which the main sedimentary facies is the distributary channel deposits.Because of the rapid progradation of the distributary channel,the distributary bay formed in them.The deposition of crevasse splay and overbank action filled the bay gradually,enlarging the upper deltaic plain.At the abandon stage of the deltaic system,and the active water channel died out.Superseding was the extensive swamp and peat swamp deposits,forming thick coalbed,which provides a sound basis for the division of the sequences.The reworked distributary channel washed and destroyed the underlying coalbed,reducing the thickness of the coalbed,even completely washed away.For the same sake,the pre delta mud can rarely be found in the study area. Sequence stratigraphy and its internal composition have been recognized through drawing up the section and the planimetric maps.The framework of the stratigraphy sequence has been established.In the framework,seven third order sequences and forty two parasequences have been identified.Among these,sequence Ⅲ is the main topic in this paper,for the deltaic system develops in the upper part of this sequence.Not only the frequent changes of the sea level but also the tectonic movement and the abundance of the deposit affect the development of the deltaic system.Our study also shows that there are two or three sets of fluvial dominated shallow water deltaic depositional sequences in the Shanxi Formation.In general,Juye coalfield located in the delta plain of the large scale shallow water deltaic depositional system.The delta plain is a better place for coal accumulation,high quality workable coal seams were formed in this system.But,because of the unequilibrium of the distribution of the interdistributary swamps in the developing process of the delta,the tectonic movement and the scouring of river channel,the distribution of the coal seams are different.The distributary channel later developed often wash the earlier coalbeds.So the interdistributary swamp on shallow water delta is the best place for peat accumulation,where coal rich units generally develop well.
Juye coalfield is a Permo carboniferous coalfield,located at the southwest part of the Shandong Province.With the guidance of the sequence stratigraphic theory and the methodology,based on the analysis of cores and well logs,the authors carry out the detailed study on the feature of the depositional system and its constitute of the Permian in the study area our.study shows that the Lower Permain is a set of sediments dominanted by deltaic depositional system.Seven sedimentary facies have been recognized in the fluvial dominated shallow water deltaic depositional system.They are distributary channel,natural levee,crevasse splay,interdistributary bay,interdistributary depression,distributary mouth bar,and distal bar.The framework of this deltaic system is the sedimentary facies combination of deltaic plain,in which the main sedimentary facies is the distributary channel deposits.Because of the rapid progradation of the distributary channel,the distributary bay formed in them.The deposition of crevasse splay and overbank action filled the bay gradually,enlarging the upper deltaic plain.At the abandon stage of the deltaic system,and the active water channel died out.Superseding was the extensive swamp and peat swamp deposits,forming thick coalbed,which provides a sound basis for the division of the sequences.The reworked distributary channel washed and destroyed the underlying coalbed,reducing the thickness of the coalbed,even completely washed away.For the same sake,the pre delta mud can rarely be found in the study area. Sequence stratigraphy and its internal composition have been recognized through drawing up the section and the planimetric maps.The framework of the stratigraphy sequence has been established.In the framework,seven third order sequences and forty two parasequences have been identified.Among these,sequence Ⅲ is the main topic in this paper,for the deltaic system develops in the upper part of this sequence.Not only the frequent changes of the sea level but also the tectonic movement and the abundance of the deposit affect the development of the deltaic system.Our study also shows that there are two or three sets of fluvial dominated shallow water deltaic depositional sequences in the Shanxi Formation.In general,Juye coalfield located in the delta plain of the large scale shallow water deltaic depositional system.The delta plain is a better place for coal accumulation,high quality workable coal seams were formed in this system.But,because of the unequilibrium of the distribution of the interdistributary swamps in the developing process of the delta,the tectonic movement and the scouring of river channel,the distribution of the coal seams are different.The distributary channel later developed often wash the earlier coalbeds.So the interdistributary swamp on shallow water delta is the best place for peat accumulation,where coal rich units generally develop well.
2001, 19(3): 394-398.
Abstract:
The abandoned channel micro facies of fluvial reservoir blocks the fluid in the lateral. During the stage of further development, this kind of micro facies is the key to the detailed description of the areal heterogeneity in reservoir and the important factor which influences the lateral remaining, oil. Three facies belts which are channel stone, interchannel stone and interchannel silt are subdivided in the reservoir description of complex meander belt stone body previously. Which is hard to identify and subdivide the abandoned river micro facies. With the more knowledge of background and characteristics of modern fluvial sedimentary, especially at the stage of further development, the average well interval of Daqing oilfield is 200～300 meter, some of that is 100 meter even. Based on the abundant data of close well logging, the identification and detail description of micro facies of complex meander belt are authentic established. This article combined modern sedimentary, output investigation with the description of channel geometry and scale to set up the conceptual model of abandoned channel facies. By using well logging curves under close well spacing, this paper interpreted the distribution character, the recognition method of channel facies on the areal and profile, and established a static model for the abandoned channel facies on flooding plain in Daqing Oilfield. Based on this method, the comprehensive prediction of reservoir and the analysis of remaining oil have been conducted. This method has a notable result in high efficiency wells.
The abandoned channel micro facies of fluvial reservoir blocks the fluid in the lateral. During the stage of further development, this kind of micro facies is the key to the detailed description of the areal heterogeneity in reservoir and the important factor which influences the lateral remaining, oil. Three facies belts which are channel stone, interchannel stone and interchannel silt are subdivided in the reservoir description of complex meander belt stone body previously. Which is hard to identify and subdivide the abandoned river micro facies. With the more knowledge of background and characteristics of modern fluvial sedimentary, especially at the stage of further development, the average well interval of Daqing oilfield is 200～300 meter, some of that is 100 meter even. Based on the abundant data of close well logging, the identification and detail description of micro facies of complex meander belt are authentic established. This article combined modern sedimentary, output investigation with the description of channel geometry and scale to set up the conceptual model of abandoned channel facies. By using well logging curves under close well spacing, this paper interpreted the distribution character, the recognition method of channel facies on the areal and profile, and established a static model for the abandoned channel facies on flooding plain in Daqing Oilfield. Based on this method, the comprehensive prediction of reservoir and the analysis of remaining oil have been conducted. This method has a notable result in high efficiency wells.
2001, 19(3): 405-409.
Abstract:
Jiyang Depression is one of the sub basins in Bohaiwan basin. Carbon dioxide (CO2 pools occur in Yangxing Huagou Pingnan area, the center of Jiyang Depression. Reservoirs of the CO2 pools are the marine carbonate rocks in lower Palaeozoic Era, the lake carbonate rocks and delta sandstone in Eogene System, and the fluvial sandstone in Neogene System. The marine carbonate rock reservoirs are in the north of the area and the reservoir spaces are the structural and solution gaps. The lake carbonate rock reservoirs are in No.4 and 1 sections of Shahejie Formation in Pinfangwang area. The delta sandstone reservoirs, which total thickness are 100m～600m,porosity range from 11.5%～33% and permeability from 6.5×10 -3 m2～83×10-3 m2, are in Shahejie Formation in Gaoqing Pingnan, Lingfanjia and Yangxing area, respectively. The fluvial sandstone reservoirs are widely distributed in Yangxing Huagou Pingnan area. In generally, the sand and mud ratios, porosity and permeability of the fluvial sandstone reservoirs in the north are higher than that in the south of the area. Seals of CO2 pools in Yangxing Huagou Pingnan area are mudstone and compact conglomerate and they all are effective seals. The mudstone seals are mainly distributed in No.3 and 1 sections of Shahejie Formation in Eogene System and upper Guantao Formation and Minghuazheng Formation in Neogene System. The compact conglomerate seals, which permeability are very low, occur in No.4 section on the sub mountain in Balibo of the north of Yangxing Huagou Pingnan area.Comparison of reservoir and seal between CO2 pools and hydrogen gas pools, two kinds of pools are of similar reservoir. And CO2 pools have poor qualitiy seal.
Jiyang Depression is one of the sub basins in Bohaiwan basin. Carbon dioxide (CO2 pools occur in Yangxing Huagou Pingnan area, the center of Jiyang Depression. Reservoirs of the CO2 pools are the marine carbonate rocks in lower Palaeozoic Era, the lake carbonate rocks and delta sandstone in Eogene System, and the fluvial sandstone in Neogene System. The marine carbonate rock reservoirs are in the north of the area and the reservoir spaces are the structural and solution gaps. The lake carbonate rock reservoirs are in No.4 and 1 sections of Shahejie Formation in Pinfangwang area. The delta sandstone reservoirs, which total thickness are 100m～600m,porosity range from 11.5%～33% and permeability from 6.5×10 -3 m2～83×10-3 m2, are in Shahejie Formation in Gaoqing Pingnan, Lingfanjia and Yangxing area, respectively. The fluvial sandstone reservoirs are widely distributed in Yangxing Huagou Pingnan area. In generally, the sand and mud ratios, porosity and permeability of the fluvial sandstone reservoirs in the north are higher than that in the south of the area. Seals of CO2 pools in Yangxing Huagou Pingnan area are mudstone and compact conglomerate and they all are effective seals. The mudstone seals are mainly distributed in No.3 and 1 sections of Shahejie Formation in Eogene System and upper Guantao Formation and Minghuazheng Formation in Neogene System. The compact conglomerate seals, which permeability are very low, occur in No.4 section on the sub mountain in Balibo of the north of Yangxing Huagou Pingnan area.Comparison of reservoir and seal between CO2 pools and hydrogen gas pools, two kinds of pools are of similar reservoir. And CO2 pools have poor qualitiy seal.
