1994 Vol. 12, No. 2
column
Display Method:
1994, 12(2): 1-9.
Abstract:
Deposits of carbonate gravity flows on the western margin of Lower Triassic Sichuan bsain may be divided into two parts : debris current and turbidity current. Debris current deposits mainly consist of four kinds of calcirudites with 1. horizontal structure ( type A ),2. graded structure ( type B ),3. disorder fabric (type C),4. matrix supported (type D). Turbidity current deposits are composed of 1. calcarenite for low density current, 2. containcalcirudite calcarenite for high dentity current. Distribution frequency curves of carbonate gravity flow deposits may be classified into four groups. It's importantly disscured differing from curves of debris and turibidity current and varying with their characteristic parameters. Assocaition sequences of gravity flow sediments may show origin and evolution of gravity flow deposits. The association sequences are as follows:1. association with debris flow deposits and micritic limestone in half-deep water environment. 2. association with cohesive debris current(type D) and turbulent debris current(type A B C). 3. association with debris current and turbidity current deposits. 4. complex association with calcilutite-debris current-turbidity current-calcilutite deposits. 1t' s studied that paleo-slope is along northeast-southwest. It dipsfo the is southeast. direction of gravity flow is from northwest to southeast. Its slope angle is about 2-9. Gravity flow deposits have linear distribution. It' s non-water channel gravity flow deposits controlled by a marginal growth fault on the background of plateform geosyncline.
Deposits of carbonate gravity flows on the western margin of Lower Triassic Sichuan bsain may be divided into two parts : debris current and turbidity current. Debris current deposits mainly consist of four kinds of calcirudites with 1. horizontal structure ( type A ),2. graded structure ( type B ),3. disorder fabric (type C),4. matrix supported (type D). Turbidity current deposits are composed of 1. calcarenite for low density current, 2. containcalcirudite calcarenite for high dentity current. Distribution frequency curves of carbonate gravity flow deposits may be classified into four groups. It's importantly disscured differing from curves of debris and turibidity current and varying with their characteristic parameters. Assocaition sequences of gravity flow sediments may show origin and evolution of gravity flow deposits. The association sequences are as follows:1. association with debris flow deposits and micritic limestone in half-deep water environment. 2. association with cohesive debris current(type D) and turbulent debris current(type A B C). 3. association with debris current and turbidity current deposits. 4. complex association with calcilutite-debris current-turbidity current-calcilutite deposits. 1t' s studied that paleo-slope is along northeast-southwest. It dipsfo the is southeast. direction of gravity flow is from northwest to southeast. Its slope angle is about 2-9. Gravity flow deposits have linear distribution. It' s non-water channel gravity flow deposits controlled by a marginal growth fault on the background of plateform geosyncline.
Sedimentary Characteristics and Models of the Beach-bar Reservoirs in Faulted down Lacustrine Basins
1994, 12(2): 20-28.
Abstract:
There are many kinds of depositional systems developed in Tertiary faulted-down lacustrine basins of East China, of which beach-bar reservoir has been stressed in recent years because of its close relation with hydrocarbon occurrence. The characteristics of the lithology,grain size,sedimentary structure and sequence, logging and seismic reflection, and distribution for both sandy beach-bar and biological grain beach-bar reservoirs have been demonstrated in faulted-down lacustrine basins of East China through comprehensive use of geological, logging and seismic reflection data. According to their location and sedimentary features, the beach-bar in Tertiary faulted-down lacustrine basins may be divided into four types,i. e. the beach-bar in lake shoreline corner,the beach-bar on subaqueous ancient uplift, the beach-bar by the short-axis delta,and open shallow lake beach-bar. ALso,their sedimentary models have been developed.These beach-bars distribute regularly at the gentle slope of a lacustrine basin through the basin evolution. The practice for oil-gas exploration has indicated the beach-bar on subaqueous ancient uplift and open shallow lake beach-bar possess the ability to accumulate oil-gas,and have become importants target for hydrocarbon exploration.
There are many kinds of depositional systems developed in Tertiary faulted-down lacustrine basins of East China, of which beach-bar reservoir has been stressed in recent years because of its close relation with hydrocarbon occurrence. The characteristics of the lithology,grain size,sedimentary structure and sequence, logging and seismic reflection, and distribution for both sandy beach-bar and biological grain beach-bar reservoirs have been demonstrated in faulted-down lacustrine basins of East China through comprehensive use of geological, logging and seismic reflection data. According to their location and sedimentary features, the beach-bar in Tertiary faulted-down lacustrine basins may be divided into four types,i. e. the beach-bar in lake shoreline corner,the beach-bar on subaqueous ancient uplift, the beach-bar by the short-axis delta,and open shallow lake beach-bar. ALso,their sedimentary models have been developed.These beach-bars distribute regularly at the gentle slope of a lacustrine basin through the basin evolution. The practice for oil-gas exploration has indicated the beach-bar on subaqueous ancient uplift and open shallow lake beach-bar possess the ability to accumulate oil-gas,and have become importants target for hydrocarbon exploration.
1994, 12(2): 37-44.
Abstract:
The sedimentation simulating experiment of the Formation and development of delta was Conducted in a Flume that is 6 m long,4. 5 m wide and 0. 8m high. in Department of Earth Resources Colorado. Sate Uriversity.The Parameters of discharge,quantity of contained sand and granulometric composition were kept unchangeable,not including the parameter of the height of the lake's level. The experiment has three main steps Ⅰ. Fixing the altitude of the Lake' s level;Ⅱ.Gradually lowering the altitude of the lake's level;Ⅲ.Gradually raising the altitude of the lake's level. We had observed how the channel was changed and the delta was formed after each step the delta's geometry and thickness of sand body were measured and sand samples were collected. The main results of our experiment are as follows: 1. We Put forward new viewpoint on formation of lobate delta,which had been considered that the formation of lobate was reformed by wave from birdfoot delta. The Experiment excludes wave action.The formation and development of lobate and birdfoot delta were controlled by the lake bottom slope is 8% lobate deltas slope at a constant discharge. Sand contents are unchangeable when can the river mouth gradually progrades.only be formed at the beginning. As the lake level is lowered,Sediments aggrade the lake bottom gradually. The gradient of the lake slope area is decreased. An embryonic form of birdfoot delta began to form. When the front of delta developed onto the lake bottom. The Shape of birdfoot delta became more obvious.Transformation of a lobate delta into a birdfoot delta was accelerated by lowering the lake level. A lobate delta remained on the lake slope when take level kept at 42cm and the experiment run for 12 hours. As the front of delta entered the lake bottom and lake level fall down from 42cm to 40cm at last to 39cm. Water running for oNy 5 hours created the embryonic form of birdfoot delta.we have been determined that a bottomslope of 2 0 0 (108' 45") is necessary for formation of a birdfoot delta 2. When lake level was raised from 37cm to 42cm geological action after stage if made the bottom slope gentle and a birdfoot delta kept developing at the beginning and the shape was obvious. later on it became less obvious, the reason for this change is that water entered the channel that had formed earlier and the development of the delta was limited. 3. To distinguish lobate and birdfoot delta other than by shape. the ratio of width to thickness of a deltas sand body is important. The ratio for lobate delte is less than 58,1. but birdfoot deltas is greater than 72,1. This has important significance to petroleum and gas explortion 4. This experiment has proved signifcant data for setting up the experimental equipment for simulation of large-scale lake basin sedimentatio. For example,the river channel is sixteen times largr and the river is thirteen times larger than the original sizes The length to width ratio of birdfoot delta is 2m:2. 28m i. e. 0. 88:1, it's nearly 1:1. 5. The probability curves and grain.size parameters obtabined from grain size analyses of the conected sand samples have shown satisfactory rasults in studing microfacies of point bar and terraces,and analgzing the differences of their hydrodynamic conditions.
