1988 Vol. 6, No. 4
column
Display Method:
1988, 6(4): 1-11.
Abstract:
The Upper Triassic Yan-Chang Formation.in the region of Zichang,Ansai, and Wuqi counties, the south of Shan-Gan-Ning Basin is a set of deltaic clastic sediments of interior fresh-water lake basin with a thickness of 1, 000-1,500m.The oil-rich Yan-Chang Fm. is one of major source reservoir beds in the southern Basin?although its intensive diageneses, extremely low porosity and permeability have led to its poor production. In recent exploring in Ansai area, the production of several wells has risen to 5-47Ton./day,and the porosties and permeabilities of productive strata Yan-Chang Fm.C6 sandstone, are relatively high. In the present paper author concentrates the attention to sedimentary facies and diageneses of Ce sandstone and considers that in the study region C6 reservoirs formed under diageneses are diagenetic trapping reservoirs, The secondary porosity growth due to dissolution of laumontite cements in sandstone heightened the porosity and permeability of Ce sandstone. The chief conclusions followed have been obtained. 1. The diagenetic processes and porosity evolution of C6 sandtone, demonstrates that,on the base of deposition, the diageneses are the principal geological agent that resulted in the regional low permeability of C6 sandstone; the creating and dissolving of laumontite cements during diageneses brought, in turn, on the occurring of C6 laumontite secondary porosity sand bodies and diagenetic tight zones, The formation of the Ce diagenetic trapping, laumontite secondary porosity sandstone reservoirs discovered in this region underwent a complex diagenetic process as mentioned above. The significance of the conclusive point is that there is some promise of success on searching for relatively high permeable trapped reservoirs in a low permeability reservoir beds region with lacking of structural trap. 2. The formation and distribution of laumontite sand bodies secondary porosity sandbodies,and diagenetic tight zones in Yan-Chang Fm.were mainly cont-trolled by source and facies of sediments associating with an available regular-ty. pressure solution-secondary enlargement type of diagenetjc tight zone occur-ed along the transitional belt between delta front and delta plain distributary Channel; Laumontite-cementing type of diagenetic tight zone appeared common-nly along theside edge zone of delta front sand bodies; and secondary porosity snnd bodies derived from dissolving of laumontite cements grew in the core part of sand bodies. Based on the studing of sand bodies diageneses, combining with analysis of source and facies of sediments, author has made a prediction on distribution of permeable sand body araes which have been conformed by the recent explorings and drillings. 3. The reaction of pore water on abundant plagioclase in C6 sand bodies compounded laumontite cements during a period of temperature lower than 80C.The vjew that laumontite occurs under a condition of high tempperature (190°C-230°C) and the appaerance of laumontite suggests a low metamorphic environment and a deadline for lrquid hydrocarbon existence has prevailed for a long time throu ghout the geological field, but it is an one-sided view. On the contrary, the creation and dissolution of laumontite jn Yan-Chang Fm.of the study region had played an extreme important role in formation of reservoirs. Moreover, a consider able amount of reserve and production have been acquired from this kind of reservoirs.
