1987 Vol. 5, No. 3
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Display Method:
1987, 5(3): 6-18.
Abstract:
Extensional basins in platform regions of China can be divided into three types; intracontinental faulted basin and rift, aulacogen, and passive continental margin. Intra continental faulted basin and rift are predominated by nonmarine deposits, with some exceptions of marine transgression in paralic basins. During the processes of rifting, basalt-red bed-evaporite association or basalt-red bed-coal bearing series association→deep water lacustrine association→red bed association could be formed successively. Rock associations in medium to small faulted basins are similar but mostly incomplete, also with differences in volcanic rock types. The strike of depositional facies belt is controlled to some extent by characteristic tectoienic-morphologic configuration of faulted basin and rift. Differences of aulacogen from rift lies in: long period of development, connected with geosyncline at a high angle and marine environment dominated in whole evolution. In the Henan-Shaanxi Aulacogen, rock associations formed during the processes of basin development are in the sequence of lower siliciclastics association, volcanic rock (dominated by potassic basalt) association, upper siliciclastics-carbonate association, as well as relatively deep water facies mud silicalite, which is basically similar to other aulacogens. Deep water association should be further investigated, however. Distribution of sedimentary facies belt is also controlled to a certain extent by tectonic-morphologic configuration. Tidal dominated environment is quite similar to modern analogues The early Cambrian sea in the southern part of Yangtze Platform where once was a passive margin was a wave-dominated shelf environment, with little differences to modern analogues. Early Paleozoic stone coals developed in the southeastern margin of the Yangtze Platform and its adjacent area probably are pel agic and hemipelagic deposits. The anoxic event relatedto a warm ocean with high sea level possibly occurred during the Sinian and early Paleozoic. The formation and distribution of some mineral resources are also controlled by ext ensional basins, such as turbidite and burial hill oil reservoirs in the Tertiary rift, phosphorite and nickel-molybdenum polymetal ore deposits in shelf region of the passive continental margin. It is rare in the world that anoxic event of oceans had made stone coal widely distributed, stone coal should be considered as an important hydrocarbon source rock. Many reports have shown that some mineral resources are closely related to aulacogen, such as Precambrian syndeposi-tional layered and massive sulfide deposits and uranium-vanadium-copper stratabo-und deposits, even the Witwaterstrand type gold-uranium pyrite ore deposits in South Africa. Therefore, it is necessary to treat extensional basins including aulacogen with a due concern.
Extensional basins in platform regions of China can be divided into three types; intracontinental faulted basin and rift, aulacogen, and passive continental margin. Intra continental faulted basin and rift are predominated by nonmarine deposits, with some exceptions of marine transgression in paralic basins. During the processes of rifting, basalt-red bed-evaporite association or basalt-red bed-coal bearing series association→deep water lacustrine association→red bed association could be formed successively. Rock associations in medium to small faulted basins are similar but mostly incomplete, also with differences in volcanic rock types. The strike of depositional facies belt is controlled to some extent by characteristic tectoienic-morphologic configuration of faulted basin and rift. Differences of aulacogen from rift lies in: long period of development, connected with geosyncline at a high angle and marine environment dominated in whole evolution. In the Henan-Shaanxi Aulacogen, rock associations formed during the processes of basin development are in the sequence of lower siliciclastics association, volcanic rock (dominated by potassic basalt) association, upper siliciclastics-carbonate association, as well as relatively deep water facies mud silicalite, which is basically similar to other aulacogens. Deep water association should be further investigated, however. Distribution of sedimentary facies belt is also controlled to a certain extent by tectonic-morphologic configuration. Tidal dominated environment is quite similar to modern analogues The early Cambrian sea in the southern part of Yangtze Platform where once was a passive margin was a wave-dominated shelf environment, with little differences to modern analogues. Early Paleozoic stone coals developed in the southeastern margin of the Yangtze Platform and its adjacent area probably are pel agic and hemipelagic deposits. The anoxic event relatedto a warm ocean with high sea level possibly occurred during the Sinian and early Paleozoic. The formation and distribution of some mineral resources are also controlled by ext ensional basins, such as turbidite and burial hill oil reservoirs in the Tertiary rift, phosphorite and nickel-molybdenum polymetal ore deposits in shelf region of the passive continental margin. It is rare in the world that anoxic event of oceans had made stone coal widely distributed, stone coal should be considered as an important hydrocarbon source rock. Many reports have shown that some mineral resources are closely related to aulacogen, such as Precambrian syndeposi-tional layered and massive sulfide deposits and uranium-vanadium-copper stratabo-und deposits, even the Witwaterstrand type gold-uranium pyrite ore deposits in South Africa. Therefore, it is necessary to treat extensional basins including aulacogen with a due concern.
1987, 5(3): 28-39.
Abstract:
During the early Cambrian to the early epoch of the middle Cambrian, the storm event took place on the Yangtze platform of China and its adjacent areas. The tempestites as well as storm sedimention in three formations from below to upward which are distributed from west to east and from south to north across this region have been found, among which the phosphatic tempestites in the Meishucun Formation in lower Cambrian are the most typical. The typical phosphatic tempestite consists of packstone and wackestone which have a lot of depositional-structural characteristics of differently evolutionary stages of storm: 1, sharp basal boundary and basal surface structures, i. e. waved gutter cast, pocket structure, reworked hardground and lag gravel. 2, graded bed consisting of phosphatic, dolostone, and remains of small shell fossils. 3, ripple cross lamination. 4, including three kinds of hummocky cross stratification: single type, overlap and amalgamated types. 5, parallel lamination with trace fossils on the top surface which was formed in post-storm stage, i. e. didymaulichnus, Jia, Caraulichnus, Gordia and Spirophycus. Three phosphatic tempestite sequences are divided by the strength of the wind-induced, storm duration and the path of storm travelling: 1, completed type. 2, quasi-completed type. 3, amalgamated type. The analysis of the phosphatic tempestite sequences show that the activity of storm impacted the Chuandian old island and the inside of the Nioushoushan old island, it seemed to be descent of the sea level between the two old islands, the sea water supplied from the outsea with the result and the upwelling current could be formed. The phosphorous-rich water moved with the upwelling current and provided the material source for the phosphatic deposits. The precipitated phosphatic were reworked and transported by the storm surge and storm current, which removed to the areas of Kunyang and Haikou where the low grade proximal phosphatic tempestite were formed, along the outside of that areas the high grade distal phosphatic tempestite were precipitated, therefore, storm and storm current not only played an important role in the formation and acceleration of the circulation as well as supply upwelling current but the driving forces phosphatic winnowing and enrichment precipitating. The important phosphatic enrichment zones and the region of commerical phosphate deposits of our country were formed in the path of the storm current and upwelling current along the western margin of the Yangtze platform.
During the early Cambrian to the early epoch of the middle Cambrian, the storm event took place on the Yangtze platform of China and its adjacent areas. The tempestites as well as storm sedimention in three formations from below to upward which are distributed from west to east and from south to north across this region have been found, among which the phosphatic tempestites in the Meishucun Formation in lower Cambrian are the most typical. The typical phosphatic tempestite consists of packstone and wackestone which have a lot of depositional-structural characteristics of differently evolutionary stages of storm: 1, sharp basal boundary and basal surface structures, i. e. waved gutter cast, pocket structure, reworked hardground and lag gravel. 2, graded bed consisting of phosphatic, dolostone, and remains of small shell fossils. 3, ripple cross lamination. 4, including three kinds of hummocky cross stratification: single type, overlap and amalgamated types. 5, parallel lamination with trace fossils on the top surface which was formed in post-storm stage, i. e. didymaulichnus, Jia, Caraulichnus, Gordia and Spirophycus. Three phosphatic tempestite sequences are divided by the strength of the wind-induced, storm duration and the path of storm travelling: 1, completed type. 2, quasi-completed type. 3, amalgamated type. The analysis of the phosphatic tempestite sequences show that the activity of storm impacted the Chuandian old island and the inside of the Nioushoushan old island, it seemed to be descent of the sea level between the two old islands, the sea water supplied from the outsea with the result and the upwelling current could be formed. The phosphorous-rich water moved with the upwelling current and provided the material source for the phosphatic deposits. The precipitated phosphatic were reworked and transported by the storm surge and storm current, which removed to the areas of Kunyang and Haikou where the low grade proximal phosphatic tempestite were formed, along the outside of that areas the high grade distal phosphatic tempestite were precipitated, therefore, storm and storm current not only played an important role in the formation and acceleration of the circulation as well as supply upwelling current but the driving forces phosphatic winnowing and enrichment precipitating. The important phosphatic enrichment zones and the region of commerical phosphate deposits of our country were formed in the path of the storm current and upwelling current along the western margin of the Yangtze platform.
1987, 5(3): 59-65.
Abstract:
Some problems on the uranium source and the resource evaluation for exogenic uranium deposits are discussed in this paper. 1. According to the exogenic mineralization and geneses of ore deposits, uranium sources can be classified into three types: (a)syngenetic, (b)reformed and (c)epigenetic. It is very important to konw the temporal and spatial distribution of various geologic bodies of uranium sources for recognizing metallogenetic provinces and belts. 2. The prerequisite for evaluation of uranium resourses is utilizing the continuous growth model of U-Pb isotopic evolution and studying the initial uranium abundance of uranium source rocks and the effects of all kinds of geological processes on uranium mobillization after diagenesis (Table 1,2). 3. According to research on petrochemical characteristics of uranium source rocks, some chemical parameters of uranium preconcentration and petrogenesis can be used as the criteria of recognization for geological bodies of uranium source (Table 3). 4. The distribution of uranium metallogenic provinces is determined by regional tectonic settings which control the maturity of the earth's crust and control the uranium prsconcentration related to the maturity. For example, the Archean granite-greenstone zones, back-arc magmatic and thrust bolts, collision foreland thrust-magmatic belts are favourable for the formation of uranium-rich granitoid, and continental rift basins and marginal sea and embayment-lagoon basins are favourable for forming uranium source beds. 5. The following evaluation criteria can be used for the determination of the metallogenetic provinces and belts of exogenic uranium deposits. a. Distribution of the geological bodies of various uranium source, initial uranium abundance and uranium mobillization in the source rocks. b. Tectonic settings and tectonic units favourable for forming various geological bodies of uranium source. c. The characteristics of sedimentary formations, facies, and paleoclimatic conditions of various uraniferous rock series. d. Epigenetic reformation of various uraniferous rock series such as structure-lithofacies-paleohydrogeologic conditions for uranium mobillization and reconcentr-ation.