The sedimentation simulating experiment of the Formation and development of delta was Conducted in a Flume that is 6 m long,4. 5 m wide and 0. 8m high. in Department of Earth Resources Colorado. Sate Uriversity.The Parameters of discharge,quantity of contained sand and granulometric composition were kept unchangeable,not including the parameter of the height of the lake's level. The experiment has three main steps Ⅰ. Fixing the altitude of the Lake' s level;Ⅱ.Gradually lowering the altitude of the lake's level;Ⅲ.Gradually raising the altitude of the lake's level. We had observed how the channel was changed and the delta was formed after each step the delta's geometry and thickness of sand body were measured and sand samples were collected. The main results of our experiment are as follows: 1. We Put forward new viewpoint on formation of lobate delta,which had been considered that the formation of lobate was reformed by wave from birdfoot delta. The Experiment excludes wave action.The formation and development of lobate and birdfoot delta were controlled by the lake bottom slope is 8% lobate deltas slope at a constant discharge. Sand contents are unchangeable when can the river mouth gradually progrades.only be formed at the beginning. As the lake level is lowered,Sediments aggrade the lake bottom gradually. The gradient of the lake slope area is decreased. An embryonic form of birdfoot delta began to form. When the front of delta developed onto the lake bottom. The Shape of birdfoot delta became more obvious.Transformation of a lobate delta into a birdfoot delta was accelerated by lowering the lake level. A lobate delta remained on the lake slope when take level kept at 42cm and the experiment run for 12 hours. As the front of delta entered the lake bottom and lake level fall down from 42cm to 40cm at last to 39cm. Water running for oNy 5 hours created the embryonic form of birdfoot delta.we have been determined that a bottomslope of 2 0 0 (108' 45") is necessary for formation of a birdfoot delta 2. When lake level was raised from 37cm to 42cm geological action after stage if made the bottom slope gentle and a birdfoot delta kept developing at the beginning and the shape was obvious. later on it became less obvious, the reason for this change is that water entered the channel that had formed earlier and the development of the delta was limited. 3. To distinguish lobate and birdfoot delta other than by shape. the ratio of width to thickness of a deltas sand body is important. The ratio for lobate delte is less than 58,1. but birdfoot deltas is greater than 72,1. This has important significance to petroleum and gas explortion 4. This experiment has proved signifcant data for setting up the experimental equipment for simulation of large-scale lake basin sedimentatio. For example,the river channel is sixteen times largr and the river is thirteen times larger than the original sizes The length to width ratio of birdfoot delta is 2m:2. 28m i. e. 0. 88:1, it's nearly 1:1. 5. The probability curves and grain.size parameters obtabined from grain size analyses of the conected sand samples have shown satisfactory rasults in studing microfacies of point bar and terraces,and analgzing the differences of their hydrodynamic conditions.
1994, 12(2): 54-62.
Abstract:
Being influenced by Landei Fracture of Triassic in Lunnan area,the elevations in the both sides on the fracture are large enough to make the alluvial fan to enter directly the lacustrine basin and to form the fan delta group deposition. The fan deltaic body can be divided into three subfacies, named fan delta plain, fan delta front and pro-fan delta. Subaquous distributary channel sand bodies in the fan delta front are mast important reservoir of oil and gas. The developing area of reseroir is located at SangTamu Horse Belt and the southern ppart. The kinds of reseroir rock are maiNy fine-coarse grained lithic sandstone with lower maturity of the mineral and texture, containning quarts 15 ~6 0%, feldspar 10~25%, rockclast 35~75%. The most important reservoir space is secondary solution pore,including intergranular solution pore, intraparticalar solution pore,oversize pore,cement-dissolved pore,secondly micro-pore, primary pore and fissures. The Triassic reservoir are characterized by deep burial,high porosity and good permeability,burial depth 4200-r5400m,porosity of 15-28. 45%, permeability of 10~4317. 9 X 10-3μm2. Finally the origin of high porosity and good permeability of Triassic reservoir is discussed under such a burial depthi: 1. Coarse grain reservoir sediments;2. Usually less than 5%of clay content; 3. With thick mudstone (12~175m)between sandbeds;4. Increasing reservoir space because of the clastic grain dissolved by organic and inorganic acids;5. Most kaolinite is of porphyritic texture,so it is not easy for them to fill the pore and throat;6. Lower geothermal gradient and deep burial in high speed and short period, etc.
Being influenced by Landei Fracture of Triassic in Lunnan area,the elevations in the both sides on the fracture are large enough to make the alluvial fan to enter directly the lacustrine basin and to form the fan delta group deposition. The fan deltaic body can be divided into three subfacies, named fan delta plain, fan delta front and pro-fan delta. Subaquous distributary channel sand bodies in the fan delta front are mast important reservoir of oil and gas. The developing area of reseroir is located at SangTamu Horse Belt and the southern ppart. The kinds of reseroir rock are maiNy fine-coarse grained lithic sandstone with lower maturity of the mineral and texture, containning quarts 15 ~6 0%, feldspar 10~25%, rockclast 35~75%. The most important reservoir space is secondary solution pore,including intergranular solution pore, intraparticalar solution pore,oversize pore,cement-dissolved pore,secondly micro-pore, primary pore and fissures. The Triassic reservoir are characterized by deep burial,high porosity and good permeability,burial depth 4200-r5400m,porosity of 15-28. 45%, permeability of 10~4317. 9 X 10-3μm2. Finally the origin of high porosity and good permeability of Triassic reservoir is discussed under such a burial depthi: 1. Coarse grain reservoir sediments;2. Usually less than 5%of clay content; 3. With thick mudstone (12~175m)between sandbeds;4. Increasing reservoir space because of the clastic grain dissolved by organic and inorganic acids;5. Most kaolinite is of porphyritic texture,so it is not easy for them to fill the pore and throat;6. Lower geothermal gradient and deep burial in high speed and short period, etc.
1994, 12(2): 72-76.
Abstract:
Abundant finely laminated algal stromatolitic dolomites occur in Wimishan Formation (Jixian System,Middle 1?roterozoic)of the Ming Tombs I?istrict,lieijing,China,which are formed in subtidal environments just above normal wave base. The finely laminated algal stromatolitic dolomites contain a lot of rudite bodies which are autochthonous storm deposits in origin. The characters of these sedimentary rudite bodies are as follows,(1)Rudites- a type of intraclasts-are same as host rocks (finely laminated stromatolitic dolomites) in composition. Each rudite is tens of cm in length and width, but is 1~2 cm or less in thickness, which can be also called flakstone, and has no rounding and little matrix. (2)Rudite bodies are lenticular shaped,thin out in three dimension space,and are 10~50 cm in thickness. ( 3 ) Rudites are radiating arranged or imbricated. (9)Abruptly or gradually contacted with host rocks latterally, sometimes both sides are gradual contacted,or both are abrupt, but sometimes one side gradual while another side abrupt contacted. These lenticular bodies are too small and too disorderly to proposed that they are formed by any normal currents,and can't be caused by normal waves, therefore, it would be formed by some suddenly, high-energy waves-i. e. storm waves. On the way to land,storm waves broken partly consolidated sediments on the floor during earlier stage of storm,then deposited the rudites (i. e. the broken sediments) into lenticular body in situ. After storm, finely laminated stromatolitic dolomites on the top of the autochthonous storm deposits by algae activity and carbonate pricipitation. The autochthonous storm deposits have a simple sequence which has only two zones-storm zone (S, radiating arranged or imbricated rudites, no rounding) and normal deposits zone(N, fine laminated stromatolitic dolomite sedimentation under fair weather).