2001, 19(3): 415-420.
Abstract:
Dagougu gola-bearing albitite belt,composed of albitite and carbonate rock,occurred as stratiform in the upper part and filled veins in the lower part in the Lechangxia Group Schist,Sinian Period．The albitite usually with banded and massive structure is composed primary of albite(80％±),quartz(1％～15％±),carbonate rock(1％--5％±),rutile(1％±),apatite(1％±)and pyrite with minor tourmnaline and magnetite；the carbonate rock。occurred in the same occurrence as those of albitite,consists predominantly of dolomite(ankerite)(> 75％),calcite(>15％),albite(5％±)with the same minor minerals as those of albitite． Main element compositions of the albitite differ from that of the Lechangxia Group Schist,the former is rich in A12O3。TiO2,Mno,Na2O。P2O5 and poor in Fe2O3,Feo,Mgo,Cao,K2O．The albitite and adjacent I．Lechangxia Group Schist lie in different domains in the major oxides variation diagram including TiO2-A12O3, AL2O3一SiO2,Mgo-Sio,TiO2-SiO2,Feo-Fe2O3,Mgo-Cao and reveal different variation tendency． The albitite has lower REE content,raring from l2．56×10-6to 55．66*10-6with lower La/Yb：1．82～6．42,La/Sm：0．96～2．99,Gd/Yb：O．99-2．71 ratios,negative Eu anomalies and weakly Ce anomalies．Chondrite-normalized patterns of REE in albitite differ from those of the Lechangxia Group Schist． Ccmbined field and geochemical data indicate that the Dagougu gold-bearing stratiform albitite do not represent the normal clastic sedimeents altered by sodium rich fluid．but owe its origin to hydrothermal sedimentation at or below the sediment-wlater interface in alkaline environment．
Dagougu gola-bearing albitite belt,composed of albitite and carbonate rock,occurred as stratiform in the upper part and filled veins in the lower part in the Lechangxia Group Schist,Sinian Period．The albitite usually with banded and massive structure is composed primary of albite(80％±),quartz(1％～15％±),carbonate rock(1％--5％±),rutile(1％±),apatite(1％±)and pyrite with minor tourmnaline and magnetite；the carbonate rock。occurred in the same occurrence as those of albitite,consists predominantly of dolomite(ankerite)(> 75％),calcite(>15％),albite(5％±)with the same minor minerals as those of albitite． Main element compositions of the albitite differ from that of the Lechangxia Group Schist,the former is rich in A12O3。TiO2,Mno,Na2O。P2O5 and poor in Fe2O3,Feo,Mgo,Cao,K2O．The albitite and adjacent I．Lechangxia Group Schist lie in different domains in the major oxides variation diagram including TiO2-A12O3, AL2O3一SiO2,Mgo-Sio,TiO2-SiO2,Feo-Fe2O3,Mgo-Cao and reveal different variation tendency． The albitite has lower REE content,raring from l2．56×10-6to 55．66*10-6with lower La/Yb：1．82～6．42,La/Sm：0．96～2．99,Gd/Yb：O．99-2．71 ratios,negative Eu anomalies and weakly Ce anomalies．Chondrite-normalized patterns of REE in albitite differ from those of the Lechangxia Group Schist． Ccmbined field and geochemical data indicate that the Dagougu gold-bearing stratiform albitite do not represent the normal clastic sedimeents altered by sodium rich fluid．but owe its origin to hydrothermal sedimentation at or below the sediment-wlater interface in alkaline environment．
2001, 19(3): 425-432.
Abstract:
Stalagmites in cave is the most comprehensive and systemetic paleo climatic environmental information contaimed in karst records. The study has shown the environmental changes in cave and at outside of the cave with the indication of the different degree in the composition of stalagmite, texture or structure, sediment or growth laminates, bedding plane structure, growth rate and environmental changes of paleo climate and so on. The reconstruction paleoenvironment by use of the preserved information in stalagmite is one of the popular project for lastest the 20 years. Under the study of the global climatic changes, high resolution dating and the change law of carbon and oxygen isotopic component of stalagmites in cave have made a great contribution to the breakthrough in the field. A large stalagmite with continuous profile of clear annual growth laminae for studying the paleoclimatic changes were found in Dongge cave of Libo area last year.Because the laminae of stalagmite is mainly composed of calcite, they are suitable to be measured by TIMS U series method to get reliable and high resolution ages compatable with other materials such as lake or marine sediments. Therefore, stalagimte may have vast vistas for geochronology study since the middle Pleistocene Epoch. Paleoclimatic information from 163.3 ka B.P. to 91.3ka B.P. have been obtained through TIMS U series dating ages and carbon and oxygen isotopic analysis to No.3 stalagmite from Dongge cave in Libo. The ages and the change of oxygen isotopic records in Libo area can compare with theⅤ and the Ⅵ stages of oxygen isotopic records of the deep sea cores(or sediments). The results shown that the records of climatic change from 163.3ka B.P. to 91.3ka B.P. in this period in Libo area underweth from the cold period to warm and humid period. It coincides with the wave motion of the global paleoclimatic change, in the meantime, the climatic change of the region also exist.
Stalagmites in cave is the most comprehensive and systemetic paleo climatic environmental information contaimed in karst records. The study has shown the environmental changes in cave and at outside of the cave with the indication of the different degree in the composition of stalagmite, texture or structure, sediment or growth laminates, bedding plane structure, growth rate and environmental changes of paleo climate and so on. The reconstruction paleoenvironment by use of the preserved information in stalagmite is one of the popular project for lastest the 20 years. Under the study of the global climatic changes, high resolution dating and the change law of carbon and oxygen isotopic component of stalagmites in cave have made a great contribution to the breakthrough in the field. A large stalagmite with continuous profile of clear annual growth laminae for studying the paleoclimatic changes were found in Dongge cave of Libo area last year.Because the laminae of stalagmite is mainly composed of calcite, they are suitable to be measured by TIMS U series method to get reliable and high resolution ages compatable with other materials such as lake or marine sediments. Therefore, stalagimte may have vast vistas for geochronology study since the middle Pleistocene Epoch. Paleoclimatic information from 163.3 ka B.P. to 91.3ka B.P. have been obtained through TIMS U series dating ages and carbon and oxygen isotopic analysis to No.3 stalagmite from Dongge cave in Libo. The ages and the change of oxygen isotopic records in Libo area can compare with theⅤ and the Ⅵ stages of oxygen isotopic records of the deep sea cores(or sediments). The results shown that the records of climatic change from 163.3ka B.P. to 91.3ka B.P. in this period in Libo area underweth from the cold period to warm and humid period. It coincides with the wave motion of the global paleoclimatic change, in the meantime, the climatic change of the region also exist.
2001, 19(3): 440-443.
Abstract:
Gyrolithes, a kind of vertical dwelling burrow, may be formed by ilaterally symmetrical animals with paired appendages and often had a brackish water origin. Abundant trace fossils of Gyrolithes were occurred in the upper part of Tataaiertage Fm.Lower Silurian of many wells from Central Tarim basin, where the sediments were extensively bioturbated by Gyrolithes animals and contained very rare trace fossils like Beaconites. Based on the sedimentological, geochemical and paleoecological features, Gyrolithes from Lower Silurian of Central Tarim basin is formed in brackish lagoon environment. This kind of trace is generally very sharp walled and unlined, reflecting the stable, cohesive nature of the substrate at the time of colonisation and burrow excavation. It remained open after the tracemaker vacated the burrow, thus allowing material from the succeeding depositional event to passively fill the open structure. If the burrow had been excavated in mud, the domicile would have collapsed upon burrow vacation, unless lined. All these features indicate that Gyrolithes is a kind of firmground controlled trace fossil.
Gyrolithes, a kind of vertical dwelling burrow, may be formed by ilaterally symmetrical animals with paired appendages and often had a brackish water origin. Abundant trace fossils of Gyrolithes were occurred in the upper part of Tataaiertage Fm.Lower Silurian of many wells from Central Tarim basin, where the sediments were extensively bioturbated by Gyrolithes animals and contained very rare trace fossils like Beaconites. Based on the sedimentological, geochemical and paleoecological features, Gyrolithes from Lower Silurian of Central Tarim basin is formed in brackish lagoon environment. This kind of trace is generally very sharp walled and unlined, reflecting the stable, cohesive nature of the substrate at the time of colonisation and burrow excavation. It remained open after the tracemaker vacated the burrow, thus allowing material from the succeeding depositional event to passively fill the open structure. If the burrow had been excavated in mud, the domicile would have collapsed upon burrow vacation, unless lined. All these features indicate that Gyrolithes is a kind of firmground controlled trace fossil.
2001, 19(3): 449-455.