The Upper Triassic Yan-Chang Formation.in the region of Zichang,Ansai, and Wuqi counties, the south of Shan-Gan-Ning Basin is a set of deltaic clastic sediments of interior fresh-water lake basin with a thickness of 1, 000-1,500m.The oil-rich Yan-Chang Fm. is one of major source reservoir beds in the southern Basin?although its intensive diageneses, extremely low porosity and permeability have led to its poor production. In recent exploring in Ansai area, the production of several wells has risen to 5-47Ton./day,and the porosties and permeabilities of productive strata Yan-Chang Fm.C6 sandstone, are relatively high. In the present paper author concentrates the attention to sedimentary facies and diageneses of Ce sandstone and considers that in the study region C6 reservoirs formed under diageneses are diagenetic trapping reservoirs, The secondary porosity growth due to dissolution of laumontite cements in sandstone heightened the porosity and permeability of Ce sandstone. The chief conclusions followed have been obtained. 1. The diagenetic processes and porosity evolution of C6 sandtone, demonstrates that,on the base of deposition, the diageneses are the principal geological agent that resulted in the regional low permeability of C6 sandstone; the creating and dissolving of laumontite cements during diageneses brought, in turn, on the occurring of C6 laumontite secondary porosity sand bodies and diagenetic tight zones, The formation of the Ce diagenetic trapping, laumontite secondary porosity sandstone reservoirs discovered in this region underwent a complex diagenetic process as mentioned above. The significance of the conclusive point is that there is some promise of success on searching for relatively high permeable trapped reservoirs in a low permeability reservoir beds region with lacking of structural trap. 2. The formation and distribution of laumontite sand bodies secondary porosity sandbodies,and diagenetic tight zones in Yan-Chang Fm.were mainly cont-trolled by source and facies of sediments associating with an available regular-ty. pressure solution-secondary enlargement type of diagenetjc tight zone occur-ed along the transitional belt between delta front and delta plain distributary Channel; Laumontite-cementing type of diagenetic tight zone appeared common-nly along theside edge zone of delta front sand bodies; and secondary porosity snnd bodies derived from dissolving of laumontite cements grew in the core part of sand bodies. Based on the studing of sand bodies diageneses, combining with analysis of source and facies of sediments, author has made a prediction on distribution of permeable sand body araes which have been conformed by the recent explorings and drillings. 3. The reaction of pore water on abundant plagioclase in C6 sand bodies compounded laumontite cements during a period of temperature lower than 80C.The vjew that laumontite occurs under a condition of high tempperature (190°C-230°C) and the appaerance of laumontite suggests a low metamorphic environment and a deadline for lrquid hydrocarbon existence has prevailed for a long time throu ghout the geological field, but it is an one-sided view. On the contrary, the creation and dissolution of laumontite jn Yan-Chang Fm.of the study region had played an extreme important role in formation of reservoirs. Moreover, a consider able amount of reserve and production have been acquired from this kind of reservoirs.
1988, 6(4): 22-32.
Abstract:
Mammiform structure ( MS ) is a newly-discovered sedimentary structure in chert, stratiform barite and carbonate manganese ores in China. The most typical example is found in Mugui area in the 250m thick Upper Devonian cherts with intercalations of basic to acid subvolcanic rocks and red and green jasper and manganese ores.MS can be seen in the thin laminated chert layer near the bottom of the acid subvolcanic rocks.The relationship between chert stratification and the morphology of MS indicates a meta-synsedimentary origin before the chert was consolidated. Most MS looks like a upside-down mamma with a diameter of several centimeters and a hight to width ratio of 1-2. It has a convex rounded top surface which intercepts with the bottom at an angle of about 60° -90°. A little hole about several millimeters in diameter can be seen near the bottom. Different zones can be recognized in the cross section from its rim inwards: 1 ) The external zone ( e-zone) consists of mudquartz which is partially recry-stallied and replaced by micro-quartz Unchangen chert is common. In some cass-es residual stratification can be noticed in chert. 2 ) The internal zone ( f-zone ) is composed nearly completely of recrystal-lized chert with remarkable spherulits of fibrous quartz. 3 ) The core zone (g-zone) is characterized by crystallization and filling. It consists of micrograined quartzs and spherulite quartzs which are connected in the form of triple comjunction ( 120° ). Both the internal zone and the core zone are wider at the top and narrow down towards the bottom, matching the configuration of MS. Its apex points directly to the little hole at the bottom of MS. The mineral composition of MS and its country rock have been determined by X-ray diffraction. Quartz is found predominant with small amounts of illite,albite and gypsum. From the country rock to. the core of MS, quartz increases slightly while illite decreases. It is considered that MS has been originated from unconsolidated chert through alteration, filling and recrysiallization in response to a SiO2-rich hydrothermal solution. With decreasing hydrothermal activity, SiO2 will precipitate in the order of quartz vein→silicified rock→silica MS→jasper→stratiform chert. MS is a special type of siliceous sinter formed at pelagic or sub pelagic basin. In addition, MS has also been reported from barite, manganese ores as well as chert elsewhere. Therefore, in addition to siliceous MS there can also be barite MS. manganese MS and probably sulfide MS. In terms of morphology, MS is similar to some other sedimentary structures, such as pit and mound, spring pits, gas pits and mud pool. But no compositional variation has been obserbedin these structures. MS can be readily distinguished from the above structures in terms of its compssition, structure; texture and occurrence. MS may provide a structural criterion for hydrothermal sedimentation geological history. The morphology and internal structure of MS can be used to determinestratigraphic sequence on the outcrop. The commonly observed sphe rulites of hydrothermal sedimentation may be confused with radiolarian siliceous rocks in shape. Particular care should be taken to avoid mistakes. The existance of MS may help to shed light on the origin of chert, barite and some manganese ores.