Abundant finely laminated algal stromatolitic dolomites occur in Wimishan Formation (Jixian System,Middle 1?roterozoic)of the Ming Tombs I?istrict,lieijing,China,which are formed in subtidal environments just above normal wave base. The finely laminated algal stromatolitic dolomites contain a lot of rudite bodies which are autochthonous storm deposits in origin. The characters of these sedimentary rudite bodies are as follows,(1)Rudites- a type of intraclasts-are same as host rocks (finely laminated stromatolitic dolomites) in composition. Each rudite is tens of cm in length and width, but is 1~2 cm or less in thickness, which can be also called flakstone, and has no rounding and little matrix. (2)Rudite bodies are lenticular shaped,thin out in three dimension space,and are 10~50 cm in thickness. ( 3 ) Rudites are radiating arranged or imbricated. (9)Abruptly or gradually contacted with host rocks latterally, sometimes both sides are gradual contacted,or both are abrupt, but sometimes one side gradual while another side abrupt contacted. These lenticular bodies are too small and too disorderly to proposed that they are formed by any normal currents,and can't be caused by normal waves, therefore, it would be formed by some suddenly, high-energy waves-i. e. storm waves. On the way to land,storm waves broken partly consolidated sediments on the floor during earlier stage of storm,then deposited the rudites (i. e. the broken sediments) into lenticular body in situ. After storm, finely laminated stromatolitic dolomites on the top of the autochthonous storm deposits by algae activity and carbonate pricipitation. The autochthonous storm deposits have a simple sequence which has only two zones-storm zone (S, radiating arranged or imbricated rudites, no rounding) and normal deposits zone(N, fine laminated stromatolitic dolomite sedimentation under fair weather).
1994, 12(2): 86-93.
Abstract:
Four sediment cores, collected in Yangpu Harbour on Hainan Island,were analyzed for textural parameters and Pb- 210, Cs-137 activities,Yangpu Harbour is tidally flushed and has sediment distribution pattern which is related primarily to the tidal current pattern. Sandy(fine and coarse sllty sand ) material is distributed along the tracts of relatively high speed tidal currents underlying the shallower regions of the harbour while finer-grained,silty muds tend to accumulate in the deeper parts of the tidal channel itself. Measurements of textural paramenters have indicated that sedimentation is episodic in many sections of the harbour with successive cycles of particle erosion and deposition leading to the variable accumulation of material,particularly in the tidal channel. Because of complex stratigraphy of interbedded layers of sand and mud,Pb-210 profiles in Yangpu Harbour reveal abnormal distributions. Since the Pb-210 activity was almost exclusively associated with the finegrained,clay,component of the sediment load,the nomalization of these data to the%clay content of the sediment permitted the determination of depositional rates,despite instances of variability in the Pb- 210 activities. The distributions of Cs- 137 in two cores were measured,both the position of the horizon (corresponding to the first appearance of Cs-137 in the environment )and the peak (corresponding to the period of maximum deposition ) have been used to determine sedimentation rates. Rates based on the position of peak of Cs- 137 profile are in good agreement with that based on Pb-210 dating,and rates based on the occurrence of the horizon are slightly larger than that based on Pb-210 dating. Sedimentation rates,determined using P1i-210 and Cs-137 dating methods,were 0. 5-2cm/y in the sediments underlying the tidal channel,and were 1~2cm/y in the sediments on the swash platform area("block gate shoal") during past 100 years.
Four sediment cores, collected in Yangpu Harbour on Hainan Island,were analyzed for textural parameters and Pb- 210, Cs-137 activities,Yangpu Harbour is tidally flushed and has sediment distribution pattern which is related primarily to the tidal current pattern. Sandy(fine and coarse sllty sand ) material is distributed along the tracts of relatively high speed tidal currents underlying the shallower regions of the harbour while finer-grained,silty muds tend to accumulate in the deeper parts of the tidal channel itself. Measurements of textural paramenters have indicated that sedimentation is episodic in many sections of the harbour with successive cycles of particle erosion and deposition leading to the variable accumulation of material,particularly in the tidal channel. Because of complex stratigraphy of interbedded layers of sand and mud,Pb-210 profiles in Yangpu Harbour reveal abnormal distributions. Since the Pb-210 activity was almost exclusively associated with the finegrained,clay,component of the sediment load,the nomalization of these data to the%clay content of the sediment permitted the determination of depositional rates,despite instances of variability in the Pb- 210 activities. The distributions of Cs- 137 in two cores were measured,both the position of the horizon (corresponding to the first appearance of Cs-137 in the environment )and the peak (corresponding to the period of maximum deposition ) have been used to determine sedimentation rates. Rates based on the position of peak of Cs- 137 profile are in good agreement with that based on Pb-210 dating,and rates based on the occurrence of the horizon are slightly larger than that based on Pb-210 dating. Sedimentation rates,determined using P1i-210 and Cs-137 dating methods,were 0. 5-2cm/y in the sediments underlying the tidal channel,and were 1~2cm/y in the sediments on the swash platform area("block gate shoal") during past 100 years.
1994, 12(2): 101-104.
Abstract:
The cosmic dust,which was found in the Cretaceous grey-brown oil-bearing sandstone occured in Tarim Basin, is siliceous cosmic dust. It was sticked on the surface of illite/smectite clay minerlas. Its shape appears to be the ideal sphere, the diameter of which is about 6Wn. And it has mosaic texture. It is the first time to find the cosmic dust in Cretaceous sedimentory rock in China. After comparing the chemical compositions of the comsic dust with those which were reported in literature,it is found they are very similar,and the Ti02/SiO2,Ti02/FeO,and Fe0/SiO2ratio values are 0. O1,0. 17 and 0. 1,respectively.
The cosmic dust,which was found in the Cretaceous grey-brown oil-bearing sandstone occured in Tarim Basin, is siliceous cosmic dust. It was sticked on the surface of illite/smectite clay minerlas. Its shape appears to be the ideal sphere, the diameter of which is about 6Wn. And it has mosaic texture. It is the first time to find the cosmic dust in Cretaceous sedimentory rock in China. After comparing the chemical compositions of the comsic dust with those which were reported in literature,it is found they are very similar,and the Ti02/SiO2,Ti02/FeO,and Fe0/SiO2ratio values are 0. O1,0. 17 and 0. 1,respectively.
1994, 12(2): 114-122.
