1991 Vol. 9, No. 1
column
Display Method:
1991, 9(1): 1-10.
Abstract:
The restricted epicontinental sea lies on the edge of a continent and surrounded by islands as a sill. The sedimentation there is characterized by the episodic sea water invasion which takes place in short period and rapidly covers a wide area. As a consequence, there always occur discontinuous depositional sequence and frequently alternation of marine and nonmarine deposits.The transgression is controlled by the openning and closing of the gateway between islands due to the sea level fluctuation.lt is the defined event transgression or episodic transgression by the authors. In view of the plate tectonics, the back-arc basins arround active margin are typical epicontinental sea, so episodic transgression happens quite often. The episodic transgressive beds are magnafacies as well as parvafacies (isochronous).Therefore they can be used as a marker of stratigraphic correlation. The Mediterranean sea had repeatedly dried at the end of Miocene due to the openning and closing of the Strait of Gibratar which caused the alternation of deep sea and Sabkha sedimentation.lt provides a good example of episodic trasgression.The East China Sea was a typical epicontinental sea in Cenozoic. the sea level fluctuation resulted from climatic change caused many times of episodic transgression and interruption of marine sedimentation and resulted in a sequence consiting of interbeded marine and non-marine deposits. We can go far back to the Carboniferous deposits in northern China where the marine beds of limestone can be traced in a wide area even though they are very thin, the fauna assemblage indicates that they are formed in a normal marine environment. No transitional sequence could be found.The boundaries between the limestone and the terrigenous deposits are always abrupt. The Late Permian deposits in Sichuan Basin are characterized by the interbedding of pelagic carbonates and coal beds.They can only be interpreted by the model of episodic transgression. The depositional characteristics of the restricted epicontinental sea depends mainly on their tectonic-topographic pattern. Such an environments is demonstrated benifit to the formation of coal and hydrocarbons.lt can be ear ted that the depositional features would be useful oil and gas survey in both different stages.
The restricted epicontinental sea lies on the edge of a continent and surrounded by islands as a sill. The sedimentation there is characterized by the episodic sea water invasion which takes place in short period and rapidly covers a wide area. As a consequence, there always occur discontinuous depositional sequence and frequently alternation of marine and nonmarine deposits.The transgression is controlled by the openning and closing of the gateway between islands due to the sea level fluctuation.lt is the defined event transgression or episodic transgression by the authors. In view of the plate tectonics, the back-arc basins arround active margin are typical epicontinental sea, so episodic transgression happens quite often. The episodic transgressive beds are magnafacies as well as parvafacies (isochronous).Therefore they can be used as a marker of stratigraphic correlation. The Mediterranean sea had repeatedly dried at the end of Miocene due to the openning and closing of the Strait of Gibratar which caused the alternation of deep sea and Sabkha sedimentation.lt provides a good example of episodic trasgression.The East China Sea was a typical epicontinental sea in Cenozoic. the sea level fluctuation resulted from climatic change caused many times of episodic transgression and interruption of marine sedimentation and resulted in a sequence consiting of interbeded marine and non-marine deposits. We can go far back to the Carboniferous deposits in northern China where the marine beds of limestone can be traced in a wide area even though they are very thin, the fauna assemblage indicates that they are formed in a normal marine environment. No transitional sequence could be found.The boundaries between the limestone and the terrigenous deposits are always abrupt. The Late Permian deposits in Sichuan Basin are characterized by the interbedding of pelagic carbonates and coal beds.They can only be interpreted by the model of episodic transgression. The depositional characteristics of the restricted epicontinental sea depends mainly on their tectonic-topographic pattern. Such an environments is demonstrated benifit to the formation of coal and hydrocarbons.lt can be ear ted that the depositional features would be useful oil and gas survey in both different stages.
1991, 9(1): 20-26.
Abstract:
This paper deals wth the development of the Archean and Early Proterozoic rock units and their be-tween tectonic features. and then discusses the relationship tectonic environment and sedimentation.The au-thors emphasized that the ancient sedimentation may be controlled by tectonic settings There are three tectcnic cycles in Precambrian occurred in eastern China, termed Qianxi. Fuping andWutai.The ancient continental crust of that period may be fotzrted just in the regions of northern China.It issuggested that, in the studying of Precambrian earth crust should be considered the tectonic settings whichassociated with sedimentary environment.For the high temperature and pressure existing in the mantle. it isbelieved the komatiite was formed in Archean, and the greenstone belt which widely spread may representedthe stablity of cratonic regions.Based on the results of investigations of Archean metamorphic sequence forseveral years, it suggests that the development of nuclei of ancient continents may be with progression andcertain tendency, such as depletion of vertical movement and increase of horizontal movement with ume.lnaddition, the characters of deformation may be from plastic change into rigid ones, thus. un thesynclinoria in NE trend stacked some fractures and led to formed pruto-taphrogens. to、、hich the EarlyProterozoic strata had been deposited, the location of w hich was at the continental margins andintracontinental settings.This tectonic pattern of framework had controlled the formation of the Pruterozoicsediments dunng that period.However, the carbonate rocky can be represent the differentanon of the ancientearth crust, such as Wutai Group which consists of basic to acidic volcanics and elastics interbedded withsome carbonate rocks, as well as with rhythmic flysch feature.The regional metamorphism is mainly derivedfrom Wutai Movement stage 1. During the Stage LI and Luhang Movement, because of the strength oftectonic movement had been depleted, there isn' t obvious regional metamorphism. The enlarging andthickening of continental crust ctiused by' tectono-thermal events, are likely to form some nuclei of ancientcontinents worldwidelv In summary，ti is emphusized that m the studying of Precambn.m wstem. the uniformitarianism is notsuitable to adapt, because of the characteristics of the earth' s crust is山fferent from the latter plates which was formed in Late Puleozoic
This paper deals wth the development of the Archean and Early Proterozoic rock units and their be-tween tectonic features. and then discusses the relationship tectonic environment and sedimentation.The au-thors emphasized that the ancient sedimentation may be controlled by tectonic settings There are three tectcnic cycles in Precambrian occurred in eastern China, termed Qianxi. Fuping andWutai.The ancient continental crust of that period may be fotzrted just in the regions of northern China.It issuggested that, in the studying of Precambrian earth crust should be considered the tectonic settings whichassociated with sedimentary environment.For the high temperature and pressure existing in the mantle. it isbelieved the komatiite was formed in Archean, and the greenstone belt which widely spread may representedthe stablity of cratonic regions.Based on the results of investigations of Archean metamorphic sequence forseveral years, it suggests that the development of nuclei of ancient continents may be with progression andcertain tendency, such as depletion of vertical movement and increase of horizontal movement with ume.lnaddition, the characters of deformation may be from plastic change into rigid ones, thus. un thesynclinoria in NE trend stacked some fractures and led to formed pruto-taphrogens. to、、hich the EarlyProterozoic strata had been deposited, the location of w hich was at the continental margins andintracontinental settings.This tectonic pattern of framework had controlled the formation of the Pruterozoicsediments dunng that period.However, the carbonate rocky can be represent the differentanon of the ancientearth crust, such as Wutai Group which consists of basic to acidic volcanics and elastics interbedded withsome carbonate rocks, as well as with rhythmic flysch feature.The regional metamorphism is mainly derivedfrom Wutai Movement stage 1. During the Stage LI and Luhang Movement, because of the strength oftectonic movement had been depleted, there isn' t obvious regional metamorphism. The enlarging andthickening of continental crust ctiused by' tectono-thermal events, are likely to form some nuclei of ancientcontinents worldwidelv In summary，ti is emphusized that m the studying of Precambn.m wstem. the uniformitarianism is notsuitable to adapt, because of the characteristics of the earth' s crust is山fferent from the latter plates which was formed in Late Puleozoic
1991, 9(1): 35-43.