Mammiform structure ( MS ) is a newly-discovered sedimentary structure in chert, stratiform barite and carbonate manganese ores in China. The most typical example is found in Mugui area in the 250m thick Upper Devonian cherts with intercalations of basic to acid subvolcanic rocks and red and green jasper and manganese ores.MS can be seen in the thin laminated chert layer near the bottom of the acid subvolcanic rocks.The relationship between chert stratification and the morphology of MS indicates a meta-synsedimentary origin before the chert was consolidated. Most MS looks like a upside-down mamma with a diameter of several centimeters and a hight to width ratio of 1-2. It has a convex rounded top surface which intercepts with the bottom at an angle of about 60° -90°. A little hole about several millimeters in diameter can be seen near the bottom. Different zones can be recognized in the cross section from its rim inwards: 1 ) The external zone ( e-zone) consists of mudquartz which is partially recry-stallied and replaced by micro-quartz Unchangen chert is common. In some cass-es residual stratification can be noticed in chert. 2 ) The internal zone ( f-zone ) is composed nearly completely of recrystal-lized chert with remarkable spherulits of fibrous quartz. 3 ) The core zone (g-zone) is characterized by crystallization and filling. It consists of micrograined quartzs and spherulite quartzs which are connected in the form of triple comjunction ( 120° ). Both the internal zone and the core zone are wider at the top and narrow down towards the bottom, matching the configuration of MS. Its apex points directly to the little hole at the bottom of MS. The mineral composition of MS and its country rock have been determined by X-ray diffraction. Quartz is found predominant with small amounts of illite,albite and gypsum. From the country rock to. the core of MS, quartz increases slightly while illite decreases. It is considered that MS has been originated from unconsolidated chert through alteration, filling and recrysiallization in response to a SiO2-rich hydrothermal solution. With decreasing hydrothermal activity, SiO2 will precipitate in the order of quartz vein→silicified rock→silica MS→jasper→stratiform chert. MS is a special type of siliceous sinter formed at pelagic or sub pelagic basin. In addition, MS has also been reported from barite, manganese ores as well as chert elsewhere. Therefore, in addition to siliceous MS there can also be barite MS. manganese MS and probably sulfide MS. In terms of morphology, MS is similar to some other sedimentary structures, such as pit and mound, spring pits, gas pits and mud pool. But no compositional variation has been obserbedin these structures. MS can be readily distinguished from the above structures in terms of its compssition, structure; texture and occurrence. MS may provide a structural criterion for hydrothermal sedimentation geological history. The morphology and internal structure of MS can be used to determinestratigraphic sequence on the outcrop. The commonly observed sphe rulites of hydrothermal sedimentation may be confused with radiolarian siliceous rocks in shape. Particular care should be taken to avoid mistakes. The existance of MS may help to shed light on the origin of chert, barite and some manganese ores.
1988, 6(4): 44-51.