Abstract:
Shengli Oilfield is located in the Southeastern Bohai Bay Basin and tectonically belongs to the jiyang Depression, oil and gas reservoirs are found in the strata of Archaeozoic, Palaeozoic,Mesozoic and Cenozoic. Studies revealed that the Carboniferous-Permian coal seams and Jurassic core-beating formations are the source rocks of coae-type gases, carbonate rocks that sedimented during Palaeozoic Era are the source rocks of high-CO2-contained natrual gases.The isotopic compition of argon is a key parameter to identify the gases source and genetic type认this oilfield. Based on the argon isotopic analytical results of 21 gas samples, associatd with carbon isotopic compositon and geological background,the present paperdealt with the distribution law of40Ar/36Ar and ' its relation with the source rocks and the age of reservoirs,then the author discussed the distribution law of the sir argon and the radio activity-generated argon in natural gases,concluded that:The isotopic composition of argon is mainly related with the age of source rocks; There is a certain rertain reservoir-time effect in the gases that generated by new strata and traped in old ones;Magamatic activity can result in the increas of argon isotopic ratio. Synthetical study of carbon and argon isotopes indicated that in the target area,gases in the Tertiary strata are bio-thermal catalysed tranzational gas and thermal catalysed oil-type gas that traped by their own source rock;There are self-origion and self-reservoir coal-type gases in Mesozoic strata. The gases in the granite-gneiss of pre-sinian were derived from Tertiary strata;palaeozoic gases probably were the mixture of middle Tertiary oil-type gases and Mesozoic coal-type gases;The formation of high-CO2-coritained gas were mainly related with magamatic activities;The genetic types of biothermal catalysed transitional gas,oil-type gas,coaltype gas and high-CO2-contained gas have the characteristics of contineously evolution of Meso-Cenozoic basins in China and gas-generating series, each type has its own argon and carbon isotopic composition and evolution feature. the average 40Ar/36Ar values of Trtiary and Mesozoic in situ sourced and reservoired gases are 335 and 564 respectively.According to the mathmatical analysis,the coefficient of reservoir-time effects were primarily calculated for the gases that sourced from new sttta and reservoired in old ones,1. 25 and 147 for Palaeozoic and pre-Sinian granite-gneiss respectivlly. It is determined that the gas in pre-Sinian is the mixture of Tertiary.oil-type gas ( 70%) and Mesozic coal-type gas (30%).High-CO2-contained gases in Pingfangwang Gasfield are the mixture of Tertiary organic hydrocarbons and inorganic CO2formed by the decomposition of carbonate rocks which resulted from magmatic activities.
Shengli Oilfield is located in the Southeastern Bohai Bay Basin and tectonically belongs to the jiyang Depression, oil and gas reservoirs are found in the strata of Archaeozoic, Palaeozoic,Mesozoic and Cenozoic. Studies revealed that the Carboniferous-Permian coal seams and Jurassic core-beating formations are the source rocks of coae-type gases, carbonate rocks that sedimented during Palaeozoic Era are the source rocks of high-CO2-contained natrual gases.The isotopic compition of argon is a key parameter to identify the gases source and genetic type认this oilfield. Based on the argon isotopic analytical results of 21 gas samples, associatd with carbon isotopic compositon and geological background,the present paperdealt with the distribution law of40Ar/36Ar and ' its relation with the source rocks and the age of reservoirs,then the author discussed the distribution law of the sir argon and the radio activity-generated argon in natural gases,concluded that:The isotopic composition of argon is mainly related with the age of source rocks; There is a certain rertain reservoir-time effect in the gases that generated by new strata and traped in old ones;Magamatic activity can result in the increas of argon isotopic ratio. Synthetical study of carbon and argon isotopes indicated that in the target area,gases in the Tertiary strata are bio-thermal catalysed tranzational gas and thermal catalysed oil-type gas that traped by their own source rock;There are self-origion and self-reservoir coal-type gases in Mesozoic strata. The gases in the granite-gneiss of pre-sinian were derived from Tertiary strata;palaeozoic gases probably were the mixture of middle Tertiary oil-type gases and Mesozoic coal-type gases;The formation of high-CO2-coritained gas were mainly related with magamatic activities;The genetic types of biothermal catalysed transitional gas,oil-type gas,coaltype gas and high-CO2-contained gas have the characteristics of contineously evolution of Meso-Cenozoic basins in China and gas-generating series, each type has its own argon and carbon isotopic composition and evolution feature. the average 40Ar/36Ar values of Trtiary and Mesozoic in situ sourced and reservoired gases are 335 and 564 respectively.According to the mathmatical analysis,the coefficient of reservoir-time effects were primarily calculated for the gases that sourced from new sttta and reservoired in old ones,1. 25 and 147 for Palaeozoic and pre-Sinian granite-gneiss respectivlly. It is determined that the gas in pre-Sinian is the mixture of Tertiary.oil-type gas ( 70%) and Mesozic coal-type gas (30%).High-CO2-contained gases in Pingfangwang Gasfield are the mixture of Tertiary organic hydrocarbons and inorganic CO2formed by the decomposition of carbonate rocks which resulted from magmatic activities.
1994, 12(2): 133-142.
Abstract:
This paper deals with the spores and pollen from the Upper Subformation of the Hekou Formation of Lower Cretaceous in Xigu District of Lanzhou, Gansu Province,China. The sporopollen assemblage of the Upper Subformation has been established,and it was named as PiceaepoTlenites-Cicatricostsporiles-TricolPoyollenites. The assemblage is characterized by the slight dominance of Gymnospermous pollen,its percentage amounts to 56. 5%. The Pteridophyta spores amounts to 42. 2%,and the Angiospermous pollen merely to 1. 4%. The Lygodiaceae of Pteridophyta is the most important family in the assemblage. The genus Cicatricosisparites is predominant. Lygodzumspurites and Trillobosprites are common. The spores of Selaginellaceae are important,too. Among them,Densoisporites is predominant,and the others are Aequitriradiles and so on. Schizaeaisparites of Schizaeaceae is of higher percentage,consisting of many species. The other families are low in the percentage,such as Cyathidiies, DelioidosPora, Lycopodiumsparites etc.. The Pinaceae pollen of the Gymnospermae is predominant. The most abundant genus is Picesepollenites,and Abietinaepollenites is next to it. The others in the family are Pinusyollenites etc.. The genus Classnpollis of Cheirolepidiaceae amounts to 11. 9%. The appering genera in other families of the Gymnospemae include Podocarpidites,EPhedripites,Rugubivesiculites,Cauialasporiles, Jiaohepolllis etc.,and the percentage of each one is low. Triodpopollenites is the only genus in the Angiospermae. In the sporo-pollen assemblage of the Upper Subformation,the first subassemblage includes old types and disaccate pollen of Gymnospermae more than the second one,and some microfossils of Dinoflagellate and Acritarch appear. But the percentages of Classapollis and Cycadopites are lower. By analysing the periods of the important genera and species in the assemblage and comparing with the known assemblages in various districts, the author cosidered that the geologicage of the assemblage is the late phase of Early Cretaceous,that is Aptian-Albian stages. So far the stratum of the Upper Subformation is the uppermost one of the Lower Cretaceous which has been found in the Minhe Basin. Based on the studies above,the paleoclimatope of the botanic community in the late phase of Early Cretaceous has been discussed according to actuopaleontolog. It is suggested that the Minhe Basin situated in the tropics or subtropics in the Early Cretaceous, where the plants were luxuriant. The climate should be humid in the early stage for the first subassemblage,and the climate should be comparatively arid in the late stage for the second one. Furthermore,the author referred plenty of material on Early Cretaceous palynology of. China,tried to interpret the paleobotanic provincialization and thought that the Minhe Basin was situated in the Transitional Zone of the Southern Region in Early Cretaceous on the traditional biogeographic provincialization. On the numerical taxonomic provincialization of Early Cretaceous palynology,China can be divided into two regions:the North Region and the South Region, which can further be divided into some provinces. The Minhe Basin is in the Northwest-Northeast Province of the North Region.
