1985 Vol. 3, No. 2
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Display Method:
1985, 3(2): 1-17.
Abstract:
It is of great significance to prospect sandbodies with good petrophysical properties in the Upper Triassic Yanchang Series of Shan-Gan-Ning Basin. This paper presents the diagenesis and digenetic' history of sandbodies in Yanchang Series, southwestern Shan-Gan-Ning Basin and the followning principal viewpoints. 1. The diagenesis of turbidite sandbodies in Yanchang Series is predominantly mechanical compaction. As the compaction has a strong effect upon the sandbodies with fine grain, more matrix and poor sorting, the low permeability turbidite sandbodies of compaction type are formed. 2. The cementation caused by authigenic minerals of diagenetic stage was extensively developed in the sandbodies of both deltaic front and distributary stream in Yanchang Series. Though the sandbodies are characterized by well sorting and less matrix contents, their primary intergranular pores are, in large, reduced by the compaction and cementation from authigenic minerals and became low permeability sandbodies of compaction-cementation type. 3. A lot of laumontite cement, carbonate cement and carbonate detritus of sandbodies were dissolved during mature stage of mesodiagenesis.The dissolution and kaolinization of feldspar were developed in some sandbodies.The dissolution resulted in the formation of the secondary porosity sandbodies in Yanchang Series. Six sandbodies of this kind have been found in the study area. 4. The development of secondary porosity sandbodies had a relation to their component, depositional texture, source of materials and sedimentary facies. The sandbodies of both deltaic front and distributary stream were favourable to form secondary porosity sandbodies. 5. With the repr.ecipitation brought about by carbonate dissolution in sandbodies, the tight cementation zones were formed. Vertically, they composed a diagenetic interval layer in the sandbodies and transversally, a diagenetic tight area. There are certain laws in distribution of the diagenetic interval layer and diagenetic tight area. The former usually appears near the mudstones of sandbodies and the latter in the transitional region of sandbodies to the region of pinching out. 6. So far, how to determine the quantity of secondary dissolution pores and especially those which inherited primary intergranular pores is a complicated and unsolved problem. This paper has proved it and suggests a feasible method. 7. The author considers that it is possible to predict the distribution of secondary porosity sandbodies in the basin based on the study of the sediment source, the depositional facies and diagenesis, and thus suggests the areas favourable for the development of secondary porosity sandbodies in the study area.
It is of great significance to prospect sandbodies with good petrophysical properties in the Upper Triassic Yanchang Series of Shan-Gan-Ning Basin. This paper presents the diagenesis and digenetic' history of sandbodies in Yanchang Series, southwestern Shan-Gan-Ning Basin and the followning principal viewpoints. 1. The diagenesis of turbidite sandbodies in Yanchang Series is predominantly mechanical compaction. As the compaction has a strong effect upon the sandbodies with fine grain, more matrix and poor sorting, the low permeability turbidite sandbodies of compaction type are formed. 2. The cementation caused by authigenic minerals of diagenetic stage was extensively developed in the sandbodies of both deltaic front and distributary stream in Yanchang Series. Though the sandbodies are characterized by well sorting and less matrix contents, their primary intergranular pores are, in large, reduced by the compaction and cementation from authigenic minerals and became low permeability sandbodies of compaction-cementation type. 3. A lot of laumontite cement, carbonate cement and carbonate detritus of sandbodies were dissolved during mature stage of mesodiagenesis.The dissolution and kaolinization of feldspar were developed in some sandbodies.The dissolution resulted in the formation of the secondary porosity sandbodies in Yanchang Series. Six sandbodies of this kind have been found in the study area. 4. The development of secondary porosity sandbodies had a relation to their component, depositional texture, source of materials and sedimentary facies. The sandbodies of both deltaic front and distributary stream were favourable to form secondary porosity sandbodies. 5. With the repr.ecipitation brought about by carbonate dissolution in sandbodies, the tight cementation zones were formed. Vertically, they composed a diagenetic interval layer in the sandbodies and transversally, a diagenetic tight area. There are certain laws in distribution of the diagenetic interval layer and diagenetic tight area. The former usually appears near the mudstones of sandbodies and the latter in the transitional region of sandbodies to the region of pinching out. 6. So far, how to determine the quantity of secondary dissolution pores and especially those which inherited primary intergranular pores is a complicated and unsolved problem. This paper has proved it and suggests a feasible method. 7. The author considers that it is possible to predict the distribution of secondary porosity sandbodies in the basin based on the study of the sediment source, the depositional facies and diagenesis, and thus suggests the areas favourable for the development of secondary porosity sandbodies in the study area.
A PRELIMINARY STUDY ON GEOCHEMICAL CHARACTERISTICS OF COAL-TYPE GAS IN ZHONGYUAN-HUABEI OIL-GAS AREA
1985, 3(2): 37-46.
Abstract:
There is a brief discussion about the naming of several main combustible natural gases in the first part of this paper. The authors suggest that the natural gas relative to the formation of oil be named oil-type gas; the one now called coal-gas be named coal type gas; however, the gas in coal bed continue to be called the coal-mine gas correponding to the oil-field associated gas in oil-type gas. The identification of methane carbon isotope which this paper briefly covers is at present considered as the main index to identify natural gases with differenrt genesis. It is also one of the geochemical indexes which are most widespreadly used at home. Argon isotope used as an identification index. Since the souce-rock ages of coal-type gas and oil-type gas respectively belong to the Carboniferous——the Per- mian and the Lower Tertiary, there is a sharp disparity in their ages. As a result, it is possible to distinguish these two kinds of natural gases according to the chronological accumulation effect of 40Ar in natural gas. The determination of the abundance ratios of 40Ar/38Ar in the natural gas of Zhongyuan-Huabei Oil-Gas area has shown that in the study area the 40Ar/36Ar ratios in the natural gas relative to the Tertiary oil-type gas are comparatively low,between 355-590; however,those relative to the coal-type gas, of Wen Well 23 in Zhongyuan Oilfield are between 930-1340. Moreover, some few gas reservoirs in Zhongyuan Oilfield have demonstrated a feature of the mixed gas of coal-type gas and oil-type gas. Merscury abundance in natural gas used as an identification indicator of coal-type gas. The determination of the mercury abundance in the natural gas of Zhong-yuan-Huabie Oil-Gas Area has shown that the average mercuy abundance of the natural gas relative to oil-type gas in Zhongyuan Oilfield is about n×102 mug/m (the same unite below). For instance, the mercury abundance of Pu Well 1-95 is abous 4.9-9.11×102, but the one, relative to coal-type gas, of both Well 23 is about 5.11×104, which is nearly about n×100 times higher than the average one relative to oil-type gas. The similar result of mercury abundance determination has been obtained in Huabei Oilfield. Therefore, there are some examples of higher mercury abundance in the natural gas relative to typical oil-type gas in the both fields. Obviously,the mercury abundance in natural gas used as an identification indicator of coal-type gas indicates several possibilities. Reseach on using the condensate carbon isotope as the identification of coal-type gas. It is an identification index that has not yet been used before. Generally speaking,very few stydies have been made on the condensate carbon isotope.The study result of the condensate carbon isotope of Zhongyuan and Sichuang oil-gas areas has initially shown that the condnsate relative to coal-type gas is comparatively consituted by heavier carbon isotopes. For instance, the 13C value of the condensate in Wen Well 23 is -24.5‰, however, those in other oil-gas wells are-27?8.5%0 namely, the condensate relative to coal-type gas is 2.5-3‰.richer in 13C than one relative to oil-type gas. The similar result has been obtained from Zhon-gba Gasfield in Sichuang Province. The the authors think that it may have a relation to the 13C enrichment of organic mother matters of lake-marsh facies of coal formation, and it is also the reflection of isotope inheritance effect.