Some problems on the uranium source and the resource evaluation for exogenic uranium deposits are discussed in this paper. 1. According to the exogenic mineralization and geneses of ore deposits, uranium sources can be classified into three types: (a)syngenetic, (b)reformed and (c)epigenetic. It is very important to konw the temporal and spatial distribution of various geologic bodies of uranium sources for recognizing metallogenetic provinces and belts. 2. The prerequisite for evaluation of uranium resourses is utilizing the continuous growth model of U-Pb isotopic evolution and studying the initial uranium abundance of uranium source rocks and the effects of all kinds of geological processes on uranium mobillization after diagenesis (Table 1,2). 3. According to research on petrochemical characteristics of uranium source rocks, some chemical parameters of uranium preconcentration and petrogenesis can be used as the criteria of recognization for geological bodies of uranium source (Table 3). 4. The distribution of uranium metallogenic provinces is determined by regional tectonic settings which control the maturity of the earth's crust and control the uranium prsconcentration related to the maturity. For example, the Archean granite-greenstone zones, back-arc magmatic and thrust bolts, collision foreland thrust-magmatic belts are favourable for the formation of uranium-rich granitoid, and continental rift basins and marginal sea and embayment-lagoon basins are favourable for forming uranium source beds. 5. The following evaluation criteria can be used for the determination of the metallogenetic provinces and belts of exogenic uranium deposits. a. Distribution of the geological bodies of various uranium source, initial uranium abundance and uranium mobillization in the source rocks. b. Tectonic settings and tectonic units favourable for forming various geological bodies of uranium source. c. The characteristics of sedimentary formations, facies, and paleoclimatic conditions of various uraniferous rock series. d. Epigenetic reformation of various uraniferous rock series such as structure-lithofacies-paleohydrogeologic conditions for uranium mobillization and reconcentr-ation.
1987, 5(3): 73-80.
Abstract:
The Huabei coal-forming area which is located in North China in Upper Paleozoic Era is one of the biggest coal-forming basins in the world. It is about more than 800,000 km2. The reconstruction of the paleographic settings is the key for further recognition the huge Huabei Basin. It makes' possible to explore new theories and discover new resources. The coal-bearing formations of Carboniferous on North China including Benxi Formation of Middle Carboniferous and Taiyuan Formation of Upper Carboniferous, are a set of, coexisting deposits which spread widely and consist of limestone with subtidal carbonate platform facies and biogenetic bank facies and the terrigenous fragment with barrier island facies, lagoon facies and tidal flat facies. The coal beds are distributed widely and stablely. So the coal-bearing formation deposit belongs to the epeiric sea and their features of paleogeographic settings are a greater number of barrier island systems of epeiric sea with coexisting clear and turbid water. Barrier island and lagoon-tidal flats are repeated many times and existed alternately. The carbonate platforms are located outside the barrier island systems. The main coal-forming conditions are the peat flat environments on tidal flats with different types: carbonate platform-peat flat, lagoon-peat, flat, back barrier-peat flat, tidal delta-peat flat and estuary-peat flat. The important basin events in coal-forming period are the storm deposits and the volcanic deposits. Due to the characters of epeiric sea, the storm deposits are distributed widely in the Huabei coal-forming basin. The main marks of storm deposits in this area are the following: the hummocky under the surface of the erosion, the storm detention bed, the hummocky cross bedding, the sequence association and the trace fossil association. The tempesitite can be divided into carbonates and terrigenous elastics in the Huabei coal-forming basin. The main types are the follows: the proximal and distal carbonate tempesitite of the undertow current type, the carbonate tempesitite of the stirring type, sandstone tempesitite of the proximal type, sandstone tempesitite of the overflow type and gravel fragment mudstoae tempesitite. The distribution of coal seams caa be influenced by the storm deposits. The volcanic event deposits occurred in the middle and the upper parts of the Taiyuan Formation. The main types are as follows; the plastic fragment tuff, tufflava, tuff and tuffite, The volcanic deposits can be divided into the accumulation under water and above water.
The Huabei coal-forming area which is located in North China in Upper Paleozoic Era is one of the biggest coal-forming basins in the world. It is about more than 800,000 km2. The reconstruction of the paleographic settings is the key for further recognition the huge Huabei Basin. It makes' possible to explore new theories and discover new resources. The coal-bearing formations of Carboniferous on North China including Benxi Formation of Middle Carboniferous and Taiyuan Formation of Upper Carboniferous, are a set of, coexisting deposits which spread widely and consist of limestone with subtidal carbonate platform facies and biogenetic bank facies and the terrigenous fragment with barrier island facies, lagoon facies and tidal flat facies. The coal beds are distributed widely and stablely. So the coal-bearing formation deposit belongs to the epeiric sea and their features of paleogeographic settings are a greater number of barrier island systems of epeiric sea with coexisting clear and turbid water. Barrier island and lagoon-tidal flats are repeated many times and existed alternately. The carbonate platforms are located outside the barrier island systems. The main coal-forming conditions are the peat flat environments on tidal flats with different types: carbonate platform-peat flat, lagoon-peat, flat, back barrier-peat flat, tidal delta-peat flat and estuary-peat flat. The important basin events in coal-forming period are the storm deposits and the volcanic deposits. Due to the characters of epeiric sea, the storm deposits are distributed widely in the Huabei coal-forming basin. The main marks of storm deposits in this area are the following: the hummocky under the surface of the erosion, the storm detention bed, the hummocky cross bedding, the sequence association and the trace fossil association. The tempesitite can be divided into carbonates and terrigenous elastics in the Huabei coal-forming basin. The main types are the follows: the proximal and distal carbonate tempesitite of the undertow current type, the carbonate tempesitite of the stirring type, sandstone tempesitite of the proximal type, sandstone tempesitite of the overflow type and gravel fragment mudstoae tempesitite. The distribution of coal seams caa be influenced by the storm deposits. The volcanic event deposits occurred in the middle and the upper parts of the Taiyuan Formation. The main types are as follows; the plastic fragment tuff, tufflava, tuff and tuffite, The volcanic deposits can be divided into the accumulation under water and above water.
1987, 5(3): 96-101.
Abstract:
Biological marker composition of sulphur-asphalt associated with Chujiazhuang natural sulphur deposit, in Shandong Province was studied in detail by means of GC-MS technique. Two unusual compounds were found, including GX and C33 thiohopane. It is indicated by the peculiarities of biological marker composition of the sulphur-asphalt that the re-concentration of sulphur was related to the reduction of organic matter and activity of bacteria in hypersaline lake sediments during the early stage of diagcncsis. The natural sulphur deposit is considered to be a stratum-bound deposit of diagenetic origin.
Biological marker composition of sulphur-asphalt associated with Chujiazhuang natural sulphur deposit, in Shandong Province was studied in detail by means of GC-MS technique. Two unusual compounds were found, including GX and C33 thiohopane. It is indicated by the peculiarities of biological marker composition of the sulphur-asphalt that the re-concentration of sulphur was related to the reduction of organic matter and activity of bacteria in hypersaline lake sediments during the early stage of diagcncsis. The natural sulphur deposit is considered to be a stratum-bound deposit of diagenetic origin.
1987, 5(3): 113-124.
Abstract:
Guangxi Sea Basin, Qin Ling Sea Basin and South Anhui-North Jiangxi Sea Basin. The slope was distributed in areas from carbonate platform to sea basin, for example , Hunan-Guizhou slope was spread between Sichuan-Guizhou-Yannan Platform and Hunan- Guangxi Basin. Distribution of phosphorites in the strata The fig.l shows that the upper Sinian strata in South China have 8 beds of phosphate-bearing rocks and phosphorites. There are 3 beds belong to Doushantuo Formation and 5 beds occurred ia Dengying Formation. The phosphorite of Doushantuo Formation: The Liujing member consists mainly of manganese-bearing micritic limestones and dolostones, 3 to 20m in thickness, widely distributed ia the Yangtze region and Western Zhejiang but in Eastera North Jiangxi, it intercalated with phosphorites. The Songlin member, 100-470m in thickness, consists chiefly of black shales, dark-grey or black limestones and marls, or in some areas. Mostly dolostones and argillaceous dolostones in which phosphorites are often intercalated. The black shale, often containing a diversity of siliceous concretions and stripe, with rich microfossils, organic matter and phosphate, are widely developed, especially in Xothern and Eastern Guizhou, Western Hunan, Hubei and Eastern-Xorthern Jiangxi Provinces. The Songlin member of Donshantuo Formation in these areas has 2 industrial ore beds of phosphorites(fig.l). Phosphorites are frequently associated with either black shales or dolostones, and occur in 2 types of depositional sequences. The first is ascendingly as follows: black shales with siliceous phosphatic concretions-→black shales with stripe and bands of interclastic phosphorites-→laminated phosphorites containing often phosphate interclasts, peloids, oncoids and stromatolites-→dolostones with phosphate bands-→dolostones with phosphate lens-→dolostones lens- dolostones (in Yichang, Hubei Province ). The second type of sequence in ascending order is argillaceous dolostones-→phosphorites-→dolostones (in Shimen, Hunan Province). The characteristic of these sequences above mentioned indicates that phosphorites in Doushantuo Formation were formed under the conditions of a warm gradually changed into an arid and a semi-arid climate, and quiet environment gradually getted to a stronger turbidity environment. The phosphorite of Dengying Formation: Although Dengying Formation has 5 beds of phosphate-bearing rocks in the Yangtze region and Western Zhejiang Province, the phosphoritic bed with industrial value occur mainly on the interruption plane between upper and lower members of Dengying Formation in Xanzhang, Hubei Province. It consists usually of phosphoritic breccias, sands, oncoids and sometimes algal laminated phosphorites, cemented mostly by dolomite, occassionally by phosphate. The types of these phosphorites will play an important role in indicating that phosphate rocks would be found at horizons of the Dengying Formation in some of other places in the Yangtze region. Regularity of the phosphorites and other mineral distribution. The upper Sinian strata in South China contain exceedingly abundant phosphorites, magnesite, manganese spars, halite, natural gas, as well as vanadium, and mercury. The most famous is the phosphorite of Doushantuo Formation They were formed under different environments and distributed within various facies belts. For example,the pure phosphorite with industrial value mainly occur in the upper part of the slope facies belt or may be formed in tidal flat of carbonate platform margins, while halite and magnesite were confined to carbonate platform lagoon facies. The algal bank facies belt is favarable for oil and gas reservoirs. The numeous blue-green algal microfossils preserved in the phosphorite and manganese carbontes stow that the occurrence of mineralization are closely related to organic reaction.