Abstract:
The Upper Ordovician flysch deposits with 1200m in thickness occurs in Western Zhejiang Province. The formation was first described by Guan Yinwen etc. in 1959, and it was considered to be shallow marine deposits. Later some reserchers regarded it as a turbidite of deep sea. The authors suggest that this formation is not a turbidite formed in deep sea but a flysch deposited in the area extending from shallow sea to tidal flat. The following characters may be listed; 1.Graded bedding shows diverse types, i.e. graded sand (Aa),graded silt(Ab),and reversal graded silt(Ac). Aa, Ab, and Ac can occur within one of the flysch rhyt-thmic beds. Ab and Ac may be combined to a bidirectional graded bedding Ab-Ac or Ac-Ab. 2.There are a large number of ripple marks, such as current ripple marks,sym-trical and asymmetrical wave built ripple marks and interference ripple marks. The asymmetrical ripple marks and foreset laminations are of bidirectional proprety. 3.There are also sandstones with wave bedding and lenticular bedding. 4.The main direction of sole marks is parallel to the shore line, and there are also bidirectional. 5.Mudstones of the uppermost part of a rhythmic bed contain pelitic or silt gravels,and they often show foreset and lenticular laminations. 6.There are three different grades of rhythmic bed, i.e. gross-rhythmic, fine-rhythmic and micro-rhythmic bedsOne gross-rhythmic bed may contain several fine rhythmic beds,and one fine-rhythmic bed may contain several micro-rhythmic beds which can only be observed by means of microscope. Graded textures, foreset laminations, lenticular beddings, flaser beddings, scour marks, and bioturbations can be found in the micro-rhythmic beds. he facts mentioned above show that the flysch rhythmic beds in the area do ot result from a single kind of process ( such as turbidity currents) in deep sea but from the combination of several processes, such as sea waves, bottom currents, tidal flows, storm surge currents and climatic effects, etc. The most favorable environment in which such diverse kinds of hydrodynamic factors take effect is the area extending from shallow sea to tidal flat. Of course, the sequences of the flysch rhythmic beds, to some extent, are similar to Bouma's Sequence-a sedimentary model about turbidites. It is not very diffic-ult to find out the intervals like A,B,C,D,and E of Bouma's Sequence in the flysch rhythmic beds. According to these characters some reserchers treated the flysch as a deep sea turbidite. It must be pointed out that there are a lot of significant phenomena being ignored by the above-mentioned reserchers. So, we must take a careful and analytic approach in the applications of Bouma's Sequence,and we may not consider the Bouma's Sequence as a conventional and universal model.
The Upper Ordovician flysch deposits with 1200m in thickness occurs in Western Zhejiang Province. The formation was first described by Guan Yinwen etc. in 1959, and it was considered to be shallow marine deposits. Later some reserchers regarded it as a turbidite of deep sea. The authors suggest that this formation is not a turbidite formed in deep sea but a flysch deposited in the area extending from shallow sea to tidal flat. The following characters may be listed; 1.Graded bedding shows diverse types, i.e. graded sand (Aa),graded silt(Ab),and reversal graded silt(Ac). Aa, Ab, and Ac can occur within one of the flysch rhyt-thmic beds. Ab and Ac may be combined to a bidirectional graded bedding Ab-Ac or Ac-Ab. 2.There are a large number of ripple marks, such as current ripple marks,sym-trical and asymmetrical wave built ripple marks and interference ripple marks. The asymmetrical ripple marks and foreset laminations are of bidirectional proprety. 3.There are also sandstones with wave bedding and lenticular bedding. 4.The main direction of sole marks is parallel to the shore line, and there are also bidirectional. 5.Mudstones of the uppermost part of a rhythmic bed contain pelitic or silt gravels,and they often show foreset and lenticular laminations. 6.There are three different grades of rhythmic bed, i.e. gross-rhythmic, fine-rhythmic and micro-rhythmic bedsOne gross-rhythmic bed may contain several fine rhythmic beds,and one fine-rhythmic bed may contain several micro-rhythmic beds which can only be observed by means of microscope. Graded textures, foreset laminations, lenticular beddings, flaser beddings, scour marks, and bioturbations can be found in the micro-rhythmic beds. he facts mentioned above show that the flysch rhythmic beds in the area do ot result from a single kind of process ( such as turbidity currents) in deep sea but from the combination of several processes, such as sea waves, bottom currents, tidal flows, storm surge currents and climatic effects, etc. The most favorable environment in which such diverse kinds of hydrodynamic factors take effect is the area extending from shallow sea to tidal flat. Of course, the sequences of the flysch rhythmic beds, to some extent, are similar to Bouma's Sequence-a sedimentary model about turbidites. It is not very diffic-ult to find out the intervals like A,B,C,D,and E of Bouma's Sequence in the flysch rhythmic beds. According to these characters some reserchers treated the flysch as a deep sea turbidite. It must be pointed out that there are a lot of significant phenomena being ignored by the above-mentioned reserchers. So, we must take a careful and analytic approach in the applications of Bouma's Sequence,and we may not consider the Bouma's Sequence as a conventional and universal model.