There is a brief discussion about the naming of several main combustible natural gases in the first part of this paper. The authors suggest that the natural gas relative to the formation of oil be named oil-type gas; the one now called coal-gas be named coal type gas; however, the gas in coal bed continue to be called the coal-mine gas correponding to the oil-field associated gas in oil-type gas. The identification of methane carbon isotope which this paper briefly covers is at present considered as the main index to identify natural gases with differenrt genesis. It is also one of the geochemical indexes which are most widespreadly used at home. Argon isotope used as an identification index. Since the souce-rock ages of coal-type gas and oil-type gas respectively belong to the Carboniferous——the Per- mian and the Lower Tertiary, there is a sharp disparity in their ages. As a result, it is possible to distinguish these two kinds of natural gases according to the chronological accumulation effect of 40Ar in natural gas. The determination of the abundance ratios of 40Ar/38Ar in the natural gas of Zhongyuan-Huabei Oil-Gas area has shown that in the study area the 40Ar/36Ar ratios in the natural gas relative to the Tertiary oil-type gas are comparatively low,between 355-590; however,those relative to the coal-type gas, of Wen Well 23 in Zhongyuan Oilfield are between 930-1340. Moreover, some few gas reservoirs in Zhongyuan Oilfield have demonstrated a feature of the mixed gas of coal-type gas and oil-type gas. Merscury abundance in natural gas used as an identification indicator of coal-type gas. The determination of the mercury abundance in the natural gas of Zhong-yuan-Huabie Oil-Gas Area has shown that the average mercuy abundance of the natural gas relative to oil-type gas in Zhongyuan Oilfield is about n×102 mug/m (the same unite below). For instance, the mercury abundance of Pu Well 1-95 is abous 4.9-9.11×102, but the one, relative to coal-type gas, of both Well 23 is about 5.11×104, which is nearly about n×100 times higher than the average one relative to oil-type gas. The similar result of mercury abundance determination has been obtained in Huabei Oilfield. Therefore, there are some examples of higher mercury abundance in the natural gas relative to typical oil-type gas in the both fields. Obviously,the mercury abundance in natural gas used as an identification indicator of coal-type gas indicates several possibilities. Reseach on using the condensate carbon isotope as the identification of coal-type gas. It is an identification index that has not yet been used before. Generally speaking,very few stydies have been made on the condensate carbon isotope.The study result of the condensate carbon isotope of Zhongyuan and Sichuang oil-gas areas has initially shown that the condnsate relative to coal-type gas is comparatively consituted by heavier carbon isotopes. For instance, the 13C value of the condensate in Wen Well 23 is -24.5‰, however, those in other oil-gas wells are-27?8.5%0 namely, the condensate relative to coal-type gas is 2.5-3‰.richer in 13C than one relative to oil-type gas. The similar result has been obtained from Zhon-gba Gasfield in Sichuang Province. The the authors think that it may have a relation to the 13C enrichment of organic mother matters of lake-marsh facies of coal formation, and it is also the reflection of isotope inheritance effect.
1985, 3(2): 57-66.
Abstract:
Because of better exposure of rock outcrop, complete succession of the rock sequence, abundant critical fossils and typical marine sediments, Wushan section in Hebeei Province has been already considered an excellent Cambrian-Ordovician boundary stratotype site in northern China. The clay samples which were collected from the atrata near the boundary have been studied with the methods of X-ray diffraction analysis, electron microscope and infrared spectrometry. Figure 1 shows the simplified stratigraphic succession of the sedimentary sequence from the Cambrian-Ordovician boundary at Wushan section of Lulong Hebei, province,China. The 6,7,8,9,11,12 and13 levels are the units of the Upper Cambrians the 14 and 15 levels are those of the Lower Ordovician. According to the results of X-ray diffraction analyses from the clay minerals of the strata near the Cambrian-Ordovician boundary section at Wushan, illite is the major component of clay minerals in all levels. It is mixed up to 22% of chlorite in the 15 level of the Lower Ordovician, with up to 15% of vermiculite in the 6,7,8 and 9 levels of the Upper Cambrian, and with up to 25% chlorite-verrniculite randomly interstratified minerals in the 12 and 13 levels of the Upper Cambrian. By the investigation of electron microscope, the grains of illite are generally rather small and the shape of illite crystals is poor. The clay samples consist of platy aggrerates of tiny flakes of clay minerals. As a whole, the common texture is of a preferred orintation parallel to the bedding, many clay grains dip at angles to the bedding and show a "swirl" or "undulation" patterns. These stocks are loose packed. This texture develops a high porosity. The illite is dioctahedral, Fe-rich and of iMd type; the chlorite belongs to ripidolite which is trioctahedral and rich in Fej the vermiculite is trioctahedral with a high charge, which may be derived form the weathered mica-like clay minerals. The crystallinity indices of all the samples, which were measured accrding to the tno methods of weaver and dunoyer de segonzac, are all in the range of non-metamorphism. By the experimenrs, it is conjectured that during the transitional period between the end of Cambrian and the beginning of Ordovician, the sedimentary environment might not be quiet because of the turbulence in the seawater and might belong to neritic depost with rich cations, such as Fe and Mg. The seawater was shallower and nearer to the terrigenous region at the end of Cambrian than in the levels 14 and 15 at the beginning of Ordovician. The composition of clay minerals is partly different at the two sides of the boundary, which is probably caused by the differences of the ancient sedimentary environments. But this change is a gradual and continous transitionl one and there is no sharp change and disconnection near the boundary. It indicates that the the deposition is continous without breaks near the boundary at Wushan of Lulong.
Because of better exposure of rock outcrop, complete succession of the rock sequence, abundant critical fossils and typical marine sediments, Wushan section in Hebeei Province has been already considered an excellent Cambrian-Ordovician boundary stratotype site in northern China. The clay samples which were collected from the atrata near the boundary have been studied with the methods of X-ray diffraction analysis, electron microscope and infrared spectrometry. Figure 1 shows the simplified stratigraphic succession of the sedimentary sequence from the Cambrian-Ordovician boundary at Wushan section of Lulong Hebei, province,China. The 6,7,8,9,11,12 and13 levels are the units of the Upper Cambrians the 14 and 15 levels are those of the Lower Ordovician. According to the results of X-ray diffraction analyses from the clay minerals of the strata near the Cambrian-Ordovician boundary section at Wushan, illite is the major component of clay minerals in all levels. It is mixed up to 22% of chlorite in the 15 level of the Lower Ordovician, with up to 15% of vermiculite in the 6,7,8 and 9 levels of the Upper Cambrian, and with up to 25% chlorite-verrniculite randomly interstratified minerals in the 12 and 13 levels of the Upper Cambrian. By the investigation of electron microscope, the grains of illite are generally rather small and the shape of illite crystals is poor. The clay samples consist of platy aggrerates of tiny flakes of clay minerals. As a whole, the common texture is of a preferred orintation parallel to the bedding, many clay grains dip at angles to the bedding and show a "swirl" or "undulation" patterns. These stocks are loose packed. This texture develops a high porosity. The illite is dioctahedral, Fe-rich and of iMd type; the chlorite belongs to ripidolite which is trioctahedral and rich in Fej the vermiculite is trioctahedral with a high charge, which may be derived form the weathered mica-like clay minerals. The crystallinity indices of all the samples, which were measured accrding to the tno methods of weaver and dunoyer de segonzac, are all in the range of non-metamorphism. By the experimenrs, it is conjectured that during the transitional period between the end of Cambrian and the beginning of Ordovician, the sedimentary environment might not be quiet because of the turbulence in the seawater and might belong to neritic depost with rich cations, such as Fe and Mg. The seawater was shallower and nearer to the terrigenous region at the end of Cambrian than in the levels 14 and 15 at the beginning of Ordovician. The composition of clay minerals is partly different at the two sides of the boundary, which is probably caused by the differences of the ancient sedimentary environments. But this change is a gradual and continous transitionl one and there is no sharp change and disconnection near the boundary. It indicates that the the deposition is continous without breaks near the boundary at Wushan of Lulong.
1985, 3(2): 75-84.
Abstract:
There are more abundant trace fossils in the Upper Permian and Huohong and Caihua formations of the Middle and Upper Devonian of Sanglang area, Southern Guizhou. They amount to 7 genus and 10 species, of which 2 genus and 4 species are new. There are Chondrites sp.,Helminthopsis sp., Planolites malinggangensis (sp.nov.), Paraachomatichnus malinggangonsis ( gen.nov., sp. nov. ) and Glockeria ? sp. in the Upper Permian. There are Glockeria ? sp., Cosmorhaphe sp., Lumbrichnus sanglan-gensis ( gen.nov., sp.nov.,) and L. sp. ia the Huohong formation of the Middle Devonian. There is Planolites sanglangensis ( sp.nov. ) in the Daihua Formation of the Upper Devonian. The Upper Permian rocks are mainly tuff, tuffaceous limestone, limestone and rudstone -with graded beds and Bouma incomplete sequence. They contain not only the deep-water organisms,such as radiolaria and siliceous sponge spicules, but also the shallow-water organisms.The trace fossils are similar to those of the assemblage of bathyal-abyssal environment trace fossils, which shows that the Upper Permian deposits should mainly be volcaniclastic turbidite with the carbonatite gravity flow deposits. Huohong Formation is rhythmic deposits corresponding to the d, e parts or b, c, d, e parts of Bouma sequence. They have also the flute cast and the load cast. The organisms are mostly the tentaculitids of plankton. The trace fossils are also similar to those of tne assemblage of bathyal-abyssal environment trace fossils. Therefore, the diposits of Huohong Formation should mainly be distal turbidites. Daihua Formation of the Upper Devonian is stripped limestone with radiolaria. Therefore, the Daihua Formation should be the deep-water gravity flow deposits.