Guangxi Sea Basin, Qin Ling Sea Basin and South Anhui-North Jiangxi Sea Basin. The slope was distributed in areas from carbonate platform to sea basin, for example , Hunan-Guizhou slope was spread between Sichuan-Guizhou-Yannan Platform and Hunan- Guangxi Basin. Distribution of phosphorites in the strata The fig.l shows that the upper Sinian strata in South China have 8 beds of phosphate-bearing rocks and phosphorites. There are 3 beds belong to Doushantuo Formation and 5 beds occurred ia Dengying Formation. The phosphorite of Doushantuo Formation: The Liujing member consists mainly of manganese-bearing micritic limestones and dolostones, 3 to 20m in thickness, widely distributed ia the Yangtze region and Western Zhejiang but in Eastera North Jiangxi, it intercalated with phosphorites. The Songlin member, 100-470m in thickness, consists chiefly of black shales, dark-grey or black limestones and marls, or in some areas. Mostly dolostones and argillaceous dolostones in which phosphorites are often intercalated. The black shale, often containing a diversity of siliceous concretions and stripe, with rich microfossils, organic matter and phosphate, are widely developed, especially in Xothern and Eastern Guizhou, Western Hunan, Hubei and Eastern-Xorthern Jiangxi Provinces. The Songlin member of Donshantuo Formation in these areas has 2 industrial ore beds of phosphorites(fig.l). Phosphorites are frequently associated with either black shales or dolostones, and occur in 2 types of depositional sequences. The first is ascendingly as follows: black shales with siliceous phosphatic concretions-→black shales with stripe and bands of interclastic phosphorites-→laminated phosphorites containing often phosphate interclasts, peloids, oncoids and stromatolites-→dolostones with phosphate bands-→dolostones with phosphate lens-→dolostones lens- dolostones (in Yichang, Hubei Province ). The second type of sequence in ascending order is argillaceous dolostones-→phosphorites-→dolostones (in Shimen, Hunan Province). The characteristic of these sequences above mentioned indicates that phosphorites in Doushantuo Formation were formed under the conditions of a warm gradually changed into an arid and a semi-arid climate, and quiet environment gradually getted to a stronger turbidity environment. The phosphorite of Dengying Formation: Although Dengying Formation has 5 beds of phosphate-bearing rocks in the Yangtze region and Western Zhejiang Province, the phosphoritic bed with industrial value occur mainly on the interruption plane between upper and lower members of Dengying Formation in Xanzhang, Hubei Province. It consists usually of phosphoritic breccias, sands, oncoids and sometimes algal laminated phosphorites, cemented mostly by dolomite, occassionally by phosphate. The types of these phosphorites will play an important role in indicating that phosphate rocks would be found at horizons of the Dengying Formation in some of other places in the Yangtze region. Regularity of the phosphorites and other mineral distribution. The upper Sinian strata in South China contain exceedingly abundant phosphorites, magnesite, manganese spars, halite, natural gas, as well as vanadium, and mercury. The most famous is the phosphorite of Doushantuo Formation They were formed under different environments and distributed within various facies belts. For example,the pure phosphorite with industrial value mainly occur in the upper part of the slope facies belt or may be formed in tidal flat of carbonate platform margins, while halite and magnesite were confined to carbonate platform lagoon facies. The algal bank facies belt is favarable for oil and gas reservoirs. The numeous blue-green algal microfossils preserved in the phosphorite and manganese carbontes stow that the occurrence of mineralization are closely related to organic reaction.
1987, 5(3): 135-148.
Abstract:
The composition of phosphorites from 25 Sinian, Cambrian and Devonian ore deposits in Eastern China were studied in this paper. We came to the conclusion that carbonate-f luorapatite is the main phosphatic mineral in the phosphorite of China. Hydroxyapatite can only be seen in recrystallised phosphorites occasionally. Principal associated minerals of the ore deposits are illite, dolomite and quartz (chalcedonite). According to the mineral associated relation, The phosphorites in China could be divided into five associated types. There are three important features in chemical composition of the phosphorites: First, the P2O5 contents change with types of ore, the sequence is the biogenic (35.04%), the micritic (34.88%-31.92%) the recrystallised (33.38%), the nodular (30.92%), the granular (29.01-28.14%) and the sandy (21.37%). Secondly, the P2O5 contents of ore change with mineralization areas, for example, the average P2O5 contents of the Cambrian ore in North China Platform and Yangtze Platform are 21.3% and 30.18% respectively. Thirdly, they change with mineralization epochs. With the squence of Sinian, Cambrian and Devonian, the CO2/P2O5 ratios reduce from 0.15 to 0.04; MgO, CO2, MnO and K2O-contents are from higher to lower; however, the Al2O3 is in a converse case. Generally, the compositional differences of phosphorites in China are determined by the differences of mineralizational background, environments, facies characteristics and mineral paragenic types primarily.
The composition of phosphorites from 25 Sinian, Cambrian and Devonian ore deposits in Eastern China were studied in this paper. We came to the conclusion that carbonate-f luorapatite is the main phosphatic mineral in the phosphorite of China. Hydroxyapatite can only be seen in recrystallised phosphorites occasionally. Principal associated minerals of the ore deposits are illite, dolomite and quartz (chalcedonite). According to the mineral associated relation, The phosphorites in China could be divided into five associated types. There are three important features in chemical composition of the phosphorites: First, the P2O5 contents change with types of ore, the sequence is the biogenic (35.04%), the micritic (34.88%-31.92%) the recrystallised (33.38%), the nodular (30.92%), the granular (29.01-28.14%) and the sandy (21.37%). Secondly, the P2O5 contents of ore change with mineralization areas, for example, the average P2O5 contents of the Cambrian ore in North China Platform and Yangtze Platform are 21.3% and 30.18% respectively. Thirdly, they change with mineralization epochs. With the squence of Sinian, Cambrian and Devonian, the CO2/P2O5 ratios reduce from 0.15 to 0.04; MgO, CO2, MnO and K2O-contents are from higher to lower; however, the Al2O3 is in a converse case. Generally, the compositional differences of phosphorites in China are determined by the differences of mineralizational background, environments, facies characteristics and mineral paragenic types primarily.
1987, 5(3): 159-170.
Abstract:
This paper deals with mineralization randomness, it is emphasized that mineralization model, the key to find hidden orebodies, should be established on the basis of probability theory. The paper shows clearly that probability distribution types of elements depend on neither their content nor their occurring form, but may be controlled by the elements' geochemical behavior which, in turn, is determined by the environment. For example, during sedimentary processes, titanium is a geochemically inactive element and no matter how low its content in sedimentary rocks is, it obeys normal distribution yet; however in the basic magmatic system titanium shows geochemically activity, and no matter how abundant its concentration in trap is, it does not obey normal distribution and results in asymmetrical distribution of positive biasness with a quite long tail. Owing to later geological events, geochemically active elements in source beds could be mobilized and transported in the oreforming solution, which, in the form of the random walk, migrates into reservoir beds and some orebodys are formed. This mineralization processes are inhomogeneity in space and have many stages in time. The sampled population of ore-forming elements then consist of a mixture of a lot of indivdual populations. For example, the content of copper occurred in copper deposits in Centeral Yunnan in China is of asymmetrical distribution with positive biasness. This distribution can be broken into three kinds of normal, which are characterized by large average value with large standard deviation. In contrast to active elements, the cumulation of geochemically inactive elements, such as iron, may result from rock-forming elements being intermittently eliminated from ore-forming system. Therefore, in sedimentary-reworking iron deposit, such as in the Shilu iron deposit, the histogram of total iron values shows an asymmeteric distribution with negative biasness, which can also be divided into three kinds of normal, but its subdistribution is characterized by large average value with small standard deviation. Owing to overlaping Poisson distributions with different means, the spatial distribution of copper deposits obeys negative binomial distribution. Frequency distribution of structural line density could well fitted negative binomial model.