Abstract:
It is important to examine the performance of a laser particle size analyser and understand the discrepancy between it and pipette and sieving methods. In the present study, the results obtained using a Cials 940 L are evaluated and compared with pipette and sieving methods using natural and artificial sediment samples. Two procedures were used to test the reproducibility of Cilas 940 L, which show that the variability of statistical parameters (mean, sorting, skewness and kurtosis) is low,indicating that the reproducibility of Cilas 940 L is satisfactory. According to the measurement of 15 mud samples, the laser sizer underestimates the fraction of clay particles with an efficiency of detection proportional to the clay content determined from pipette analysis. The results obtained with the Cilas 940 L show somewhat greater mean size and lower sorting than the pipette method. The results of measurement on glass particles by Cilas 940 L are in agreement with the sieving method but have larger mean sizes and lower sorting than sieving analysis for natural sediment. Differences in the results between the laser method and pipette/sieving methods may be attributed to the various principles of the methods and the particle property (e.g. non sphericity of particles). For a geologist, it should be realized that there are limitations of modern instruments,and the grain size data obtained by different methods must be utilized and analysed in an appropriate way.
It is important to examine the performance of a laser particle size analyser and understand the discrepancy between it and pipette and sieving methods. In the present study, the results obtained using a Cials 940 L are evaluated and compared with pipette and sieving methods using natural and artificial sediment samples. Two procedures were used to test the reproducibility of Cilas 940 L, which show that the variability of statistical parameters (mean, sorting, skewness and kurtosis) is low,indicating that the reproducibility of Cilas 940 L is satisfactory. According to the measurement of 15 mud samples, the laser sizer underestimates the fraction of clay particles with an efficiency of detection proportional to the clay content determined from pipette analysis. The results obtained with the Cilas 940 L show somewhat greater mean size and lower sorting than the pipette method. The results of measurement on glass particles by Cilas 940 L are in agreement with the sieving method but have larger mean sizes and lower sorting than sieving analysis for natural sediment. Differences in the results between the laser method and pipette/sieving methods may be attributed to the various principles of the methods and the particle property (e.g. non sphericity of particles). For a geologist, it should be realized that there are limitations of modern instruments,and the grain size data obtained by different methods must be utilized and analysed in an appropriate way.
2001, 19(3): 459-464.
Abstract:
Oil migration effect of the western slope, Jinhu Depression of Subei Basin, Eastern China is observed on the base of detailed work of investigating genetic mechanism and source rock of the petroleum. The methods of the study adopted include non hydrocarbon and absolute quantitative analysis of biomarkers and the other kind of the compounds in different fractions by co injection of standard compounds. The main method is emphasized on studying the migration fractionation effect of pyrrolic nitrogen compounds in the oil. The other two kind compounds' migration fractionation effect is also observed, which are dibenzofuran and dibenzothiophene series with the similar molecular structure as the pyrrolic nitrogen compounds. The result indicates that the pyrrolic nitrogen compound in the oil has apparent migration fractionation effects, which infer the oil migration direction of the area is form northeast to southwest, and the Shanghe Sag is the main source cooker of the oil. The migration fractionation effects could also be observed in the other two kind compound series dibenzofuran and dibenzothiophene bearing oxygen and sulfur heteroatom respectively, which make the compounds having strong polarity too. However, their fractionation effects are not apparent as the nitrogenic compound. The migration fractionation effects of the three compounds increase according to the order of dibenzoghiophene, dibenzofuran and nitrogen compounds, which infer the polarity of the three kind compounds increasing according to the order. It is probably the hetroatoms in the compounds determining the chemical characteristics of the compounds. The results also indicate that the absolute quantitative analysis is very useful in study petroleum migration, the migration fractionation effect could be observed from the abundance variation of some high molecular compounds, especially the heterocyclic compounds such as NSO' compounds metioned above.
Oil migration effect of the western slope, Jinhu Depression of Subei Basin, Eastern China is observed on the base of detailed work of investigating genetic mechanism and source rock of the petroleum. The methods of the study adopted include non hydrocarbon and absolute quantitative analysis of biomarkers and the other kind of the compounds in different fractions by co injection of standard compounds. The main method is emphasized on studying the migration fractionation effect of pyrrolic nitrogen compounds in the oil. The other two kind compounds' migration fractionation effect is also observed, which are dibenzofuran and dibenzothiophene series with the similar molecular structure as the pyrrolic nitrogen compounds. The result indicates that the pyrrolic nitrogen compound in the oil has apparent migration fractionation effects, which infer the oil migration direction of the area is form northeast to southwest, and the Shanghe Sag is the main source cooker of the oil. The migration fractionation effects could also be observed in the other two kind compound series dibenzofuran and dibenzothiophene bearing oxygen and sulfur heteroatom respectively, which make the compounds having strong polarity too. However, their fractionation effects are not apparent as the nitrogenic compound. The migration fractionation effects of the three compounds increase according to the order of dibenzoghiophene, dibenzofuran and nitrogen compounds, which infer the polarity of the three kind compounds increasing according to the order. It is probably the hetroatoms in the compounds determining the chemical characteristics of the compounds. The results also indicate that the absolute quantitative analysis is very useful in study petroleum migration, the migration fractionation effect could be observed from the abundance variation of some high molecular compounds, especially the heterocyclic compounds such as NSO' compounds metioned above.
2001, 19(3): 469-473.
Abstract:
Gas chromatography isotope ratio mass spectrometry (GC IRMS) has been widely applied in the various fields of organic geochemistry, e.g. identifying organic source, correlating oil with possible source rocks, and reconstructing paleoenvironment and paleoclimate. The carbon isotopic composition of n alkanes from oils and extracts has played an important role in oil and natural gas geochemistry. Previous studies indicate that the hydrocarbon generation and expulsion has obvious effects on the distribution of n alkanes and other biomarkers, e.g. steranes and terpanes. This paper tries to reveal the characteristics of carbon isotopic composition of n alkanes during hydrocarbon generation and expulsion by determining the δ 13 C values of the n alkanes in the pyrolysates (residual oils and expelled oils). The results indicate that the liquid n alkanes are mainly derived from the primary cracking of kerogen during the early hydrocarbon generation, so,whether in the expelled oils or in the residual oils, their isotopic compositions have no obvious variation (less than 2‰) with increasing temperature, and display a similar distribution. It suggests that they can be used in oil/oil correlation. However, at the peak of hydrocarbon generation, the second cracking of those heavy hydrocarbons formed at the early stage, such as asphaltene, NSO fraction, and n alkanes with high carbon number, makes the remaining n alkanes markedly riched13 C in carbon isotope, especially for the heavily weighed fraction. Significant differences (1 to 4‰) in the carbon isotopic compositions are observed between the n alkanes in the residual oils or the expelled oils generated at this stage and those formed at the former stage. Since thermal maturation has effects on the carbon isotopic compositions of n alkanes due to different generation mechanisms may occur at the different stages, therefore, to explain the significant difference when taking the oil/oil and oil/source correlations, we also need consider thermal maturation other than organic source. The conclusion of heterogeneity should not be made easily. In addition, the experimental results show that the hydrocarbon expulsion has no considerable effect on the carbon isotopic composition of the liquid n alkanes.
Gas chromatography isotope ratio mass spectrometry (GC IRMS) has been widely applied in the various fields of organic geochemistry, e.g. identifying organic source, correlating oil with possible source rocks, and reconstructing paleoenvironment and paleoclimate. The carbon isotopic composition of n alkanes from oils and extracts has played an important role in oil and natural gas geochemistry. Previous studies indicate that the hydrocarbon generation and expulsion has obvious effects on the distribution of n alkanes and other biomarkers, e.g. steranes and terpanes. This paper tries to reveal the characteristics of carbon isotopic composition of n alkanes during hydrocarbon generation and expulsion by determining the δ 13 C values of the n alkanes in the pyrolysates (residual oils and expelled oils). The results indicate that the liquid n alkanes are mainly derived from the primary cracking of kerogen during the early hydrocarbon generation, so,whether in the expelled oils or in the residual oils, their isotopic compositions have no obvious variation (less than 2‰) with increasing temperature, and display a similar distribution. It suggests that they can be used in oil/oil correlation. However, at the peak of hydrocarbon generation, the second cracking of those heavy hydrocarbons formed at the early stage, such as asphaltene, NSO fraction, and n alkanes with high carbon number, makes the remaining n alkanes markedly riched13 C in carbon isotope, especially for the heavily weighed fraction. Significant differences (1 to 4‰) in the carbon isotopic compositions are observed between the n alkanes in the residual oils or the expelled oils generated at this stage and those formed at the former stage. Since thermal maturation has effects on the carbon isotopic compositions of n alkanes due to different generation mechanisms may occur at the different stages, therefore, to explain the significant difference when taking the oil/oil and oil/source correlations, we also need consider thermal maturation other than organic source. The conclusion of heterogeneity should not be made easily. In addition, the experimental results show that the hydrocarbon expulsion has no considerable effect on the carbon isotopic composition of the liquid n alkanes.
2001, 19(3): 481-487.