There are more abundant trace fossils in the Upper Permian and Huohong and Caihua formations of the Middle and Upper Devonian of Sanglang area, Southern Guizhou. They amount to 7 genus and 10 species, of which 2 genus and 4 species are new. There are Chondrites sp.,Helminthopsis sp., Planolites malinggangensis (sp.nov.), Paraachomatichnus malinggangonsis ( gen.nov., sp. nov. ) and Glockeria ? sp. in the Upper Permian. There are Glockeria ? sp., Cosmorhaphe sp., Lumbrichnus sanglan-gensis ( gen.nov., sp.nov.,) and L. sp. ia the Huohong formation of the Middle Devonian. There is Planolites sanglangensis ( sp.nov. ) in the Daihua Formation of the Upper Devonian. The Upper Permian rocks are mainly tuff, tuffaceous limestone, limestone and rudstone -with graded beds and Bouma incomplete sequence. They contain not only the deep-water organisms,such as radiolaria and siliceous sponge spicules, but also the shallow-water organisms.The trace fossils are similar to those of the assemblage of bathyal-abyssal environment trace fossils, which shows that the Upper Permian deposits should mainly be volcaniclastic turbidite with the carbonatite gravity flow deposits. Huohong Formation is rhythmic deposits corresponding to the d, e parts or b, c, d, e parts of Bouma sequence. They have also the flute cast and the load cast. The organisms are mostly the tentaculitids of plankton. The trace fossils are also similar to those of tne assemblage of bathyal-abyssal environment trace fossils. Therefore, the diposits of Huohong Formation should mainly be distal turbidites. Daihua Formation of the Upper Devonian is stripped limestone with radiolaria. Therefore, the Daihua Formation should be the deep-water gravity flow deposits.
1985, 3(2): 97-107.
Abstract:
Based on the survey, analysis, correlation of systmatic facies section, transverse trace of outcrops, and study in the laboratory, the carbonate strata of the Upper and Middle Devonian Series in this area may be classified into two facies regions, three facies belts and six microfacies. (1) The continental margin facies region with al'ittoral facies belt which can be subdivided into a supratidal local swamp facies and a littoral terrigenous clastic shoal facies. The basic characteristic of the littoral local swamp facies is that it consists chiefly of thin beded, carbonaceous shales and micrites. In the latter there are abundant shell fossils and coral fragments together with mud-crack and birdseye structures, knotty and banded limestones are common. The littoral terrigenous clastic shoal facies is a set of coarse clastic rocks-mainly calcareous-quartz sandstones, sandstones with gravels, conglomerates and minor siltstones, containing more marine fossils. Glauconite occurs ubiquitously in these rocks. Gentle "teepee" type cross bedding and ripple bedding occur in sandstones and siltstones, they are generally reverse-graded beddings. The platform facies region contains a restricted platform facies belt and an open platform facies zone. The restricted platform facies belt can be divided into an intertidal mud flat facies and a tidal channel bar facies. The former is the most developed and consists essentially of two rock types, i.e. the first is chiefly made of limestones, which consist mainly of thin to medium beded micrites with widely developed laminated limestones and a few intercalated psephitic limestones. They are possessed of lenticular bedding, birdseye structure, etc and few fossils. The second is composed mainly of dolomites, which are considered to be formed in diagenetic stage. Relict and metasomatic-relict structures are widely developed in the rocks. Based on their structures, the original rocks restored were domina- tively micrites and lamellar limestones. The dolomites, as a petrographic unit, are regionally distributed. The tidal channel bar facies is in locally intermittent distribution. The tidal channel subfacies is characterized by oncoid limestones intercalated with bioclastic limestones,grainstones, etc, while the bar subfacies by oolite-bearing psammitic limestone, psammitiic limestone, psephitic limestone and bioclastic limestone with subaqueous scour planes. The open platform facies belt consists of a backshoal open platform facies and an intraplatform oal-biosh facies.In the former predominate micrite,algal pellet limestone and grainstone with abundant fossils and horizontal stratifications. The latter was the accumulation of bioclasts-mainly branched and massive Stromatopora. Based on the observation, these organisms grew in situ or were transported in a short distance. The abundance of lead and zinc of carbonate strata in this generally 3 to 4 times higher than the Clark Value of lead and zinc in carbonate, rocks even amounting to 6 times higher than that. The intertidal mud-flat facies about 300-meter thick is considered to control lead and zinc mineralization zone. According to the syntesis of other data, the authors infer that brines and metals for the lead and zinc mineralization were provided by the Intertidal mud-flat,facies, which was the main source-bed.
Based on the survey, analysis, correlation of systmatic facies section, transverse trace of outcrops, and study in the laboratory, the carbonate strata of the Upper and Middle Devonian Series in this area may be classified into two facies regions, three facies belts and six microfacies. (1) The continental margin facies region with al'ittoral facies belt which can be subdivided into a supratidal local swamp facies and a littoral terrigenous clastic shoal facies. The basic characteristic of the littoral local swamp facies is that it consists chiefly of thin beded, carbonaceous shales and micrites. In the latter there are abundant shell fossils and coral fragments together with mud-crack and birdseye structures, knotty and banded limestones are common. The littoral terrigenous clastic shoal facies is a set of coarse clastic rocks-mainly calcareous-quartz sandstones, sandstones with gravels, conglomerates and minor siltstones, containing more marine fossils. Glauconite occurs ubiquitously in these rocks. Gentle "teepee" type cross bedding and ripple bedding occur in sandstones and siltstones, they are generally reverse-graded beddings. The platform facies region contains a restricted platform facies belt and an open platform facies zone. The restricted platform facies belt can be divided into an intertidal mud flat facies and a tidal channel bar facies. The former is the most developed and consists essentially of two rock types, i.e. the first is chiefly made of limestones, which consist mainly of thin to medium beded micrites with widely developed laminated limestones and a few intercalated psephitic limestones. They are possessed of lenticular bedding, birdseye structure, etc and few fossils. The second is composed mainly of dolomites, which are considered to be formed in diagenetic stage. Relict and metasomatic-relict structures are widely developed in the rocks. Based on their structures, the original rocks restored were domina- tively micrites and lamellar limestones. The dolomites, as a petrographic unit, are regionally distributed. The tidal channel bar facies is in locally intermittent distribution. The tidal channel subfacies is characterized by oncoid limestones intercalated with bioclastic limestones,grainstones, etc, while the bar subfacies by oolite-bearing psammitic limestone, psammitiic limestone, psephitic limestone and bioclastic limestone with subaqueous scour planes. The open platform facies belt consists of a backshoal open platform facies and an intraplatform oal-biosh facies.In the former predominate micrite,algal pellet limestone and grainstone with abundant fossils and horizontal stratifications. The latter was the accumulation of bioclasts-mainly branched and massive Stromatopora. Based on the observation, these organisms grew in situ or were transported in a short distance. The abundance of lead and zinc of carbonate strata in this generally 3 to 4 times higher than the Clark Value of lead and zinc in carbonate, rocks even amounting to 6 times higher than that. The intertidal mud-flat facies about 300-meter thick is considered to control lead and zinc mineralization zone. According to the syntesis of other data, the authors infer that brines and metals for the lead and zinc mineralization were provided by the Intertidal mud-flat,facies, which was the main source-bed.
1985, 3(2): 119-128.