1988, 6(4): 72-80.
Abstract:
Huoxi coal basin is one of the six large coal basins in Province Shanxi. The study on sedimentary environments was carried out by complex methods including 55 isopach maps of main coal seams and sand bodies, a lot of trace elements analysis, X-ray diffraction analysis and DTA of clay minerals, rock identification under microscope, etc. The composition of coal-bearing sequencse, rock structur e probability cumulative curves of sandstone grain-size, electric log, analysis data of trace elements and the shape of coal seams and sand bodies are illustrated in detail. On basis of all these environmental criteria the coal-bearing formation was devided into six cycles and each environment was analysed. The middle Carboniferous Benxi Group is mainly lagoon-tidal flat deposits. The Upper Carboniferous Taiyuan Group is mainly lower delta-plain deposits. The lower Permian Shanxi Group is mainly upper delta-plain deposits. The thickness and distribution of coal seams are appe-arently controled by depositional environments. In this area,besides the good coal forming condition in environments of transition zone, as revealed by J.C. Home et al (1978), good coal forming condition exist in the environments of upper delta-plain and lago-ontidal flat too. There are two kinds of space relationship between the thicker belts of coal seam and the underlying sand body. First kind is superimposed position. Second kind is staggered position. First kind includes two varieties. One is coal seam formed on basis of tidal beach-barrier, the other is coal seam formed in environments of distributary mouth bar and distributary channel on lower parts of lower deltaplain. Second kind is coal seam formed in environments of distributary channel in transition zone and upper deltaplain. The thicker belts of coal seam and underlying sand body are in staggered position. The space relation-ship of thicker belts of coal seam and underlying sand body not only can play positive rolefor coal searching and exploration, and slso can serve as a new useful criterion for environmental analysis.
Huoxi coal basin is one of the six large coal basins in Province Shanxi. The study on sedimentary environments was carried out by complex methods including 55 isopach maps of main coal seams and sand bodies, a lot of trace elements analysis, X-ray diffraction analysis and DTA of clay minerals, rock identification under microscope, etc. The composition of coal-bearing sequencse, rock structur e probability cumulative curves of sandstone grain-size, electric log, analysis data of trace elements and the shape of coal seams and sand bodies are illustrated in detail. On basis of all these environmental criteria the coal-bearing formation was devided into six cycles and each environment was analysed. The middle Carboniferous Benxi Group is mainly lagoon-tidal flat deposits. The Upper Carboniferous Taiyuan Group is mainly lower delta-plain deposits. The lower Permian Shanxi Group is mainly upper delta-plain deposits. The thickness and distribution of coal seams are appe-arently controled by depositional environments. In this area,besides the good coal forming condition in environments of transition zone, as revealed by J.C. Home et al (1978), good coal forming condition exist in the environments of upper delta-plain and lago-ontidal flat too. There are two kinds of space relationship between the thicker belts of coal seam and the underlying sand body. First kind is superimposed position. Second kind is staggered position. First kind includes two varieties. One is coal seam formed on basis of tidal beach-barrier, the other is coal seam formed in environments of distributary mouth bar and distributary channel on lower parts of lower deltaplain. Second kind is coal seam formed in environments of distributary channel in transition zone and upper deltaplain. The thicker belts of coal seam and underlying sand body are in staggered position. The space relation-ship of thicker belts of coal seam and underlying sand body not only can play positive rolefor coal searching and exploration, and slso can serve as a new useful criterion for environmental analysis.
1988, 6(4): 93-99.
Abstract:
Based on modern organic metamorphism theories, maturity of organic matter (often expressed as vitrinite reflectance Ro ) can be modelled as a function of geologic time and paleogeotemperatures ( i.e., the thermal history): M=F(t, T). ( 1 ) When the paleogeothermal gradient is estimated, the thermal history varies with the erroded thickness X: T = f (X, t) ( 2 ) Thus the model predicted maturity M is 8 function of the eroded thickness.If a series of vitrinhte reflectance data below the unconformity are available in a well eg. (Roi, i = 1, 2,……, m ), an object function can be setablished as: I=Σ[Rc(Mi)-Roi]2( 3 ) where Rc(Mi ) is the calculated vitrinite reflectance from predicted, maturity corresponding to each measured ROi.Therefore I is obciously a function of the eroded thickness.The computer program is deaigned to search for an optimal X which gives the smallest value of I, ie.. the best fit of the calculated maturity to the measured. Application of the method in two actuat wells is given to show the validity of the method.