Abstract:
The lower to middle Silurian strata are well exposed in Bajiaokou area, which is geologically located in the southern part of the Qinling orogenic belt. This sequence has been intensely studied by means of biostratigraphy in recent years, but less effort was made to address its lithofacies problems.As a result, this study is earned out to approach the facies analyses and paleoenvironmental interpretation of this sequence. The interpretation of the strata as a deep-water turbidite system is based on the following lines of evidence: the strata show typical sedimentary features of sediment gravity flows, mainly turbidity current, and the turbidite facies A to G (Mutti and Ricci Lucchi, 1972) are recognized; there are no phenomina of wave reworking; fossils are exclusively graptolites and no shallow-water benthic fossils are found; trace fossils also indicate deep water settings.The turbidite facies can be grouped into sevaral distinct facies associations indicative of different depositional elements of this turbidite system, those that are discussed in detail include: basin plain facies assiciation. lobe fringe facies association, sandstone lobe facies association, channel-lobe transition facies association, channel-levee complex facies association, and basinal slope facies association. To identify the diverse turbidite facies and facies associations, some new criteria are employed, such as different sorts of scours, and the channel-lobe transition element is particularly stressed because its importance was ignored in the previous work.The turbidite system is divided into four stages, and the developmental trend is form basin plain deposit to proximal deposit. It is concluded that this turbidite system was developed in an immature passive continental margin and quite similar to the slope apron turbidite deposit because of the absence of major channel fill of inner fan deposit.
The lower to middle Silurian strata are well exposed in Bajiaokou area, which is geologically located in the southern part of the Qinling orogenic belt. This sequence has been intensely studied by means of biostratigraphy in recent years, but less effort was made to address its lithofacies problems.As a result, this study is earned out to approach the facies analyses and paleoenvironmental interpretation of this sequence. The interpretation of the strata as a deep-water turbidite system is based on the following lines of evidence: the strata show typical sedimentary features of sediment gravity flows, mainly turbidity current, and the turbidite facies A to G (Mutti and Ricci Lucchi, 1972) are recognized; there are no phenomina of wave reworking; fossils are exclusively graptolites and no shallow-water benthic fossils are found; trace fossils also indicate deep water settings.The turbidite facies can be grouped into sevaral distinct facies associations indicative of different depositional elements of this turbidite system, those that are discussed in detail include: basin plain facies assiciation. lobe fringe facies association, sandstone lobe facies association, channel-lobe transition facies association, channel-levee complex facies association, and basinal slope facies association. To identify the diverse turbidite facies and facies associations, some new criteria are employed, such as different sorts of scours, and the channel-lobe transition element is particularly stressed because its importance was ignored in the previous work.The turbidite system is divided into four stages, and the developmental trend is form basin plain deposit to proximal deposit. It is concluded that this turbidite system was developed in an immature passive continental margin and quite similar to the slope apron turbidite deposit because of the absence of major channel fill of inner fan deposit.
1991, 9(1): 54-62.
Abstract:
The early diagenesis of terrigenous elastics in the area of the Estuary of Yangtze River and the adjacent shelf is studied. Especially, the process and mechanism are deeply analyzed in a comparative way. to provide evidences for recognizing that of the similar sediments formed in geological time. l.The study makes it clear that the process during the chemical reactions of sediment pore water is a series of metastable balance stages.The change in concentration of major ions in the pore water at a vertical section and the relative relation with reactors are analyzed with the principle of metastable chemical balance.The formation of authigenic minerals (such as glauconite. pyrite, calcite etc.) and cements and the solution of clastic minerals in the early diagenetic stage are demonsttrated.The assemblage of minerals produced in ths stage together with the typomorphic characteristics constitutes an important evidence to recognize the ancient similar diagenetic stages. 2.In the esturine depositional areas where abound with argillaceous sediment and organic matters; bacteria is predominant, sediment rate is high and bacterial decomposition of organic matter is strong. resultion in zonation of chemical reactions which is apparent in the vertical section from top to bottom: oxidizing zone, nitrate reducing zone, sulphate reducing zone and carbonte reducing zone, each with the respactive chemical reaction process and products. Thus, the structural section of biochemical zones gives another important sign for discovering the ancient similar earlier diagenesis. 3. In the zonation of earlier diagenesis of argillaceous sediment, bacteria play a main part.The study shows that when bacteria decompose organic matter and produce carbonate, the δ13C value is relatively low (-12‰-15‰); and only when the carbon isotope is fractionated (in carbonate reducing zone) δ13/C value becomes higher regularly.With the changes of δ13C values, it is also possible to obtain signs for identifying the ancient similar diagenetic stages. 4.Compared with argillaceous sediment, sand sediment are characterized by poorer organic matter, weaker bacterial activity faster sedimention and restricted ion diffusion is the early diagenesis.lt is the flowing of pore water under the compression effect which becomes an important role.Sand sediment in the estuary restrained by wedges of saline and fresh water appears often surrounded by pH gradient zones which influence directly on formation of cements; or a geochemical trap zone which is significant for oil and gas reservoir.
The early diagenesis of terrigenous elastics in the area of the Estuary of Yangtze River and the adjacent shelf is studied. Especially, the process and mechanism are deeply analyzed in a comparative way. to provide evidences for recognizing that of the similar sediments formed in geological time. l.The study makes it clear that the process during the chemical reactions of sediment pore water is a series of metastable balance stages.The change in concentration of major ions in the pore water at a vertical section and the relative relation with reactors are analyzed with the principle of metastable chemical balance.The formation of authigenic minerals (such as glauconite. pyrite, calcite etc.) and cements and the solution of clastic minerals in the early diagenetic stage are demonsttrated.The assemblage of minerals produced in ths stage together with the typomorphic characteristics constitutes an important evidence to recognize the ancient similar diagenetic stages. 2.In the esturine depositional areas where abound with argillaceous sediment and organic matters; bacteria is predominant, sediment rate is high and bacterial decomposition of organic matter is strong. resultion in zonation of chemical reactions which is apparent in the vertical section from top to bottom: oxidizing zone, nitrate reducing zone, sulphate reducing zone and carbonte reducing zone, each with the respactive chemical reaction process and products. Thus, the structural section of biochemical zones gives another important sign for discovering the ancient similar earlier diagenesis. 3. In the zonation of earlier diagenesis of argillaceous sediment, bacteria play a main part.The study shows that when bacteria decompose organic matter and produce carbonate, the δ13C value is relatively low (-12‰-15‰); and only when the carbon isotope is fractionated (in carbonate reducing zone) δ13/C value becomes higher regularly.With the changes of δ13C values, it is also possible to obtain signs for identifying the ancient similar diagenetic stages. 4.Compared with argillaceous sediment, sand sediment are characterized by poorer organic matter, weaker bacterial activity faster sedimention and restricted ion diffusion is the early diagenesis.lt is the flowing of pore water under the compression effect which becomes an important role.Sand sediment in the estuary restrained by wedges of saline and fresh water appears often surrounded by pH gradient zones which influence directly on formation of cements; or a geochemical trap zone which is significant for oil and gas reservoir.
1991, 9(1): 73-80.