Abstract:
The ironstone is gray, dark purple micriti, intraclast siderite with an interla-yer of purple intraclast hematite of 1-5.5m thick. It is found on the quartzose sandstone and coal bed of river and lake-shore facies in lower Jurassic, it is 2-10m thick. Its roof is lacustrine sandstone and shale, being 2-15m thick.This stratigra-phic section is called Qijiang segment, it is distributed at Chongqing, Qijiang, Shizhu and Lichuan, etc. The industrial deposit is accumulated in the south and north of Qijiang ( Figure 1,3). Without exception the ironstones are all accumulated over the peat-swamp deposits that include coal-bed and carbonaceous shale ( Figures,6 ) . Terefore, there is no ironstone accumulated over the sediments of river-lake-shore and argillaceous swamp of the adjoining area. The underlying strata of Qijiang segment are late Triassic yellow medium-fine grained feldspathic quartzite sandstone with an interlayer of little claystone and coalbed, its thickness is between 200 and 600m. During ironstone deposition, the old-land of Proterozoic metamorphic rock was exposed in the southeast area, the half-deep water lake occured in the north area and between these two areas there was river-lake-shore plain on which were distributed some peat-swamps. After the peat was formed, the cover water of these swamps was slightly deepened. As the water medium was reduced by base peat,Eh of the pore water in the lower peat-bed was Omv± and it rose to 400-600mv on the upper limnetic water,thus forming the vertical-divided zone of oxidation-reduction of limnetic water. When pH ( or pH value ) of the peat-limnetic water generally 5 to 6, the oxidation-reduction boundary of the ferri-oxide-ferri-carbonate was between 150 and 280mv (figure 8 ). The ferri-rock of old-landformed Fe(HCO3)2 with greater solubility under the action of organism. Fe ( HCO3 ) 2 came into half-solid sediments of late Trias and was transported toward north in phreatic form. The ferri-ground water in fused peat limnetic. The difficultly solvable Fe(OH)3 was formed and deposited in micriinite by oxidization of oxygen and ferri-germ when Fe2+reached above the ferri oxidation-reduction boundary. Then siderite-micrite ironstone was formed by the reduct-replacement of limnetic base medium. With the thickening of accumulation of ferri sediments, the reductive ability of base medium was weakened and therefore, hematite micrite ironstone was formed. The intrusion of river water or the wave action produced intraclast-ironstone. The roof and floor of some ironstone are generally accompanied by redox-rock both at home and abroad and it seems that the mechanism of formation is the same. This paper shows the prospect direction of this kind of iron ore and presents some new ideas about the origin of ironstone.
The ironstone is gray, dark purple micriti, intraclast siderite with an interla-yer of purple intraclast hematite of 1-5.5m thick. It is found on the quartzose sandstone and coal bed of river and lake-shore facies in lower Jurassic, it is 2-10m thick. Its roof is lacustrine sandstone and shale, being 2-15m thick.This stratigra-phic section is called Qijiang segment, it is distributed at Chongqing, Qijiang, Shizhu and Lichuan, etc. The industrial deposit is accumulated in the south and north of Qijiang ( Figure 1,3). Without exception the ironstones are all accumulated over the peat-swamp deposits that include coal-bed and carbonaceous shale ( Figures,6 ) . Terefore, there is no ironstone accumulated over the sediments of river-lake-shore and argillaceous swamp of the adjoining area. The underlying strata of Qijiang segment are late Triassic yellow medium-fine grained feldspathic quartzite sandstone with an interlayer of little claystone and coalbed, its thickness is between 200 and 600m. During ironstone deposition, the old-land of Proterozoic metamorphic rock was exposed in the southeast area, the half-deep water lake occured in the north area and between these two areas there was river-lake-shore plain on which were distributed some peat-swamps. After the peat was formed, the cover water of these swamps was slightly deepened. As the water medium was reduced by base peat,Eh of the pore water in the lower peat-bed was Omv± and it rose to 400-600mv on the upper limnetic water,thus forming the vertical-divided zone of oxidation-reduction of limnetic water. When pH ( or pH value ) of the peat-limnetic water generally 5 to 6, the oxidation-reduction boundary of the ferri-oxide-ferri-carbonate was between 150 and 280mv (figure 8 ). The ferri-rock of old-landformed Fe(HCO3)2 with greater solubility under the action of organism. Fe ( HCO3 ) 2 came into half-solid sediments of late Trias and was transported toward north in phreatic form. The ferri-ground water in fused peat limnetic. The difficultly solvable Fe(OH)3 was formed and deposited in micriinite by oxidization of oxygen and ferri-germ when Fe2+reached above the ferri oxidation-reduction boundary. Then siderite-micrite ironstone was formed by the reduct-replacement of limnetic base medium. With the thickening of accumulation of ferri sediments, the reductive ability of base medium was weakened and therefore, hematite micrite ironstone was formed. The intrusion of river water or the wave action produced intraclast-ironstone. The roof and floor of some ironstone are generally accompanied by redox-rock both at home and abroad and it seems that the mechanism of formation is the same. This paper shows the prospect direction of this kind of iron ore and presents some new ideas about the origin of ironstone.
1985, 3(2): 141-150.
Abstract:
Some maincharacteristics of grain-size distribution of sand-gravel sediments have been presented in this paper through the grain-size analysis of Halahu lake-shore sediments. Most of the lake-shore sediments are of unimodal form in sizehistogram，and the sorting of their grain size is m oderately better.The parametervalues of lake-shore gravelsare 81=0.462-0.935,SK1=-0.169-+0.134,Kg=0.961-1.414.The skewness(SK1)of lake-beach sands is predominately negative, and their stand-and deviation (81)ranges 0.691-1.854.Saltation and traction populations show theirdo minance in probability curve of grain size of lake-beach sands, w hick indicatesm oderate sorting.Most of the longest axes(a-axes)of lake-shore gravels are parallelto the direction of lake- shore, line,and ab - planes of gravels dip to lake directionat an average angle about 80.It is suggested that the research on the characteristicsof grain size distribution of lake-shore sand-gravel sediments be of great import-ante to the study of sedimentary environment and the identification of the genetictype of ancient lake deposits.
Some maincharacteristics of grain-size distribution of sand-gravel sediments have been presented in this paper through the grain-size analysis of Halahu lake-shore sediments. Most of the lake-shore sediments are of unimodal form in sizehistogram，and the sorting of their grain size is m oderately better.The parametervalues of lake-shore gravelsare 81=0.462-0.935,SK1=-0.169-+0.134,Kg=0.961-1.414.The skewness(SK1)of lake-beach sands is predominately negative, and their stand-and deviation (81)ranges 0.691-1.854.Saltation and traction populations show theirdo minance in probability curve of grain size of lake-beach sands, w hick indicatesm oderate sorting.Most of the longest axes(a-axes)of lake-shore gravels are parallelto the direction of lake- shore, line,and ab - planes of gravels dip to lake directionat an average angle about 80.It is suggested that the research on the characteristicsof grain size distribution of lake-shore sand-gravel sediments be of great import-ante to the study of sedimentary environment and the identification of the genetictype of ancient lake deposits.
1985, 3(2): 18-36.