Abstract:
The evoIution of strontium isotopic composition of originaI seawater is a function of geoIogicaI time，and mainIy controIIed by the gIobaI sea-IeveI changes. The evoIutionaI curves of the strontium isotopic composition of Carboniferous and Permian marine carbonate rocks，Upper Yangtze PIatform is guite consistent with trend of the sea-IeveI changes. This variation curve of the strontium isotope shows the foIIowing facts： 1）The gIobaI sea-IeveI rise is corresponding to the faIIing of strontium isotope. The point of the minimum vaIue of 87 Sr / 86 Sr in the earIy Carboniferous is just the position of maximum fIooding surface for the period of earIy Carboniferous，of which the numeric age is 342 Ma. This key point is just Iocated at the boundary of Tournaisian and Visean，for the Huishui section in Guizhou of Province，which is Iocated at the boundary between Jiusi and Shangsi formation. 2）The Iate Carboniferous is a period of gIobaI sea-IeveI faIIing. 3）The Permian，from the beginning to the end，is a period of gIobaI sea-IeveI rise. During the Iate Permian，we can see that the sea IeveI was rising unceasingIy and the marine water became deepIy in short time. 4）The Iate Permian is provided with the strontium isotopic minimum of marine carbonate rocks throughout the Late PaIaeozoic，representing the gIobaI marine fIooding event. The numeric age of the fIooding is 250 Ma，which nears to the Permian-Triassic boundary. 5）The mass extinction at the boundary of Permian-Triassic is probabIy due to the gIobaI marine fIooding event of Iate Permian.
The evoIution of strontium isotopic composition of originaI seawater is a function of geoIogicaI time，and mainIy controIIed by the gIobaI sea-IeveI changes. The evoIutionaI curves of the strontium isotopic composition of Carboniferous and Permian marine carbonate rocks，Upper Yangtze PIatform is guite consistent with trend of the sea-IeveI changes. This variation curve of the strontium isotope shows the foIIowing facts： 1）The gIobaI sea-IeveI rise is corresponding to the faIIing of strontium isotope. The point of the minimum vaIue of 87 Sr / 86 Sr in the earIy Carboniferous is just the position of maximum fIooding surface for the period of earIy Carboniferous，of which the numeric age is 342 Ma. This key point is just Iocated at the boundary of Tournaisian and Visean，for the Huishui section in Guizhou of Province，which is Iocated at the boundary between Jiusi and Shangsi formation. 2）The Iate Carboniferous is a period of gIobaI sea-IeveI faIIing. 3）The Permian，from the beginning to the end，is a period of gIobaI sea-IeveI rise. During the Iate Permian，we can see that the sea IeveI was rising unceasingIy and the marine water became deepIy in short time. 4）The Iate Permian is provided with the strontium isotopic minimum of marine carbonate rocks throughout the Late PaIaeozoic，representing the gIobaI marine fIooding event. The numeric age of the fIooding is 250 Ma，which nears to the Permian-Triassic boundary. 5）The mass extinction at the boundary of Permian-Triassic is probabIy due to the gIobaI marine fIooding event of Iate Permian.
2001, 19(3): 327-332,356.
Abstract:
The Middle Triassic was the changing turning period of South China from marine sedimentary basin to continental deposits or even erosion. In this paper, South China is subdivided into four sedimentary provinces: Cathaysia sedimentary province, Low Yangtze sedimentary province, Upper Yangtze sedimentary province and Youjiang sedimentary province, among which the distribution and variation of the lithostratigraphic sequences, lithofacies and biotas are summarized. Each sedimentary province has similar stratigraphic sequence and unique lithofacies though the difference between the Anisian and the Ladinian is apparent. In the Anisian, carbonate rocks are mainly on Yangtze block, while clastic sediments are mostly distributed in Cathaysia and Youjiang sedimentary provinces. The mixed sequences of carbonate and clastic rocks mainly occur at the transition areas between the sedimentary provinces. In the Ladinian, carbonate sediments were limited, mainly in Upper Yangtze sedimentary province. Cathaysia, Lower Yangtze and Youjiang provinces were occupied by clastic sediments. In addition, biotas were of distinctive assemblages and associated biotic groups in various lithofacies. In Youjiang province, Daonella group and ammonoids are the most distinctive biota, while Upper Yangtze province is characteristic of widespread Costatoria subgroup, Cathaysia and Lower Yangtze provinces are predominated by Asoella subgroup. So there is a close relationship between the biotic paleoecology and the lithofacies as well as the sedimentary facies in South China during the Middle Triassic. The Cathaysia block and the Lower Yangtze sedimentary province belonged to a single sedimentary paleogeographic unit while the Upper Yangtze and Youjiang sedimentary provinces were another affiliated unit in the Middle Triassic. The paleogeographic pattern of the former was a continent marginal sedimentary basin declining northwestward. From the Anisian to the Ladinian, the sedimentary facies zones migrated northwestward rapidly. The whole region finished the transformation from sea to land in the latest Anisian. In the latter, the Middle Triassic paleogeography was a typical pattern of continental margin deepening from north to south, accompanied by an accordant differentiation of sedimentary facies. From the Anisian to the Ladinian, the enormous shallow carbonate platform, the main body of Upper Yangtze province, became shallower and saltier, and the clastic turbidites, the main body of Youjiang province, gradually expanded over the carbonate platform. Consequently, the Middle Triassic completely records the course of each sedimentary province from sea to land and their relationship, which is important to study the regional tectonics and geological history of South China. There exists a great interrelationship between the biotic paleoecology and the lithofacies as well as the sedimentary facies in South China during the Middle Triassic. The variation of ecological types and the change of biotic composition well show the history of the regional paleogeographic change and the development of sedimentary basin in this region. Cathaysia Lower Yangtze and Upper Yangtze-Youjiang were two separate sedimentary basin and have quite different evolutionary histories, which indicates that they had different dynamics in the transition from sea to land.
The Middle Triassic was the changing turning period of South China from marine sedimentary basin to continental deposits or even erosion. In this paper, South China is subdivided into four sedimentary provinces: Cathaysia sedimentary province, Low Yangtze sedimentary province, Upper Yangtze sedimentary province and Youjiang sedimentary province, among which the distribution and variation of the lithostratigraphic sequences, lithofacies and biotas are summarized. Each sedimentary province has similar stratigraphic sequence and unique lithofacies though the difference between the Anisian and the Ladinian is apparent. In the Anisian, carbonate rocks are mainly on Yangtze block, while clastic sediments are mostly distributed in Cathaysia and Youjiang sedimentary provinces. The mixed sequences of carbonate and clastic rocks mainly occur at the transition areas between the sedimentary provinces. In the Ladinian, carbonate sediments were limited, mainly in Upper Yangtze sedimentary province. Cathaysia, Lower Yangtze and Youjiang provinces were occupied by clastic sediments. In addition, biotas were of distinctive assemblages and associated biotic groups in various lithofacies. In Youjiang province, Daonella group and ammonoids are the most distinctive biota, while Upper Yangtze province is characteristic of widespread Costatoria subgroup, Cathaysia and Lower Yangtze provinces are predominated by Asoella subgroup. So there is a close relationship between the biotic paleoecology and the lithofacies as well as the sedimentary facies in South China during the Middle Triassic. The Cathaysia block and the Lower Yangtze sedimentary province belonged to a single sedimentary paleogeographic unit while the Upper Yangtze and Youjiang sedimentary provinces were another affiliated unit in the Middle Triassic. The paleogeographic pattern of the former was a continent marginal sedimentary basin declining northwestward. From the Anisian to the Ladinian, the sedimentary facies zones migrated northwestward rapidly. The whole region finished the transformation from sea to land in the latest Anisian. In the latter, the Middle Triassic paleogeography was a typical pattern of continental margin deepening from north to south, accompanied by an accordant differentiation of sedimentary facies. From the Anisian to the Ladinian, the enormous shallow carbonate platform, the main body of Upper Yangtze province, became shallower and saltier, and the clastic turbidites, the main body of Youjiang province, gradually expanded over the carbonate platform. Consequently, the Middle Triassic completely records the course of each sedimentary province from sea to land and their relationship, which is important to study the regional tectonics and geological history of South China. There exists a great interrelationship between the biotic paleoecology and the lithofacies as well as the sedimentary facies in South China during the Middle Triassic. The variation of ecological types and the change of biotic composition well show the history of the regional paleogeographic change and the development of sedimentary basin in this region. Cathaysia Lower Yangtze and Upper Yangtze-Youjiang were two separate sedimentary basin and have quite different evolutionary histories, which indicates that they had different dynamics in the transition from sea to land.
2001, 19(3): 340-344.
Abstract:
During Early Permian, the palaeo ocean in East Kunlun and Animaqing area was composed of three depositional regions. They are the back arc basin in the southern slope of East Kunlun, reef island belt from Tuosuo Lake to Huashixia and deep ocean in Animaqing. The reef island belt from Tusuo Lake to Huashixia is mainly composed of massive reef limestone and bioclastic limestone. The back arc basin in the southern slope of East Kunlun was widely scattered by short dimension reef islands or carbonate buildups and relatively deep basins among the reef islands. However, the Animaqing ocean was dominated by deep ocean ooze and radiolarian chert. Carbonate palaeo-seamounts can also be found in Animaqing ocean. Although there are many well developed reefs in the southern slope of East Kunlun, the reef islands and carbonate buildups were distributed irregularly in this area. Carbonate palaeo seamounts in Animaqing ocean are relatively smaller and reef limestone is less developed, but the palaeo seamounts usually range like a string of beads. Basin sediments between the reef islands in the southern slope of East Kunlun are mainly composed of middle thin layer of limestone embedded with black slate, and basin ooze with different color can also be found in some places. Basin sediments in Animaqing ocean is characterized by widely distributed deep ocean ooze. However, blue green ooze can be found more easily in the southern slope of East Kunlun than in Animaqing.