Abstract:
Xialei manganese ore deposit consists of three ore beds. And the microfacies of the ore beds can be grouped into three types: 1. Cold water autochthonous chemical sedimentary manganese carbonate orebeds. 2. Hydrothemal autochthonous colloidal- chemical sedimentary silicatemanganese carbonate orebeds.3. Allochthonous recleposited gravity folw silicate-manganese carbonate orebeds. In the hydrothemal sedimentary manganese ore deposit, besides of manganese carbonate minerals, the associated minerals are rhodonite, biotite, actinolite, chlorite, manganese epidote, and manganoferro antigorite.Minerals such as hcmatite. potash-feldspar, barite, garnet and braunite, often shown as minor or local accumulated minerals. These hydrothermal minerals are often mixed and formed laminae, thin beds, bands, oolitics of pisolitic grains, horizontal or fine wavy laminae.Oolites and pisolitic grains which rich in manganese orebeds show obvious boundary, their cores are constituted by manganese carbonate and silicate minerals, no elastics were found. The colloidal-chemical deposits as a core, continously deposition and growth around it and the grains were formed, Oolitic, pisolitic grains and hydrothermal minerals are roughly distributed over the same range, and they have genetic relationship. The ore deposit may be fall into three zones in horizontal, (1) inner-zone composed of manganese carbonate, silicate and oxide minerals mixture. (2) biotite-manganese carbonate transitional zone. (3) outer manganese carbonate zone. Muddy limestone in the bottom of orebeds has a δC13 value of 0.03 per mil, this proved that the carbon came from seawater.The δC13values of manganese carbonate has a range from-2.83 to -14.29 per mil, averaged about -7.06 per mil, this value is roughly accord with that of the carbonates originated from magma, thus, it can be considered that the carbon was from deep basic magma. The mineralization model is summariaed as follows: In the trough in platform, when basic magma intruded, hot juvenile gas, liquid and dissolved mineralizing material ascended along cracks, therefore, resulted in the convection of seawater and subsurface water. Some dissolvable matter were leached and extracted, then were carried to the segs located in the bottom of the trough and a hot water pool formed.The silicate-carbonates' manganese were deposited.The sediments on the low slope zone were transported by gravity flow to the trough and covered autochthonous deposits.
Xialei manganese ore deposit consists of three ore beds. And the microfacies of the ore beds can be grouped into three types: 1. Cold water autochthonous chemical sedimentary manganese carbonate orebeds. 2. Hydrothemal autochthonous colloidal- chemical sedimentary silicatemanganese carbonate orebeds.3. Allochthonous recleposited gravity folw silicate-manganese carbonate orebeds. In the hydrothemal sedimentary manganese ore deposit, besides of manganese carbonate minerals, the associated minerals are rhodonite, biotite, actinolite, chlorite, manganese epidote, and manganoferro antigorite.Minerals such as hcmatite. potash-feldspar, barite, garnet and braunite, often shown as minor or local accumulated minerals. These hydrothermal minerals are often mixed and formed laminae, thin beds, bands, oolitics of pisolitic grains, horizontal or fine wavy laminae.Oolites and pisolitic grains which rich in manganese orebeds show obvious boundary, their cores are constituted by manganese carbonate and silicate minerals, no elastics were found. The colloidal-chemical deposits as a core, continously deposition and growth around it and the grains were formed, Oolitic, pisolitic grains and hydrothermal minerals are roughly distributed over the same range, and they have genetic relationship. The ore deposit may be fall into three zones in horizontal, (1) inner-zone composed of manganese carbonate, silicate and oxide minerals mixture. (2) biotite-manganese carbonate transitional zone. (3) outer manganese carbonate zone. Muddy limestone in the bottom of orebeds has a δC13 value of 0.03 per mil, this proved that the carbon came from seawater.The δC13values of manganese carbonate has a range from-2.83 to -14.29 per mil, averaged about -7.06 per mil, this value is roughly accord with that of the carbonates originated from magma, thus, it can be considered that the carbon was from deep basic magma. The mineralization model is summariaed as follows: In the trough in platform, when basic magma intruded, hot juvenile gas, liquid and dissolved mineralizing material ascended along cracks, therefore, resulted in the convection of seawater and subsurface water. Some dissolvable matter were leached and extracted, then were carried to the segs located in the bottom of the trough and a hot water pool formed.The silicate-carbonates' manganese were deposited.The sediments on the low slope zone were transported by gravity flow to the trough and covered autochthonous deposits.
1991, 9(1): 87-96.
Abstract:
Having studied the detailed coal petrological characteristics of more than 300 polished coal blocks sampled from eleven coalfields in China the authors have discovered a kind of organic maceral in coals with a high reflectance and strong anisotropy. Some of it conserves clearly the appearance and structure of exinite.According to the original maceral which is changed into anisotropic exinite. it can be divided into six types: anisotropic alginite. anisotropic sporinite. anisotropic cutinite. anisotropic exsudatmite. anisotropic bituminite and anixotropic liptodetrinitc. furthermore there is an amorphous anisotropic matter in coals. Anisotropic exinite is formed gradually by some of exinite during the coalifieation.ft occurs first in flame coal stage, and distributes frequently in coals with rank higher than gas coal stage. The statistics show that the content of anisotropic exinite in coals investigated varies from zero to 1.8%. and that the total content of anisotropic matter in coals is less than 12.74%. commonly from 1.0 to 4.0%. which is much less than that of exinite in specimens sampled from the same coal and the similar coal petrological type, but different coal rank. Since the changing of coal- forming environments and the difference of coal- forming plants, the exinite of same type may have different characteristics.The fluorescent intnsity and reflectance of exinite is the mark of its thermal activities, which will control its evolution processes and final products during the coalirlcation.On the bases of these facts, therefore, the exinite can be grouped into three types according to their optical evolution during the coahfication: l.Thc exinite of extreme thermal activity, such as fluorinite. terpenite and so on. evolutes completely into hydrocarbons. 2.The exinite of large thermal activity, such as some of alginite, resinite, sporinite, cutinite and so on, change into the anisotropic exinite as they draining off the liquid hydrocarbon. 3.And the exinite with less thermal activity shares gradually the same optical properties with intergrowth vitrinite during the coalification.
Having studied the detailed coal petrological characteristics of more than 300 polished coal blocks sampled from eleven coalfields in China the authors have discovered a kind of organic maceral in coals with a high reflectance and strong anisotropy. Some of it conserves clearly the appearance and structure of exinite.According to the original maceral which is changed into anisotropic exinite. it can be divided into six types: anisotropic alginite. anisotropic sporinite. anisotropic cutinite. anisotropic exsudatmite. anisotropic bituminite and anixotropic liptodetrinitc. furthermore there is an amorphous anisotropic matter in coals. Anisotropic exinite is formed gradually by some of exinite during the coalifieation.ft occurs first in flame coal stage, and distributes frequently in coals with rank higher than gas coal stage. The statistics show that the content of anisotropic exinite in coals investigated varies from zero to 1.8%. and that the total content of anisotropic matter in coals is less than 12.74%. commonly from 1.0 to 4.0%. which is much less than that of exinite in specimens sampled from the same coal and the similar coal petrological type, but different coal rank. Since the changing of coal- forming environments and the difference of coal- forming plants, the exinite of same type may have different characteristics.The fluorescent intnsity and reflectance of exinite is the mark of its thermal activities, which will control its evolution processes and final products during the coalirlcation.On the bases of these facts, therefore, the exinite can be grouped into three types according to their optical evolution during the coahfication: l.Thc exinite of extreme thermal activity, such as fluorinite. terpenite and so on. evolutes completely into hydrocarbons. 2.The exinite of large thermal activity, such as some of alginite, resinite, sporinite, cutinite and so on, change into the anisotropic exinite as they draining off the liquid hydrocarbon. 3.And the exinite with less thermal activity shares gradually the same optical properties with intergrowth vitrinite during the coalification.
1991, 9(1): 106-114.
