1992 Vol. 10, No. 2
column
Display Method:
1992, 10(2): 1-8.
Abstract:
Yangtze Platform was a relatively active one. In Late Paleozoic, there were both stable and relatively active depositional areas on it, resulted in the forming of two different sedimentary formations: the platform type and the intraplatform trough type. Inplatform type of formation region, five majof formations can be subdivided according to rock assembleage in different areas: A) nonmarine- alternately marine and nonmarine- marine clastic formation; B) marine carbonate formation; C) alternately marine and nonmarine cabonate- clastic formation; D) alternately marine and nonmarine, coal-bearing clastic formation; and E) nonmarine volcanic rock-volcaniclastic rock formation. The intraplatform trough type can be detailly classified to five major formations: A) silicalite- siliceous mudstone formation; B) mudstone- marl- silicalite formation; C) limestone-silicalite formation; D) mudstone-marl formation; E) vocanic rodk for- malion. In Late Paleozoic, distribution characteristics of sedimentary formations in space and time on the Yangtze Platform were clossly related to crustal activity, tectonic background and paleogeography. In the early stage of Early Devonian, nonmarine clastic formation was widely distributied owing to the influence of the Caledonian movement. In middle Devonian, the area of transgression was widening, and marine carbonate formation began to be formed. Alternately marine and nonmarine clastic formation and marine clastic formation deposited in the shore areas near old-land. Intraplatform trough type of formations were formed on the carbonate platform in Guangxi, Hunan and Guangdong region. In Late Permian, Yangtze Platform was generally raised. Alternately marine and nonmarine, coal-bearing clastic formation was formed. Marine carbonate formtion and coal-bearing cabonate formation were formed gradually toward the center of basin. Spreading law of sedimentary formtions on the Yangtze Platgorm was not synchronously. Three sedimentary formation cycles are generally developed on Yangtze Platform, and every cycle was evoluled from clastic formation to carbonate formation. But there was only one sedimentary formtion cycly developed in Mianzhou, Sichuan and Liucheng, Guangxi. Indicates that the crustal was in a long stable stage in these two areas. In a given tectonic structure unit, pilling-up sequences of sedimentary formations can reflect the development feature of crustal activity and the process of geological history. The types of sedimentary formations in Paleozoic on Yangtze Platform were formed in a certain period of crustal development in a certain tectonic structure units. They were the products of crustal movement. he major activities of crustal were regional elevation and subsidence movement and local extensional action. The regional elevation and subsidence movement resulted in the elevation and subsidence of sea level as well as transgression and regression, it also controlled the forming, spreading character and developing degree of different sedimentary formations- The local extensional action resulted in the forming of aulacogen, fault depression and paleofift basins, it also controlled the forming and development of intraplatform trough formations. Rock assembleage and the developed degree of intraplatform trough sedimentary formations in Guangxi, Hunan and Guangdong arc closely related to the evolution stages of aulacogen: its occurrence, development, weakness and disappearance.
Yangtze Platform was a relatively active one. In Late Paleozoic, there were both stable and relatively active depositional areas on it, resulted in the forming of two different sedimentary formations: the platform type and the intraplatform trough type. Inplatform type of formation region, five majof formations can be subdivided according to rock assembleage in different areas: A) nonmarine- alternately marine and nonmarine- marine clastic formation; B) marine carbonate formation; C) alternately marine and nonmarine cabonate- clastic formation; D) alternately marine and nonmarine, coal-bearing clastic formation; and E) nonmarine volcanic rock-volcaniclastic rock formation. The intraplatform trough type can be detailly classified to five major formations: A) silicalite- siliceous mudstone formation; B) mudstone- marl- silicalite formation; C) limestone-silicalite formation; D) mudstone-marl formation; E) vocanic rodk for- malion. In Late Paleozoic, distribution characteristics of sedimentary formations in space and time on the Yangtze Platform were clossly related to crustal activity, tectonic background and paleogeography. In the early stage of Early Devonian, nonmarine clastic formation was widely distributied owing to the influence of the Caledonian movement. In middle Devonian, the area of transgression was widening, and marine carbonate formation began to be formed. Alternately marine and nonmarine clastic formation and marine clastic formation deposited in the shore areas near old-land. Intraplatform trough type of formations were formed on the carbonate platform in Guangxi, Hunan and Guangdong region. In Late Permian, Yangtze Platform was generally raised. Alternately marine and nonmarine, coal-bearing clastic formation was formed. Marine carbonate formtion and coal-bearing cabonate formation were formed gradually toward the center of basin. Spreading law of sedimentary formtions on the Yangtze Platgorm was not synchronously. Three sedimentary formation cycles are generally developed on Yangtze Platform, and every cycle was evoluled from clastic formation to carbonate formation. But there was only one sedimentary formtion cycly developed in Mianzhou, Sichuan and Liucheng, Guangxi. Indicates that the crustal was in a long stable stage in these two areas. In a given tectonic structure unit, pilling-up sequences of sedimentary formations can reflect the development feature of crustal activity and the process of geological history. The types of sedimentary formations in Paleozoic on Yangtze Platform were formed in a certain period of crustal development in a certain tectonic structure units. They were the products of crustal movement. he major activities of crustal were regional elevation and subsidence movement and local extensional action. The regional elevation and subsidence movement resulted in the elevation and subsidence of sea level as well as transgression and regression, it also controlled the forming, spreading character and developing degree of different sedimentary formations- The local extensional action resulted in the forming of aulacogen, fault depression and paleofift basins, it also controlled the forming and development of intraplatform trough formations. Rock assembleage and the developed degree of intraplatform trough sedimentary formations in Guangxi, Hunan and Guangdong arc closely related to the evolution stages of aulacogen: its occurrence, development, weakness and disappearance.
1992, 10(2): 19-27.
Abstract:
Wumishan Formation of middle Proterozoic in Jixian county, Tianjin, mainly consist of bio-dolostone, about 3000m in thickness. As the results of field section survey, microscopic analysis of thin sections and electronmicroocopic scanner of rock deperis, the whole process of development and evolution of oncolite is recognized. The dispersal grain is the embryonic form of oncolite, its different pattern and character of coat reflect various occurence in the early stage of coated grain. If we regard the whole process of growth from initial dispersal grains to resultant product of oncolite as a series of processes, its growth envi-ronment is not confined to conventional recognization-sedimentary medium is a shaking and low-energy state. Vertical sequence of Wumishan Formation show spiral-rhythm accumlation and within each sequence algal coat from dispersal grain to oncolite also display synchronous evolution rhythm. Diameter of grams varies from 0.5-2mm to 10-20mm. Periodical and sprial evolution series of algal coat arc from simple to com plex. Macroscopically, disperal grains are black-brown spherical grains, containing much organic materials. They float and disperse in the dolostone. Under polarization microsoope. they are radiation concentric, winkle pisolit and flat leaf. Under electronic microscope, a flower is formed by a few slices of dolostone gathered together, with diameter of several to tens of μm.
Wumishan Formation of middle Proterozoic in Jixian county, Tianjin, mainly consist of bio-dolostone, about 3000m in thickness. As the results of field section survey, microscopic analysis of thin sections and electronmicroocopic scanner of rock deperis, the whole process of development and evolution of oncolite is recognized. The dispersal grain is the embryonic form of oncolite, its different pattern and character of coat reflect various occurence in the early stage of coated grain. If we regard the whole process of growth from initial dispersal grains to resultant product of oncolite as a series of processes, its growth envi-ronment is not confined to conventional recognization-sedimentary medium is a shaking and low-energy state. Vertical sequence of Wumishan Formation show spiral-rhythm accumlation and within each sequence algal coat from dispersal grain to oncolite also display synchronous evolution rhythm. Diameter of grams varies from 0.5-2mm to 10-20mm. Periodical and sprial evolution series of algal coat arc from simple to com plex. Macroscopically, disperal grains are black-brown spherical grains, containing much organic materials. They float and disperse in the dolostone. Under polarization microsoope. they are radiation concentric, winkle pisolit and flat leaf. Under electronic microscope, a flower is formed by a few slices of dolostone gathered together, with diameter of several to tens of μm.