Based on modern organic metamorphism theories, maturity of organic matter (often expressed as vitrinite reflectance Ro ) can be modelled as a function of geologic time and paleogeotemperatures ( i.e., the thermal history): M=F(t, T). ( 1 ) When the paleogeothermal gradient is estimated, the thermal history varies with the erroded thickness X: T = f (X, t) ( 2 ) Thus the model predicted maturity M is 8 function of the eroded thickness.If a series of vitrinhte reflectance data below the unconformity are available in a well eg. (Roi, i = 1, 2,……, m ), an object function can be setablished as: I=Σ[Rc(Mi)-Roi]2( 3 ) where Rc(Mi ) is the calculated vitrinite reflectance from predicted, maturity corresponding to each measured ROi.Therefore I is obciously a function of the eroded thickness.The computer program is deaigned to search for an optimal X which gives the smallest value of I, ie.. the best fit of the calculated maturity to the measured. Application of the method in two actuat wells is given to show the validity of the method.
1988, 6(4): 108-119.
Abstract:
In this paper, not only the already well known molecular fossil indicators have been summarized, but also some new ones are proposed for analysis of pale-oenvironments of a sedimentary basin, and the adaptability of them for this is verified and reviewed. Molecular fossils are biogenic molecules, coming from the remains of organism in sediments and being of a certain implication in sedimentology or/and paleontology. Although experienced changes in diagenesis, yet they keep the carbon skeleton inherited from their biological precursors. Only n-alkanes, isoprenoid hydrocarbons, steranes and terpanes are detailed in this paper. l.Up to now, n-alkanes have been effective indicators of the sourceof organic matter in sedimentary rocks and crude oils. Generally, if the organic matter is made up mainly of the" terrigenous"type, it reflects a sedimentary environment of fluvial, or deltaic, or marginal facies in a basin. On the contrary, if the organic matter is made up mainly of the " autochonous in basin" type, it reflects an environment of central basin facies or lacking terrigenous substances. 2.A preference of even over odd carbon number n-alkanes ( i.e.OEP or CPI<1) is an indicator or reducing-even strong reduing environments. It is shown, by a systematic comparison of the contents of pyrite-Fe, a reductive authigeni c mineral indicator, in Fe-containing minerals with the CPI of the rocks from the Lower Tertiary in Dongpu Basin,that there is a quite good correlation between them (Fig.2,a). For the samples with CPI<1, their contents of pyrite-Fe in Fe-con taining minerals all are over 50%. As the CPI values are getting smaller, the contents of pyrite-Fe higher; furthermore the correlation between them is much better. It is indicated by the comparison that the OEP or CPI indicator to reduc-ti on,even strong reduction would be adaptible to paleoenvironmental analysis, least in our cas es. 3.A predominance of n-C22 in a-alkanes may be an indicator of hypersalino environments. There are the predominances of n-C22 in many rocks and crude oils formed in hypersaline environments from the lower Tertiary basins of Dongpu and Subei (Fig.3 ).However, the evaporites (Fig.3,No.84009, 84010 and 84016)and,in a series of the rocks in an order of increasing salinity formed in hypersaline environments(Fig.3, from No. 84052 to 84055), No. 84052 and 48053 have no such a predominance, which shows that the n-C22 predominancn in n-alkanes may be an indicator of hypersalinity only within a certain range. 4.Isoprenoid alkanes such as C20(phytane), C25,C30 and C40 are the indicators of archaeodacteria activity.In the basins of Dongpu and Subei, as well as some of other Cenozoic and Mesozoic basins of China, strong predominances of phytane have been found, the content of Ph is several to tens times that both of Pr and n-C18 in a rock. Such a strong predominance of phytane probably is a molecular indicator of extreme halophile archaeobacteria activitiy. The C16-C30, esp. the C25, C17 etc. regular isoprenoid alkane have been found in the basins mentioned above (Fig.4). They may be a molecular indicator of the activities of thermoacidophiles or extreme halophiles. 5.Pr/Ph is an oxidation-reduction indicator. It is found, by a systemtic comp-arision between the Pr/Ph and the contents of pyrite-Fe like section 2, that the Pr/Ph of the rocks from Dongpu Basin are18 and Ph》Pr). On the contrary, generally, there is no such a predominance in the rocks forned under relatively freshening conditions. 7.A relativaly high abundance of C25 regular