Abstract:
In technology field the refractory clays with Al2O3 46% are called high alumina clays among which Al/Si≥2.6 is called bauxite.Paleozoic high alumina clay-dauxite deposits are aboundant in China. They are mainly distributed in Shanxi and Henan provinces. It is known that there are more than 100 occurrences of high alumina clay-bauxite deposit in the two provinces. Their reserve is about several hundred million tons.Almost all of high alumina clay-bauxite deposits in the two provinces occur at the lower part of the Middle Carboniferous series which overlay the Middle Ordo-vician series limestone as uncomformity.This paper suggests that the material sources of the deposits are mainly the products of weathered aluminium silicates on the peneplainized continent under hot and humid climate(i.e.colloform of Al protected by humic acid or colloidal solution of Al.Ti.Fe.Si, gel of Al in form of suspension,kaolinite, hydromica and detritus of heavy minerals). The next is the minor weathered residues of carbonte derived from some rises. Both of the products and residues were transported by braided rivers. Most of them deposited in lakes and very few in swamps. During the sedimentation the ore was generally in gel, oolite or fragmental texture, Indicating colloid-mechanical mixed deposition. In the diagenetic process diaspore, chlorite and pyrite were formed under redu-ction and alkaline conditions; and diaspore or boehmite and kaolinite under acidcondition.In the epigenetic process diaspore and kaolinite were recrystallized and ordered as temperature and pressure increased. Diaspore was formed by desilication of kao-linite under alkaline condition. Kaolinite could be converted to dickite or diaspore to which silica was added was converted into dickite under acid condition. Also diaspore to which silica was added turned into kaolinite and prophyllite under acid condition.At the late stage kaolinite and other clay minerals were desilicated and became gibbsite due to the leaching of some organic acid, sulpuric acid produced by some weathered pyrite and carbonic acid. At the same time, high alumina clay-bauxite deposits were getting higher in quality as Fe and Ti were removed. Under acid condition of water media and with the existence of proper content of SiO2 solution kaolinite, galapectite and other clay minerals were formed by filling and replacement at the active of underground water. On the contrary, under alkaline condition and with the existence zone of some alkaline or alkaline-earth metal cation, hydromica, montmorillonite, mixed layer of chlorite-vermiculite and mixed layer of hydromica-montmorillonite were also formed by the same two actions, so that the quality of the high alumina clay-bauxite deposits was getting worse.By late weathering and leaching the ore became porous and honeycomb-like due to the leaching out of pyrite or became pale, because of the oxidazation of a small amount of contaminated organic matters. However, the weathering and leaching which were beneficial to the raise of ore quality are oftn neglected.The following heavy minerals are of terrigenous elastics: zircon, rutile, ilmen-ite, tournaline, magnetite, anatasc, brookite, sphene, leucoxene, pyroxene quartz garnet, gahnite,monacite, xenotime,epidote and so on, the epigen'etic minerals are anatase,zircon, rutile,magnetite and corundum.In addition, another two kinds of high alumina clay deposits occur in theUpper Carboniferous stratigraphy of North Shanxi.1. Humic acid leaching type: This kind of deposits is mainly formed during dia-genesis. Silica and other impurities in clay bed and the top part of coalseam were leached away by humic acid. The dominant mineral is kaolinite next to it are boe-chmite and so on. The deposits in Huairen district are big in size. The ore is a kind of light-grey and black-grey, dense(fine grained) high alumina clay. The content of harmful impurities is very low. It is valuable in industry though the ratio of A/S is lower.The deposits in Baode district are small in size. The ore is purer. The dominant mineral is coarse myrme
In technology field the refractory clays with Al2O3 46% are called high alumina clays among which Al/Si≥2.6 is called bauxite.Paleozoic high alumina clay-dauxite deposits are aboundant in China. They are mainly distributed in Shanxi and Henan provinces. It is known that there are more than 100 occurrences of high alumina clay-bauxite deposit in the two provinces. Their reserve is about several hundred million tons.Almost all of high alumina clay-bauxite deposits in the two provinces occur at the lower part of the Middle Carboniferous series which overlay the Middle Ordo-vician series limestone as uncomformity.This paper suggests that the material sources of the deposits are mainly the products of weathered aluminium silicates on the peneplainized continent under hot and humid climate(i.e.colloform of Al protected by humic acid or colloidal solution of Al.Ti.Fe.Si, gel of Al in form of suspension,kaolinite, hydromica and detritus of heavy minerals). The next is the minor weathered residues of carbonte derived from some rises. Both of the products and residues were transported by braided rivers. Most of them deposited in lakes and very few in swamps. During the sedimentation the ore was generally in gel, oolite or fragmental texture, Indicating colloid-mechanical mixed deposition. In the diagenetic process diaspore, chlorite and pyrite were formed under redu-ction and alkaline conditions; and diaspore or boehmite and kaolinite under acidcondition.In the epigenetic process diaspore and kaolinite were recrystallized and ordered as temperature and pressure increased. Diaspore was formed by desilication of kao-linite under alkaline condition. Kaolinite could be converted to dickite or diaspore to which silica was added was converted into dickite under acid condition. Also diaspore to which silica was added turned into kaolinite and prophyllite under acid condition.At the late stage kaolinite and other clay minerals were desilicated and became gibbsite due to the leaching of some organic acid, sulpuric acid produced by some weathered pyrite and carbonic acid. At the same time, high alumina clay-bauxite deposits were getting higher in quality as Fe and Ti were removed. Under acid condition of water media and with the existence of proper content of SiO2 solution kaolinite, galapectite and other clay minerals were formed by filling and replacement at the active of underground water. On the contrary, under alkaline condition and with the existence zone of some alkaline or alkaline-earth metal cation, hydromica, montmorillonite, mixed layer of chlorite-vermiculite and mixed layer of hydromica-montmorillonite were also formed by the same two actions, so that the quality of the high alumina clay-bauxite deposits was getting worse.By late weathering and leaching the ore became porous and honeycomb-like due to the leaching out of pyrite or became pale, because of the oxidazation of a small amount of contaminated organic matters. However, the weathering and leaching which were beneficial to the raise of ore quality are oftn neglected.The following heavy minerals are of terrigenous elastics: zircon, rutile, ilmen-ite, tournaline, magnetite, anatasc, brookite, sphene, leucoxene, pyroxene quartz garnet, gahnite,monacite, xenotime,epidote and so on, the epigen'etic minerals are anatase,zircon, rutile,magnetite and corundum.In addition, another two kinds of high alumina clay deposits occur in theUpper Carboniferous stratigraphy of North Shanxi.1. Humic acid leaching type: This kind of deposits is mainly formed during dia-genesis. Silica and other impurities in clay bed and the top part of coalseam were leached away by humic acid. The dominant mineral is kaolinite next to it are boe-chmite and so on. The deposits in Huairen district are big in size. The ore is a kind of light-grey and black-grey, dense(fine grained) high alumina clay. The content of harmful impurities is very low. It is valuable in industry though the ratio of A/S is lower.The deposits in Baode district are small in size. The ore is purer. The dominant mineral is coarse myrme
1985, 3(2): 47-56.
Abstract:
The reservoirs of sandstones of the Lower Tertiary in Dongying Degression,Shandong were proved to be quite developed.The writer tried to determine the structure type, genesis, abundance, distridution of secondary pores and their controlling factors so as to distinguish the varying sequence of diagenesis and its effect on secondary pores by the careful observation of hand specimen, thin sections of the rock, cast thin section, the natural plane of fracture, rounded face of the sample and the surface of the sand grain using stero-microscope, polarizing microscope and scanning electron-microscope. It is suggested that the marks to identify the secondary pores of sandstone in this area are as follows: partial dissolution, corroded grain, overquantity of pores, leaked skeletons, moldic pores, attaching-granular pores, residual carbonate cements, elongate pores,inhomogeneity of packing, oversized pores,immersion carbonate matrix or cement, crashed grains, gaps of rock etc. Secondary pores in this araea consist of seven types of structures, such as secondary intergranular pores,moldic pores,attaching-granular pores, intra-constituent pores, oversized pores, intergranular intercrystal pores and fracture pores. The first five of them result from the dissolution in deep subground with the largest amount,widest distribution and they are of great significance;while fracture pores brought about by overying pressure and structure action, and intercrystal pores are caused by constriction of recrystal in carbonate matrix. These two types of pores have less amount and are of little importance. The secondary pores of the lower Tertiary sandstone in this area are not so well developed as the primary ones,but they have a regular distribution they develop better in north then in south, and better in the deeps than in shallows. The lateral distribution of secondary pores is controlled by the structure of the basin while vertical distribution is determined by the combination of sedimentary facies and the mineral composition and texture and structure of sandstone have somesthing to do with the development of secondary pores. In a word, the developed faults and the reservoirs close to the source rocks and the massive coarser sandstone rich in dissoluble compositions provide a suitable condition for the development of seconday pores. There is a close relationship between secondary pores and diagenesis. The complex diagenetic change of the rocks especially the early cementation of mosaic Fe-calcite, replacement of carbonate and dedolomitization in the depth were indirectly suitable for forming secondary pores. Mechanical compaction could result in little amount of pores and fractures, but it mainly destoried the pores which were formed before. The transformation of clay minerals and the dissolution of the acid water produced by thermal maturity of organic mattter were the main factors of forming secondry pores. It is concluded that 1 ), secondary pores occur in many oil reservirs, of which some are predomnant with secondary pores, so secondary pores are the main parts of the sandstone reservoirs in this areas 2), secondary pores concentrated over the threshold value pores become the path along which hydrocarbon migrate upward, this provides a useful information for the determination of threshold value; 3), secondary pores deepen the effective pores of sandstone, based on which the guideline could be given and the exploration of the oil formation near source rocks should be made; 4), the reservoirs with secondary pores have developed carbonate cements, larger mechanical strength, a better results of acidization and the connection of pores caused by long-term flow of acid water are advantageous to the development of the oil field.