1992, 10(2): 39-44.
Abstract:
The argument about the sedimentary environment of the carbonatite in Jishou District of Western Hunan focus on that whether the carbonatite deposited in a pelagic continental margin sea or a carbonate tidal flat of shallow water. The authors agree on the latter viewpoint. The main evidence of the carbonatite formed in shallow water is as follows. The dominant associations of the Cambrian carbonatite in the district are laminated microcrystalline limestones, calcareous dolomite, dolomite, dolomitized sparitic grainstone, terrigenous elastics bearing clay-dolomite and calcirudite. The genetic indices of shallow water are the various cross bedding, scour and cutting structure, unsymmetrical ripple-marks and incomplete mud cracks, etc. The materials in the rock fabric, such as oolites, intraclasts, bioclasts, algal lumps, pellets and clays, silts and the well-rounded zircons and tourmalines, etc., are all belong to the deposits of shallow water. The remnant fabric of dolomite and lime-dolomite also indicates that the origin rock formed in very shallow water. Moreover, the components and structures of the calcirudite (dol.) in limestone and dolomite imply that they were storm deposit. According to the above evidence, the authors point out that the sedimentary environment of the Cambrian carbonatite in the district should be a carbonate tidal flat.
The argument about the sedimentary environment of the carbonatite in Jishou District of Western Hunan focus on that whether the carbonatite deposited in a pelagic continental margin sea or a carbonate tidal flat of shallow water. The authors agree on the latter viewpoint. The main evidence of the carbonatite formed in shallow water is as follows. The dominant associations of the Cambrian carbonatite in the district are laminated microcrystalline limestones, calcareous dolomite, dolomite, dolomitized sparitic grainstone, terrigenous elastics bearing clay-dolomite and calcirudite. The genetic indices of shallow water are the various cross bedding, scour and cutting structure, unsymmetrical ripple-marks and incomplete mud cracks, etc. The materials in the rock fabric, such as oolites, intraclasts, bioclasts, algal lumps, pellets and clays, silts and the well-rounded zircons and tourmalines, etc., are all belong to the deposits of shallow water. The remnant fabric of dolomite and lime-dolomite also indicates that the origin rock formed in very shallow water. Moreover, the components and structures of the calcirudite (dol.) in limestone and dolomite imply that they were storm deposit. According to the above evidence, the authors point out that the sedimentary environment of the Cambrian carbonatite in the district should be a carbonate tidal flat.
1992, 10(2): 54-61.
Abstract:
Kunming Basin is a late Cenozoic fault lake basin in Yunnan Plateau with an area of aboui 1. 000km2. The present lake Dianchi is about 300km~3 in area with its mean water level 1,886m a.s.l.The two cores (Chad Chao2) taken from the east shore of Chaohai Bay of the northern Dianchi Lake were ac-cumululed in the latest 50, 000 years with a depth of about 20m of each. The sites where the two cores are drilled was in the environment with lower energy all the time, so he sediments are ralatively fine, most of their mean grain sizes are above 4φ. Based on the analyses of lithological characters, sedimentary structures, grain sizes and biological fossils, four main sedimentary facieses may be identified in the two cores, i.e, deltaic plain, lacus, delta-front and lakeside swamp, adn may be subdivided into nine subfacieses. The average sedimentation rates of the two cores are about 40cm/1000a. Magnetite with a little maghemite and haematite are the main ferromagnetic minerals in the sediments, which are concentrated in teh silt fraction, especially in teh fine and very fine fractions. The secondary magnetite derived from the catchment may cling to coarser clay partiche's as a pellicle.The sediment susceptibility value is related with the sediment grain size composition. The susceptibility measurement made on the cores' sediments show that in deltaic plain sediments the susceptibility values increase as the sedimentary dynamic decreases, the susceptibility values of distributary, natural level and flood plain sediments are 31.7× 10-8, 62.4× 10-8, and 154.1× 10-8SI, respectively.The susceptibility value of subaqueous river sediment is 46.3 × 10-8SI, that of river mouth bar sediment is 71.4× 10-8SI, lake-shore sediment 34× 10-8SI, off-shore shallow lake sediment 129. 7× 10-8SI.The lowest susceptibility value of swamp sediment is only 3.8 × 10-8SI.The sediment related with human activity has a very high susceptibility value of 260.7 × 10-8SI. The two cores' susceptibility curves are characterized by Ⅰ. intermediate variations and comparatively higher susceptibility values of deltaic plain sedimemts; Ⅱ. great variations and high susceptibility values of lake sediments, reflection the transgression adn regression of the lake; Ⅲ .smaller variations and comparatively lower susceptibility values of lake-shore and delta-front sediments; Ⅳ.comparatively stable and lower susceptibility values of lake-side swamp sediment; Ⅴ .very high susceptibility values of the sediment related with human activity. Both of the two cores show a complete lake transgression.It mainly occured between 38, 000 and 28, 000 years B.P., and may be correlated to the third oxygen-isotope stage recorded in deep sea cores.The susceptibility curves drawed according to the results of susceptibility measursment may give evidences to the transgression and regression of the lake and the sedimentary environmental changes.
Kunming Basin is a late Cenozoic fault lake basin in Yunnan Plateau with an area of aboui 1. 000km2. The present lake Dianchi is about 300km~3 in area with its mean water level 1,886m a.s.l.The two cores (Chad Chao2) taken from the east shore of Chaohai Bay of the northern Dianchi Lake were ac-cumululed in the latest 50, 000 years with a depth of about 20m of each. The sites where the two cores are drilled was in the environment with lower energy all the time, so he sediments are ralatively fine, most of their mean grain sizes are above 4φ. Based on the analyses of lithological characters, sedimentary structures, grain sizes and biological fossils, four main sedimentary facieses may be identified in the two cores, i.e, deltaic plain, lacus, delta-front and lakeside swamp, adn may be subdivided into nine subfacieses. The average sedimentation rates of the two cores are about 40cm/1000a. Magnetite with a little maghemite and haematite are the main ferromagnetic minerals in the sediments, which are concentrated in teh silt fraction, especially in teh fine and very fine fractions. The secondary magnetite derived from the catchment may cling to coarser clay partiche's as a pellicle.The sediment susceptibility value is related with the sediment grain size composition. The susceptibility measurement made on the cores' sediments show that in deltaic plain sediments the susceptibility values increase as the sedimentary dynamic decreases, the susceptibility values of distributary, natural level and flood plain sediments are 31.7× 10-8, 62.4× 10-8, and 154.1× 10-8SI, respectively.The susceptibility value of subaqueous river sediment is 46.3 × 10-8SI, that of river mouth bar sediment is 71.4× 10-8SI, lake-shore sediment 34× 10-8SI, off-shore shallow lake sediment 129. 7× 10-8SI.The lowest susceptibility value of swamp sediment is only 3.8 × 10-8SI.The sediment related with human activity has a very high susceptibility value of 260.7 × 10-8SI. The two cores' susceptibility curves are characterized by Ⅰ. intermediate variations and comparatively higher susceptibility values of deltaic plain sedimemts; Ⅱ. great variations and high susceptibility values of lake sediments, reflection the transgression adn regression of the lake; Ⅲ .smaller variations and comparatively lower susceptibility values of lake-shore and delta-front sediments; Ⅳ.comparatively stable and lower susceptibility values of lake-side swamp sediment; Ⅴ .very high susceptibility values of the sediment related with human activity. Both of the two cores show a complete lake transgression.It mainly occured between 38, 000 and 28, 000 years B.P., and may be correlated to the third oxygen-isotope stage recorded in deep sea cores.The susceptibility curves drawed according to the results of susceptibility measursment may give evidences to the transgression and regression of the lake and the sedimentary environmental changes.