This paper deals with mineralization randomness, it is emphasized that mineralization model, the key to find hidden orebodies, should be established on the basis of probability theory. The paper shows clearly that probability distribution types of elements depend on neither their content nor their occurring form, but may be controlled by the elements' geochemical behavior which, in turn, is determined by the environment. For example, during sedimentary processes, titanium is a geochemically inactive element and no matter how low its content in sedimentary rocks is, it obeys normal distribution yet; however in the basic magmatic system titanium shows geochemically activity, and no matter how abundant its concentration in trap is, it does not obey normal distribution and results in asymmetrical distribution of positive biasness with a quite long tail. Owing to later geological events, geochemically active elements in source beds could be mobilized and transported in the oreforming solution, which, in the form of the random walk, migrates into reservoir beds and some orebodys are formed. This mineralization processes are inhomogeneity in space and have many stages in time. The sampled population of ore-forming elements then consist of a mixture of a lot of indivdual populations. For example, the content of copper occurred in copper deposits in Centeral Yunnan in China is of asymmetrical distribution with positive biasness. This distribution can be broken into three kinds of normal, which are characterized by large average value with large standard deviation. In contrast to active elements, the cumulation of geochemically inactive elements, such as iron, may result from rock-forming elements being intermittently eliminated from ore-forming system. Therefore, in sedimentary-reworking iron deposit, such as in the Shilu iron deposit, the histogram of total iron values shows an asymmeteric distribution with negative biasness, which can also be divided into three kinds of normal, but its subdistribution is characterized by large average value with small standard deviation. Owing to overlaping Poisson distributions with different means, the spatial distribution of copper deposits obeys negative binomial distribution. Frequency distribution of structural line density could well fitted negative binomial model.
1987, 5(3): 180-180.
Abstract:
A flysch belt of E-W trend sedimented from late Paleozoic to early Mesozoic, outcrops in the Qinling Mountains. The following evidences support that the flysch deposited on active margin north of the Yangtze Plate; 1 ) the flysch belt is now located south to the suture zone of Yangtze and North China Plates; 2 ) the strata conformably underlying the flysch are all characterized by lithofacies and fossils of the Yangtze type; 3 ) paleocurrent data ( from N to S ) show that there was an ancient source area for detritus in the north of the flysch belt, which is represented now by remnent blocks of mobilized basement; 4) pyroclastics in the flysch mean that the source area might be a series of islands related to southward plate subduc-tion. It should be noted that north inclined structures now in Qinling resulted from southward overthrust. A reasonable explanation for the phenomenon is plate flip: before T2, oceanic crust of the paleotethys north to the Yangtze Plate subducted southward, resulting in an active continental margin; after T2, while the paleotethys was entirely consumed, the North China Plate behind the oceanic crust overthrust onto the Yangtze Plate, resulting in the building up of nowadays Qinling.
A flysch belt of E-W trend sedimented from late Paleozoic to early Mesozoic, outcrops in the Qinling Mountains. The following evidences support that the flysch deposited on active margin north of the Yangtze Plate; 1 ) the flysch belt is now located south to the suture zone of Yangtze and North China Plates; 2 ) the strata conformably underlying the flysch are all characterized by lithofacies and fossils of the Yangtze type; 3 ) paleocurrent data ( from N to S ) show that there was an ancient source area for detritus in the north of the flysch belt, which is represented now by remnent blocks of mobilized basement; 4) pyroclastics in the flysch mean that the source area might be a series of islands related to southward plate subduc-tion. It should be noted that north inclined structures now in Qinling resulted from southward overthrust. A reasonable explanation for the phenomenon is plate flip: before T2, oceanic crust of the paleotethys north to the Yangtze Plate subducted southward, resulting in an active continental margin; after T2, while the paleotethys was entirely consumed, the North China Plate behind the oceanic crust overthrust onto the Yangtze Plate, resulting in the building up of nowadays Qinling.
1987, 5(3): 4-5.
Abstract:
Prof.Ye Lianjun has already in geoscience for 50 years since he graduatedfrom the Department of Geology,Beijing University in 1937.As a geologist,especially a sedimentologist,he is well known both in China and in the world.Heis a member of Devision,the Academia Sinica,deputy director of the Division ofEarth Science the Academia Sinica,chairman of the Scientific Researh Committeeand Degree Committee of Institute of Geology,Academia Sinica,deputy councilpresident of China Society of Sedimentology，standing council member and honorary council member of China Society of Petroleum，council president of the Society of Oceanography of Beijing and a member of the Committee on Sedimeatology，IUGS.He was also a couacil member of international association of sedirnentologists untill 1986.
Prof.Ye Lianjun has already in geoscience for 50 years since he graduatedfrom the Department of Geology,Beijing University in 1937.As a geologist,especially a sedimentologist,he is well known both in China and in the world.Heis a member of Devision,the Academia Sinica,deputy director of the Division ofEarth Science the Academia Sinica,chairman of the Scientific Researh Committeeand Degree Committee of Institute of Geology,Academia Sinica,deputy councilpresident of China Society of Sedimentology，standing council member and honorary council member of China Society of Petroleum，council president of the Society of Oceanography of Beijing and a member of the Committee on Sedimeatology，IUGS.He was also a couacil member of international association of sedirnentologists untill 1986.
1987, 5(3): 19-27.
Abstract:
The study area is located on the southwest of Kunming and the west of Dianchi Lake in the eastern Yunnan, where is an important phosphorous producting area in China. Two phosphorous deposits are involved in this area (Fig. 1) - the Kunyang phosphorite deposits and the Haikou phosphorite deposits. They are well known for the great reserves and outstanding quality. The stratigraphy of phosphorite-bearing layers are considered as the Zhongyichun member, Yuhuchun Formation in the Meishuchun section of Kunyang (Fig.2), which is one of the international candidate sections of Cambrian /Precambrian boudary. The tectonic setting of the eastern Yannan during the early Cambrian when the phosphorite was deposited, the Yangtze cratonic massif occurred as a platform and was flanked by the Yunnan-Qinghai-Tibet sea basin on the West and the South China Sea trough on the east. The middle of Yunnan and Xiushoushan paleoconti-nents extended along the west and east margins of craton respectively and a rift basin was in the middle. Early Cambrian phosphorite was deposited in embayment lagoon environment. Fig. 4 shows the paleogeography of that time. Several favourable conditions were provided to the enrichment of phosphorite deposits in the embayment lagoon, because of the paleogeography situation. 1. The dispersion phosphorous in deep sea could continuously migrate to the shallow bay by upwellings since the bay was connected with the deep sea basin and trough. 2. Certain amount of phosphorous was supplied by the runoff from the paleocontinents which has high basic amount of phosphorous. 3. Due to the continuous supply of phosphorous and other biogenic elements by upwelling and river discharge, the shallow bay was rich in organisms. There are bacteria and algae (plate I -1, 2, 3, 4) which are well known as the abundant organisms in the early Cambrian. The small shelly fossils, as the pioneer of Phanerozoic invertebrates also occurred. Those organisms efficently fixed the dispersive phosphorous of sea water and made the possibility for them to deposit on the bottom of bay. These three points mentioned above provided favourable conditions for the shallow bay to collect phosphorous, and never lose or only lose little of them.As a result, a great quantity of phosphate could be accumulated. However, the distribution of the Kunyang and Haikou phosphorite deposits indicates that the final enrichment of phosphorous must be controlled by particular factors. The Kunyang and Haikou phosphorite deposits lie along two flanks of the Xiangtiaochong anticline (Fig. 3) in the middle-west part of the shallow bay. A paleosubmarine uplift is inferred between two deposits by the study of tectonics (Fig. 7), the thickness of ore layers and sedimantary facies. It is predicted that the extended is parallel to the trend of Xiangtiaochong anticline. 1. Tectonic setting. In addition to the longitudinal fault system created the rift basin, there is latitudinal-horst fault system which could be thought as the geological background for the paleo-submarine uplift. 2. Thickness. According to the exploration data, the thickness of ore layers of two deposits has a increasing tendency along the downdip slops of the inferred uplift with a ratio of one or two permillage. 3. Sedmmentary facies. There are a lot of differences in the thickness of ore layers, lithology and the sedimentary characters (Fig. 5, 6) between the Kunyang and Haikou deposits which are only less than 10km apart. Also mud cracks are observed as the exposure features. Scourand fill structures and cross bedding (plate I-7) are common and some slump structures (plate I-8) have been found with northward and southward dip along two flanks of inferred uplift respectively. In fact, it could be concluded that the paleosubmarine uplift existed and uplift was considered as an important control factor of phosphorite enrichment. It is based on: 1. The submarine uplift created a warm, disturbed and very shallow water environment (Fig. 7) along two flanks. This kind of environment was favourable
The study area is located on the southwest of Kunming and the west of Dianchi Lake in the eastern Yunnan, where is an important phosphorous producting area in China. Two phosphorous deposits are involved in this area (Fig. 1) - the Kunyang phosphorite deposits and the Haikou phosphorite deposits. They are well known for the great reserves and outstanding quality. The stratigraphy of phosphorite-bearing layers are considered as the Zhongyichun member, Yuhuchun Formation in the Meishuchun section of Kunyang (Fig.2), which is one of the international candidate sections of Cambrian /Precambrian boudary. The tectonic setting of the eastern Yannan during the early Cambrian when the phosphorite was deposited, the Yangtze cratonic massif occurred as a platform and was flanked by the Yunnan-Qinghai-Tibet sea basin on the West and the South China Sea trough on the east. The middle of Yunnan and Xiushoushan paleoconti-nents extended along the west and east margins of craton respectively and a rift basin was in the middle. Early Cambrian phosphorite was deposited in embayment lagoon environment. Fig. 4 shows the paleogeography of that time. Several favourable conditions were provided to the enrichment of phosphorite deposits in the embayment lagoon, because of the paleogeography situation. 1. The dispersion phosphorous in deep sea could continuously migrate to the shallow bay by upwellings since the bay was connected with the deep sea basin and trough. 2. Certain amount of phosphorous was supplied by the runoff from the paleocontinents which has high basic amount of phosphorous. 3. Due to the continuous supply of phosphorous and other biogenic elements by upwelling and river discharge, the shallow bay was rich in organisms. There are bacteria and algae (plate I -1, 2, 3, 4) which are well known as the abundant organisms in the early Cambrian. The small shelly fossils, as the pioneer of Phanerozoic invertebrates also occurred. Those organisms efficently fixed the dispersive phosphorous of sea water and made the possibility for them to deposit on the bottom of bay. These three points mentioned above provided favourable conditions for the shallow bay to collect phosphorous, and never lose or only lose little of them.As a result, a great quantity of phosphate could be accumulated. However, the distribution of the Kunyang and Haikou phosphorite deposits indicates that the final enrichment of phosphorous must be controlled by particular factors. The Kunyang and Haikou phosphorite deposits lie along two flanks of the Xiangtiaochong anticline (Fig. 3) in the middle-west part of the shallow bay. A paleosubmarine uplift is inferred between two deposits by the study of tectonics (Fig. 7), the thickness of ore layers and sedimantary facies. It is predicted that the extended is parallel to the trend of Xiangtiaochong anticline. 1. Tectonic setting. In addition to the longitudinal fault system created the rift basin, there is latitudinal-horst fault system which could be thought as the geological background for the paleo-submarine uplift. 2. Thickness. According to the exploration data, the thickness of ore layers of two deposits has a increasing tendency along the downdip slops of the inferred uplift with a ratio of one or two permillage. 3. Sedmmentary facies. There are a lot of differences in the thickness of ore layers, lithology and the sedimentary characters (Fig. 5, 6) between the Kunyang and Haikou deposits which are only less than 10km apart. Also mud cracks are observed as the exposure features. Scourand fill structures and cross bedding (plate I-7) are common and some slump structures (plate I-8) have been found with northward and southward dip along two flanks of inferred uplift respectively. In fact, it could be concluded that the paleosubmarine uplift existed and uplift was considered as an important control factor of phosphorite enrichment. It is based on: 1. The submarine uplift created a warm, disturbed and very shallow water environment (Fig. 7) along two flanks. This kind of environment was favourable
1987, 5(3): 40-58.