Abstract:
Poyang Lake, located in the south of the middle reaches of Yangtze River, is the largest freshwater lake in China, with an area of 4646km2 and a capacity of 333 hundred million m3 respectively.It's run-off to the Yangtze River is 1457 hundred million m3 every year, which is larger than the total amount of that of the Yellow, Huaihe and Haihe rivers to the seas. It is one of the seasonal transit of water, where the islands and islets, beach-sands and branching streams and channels are distributed crisscross. In addition, many dykes were built widely and blindly around it, which have caused the serious loss of water and soil. Many factors, such as mentioned above, form the landforms- complicated topography and hydrologic conditions made its environment very complicated. It is a new technique developed recently in more than a decade that sedimentation rates in lakes are determined with radioisotopes 137Cs and 210Pb, 137Cs is an artificial nuclide of fall-out from nuclear tesling in atmospheric layer, the highest fall rate of which in the whole world occurred in 1963. It is the stratification of sedimentation in the lake in 1963. if only the maximum peak value of 137Cs in the layer in the vertical depth of the sediment undissturbed at the bottom of the lake should be determined; thus, its sedimentation rate will be obtained. 210Pb is a natural nuclide, if only the relation between the vertical depth of the sediment undisturbed at the bottom and the reduction of 210Pb activity index could be detetmined, its sedimentation rate will be obtained. A method of contrasting 137Cs to 210Pb has been used to give the high range of the lake 11.1-14.6m. water level based on Yellow Sea, and sedimentation rates in the region of the lake, 1.0-3.7mm · a-1, average 2.2mm · a-1.Moreover, contrasting 137Cs method to 210Pb method, and results checked by γ spectrum method are discussed.The results of sedimentation rate determined by 137Cs method are as the same of those by y spectrum method.Because both of the method are carried out with rather strong raclio-activity of 137Cs from nuclear testing in the sediment and the obvious charac+eristic of its maximum peak value of 137Cs in 1963. which especially helpful in determining year order, an accurate sedimentation rate will be obtained. The sedimentation rate measured by 210Pb method is about 16% lower than that by 137Cs or γ spectrum method, because 210Pb activity in the sediment at the bottom is weaker and. furthermore, during the course of 210Pb both from atmosphere to the bottom of the lake with complicated environment and in its separation and purification, a lot of disturbing factors easily cause errors as to lead a lower result.Therfore, it is very important to choose a proper location for sampling and it is necessary to apply two methods of determining year order to contrast sedimentation rates so as to reach satisfactory results.Thus, valuable basic information will be offered for esploration, and harnessing of the Poyang Lake.
Poyang Lake, located in the south of the middle reaches of Yangtze River, is the largest freshwater lake in China, with an area of 4646km2 and a capacity of 333 hundred million m3 respectively.It's run-off to the Yangtze River is 1457 hundred million m3 every year, which is larger than the total amount of that of the Yellow, Huaihe and Haihe rivers to the seas. It is one of the seasonal transit of water, where the islands and islets, beach-sands and branching streams and channels are distributed crisscross. In addition, many dykes were built widely and blindly around it, which have caused the serious loss of water and soil. Many factors, such as mentioned above, form the landforms- complicated topography and hydrologic conditions made its environment very complicated. It is a new technique developed recently in more than a decade that sedimentation rates in lakes are determined with radioisotopes 137Cs and 210Pb, 137Cs is an artificial nuclide of fall-out from nuclear tesling in atmospheric layer, the highest fall rate of which in the whole world occurred in 1963. It is the stratification of sedimentation in the lake in 1963. if only the maximum peak value of 137Cs in the layer in the vertical depth of the sediment undissturbed at the bottom of the lake should be determined; thus, its sedimentation rate will be obtained. 210Pb is a natural nuclide, if only the relation between the vertical depth of the sediment undisturbed at the bottom and the reduction of 210Pb activity index could be detetmined, its sedimentation rate will be obtained. A method of contrasting 137Cs to 210Pb has been used to give the high range of the lake 11.1-14.6m. water level based on Yellow Sea, and sedimentation rates in the region of the lake, 1.0-3.7mm · a-1, average 2.2mm · a-1.Moreover, contrasting 137Cs method to 210Pb method, and results checked by γ spectrum method are discussed.The results of sedimentation rate determined by 137Cs method are as the same of those by y spectrum method.Because both of the method are carried out with rather strong raclio-activity of 137Cs from nuclear testing in the sediment and the obvious charac+eristic of its maximum peak value of 137Cs in 1963. which especially helpful in determining year order, an accurate sedimentation rate will be obtained. The sedimentation rate measured by 210Pb method is about 16% lower than that by 137Cs or γ spectrum method, because 210Pb activity in the sediment at the bottom is weaker and. furthermore, during the course of 210Pb both from atmosphere to the bottom of the lake with complicated environment and in its separation and purification, a lot of disturbing factors easily cause errors as to lead a lower result.Therfore, it is very important to choose a proper location for sampling and it is necessary to apply two methods of determining year order to contrast sedimentation rates so as to reach satisfactory results.Thus, valuable basic information will be offered for esploration, and harnessing of the Poyang Lake.
1991, 9(1): 123-128.
Abstract:
South Hua mountain and West Hua mountain located in the northwest margin of Liupanshan Basin: Haiyuan County. Ningxia. The strata developed there are lacustrine deposits, organic- riched dark mudstone of lower Cretaceous with a thickness of from 200m to 800m. The overlying strata are sandstone rudyte of Sikouzi formation (E25); and mudstone. gypsum layers of Qingshuiying formation IE39).The strata are ideal assemblages of source rock, reservoir and cap for oil. but commercial oil has not been found.Based on the analysis of samples and TTI calculations, the burial depth of oil-generating strata is not deep enough to reach the oil forming threshold. It was reported in 1986 that South and West Hua mourtains are the northeastern uprakss of nappe structure in Qilianshan fold belt. The mountains as a overthrust sheet, which's thickness is more than 3200m, upthrusted on the oil-generating strata and made the burial depth enlarged then the condition of temperature increasing is available and oil-generating threshold can be got into. Moreover, overthrust belt led to the formation of special oil and gas pool.The key work of this region is searching for structural traps under nappe structure by the aid of physical survey.
South Hua mountain and West Hua mountain located in the northwest margin of Liupanshan Basin: Haiyuan County. Ningxia. The strata developed there are lacustrine deposits, organic- riched dark mudstone of lower Cretaceous with a thickness of from 200m to 800m. The overlying strata are sandstone rudyte of Sikouzi formation (E25); and mudstone. gypsum layers of Qingshuiying formation IE39).The strata are ideal assemblages of source rock, reservoir and cap for oil. but commercial oil has not been found.Based on the analysis of samples and TTI calculations, the burial depth of oil-generating strata is not deep enough to reach the oil forming threshold. It was reported in 1986 that South and West Hua mourtains are the northeastern uprakss of nappe structure in Qilianshan fold belt. The mountains as a overthrust sheet, which's thickness is more than 3200m, upthrusted on the oil-generating strata and made the burial depth enlarged then the condition of temperature increasing is available and oil-generating threshold can be got into. Moreover, overthrust belt led to the formation of special oil and gas pool.The key work of this region is searching for structural traps under nappe structure by the aid of physical survey.
1991, 9(1): 11-19.