1992, 10(2): 69-78.
Abstract:
Algal and nonalgal dolomites develop extensively in Sinian System, Southwest of Sichuan Basin, which arc good natural gas reservoir beds. Some experts have done much basic research on their origin, but they had got dif ferents conclusions. Based on the previous works and the combinations of global and reginal tectonizations with advanced laboratory analyses, the medium conditions and origin of dolomites, have been deeply analysed, it was proposed that Sinian System dolomites consiste of primary dolomites and secondary dolomites. It is the first time that the unit cell parameters and crystalinity have been used for distinguishing primary dolomites from secondary dolomites. The developing of algal dolomites, microlite and micritic dolomites were controlled by the factors such as global tectonic settings, sea level changing, hot palaeoclimate, evaprat tidal flat environment, strong and weak of water dynamics and so on. These dolomites were percipitated in marine tidal enviroment by trapping, cohering, and biochemical processes of blue-green algals. They have lower crystallinity from 0.682 to 0.744 with average of 0.696, higher salinity, higher contents of trace elements (Sr, Ba, Sb, Sn, Cu) , and Mg/Ca ratio gererally lower than 0.5. The a。 and c。 of their unit cells are smaller than those of standard dolomites, its crystall is fine and has a low automorphic degree. Pure fine-crystall dolomites were developed by dolomitization under the environment that salty enviroment have had changed by air-water in early diagenetic stage. They constitute of rhythmic structure, the colour of cathodoluminesence consist of yellowish red and dark red. Fine-crystall quartz contained dolomites with dark red cathodoluminesence colour were fomred in late diagenetic stage of deeply burial enviromnt by dolomitization, residual quartz is wide spreaded in it, crystallinity of this kind of dolomite is higher (0.896-0.992) and its δ~(18)Ois light (-8.64-9.01‰) with the Mg/Ca greater than 0.5, its unit cell a。 is 4.876A and c。 is 15.249A which are similar to those of standard dolomite, and its crystall is croase, possesing a high automorphic degree.
Algal and nonalgal dolomites develop extensively in Sinian System, Southwest of Sichuan Basin, which arc good natural gas reservoir beds. Some experts have done much basic research on their origin, but they had got dif ferents conclusions. Based on the previous works and the combinations of global and reginal tectonizations with advanced laboratory analyses, the medium conditions and origin of dolomites, have been deeply analysed, it was proposed that Sinian System dolomites consiste of primary dolomites and secondary dolomites. It is the first time that the unit cell parameters and crystalinity have been used for distinguishing primary dolomites from secondary dolomites. The developing of algal dolomites, microlite and micritic dolomites were controlled by the factors such as global tectonic settings, sea level changing, hot palaeoclimate, evaprat tidal flat environment, strong and weak of water dynamics and so on. These dolomites were percipitated in marine tidal enviroment by trapping, cohering, and biochemical processes of blue-green algals. They have lower crystallinity from 0.682 to 0.744 with average of 0.696, higher salinity, higher contents of trace elements (Sr, Ba, Sb, Sn, Cu) , and Mg/Ca ratio gererally lower than 0.5. The a。 and c。 of their unit cells are smaller than those of standard dolomites, its crystall is fine and has a low automorphic degree. Pure fine-crystall dolomites were developed by dolomitization under the environment that salty enviroment have had changed by air-water in early diagenetic stage. They constitute of rhythmic structure, the colour of cathodoluminesence consist of yellowish red and dark red. Fine-crystall quartz contained dolomites with dark red cathodoluminesence colour were fomred in late diagenetic stage of deeply burial enviromnt by dolomitization, residual quartz is wide spreaded in it, crystallinity of this kind of dolomite is higher (0.896-0.992) and its δ~(18)Ois light (-8.64-9.01‰) with the Mg/Ca greater than 0.5, its unit cell a。 is 4.876A and c。 is 15.249A which are similar to those of standard dolomite, and its crystall is croase, possesing a high automorphic degree.
1992, 10(2): 88-93.
Abstract:
Some Mollusks such as Cyclina sinensis (Gmelin) could live in the distributary channel deposits very close to Yellow River mouth, although the sedimentary rate is high there. The escape traces can over 40cm long, accompaning with the thichening deposition. Following results were presented in the paper. 1. Distribution of mollusks in the Huanghe Horbour's intertidal zone: Above the mean high tidal line was Glaucomya chinsis ( Gray) zone. Under the mean high tidal line was Aloidis laevis- Cyclina sinensis-Sinonovacula zone. Glaucomya chinensis (Gray) was considered to be of greater significant for analying Huanghe River delta's fades. 2.Bioturbation models of Mollusks: There are three main types: tidal flat, distributary mouth and single river mouth.The tidal flat type may be a characteristic bed for us to divide defferent Yellow River delta lobes. 3. Sedimentary rate is the main factor that affect the Mollusks' living. The stage of deposition, such as season, could be shown through study bio-escape sedimentary structure. The plants, Phragmites communis Trin.and Polygonum hydropiper L., can live in lateral bar deposits of the active Yellow River distributary channel. During the flood season in 1988, the stems of these plants were partly buried by silt, but sprouted new roots and revived when sedimentary rate decreased. The longths of these plants escape traces can as long as 90-120cm.
Some Mollusks such as Cyclina sinensis (Gmelin) could live in the distributary channel deposits very close to Yellow River mouth, although the sedimentary rate is high there. The escape traces can over 40cm long, accompaning with the thichening deposition. Following results were presented in the paper. 1. Distribution of mollusks in the Huanghe Horbour's intertidal zone: Above the mean high tidal line was Glaucomya chinsis ( Gray) zone. Under the mean high tidal line was Aloidis laevis- Cyclina sinensis-Sinonovacula zone. Glaucomya chinensis (Gray) was considered to be of greater significant for analying Huanghe River delta's fades. 2.Bioturbation models of Mollusks: There are three main types: tidal flat, distributary mouth and single river mouth.The tidal flat type may be a characteristic bed for us to divide defferent Yellow River delta lobes. 3. Sedimentary rate is the main factor that affect the Mollusks' living. The stage of deposition, such as season, could be shown through study bio-escape sedimentary structure. The plants, Phragmites communis Trin.and Polygonum hydropiper L., can live in lateral bar deposits of the active Yellow River distributary channel. During the flood season in 1988, the stems of these plants were partly buried by silt, but sprouted new roots and revived when sedimentary rate decreased. The longths of these plants escape traces can as long as 90-120cm.
1992, 10(2): 100-108.