This paper deals with the spores and pollen from the Upper Subformation of the Hekou Formation of Lower Cretaceous in Xigu District of Lanzhou, Gansu Province,China. The sporopollen assemblage of the Upper Subformation has been established,and it was named as PiceaepoTlenites-Cicatricostsporiles-TricolPoyollenites. The assemblage is characterized by the slight dominance of Gymnospermous pollen,its percentage amounts to 56. 5%. The Pteridophyta spores amounts to 42. 2%,and the Angiospermous pollen merely to 1. 4%. The Lygodiaceae of Pteridophyta is the most important family in the assemblage. The genus Cicatricosisparites is predominant. Lygodzumspurites and Trillobosprites are common. The spores of Selaginellaceae are important,too. Among them,Densoisporites is predominant,and the others are Aequitriradiles and so on. Schizaeaisparites of Schizaeaceae is of higher percentage,consisting of many species. The other families are low in the percentage,such as Cyathidiies, DelioidosPora, Lycopodiumsparites etc.. The Pinaceae pollen of the Gymnospermae is predominant. The most abundant genus is Picesepollenites,and Abietinaepollenites is next to it. The others in the family are Pinusyollenites etc.. The genus Classnpollis of Cheirolepidiaceae amounts to 11. 9%. The appering genera in other families of the Gymnospemae include Podocarpidites,EPhedripites,Rugubivesiculites,Cauialasporiles, Jiaohepolllis etc.,and the percentage of each one is low. Triodpopollenites is the only genus in the Angiospermae. In the sporo-pollen assemblage of the Upper Subformation,the first subassemblage includes old types and disaccate pollen of Gymnospermae more than the second one,and some microfossils of Dinoflagellate and Acritarch appear. But the percentages of Classapollis and Cycadopites are lower. By analysing the periods of the important genera and species in the assemblage and comparing with the known assemblages in various districts, the author cosidered that the geologicage of the assemblage is the late phase of Early Cretaceous,that is Aptian-Albian stages. So far the stratum of the Upper Subformation is the uppermost one of the Lower Cretaceous which has been found in the Minhe Basin. Based on the studies above,the paleoclimatope of the botanic community in the late phase of Early Cretaceous has been discussed according to actuopaleontolog. It is suggested that the Minhe Basin situated in the tropics or subtropics in the Early Cretaceous, where the plants were luxuriant. The climate should be humid in the early stage for the first subassemblage,and the climate should be comparatively arid in the late stage for the second one. Furthermore,the author referred plenty of material on Early Cretaceous palynology of. China,tried to interpret the paleobotanic provincialization and thought that the Minhe Basin was situated in the Transitional Zone of the Southern Region in Early Cretaceous on the traditional biogeographic provincialization. On the numerical taxonomic provincialization of Early Cretaceous palynology,China can be divided into two regions:the North Region and the South Region, which can further be divided into some provinces. The Minhe Basin is in the Northwest-Northeast Province of the North Region.
1994, 12(2): 10-19.
Abstract:
The Ynashan sedimentary basin of Changchengian (1800-1400Ma) of the Mid-Proterozoic is located in North China. Sedimental accumulations of the basin were first one with nature of the covering strata after formation of the crystalline basement of the Archaeozoic-Early Proterozoic.The sedimentary environmental evolutions are described as follows:axial river-fans and braid rivers in alluvial environments,sandy tidal-shallow shoal or bar in marine,mud and carbonate tidal or lagoon in the early Changchengian;and debris-carbonate tidal or shoal with silica from volcanical provenance and fan-dalta,carbonate ringing flatform-slop-basinal facies in the late Changchengian. This shows evolutions of the environmental system from restricted to openning conditions. Alluvial fans, fan-dalta,debris turbidites, carbonate slump breccia,carbonate gravity flow(including grain-flow ), volcanical debris flow and volcanical silica mixed sediments were deposited in the basin. Formation of these facies were controlled by structural action in contemporaneity.Rhythmic shale-micrite carbonates with carbonate dissolution structures and concretion-liked carbonates in the late show the characteristics of deep water carbonate. The sedimentary hydrodynamics of the basin was generally in the condition of mid-low energy due to relatively restricted environments. Framework of the basinal structures consisted of the NE marginal faults and the NW transfer faults. The general longitudal extend and development of the basin were controlled with the Xinglong-Lingyuan fault in the north margin. The vertical of the basin shows a asymmetric shape and main subsidence axis inclines to the north. The basin evolved from narrow half graben to broad downwarp.The facies, environments and structures of the basin were Characteristic of a fail-rift (aulacogen).It showed the process of crust breakup of North China in the early and downwarp subsidence in the late of Changchengian.
The Ynashan sedimentary basin of Changchengian (1800-1400Ma) of the Mid-Proterozoic is located in North China. Sedimental accumulations of the basin were first one with nature of the covering strata after formation of the crystalline basement of the Archaeozoic-Early Proterozoic.The sedimentary environmental evolutions are described as follows:axial river-fans and braid rivers in alluvial environments,sandy tidal-shallow shoal or bar in marine,mud and carbonate tidal or lagoon in the early Changchengian;and debris-carbonate tidal or shoal with silica from volcanical provenance and fan-dalta,carbonate ringing flatform-slop-basinal facies in the late Changchengian. This shows evolutions of the environmental system from restricted to openning conditions. Alluvial fans, fan-dalta,debris turbidites, carbonate slump breccia,carbonate gravity flow(including grain-flow ), volcanical debris flow and volcanical silica mixed sediments were deposited in the basin. Formation of these facies were controlled by structural action in contemporaneity.Rhythmic shale-micrite carbonates with carbonate dissolution structures and concretion-liked carbonates in the late show the characteristics of deep water carbonate. The sedimentary hydrodynamics of the basin was generally in the condition of mid-low energy due to relatively restricted environments. Framework of the basinal structures consisted of the NE marginal faults and the NW transfer faults. The general longitudal extend and development of the basin were controlled with the Xinglong-Lingyuan fault in the north margin. The vertical of the basin shows a asymmetric shape and main subsidence axis inclines to the north. The basin evolved from narrow half graben to broad downwarp.The facies, environments and structures of the basin were Characteristic of a fail-rift (aulacogen).It showed the process of crust breakup of North China in the early and downwarp subsidence in the late of Changchengian.
1994, 12(2): 29-36.