Abstract:
The Permian System of Western Shanxi has now recognized that it mainly consists of fluvial sediments, and the ancient rivers in this area can be divided into three main types as meandering, braided and anastomosed. The depositional sequences of meandering river are typified by the development of point bars, flood plains and crevasse-splays. Lower and upper point bars with erosive contacts between them have been found in the Permian.In extreme circumstances deposits of crevasse-splays can be found as many as 11 layers within a single depositional sequence of the meandering river which indicates a very frequent occurrence of floods.Possible sand dune deposits have been suggested in some of the meandering rives. The depositional sequences that are rich in sandstones are believed to form in braided rivers.Flood plain sediments are much thinner than the channel's and their thickness is in the ratio of 0.25-0.5.The sequences are normally poor in crevasse-splays and levee deposits. Braided-meandering rivers are proposed the environment for those depositional sequences which are both rich in channel and flood plain sediments, but lack of natural levee and crevasse-splay deposits.Various scales of trough cross bedding prevail in channel sediments in these sequences. The repeatedly overlapping of channel sand bodies and the development of coal in marshes or bogs are used as the evidences of asastomosed river in the area. While the sediments overlaying just above coastal deposits, indicate the once existed flat plain when anastomosed channel was developing.
The Permian System of Western Shanxi has now recognized that it mainly consists of fluvial sediments, and the ancient rivers in this area can be divided into three main types as meandering, braided and anastomosed. The depositional sequences of meandering river are typified by the development of point bars, flood plains and crevasse-splays. Lower and upper point bars with erosive contacts between them have been found in the Permian.In extreme circumstances deposits of crevasse-splays can be found as many as 11 layers within a single depositional sequence of the meandering river which indicates a very frequent occurrence of floods.Possible sand dune deposits have been suggested in some of the meandering rives. The depositional sequences that are rich in sandstones are believed to form in braided rivers.Flood plain sediments are much thinner than the channel's and their thickness is in the ratio of 0.25-0.5.The sequences are normally poor in crevasse-splays and levee deposits. Braided-meandering rivers are proposed the environment for those depositional sequences which are both rich in channel and flood plain sediments, but lack of natural levee and crevasse-splay deposits.Various scales of trough cross bedding prevail in channel sediments in these sequences. The repeatedly overlapping of channel sand bodies and the development of coal in marshes or bogs are used as the evidences of asastomosed river in the area. While the sediments overlaying just above coastal deposits, indicate the once existed flat plain when anastomosed channel was developing.
1991, 9(1): 27-34.
Abstract:
The accumulation of organisms' dead hardparts can directly influence the structure and dynamic of nature of the sea floor.Biotic changes driven by such lives and dean interactions of living and dead have recently been termed Taphonomic Feedback, acording to Kidwell (1983).The taphonomic feedback stresses (1) the roie of post-mort processes in the availability of hardparts, and (2) that not only does the life assemblage influence the dead assemblage (living Organisms is the source of the dead assemblage), but also the accumulations of the dead assemblage affect the living one (dead hardparts provide the suitable substrata for epibiontic organisms). After those animals and plants which have hard skeletons died, their soft tissues decay very rapidly, and their skeletons will be disarticulated and fragmented by current, wave, storm and bioturbation.The discarded skeletal materials can change the physical characteristics of benthic habitats through providing 'island of hard substrata in soft-bottom habitats to some epibionts (e.g.encrusting and boring organisms) With hardpari accumulations in abundance, the sea floor will be transformed into a coarser, firmer and topographically more comple benthic habitat. Many coarse substratumlike, firm substratum- like and hardground-like epibionts, such as encrusting organisms (including animals and plants), can settle down and develop on it.It is one of the importaftt factors that cotrols the development and distribution of reefs and bioherms.Here the paper goes into details on this field, according to the informations got from home and abroad. Generally, although the development of reefs and bioherms is controlled by the temperature, salinity, depth and turbidity of water, wave activity, nutrient nature, sedimentation rates and so on, the substrata, which controlling the development of reef stabilization, are also very important.lt has been overlooked by many authors. Usually, the pioneer communities of reefs and bioherms develop on the petrological hardgrounds (e.g.many modern reffrs settling on the dead and or crmant volcanos in South Pacific), or on the biological hardgrounds whi, are made by encrusting organisms on the surface of biociastic banks of some bioherms (e.g.many Paleozoic and Mesozoic reefs, some modem reefs. The biological hardgrounds as the settling svbstrata are very commonfor the reefs and bioherms during geological time in China ( See Table). Because many Paleozoic reefs and bioherms deve'oned on the bioclastic banks mainly concentrated by current and wave activity from dead hardparts on carbonate plateform. the pioneer organisms of those reefs and bioherms, such as encrusting bryozoans, encrusting stromatopora, encrusting sponges, some cocals, spongiostromas, encrusting foraminiferas and some bivalves. cncruste on the bioclastic banks, made biological hardgrounds for other reef-building organisms to colonize. Most often the reefs and bioherms have bioc'as'ic banks as their settling bases, which process shown the taphonomic feedback influpnce. The authors have investigated one of the carly Silurlan coral-stromatoporoids reef, which is about 150m thick and located at Guangyean. northwest of Sichuan. and discovered that the reef shows very strong taphonomic feedback control.The develonment of this recf can be divided into two petiods, the stabilization of the first period is on the biological harground encrusting by some favosites and stromatoporcids on biocl astic bank, the rcef become more and more largcr ti the end of the stabilization. The second period is on the tidal-flat sediments with firm substraturn characteristics. it shows somehnos petrological hardground nature.The Bryczoan-coral reefs of early Carboniferons. locatcd in Tianling. Guangxi. also shcwn very strong taphonomic feedback influence.
The accumulation of organisms' dead hardparts can directly influence the structure and dynamic of nature of the sea floor.Biotic changes driven by such lives and dean interactions of living and dead have recently been termed Taphonomic Feedback, acording to Kidwell (1983).The taphonomic feedback stresses (1) the roie of post-mort processes in the availability of hardparts, and (2) that not only does the life assemblage influence the dead assemblage (living Organisms is the source of the dead assemblage), but also the accumulations of the dead assemblage affect the living one (dead hardparts provide the suitable substrata for epibiontic organisms). After those animals and plants which have hard skeletons died, their soft tissues decay very rapidly, and their skeletons will be disarticulated and fragmented by current, wave, storm and bioturbation.The discarded skeletal materials can change the physical characteristics of benthic habitats through providing 'island of hard substrata in soft-bottom habitats to some epibionts (e.g.encrusting and boring organisms) With hardpari accumulations in abundance, the sea floor will be transformed into a coarser, firmer and topographically more comple benthic habitat. Many coarse substratumlike, firm substratum- like and hardground-like epibionts, such as encrusting organisms (including animals and plants), can settle down and develop on it.It is one of the importaftt factors that cotrols the development and distribution of reefs and bioherms.Here the paper goes into details on this field, according to the informations got from home and abroad. Generally, although the development of reefs and bioherms is controlled by the temperature, salinity, depth and turbidity of water, wave activity, nutrient nature, sedimentation rates and so on, the substrata, which controlling the development of reef stabilization, are also very important.lt has been overlooked by many authors. Usually, the pioneer communities of reefs and bioherms develop on the petrological hardgrounds (e.g.many modern reffrs settling on the dead and or crmant volcanos in South Pacific), or on the biological hardgrounds whi, are made by encrusting organisms on the surface of biociastic banks of some bioherms (e.g.many Paleozoic and Mesozoic reefs, some modem reefs. The biological hardgrounds as the settling svbstrata are very commonfor the reefs and bioherms during geological time in China ( See Table). Because many Paleozoic reefs and bioherms deve'oned on the bioclastic banks mainly concentrated by current and wave activity from dead hardparts on carbonate plateform. the pioneer organisms of those reefs and bioherms, such as encrusting bryozoans, encrusting stromatopora, encrusting sponges, some cocals, spongiostromas, encrusting foraminiferas and some bivalves. cncruste on the bioclastic banks, made biological hardgrounds for other reef-building organisms to colonize. Most often the reefs and bioherms have bioc'as'ic banks as their settling bases, which process shown the taphonomic feedback influpnce. The authors have investigated one of the carly Silurlan coral-stromatoporoids reef, which is about 150m thick and located at Guangyean. northwest of Sichuan. and discovered that the reef shows very strong taphonomic feedback control.The develonment of this recf can be divided into two petiods, the stabilization of the first period is on the biological harground encrusting by some favosites and stromatoporcids on biocl astic bank, the rcef become more and more largcr ti the end of the stabilization. The second period is on the tidal-flat sediments with firm substraturn characteristics. it shows somehnos petrological hardground nature.The Bryczoan-coral reefs of early Carboniferons. locatcd in Tianling. Guangxi. also shcwn very strong taphonomic feedback influence.