Abstract:
East China Sea Basin is a large Cenozoic sedimentary basin developed in the eastern continental shelf area of China, with 250000km of the area and over 12000 m of maximum thickness. Four depositional se quences have been interpreted in the basin, based on the study and analysis of seismic stratigraphy, drilling lilhological and paleontologic data and so on. These sequences are sequence Ⅰ late Cretaceous-Paleocene with the largest thickness of 85000m, distributed only in the west of the basin, sequence Ⅱ Eocene with maximum thickness of 6000 m in the east and about 1000m in the west, sequence ⅢOligocene-Miocene with up to 5000m of largest thickness, and sequence Ⅳ Pliocene-Quaternary with sedimentary thickness of approximately 2000m. The boundaries between these sequences are all angle unconformity. These sequences are characterijed by different evolution, lithology, paleontology and depositional environment. Sedimentary environments were analysed: Neritic fades and alternative marine and terrestrial facies appeared in the west of the basin with sea transgression from southeast in late Cretaceous-Paleocene. In Eosene neritic facies developed predominantly in the southwest of the basin, and in the east of Oligocene fluviolacustrine facies appeared and developed only in the basin alternative estuary and lake fades occured. the east, and in Miocene fluviolacustrine facies developed dominantly with swamp subfacis. in the both south and north extremities some local areas were affected by sea water. From Pliocene to Quaternary sedimentary environment changed gradually from fluvial to littoral and neritic facies. The article indicates various assemblages of source rocks, reserviors and sealing rocks formed by different sedimentary enviton ments. Main source rocks are Paleoeene in the west of the basin and Eocene in the east of it, and late Cretaceous is possible significant source rock and Oligocene and lower Miocene is favorable source rocks in the east.. Even though only a few wells have been drilled in the basin potential prospects have been show already. It is believed with our confidence that there are geological conditions to form large oil and gas field m East China Sea Basin
East China Sea Basin is a large Cenozoic sedimentary basin developed in the eastern continental shelf area of China, with 250000km of the area and over 12000 m of maximum thickness. Four depositional se quences have been interpreted in the basin, based on the study and analysis of seismic stratigraphy, drilling lilhological and paleontologic data and so on. These sequences are sequence Ⅰ late Cretaceous-Paleocene with the largest thickness of 85000m, distributed only in the west of the basin, sequence Ⅱ Eocene with maximum thickness of 6000 m in the east and about 1000m in the west, sequence ⅢOligocene-Miocene with up to 5000m of largest thickness, and sequence Ⅳ Pliocene-Quaternary with sedimentary thickness of approximately 2000m. The boundaries between these sequences are all angle unconformity. These sequences are characterijed by different evolution, lithology, paleontology and depositional environment. Sedimentary environments were analysed: Neritic fades and alternative marine and terrestrial facies appeared in the west of the basin with sea transgression from southeast in late Cretaceous-Paleocene. In Eosene neritic facies developed predominantly in the southwest of the basin, and in the east of Oligocene fluviolacustrine facies appeared and developed only in the basin alternative estuary and lake fades occured. the east, and in Miocene fluviolacustrine facies developed dominantly with swamp subfacis. in the both south and north extremities some local areas were affected by sea water. From Pliocene to Quaternary sedimentary environment changed gradually from fluvial to littoral and neritic facies. The article indicates various assemblages of source rocks, reserviors and sealing rocks formed by different sedimentary enviton ments. Main source rocks are Paleoeene in the west of the basin and Eocene in the east of it, and late Cretaceous is possible significant source rock and Oligocene and lower Miocene is favorable source rocks in the east.. Even though only a few wells have been drilled in the basin potential prospects have been show already. It is believed with our confidence that there are geological conditions to form large oil and gas field m East China Sea Basin
1992, 10(2): 119-125.
Abstract:
During the process of petroleum migration, it would develop compositional fractionation by mutual effect of stationary-mobile phase, called "Geochromatograph" In this paper, samples of natural gas and condensate oil have been collected from two typical gas fields in Sichuan Basin-Weiyuan and Zhongba Gas Fields, which are different in age of source beds, reservior strata、precursor and maturity.Results of GC and GC-MS analysis reveal a regular compositional variation of the hydrocarbons within the well- locality sections, which is different from that caused by either gravitational fractionation or diffusive homogenization, suggesting the geochromatographic effusive. Along the direction from wing to top of anticlinal gas traps, parameters such as C1 / (C2+C3) 、 iC4/ nC4、 CH4% 、 N2、 △R1 and △R3 show increasing trend, while iC4/ C3 and CH4/ N2 show decreasing tendency; among condensate oil parameters, cyclohexane/ normalheptane、 ethylcyclohexane / (D+P) dimethylbenzene、 Pr/Ph、 ACL1 and ACI2 increase, while ABI1 and ABI2 show decreasing trend. During the percolative migration process, besides the molecular weight、 molecular volumn and so on, polarity difference is the dominant factor for controlling the relative migration velocity of different composition. Polarity different derives from both variances of molecular length and molecular structure, but structure factor plays a much more important role than the former. Among parameters illustrating the geochromatography, △R3 and ABI1 are the best ones with two remarkable features in common: 1. highest resolution in responding to the fractionation, 2. mono-explanatory for migration. While ABI1 value has been least influenced by the evaperative depletion of condensate oil samples during the transportation, showing its stable geochemical property.
During the process of petroleum migration, it would develop compositional fractionation by mutual effect of stationary-mobile phase, called "Geochromatograph" In this paper, samples of natural gas and condensate oil have been collected from two typical gas fields in Sichuan Basin-Weiyuan and Zhongba Gas Fields, which are different in age of source beds, reservior strata、precursor and maturity.Results of GC and GC-MS analysis reveal a regular compositional variation of the hydrocarbons within the well- locality sections, which is different from that caused by either gravitational fractionation or diffusive homogenization, suggesting the geochromatographic effusive. Along the direction from wing to top of anticlinal gas traps, parameters such as C1 / (C2+C3) 、 iC4/ nC4、 CH4% 、 N2、 △R1 and △R3 show increasing trend, while iC4/ C3 and CH4/ N2 show decreasing tendency; among condensate oil parameters, cyclohexane/ normalheptane、 ethylcyclohexane / (D+P) dimethylbenzene、 Pr/Ph、 ACL1 and ACI2 increase, while ABI1 and ABI2 show decreasing trend. During the percolative migration process, besides the molecular weight、 molecular volumn and so on, polarity difference is the dominant factor for controlling the relative migration velocity of different composition. Polarity different derives from both variances of molecular length and molecular structure, but structure factor plays a much more important role than the former. Among parameters illustrating the geochromatography, △R3 and ABI1 are the best ones with two remarkable features in common: 1. highest resolution in responding to the fractionation, 2. mono-explanatory for migration. While ABI1 value has been least influenced by the evaperative depletion of condensate oil samples during the transportation, showing its stable geochemical property.
1992, 10(2): 135-142.
Abstract:
Liaohe Basin is a fault basin of rift valley type formed in Cenozoic Era. In this basin there are several sets of natural gas source rocks and good geological circumstances for the origination of natural gases. It has been proven by geologic exploration that there are plenty of natural gas resources in this basin. The result of the analysis of the chemical and isotopic compositions of 80 natural gas samples shows that the main components of the natural gases in Liaohe Basin are hydrocarbons. The proportion of hydrocarbons in the total natural gas components is higher than 90%. The carbon isotopic composition of methane ranges mainly from -35‰ to 55‰ (PDB), with the lightest -60.7‰ and heaviest -29‰. The hydrogen isotopic composition of methane ranges from -185‰ to 275‰ (SMOW) . The carbon isotopic compositions of ethane and propane range from -25‰ to -33‰ (PDB) and -24‰ to -30‰ (PDB), respectively. Based on the analysis of the chemical compositions and isotopic compositions of the gaseous hydrocarbons, the geneses of the gaseous hydrocarbons is discussed and five genetic types of gaseous hydrocarbons have been identified as follows. Tyep A: Biogenic gas, C1 / Σ Cn is 0.99, the component of ethane heavier hydrocarbons (C2+) is Carbon isotopic composition of the methane (δ13CCH4 ) is -60.7‰(PDB) , hydrogen isotopic composition of the methane (δCCH4 ) is-204‰ (SMOW) . Type B: Gas of transitional zone, C1 / Σ Cn is 0.95, C2+ 5% , δ13CCH4 ranges from - 50‰ to -55‰, δ13CCH4 ranges from -225‰ to -275‰. Natural gas of these characteristics was considered as a mixture of biogenic and thermogenic gas in the past. In some areas it could be possible, but in Liaohe Basin, this type of gas was original both in generation and in reservation. Type C: Low mature to mature oil-associated gas, C1 / Σ Cn ranges from 0.45 to 0.95, δ13CCH4 ranges from - 40‰ to -50‰ , δ13CCH4 ranges from - 200‰ to-260‰, δ13C3-δ13C22>‰ and δ13C2-δ13C12>‰ value ranges from 10‰ to 20‰. Type D: High mature and condensate generated gas, C1 / Σ Cn ranges from 0.45 to 0.95、 δ13CCH4 ranges from -185‰ to -235‰, δ13C3-δ13C22>‰ and δ13C2-δ13C1 14‰. Type E: Gas produced from kerogen of type Ⅲ, C1 /ΣCn is 0.96, C2+5%, carbon and gydrogen isotopic compositions of the methane are -29‰ and -194‰, respectively. This type of gas was generated from the coal-bearing strata of Mesozoic Erathem.