During Early Permian, the palaeo ocean in East Kunlun and Animaqing area was composed of three depositional regions. They are the back arc basin in the southern slope of East Kunlun, reef island belt from Tuosuo Lake to Huashixia and deep ocean in Animaqing. The reef island belt from Tusuo Lake to Huashixia is mainly composed of massive reef limestone and bioclastic limestone. The back arc basin in the southern slope of East Kunlun was widely scattered by short dimension reef islands or carbonate buildups and relatively deep basins among the reef islands. However, the Animaqing ocean was dominated by deep ocean ooze and radiolarian chert. Carbonate palaeo-seamounts can also be found in Animaqing ocean. Although there are many well developed reefs in the southern slope of East Kunlun, the reef islands and carbonate buildups were distributed irregularly in this area. Carbonate palaeo seamounts in Animaqing ocean are relatively smaller and reef limestone is less developed, but the palaeo seamounts usually range like a string of beads. Basin sediments between the reef islands in the southern slope of East Kunlun are mainly composed of middle thin layer of limestone embedded with black slate, and basin ooze with different color can also be found in some places. Basin sediments in Animaqing ocean is characterized by widely distributed deep ocean ooze. However, blue green ooze can be found more easily in the southern slope of East Kunlun than in Animaqing.
2001, 19(3): 351-356.
Abstract:
In the profile of quaternary stratum, near Northern Wudu county seat, Gansu province, there was a set of diamicton, covering by the loess, containing a lot of clastic fragment and partly clay. The landform, in which when it occurred, had been eroded and destroyed, and the cause for this diamicton is unclear. After studying on the diamicton 's characteristics and geological and geomorphologic environment, we identified this diamicton as the rock avalanche deposit. We also found that the deposit had the "sequence" in the vertical section, and divided the typical rock avalanche (containing partly soil) deposit into five "layer sequence": covers or erosive surface (A); colliding separating layer (B); separating sliding layer(C); sliding layer (D); and beneath layer (E). Each layer has special depositional characteristics. The layers indicated that the rock avalanches are interstratified when they are moving and accumulating, because of the differences in dynamical process and depositional process. After studying the soil contain, grain size, gravel fabrication, deposit structure and texture which can show the characteristics of dynamics and movement, in the five deposit section, and studying the geological and geomorphologic environment, we deduce, that, the paleo rock avalanche, in Wudu, occurred in Q31 period and caused by rainstorm. The rock blocks had been detached from the high cliff consisting of metamorphic limestone, in north of Wudou county seat, fall down, separated into piece, and moved to south, and piled up. We also found that the rock avalanche gradually changed into debris flow, because of mixing with a lot of mud and water.
In the profile of quaternary stratum, near Northern Wudu county seat, Gansu province, there was a set of diamicton, covering by the loess, containing a lot of clastic fragment and partly clay. The landform, in which when it occurred, had been eroded and destroyed, and the cause for this diamicton is unclear. After studying on the diamicton 's characteristics and geological and geomorphologic environment, we identified this diamicton as the rock avalanche deposit. We also found that the deposit had the "sequence" in the vertical section, and divided the typical rock avalanche (containing partly soil) deposit into five "layer sequence": covers or erosive surface (A); colliding separating layer (B); separating sliding layer(C); sliding layer (D); and beneath layer (E). Each layer has special depositional characteristics. The layers indicated that the rock avalanches are interstratified when they are moving and accumulating, because of the differences in dynamical process and depositional process. After studying the soil contain, grain size, gravel fabrication, deposit structure and texture which can show the characteristics of dynamics and movement, in the five deposit section, and studying the geological and geomorphologic environment, we deduce, that, the paleo rock avalanche, in Wudu, occurred in Q31 period and caused by rainstorm. The rock blocks had been detached from the high cliff consisting of metamorphic limestone, in north of Wudou county seat, fall down, separated into piece, and moved to south, and piled up. We also found that the rock avalanche gradually changed into debris flow, because of mixing with a lot of mud and water.
2001, 19(3): 363-367.
Abstract:
The paper discusses the features of Early Neocene's sequence stratigraphy and sedimentary system of Qikou sag by employing large mount of materials such as seismic data, logging data, observation results of rock cores and new rule. There are one secondary sequence and six third level sequences of Early Neocene in Qikou sag. Based on studies of controlling factors of sequence development, we conclude that there are two kinds of sequence developed in Qikou sag, which are tectonic sequence and climate sequence. Sequence 1, sequence 3,sequence 4, sequence 5 and sequence 6 are tectonic sequence because the action of the boundary faults controls the space of sedimentation. Sequence 2 is the climate sequence. During the sedimentation of sequence 2, the primary controlling factor on the sequence model is climate and the changes of lake level are not influenced by the uplift of basement rock and the action of boundary faults. During progression period, fan head, mid fan and far end of alluvial fan or fan delta developed on different fault terraces, turbidity fan and gravity flow deposits developed in deeply depressed position. During high stand, wedge and lenses shaped deposits of delta occured on the whole basin. The development of sequence controls the rock's reservoir proporty. The sag's tectonic feature influences the distribution of the sequence and the third level fault has eminent influence on sand bodies. For example, fan head, mid fan and far end of alluvial fan or fan delta developed near the lower part of the faults. These findings could be used to predict the location of sand bodies and have great significances in directing the petroleum exploration.
The paper discusses the features of Early Neocene's sequence stratigraphy and sedimentary system of Qikou sag by employing large mount of materials such as seismic data, logging data, observation results of rock cores and new rule. There are one secondary sequence and six third level sequences of Early Neocene in Qikou sag. Based on studies of controlling factors of sequence development, we conclude that there are two kinds of sequence developed in Qikou sag, which are tectonic sequence and climate sequence. Sequence 1, sequence 3,sequence 4, sequence 5 and sequence 6 are tectonic sequence because the action of the boundary faults controls the space of sedimentation. Sequence 2 is the climate sequence. During the sedimentation of sequence 2, the primary controlling factor on the sequence model is climate and the changes of lake level are not influenced by the uplift of basement rock and the action of boundary faults. During progression period, fan head, mid fan and far end of alluvial fan or fan delta developed on different fault terraces, turbidity fan and gravity flow deposits developed in deeply depressed position. During high stand, wedge and lenses shaped deposits of delta occured on the whole basin. The development of sequence controls the rock's reservoir proporty. The sag's tectonic feature influences the distribution of the sequence and the third level fault has eminent influence on sand bodies. For example, fan head, mid fan and far end of alluvial fan or fan delta developed near the lower part of the faults. These findings could be used to predict the location of sand bodies and have great significances in directing the petroleum exploration.
2001, 19(3): 375-380.
Abstract:
Numerous Meszoic Cenozoic small scale fault basins in China contain extermely thick coal seam with low ash content,but it is difficult to explain the genesis of such kind of coal seam only by in situ coal forming theory.Based on the research of the depositional dynamics of Fushun coal bearing basin,and analysis on coal bodies in main coal seam of Guchengzi Formation,the depositional environment of this kind of coal seam has been interpreted,together with the analysis on sedimentary features of root and trunk fossils within the coal seam. It shows that the basins depositional dynamic process was controlled by the lake level,tectonic subsidence and provenance.The paleoclimate influence the lake level changes,wave storm,function,source type and rate of sediment supply to a certain extent,even the plant type Fushun basins water depth is about 10 m at the basin edge where developed a large amount of water plants.The relative ideal water depth of depocenter may be 30～100 m. Because of syn sedimentary falt network activity,variation of water depth is in the form of sudden change in horizontal water body.Its depositional dynamic system is composed of perturbation lagging dynamic system,hypautochthonous dynamic system and allochthonous dynamic system.Allochthony depositional dynamics acts as the leading factor in lakeside(10 m) slope (10～30 m) basin(30 m) environment.Because Fushun basin is in high speed subsidence with low speed sediment supply during Guchengzi Period,the intraclastic deposition is active,therefore,the extremely thick coal seam can be used as an example of deeper water coal accumulation mode.