1991, 9(1): 44-53.
Abstract:
There are a good many geological bodies consist of calcite conglomerate and breccia etc.in the carbonate rock region of southern China, which are very complex and appear minor axis and random shapes on horizontal, their diameters reach several tens to thousands of meters, on section, they appear as columnar, tubal of reef-like shape etc. on the basis of detailed research of the geological bodies, the characteristics sedimentogenesis have been recognized in ancient karst depression of caves of Diwa (geodepression) stage. In southern China, the paoaeo-karstification can be devided into two periods: the preliminary-mobile and the climas-mobile period of Diwa development.their characteristics are shown in table 1. Palaeo-karst sedimentary rocks of Diwa stage are a set of unstable diamictite dominated by breccia and psephite.The rocks were formed by collapse, subsurface flow by gravity, underground lake and river and so on sedimentation. Pala -karst sedimentary bodies are dispersed in Diwa, existed in palaeo-superimposed depression which was formed in Diwa stage by multi-karstification.The depression imagines in satellite or aero photograph are as ringlike diagram. Palaeo-karst sedimentary rocks have been widely grown metasomasised by petrogenetic and later period actions, except for syngenetic and petrogenetic dolomitization, auto-silicificatin and calcitization-calcite recrystallization are mainly in them.
There are a good many geological bodies consist of calcite conglomerate and breccia etc.in the carbonate rock region of southern China, which are very complex and appear minor axis and random shapes on horizontal, their diameters reach several tens to thousands of meters, on section, they appear as columnar, tubal of reef-like shape etc. on the basis of detailed research of the geological bodies, the characteristics sedimentogenesis have been recognized in ancient karst depression of caves of Diwa (geodepression) stage. In southern China, the paoaeo-karstification can be devided into two periods: the preliminary-mobile and the climas-mobile period of Diwa development.their characteristics are shown in table 1. Palaeo-karst sedimentary rocks of Diwa stage are a set of unstable diamictite dominated by breccia and psephite.The rocks were formed by collapse, subsurface flow by gravity, underground lake and river and so on sedimentation. Pala -karst sedimentary bodies are dispersed in Diwa, existed in palaeo-superimposed depression which was formed in Diwa stage by multi-karstification.The depression imagines in satellite or aero photograph are as ringlike diagram. Palaeo-karst sedimentary rocks have been widely grown metasomasised by petrogenetic and later period actions, except for syngenetic and petrogenetic dolomitization, auto-silicificatin and calcitization-calcite recrystallization are mainly in them.
1991, 9(1): 63-72.
Abstract:
Early Sinian black manganese carbonate deposits of the Datangpo formation are distributed in eastern Guizhou and western Hunan Provincce. The formation comprises a belt which extending for 200 km along depositional strike and 40 km perpendicular to the strike. The manganese precipitation is located in an extension in the passive continental margin of the Yangtze plate. The Datanpo formation is interbedded between two sequences that have been interpreted sa glacial diamictites. The formation comprises manganese ore and Mn- rich shale which show fine. graded laminations, with A-B-C, A-B-E Bourna sequences. The Mn-rich shale contains algae and fungi and acritarchs as reported previously; but the radiolaria have been found for the first time, and the radiolaria from Early Sinian has not been reported in the world. These features suggest that the deposition in a relatively deep water marine setting under conditions of anoxia which could have been caused by melting and a sea-level rise. The manganese ore bodies comprise lens and pillow-shaped structure which show a structure of successive concentric layer, and are cut by many fine baritite veinlets. Particularly, veinlets are concentrated in individual layer, and usually terminated at layer boundaries. This indicates that veins filled the fissures of shrinkage which was produced during the manganese ore cooling and separating phases. It is suggested that the manganese originates from hydrothermal exhalation and extrusion at the sea floor. It is precipitated as the successive concentric layers around a nucleus, thus building- up a pillow-shaped body. The δ34S signature (average 48. 3‰) of the manganese ore is typical of a hydrothermal origin. We suggest that glacial melting at the begining of Dagangpo formation brought about a major sea-level rise and the resulting transgression established a relatively deep marine environment. Hydrothemal exhalattion at the sea bottom could have resulted in a divsion of the sea water column with anoxic bottom water conditions and Precipitated the syngenetic manganese deposits.
Early Sinian black manganese carbonate deposits of the Datangpo formation are distributed in eastern Guizhou and western Hunan Provincce. The formation comprises a belt which extending for 200 km along depositional strike and 40 km perpendicular to the strike. The manganese precipitation is located in an extension in the passive continental margin of the Yangtze plate. The Datanpo formation is interbedded between two sequences that have been interpreted sa glacial diamictites. The formation comprises manganese ore and Mn- rich shale which show fine. graded laminations, with A-B-C, A-B-E Bourna sequences. The Mn-rich shale contains algae and fungi and acritarchs as reported previously; but the radiolaria have been found for the first time, and the radiolaria from Early Sinian has not been reported in the world. These features suggest that the deposition in a relatively deep water marine setting under conditions of anoxia which could have been caused by melting and a sea-level rise. The manganese ore bodies comprise lens and pillow-shaped structure which show a structure of successive concentric layer, and are cut by many fine baritite veinlets. Particularly, veinlets are concentrated in individual layer, and usually terminated at layer boundaries. This indicates that veins filled the fissures of shrinkage which was produced during the manganese ore cooling and separating phases. It is suggested that the manganese originates from hydrothermal exhalation and extrusion at the sea floor. It is precipitated as the successive concentric layers around a nucleus, thus building- up a pillow-shaped body. The δ34S signature (average 48. 3‰) of the manganese ore is typical of a hydrothermal origin. We suggest that glacial melting at the begining of Dagangpo formation brought about a major sea-level rise and the resulting transgression established a relatively deep marine environment. Hydrothemal exhalattion at the sea bottom could have resulted in a divsion of the sea water column with anoxic bottom water conditions and Precipitated the syngenetic manganese deposits.
1991, 9(1): 81-86.