Abstract:
Anoxic environments developed best in Permian,especially in Gufeng and Dalong Stages in the Middle and Lower Yangtze region. Special complex of anoxic sediments of "black shale-chert- limestone "was formed in this kind of environments. According to palaeoecology and sedimentary petrology,anoxic sediments can be divided into two kinds, dysaerobic and anaerobic sediments. Anaerobic sediments are characterized by black and dark-grey, thin-beded or laminated,organicrich, and phosphoric-rich chert, shale and mud-bearing limestone, which are devoid of benthic fossils and biodisturbance,but bear plankton fossils, e. g. radiolaria and Ammonoids. Dysaerobic sediments are characterized by black-grey and dark-grey, thin or middle-beded,organic-rich and phosphoric-rich shale, mud-bearing limestone and chert, which are devoid of epifaunal fossils, but bear infauna,plankton fossils and biodisturbance. The distribution of anoxic sediments of Permian in the study area,is closely related to the framework of lithofaces and palaeogeography. Anoxic sediments of Gufeng Formation are distributed in the north and south of Lower Yangtze region,and those of Dalong Formation in the north of Lower and Middle Yangtze region,both of which are closely related to deeper slope and basin. There are two main origins of anoxic environments of Permian in the region. One is the euxinic orgin. Under the palaeogeographic conditions of low paleolatitude of Permian,high temperature of marine water,low energy of marine water and subaqueous relief of "twofold platform and basin"result in the euxinic condition of deeper water layers. The other orgin is the influence of upwelling.The active upwelling coming from the northward ocean promotes high biologic productivity,and in turn the recycling of dead organic matter in the water column creates a very high oxygen demand which can trigger anoxic conditions in deeper water layers under the upwelling. The distribution of anoxic and aerobic environments is determined by the depth of marine water. The sedimentary model of anoxic environments of Permian in the region is established on the basis of comprehensive analysis. The depth of sea floor of anoxic environments is analyzed from the viewpoint of palaeogeography, petrology,and comparative study of modern anoxic environments. It is estimated that the sea floor of anoxic envirionments of Permian in the study area is not very deep. The depth of dysaerobic environments is less than 300m,and anaerobic environments less than carbonate compensation depth(CCD). Abundant organic matter in the anoxic sediments may result in.the formation of potential hydrocarbon source beds. According to the difference of various anoxic sediments, We classified three kinds of potential hydrocarbon source beds, and estimated the distribution of those beds in the study area. Research shows that there are excellent conditions of the formation of oil and gas in Permian of the Lower and Middle Yangtze region.
Anoxic environments developed best in Permian,especially in Gufeng and Dalong Stages in the Middle and Lower Yangtze region. Special complex of anoxic sediments of "black shale-chert- limestone "was formed in this kind of environments. According to palaeoecology and sedimentary petrology,anoxic sediments can be divided into two kinds, dysaerobic and anaerobic sediments. Anaerobic sediments are characterized by black and dark-grey, thin-beded or laminated,organicrich, and phosphoric-rich chert, shale and mud-bearing limestone, which are devoid of benthic fossils and biodisturbance,but bear plankton fossils, e. g. radiolaria and Ammonoids. Dysaerobic sediments are characterized by black-grey and dark-grey, thin or middle-beded,organic-rich and phosphoric-rich shale, mud-bearing limestone and chert, which are devoid of epifaunal fossils, but bear infauna,plankton fossils and biodisturbance. The distribution of anoxic sediments of Permian in the study area,is closely related to the framework of lithofaces and palaeogeography. Anoxic sediments of Gufeng Formation are distributed in the north and south of Lower Yangtze region,and those of Dalong Formation in the north of Lower and Middle Yangtze region,both of which are closely related to deeper slope and basin. There are two main origins of anoxic environments of Permian in the region. One is the euxinic orgin. Under the palaeogeographic conditions of low paleolatitude of Permian,high temperature of marine water,low energy of marine water and subaqueous relief of "twofold platform and basin"result in the euxinic condition of deeper water layers. The other orgin is the influence of upwelling.The active upwelling coming from the northward ocean promotes high biologic productivity,and in turn the recycling of dead organic matter in the water column creates a very high oxygen demand which can trigger anoxic conditions in deeper water layers under the upwelling. The distribution of anoxic and aerobic environments is determined by the depth of marine water. The sedimentary model of anoxic environments of Permian in the region is established on the basis of comprehensive analysis. The depth of sea floor of anoxic environments is analyzed from the viewpoint of palaeogeography, petrology,and comparative study of modern anoxic environments. It is estimated that the sea floor of anoxic envirionments of Permian in the study area is not very deep. The depth of dysaerobic environments is less than 300m,and anaerobic environments less than carbonate compensation depth(CCD). Abundant organic matter in the anoxic sediments may result in.the formation of potential hydrocarbon source beds. According to the difference of various anoxic sediments, We classified three kinds of potential hydrocarbon source beds, and estimated the distribution of those beds in the study area. Research shows that there are excellent conditions of the formation of oil and gas in Permian of the Lower and Middle Yangtze region.
1994, 12(2): 45-53.
Abstract:
The barrier-lagoon systems(BLS)are widely distributed in the southwesten Inner Mongolia Autonomous Region during Carboniferous Period. The lagoon deposits of different stages in the systems are superimposed mutually,forming various sequences,with a great thickness. This is hard to be formed and preserved in the Holocene. According to sedimentological characteristics and depositional sequence,the transgressive,regressive,stationary and locally transgressive barrier lagoon systems in the carboniferous deposits of the studied area have been recognized, which are similar to the types in Holocene. It confirms that the stratigraphic models of barrier-lagoon systems summarized in the study of Holocene are helpful for recognition and study of the analogies in the geological time. However,the barrier-lagoon systems of the Carboniferous Period in the studied area have been formed in broad space for a long time,they are usually compound,such as transgressive-locally transgressive,stationary-locally transgressive BLS. In addition,the stationary BLS is characterized by both underlying and overlying strata to be terrestrial in Holocene,but the counterparts in the carboniferous deposits of the studied area are characterized by superimposition of more than ten barrier-lagoon sequences almost in the same area for a long time under conditions of continuous tectonic subsidence and stabilization of coastline. The transgressive barrier-lagoon systems occur in transgressive sequence and have lagoon deposits exceeding the coincident barrier sands in thickness. The formation model for BLS has been established.
The barrier-lagoon systems(BLS)are widely distributed in the southwesten Inner Mongolia Autonomous Region during Carboniferous Period. The lagoon deposits of different stages in the systems are superimposed mutually,forming various sequences,with a great thickness. This is hard to be formed and preserved in the Holocene. According to sedimentological characteristics and depositional sequence,the transgressive,regressive,stationary and locally transgressive barrier lagoon systems in the carboniferous deposits of the studied area have been recognized, which are similar to the types in Holocene. It confirms that the stratigraphic models of barrier-lagoon systems summarized in the study of Holocene are helpful for recognition and study of the analogies in the geological time. However,the barrier-lagoon systems of the Carboniferous Period in the studied area have been formed in broad space for a long time,they are usually compound,such as transgressive-locally transgressive,stationary-locally transgressive BLS. In addition,the stationary BLS is characterized by both underlying and overlying strata to be terrestrial in Holocene,but the counterparts in the carboniferous deposits of the studied area are characterized by superimposition of more than ten barrier-lagoon sequences almost in the same area for a long time under conditions of continuous tectonic subsidence and stabilization of coastline. The transgressive barrier-lagoon systems occur in transgressive sequence and have lagoon deposits exceeding the coincident barrier sands in thickness. The formation model for BLS has been established.
1994, 12(2): 63-71.