Liaohe Basin is a fault basin of rift valley type formed in Cenozoic Era. In this basin there are several sets of natural gas source rocks and good geological circumstances for the origination of natural gases. It has been proven by geologic exploration that there are plenty of natural gas resources in this basin. The result of the analysis of the chemical and isotopic compositions of 80 natural gas samples shows that the main components of the natural gases in Liaohe Basin are hydrocarbons. The proportion of hydrocarbons in the total natural gas components is higher than 90%. The carbon isotopic composition of methane ranges mainly from -35‰ to 55‰ (PDB), with the lightest -60.7‰ and heaviest -29‰. The hydrogen isotopic composition of methane ranges from -185‰ to 275‰ (SMOW) . The carbon isotopic compositions of ethane and propane range from -25‰ to -33‰ (PDB) and -24‰ to -30‰ (PDB), respectively. Based on the analysis of the chemical compositions and isotopic compositions of the gaseous hydrocarbons, the geneses of the gaseous hydrocarbons is discussed and five genetic types of gaseous hydrocarbons have been identified as follows. Tyep A: Biogenic gas, C1 / Σ Cn is 0.99, the component of ethane heavier hydrocarbons (C2+) is Carbon isotopic composition of the methane (δ13CCH4 ) is -60.7‰(PDB) , hydrogen isotopic composition of the methane (δCCH4 ) is-204‰ (SMOW) . Type B: Gas of transitional zone, C1 / Σ Cn is 0.95, C2+ 5% , δ13CCH4 ranges from - 50‰ to -55‰, δ13CCH4 ranges from -225‰ to -275‰. Natural gas of these characteristics was considered as a mixture of biogenic and thermogenic gas in the past. In some areas it could be possible, but in Liaohe Basin, this type of gas was original both in generation and in reservation. Type C: Low mature to mature oil-associated gas, C1 / Σ Cn ranges from 0.45 to 0.95, δ13CCH4 ranges from - 40‰ to -50‰ , δ13CCH4 ranges from - 200‰ to-260‰, δ13C3-δ13C22>‰ and δ13C2-δ13C12>‰ value ranges from 10‰ to 20‰. Type D: High mature and condensate generated gas, C1 / Σ Cn ranges from 0.45 to 0.95、 δ13CCH4 ranges from -185‰ to -235‰, δ13C3-δ13C22>‰ and δ13C2-δ13C1 14‰. Type E: Gas produced from kerogen of type Ⅲ, C1 /ΣCn is 0.96, C2+5%, carbon and gydrogen isotopic compositions of the methane are -29‰ and -194‰, respectively. This type of gas was generated from the coal-bearing strata of Mesozoic Erathem.
1992, 10(2): 9-18.
Abstract:
The radiolarian cherts in the Wenbei region of Shaanxi Province are a formation of pelagic sediments formed within the North China Platform. These radiolarian cherts are black in color, composed mainly of chalcedony, abound in "ghosts" or netted skeletons of radiolarians and show well-devoloped liminations. They contain some interbedded thin siliceous shales, and in stratigraphic section are associated with turbidite limestones and tuffs. The well visible relict organic texture and diagenetic replacement fabrics in the cherts suggest that the rocks are chiefly derived from biogenic opals by dissolution-reprecipitation processes during the early diagenetic stage, while free SiO2 released by volcanic ash constitutes a very limited content. In terms of age, the radiolarian cherts in the Weibei region can be correlated to the Caradocian stage of the Middle Ordvician. This corresponds to a time when there was a rise of the global sea level, and when the ancient Qinling ocean basin was undergonig vigorous spreading and subduction. The subsidence occurred in the southern margin of the North China Platform made a deep-water back-arc basin on its northern margin which lay in the Weibei region. During this period, the study area was located right within low latitudes of the eguator. A broad shallow water carbonate platform which existed to the north of North China impeded effectively the introduction of terrigenous clastic sediments into the basin from the north. The widespreded bedded cherts in the Qinling region indicates that the open sea was a zone of up welling ocean currents characterized by high planktonic organism productivity. All these factors were favourable conditons for the deposition of radiolarian cherts. Becaues calcareous planktonic organisms had not yet flourished at that time, radiolatian chert deposition might not have been controled by CCD, and the water depth probably was much shallower than that of their modern analogue.
The radiolarian cherts in the Wenbei region of Shaanxi Province are a formation of pelagic sediments formed within the North China Platform. These radiolarian cherts are black in color, composed mainly of chalcedony, abound in "ghosts" or netted skeletons of radiolarians and show well-devoloped liminations. They contain some interbedded thin siliceous shales, and in stratigraphic section are associated with turbidite limestones and tuffs. The well visible relict organic texture and diagenetic replacement fabrics in the cherts suggest that the rocks are chiefly derived from biogenic opals by dissolution-reprecipitation processes during the early diagenetic stage, while free SiO2 released by volcanic ash constitutes a very limited content. In terms of age, the radiolarian cherts in the Weibei region can be correlated to the Caradocian stage of the Middle Ordvician. This corresponds to a time when there was a rise of the global sea level, and when the ancient Qinling ocean basin was undergonig vigorous spreading and subduction. The subsidence occurred in the southern margin of the North China Platform made a deep-water back-arc basin on its northern margin which lay in the Weibei region. During this period, the study area was located right within low latitudes of the eguator. A broad shallow water carbonate platform which existed to the north of North China impeded effectively the introduction of terrigenous clastic sediments into the basin from the north. The widespreded bedded cherts in the Qinling region indicates that the open sea was a zone of up welling ocean currents characterized by high planktonic organism productivity. All these factors were favourable conditons for the deposition of radiolarian cherts. Becaues calcareous planktonic organisms had not yet flourished at that time, radiolatian chert deposition might not have been controled by CCD, and the water depth probably was much shallower than that of their modern analogue.
1992, 10(2): 28-38.