The reservoirs of sandstones of the Lower Tertiary in Dongying Degression,Shandong were proved to be quite developed.The writer tried to determine the structure type, genesis, abundance, distridution of secondary pores and their controlling factors so as to distinguish the varying sequence of diagenesis and its effect on secondary pores by the careful observation of hand specimen, thin sections of the rock, cast thin section, the natural plane of fracture, rounded face of the sample and the surface of the sand grain using stero-microscope, polarizing microscope and scanning electron-microscope. It is suggested that the marks to identify the secondary pores of sandstone in this area are as follows: partial dissolution, corroded grain, overquantity of pores, leaked skeletons, moldic pores, attaching-granular pores, residual carbonate cements, elongate pores,inhomogeneity of packing, oversized pores,immersion carbonate matrix or cement, crashed grains, gaps of rock etc. Secondary pores in this araea consist of seven types of structures, such as secondary intergranular pores,moldic pores,attaching-granular pores, intra-constituent pores, oversized pores, intergranular intercrystal pores and fracture pores. The first five of them result from the dissolution in deep subground with the largest amount,widest distribution and they are of great significance;while fracture pores brought about by overying pressure and structure action, and intercrystal pores are caused by constriction of recrystal in carbonate matrix. These two types of pores have less amount and are of little importance. The secondary pores of the lower Tertiary sandstone in this area are not so well developed as the primary ones,but they have a regular distribution they develop better in north then in south, and better in the deeps than in shallows. The lateral distribution of secondary pores is controlled by the structure of the basin while vertical distribution is determined by the combination of sedimentary facies and the mineral composition and texture and structure of sandstone have somesthing to do with the development of secondary pores. In a word, the developed faults and the reservoirs close to the source rocks and the massive coarser sandstone rich in dissoluble compositions provide a suitable condition for the development of seconday pores. There is a close relationship between secondary pores and diagenesis. The complex diagenetic change of the rocks especially the early cementation of mosaic Fe-calcite, replacement of carbonate and dedolomitization in the depth were indirectly suitable for forming secondary pores. Mechanical compaction could result in little amount of pores and fractures, but it mainly destoried the pores which were formed before. The transformation of clay minerals and the dissolution of the acid water produced by thermal maturity of organic mattter were the main factors of forming secondry pores. It is concluded that 1 ), secondary pores occur in many oil reservirs, of which some are predomnant with secondary pores, so secondary pores are the main parts of the sandstone reservoirs in this areas 2), secondary pores concentrated over the threshold value pores become the path along which hydrocarbon migrate upward, this provides a useful information for the determination of threshold value; 3), secondary pores deepen the effective pores of sandstone, based on which the guideline could be given and the exploration of the oil formation near source rocks should be made; 4), the reservoirs with secondary pores have developed carbonate cements, larger mechanical strength, a better results of acidization and the connection of pores caused by long-term flow of acid water are advantageous to the development of the oil field.
1985, 3(2): 67-74.
Abstract:
From the field observation and study on petrology and paleobiology of the siliceous rocks of Maokou FormationCthe Lower Permian),Southeast Hubei Province, we have found many radiolarias, such as Stauroloche sp., Cenellipsis sp., Cenosph-aera sp., etc. and other geological evidences, which clearly indicate that these rocks accumulated in the environment close to the depth of calcite compositiou, and underwent a series of diagenetic changes, such as solution, redistribution, recrystallization and metasomatism after the depositon. All the processes of diagenetic changes are indicated by the following table. Processes of diagenetic changes of siliceous rocks The depth of depositional water has three differeent stages of changing from shallowness to deepness, which are consistent with the three divisional secti ons of siliceous rocks. The first stage of its deposition has argillaceous and silty siliceous rocks in the lower section and straum of concretion-bearing with collophanite in the floor section. They usually accumulate at the edge of shelf in the depth of about 100-200 meters. The second stage has banded siliceous rocks. They are mainly composed of siliceous sediment and carbonate. The presence of carbonate indicates that they have accumulated near CCD.The absence in carbonate,except radiolarias, of fossil community of fusulina and other foraminifera which were usually well developed in Permian incicates that the then depth of deposition was so deep that the calcareous skeletons of plankton were fully dissolved with no remainder left. The depositions in the third stage are rediolarias-bearing siliceous rocks without terrigenous fragment and carbonate.Its sedimentary environment was all situated under CCD. Obviously the siliceous rocks of Maokou formation (the Lower Permian ) in Southeast Hubei Province have deposited under sedimentary condition of trangression. Its southern zone, including Yangxin, Tongshan, Chongyang and Puqi, commonly locates in carbonate platform and has deposited biomicritic and biospar limestones? the northern zone, including Wuchang, Dayie, Huangshi and Guanji, has formed deep-water basin as a result of the crustal differential movement, and deposited siliceous rocks which represent the deep-water sediment. The sedimentary environment is located between the old land and the old rise on the broad shallow sea inside the platform. There was a western wind coming from the old equator through the continent to the sea surface,then it caused the rising of the colder ocean current, therefore, there was a great deal of radiolaras to breed. The deposition of the radiolaria-bearing siliceous rocks is obviously associated with the sink of the banded-active depression inside the platform. This sink of the banded-active depression has an influence not only on the sediment of Maokou formation ( the Lower Permian ) , but also obviously on the sediment of Lungton formation ( the Upper Permian ) .
From the field observation and study on petrology and paleobiology of the siliceous rocks of Maokou FormationCthe Lower Permian),Southeast Hubei Province, we have found many radiolarias, such as Stauroloche sp., Cenellipsis sp., Cenosph-aera sp., etc. and other geological evidences, which clearly indicate that these rocks accumulated in the environment close to the depth of calcite compositiou, and underwent a series of diagenetic changes, such as solution, redistribution, recrystallization and metasomatism after the depositon. All the processes of diagenetic changes are indicated by the following table. Processes of diagenetic changes of siliceous rocks The depth of depositional water has three differeent stages of changing from shallowness to deepness, which are consistent with the three divisional secti ons of siliceous rocks. The first stage of its deposition has argillaceous and silty siliceous rocks in the lower section and straum of concretion-bearing with collophanite in the floor section. They usually accumulate at the edge of shelf in the depth of about 100-200 meters. The second stage has banded siliceous rocks. They are mainly composed of siliceous sediment and carbonate. The presence of carbonate indicates that they have accumulated near CCD.The absence in carbonate,except radiolarias, of fossil community of fusulina and other foraminifera which were usually well developed in Permian incicates that the then depth of deposition was so deep that the calcareous skeletons of plankton were fully dissolved with no remainder left. The depositions in the third stage are rediolarias-bearing siliceous rocks without terrigenous fragment and carbonate.Its sedimentary environment was all situated under CCD. Obviously the siliceous rocks of Maokou formation (the Lower Permian ) in Southeast Hubei Province have deposited under sedimentary condition of trangression. Its southern zone, including Yangxin, Tongshan, Chongyang and Puqi, commonly locates in carbonate platform and has deposited biomicritic and biospar limestones? the northern zone, including Wuchang, Dayie, Huangshi and Guanji, has formed deep-water basin as a result of the crustal differential movement, and deposited siliceous rocks which represent the deep-water sediment. The sedimentary environment is located between the old land and the old rise on the broad shallow sea inside the platform. There was a western wind coming from the old equator through the continent to the sea surface,then it caused the rising of the colder ocean current, therefore, there was a great deal of radiolaras to breed. The deposition of the radiolaria-bearing siliceous rocks is obviously associated with the sink of the banded-active depression inside the platform. This sink of the banded-active depression has an influence not only on the sediment of Maokou formation ( the Lower Permian ) , but also obviously on the sediment of Lungton formation ( the Upper Permian ) .
1985, 3(2): 85-96.