Abstract:
The working area deals with five provinces, i. e. Jiangsu, Zhejiang. Anhui, Jiangxi and Hubei. It is mainly in the lower Yangtze Valley and also includes a part of the middle Yangtze Valley. Qinglong Group of lower-middle Triassic is widely distributed in the area and especially well outcropped along the Yangtze River. The greatest thickness of Qinglong Group is more than 1260 meters and there exist various sedimentary rocks and a well potential of oil and gas. Qinglong Group can be divided into four formations. They are Yinkeng Formation, Helongshan Formation, Biandanshan Formation and Dongmaanshan Formation ascendently. The first three formation belong to lower Triassic and the last one to Middle Triassic. There are three kinds of different rocks in the Qinglong group, i. e. carbonte rocks, clastic rocks and evaporites. Carbonte rocks including limestone and dolostone are most widely distributed in the area. The limestone can be divided into the following types: shallow-water grainstone, stromatolitic limestone, gravity flow limestone, tempestits, ( in situ ) microcrystalline limestone, nodule limestone and ''worm'' limestone. The dolostone can be classified into penecontemporaneous and postpenecontemporaneous dolostone. This paper using "the single factor analysis and comprehenisve mapping method" which was initiated by the author. "The single factor" is that it can independently reflect some respects of sedimentary environments such as lithological, paleontologi-cal of other characteristics. This method includes three steps. Firstly, a thorough lithological study for every section sepecially basic section should be made in order to obtain various firsthand, complete, reliable qualitative and quantitative data, especially the latter. Secondly, the single factors should be selected from the quantitative data, then the content (%) of various single factors of each mapping unit can be obtained, and the fundamental single factor maps ( mainly isoline maps ) of each mapping unit can be drawn. These fundamental single factor maps can quantitatively reflect characteristics of sedimentary environments from different respects. This is "the single factor analysis". Thirdly, on the basis of these fundamental single factor maps of every mapping unit, combined with other quantitative and qualitative information and other regional geological information, discarding the dross and selecting theessential, through comprehensive analysis and judgement, the lithofacies paleogeographic map of the mapping unit in the area can be worked out. This is "comprehensive mapping". In this paper, the following single factors were selected: thickness, shallow-water grains content, penecontemporaneous dolostone content, gravity flow sediment content, the sedimentary thickness ratio of deep-water to shallow-water, terrigenous materials content, thickness of dark colour bed and of gypsum rock bed. In Yinkeng Formation, the five maps of fundamental single factor were drawn. They are the isopach map, the isoline map of the sedimentary thickness ratio of deep water to shallow water, the isoline map of gravity flow sedimentary content (%), the isoline map of shallow-water grain content (%) and the isoline map of terrigenous material content (%). With the comprehension of these fundamental single factor maps combined with other environmental indicators, through analysis and comprehensive judgement, the lithofacies paleogeographic map in Yinkeng Age of Early Triassic in the lower Yangtze Valley was worked out. With the same method, we had drawn the lithofacies paleogeographic maps of Helongshan Age, Biaadanshan Age and Dongmaanshan Age. In Yinkeng Age, the lower Yangtze Sea had such a Paleogeographic feature characterized by "four division" as shallow-water clastic rock platform, shallow-water carbonate rock platform, deep-water slope and deep-water basin from south to north. The shallow-water clastic rock platform was mainly composed of mudstone, shale and siltstone which was the marginal facies zone of "Cathay Old Land" in the south of the
The working area deals with five provinces, i. e. Jiangsu, Zhejiang. Anhui, Jiangxi and Hubei. It is mainly in the lower Yangtze Valley and also includes a part of the middle Yangtze Valley. Qinglong Group of lower-middle Triassic is widely distributed in the area and especially well outcropped along the Yangtze River. The greatest thickness of Qinglong Group is more than 1260 meters and there exist various sedimentary rocks and a well potential of oil and gas. Qinglong Group can be divided into four formations. They are Yinkeng Formation, Helongshan Formation, Biandanshan Formation and Dongmaanshan Formation ascendently. The first three formation belong to lower Triassic and the last one to Middle Triassic. There are three kinds of different rocks in the Qinglong group, i. e. carbonte rocks, clastic rocks and evaporites. Carbonte rocks including limestone and dolostone are most widely distributed in the area. The limestone can be divided into the following types: shallow-water grainstone, stromatolitic limestone, gravity flow limestone, tempestits, ( in situ ) microcrystalline limestone, nodule limestone and ''worm'' limestone. The dolostone can be classified into penecontemporaneous and postpenecontemporaneous dolostone. This paper using "the single factor analysis and comprehenisve mapping method" which was initiated by the author. "The single factor" is that it can independently reflect some respects of sedimentary environments such as lithological, paleontologi-cal of other characteristics. This method includes three steps. Firstly, a thorough lithological study for every section sepecially basic section should be made in order to obtain various firsthand, complete, reliable qualitative and quantitative data, especially the latter. Secondly, the single factors should be selected from the quantitative data, then the content (%) of various single factors of each mapping unit can be obtained, and the fundamental single factor maps ( mainly isoline maps ) of each mapping unit can be drawn. These fundamental single factor maps can quantitatively reflect characteristics of sedimentary environments from different respects. This is "the single factor analysis". Thirdly, on the basis of these fundamental single factor maps of every mapping unit, combined with other quantitative and qualitative information and other regional geological information, discarding the dross and selecting theessential, through comprehensive analysis and judgement, the lithofacies paleogeographic map of the mapping unit in the area can be worked out. This is "comprehensive mapping". In this paper, the following single factors were selected: thickness, shallow-water grains content, penecontemporaneous dolostone content, gravity flow sediment content, the sedimentary thickness ratio of deep-water to shallow-water, terrigenous materials content, thickness of dark colour bed and of gypsum rock bed. In Yinkeng Formation, the five maps of fundamental single factor were drawn. They are the isopach map, the isoline map of the sedimentary thickness ratio of deep water to shallow water, the isoline map of gravity flow sedimentary content (%), the isoline map of shallow-water grain content (%) and the isoline map of terrigenous material content (%). With the comprehension of these fundamental single factor maps combined with other environmental indicators, through analysis and comprehensive judgement, the lithofacies paleogeographic map in Yinkeng Age of Early Triassic in the lower Yangtze Valley was worked out. With the same method, we had drawn the lithofacies paleogeographic maps of Helongshan Age, Biaadanshan Age and Dongmaanshan Age. In Yinkeng Age, the lower Yangtze Sea had such a Paleogeographic feature characterized by "four division" as shallow-water clastic rock platform, shallow-water carbonate rock platform, deep-water slope and deep-water basin from south to north. The shallow-water clastic rock platform was mainly composed of mudstone, shale and siltstone which was the marginal facies zone of "Cathay Old Land" in the south of the
1987, 5(3): 66-72.
Abstract:
The bioclastic limestone, most of which consist of coral fragment, is sedimented at northwest beach of the Weizhou Island, Guangxi A dolomite was discovered in its intergranular space. The age of bioclastic limestone, determined by C14, is about 2120 ± 90 years. The dolomite formed perhaps later than it. So it ought to belong to modern dolomite. The dolomite possesses variant crystal size, most of which are about 2-0.5mm. The crystal is perfect clear, transparent, and most of them are the aggregate form. The dolomite is characterized by optic monoaxial crystal negative optic character, No=1.678 Ne =1.514. specific gravity-equals 3.1, hardness equals 4. The dolomite was deiinitely testified by staining method, differential thermal analysis, infrared spectrometry and X-ray. According to lower much value of the δ13C , δ13C and seeping diagenetic environment in which the bioclastic limestone exists. we can firmly belive that the dolomite formed under the condition where mixed fresh water in to sea water.