Abstract:
The clayey coal-partings (tonsteins) of altered synsedimentary volcanic ash-fall origin are well developed in the Late- Permian coal-bearing formation of eastern Yunnan Province, an area of approximately 100, 000km~2. Because of their unique origin and stable lateral distribution over vast areas, great importance has been attached to the studies of tonsteins (i.e., unconventional claystones) . More than 20 layers (with a thickness in the range of 3-6 cm) of tonsteins were identified from the coal-bearing sequence 200-250 m thick. In order to distinguish tonsteins from the co-existing conventional claystones macroscopically and microscopically, to search for convergence of evidence on the origin of tonsteins from different approaches, to characteriae the individuality of tonsteins from different horizons, as well as to figure out the directions from which the source materials were derived, special techniques such as panned-concentrate separation, statistical and morphological analyses were performed on zircon minerals from claystones of two different origins and diageneses. The results demonstrate the fact that zircons of these two different origins are greatly different in their contents, morphological features and related parametric statistical patterns. The surficial features of these crystal solids also show apparent difference in origin. Tonsteins from the same area but different horizons are characterized by different zircon contents and different morphological paramieric statistical patterns. Tonsteins of the same horizon show close statistical associations in terms of zircon content and morphological parameters; there are continuous variations in statistical patterns in response to changes in lateral distribution of the same layer of tonstein. It was made possible to identify the different paths and directions in which the source materials of tonsteins (i.e., the volcanic ash-falls) or conventional claystones (i.e., the terrigenous clastic sediments) were derived and transported. Therefore, it is important to recognize the source materials and their nature and orgin by studying systematically the characteritics of zircons in various rocks (including tonsteins) along the profile of a coal-bearing formaiton, in order to provide the basic data as an aid in establishing the stratigraphic sequence, facilitating the more precise coal correlation in a mining area as well as improving the stratigraphic correlation on a reginal scale
The clayey coal-partings (tonsteins) of altered synsedimentary volcanic ash-fall origin are well developed in the Late- Permian coal-bearing formation of eastern Yunnan Province, an area of approximately 100, 000km~2. Because of their unique origin and stable lateral distribution over vast areas, great importance has been attached to the studies of tonsteins (i.e., unconventional claystones) . More than 20 layers (with a thickness in the range of 3-6 cm) of tonsteins were identified from the coal-bearing sequence 200-250 m thick. In order to distinguish tonsteins from the co-existing conventional claystones macroscopically and microscopically, to search for convergence of evidence on the origin of tonsteins from different approaches, to characteriae the individuality of tonsteins from different horizons, as well as to figure out the directions from which the source materials were derived, special techniques such as panned-concentrate separation, statistical and morphological analyses were performed on zircon minerals from claystones of two different origins and diageneses. The results demonstrate the fact that zircons of these two different origins are greatly different in their contents, morphological features and related parametric statistical patterns. The surficial features of these crystal solids also show apparent difference in origin. Tonsteins from the same area but different horizons are characterized by different zircon contents and different morphological paramieric statistical patterns. Tonsteins of the same horizon show close statistical associations in terms of zircon content and morphological parameters; there are continuous variations in statistical patterns in response to changes in lateral distribution of the same layer of tonstein. It was made possible to identify the different paths and directions in which the source materials of tonsteins (i.e., the volcanic ash-falls) or conventional claystones (i.e., the terrigenous clastic sediments) were derived and transported. Therefore, it is important to recognize the source materials and their nature and orgin by studying systematically the characteritics of zircons in various rocks (including tonsteins) along the profile of a coal-bearing formaiton, in order to provide the basic data as an aid in establishing the stratigraphic sequence, facilitating the more precise coal correlation in a mining area as well as improving the stratigraphic correlation on a reginal scale
1992, 10(2): 45-53.
Abstract:
Rice- shaped dolomite crystals exist in dolomite- patched micritic, biomicritic, intraclastic andstrornatolitic limestones in an Ordovician nearshore, carbonate succession, reaching their highest concen-trations promixal to worm burrows and pore space between intraclasts. The crystals are elongaterhombohedra and appear to be elongate hexagons, parallelograms or trapezoids and look like rice grains inthin sections. No internal zoning or foggy cores are present but numc;rous minute calcite "enclusions" distrib-ute parallel to the boundary of the crystals. The C-axis is perpendicular to the longer boundary of the crystalIt contains higher Fe, Mn, Na and Ba than surrounding calcite micrite which contains a greater proportion of Sr, especially its Fe and Ba are tens of times higher than those of calcite. C-axis orientation negatesthe dolomite representing replacement of gypsum.It can not be ureated by an ordinary dolomitization or thereplacement of norsethite and is suggested to form in a process that the precipitated magnesian calcite.is recrystallized into its inherent crystallographic shape, then followed by exsolution accompanied by ex-change of calcium for magnesium ions under conditions of increased pressure. The agent triggering therecrystallization of magnesian calcite is probablyinpenecontamporaueous of early diagenetie interstitial wat er with high Mg/‘Ca ratio, in which there may be some substance that can release chemical energy not on、to dehydrate Mg2+ but also to order the entering of the ions into lattice. As the water solution permeates thesediments downward and upper layers are dolomitized, the substance (or its energel is consumed gridnally, the concentration of which could become as less as can only carry out dehydration of Ioci1 ion, but cat not make the activity of the cans ordered whrn the solution reaches the lower livers, As a result, parts，mignesian calcite in the lower sediments ire favoured to grow up trir;sforming W their inheren}rvstallographic shape. Some $a compound seems to be a candidate 1-or the substance
Rice- shaped dolomite crystals exist in dolomite- patched micritic, biomicritic, intraclastic andstrornatolitic limestones in an Ordovician nearshore, carbonate succession, reaching their highest concen-trations promixal to worm burrows and pore space between intraclasts. The crystals are elongaterhombohedra and appear to be elongate hexagons, parallelograms or trapezoids and look like rice grains inthin sections. No internal zoning or foggy cores are present but numc;rous minute calcite "enclusions" distrib-ute parallel to the boundary of the crystals. The C-axis is perpendicular to the longer boundary of the crystalIt contains higher Fe, Mn, Na and Ba than surrounding calcite micrite which contains a greater proportion of Sr, especially its Fe and Ba are tens of times higher than those of calcite. C-axis orientation negatesthe dolomite representing replacement of gypsum.It can not be ureated by an ordinary dolomitization or thereplacement of norsethite and is suggested to form in a process that the precipitated magnesian calcite.is recrystallized into its inherent crystallographic shape, then followed by exsolution accompanied by ex-change of calcium for magnesium ions under conditions of increased pressure. The agent triggering therecrystallization of magnesian calcite is probablyinpenecontamporaueous of early diagenetie interstitial wat er with high Mg/‘Ca ratio, in which there may be some substance that can release chemical energy not on、to dehydrate Mg2+ but also to order the entering of the ions into lattice. As the water solution permeates thesediments downward and upper layers are dolomitized, the substance (or its energel is consumed gridnally, the concentration of which could become as less as can only carry out dehydration of Ioci1 ion, but cat not make the activity of the cans ordered whrn the solution reaches the lower livers, As a result, parts，mignesian calcite in the lower sediments ire favoured to grow up trir;sforming W their inheren}rvstallographic shape. Some $a compound seems to be a candidate 1-or the substance
1992, 10(2): 62-68.
Abstract:
The ultimate aim of historical sedimentology is to expound characteristics of vertical sequences of the sedimentary records from larger time-space scale and explain its evolution process in time and the distributary pattern in space. That is, historical connection of the sedimentary sequences in time-space evolution would be interpreted. Maximum Entropy Matrix (MEM) anlysis in Mathematics days an important role on this object. It is very clear that the fundamental principle taking the isochronous sedimentary sequences, which have a obvious characteristic of sandstone and mudstone interbed structure, to be undergone MEM anely sis. That is, sandstone sediments of channel deposition which arise random or disorderly and unsystematicly at the sequence contains actually the cyclicity of sub-cyclicity, and it reflects the periodicity of the channel evolution at the time vector. Thus, we can separate the main periodicity (main frequency) of the cyclioty sandstone with MEM analysis and take it as a parameter to determine the relativity of isochronous sedimentary sequences. If the two isochronous sedimentary sequences have the same or similar amoum of main frequency of the channel sandstone arising, the sequences are of relativity in contribution facton of similarity in sedimentary environment. This paper takes Zhenchuanpu gas- bearing area in the east of Eerduosi Basin locates in western . North-China Platform as an example, and put forwards the MEM analysis method to the isochronous sedimentary sequences so as to look for the historical forming relationship in every straligraphic sequences and the close relationship. Thus the paper has relatively well resolved the problems of palaeocurient direction, the form of river channel and the shoreline of lake etc. The study shows that the MEM analysis method of stratigraphic sequences may help petroleum geologists to rebuild llthofacies and palaeogeography using lithic logging sectiones. The study results indicate that the sedimentary provenance of the lower Shihezi Formation of lower Permian System in Zhenchuanpu area is along the northeastern Baode-Fugu, the palaeocurrent direction is 30-60° , and there are two river systems and three stable main channels. When in the optimu filting wave stage m= 62 and spectrum span k = 200. it is optimum to the MEM analysis effect of the stratigraphic sequences of the lower Shihezi Formation. The premise of the relativity correlation of sedimentary sequences is the isochronous character about the boundary of sequences top and bottom. Seismic stratigraphy may satisfactorily resolve this question.