Abstract:
In Western Xicheng Lead-Zinc Orefield. the Xihanshui carbonate formation of Middle Devonian developed well, the total thickness is about 1675m and the lithofacies change obviously.The lower part is a series of thick marine carbonate and the upper consists mainly of clastic rocks, Dengjiashan deposit and tens of other mineral points occur n the contact zone of Xihanshui reef limestone with phyllite. There are about ten kinds of rocks recognized in the corbonate formation.They are micritic limestone. powdery crystal limestone, bioclastic bearing limestone, sand clastic limestone, deformed faecal pellet limestone, oditic limestine, rudstone, bioclastic limestone, and reef limestone. The following is the interpretation of the sedimentary environment of Xihanshui carbonate formation. l.D61a and D62a strate Mainly consist of grey thinly micritic limestone, lamintated powdery crystal limestone, bioclastic bearing powder crystal limestone and silty shale, thin to middle and cross beddings and 15 to 25 percent of bioclasts are contained. The lower part sedimented from intertidal shallow depression. The upper part of oolitic limestone and deformed sand clastic limestone were fromed in intertida! shallow beach of subtidal shallow oolitic beach. 2.D63a, D64a and D65a strata The rocks are rudstone, bioclast poudery crystal limestone, reef limestone and bioclast limestone which were formed in subtidal bioherm and backreef limited shallow basin. Reef appeared as barrier reef which roughly parallel to the coastline, stretched tens of kilometres and thickness is about 700m. on the landward side of the barrier reef, a backreef limited shallow basin was formed where bioherm podwery crystal limestone and lead and zirie deposited and formed the source bed.Bioherm is contributive to the removing accumulation of ore-forming, the fact that the commercial ore bodies occur in the top of bioherm or the contact zone of bioherm with phyllite is an evidence. 3.D66a. D67a and D68a strta Grey silty powdery crystal limestone and bioclast powdery crystal limestone are the main rocks which were formed in the intertidal shallow depression. According to the analysis above, the changes of sedimentary environments of Xihanshui carbonate formation can be outlined as: from intertidal shallow depression procecced to ir.tertidal shallow beach, suhtidal bioherm, backreef Limited shallow basin till to intertidal shallow depression.
In Western Xicheng Lead-Zinc Orefield. the Xihanshui carbonate formation of Middle Devonian developed well, the total thickness is about 1675m and the lithofacies change obviously.The lower part is a series of thick marine carbonate and the upper consists mainly of clastic rocks, Dengjiashan deposit and tens of other mineral points occur n the contact zone of Xihanshui reef limestone with phyllite. There are about ten kinds of rocks recognized in the corbonate formation.They are micritic limestone. powdery crystal limestone, bioclastic bearing limestone, sand clastic limestone, deformed faecal pellet limestone, oditic limestine, rudstone, bioclastic limestone, and reef limestone. The following is the interpretation of the sedimentary environment of Xihanshui carbonate formation. l.D61a and D62a strate Mainly consist of grey thinly micritic limestone, lamintated powdery crystal limestone, bioclastic bearing powder crystal limestone and silty shale, thin to middle and cross beddings and 15 to 25 percent of bioclasts are contained. The lower part sedimented from intertidal shallow depression. The upper part of oolitic limestone and deformed sand clastic limestone were fromed in intertida! shallow beach of subtidal shallow oolitic beach. 2.D63a, D64a and D65a strata The rocks are rudstone, bioclast poudery crystal limestone, reef limestone and bioclast limestone which were formed in subtidal bioherm and backreef limited shallow basin. Reef appeared as barrier reef which roughly parallel to the coastline, stretched tens of kilometres and thickness is about 700m. on the landward side of the barrier reef, a backreef limited shallow basin was formed where bioherm podwery crystal limestone and lead and zirie deposited and formed the source bed.Bioherm is contributive to the removing accumulation of ore-forming, the fact that the commercial ore bodies occur in the top of bioherm or the contact zone of bioherm with phyllite is an evidence. 3.D66a. D67a and D68a strta Grey silty powdery crystal limestone and bioclast powdery crystal limestone are the main rocks which were formed in the intertidal shallow depression. According to the analysis above, the changes of sedimentary environments of Xihanshui carbonate formation can be outlined as: from intertidal shallow depression procecced to ir.tertidal shallow beach, suhtidal bioherm, backreef Limited shallow basin till to intertidal shallow depression.
1991, 9(1): 97-105.
Abstract:
Based on geochemical characteristics of stable helium, argon, carbon and nitrogen isotopes for natural gas, origins of nonhydrocarbons and fluids are discussed. 3He/4He ratios in natural gas are 1.14-4.54 times as much as that in the air. Stable isotope compositions of argon of natural gas are rich in 40Ar (40Ar/ 36Ar=450-841).Carbon isotope compositions (δ13CPDB) of carbon dioxide vary from-20‰ to -2‰.The δ15 Nvalues of natural gases range between -57.7‰ and 95.1‰.The values (Q) of heat fluid in the Sanshui Basin calculated depend on 2He 3He ratios, change from 72 mWm 2to 82 mWm-2.The high values of heat fluid and isotopic ratios of He. Ar. C and N have a relation to ancient volcanos. The geochemical qualities of stable isotopes of He, Ar, C and N in natural gases indicate that there are strong deep (matter and heat) fluids in the Sanshui basin.Part of He, Ar and N in some reservoirs came from the mantle. Nonhydrocarbons originated from the crust are mixed in various kinds of natural gases. Carbon dioxide in natural gases is mainly originated from the crust, CO2 depleted in 13C is mainly originated from degradation of organic matter in strata; but CO2 enriched in 13C are from reaction between carbonate rocks and under ground water and thermal fluids, and mixed in CO2 from the deep earth. An amount of heat fluid was derived from the upper mantle.
Based on geochemical characteristics of stable helium, argon, carbon and nitrogen isotopes for natural gas, origins of nonhydrocarbons and fluids are discussed. 3He/4He ratios in natural gas are 1.14-4.54 times as much as that in the air. Stable isotope compositions of argon of natural gas are rich in 40Ar (40Ar/ 36Ar=450-841).Carbon isotope compositions (δ13CPDB) of carbon dioxide vary from-20‰ to -2‰.The δ15 Nvalues of natural gases range between -57.7‰ and 95.1‰.The values (Q) of heat fluid in the Sanshui Basin calculated depend on 2He 3He ratios, change from 72 mWm 2to 82 mWm-2.The high values of heat fluid and isotopic ratios of He. Ar. C and N have a relation to ancient volcanos. The geochemical qualities of stable isotopes of He, Ar, C and N in natural gases indicate that there are strong deep (matter and heat) fluids in the Sanshui basin.Part of He, Ar and N in some reservoirs came from the mantle. Nonhydrocarbons originated from the crust are mixed in various kinds of natural gases. Carbon dioxide in natural gases is mainly originated from the crust, CO2 depleted in 13C is mainly originated from degradation of organic matter in strata; but CO2 enriched in 13C are from reaction between carbonate rocks and under ground water and thermal fluids, and mixed in CO2 from the deep earth. An amount of heat fluid was derived from the upper mantle.
1991, 9(1): 115-121.
Abstract:
Shaanxi-Gansu-Ningxia Basin is a depression basin, in which a lot of oil and coal formed during the Paleozoic and the Mesozoic.The present landforms can be divided into three belts: desert, loess and the transitional zone betweenthem two. It is confirmed by the experts at home and abroad that the soil-mercury above and around an oil and gas accumulations is relatively abundant. In the study aera, the distribution of soil- mercury in the transitional zone is shown as monopeak; but for desert and loess, and thermal decomposed soil-mercury of transitional zone, are di- and / or polypeaks which coincide with the features of that in oil and gas region.The different distribution of soil-mercury are contribute to the differences of soil and water's chemical composition and geological background, concertration in desert is higher than that in loess and varies widely, the transitional zone shows the mixed feature. For the study of occurence of soil- mercury, two temperature programming experiments were designed, one is from 100℃ to 800℃ with an interval of 50℃ ; the other is 80℃ to 300℃ , steped by 20℃. The results show that two main forms of soil-mercury, i.e.absorbed simple substance mercury and mercury chloride (HgCl2).but there is no mercury compounds in soil when the temperature is higher than 350℃. Soil-mercury in the basin is combined by two sources, autochthonous and allo chthonous, the undery-ing oil and gas are being the main resources of the allochthonous mercury.