The bioclastic limestone, most of which consist of coral fragment, is sedimented at northwest beach of the Weizhou Island, Guangxi A dolomite was discovered in its intergranular space. The age of bioclastic limestone, determined by C14, is about 2120 ± 90 years. The dolomite formed perhaps later than it. So it ought to belong to modern dolomite. The dolomite possesses variant crystal size, most of which are about 2-0.5mm. The crystal is perfect clear, transparent, and most of them are the aggregate form. The dolomite is characterized by optic monoaxial crystal negative optic character, No=1.678 Ne =1.514. specific gravity-equals 3.1, hardness equals 4. The dolomite was deiinitely testified by staining method, differential thermal analysis, infrared spectrometry and X-ray. According to lower much value of the δ13C , δ13C and seeping diagenetic environment in which the bioclastic limestone exists. we can firmly belive that the dolomite formed under the condition where mixed fresh water in to sea water.
1987, 5(3): 81-95.
Abstract:
1. The iridium anomaly and the rare event The iridium anomaly was discovered in the lower Cambrian Ni-Mo polyelement layers by means of Instrumental Neutron Activiation Analyse (INAA) in 1982. Since then systematic and detailed studies were made on 6 sections in Yangtze Platform. 67 samples were analysed by means of INAA and 17 iridium anomalies were found in different rocks, mostly Ni-Mo polyelement layers. It is noteworthy that high value of iridium in phosphatic and barite-pyrite concretions have also been discovered, indicating the reconcentration of iridium during the early diagenetic stage (Table 1). The abundance of the noble metals in the lower Cambrian Ni-Mo polyelement layers, the Cretaceous-Tertiary boundary clays, basalt and chondrite is listed in Table 2. Fig.2 shows the abundance of the noble metals relative to that of C1 chondrite. Most metals in Ni-Mo polyelement layers such as Os, Pt, Co and Pd have flat distribution pattern, but Ni and Au have a high concentration, Ir content is much low. The iridium anomaly has a wide distribution both in space and in time which extends intermittently about 1600 km on Yangtze Platform(Fig. 1). No.l is the Dayuan section in Guizhou Province where iridium anomaly is found in phosphorite, black dolomitic siltstone and Ni-Mo polyelement layer. No.2 is the Xintugou section in Guizhou Province, where high iridium content is found in phosphatic concretions and Ni-Mo polyelement layers. NO.3 is the Tianmenshan section in Hunan Province, where iridium anomalies are discovered in Ni-Mo polyelement layers and black muddy siliceous rock. No.4 is the Yanglingshan section in Jiangxi Province, where high iridium content are found in black siliceous rock and barite-pyrite concretion. No.5 is the Nanshan section in Jiangxi Province, but no iridium anomaly is found there. No.6 is the Jianglong section in Zhejiang Province, where iridium anomalies are discovered in phosphorite and Ni-Mo polyelement layer. Stratigraphically the layers of high concentration of iridium are located mainly about 30cm to 2m sometimes 5m or over, above the underlying dolostone. The iridium anomaly can be found in two types of sedimentary sequences and various rocks, which quite different from each other in sedimentary environment. So from mentioned above, the iridium anomaly would be interpreted as an indicator of a rare event, related to extraterrestrial factors. 2. Iridium and other polyelement concentrations Iridium coexists with more than 30 elements, in order to make clear the relations among them, more detailed studies were done in the Xintugou section. We collected 16 samples for INAA from the Xintugou section, with 1.56m in thickness. Plate I shows the geological occurrences of Ni-Mo polyelement layer (Gx115), underlying phosphatic lenticle (Gx114) and overlying black silty shale (Gx116) from Xintugou section. Plate I-2 indicates a sample of Ni-Mo polyelement ore, consisting of "clastic" sulfides (A1) with 7cm in thickness and limestone (A2) with 1cm in thickness. Using reflected light microscope, we have selected three samples for INAA which consist mainly of Ni-sulphides (a), Mo-sulphides (b) and Fe-sulphides (c) respectively. The result of INAA indicates the high content of iridium as well as those of Ni, Mo, Zn, As, Se, Co, Au (Tab.3, Fig.3), U and REE are concentrated mainly in Ni-Mo polyelement layers, phosphatic lenticles, concretions and phosphorite beds (Fig. 4, 5). It is noteworthy that the coexistence of the polyelements does not indicate that they have only one material source. In the light of their geochemical characterestics and the abundance in the crust and chondrite, we consider that the platinum metals, Au, Ni, Co, Se, as well as part of Fe would have mainly an extraterrestrial origin, whereas U, Th, Ba, REE, Zn, Sb etc. would come from the continent or ocean, especially from the hot springs, hot brines and volcanic eruptions. In the anoxic environment rich in sapropel and sulfur these multisource elements can coexist together. 3. Black shale series and anoxic event B
1. The iridium anomaly and the rare event The iridium anomaly was discovered in the lower Cambrian Ni-Mo polyelement layers by means of Instrumental Neutron Activiation Analyse (INAA) in 1982. Since then systematic and detailed studies were made on 6 sections in Yangtze Platform. 67 samples were analysed by means of INAA and 17 iridium anomalies were found in different rocks, mostly Ni-Mo polyelement layers. It is noteworthy that high value of iridium in phosphatic and barite-pyrite concretions have also been discovered, indicating the reconcentration of iridium during the early diagenetic stage (Table 1). The abundance of the noble metals in the lower Cambrian Ni-Mo polyelement layers, the Cretaceous-Tertiary boundary clays, basalt and chondrite is listed in Table 2. Fig.2 shows the abundance of the noble metals relative to that of C1 chondrite. Most metals in Ni-Mo polyelement layers such as Os, Pt, Co and Pd have flat distribution pattern, but Ni and Au have a high concentration, Ir content is much low. The iridium anomaly has a wide distribution both in space and in time which extends intermittently about 1600 km on Yangtze Platform(Fig. 1). No.l is the Dayuan section in Guizhou Province where iridium anomaly is found in phosphorite, black dolomitic siltstone and Ni-Mo polyelement layer. No.2 is the Xintugou section in Guizhou Province, where high iridium content is found in phosphatic concretions and Ni-Mo polyelement layers. NO.3 is the Tianmenshan section in Hunan Province, where iridium anomalies are discovered in Ni-Mo polyelement layers and black muddy siliceous rock. No.4 is the Yanglingshan section in Jiangxi Province, where high iridium content are found in black siliceous rock and barite-pyrite concretion. No.5 is the Nanshan section in Jiangxi Province, but no iridium anomaly is found there. No.6 is the Jianglong section in Zhejiang Province, where iridium anomalies are discovered in phosphorite and Ni-Mo polyelement layer. Stratigraphically the layers of high concentration of iridium are located mainly about 30cm to 2m sometimes 5m or over, above the underlying dolostone. The iridium anomaly can be found in two types of sedimentary sequences and various rocks, which quite different from each other in sedimentary environment. So from mentioned above, the iridium anomaly would be interpreted as an indicator of a rare event, related to extraterrestrial factors. 2. Iridium and other polyelement concentrations Iridium coexists with more than 30 elements, in order to make clear the relations among them, more detailed studies were done in the Xintugou section. We collected 16 samples for INAA from the Xintugou section, with 1.56m in thickness. Plate I shows the geological occurrences of Ni-Mo polyelement layer (Gx115), underlying phosphatic lenticle (Gx114) and overlying black silty shale (Gx116) from Xintugou section. Plate I-2 indicates a sample of Ni-Mo polyelement ore, consisting of "clastic" sulfides (A1) with 7cm in thickness and limestone (A2) with 1cm in thickness. Using reflected light microscope, we have selected three samples for INAA which consist mainly of Ni-sulphides (a), Mo-sulphides (b) and Fe-sulphides (c) respectively. The result of INAA indicates the high content of iridium as well as those of Ni, Mo, Zn, As, Se, Co, Au (Tab.3, Fig.3), U and REE are concentrated mainly in Ni-Mo polyelement layers, phosphatic lenticles, concretions and phosphorite beds (Fig. 4, 5). It is noteworthy that the coexistence of the polyelements does not indicate that they have only one material source. In the light of their geochemical characterestics and the abundance in the crust and chondrite, we consider that the platinum metals, Au, Ni, Co, Se, as well as part of Fe would have mainly an extraterrestrial origin, whereas U, Th, Ba, REE, Zn, Sb etc. would come from the continent or ocean, especially from the hot springs, hot brines and volcanic eruptions. In the anoxic environment rich in sapropel and sulfur these multisource elements can coexist together. 3. Black shale series and anoxic event B
1987, 5(3): 105-112.