The ultimate aim of historical sedimentology is to expound characteristics of vertical sequences of the sedimentary records from larger time-space scale and explain its evolution process in time and the distributary pattern in space. That is, historical connection of the sedimentary sequences in time-space evolution would be interpreted. Maximum Entropy Matrix (MEM) anlysis in Mathematics days an important role on this object. It is very clear that the fundamental principle taking the isochronous sedimentary sequences, which have a obvious characteristic of sandstone and mudstone interbed structure, to be undergone MEM anely sis. That is, sandstone sediments of channel deposition which arise random or disorderly and unsystematicly at the sequence contains actually the cyclicity of sub-cyclicity, and it reflects the periodicity of the channel evolution at the time vector. Thus, we can separate the main periodicity (main frequency) of the cyclioty sandstone with MEM analysis and take it as a parameter to determine the relativity of isochronous sedimentary sequences. If the two isochronous sedimentary sequences have the same or similar amoum of main frequency of the channel sandstone arising, the sequences are of relativity in contribution facton of similarity in sedimentary environment. This paper takes Zhenchuanpu gas- bearing area in the east of Eerduosi Basin locates in western . North-China Platform as an example, and put forwards the MEM analysis method to the isochronous sedimentary sequences so as to look for the historical forming relationship in every straligraphic sequences and the close relationship. Thus the paper has relatively well resolved the problems of palaeocurient direction, the form of river channel and the shoreline of lake etc. The study shows that the MEM analysis method of stratigraphic sequences may help petroleum geologists to rebuild llthofacies and palaeogeography using lithic logging sectiones. The study results indicate that the sedimentary provenance of the lower Shihezi Formation of lower Permian System in Zhenchuanpu area is along the northeastern Baode-Fugu, the palaeocurrent direction is 30-60° , and there are two river systems and three stable main channels. When in the optimu filting wave stage m= 62 and spectrum span k = 200. it is optimum to the MEM analysis effect of the stratigraphic sequences of the lower Shihezi Formation. The premise of the relativity correlation of sedimentary sequences is the isochronous character about the boundary of sequences top and bottom. Seismic stratigraphy may satisfactorily resolve this question.
1992, 10(2): 79-87.
Abstract:
The present paper focus on the depositional enviroment and its relationship with the life and the preservation of graptolites in the Silurian Wuxihe Formation, southern Shaanxi. First, The authors collected the fossils layer by layer in about one square metre and got the statistics of the fossils on the surface of each layer Then drawn the dead curves of some spcial species and analysed the characteristics and the content of some elements in country rocks, such as Fe++. Fe+++, S, C and pH, and so on, main conclusions obtained as follows: 1 .The depositional enviroment was a cutoff basin, the bottom water current was confined and the condition was reducing, so there no benthonic arganism could survive. 2.The rock types of Wuxiahe Formation is turbite, consisting of siltstone, silty shale, shale and black mudstone, correspond to the B、 C、 D and E divisions of the Bouma sequence, respectively, while A-divi sion(some time B-division) is lacuna, 3.The graptolites is richest in the siltyshale and shale, less in the mudstone and none in the siltstone. 4.The change of the graptolites abundance is mainly resulted from its sedimentary environment and the invasion of the turbidity current. When the current reached to the basin from the Yangtze Platform, croase sediments (sands) will deposite first, the dropping graptolites carcasses might be tear to shreds by the current so, none fossils was found in sandstone.while with the diffusion of the fine-grained particles to the upper water body, associate H2S which agitated up by turbidity current form the bottom of basin, with most of the graptolites would be killed and their carcasses can be preserved at the bottom, of basinso a great deal of graptotite fossiles can be found in silty shale and shale(corespond to D1 and D2 division of Bouma sequenco).
The present paper focus on the depositional enviroment and its relationship with the life and the preservation of graptolites in the Silurian Wuxihe Formation, southern Shaanxi. First, The authors collected the fossils layer by layer in about one square metre and got the statistics of the fossils on the surface of each layer Then drawn the dead curves of some spcial species and analysed the characteristics and the content of some elements in country rocks, such as Fe++. Fe+++, S, C and pH, and so on, main conclusions obtained as follows: 1 .The depositional enviroment was a cutoff basin, the bottom water current was confined and the condition was reducing, so there no benthonic arganism could survive. 2.The rock types of Wuxiahe Formation is turbite, consisting of siltstone, silty shale, shale and black mudstone, correspond to the B、 C、 D and E divisions of the Bouma sequence, respectively, while A-divi sion(some time B-division) is lacuna, 3.The graptolites is richest in the siltyshale and shale, less in the mudstone and none in the siltstone. 4.The change of the graptolites abundance is mainly resulted from its sedimentary environment and the invasion of the turbidity current. When the current reached to the basin from the Yangtze Platform, croase sediments (sands) will deposite first, the dropping graptolites carcasses might be tear to shreds by the current so, none fossils was found in sandstone.while with the diffusion of the fine-grained particles to the upper water body, associate H2S which agitated up by turbidity current form the bottom of basin, with most of the graptolites would be killed and their carcasses can be preserved at the bottom, of basinso a great deal of graptotite fossiles can be found in silty shale and shale(corespond to D1 and D2 division of Bouma sequenco).
1992, 10(2): 94-99.
Abstract:
During the last glacial stage, the sea level of the world fell down generally with a mean range of about 130 m in East Asia. The continental shelves of Bohai Sea, Yellow Sea and most of East Chian Sea were exposed and turned into land. The influence of southeastern monsoon downhilled, the cold high pressure from Siberia which controlling Asia became stronger and stronger and the area influenced by it was far larger than the present one. When the continental glaciations of mid-high latitude in Europe and America were developed in a large scale, desert and prairie landscapes appeared at the same latitude in Asia because of less precipitation. Bohai Sea was an inland basin located in the centre of Asia during the glacial time and lay about several hundreds of kilometers away from the sea. Because the hills of Liaodong Peninsula, Miao Islands and Shandong Peninsula which are located to the southeast of Bohai Sea resisted the southeastern wind in summer, there was little rainfall there. Under the northwestern blowing it appeared that the topography was reformed and the material was differentiated. Thus, the abundant loose sediments distributed on the sea floor of Bohai Sea supplied enough material for the development of desert. The sandy sediments in Bohai Basin were accumulated to form sand dunes and further to developed into deserts locally. And the silty and clayey materials were blown down to the slope of hills or in the valley located to the southeast of the basin and formed loess there. The 14C dating of the calcareous dolls in the loess suggested that the loess was formed during 12000-25000 B.P. which was the flourish time of the Warm glacial. The dunes consists dominantly of well sorted and rounded medium-fine sand, which is coarse in the northwest and fine in the southeast. At present, the dunes in the central Bohai Sea are covered by the Holocene sediment. The underlying dune sediments have clearly foreset laminae with a high declimation. The dune sediments located in the east and the west of the Bohai Sea are still exposed on the seafloor, and the shape of the dunes was destroyed by the reworking of tidal current and wave. Up to now, about a quarter of Bogai Sea is covered by relict sandy sediments. The lithologic character of the sediments and the subbottom profiler records suggest that the ancient desert mainly distributed in the central Bohai Sea and Liaodong Bay, with relatively less developed in Bohai Bay, and no ancient desert had been formed in Laizhou Bay at the last glaciation.