Abstract:
The author discussed the Holocene sedimentary facies and its evolution,based mainly upon data of the eight drill-holes and also upon other several dozens of reference drill-holes, as well as the field investigation of the buried tidal sand bodies in the studied area for the first time. Characteristics of the sediments in the cores have been studied about their textures, structures,minerals and macrofossils. Radiometric dating 14C carried out for the important levels. It is non-marine facies of Pleistocene that underlay the sediment of Holocene with unconformity between them: The topography of the area at the end of Pleistocene inclined from northwest towards southeast which influenced the Holocene transgression obviously. The Holocene sedimentary sequence can be divided into the lower transgressive and the upper regressive one, consisting of beach facies(contains estuary-bay in sbme part of the area),near- shore neritic facies(tidal sand body facies)and tidal flat facies etc. It is obvious that facies change horizontally. In different environment appear different sedimentary sequences. The sequence can be classified into four types,which were discussed加detail in this paper. For all the four types,the best developed area is in the southeast part of the studied area, and the worst is in the northwest. The buried tidal sand bodies can be crassified into three types:Ⅰ)near-shore tidal sand bars;Ⅱ)tidal sand waves ;Ⅲnear-shore tidal sand ridges. They were formed and preserved successively along with the cycle of transgression and regression,and their distribution pattern was controlled by shift of the Changjiang river towards southeast during the Holocene.
The author discussed the Holocene sedimentary facies and its evolution,based mainly upon data of the eight drill-holes and also upon other several dozens of reference drill-holes, as well as the field investigation of the buried tidal sand bodies in the studied area for the first time. Characteristics of the sediments in the cores have been studied about their textures, structures,minerals and macrofossils. Radiometric dating 14C carried out for the important levels. It is non-marine facies of Pleistocene that underlay the sediment of Holocene with unconformity between them: The topography of the area at the end of Pleistocene inclined from northwest towards southeast which influenced the Holocene transgression obviously. The Holocene sedimentary sequence can be divided into the lower transgressive and the upper regressive one, consisting of beach facies(contains estuary-bay in sbme part of the area),near- shore neritic facies(tidal sand body facies)and tidal flat facies etc. It is obvious that facies change horizontally. In different environment appear different sedimentary sequences. The sequence can be classified into four types,which were discussed加detail in this paper. For all the four types,the best developed area is in the southeast part of the studied area, and the worst is in the northwest. The buried tidal sand bodies can be crassified into three types:Ⅰ)near-shore tidal sand bars;Ⅱ)tidal sand waves ;Ⅲnear-shore tidal sand ridges. They were formed and preserved successively along with the cycle of transgression and regression,and their distribution pattern was controlled by shift of the Changjiang river towards southeast during the Holocene.
1994, 12(2): 77-85.
Abstract:
The authors have identified a series of mixed thick deep-water gravity current sediments in Ying taogou Formation of middle-Ordovician in the east margin of Bayanhavte basin,It included carbonate slump breccias,graded fine conglomerates,sandy gravels, dassic turbidites, grey-green shales etc. Carbonate slump breccias were formed in clastic-skirt, which located under proximal sea-bottom near to fault steep cliff, and terrigenous turbidite were originated from paleo-weathered crust by turbidity current. By studying the vertical sequence,the authors consider that this Formation are generally represented a H grade cycle,corresponding to a second crust rising-falling cycle, which formed during the period when aulacogen subsided deepestly and were mainly defined by paleostructure.And each conplex of terrigenous sediment and infrobasinal sediment represented a grade cycle,corresponding to a low-graded sea-level-charnging cycle.
The authors have identified a series of mixed thick deep-water gravity current sediments in Ying taogou Formation of middle-Ordovician in the east margin of Bayanhavte basin,It included carbonate slump breccias,graded fine conglomerates,sandy gravels, dassic turbidites, grey-green shales etc. Carbonate slump breccias were formed in clastic-skirt, which located under proximal sea-bottom near to fault steep cliff, and terrigenous turbidite were originated from paleo-weathered crust by turbidity current. By studying the vertical sequence,the authors consider that this Formation are generally represented a H grade cycle,corresponding to a second crust rising-falling cycle, which formed during the period when aulacogen subsided deepestly and were mainly defined by paleostructure.And each conplex of terrigenous sediment and infrobasinal sediment represented a grade cycle,corresponding to a low-graded sea-level-charnging cycle.
1994, 12(2): 94-100.
Abstract:
The measurement of anisotropy of magnetic susceptibility (AMS) is a newly developed method that is used to investigate the sedimentary fabric of the sediments. The measurement of AMS on the loess in Central China showed that the primary eolian loess and the secondary aqueous loess different sediments which deposited in different medium-air or water, and there is distinct fabric from each other,so according to the difference we could distinguish the two sorts of sediments. On the basis of analysis on the theory and method to investigate the sedimentary fabric of loess-like sediment by the measurement of AMS,the paper attempts to use the method on the study of Xiashu loess in Nanjing. The results of the measurement show that the AMS of Xiashu loess is not clear,the percent age of anisotropy (P) is 1. 004
The measurement of anisotropy of magnetic susceptibility (AMS) is a newly developed method that is used to investigate the sedimentary fabric of the sediments. The measurement of AMS on the loess in Central China showed that the primary eolian loess and the secondary aqueous loess different sediments which deposited in different medium-air or water, and there is distinct fabric from each other,so according to the difference we could distinguish the two sorts of sediments. On the basis of analysis on the theory and method to investigate the sedimentary fabric of loess-like sediment by the measurement of AMS,the paper attempts to use the method on the study of Xiashu loess in Nanjing. The results of the measurement show that the AMS of Xiashu loess is not clear,the percent age of anisotropy (P) is 1. 004
1994, 12(2): 105-113.
Abstract:
The Lower Paleozoic Gas field in the central part of Oerhtossu Basin is of underpressure gas reservoir with the source rock and reservoir rock of carbonate complex of Ordovician,and its cap rock is alum clay of Middle Carboniferous. This gas field is located at the relatively low part of the regional monocilne which inclines to west. The pressure coefficient of the top of Ordovician gas reservoir on Shancan-1 Well and Lin-1 Well is about 0. 91. This type of underpressure gas reservoir can be seen in USA, Canada and prior USSR. The characters of underpressure reservoir for Oerhtossu are similar to the underpressure reservoir of Lower Cretaceous of Elmworth and Upper Cretaceous of Medician Hat in Alberta of Canada,and the Clinton sandston of Silurian in Ohio of United States. Their common characters are reservoir being saturated with gas, and the water saturation being lower than 38%,no formation water being produced. However, the reservoir saturated with gas dose not always developed underpressure. In this type of gas reservoir,underpressure developed or not relates to the open degree of gas reservoir and the generation rate of hydrocarbon. The developing of underpressure gas reserevoir of weathering crust in Oerhtossu Basin is not only due to it saturated with gas,so the fomational pressure of overlying strata can't be transmited efficiently, but also caused by it's gas generation rate decreased since Upper Cretaceous. The natureal gas of studied area accumulates abundantly at the top of weathering crust with it's thickness being 30-80m,pores and miarolitics are developed strongly in the weathering crust of Jingbian-Hengshan and then composes a good reservoir. The flow potential calculation shows that simply used the buoyance or overpressure value to indicate the migration direction is unilateral.There is no free water in the reservoir today,and it is similar that buoyance isn't a driven force of gas secondary migration at present. In the end of Jurassic,however, the gas potentials at the section of Shancan-1 to Yu-1 Well were higher at east and west ends and lower at central part,higher at the bottom and becoming lower at the top of Ordovician. So the migration directions of gas were from east and west ends to central and from bottom to top. The writers guess that the buoyance is a driven force of gas migration at that time. At present,there is no obvious potential difference between east and west at this section, and it is similar that there does not occur lateral migration of long distance. The gas migration paths at Shancan-1 and Lin-1 Wells are mainly along the direction of maximum potential gradient, from the bottom to the top of Ordovician. The low gas potential areas indicating migration direction combined with the reservoir of high pores,miarolitics and seams are the richly accumulated areas of gas.