Numerous Meszoic Cenozoic small scale fault basins in China contain extermely thick coal seam with low ash content,but it is difficult to explain the genesis of such kind of coal seam only by in situ coal forming theory.Based on the research of the depositional dynamics of Fushun coal bearing basin,and analysis on coal bodies in main coal seam of Guchengzi Formation,the depositional environment of this kind of coal seam has been interpreted,together with the analysis on sedimentary features of root and trunk fossils within the coal seam. It shows that the basins depositional dynamic process was controlled by the lake level,tectonic subsidence and provenance.The paleoclimate influence the lake level changes,wave storm,function,source type and rate of sediment supply to a certain extent,even the plant type Fushun basins water depth is about 10 m at the basin edge where developed a large amount of water plants.The relative ideal water depth of depocenter may be 30～100 m. Because of syn sedimentary falt network activity,variation of water depth is in the form of sudden change in horizontal water body.Its depositional dynamic system is composed of perturbation lagging dynamic system,hypautochthonous dynamic system and allochthonous dynamic system.Allochthony depositional dynamics acts as the leading factor in lakeside(10 m) slope (10～30 m) basin(30 m) environment.Because Fushun basin is in high speed subsidence with low speed sediment supply during Guchengzi Period,the intraclastic deposition is active,therefore,the extremely thick coal seam can be used as an example of deeper water coal accumulation mode.
2001, 19(3): 386-393.
Abstract:
On the basis of the characteristics of architectural elements, sandstone grain size analysis, and fluvial styles of the Upper Members of Guantao Formation in Gudao oilfield, and according to stream features of 16 kinds proposed by Miall, we believe that it belongs to fine grain meandering stream. Among architectural elements, floodplain fines (FF), crevasse splay (CS) and lateral accretion macroform (LA) developed extensively, and levee (LV) and crevasse channel (CR) also developed. The channel sinuosity (P) is more than 2.2. The channel is 100～300 meters wide. The channel meander wavelength is 1 000～1 770 meters. The stream may be adjacent to an estuary, and development of sandstone bodies may be subject to fluctuation of sea level.
On the basis of the characteristics of architectural elements, sandstone grain size analysis, and fluvial styles of the Upper Members of Guantao Formation in Gudao oilfield, and according to stream features of 16 kinds proposed by Miall, we believe that it belongs to fine grain meandering stream. Among architectural elements, floodplain fines (FF), crevasse splay (CS) and lateral accretion macroform (LA) developed extensively, and levee (LV) and crevasse channel (CR) also developed. The channel sinuosity (P) is more than 2.2. The channel is 100～300 meters wide. The channel meander wavelength is 1 000～1 770 meters. The stream may be adjacent to an estuary, and development of sandstone bodies may be subject to fluctuation of sea level.
2001, 19(3): 399-404.
Abstract:
Turpan Hami basin is a Mesozoic Cenozoic compound basin with a complex evolutionary history in the Tianshan orogenic belt.It is a typical continental oil and gas bearing basin of coal derived hydrocarbon.Forming oil bearing sandbodies of pre Jurassic(Triassic) oil and gas accumulation in the southern belt of basin is obviously controlled by sedimentary facies,high geothermal gradient and Indo China movement.The pluvial delta sandbodies distributed in the southern basin are the first set of good oil bearing sandbodies because they lie on a suitable place near oil generation center due to strata uplifting in Indo China movement,and had a dynamic foundation of producing secondary porosity as well as trapping early mature oil which heated by magma bodies and Indo China structural heat event.The second,third, fourth set of oil bearing sandbodies of Jurassic in this area are the braided deltas with south terrigenous sediments and pluvial deltas with north terrigenous sedinents,and they have the characteristics of multiple layers of sandbodies,strongly repeated in the upper and lower part,with fairly good original physical quality.They depend on coal measure source rocks and hydrocarbon migrated southwards in short distance.
Turpan Hami basin is a Mesozoic Cenozoic compound basin with a complex evolutionary history in the Tianshan orogenic belt.It is a typical continental oil and gas bearing basin of coal derived hydrocarbon.Forming oil bearing sandbodies of pre Jurassic(Triassic) oil and gas accumulation in the southern belt of basin is obviously controlled by sedimentary facies,high geothermal gradient and Indo China movement.The pluvial delta sandbodies distributed in the southern basin are the first set of good oil bearing sandbodies because they lie on a suitable place near oil generation center due to strata uplifting in Indo China movement,and had a dynamic foundation of producing secondary porosity as well as trapping early mature oil which heated by magma bodies and Indo China structural heat event.The second,third, fourth set of oil bearing sandbodies of Jurassic in this area are the braided deltas with south terrigenous sediments and pluvial deltas with north terrigenous sedinents,and they have the characteristics of multiple layers of sandbodies,strongly repeated in the upper and lower part,with fairly good original physical quality.They depend on coal measure source rocks and hydrocarbon migrated southwards in short distance.
2001, 19(3): 410-414.
Abstract:
A good deal of attention has been paid to the relation and unity of the tectonic process and sedimentation．It is very obvious that the sedimentary process of the terrestrial basin is controlled by tectogenesis．The sedimentary evolution of the basin is the reflection of the tectonic evolution．The sedimentary process of the terrestrial basin has unique characteristics．(1)The scope of the terrestrial basin is mainly controlled by the fault zones．(2)The regional tectonic cycle obviously controls the sedimentary sequence boundary of the terrestrial basin．The periodicity of tectogenesis causes the periodic change of the sedimentary sequence．(3)The sedimentary model of the terrestrial basin is obviously controlled by the tectonic framework．(4)There are many surprising sedimentary events in sedimentary formation of the terrestrial basin．(5)Owing to the influence of the tectonics,the deformation frequently occurs in the sedimentary deposit．(6)Because the sediments of the terrestrial basin have the short-distance transport,the sediments．have the low mature index．(7)There are more sedimentary centres,more matter-sources,narrow sedimentary facies-zone and the quick facies change in the terrestrial basin． According to the background of the tectonic dynamics．the terrestrial basin can be divided into the extension basin．the compression basin and the shear basin．The three basins differ gready in the sedimentary characteristics．The extension basin is usually directed at rift basin the border of the extension basin is mainly the normal fault or growth fault．The plane shape of the extension is zone-shape．The sedimentary deposit of the extension basin has not strong deformation．the thickness of the sediment on the downthrow wall is greater than that the sediment on the upcast wall．The periodic change of the tectogenesis cause the enlarging or the contract the extension basin． The compression basin is usually directed at the terrestrial foreland basin．The shape of the compression basin is usually dustpan shape．The sedimentary deposit of the compression basin has usually the strong deformation．The sedimentary center of the compression basin moves to the foreland．The evolution of the compression basin has relation to the evolution of theorogenic belt．The developing process of the compression basin is a contract process．The shear basin is usually directed at the strike-slip basin．The plane shape of the shear basin is usually rhombus．The plane constitution is usually a string of beads．The evolution of the shear basin is controlled by the master fault,The developing process of the shear basin is an enlarging process．The sedimentary center of the shear basin moves to the strike of the master fault．
A good deal of attention has been paid to the relation and unity of the tectonic process and sedimentation．It is very obvious that the sedimentary process of the terrestrial basin is controlled by tectogenesis．The sedimentary evolution of the basin is the reflection of the tectonic evolution．The sedimentary process of the terrestrial basin has unique characteristics．(1)The scope of the terrestrial basin is mainly controlled by the fault zones．(2)The regional tectonic cycle obviously controls the sedimentary sequence boundary of the terrestrial basin．The periodicity of tectogenesis causes the periodic change of the sedimentary sequence．(3)The sedimentary model of the terrestrial basin is obviously controlled by the tectonic framework．(4)There are many surprising sedimentary events in sedimentary formation of the terrestrial basin．(5)Owing to the influence of the tectonics,the deformation frequently occurs in the sedimentary deposit．(6)Because the sediments of the terrestrial basin have the short-distance transport,the sediments．have the low mature index．(7)There are more sedimentary centres,more matter-sources,narrow sedimentary facies-zone and the quick facies change in the terrestrial basin． According to the background of the tectonic dynamics．the terrestrial basin can be divided into the extension basin．the compression basin and the shear basin．The three basins differ gready in the sedimentary characteristics．The extension basin is usually directed at rift basin the border of the extension basin is mainly the normal fault or growth fault．The plane shape of the extension is zone-shape．The sedimentary deposit of the extension basin has not strong deformation．the thickness of the sediment on the downthrow wall is greater than that the sediment on the upcast wall．The periodic change of the tectogenesis cause the enlarging or the contract the extension basin． The compression basin is usually directed at the terrestrial foreland basin．The shape of the compression basin is usually dustpan shape．The sedimentary deposit of the compression basin has usually the strong deformation．The sedimentary center of the compression basin moves to the foreland．The evolution of the compression basin has relation to the evolution of theorogenic belt．The developing process of the compression basin is a contract process．The shear basin is usually directed at the strike-slip basin．The plane shape of the shear basin is usually rhombus．The plane constitution is usually a string of beads．The evolution of the shear basin is controlled by the master fault,The developing process of the shear basin is an enlarging process．The sedimentary center of the shear basin moves to the strike of the master fault．
2001, 19(3): 421-424.