During the last glacial stage, the sea level of the world fell down generally with a mean range of about 130 m in East Asia. The continental shelves of Bohai Sea, Yellow Sea and most of East Chian Sea were exposed and turned into land. The influence of southeastern monsoon downhilled, the cold high pressure from Siberia which controlling Asia became stronger and stronger and the area influenced by it was far larger than the present one. When the continental glaciations of mid-high latitude in Europe and America were developed in a large scale, desert and prairie landscapes appeared at the same latitude in Asia because of less precipitation. Bohai Sea was an inland basin located in the centre of Asia during the glacial time and lay about several hundreds of kilometers away from the sea. Because the hills of Liaodong Peninsula, Miao Islands and Shandong Peninsula which are located to the southeast of Bohai Sea resisted the southeastern wind in summer, there was little rainfall there. Under the northwestern blowing it appeared that the topography was reformed and the material was differentiated. Thus, the abundant loose sediments distributed on the sea floor of Bohai Sea supplied enough material for the development of desert. The sandy sediments in Bohai Basin were accumulated to form sand dunes and further to developed into deserts locally. And the silty and clayey materials were blown down to the slope of hills or in the valley located to the southeast of the basin and formed loess there. The 14C dating of the calcareous dolls in the loess suggested that the loess was formed during 12000-25000 B.P. which was the flourish time of the Warm glacial. The dunes consists dominantly of well sorted and rounded medium-fine sand, which is coarse in the northwest and fine in the southeast. At present, the dunes in the central Bohai Sea are covered by the Holocene sediment. The underlying dune sediments have clearly foreset laminae with a high declimation. The dune sediments located in the east and the west of the Bohai Sea are still exposed on the seafloor, and the shape of the dunes was destroyed by the reworking of tidal current and wave. Up to now, about a quarter of Bogai Sea is covered by relict sandy sediments. The lithologic character of the sediments and the subbottom profiler records suggest that the ancient desert mainly distributed in the central Bohai Sea and Liaodong Bay, with relatively less developed in Bohai Bay, and no ancient desert had been formed in Laizhou Bay at the last glaciation.
1992, 10(2): 109-118.
Abstract:
From the cyclic points of view, the present paper deals with the relationship between the underground water flow and hydrocarbons in Jiuxi basin. Two hydrogeological cycles can be classified in Jiuxi basin: Cretaceous and Cenozoic hydrogeological cycles, and each cycle can be further divided into two stages: compaction-driven and gravity underground water flow stages. Due to sedimentary great thickness and rapid depositional rates in Cenozoic hydrogeological cycle, compaction-driven hydrodynamic system was active and centrifugal, resulting in discharge zones in the southern and northern basin. Cap discharge favourable for hydrocarbon accumulation was formed in the southern basin because of caprocks of high quality and great thickness, and open discharge giving rise to hydrcarbon loss was formed in the northern basin because of caprocks of poor quality. After Ximalaya movement, the basin was uplifted and centripetal gravity flow should be formed due to the elevated periphery, but the compaction-driven hydrodynamic system in the southern basin was not replaced by the grqvity flow system because of caprocks of high quality. Despite of strong uplift of Qilianshan, the dominance of compaction-driven hydrodynamic system has continued to the present. In the northern basin due to caprocks of poor quality, the gravity flow system replaced rapidly the compaction-driven flow system and thd present flow direction reflects the hydrodynamic state of that stage. The late strong uplift of Qilianshen give rise to the tilt of the basin to the north and the flow direction in the northern basin is not changed because of shout time and low permeability. The investigation of the hydrodynamic and hydrochemical fields indicates that the hydrocarbon accumulation zone of the southern basin is arranged in the stagnant zones of discharge in the compaction-driven flow of the Cenozoic hydrogeological cycle, and the northern zone is in gravity flow stage. With the finite difference method in the permeable equation for the underground water in hydrogeology, the hydrodynamic configurations in different stages in the consolidation basin are obtained in the preaent paper, the water currents after the maturity of the source rocks are examined in details, and in consequence, the hydraulic trap zones favourable for the migration and accumulation of hydrocarbons can be proposed here-the low hydraulic head zones in the high hydraulic zones, the zones of steep hydraulic head gradient, i.e., the stagnant zones of discharge.
From the cyclic points of view, the present paper deals with the relationship between the underground water flow and hydrocarbons in Jiuxi basin. Two hydrogeological cycles can be classified in Jiuxi basin: Cretaceous and Cenozoic hydrogeological cycles, and each cycle can be further divided into two stages: compaction-driven and gravity underground water flow stages. Due to sedimentary great thickness and rapid depositional rates in Cenozoic hydrogeological cycle, compaction-driven hydrodynamic system was active and centrifugal, resulting in discharge zones in the southern and northern basin. Cap discharge favourable for hydrocarbon accumulation was formed in the southern basin because of caprocks of high quality and great thickness, and open discharge giving rise to hydrcarbon loss was formed in the northern basin because of caprocks of poor quality. After Ximalaya movement, the basin was uplifted and centripetal gravity flow should be formed due to the elevated periphery, but the compaction-driven hydrodynamic system in the southern basin was not replaced by the grqvity flow system because of caprocks of high quality. Despite of strong uplift of Qilianshan, the dominance of compaction-driven hydrodynamic system has continued to the present. In the northern basin due to caprocks of poor quality, the gravity flow system replaced rapidly the compaction-driven flow system and thd present flow direction reflects the hydrodynamic state of that stage. The late strong uplift of Qilianshen give rise to the tilt of the basin to the north and the flow direction in the northern basin is not changed because of shout time and low permeability. The investigation of the hydrodynamic and hydrochemical fields indicates that the hydrocarbon accumulation zone of the southern basin is arranged in the stagnant zones of discharge in the compaction-driven flow of the Cenozoic hydrogeological cycle, and the northern zone is in gravity flow stage. With the finite difference method in the permeable equation for the underground water in hydrogeology, the hydrodynamic configurations in different stages in the consolidation basin are obtained in the preaent paper, the water currents after the maturity of the source rocks are examined in details, and in consequence, the hydraulic trap zones favourable for the migration and accumulation of hydrocarbons can be proposed here-the low hydraulic head zones in the high hydraulic zones, the zones of steep hydraulic head gradient, i.e., the stagnant zones of discharge.
1992, 10(2): 126-134.
Abstract:
Aromatic hydrocarbons in Sunniland oils and source rocks from South Florida Basin, USA , is analysed, in order to probe into the distribution characteristics of aromatic hydrocarbons and environmental paleoreconstruction. Sunniland oils and source rocks are richer in naphthalenes, phenanthrenes, dibenzothiophenes and triaromatic steroids; and methyldibenzothiophene isomers show V pattern. The relative abundances of fluorences, dibenzofurans and dibenzothiophenes and other geochemical characteristics such as Pr / Ph 1, the even preference of n-alkanes in the region C22-C30, low concentrations or absence of bicyclic sesquiterpanes and abundant aromatic-sulfur compounds indicate that Sunnliandd oils and source rocks were formed under the marine strongly reducing hypersaline environment. Some compounds such as D- ring aromatized 8, 14-secohopanes, long-chain alkylbenzenes and long-chain alkylbenzothiophenes and very abundant extented hopanes (C31-C35) and C24, C26 tetracyclic terpanes suggest that Sunniland organic matter can be related to the bacterial input. Maturity parameters (MPI1, MPI3, MDR4, 1, etc.) indicate that Sunniland oils and sourc rocks are immature to marginally mature.
Aromatic hydrocarbons in Sunniland oils and source rocks from South Florida Basin, USA , is analysed, in order to probe into the distribution characteristics of aromatic hydrocarbons and environmental paleoreconstruction. Sunniland oils and source rocks are richer in naphthalenes, phenanthrenes, dibenzothiophenes and triaromatic steroids; and methyldibenzothiophene isomers show V pattern. The relative abundances of fluorences, dibenzofurans and dibenzothiophenes and other geochemical characteristics such as Pr / Ph 1, the even preference of n-alkanes in the region C22-C30, low concentrations or absence of bicyclic sesquiterpanes and abundant aromatic-sulfur compounds indicate that Sunnliandd oils and source rocks were formed under the marine strongly reducing hypersaline environment. Some compounds such as D- ring aromatized 8, 14-secohopanes, long-chain alkylbenzenes and long-chain alkylbenzothiophenes and very abundant extented hopanes (C31-C35) and C24, C26 tetracyclic terpanes suggest that Sunniland organic matter can be related to the bacterial input. Maturity parameters (MPI1, MPI3, MDR4, 1, etc.) indicate that Sunniland oils and sourc rocks are immature to marginally mature.