Abstract:
According to the analysis of cores Ch1(99 m), Ch2(63 m) and Ch3 ( 39 m), which were drilled in the outside of Changjiang River estary by the Institute of oceanology, Academia Sineca, the submerged delta of the Changjiang River formed in post glacial period consists of foreset, bottomset and marginal deposit. The fore set usually is over 10-14m in depth, divided into two parts: the upper part is generally composed of yellowish silts which contain many marine mollusk larva shells, and the lower part is the interbeds of thin silt and clay layers, both indicate the variablity of sedimentary environments. The lower boundary of the bottomset is at the depth of 22.07-46.5m, it is about 20-30 m thick and consists of grey clay sediments showing a stable and fine grain depositional period. Most of the cores contain thin silt layers in the bottomset by which the bottomset also can be divided into two parts, the upper softer part and the lower harder part. The marinal deposit is mainly composed of thin unsorted silt-fine sands it contains a lot of well preserved marine mollusk fossils, representing a typical littoral environment. Under the marginal deposit is the silt sediment formed in Wurm glacial term during the low sea level, in which developed thin peat sediments e.g. at the depth of 36.14-36.16 m in core Ch1 , the dark pure peats with 14C age of 10790 ± 120 years B.P., and at 48.4m, with 14C age 18740 ± 650 years B.P.. In the middle Late Pleistocene, a set of graval sediments in Ch1 deposited at 76.03-76.10 m. There are the preserved truncks with 14C age36000 years B. P. We found an individual of Pseudorotalia gaimardii at 62 m and 70m respectively, and some fresh water Lamprotula sp. at 76 m and 84 m. Beneath 84.24m there is a discontinuous surface. The middle Pleistocene sediment of Ch1 consists of clay layer intercalated with fine sand. The thermoluminescent dating at 88.2 m, 88.3m and 91.8m are (215 ± 10.7)×103, (233±11.6)×103 and (255± 12.3)×103 years respectively. There is a discontinuous surface at 91.96 m. From the above-mentioned data, the studied area was a land deposit environment in the late Middle Plesitocene. During the subinterglacial of Wurm glaciation a transgression occurred, later, in the Wiirm glaciation maximum it became a lake environment. Finally, when the climate was getting warmer in Holocene, the area changed to a neritic environment again and with the growth of the river estary delta, the mordern submerged delta system of the Changjiang River has formed.
According to the analysis of cores Ch1(99 m), Ch2(63 m) and Ch3 ( 39 m), which were drilled in the outside of Changjiang River estary by the Institute of oceanology, Academia Sineca, the submerged delta of the Changjiang River formed in post glacial period consists of foreset, bottomset and marginal deposit. The fore set usually is over 10-14m in depth, divided into two parts: the upper part is generally composed of yellowish silts which contain many marine mollusk larva shells, and the lower part is the interbeds of thin silt and clay layers, both indicate the variablity of sedimentary environments. The lower boundary of the bottomset is at the depth of 22.07-46.5m, it is about 20-30 m thick and consists of grey clay sediments showing a stable and fine grain depositional period. Most of the cores contain thin silt layers in the bottomset by which the bottomset also can be divided into two parts, the upper softer part and the lower harder part. The marinal deposit is mainly composed of thin unsorted silt-fine sands it contains a lot of well preserved marine mollusk fossils, representing a typical littoral environment. Under the marginal deposit is the silt sediment formed in Wurm glacial term during the low sea level, in which developed thin peat sediments e.g. at the depth of 36.14-36.16 m in core Ch1 , the dark pure peats with 14C age of 10790 ± 120 years B.P., and at 48.4m, with 14C age 18740 ± 650 years B.P.. In the middle Late Pleistocene, a set of graval sediments in Ch1 deposited at 76.03-76.10 m. There are the preserved truncks with 14C age36000 years B. P. We found an individual of Pseudorotalia gaimardii at 62 m and 70m respectively, and some fresh water Lamprotula sp. at 76 m and 84 m. Beneath 84.24m there is a discontinuous surface. The middle Pleistocene sediment of Ch1 consists of clay layer intercalated with fine sand. The thermoluminescent dating at 88.2 m, 88.3m and 91.8m are (215 ± 10.7)×103, (233±11.6)×103 and (255± 12.3)×103 years respectively. There is a discontinuous surface at 91.96 m. From the above-mentioned data, the studied area was a land deposit environment in the late Middle Plesitocene. During the subinterglacial of Wurm glaciation a transgression occurred, later, in the Wiirm glaciation maximum it became a lake environment. Finally, when the climate was getting warmer in Holocene, the area changed to a neritic environment again and with the growth of the river estary delta, the mordern submerged delta system of the Changjiang River has formed.
1987, 5(3): 125-134.
Abstract:
The sedimentary environment of Carboniferous in the northwest border of Junggar Basin is regarded as a shallow-sea by preceding scientists. However, many deep-water in indicators including gravity flow have been found recently by the authors in the Carboniferous stratum of this area, thus an objection to the preceding conclusion is raised. According to incompletely-emerged profiles, the total thickness of Carboniferous sediments in the study area is about 5000-7000 meters and they are mainly a set of clastic sediments. In the early period of Early Carboniferous, transgression happened on the basis of the Devonian terrestrial sedimentation in the north-border region of the Aerjiatishan Mountain and the sedimentary sequence of shallow-sea tempestite was formed with the increase of sea level. In the middle-late period of Early Carboniferous, a set of thick clastic flysch facics generated by turbidity current, 1631-4574 meters in thickness, was taking shape in the Zhayier Mountain region, The proximal turbidite and contourite with the developed A and B sections of the Bouma sequence as well as the debris flow deposit were found in this flysch facies, and various deep-water indicators, including deep-water trace fossils and deep-water siliceous radiolaria, were also discovered, for example, Taphrhelminthopsis sp. in the subface of turbidite sandstones and Scolecocoprus sp, attached on the bedding surface of black mudstones. Middle Carboniferous sediments, 2300 meters in thichness, outcrop completely in the Halaalate Mountain region and shallow-layer turbidites are well developed upwards and downwards, especially in the lower section. They are composed o the B-E or C-E sections of the Bouma sequence. The siltstones In the C section are rich in trace fossil, Zoophycos, while in the mudstones of the E section are abundant siliceous radiolaria. In addition, on the bedding surface, such associations of deep-sea trace fossils have been found, such as Cosmorhaphe sp. Scolarituba sp. hetminthoida Labyrinthica, Scolecocoprus sp, etc. However, in the middle part of this series, grain sizebecomes-sharply coarse and this bed is composed of gravel-bearing coarse sandstones and coarse-grain graywackes. It is apparently charactized by the proximal turbidite and fluxoturbidite and forms a complete prograding sequence of turbidite fan with the thin-layer turbidite in the lower section. The regession of Upper Carboniferous appeared in a shallow-sea environment.
The sedimentary environment of Carboniferous in the northwest border of Junggar Basin is regarded as a shallow-sea by preceding scientists. However, many deep-water in indicators including gravity flow have been found recently by the authors in the Carboniferous stratum of this area, thus an objection to the preceding conclusion is raised. According to incompletely-emerged profiles, the total thickness of Carboniferous sediments in the study area is about 5000-7000 meters and they are mainly a set of clastic sediments. In the early period of Early Carboniferous, transgression happened on the basis of the Devonian terrestrial sedimentation in the north-border region of the Aerjiatishan Mountain and the sedimentary sequence of shallow-sea tempestite was formed with the increase of sea level. In the middle-late period of Early Carboniferous, a set of thick clastic flysch facics generated by turbidity current, 1631-4574 meters in thickness, was taking shape in the Zhayier Mountain region, The proximal turbidite and contourite with the developed A and B sections of the Bouma sequence as well as the debris flow deposit were found in this flysch facies, and various deep-water indicators, including deep-water trace fossils and deep-water siliceous radiolaria, were also discovered, for example, Taphrhelminthopsis sp. in the subface of turbidite sandstones and Scolecocoprus sp, attached on the bedding surface of black mudstones. Middle Carboniferous sediments, 2300 meters in thichness, outcrop completely in the Halaalate Mountain region and shallow-layer turbidites are well developed upwards and downwards, especially in the lower section. They are composed o the B-E or C-E sections of the Bouma sequence. The siltstones In the C section are rich in trace fossil, Zoophycos, while in the mudstones of the E section are abundant siliceous radiolaria. In addition, on the bedding surface, such associations of deep-sea trace fossils have been found, such as Cosmorhaphe sp. Scolarituba sp. hetminthoida Labyrinthica, Scolecocoprus sp, etc. However, in the middle part of this series, grain sizebecomes-sharply coarse and this bed is composed of gravel-bearing coarse sandstones and coarse-grain graywackes. It is apparently charactized by the proximal turbidite and fluxoturbidite and forms a complete prograding sequence of turbidite fan with the thin-layer turbidite in the lower section. The regession of Upper Carboniferous appeared in a shallow-sea environment.
1987, 5(3): 149-158.
Abstract:
The centeral Guangxi Province is located in a platform which was consolidated-in Caledonian orogeny. Stratiform barite deposit (SB) and vein Pb-Zn-barite deposit (VB) occur in a rift basin in Devonian system. The Devonian lithologic units are listed here: (1) red clastic rocks of littoral and facies, (2) lutite-carbonate of neritic facies, (3) chert layer and banded limestone. The SB occurs in the chert layer in Upper Devonian system and the VB occurs in the neritic strata in Middle and Lower Devonian system. In space the VB is located in both sides of the basin, but the SB occurs in the middle of the chert layer which is 150m in thickness in the western side of the basin, and ore layer is more stable in thickness and extends up to several km. The apicall, floor and band plates of the ore layer are the chert layers. Grey and grey-black SB with banded and striped structures is composed of fine, grey barite. The section of the barite layer shows symmetricl eye shape. Composition of the SB is very simple. The radiospherical barite is located in the outside of eye structure. Fluid inclusions are very rare and very tiny, whose homogenous temperature is about 140℃, and the enclosure system is SO4-Cl-Na-K. The δ(34)S values of the barite is about +29‰. SB is associated with stratiform Mn, U, Mo mineralization. However, VB occurs in clusters containing basemetal veins (PV), basemetal-barite veins (VB) and single barite veins (MVB). The ore veins show zonation in horizontal and vertical directions. The horizontal zoning of the barite vein cluster is PV, VB, MVB outside around a deep fault controlling the rift basin, and the vertical zoning displays its feature in extended depth of the oreveins, mineralization temperature, mineral composition and country rock alteration etc. The δ_(34)S‰ values of VB are 19-30 (average 26.5), of MVB are about 23-26 (average 25.1). The enclosure system in MVB is SO4-Cl-Xa-K. VB and SB are different produces of same mineralization, the envidences are: (1) VB and SB occur in the same rift basin, and are closely associated with each other, VB is located under the SB layer, (2) ore composition, structure, texture, feature and temperature of mineralizing solution, ore-bearing country rocks (from silication rock to chert layer) and country rock alterations are similar and display obvious and systematic evolution from VB to SB,(3) the δ(54)S values of VB and SB are similar and approximated to the average value of sulfate in Later Devonian marine water, but are not similar to average value of sulfate in Early Devonian water, so that we propose a thermal water mineralization model. The study indicates the SB and country rock-chert layer are typically deposited by thermal water, so it is necessary to propose a stratiform-vein type deposit which is typical representation of thermal water mineralization.