Shaanxi-Gansu-Ningxia Basin is a depression basin, in which a lot of oil and coal formed during the Paleozoic and the Mesozoic.The present landforms can be divided into three belts: desert, loess and the transitional zone betweenthem two. It is confirmed by the experts at home and abroad that the soil-mercury above and around an oil and gas accumulations is relatively abundant. In the study aera, the distribution of soil- mercury in the transitional zone is shown as monopeak; but for desert and loess, and thermal decomposed soil-mercury of transitional zone, are di- and / or polypeaks which coincide with the features of that in oil and gas region.The different distribution of soil-mercury are contribute to the differences of soil and water's chemical composition and geological background, concertration in desert is higher than that in loess and varies widely, the transitional zone shows the mixed feature. For the study of occurence of soil- mercury, two temperature programming experiments were designed, one is from 100℃ to 800℃ with an interval of 50℃ ; the other is 80℃ to 300℃ , steped by 20℃. The results show that two main forms of soil-mercury, i.e.absorbed simple substance mercury and mercury chloride (HgCl2).but there is no mercury compounds in soil when the temperature is higher than 350℃. Soil-mercury in the basin is combined by two sources, autochthonous and allo chthonous, the undery-ing oil and gas are being the main resources of the allochthonous mercury.
1991, 9(1): 129-135.
Abstract:
Based on the mineral compositions of shell fossils formed in prior to Cambrian period, it has been found that all the known biogenic minerals were calcium-minerals, and two third of them are composed of calcium phosphate. With the evolution of biota, the composition of marine skeletons had changed greatly during the Phanerozoic. In the Palaeozoic it was dominated calcite-secreting inverbrate; the Cenozoic and modern seas were characterised by organisms which secreted aragonite and Mg-calcite skeletons, and the Mesozoic seas contained roughly equal numbers of each.This paper, therefore, aims to discuss these problems thermodynamically. 1.Thermodynamic analysis of the forming sequence of carbonate and phosphate minerals. Under the condition of modern seawater, i.e. assumed pH = 8, the total concentration of carbon (∑ [C]) is 1.2×10-3M, and that of phosphorus (∑ [P]) is 2×10-6M.The calculation indicates that αco32- is 8.44×10-3M, and αpo43- is 3.5 × 10-9M.According to the mass-action rule and the Ernst' s equation △Gro = -RT · lnk, the calculated results of αca2+which make the CaCO3and Ca3 (PO4) 2precipitated are: For carbonates αCa2+= 10-3.28M (calcite); αCa2+= 10+3.06M (aragonite) For phosphate αCa2+= 10-3.93M. It shows that the precipitation of phosphate took place first followed by the calcite, and the last was the aragonite. 2. Activity-pH diagram of carbonate and phosphate minerals Based on the fact that there are two types of mineral associations-carbonate (calcite and aragonite) and phosphate minerals in shell fossils, the elements, i. e. carbon, phosphorus, and calcium, are taken into account.They are not related to the Eh condition of environment, because they are not variable-valence elements. As H2CO3 and H3PO4 are polyhydric acids, the incomplete multistage ionization will take place and the αco32- and αpo43- will be controlled by the pH of solutions.Thus, the lowest activity of Ca2+under which CaCO3and Ca3 (PO4) 2 precipitations take place can be calculated by means of the αco32- and αpo43-present in solution at various pH.The logαca2+-pH diagram (Fig.l) can be constructed by using these results. 3.Palaeoenvironment analysis of formation of shell fossils Also it can be seen clearly from Fig. 1, that the precipitation of phosphate minerals take place at pH>2.2, but it does not mean that the phosphate shell can be formed at the early stage of palaeo- ocean evolution under which the pH values were very low in palaeo-seawater.It can be considered that the formation of shells not only depends on the increase of pH values, but also the increase of Ca2+concentrations in seawater.It has been revealed from some gelolgical history information that before the Proterozoic the phosphate deposition took place in local areas on small scale. In Sinian period ( by that time the palaeo-ocean had been formed 2000-2500m · a) the whole earth deposition of phosphates began on large scale followed by the formation of phosphate shells.It was not before long that the carbonate shells formed widely, it indicated that the pH values of seawater were close to 6 at the end of Proterozoic period. With the increase of pH values reached to 6.45 in Cambrian period, carbonate shells, particularly calcite shells with lower solubility, were widely devoloped. From Meso/oic period the formation of aragonite and calcite shells was the result of pH values' increase of the seawater. From Cenozoic to present the pH values of seawater increased gradually up to about 8.1. During this period the aragonite shells were dominant too.
Based on the mineral compositions of shell fossils formed in prior to Cambrian period, it has been found that all the known biogenic minerals were calcium-minerals, and two third of them are composed of calcium phosphate. With the evolution of biota, the composition of marine skeletons had changed greatly during the Phanerozoic. In the Palaeozoic it was dominated calcite-secreting inverbrate; the Cenozoic and modern seas were characterised by organisms which secreted aragonite and Mg-calcite skeletons, and the Mesozoic seas contained roughly equal numbers of each.This paper, therefore, aims to discuss these problems thermodynamically. 1.Thermodynamic analysis of the forming sequence of carbonate and phosphate minerals. Under the condition of modern seawater, i.e. assumed pH = 8, the total concentration of carbon (∑ [C]) is 1.2×10-3M, and that of phosphorus (∑ [P]) is 2×10-6M.The calculation indicates that αco32- is 8.44×10-3M, and αpo43- is 3.5 × 10-9M.According to the mass-action rule and the Ernst' s equation △Gro = -RT · lnk, the calculated results of αca2+which make the CaCO3and Ca3 (PO4) 2precipitated are: For carbonates αCa2+= 10-3.28M (calcite); αCa2+= 10+3.06M (aragonite) For phosphate αCa2+= 10-3.93M. It shows that the precipitation of phosphate took place first followed by the calcite, and the last was the aragonite. 2. Activity-pH diagram of carbonate and phosphate minerals Based on the fact that there are two types of mineral associations-carbonate (calcite and aragonite) and phosphate minerals in shell fossils, the elements, i. e. carbon, phosphorus, and calcium, are taken into account.They are not related to the Eh condition of environment, because they are not variable-valence elements. As H2CO3 and H3PO4 are polyhydric acids, the incomplete multistage ionization will take place and the αco32- and αpo43- will be controlled by the pH of solutions.Thus, the lowest activity of Ca2+under which CaCO3and Ca3 (PO4) 2 precipitations take place can be calculated by means of the αco32- and αpo43-present in solution at various pH.The logαca2+-pH diagram (Fig.l) can be constructed by using these results. 3.Palaeoenvironment analysis of formation of shell fossils Also it can be seen clearly from Fig. 1, that the precipitation of phosphate minerals take place at pH>2.2, but it does not mean that the phosphate shell can be formed at the early stage of palaeo- ocean evolution under which the pH values were very low in palaeo-seawater.It can be considered that the formation of shells not only depends on the increase of pH values, but also the increase of Ca2+concentrations in seawater.It has been revealed from some gelolgical history information that before the Proterozoic the phosphate deposition took place in local areas on small scale. In Sinian period ( by that time the palaeo-ocean had been formed 2000-2500m · a) the whole earth deposition of phosphates began on large scale followed by the formation of phosphate shells.It was not before long that the carbonate shells formed widely, it indicated that the pH values of seawater were close to 6 at the end of Proterozoic period. With the increase of pH values reached to 6.45 in Cambrian period, carbonate shells, particularly calcite shells with lower solubility, were widely devoloped. From Meso/oic period the formation of aragonite and calcite shells was the result of pH values' increase of the seawater. From Cenozoic to present the pH values of seawater increased gradually up to about 8.1. During this period the aragonite shells were dominant too.