Abstract:
In Ziyang area, another gas bearing block in Sichuan Basin has been found in Sinian Dengying Formation. Dengying Formation is a set of carbonate sediments, which includes algal granula dolostone, algal cementation dolostone, micrite dolostone and crystal powder cryptomere dolostone. To the origin of the gas bearing block, there are some different explanations: 1) the result of weathering, meteoric water leaching and later tectonic process; 2) formed by recrystallization and later burial dissolution; 3) generated by dolomitization and dissolution; 4) main control factor being paleokarst. According to the study of seven drills, regional exposure characteristic and tectonic evolution history, it can be concluded that paleokarst existed in Dengying Formation in this area and it took place during Tongwan Movement at the end of Sinian. Paleokarst profile can be divided into three zones: surface, vadose and phreatic dissolution zones. In the vadose and phreatic dissolution zones, four karst forms can be found: dissolved fissure, spelaeum, dissolved hollow and cave. In this area, two karst cycles can be identified in Dengying Formation. The layer which formed by superposition of phreatic dissolution zone in first cycle and vadose zone in second cycle is the position where karst is the most developed, and the maximum vugular pore space is 42.5%. According to study, it can be found that Cambrian silicon phosphorus sediments have the characteristics of compensation sedimentation, which lie on the relic Dengsan and Dengsi section. On the basis of thickness of silicon phosphorus sediments, the paleokarst topography can be reconstructed,i.e: in south west, it is mosor high land; in north east, it is mosor bottom; between them there is a mosor slope. All topography shows from higher in south west to lower in north east. All of these provide the necessary information for the research on reservoir characteristics and forecast prospecting targets.
In Ziyang area, another gas bearing block in Sichuan Basin has been found in Sinian Dengying Formation. Dengying Formation is a set of carbonate sediments, which includes algal granula dolostone, algal cementation dolostone, micrite dolostone and crystal powder cryptomere dolostone. To the origin of the gas bearing block, there are some different explanations: 1) the result of weathering, meteoric water leaching and later tectonic process; 2) formed by recrystallization and later burial dissolution; 3) generated by dolomitization and dissolution; 4) main control factor being paleokarst. According to the study of seven drills, regional exposure characteristic and tectonic evolution history, it can be concluded that paleokarst existed in Dengying Formation in this area and it took place during Tongwan Movement at the end of Sinian. Paleokarst profile can be divided into three zones: surface, vadose and phreatic dissolution zones. In the vadose and phreatic dissolution zones, four karst forms can be found: dissolved fissure, spelaeum, dissolved hollow and cave. In this area, two karst cycles can be identified in Dengying Formation. The layer which formed by superposition of phreatic dissolution zone in first cycle and vadose zone in second cycle is the position where karst is the most developed, and the maximum vugular pore space is 42.5%. According to study, it can be found that Cambrian silicon phosphorus sediments have the characteristics of compensation sedimentation, which lie on the relic Dengsan and Dengsi section. On the basis of thickness of silicon phosphorus sediments, the paleokarst topography can be reconstructed,i.e: in south west, it is mosor high land; in north east, it is mosor bottom; between them there is a mosor slope. All topography shows from higher in south west to lower in north east. All of these provide the necessary information for the research on reservoir characteristics and forecast prospecting targets.
2001, 19(3): 433-439.
Abstract:
By remote sensing technique, we found four vortex structures,including the vortex structure of the west Qilian mountain, Saishenteng mountain vortex structure of the north margin of Qaidam,Qimantage mountain arcuate shear structure of the southwest of Qaidam and big scale vortex structure of the east of Qilian mountain. We analyzed geodynamic mechanism of these vortex structure formation. As for the genesis of the vortex structure, many people have discussed it before. Li Siguang studied its forming mechanism from the change of earth spinning velocity. We believe that it was the result of the long range effect of structure active stress of plate margin affected intraplate. From the early research achievements in the region and map of China satellite image (1∶2,500,000), forming present tectonic framework of the northeast of Qinghai Tibet plateau stems from three forces. Thefirst is that Indian plate underthrusts to the north, and collides Eurasian plate, and pushes the south of Eurasian plate by big M shape since the late Cretaceous; the second is that obstruction of Siberian plate intensely shifting to the south, and relative Monglian arc pushing Indian plate since Cenozoic; the third is that obstruction of Erduosi block when Qinghai Tibet plateau pushing to the east. The first is the main among three forces. The three together caused the northeast of Qinghai Tibet plateau into the large compresso stress field. By further research, late Cretaceous Tertiary principal stress is about SN, which caused a series of NW right lateral strike slip faults in the north of Qinghai Tibet plateau. When mass between two NW right lateral strike slip faults moved to the west, it existed left lateral tendency; when encountering obstruction of Tarim block, it further rotated to the left,that is the reason that forming a series of vortex structures of cyclic plane rotating to the right, such as the vortex structure of the west Qilian mountain, Saishenteng mountain vortex structure of the north margin of Qaidam and Qimantage mountain arcuate shear structure of the southwest of Qaidam. Since Pliocene, main stress turned to NNE NE. Affected by change of regional stress field, Arjin fault was intensely left lateral and lead to the north of the whole Qinghai Tibet plateau escaping to the east, whose results were that forming rotation of cyclic plane anti clockwise, when Qinghai Tibet plateau escaping to the east and Erduosi block obstructing it. Present intensely active big scale vortex structure is the evidence of the kinetic process in the east of Qilian. We also analyzed the relation of these vortex structure with oil and gas distribution. Generally speaking, twisted anticline belts emerge at the end of the twisted vortex structures, whose types of oil and gas reservoir are main anticline reservoir. In the head of vortex structure, there exists the most intense shear stress, which appears intense tenso shear stress area in the outer of head and intense compresso shear stress area in the inner. The former leads to tenso shear stress fault and relative tension crack which formed fault block or structural fracture reservoirs, and the latter leads to compresso shear fault block, which formed complicated fault block reservoirs. For the condition of oil and gas migration and congregation, the positions of stress concentration or strength, such as the nuclear column of vortex structure or convergent position of broom shape structure, are advantageous for forming deep oil generating whirl structures, and disadvantageous for congregation of oil and gas. But the positions of the end of vortex structures or scattering part of broom shape structure, are advantageous for forming diagonal shear anticline and the pointing position of oil and gas migration and congregation. This paper pointed out that the theories that Tapponnier put forward "strike slip line field" and structure escaping" had two distinct insufficience and at the same time, our findings and studies are supplememt to these theories.We also pointed out
By remote sensing technique, we found four vortex structures,including the vortex structure of the west Qilian mountain, Saishenteng mountain vortex structure of the north margin of Qaidam,Qimantage mountain arcuate shear structure of the southwest of Qaidam and big scale vortex structure of the east of Qilian mountain. We analyzed geodynamic mechanism of these vortex structure formation. As for the genesis of the vortex structure, many people have discussed it before. Li Siguang studied its forming mechanism from the change of earth spinning velocity. We believe that it was the result of the long range effect of structure active stress of plate margin affected intraplate. From the early research achievements in the region and map of China satellite image (1∶2,500,000), forming present tectonic framework of the northeast of Qinghai Tibet plateau stems from three forces. Thefirst is that Indian plate underthrusts to the north, and collides Eurasian plate, and pushes the south of Eurasian plate by big M shape since the late Cretaceous; the second is that obstruction of Siberian plate intensely shifting to the south, and relative Monglian arc pushing Indian plate since Cenozoic; the third is that obstruction of Erduosi block when Qinghai Tibet plateau pushing to the east. The first is the main among three forces. The three together caused the northeast of Qinghai Tibet plateau into the large compresso stress field. By further research, late Cretaceous Tertiary principal stress is about SN, which caused a series of NW right lateral strike slip faults in the north of Qinghai Tibet plateau. When mass between two NW right lateral strike slip faults moved to the west, it existed left lateral tendency; when encountering obstruction of Tarim block, it further rotated to the left,that is the reason that forming a series of vortex structures of cyclic plane rotating to the right, such as the vortex structure of the west Qilian mountain, Saishenteng mountain vortex structure of the north margin of Qaidam and Qimantage mountain arcuate shear structure of the southwest of Qaidam. Since Pliocene, main stress turned to NNE NE. Affected by change of regional stress field, Arjin fault was intensely left lateral and lead to the north of the whole Qinghai Tibet plateau escaping to the east, whose results were that forming rotation of cyclic plane anti clockwise, when Qinghai Tibet plateau escaping to the east and Erduosi block obstructing it. Present intensely active big scale vortex structure is the evidence of the kinetic process in the east of Qilian. We also analyzed the relation of these vortex structure with oil and gas distribution. Generally speaking, twisted anticline belts emerge at the end of the twisted vortex structures, whose types of oil and gas reservoir are main anticline reservoir. In the head of vortex structure, there exists the most intense shear stress, which appears intense tenso shear stress area in the outer of head and intense compresso shear stress area in the inner. The former leads to tenso shear stress fault and relative tension crack which formed fault block or structural fracture reservoirs, and the latter leads to compresso shear fault block, which formed complicated fault block reservoirs. For the condition of oil and gas migration and congregation, the positions of stress concentration or strength, such as the nuclear column of vortex structure or convergent position of broom shape structure, are advantageous for forming deep oil generating whirl structures, and disadvantageous for congregation of oil and gas. But the positions of the end of vortex structures or scattering part of broom shape structure, are advantageous for forming diagonal shear anticline and the pointing position of oil and gas migration and congregation. This paper pointed out that the theories that Tapponnier put forward "strike slip line field" and structure escaping" had two distinct insufficience and at the same time, our findings and studies are supplememt to these theories.We also pointed out
2001, 19(3): 444-448.