The Lower Paleozoic Gas field in the central part of Oerhtossu Basin is of underpressure gas reservoir with the source rock and reservoir rock of carbonate complex of Ordovician,and its cap rock is alum clay of Middle Carboniferous. This gas field is located at the relatively low part of the regional monocilne which inclines to west. The pressure coefficient of the top of Ordovician gas reservoir on Shancan-1 Well and Lin-1 Well is about 0. 91. This type of underpressure gas reservoir can be seen in USA, Canada and prior USSR. The characters of underpressure reservoir for Oerhtossu are similar to the underpressure reservoir of Lower Cretaceous of Elmworth and Upper Cretaceous of Medician Hat in Alberta of Canada,and the Clinton sandston of Silurian in Ohio of United States. Their common characters are reservoir being saturated with gas, and the water saturation being lower than 38%,no formation water being produced. However, the reservoir saturated with gas dose not always developed underpressure. In this type of gas reservoir,underpressure developed or not relates to the open degree of gas reservoir and the generation rate of hydrocarbon. The developing of underpressure gas reserevoir of weathering crust in Oerhtossu Basin is not only due to it saturated with gas,so the fomational pressure of overlying strata can't be transmited efficiently, but also caused by it's gas generation rate decreased since Upper Cretaceous. The natureal gas of studied area accumulates abundantly at the top of weathering crust with it's thickness being 30-80m,pores and miarolitics are developed strongly in the weathering crust of Jingbian-Hengshan and then composes a good reservoir. The flow potential calculation shows that simply used the buoyance or overpressure value to indicate the migration direction is unilateral.There is no free water in the reservoir today,and it is similar that buoyance isn't a driven force of gas secondary migration at present. In the end of Jurassic,however, the gas potentials at the section of Shancan-1 to Yu-1 Well were higher at east and west ends and lower at central part,higher at the bottom and becoming lower at the top of Ordovician. So the migration directions of gas were from east and west ends to central and from bottom to top. The writers guess that the buoyance is a driven force of gas migration at that time. At present,there is no obvious potential difference between east and west at this section, and it is similar that there does not occur lateral migration of long distance. The gas migration paths at Shancan-1 and Lin-1 Wells are mainly along the direction of maximum potential gradient, from the bottom to the top of Ordovician. The low gas potential areas indicating migration direction combined with the reservoir of high pores,miarolitics and seams are the richly accumulated areas of gas.
1994, 12(2): 123-132.
Abstract:
Over 30 trace elements(with concentration lower than l%o) from 46 samples have been determined during the study by various techniques,including INAA and ICP. These samples were collected from the synsedimentary volcanic ash derived tonsteins, non-cineritic claystones, and the coal seams within the coal-bearing formation of the eastern Yunnan and western Guizhou Provinces. The analytical results demonstrate the fact that the concentrations of various trace elements source materials. The terrigenous non-cineritic claystones are characterized by their high contents in V,Ti,Sc,Cr,Co, and Ni,medium contents in Nb, Ta, Hf, Zr and REE,and low in The U and Th/U ratio,with an indistinct negative anomaly of SEu(0. 63-0. 93),which is, in overall, consistent with the properties of the basalt from the erosional region. On the other hand,tonsteins are low in V,Ti,Sc,Cr,Co, and Ni, contents, medium to high in REE,Nb,Ta,Hf,Zr, Th and U, and high in Th/U ratio, with a distinct bEu anomaly (normally in the range of 0. 2-0. 4 ). The characteristics of tonstein geochemistry of trace elements can be distinguished from those of the non-cineritic claystones, as indicative of their unique volcanic ash-fall origin. As far as the tonsteins are concerned,those from the lower section (P2.1) of the coal-bearing formation are high in Li,13e, Ti, Zr, Hf, Nb, Ta and REE contents, as compared to those from the middle and upper sections (P2.2+3). As shown on the plots of correlations between Hf-Ta,Ti-Ta,Ti-V,Hf-Sc, Lu-Hf and Lu-Th,tonsteins from P2.1.1horizon always fall in an isolated distribution area,separating from the tonsteins of P2.2+3 horizon. These results suggest that from the tonsteins from the two different horizons were probably derived comparison of the concentration and assemblage of trace elements between various magmatic rocks, the source materials of tonsteins from Pz.1horizon were mostly compased of alkalene volcanic ash,whereas those from Pz.z+a were apparently acidic. Based on a convergence of evidence obtained from different approaches,including the analytical results of the distribution and assemblage of trace elements in tonsteins, it is discovered that the tonsteins from different horizons are ofter characterized by their unique properties,which remain quite consistent over a great lateral extent. An integrated and customized use of these properties makes possible the establishment of tonstein stratigtaphy, thus facilitating the more precise and reliable coal seam correlation.
Over 30 trace elements(with concentration lower than l%o) from 46 samples have been determined during the study by various techniques,including INAA and ICP. These samples were collected from the synsedimentary volcanic ash derived tonsteins, non-cineritic claystones, and the coal seams within the coal-bearing formation of the eastern Yunnan and western Guizhou Provinces. The analytical results demonstrate the fact that the concentrations of various trace elements source materials. The terrigenous non-cineritic claystones are characterized by their high contents in V,Ti,Sc,Cr,Co, and Ni,medium contents in Nb, Ta, Hf, Zr and REE,and low in The U and Th/U ratio,with an indistinct negative anomaly of SEu(0. 63-0. 93),which is, in overall, consistent with the properties of the basalt from the erosional region. On the other hand,tonsteins are low in V,Ti,Sc,Cr,Co, and Ni, contents, medium to high in REE,Nb,Ta,Hf,Zr, Th and U, and high in Th/U ratio, with a distinct bEu anomaly (normally in the range of 0. 2-0. 4 ). The characteristics of tonstein geochemistry of trace elements can be distinguished from those of the non-cineritic claystones, as indicative of their unique volcanic ash-fall origin. As far as the tonsteins are concerned,those from the lower section (P2.1) of the coal-bearing formation are high in Li,13e, Ti, Zr, Hf, Nb, Ta and REE contents, as compared to those from the middle and upper sections (P2.2+3). As shown on the plots of correlations between Hf-Ta,Ti-Ta,Ti-V,Hf-Sc, Lu-Hf and Lu-Th,tonsteins from P2.1.1horizon always fall in an isolated distribution area,separating from the tonsteins of P2.2+3 horizon. These results suggest that from the tonsteins from the two different horizons were probably derived comparison of the concentration and assemblage of trace elements between various magmatic rocks, the source materials of tonsteins from Pz.1horizon were mostly compased of alkalene volcanic ash,whereas those from Pz.z+a were apparently acidic. Based on a convergence of evidence obtained from different approaches,including the analytical results of the distribution and assemblage of trace elements in tonsteins, it is discovered that the tonsteins from different horizons are ofter characterized by their unique properties,which remain quite consistent over a great lateral extent. An integrated and customized use of these properties makes possible the establishment of tonstein stratigtaphy, thus facilitating the more precise and reliable coal seam correlation.