Abstract:
There is a set of tidal flat deposits, with the correlated geochronological data about 1950 m.y., made of sand-silty mudstone interlayers in Changzhougou Formation of Changcheng -System in the lower part of the Upper Precambrian strata in Ming Tombs, Beijing. Many shallow water sedimentary structures can be found in the strata, such as: ripple mark, mud crack, ice model(?), runzel,rain print model, herringbone cross-bedding, flaser and lenticular bedding, etc. showing tidal flat depositional environment. It is worth noticing that among the interlayers of sand-silty mudstone there are so many burrow-like tube filling structures (See Fig.l, Fig.7, Plate I-1,2,3 and 5, Plate II 3 and 5), which have been compared by the authors with folded mud crack filling structures, ball and pillow structure, load deformation, frozen crack filling structre, sandbody liquidization structure and water escape structure, etc., but all of those sedimentary structures are helpless to interpret the genesis of the burrow-like tube filling structures in this paper. But there are many obvious similarities between the burrow-like tube filling structures and the so-called oldest Metazoan trace fossils or dubiofossils discovered by E.G Kauffman and J. R. Steidtmann in Medicine Peak Quartzite, Wyoming, U. S.A. The Medicine Peak Quartzite dated at 2000 m.y.B.P*, which is roughly coincident with the geological age of Changzhougou Formation of the Upper Precambrian Strata in Ming Tombs, Beijing. So, are these the oldest Metazoan trace fossils also? And there is also one more question- had some catastrophic events happened since 2000 m.y.B.P.to Phanerozoic so as to eliminate these oldest lives in such a long period? The authors have paid attention to the comments on the reports about the so-called oldest Metazoan trace fossils made by P.E. Cloud, H. Clemmey, J.W. Durham, and C.W. Byers, et al. It is supposed that if there was not any possibility for the existence of the oldest Metazoan trace fossils in sediments at 2000 m.y. B.P., there must be an extreme situation for the genesis of burrow-like tube filling structures either in Medicine Peak Quartzite, Wyoming or in Changzhougou Formation in Ming Tombs, Beijing. However, it is necessary for us to deal with the kinetic mechanism of burrow-like tube filling structures continuously. Fortunately, we have found a kind of traces distributed on the mudy siltstone bed surface in the middle part of Changzhougou Fr. overlaid on the layers, envoling burrow-like tube filling structures in the tidal deposits of the lower part of the Upper Precambrian Strata as mentioned above. We try to judge by the appearances of those traces as a kind of the oldest Metazoan trace fossils, according to the regular narrow grooves with two widges. The diameter of grooves is about 3mm and the widge width about 1.2mm. Those traces can be slightly straight or curved, they look very like crawled trails by some fine earthworms, however it was a long past story before 1900m.y A Canadian famous geologist, Dr.R.A. Rahmani had a look of the oldest Metazoan trace fossil on the outcrop of Changzhougou Fr. in the Ming Tombs District, when he was invited for making lectures in Beijing. Dr. R. A.Rahmani considered that was a kind of true trace fossil characterized by very regular grooves as the trace fossil Gyrochortae in Cretaceous Strata. It will be a definite support to Dr. E. G. Kauffman and Dr. J. R.Steidtmann's theory about the existence of the oldest Metazoan trace fossils in the early Proterozoic period, if the real oldest Metazoan trace fossil in the Changzhougou Fr. of the lower part of Upper Precambrian Strata (about 1900m. y. BP) in the Ming Tombs District, Beijing, China, is demonstrated.
There is a set of tidal flat deposits, with the correlated geochronological data about 1950 m.y., made of sand-silty mudstone interlayers in Changzhougou Formation of Changcheng -System in the lower part of the Upper Precambrian strata in Ming Tombs, Beijing. Many shallow water sedimentary structures can be found in the strata, such as: ripple mark, mud crack, ice model(?), runzel,rain print model, herringbone cross-bedding, flaser and lenticular bedding, etc. showing tidal flat depositional environment. It is worth noticing that among the interlayers of sand-silty mudstone there are so many burrow-like tube filling structures (See Fig.l, Fig.7, Plate I-1,2,3 and 5, Plate II 3 and 5), which have been compared by the authors with folded mud crack filling structures, ball and pillow structure, load deformation, frozen crack filling structre, sandbody liquidization structure and water escape structure, etc., but all of those sedimentary structures are helpless to interpret the genesis of the burrow-like tube filling structures in this paper. But there are many obvious similarities between the burrow-like tube filling structures and the so-called oldest Metazoan trace fossils or dubiofossils discovered by E.G Kauffman and J. R. Steidtmann in Medicine Peak Quartzite, Wyoming, U. S.A. The Medicine Peak Quartzite dated at 2000 m.y.B.P*, which is roughly coincident with the geological age of Changzhougou Formation of the Upper Precambrian Strata in Ming Tombs, Beijing. So, are these the oldest Metazoan trace fossils also? And there is also one more question- had some catastrophic events happened since 2000 m.y.B.P.to Phanerozoic so as to eliminate these oldest lives in such a long period? The authors have paid attention to the comments on the reports about the so-called oldest Metazoan trace fossils made by P.E. Cloud, H. Clemmey, J.W. Durham, and C.W. Byers, et al. It is supposed that if there was not any possibility for the existence of the oldest Metazoan trace fossils in sediments at 2000 m.y. B.P., there must be an extreme situation for the genesis of burrow-like tube filling structures either in Medicine Peak Quartzite, Wyoming or in Changzhougou Formation in Ming Tombs, Beijing. However, it is necessary for us to deal with the kinetic mechanism of burrow-like tube filling structures continuously. Fortunately, we have found a kind of traces distributed on the mudy siltstone bed surface in the middle part of Changzhougou Fr. overlaid on the layers, envoling burrow-like tube filling structures in the tidal deposits of the lower part of the Upper Precambrian Strata as mentioned above. We try to judge by the appearances of those traces as a kind of the oldest Metazoan trace fossils, according to the regular narrow grooves with two widges. The diameter of grooves is about 3mm and the widge width about 1.2mm. Those traces can be slightly straight or curved, they look very like crawled trails by some fine earthworms, however it was a long past story before 1900m.y A Canadian famous geologist, Dr.R.A. Rahmani had a look of the oldest Metazoan trace fossil on the outcrop of Changzhougou Fr. in the Ming Tombs District, when he was invited for making lectures in Beijing. Dr. R. A.Rahmani considered that was a kind of true trace fossil characterized by very regular grooves as the trace fossil Gyrochortae in Cretaceous Strata. It will be a definite support to Dr. E. G. Kauffman and Dr. J. R.Steidtmann's theory about the existence of the oldest Metazoan trace fossils in the early Proterozoic period, if the real oldest Metazoan trace fossil in the Changzhougou Fr. of the lower part of Upper Precambrian Strata (about 1900m. y. BP) in the Ming Tombs District, Beijing, China, is demonstrated.
1985, 3(2): 108-118.
Abstract:
The application of microfacies markers to the identification of sedimentary facies has been rarely found at home and abroad. It only shows a preliminary attempt at present. With the progress of the exploration and development of the Jiyang Sag, it has been a main task to seek non-anticline reservoirs. It is an important way to search lithological reservoirs according to the types of genesis and depositional conditions of various kinds of sand bodies. Consequently, in unknown areas it is an urgent subject to study the microfacies markers in the precent oil and gas exploration by the thin section analysis of cuttings. Therefore, the writer has observed over 600 thin sections of cores and cuttings from 7 cored wells and 25 cut wells in Dongying and Zhanhua depressions. Based on them,9 types including 15 microfacies markers and other markers have been obtained in Tertiary clastic rocks in this area (Table 1). With these markers, the following has been classified' two sedimentary systems above and below water and 11 microfacies (including deep-lake channel of gravity, semi deep-lake turbidite fan, shallow lake fan, sand in lake bank, sand in shallow bank, estuarine bar. subaqueous sand barrier,distributary channel,levee,alluvial channel and alluvial fan, etc.)of fourtypes of currents(subaqueous gravity current, wave-lake current,drag current above water and mud-rock flow). The identification of two sedimentary systems and sediments of four types of currents of the Tertiary clastic rocks in the study area are discribed as follows: Various dissimilar grains and cryptocrystalline carbonate cements can not be seen in sedimentary system above water. On the contrary, they appear in subaqueous sedimentary system. The sediments of subaqueous gravity current are characterized by "mixed" fabric, "porphyritic" fabric, "lime-mud matrix" support, tearing fragments, mixed types of dissimilar grains with small quantity, sliding deformed bedding, graded bedding or load texture, etc.. The characteristics of the sediments of the current along the shore are a high maturity composition and fabric, uniformly arranged fragments and reversed rhythm, and more dissimilar grains and cryptocrystalline carbonate cements. The fluvial and mud-rock flow sediments have a low maturity of composition and texture, fragments with oriented arrangement or uniform distribution, and markable normal rhythm. Especially, the mud-rock flow sediments have lower maturity of texture and composition, disordered fragments and "matrix" support, without notable rhythm. Moreover, in light of the differentiation of 15 microfacies markers in clastic rocks and the characteristics of other markers as well, 11 microfacies can be further identified (Table 1). The results show that it is difficult to analyze the origin of sandbodies due to the complex conditions of the formation of sand bodies in downfaulted basin in the area, such as, more types of matrix, close to sources,rapid sedimentation and a large change of paleogeomorphology and hydrodynamics, etc.. The origin and regularity of distribution of various types of sand-bodies have been recognized by general macro-microanalysis information. In each stage of each sedimentation period, the basin underwent expansion梒ontraction-e xpansion, during which sandbodies with different origins were formed. This was closely related to the depositonal environment and oscillation of the earth crust (Table 2).Based on this understanding,the preliminary prediction on the distribution of sandbodies is presented by the author. The practice indicates that a better and faster result can be achieved in the respect of broadering the new area of prospecting through the analysis of the genesis of sandbodies and the prediction of new sandbodies by classifying sedimentary facies with the micro-indicators of the sections-of cores and cuttings, thus becoming an effective guidance in oil exploration of this area.