Abstract:
Length slow chalcedony (LSC) was commonly used as an indicator of evaporitional environments. LSC was also distributed widely in the chrysanthemum stone, the pseudomorph of a kind of nodular celestite, from the Permian Chihsia Formation of South China. A number of lines of evidence indicated the Chihsia Formation was accumulated in a shallow carbonate platform with normal salinity. Based on microscopic observation, a comprehensive replacement succession has been established for the celestite pseudomorph as: celestite(fine-grained cloudy calcite(LSC) (Fig.Ⅰ B, C, D)(clear granular calcite(euhedral calcite crystal (in LSC) (Fig.Ⅰ B)(clear calcite (Fig.Ⅰ C). The original celestite has also been replaced directly by LSC at places. The latest generation of coarse calcite is related to calcite vein (Fig.Ⅰ C). Electronic microprobe analysis on the replacement calcites (Table 1) shows higher magnesium content in the replacement calcites of early phase ( including fine grained cloudy calcite and clear granular calcite) than those of later phase, indicating a magnesium rich diagenetic environment. In addition, tiny celestite detected by electronic scanning microscope in the replacement calcites of early phase and strontianite in the replacement calcite of later phase indicate the geochemical compositional transition of diagenetic fluids from sulfate rich to carbonate rich. The LSC was thus formed in a fluid rich in sulfate and magnesium, agreeing well with reported cases from evaporitional and non evaporitional environments. The possibility of evaporitional sedimentary environments or saline diagenetic conditions favoring the formation of LSC, thus, was excluded for the Chihsian LSC. The LSC should not be used, by itself, as a reliable indicator of evaporitional environment of deposition.
Length slow chalcedony (LSC) was commonly used as an indicator of evaporitional environments. LSC was also distributed widely in the chrysanthemum stone, the pseudomorph of a kind of nodular celestite, from the Permian Chihsia Formation of South China. A number of lines of evidence indicated the Chihsia Formation was accumulated in a shallow carbonate platform with normal salinity. Based on microscopic observation, a comprehensive replacement succession has been established for the celestite pseudomorph as: celestite(fine-grained cloudy calcite(LSC) (Fig.Ⅰ B, C, D)(clear granular calcite(euhedral calcite crystal (in LSC) (Fig.Ⅰ B)(clear calcite (Fig.Ⅰ C). The original celestite has also been replaced directly by LSC at places. The latest generation of coarse calcite is related to calcite vein (Fig.Ⅰ C). Electronic microprobe analysis on the replacement calcites (Table 1) shows higher magnesium content in the replacement calcites of early phase ( including fine grained cloudy calcite and clear granular calcite) than those of later phase, indicating a magnesium rich diagenetic environment. In addition, tiny celestite detected by electronic scanning microscope in the replacement calcites of early phase and strontianite in the replacement calcite of later phase indicate the geochemical compositional transition of diagenetic fluids from sulfate rich to carbonate rich. The LSC was thus formed in a fluid rich in sulfate and magnesium, agreeing well with reported cases from evaporitional and non evaporitional environments. The possibility of evaporitional sedimentary environments or saline diagenetic conditions favoring the formation of LSC, thus, was excluded for the Chihsian LSC. The LSC should not be used, by itself, as a reliable indicator of evaporitional environment of deposition.
2001, 19(3): 456-458,473.
Abstract:
A common problem in single grain fission track analysis by the external method is the detection of component ages when a sample contains grain with several different true ages．Further analysis is required if the ages failed to pass the x2 test．This paper introduces the maximum likelihood method for the estimatida of proportions and agesd age components．The method is applied to three core samples from Subei basin．The 144 single grain ages from these samples failed to pass the x2 test and our analysis yields two true age components for these grains(70 Ma and 167 Ma)．This result shows that there exist two different provenances for the sedimemts from Subei basin,which is in Line with the previous sedimentological studies．
A common problem in single grain fission track analysis by the external method is the detection of component ages when a sample contains grain with several different true ages．Further analysis is required if the ages failed to pass the x2 test．This paper introduces the maximum likelihood method for the estimatida of proportions and agesd age components．The method is applied to three core samples from Subei basin．The 144 single grain ages from these samples failed to pass the x2 test and our analysis yields two true age components for these grains(70 Ma and 167 Ma)．This result shows that there exist two different provenances for the sedimemts from Subei basin,which is in Line with the previous sedimentological studies．
2001, 19(3): 465-468.
Abstract:
Through the thermal simulation on original coal rocks in Jurassic system and the coal with different mediums from 250 ℃ to 550 ℃, with a stepwise heating stage of 50 ℃,the characteristics of their gaseous and liquid products are systematically analyzed. The result shows that the process of coal generation hydrocarbon is comprehensive and complicated. Oil and gas generated from the coal rock is related to its environment,e.g.the water and clayminerals can help this process.The yielding rate of gas products is increased with the rising temperature.Different mediums added in the simulation experiment can effectively reduce the temperature of hydrocarbon generation,and they are especially helpful to liquid hydrocarbon generation.
Through the thermal simulation on original coal rocks in Jurassic system and the coal with different mediums from 250 ℃ to 550 ℃, with a stepwise heating stage of 50 ℃,the characteristics of their gaseous and liquid products are systematically analyzed. The result shows that the process of coal generation hydrocarbon is comprehensive and complicated. Oil and gas generated from the coal rock is related to its environment,e.g.the water and clayminerals can help this process.The yielding rate of gas products is increased with the rising temperature.Different mediums added in the simulation experiment can effectively reduce the temperature of hydrocarbon generation,and they are especially helpful to liquid hydrocarbon generation.
2001, 19(3): 474-480.
Abstract:
In this paper ocurrence and distribution patterns are presented of isoprenoid and straight chain alcohols in twenty three exposed rocks from the Eocene Green River Formation at the Trail Dugway and the Hiawatha Creek sections. The Trail Dugway section of the Laney Shale Member was deposited in the center of a shallow, hydrologically closed, alkaline to highly saline lake under semi humid to semi arid climatic conditions. This sediment contains alginite rich organic matter in high concentrations. The Hiawatha Creek section of the Luman Tongue Member, representing the lake center, shoreline and lake plain facies, was accumulated in a hydrologically open freshwater lake under humid climatic conditions. Both sections are located in the Washikie Basin, Wyoming, USA. Abundant isoprenoid alcohols with carbon number from 11 to 20 were dectected to be of diversity of isomers in all samples. Straight chain alcohols range from 10 to 33 with the hydroxyl group at every theoretically possible positions. The concenration of primary alcohols is low. The results show that the organic matter of the Green River Formation suffered two times from biodegradation, during the sedimentation and after the uplift, respectively. While primary alcohols show a dominant biogenic origin, the mid chain alcohols evidence the second biodegradation of alkanes after the sediments were uplifted to the present position. The notably high Oxygen Indices of the Green River Oil Shale is attributed to the second biodegradation. The distribution patterns of mid chain alcohols are related to the input of organic materials, sedimentary environments, and the degree of the first biodegradation. The mid chain alcohols of Laney Shale sediments are dominated by short chain components, which is consistent with the semi arid climate with insignificant terrestrial run off. On the other hand, a significant proportion of long chain constituents in the Luman Tongue section indicates that abundant higher plant material was swept into the lake during times of more humid climatic conditions. Data reveal that the saline sedimentary environment of Laney Shale is more favourable for preservation of organic matter from biodegradation than that of the freshwater Luman Tongue.
In this paper ocurrence and distribution patterns are presented of isoprenoid and straight chain alcohols in twenty three exposed rocks from the Eocene Green River Formation at the Trail Dugway and the Hiawatha Creek sections. The Trail Dugway section of the Laney Shale Member was deposited in the center of a shallow, hydrologically closed, alkaline to highly saline lake under semi humid to semi arid climatic conditions. This sediment contains alginite rich organic matter in high concentrations. The Hiawatha Creek section of the Luman Tongue Member, representing the lake center, shoreline and lake plain facies, was accumulated in a hydrologically open freshwater lake under humid climatic conditions. Both sections are located in the Washikie Basin, Wyoming, USA. Abundant isoprenoid alcohols with carbon number from 11 to 20 were dectected to be of diversity of isomers in all samples. Straight chain alcohols range from 10 to 33 with the hydroxyl group at every theoretically possible positions. The concenration of primary alcohols is low. The results show that the organic matter of the Green River Formation suffered two times from biodegradation, during the sedimentation and after the uplift, respectively. While primary alcohols show a dominant biogenic origin, the mid chain alcohols evidence the second biodegradation of alkanes after the sediments were uplifted to the present position. The notably high Oxygen Indices of the Green River Oil Shale is attributed to the second biodegradation. The distribution patterns of mid chain alcohols are related to the input of organic materials, sedimentary environments, and the degree of the first biodegradation. The mid chain alcohols of Laney Shale sediments are dominated by short chain components, which is consistent with the semi arid climate with insignificant terrestrial run off. On the other hand, a significant proportion of long chain constituents in the Luman Tongue section indicates that abundant higher plant material was swept into the lake during times of more humid climatic conditions. Data reveal that the saline sedimentary environment of Laney Shale is more favourable for preservation of organic matter from biodegradation than that of the freshwater Luman Tongue.