The centeral Guangxi Province is located in a platform which was consolidated-in Caledonian orogeny. Stratiform barite deposit (SB) and vein Pb-Zn-barite deposit (VB) occur in a rift basin in Devonian system. The Devonian lithologic units are listed here: (1) red clastic rocks of littoral and facies, (2) lutite-carbonate of neritic facies, (3) chert layer and banded limestone. The SB occurs in the chert layer in Upper Devonian system and the VB occurs in the neritic strata in Middle and Lower Devonian system. In space the VB is located in both sides of the basin, but the SB occurs in the middle of the chert layer which is 150m in thickness in the western side of the basin, and ore layer is more stable in thickness and extends up to several km. The apicall, floor and band plates of the ore layer are the chert layers. Grey and grey-black SB with banded and striped structures is composed of fine, grey barite. The section of the barite layer shows symmetricl eye shape. Composition of the SB is very simple. The radiospherical barite is located in the outside of eye structure. Fluid inclusions are very rare and very tiny, whose homogenous temperature is about 140℃, and the enclosure system is SO4-Cl-Na-K. The δ(34)S values of the barite is about +29‰. SB is associated with stratiform Mn, U, Mo mineralization. However, VB occurs in clusters containing basemetal veins (PV), basemetal-barite veins (VB) and single barite veins (MVB). The ore veins show zonation in horizontal and vertical directions. The horizontal zoning of the barite vein cluster is PV, VB, MVB outside around a deep fault controlling the rift basin, and the vertical zoning displays its feature in extended depth of the oreveins, mineralization temperature, mineral composition and country rock alteration etc. The δ_(34)S‰ values of VB are 19-30 (average 26.5), of MVB are about 23-26 (average 25.1). The enclosure system in MVB is SO4-Cl-Xa-K. VB and SB are different produces of same mineralization, the envidences are: (1) VB and SB occur in the same rift basin, and are closely associated with each other, VB is located under the SB layer, (2) ore composition, structure, texture, feature and temperature of mineralizing solution, ore-bearing country rocks (from silication rock to chert layer) and country rock alterations are similar and display obvious and systematic evolution from VB to SB,(3) the δ(54)S values of VB and SB are similar and approximated to the average value of sulfate in Later Devonian marine water, but are not similar to average value of sulfate in Early Devonian water, so that we propose a thermal water mineralization model. The study indicates the SB and country rock-chert layer are typically deposited by thermal water, so it is necessary to propose a stratiform-vein type deposit which is typical representation of thermal water mineralization.
1987, 5(3): 171-179.
Abstract:
The mechanism and process of glauconite formation are discussed in this paper. The glauconite grains, sampled from the continental shelf of north part of South China Sea ( 116°08'-116°17'E, 21°20'-21°35'N ) and from the upper slop of East China Sea ( 128°00'E, 30°00'N), have various kinds of morphologies, most of them are as the infillings of foraminiferal shells. Their colour ranges coutinuously from dark, through greenish-black and greenish-yellow, to light yellow. The light colour grains usually contain the remains of organic shells. It can be divided into four stages for glauconite formation according to their colours and morphologies. By using the quantitative analysis of X-ray diffraction, the SEM photomicrographic observation, the chemical analysis and the synthetic experiment, in order to reveal the genesis of the glauconite within the shells of organism. From the analysis of sedimentary environment it is obvious that the biogenetic glauconite grains were formed in the sediments of outer continental shelf and the upper part of continental slop,water depth from 200-400m. The temperature, salinity and pH value favourable for the glauconite formation were the same as those value of normal sea water. The type of sediments in which the glauconite were found was well sorted sand with plenty of organic shells. In this region a steady sediment/sea-water interface was occurred, due to the absence of recent terrigenous sedimentation, which was known as the relict sedimentary region. It should be emphasized, however, that the most important factor for the glauconization was the microenvironment within the organic shells. The microenvironment was established by the decomposition of organisms after they had died and sunk to the sea bottom. The process of glauconization began in the shell where was a slightly reducing condition which was certainly favourable for the migration of active ferrous hydroxide from nearby sediment/sea-water interface into the organic shells. The ferrous hydroxide with Al-Mg hydroxides, and absorbing gelatinous silica, precipitated in the shells and subsequantly crystallized into iron-rich hydrous phyllosilicate. Its internal structure shown by SEM photomicrographs appeared to be an aggregate of random folia with curved edges or/and flake. The crystal structure was disorderly interstratified glauconite with the expansion layer about 63-68% bacause of the shortage of potasium in the structure. It was the initial stage of glauconization that was characterized by the enrichment of iron and lack of potasium in composition and light yellow in colour (NB-4, ZB-4). With the process of aging and gelatination, the authigenic crystallites tended to get arranged as roselike flakes. The break-down of organic shells around the authigenic mineral led to the contact of the grains with sea-water of/and interstitial water. The absorption of potasium reduced the expansible layer to 48-54%. At this stage the grains began to appear green resulting in yellow-green glauconite ( NB-3 and ZB-3). During the growth further the interlayered water was driven out owing to the absorption and fixation of potasium in the structure. As a result, cracks occurred on the surface of the grains. The cracks, in turn, enlarged the extent of metasomatism. The folia got orientedly and closely arranged. The impurities in the grains almost diminished. The grains got greener and dark and the expansion layer decreased to 42-45% at this stage ( NB-2 and ZB-2). Finaly, the authigenic growth of crystallite, the progressive absorption of potasium, the metasomatism of impurities made the structure of the grains more closely and oriented arranged, the surface of the grains more cracked. The crystal structure was changed from mainly expansible to nearly non-expansible ( 25-35%for NB-1 and ZB-1). Such dark glauconite grains are the well evolved grauconite in the modern marine sediments.
The mechanism and process of glauconite formation are discussed in this paper. The glauconite grains, sampled from the continental shelf of north part of South China Sea ( 116°08'-116°17'E, 21°20'-21°35'N ) and from the upper slop of East China Sea ( 128°00'E, 30°00'N), have various kinds of morphologies, most of them are as the infillings of foraminiferal shells. Their colour ranges coutinuously from dark, through greenish-black and greenish-yellow, to light yellow. The light colour grains usually contain the remains of organic shells. It can be divided into four stages for glauconite formation according to their colours and morphologies. By using the quantitative analysis of X-ray diffraction, the SEM photomicrographic observation, the chemical analysis and the synthetic experiment, in order to reveal the genesis of the glauconite within the shells of organism. From the analysis of sedimentary environment it is obvious that the biogenetic glauconite grains were formed in the sediments of outer continental shelf and the upper part of continental slop,water depth from 200-400m. The temperature, salinity and pH value favourable for the glauconite formation were the same as those value of normal sea water. The type of sediments in which the glauconite were found was well sorted sand with plenty of organic shells. In this region a steady sediment/sea-water interface was occurred, due to the absence of recent terrigenous sedimentation, which was known as the relict sedimentary region. It should be emphasized, however, that the most important factor for the glauconization was the microenvironment within the organic shells. The microenvironment was established by the decomposition of organisms after they had died and sunk to the sea bottom. The process of glauconization began in the shell where was a slightly reducing condition which was certainly favourable for the migration of active ferrous hydroxide from nearby sediment/sea-water interface into the organic shells. The ferrous hydroxide with Al-Mg hydroxides, and absorbing gelatinous silica, precipitated in the shells and subsequantly crystallized into iron-rich hydrous phyllosilicate. Its internal structure shown by SEM photomicrographs appeared to be an aggregate of random folia with curved edges or/and flake. The crystal structure was disorderly interstratified glauconite with the expansion layer about 63-68% bacause of the shortage of potasium in the structure. It was the initial stage of glauconization that was characterized by the enrichment of iron and lack of potasium in composition and light yellow in colour (NB-4, ZB-4). With the process of aging and gelatination, the authigenic crystallites tended to get arranged as roselike flakes. The break-down of organic shells around the authigenic mineral led to the contact of the grains with sea-water of/and interstitial water. The absorption of potasium reduced the expansible layer to 48-54%. At this stage the grains began to appear green resulting in yellow-green glauconite ( NB-3 and ZB-3). During the growth further the interlayered water was driven out owing to the absorption and fixation of potasium in the structure. As a result, cracks occurred on the surface of the grains. The cracks, in turn, enlarged the extent of metasomatism. The folia got orientedly and closely arranged. The impurities in the grains almost diminished. The grains got greener and dark and the expansion layer decreased to 42-45% at this stage ( NB-2 and ZB-2). Finaly, the authigenic growth of crystallite, the progressive absorption of potasium, the metasomatism of impurities made the structure of the grains more closely and oriented arranged, the surface of the grains more cracked. The crystal structure was changed from mainly expansible to nearly non-expansible ( 25-35%for NB-1 and ZB-1). Such dark glauconite grains are the well evolved grauconite in the modern marine sediments.