The application of microfacies markers to the identification of sedimentary facies has been rarely found at home and abroad. It only shows a preliminary attempt at present. With the progress of the exploration and development of the Jiyang Sag, it has been a main task to seek non-anticline reservoirs. It is an important way to search lithological reservoirs according to the types of genesis and depositional conditions of various kinds of sand bodies. Consequently, in unknown areas it is an urgent subject to study the microfacies markers in the precent oil and gas exploration by the thin section analysis of cuttings. Therefore, the writer has observed over 600 thin sections of cores and cuttings from 7 cored wells and 25 cut wells in Dongying and Zhanhua depressions. Based on them,9 types including 15 microfacies markers and other markers have been obtained in Tertiary clastic rocks in this area (Table 1). With these markers, the following has been classified' two sedimentary systems above and below water and 11 microfacies (including deep-lake channel of gravity, semi deep-lake turbidite fan, shallow lake fan, sand in lake bank, sand in shallow bank, estuarine bar. subaqueous sand barrier,distributary channel,levee,alluvial channel and alluvial fan, etc.)of fourtypes of currents(subaqueous gravity current, wave-lake current,drag current above water and mud-rock flow). The identification of two sedimentary systems and sediments of four types of currents of the Tertiary clastic rocks in the study area are discribed as follows: Various dissimilar grains and cryptocrystalline carbonate cements can not be seen in sedimentary system above water. On the contrary, they appear in subaqueous sedimentary system. The sediments of subaqueous gravity current are characterized by "mixed" fabric, "porphyritic" fabric, "lime-mud matrix" support, tearing fragments, mixed types of dissimilar grains with small quantity, sliding deformed bedding, graded bedding or load texture, etc.. The characteristics of the sediments of the current along the shore are a high maturity composition and fabric, uniformly arranged fragments and reversed rhythm, and more dissimilar grains and cryptocrystalline carbonate cements. The fluvial and mud-rock flow sediments have a low maturity of composition and texture, fragments with oriented arrangement or uniform distribution, and markable normal rhythm. Especially, the mud-rock flow sediments have lower maturity of texture and composition, disordered fragments and "matrix" support, without notable rhythm. Moreover, in light of the differentiation of 15 microfacies markers in clastic rocks and the characteristics of other markers as well, 11 microfacies can be further identified (Table 1). The results show that it is difficult to analyze the origin of sandbodies due to the complex conditions of the formation of sand bodies in downfaulted basin in the area, such as, more types of matrix, close to sources,rapid sedimentation and a large change of paleogeomorphology and hydrodynamics, etc.. The origin and regularity of distribution of various types of sand-bodies have been recognized by general macro-microanalysis information. In each stage of each sedimentation period, the basin underwent expansion梒ontraction-e xpansion, during which sandbodies with different origins were formed. This was closely related to the depositonal environment and oscillation of the earth crust (Table 2).Based on this understanding,the preliminary prediction on the distribution of sandbodies is presented by the author. The practice indicates that a better and faster result can be achieved in the respect of broadering the new area of prospecting through the analysis of the genesis of sandbodies and the prediction of new sandbodies by classifying sedimentary facies with the micro-indicators of the sections-of cores and cuttings, thus becoming an effective guidance in oil exploration of this area.
1985, 3(2): 129-140.
Abstract:
The Zhujiang river mouth is a drainage basin of Zhujiang river system. The amount of yearly average runoff is totally 341.2xl08m3, and the amount of annual suspended silt is 83.36 million tons, 80% of which enters into the Zhujiang river mouth area. A large area of silt-clay or sandy deposits has been formed under the coaction of the river and the sea. Dynamic and environmental features at the Zhujiang mouth are as follows: 1 The discharges of runoff and suspended silt mainly occur during the flood season, and respectively account for 80% and 81--95% of the annul amounts; 2 Water mass of the South China Sea is a constant influence on the river mouthj 3 River flow and tidal current at each river mouth or estuary are different from one another in intensity) 4 Water currents flowing at river mouths or estuaries are to-and-fro currents, but outside they are rotative currents; 5 The nearshore current mainly flows southwe-stward; 6 A large amount of organic matters and chemical elements is carried into the estuary. According to the dynamic and environmental condintions,three types of sedim- entation can be classified at the Zhujiang mouth: 1 Distributary mouths(including Jiaomen,Honggili,Hengmen,Medaomen,Jitimen,Hutiaomen),at which runoff affection is dominent and tidal affection is weaker; 2 Esturies(river mouths are mainly affected by tide), such as, Lingdinyang(Humen) and Huangmaohai(Yamen). Their yearly runoff is far smaller than the tidal current and varies a lot. At estuaries, salt water is mixed with fresh water and a sharp variation occurs because of the flood season and low-water season; 3 Shelf shallow sea, which is not only affected by tidal, sea and inshore currents, but also affected by river fresh water. However, its sedimentary environment is dominated by sea factors. Its main sedimentary facies are river-mouth sand bar, forelandaccretion bed, alluvial-river bed, subaerial or subaquatic levees, interdistributary bay, flood-tide trough, predelta, tidal channel, tidal sand bar, tidal flat and shelf shallow sea.
The Zhujiang river mouth is a drainage basin of Zhujiang river system. The amount of yearly average runoff is totally 341.2xl08m3, and the amount of annual suspended silt is 83.36 million tons, 80% of which enters into the Zhujiang river mouth area. A large area of silt-clay or sandy deposits has been formed under the coaction of the river and the sea. Dynamic and environmental features at the Zhujiang mouth are as follows: 1 The discharges of runoff and suspended silt mainly occur during the flood season, and respectively account for 80% and 81--95% of the annul amounts; 2 Water mass of the South China Sea is a constant influence on the river mouthj 3 River flow and tidal current at each river mouth or estuary are different from one another in intensity) 4 Water currents flowing at river mouths or estuaries are to-and-fro currents, but outside they are rotative currents; 5 The nearshore current mainly flows southwe-stward; 6 A large amount of organic matters and chemical elements is carried into the estuary. According to the dynamic and environmental condintions,three types of sedim- entation can be classified at the Zhujiang mouth: 1 Distributary mouths(including Jiaomen,Honggili,Hengmen,Medaomen,Jitimen,Hutiaomen),at which runoff affection is dominent and tidal affection is weaker; 2 Esturies(river mouths are mainly affected by tide), such as, Lingdinyang(Humen) and Huangmaohai(Yamen). Their yearly runoff is far smaller than the tidal current and varies a lot. At estuaries, salt water is mixed with fresh water and a sharp variation occurs because of the flood season and low-water season; 3 Shelf shallow sea, which is not only affected by tidal, sea and inshore currents, but also affected by river fresh water. However, its sedimentary environment is dominated by sea factors. Its main sedimentary facies are river-mouth sand bar, forelandaccretion bed, alluvial-river bed, subaerial or subaquatic levees, interdistributary bay, flood-tide trough, predelta, tidal channel, tidal sand bar, tidal flat and shelf shallow sea.