In this paper, not only the already well known molecular fossil indicators have been summarized, but also some new ones are proposed for analysis of pale-oenvironments of a sedimentary basin, and the adaptability of them for this is verified and reviewed. Molecular fossils are biogenic molecules, coming from the remains of organism in sediments and being of a certain implication in sedimentology or/and paleontology. Although experienced changes in diagenesis, yet they keep the carbon skeleton inherited from their biological precursors. Only n-alkanes, isoprenoid hydrocarbons, steranes and terpanes are detailed in this paper. l.Up to now, n-alkanes have been effective indicators of the sourceof organic matter in sedimentary rocks and crude oils. Generally, if the organic matter is made up mainly of the" terrigenous"type, it reflects a sedimentary environment of fluvial, or deltaic, or marginal facies in a basin. On the contrary, if the organic matter is made up mainly of the " autochonous in basin" type, it reflects an environment of central basin facies or lacking terrigenous substances. 2.A preference of even over odd carbon number n-alkanes ( i.e.OEP or CPI<1) is an indicator or reducing-even strong reduing environments. It is shown, by a systematic comparison of the contents of pyrite-Fe, a reductive authigeni c mineral indicator, in Fe-containing minerals with the CPI of the rocks from the Lower Tertiary in Dongpu Basin,that there is a quite good correlation between them (Fig.2,a). For the samples with CPI<1, their contents of pyrite-Fe in Fe-con taining minerals all are over 50%. As the CPI values are getting smaller, the contents of pyrite-Fe higher; furthermore the correlation between them is much better. It is indicated by the comparison that the OEP or CPI indicator to reduc-ti on,even strong reduction would be adaptible to paleoenvironmental analysis, least in our cas es. 3.A predominance of n-C22 in a-alkanes may be an indicator of hypersalino environments. There are the predominances of n-C22 in many rocks and crude oils formed in hypersaline environments from the lower Tertiary basins of Dongpu and Subei (Fig.3 ).However, the evaporites (Fig.3,No.84009, 84010 and 84016)and,in a series of the rocks in an order of increasing salinity formed in hypersaline environments(Fig.3, from No. 84052 to 84055), No. 84052 and 48053 have no such a predominance, which shows that the n-C22 predominancn in n-alkanes may be an indicator of hypersalinity only within a certain range. 4.Isoprenoid alkanes such as C20(phytane), C25,C30 and C40 are the indicators of archaeodacteria activity.In the basins of Dongpu and Subei, as well as some of other Cenozoic and Mesozoic basins of China, strong predominances of phytane have been found, the content of Ph is several to tens times that both of Pr and n-C18 in a rock. Such a strong predominance of phytane probably is a molecular indicator of extreme halophile archaeobacteria activitiy. The C16-C30, esp. the C25, C17 etc. regular isoprenoid alkane have been found in the basins mentioned above (Fig.4). They may be a molecular indicator of the activities of thermoacidophiles or extreme halophiles. 5.Pr/Ph is an oxidation-reduction indicator. It is found, by a systemtic comp-arision between the Pr/Ph and the contents of pyrite-Fe like section 2, that the Pr/Ph of the rocks from Dongpu Basin are18 and Ph》Pr). On the contrary, generally, there is no such a predominance in the rocks forned under relatively freshening conditions. 7.A relativaly high abundance of C25 regular
1988, 6(4): 12-21.
Abstract:
The Guanwushan Formation consists of three types of dolomite; medium crystal line dolomite which occurred in biostrome environment, micrite dolomite in lagoon and fine crystalline dolomite in tidal flat. The first type of dolomite, distributed in the lower part of Guanwushan Formation, is characterized as follow: 1 ) containing abundant reef-forming organisms and other fossils, 2 ) 100-500μm in size, euhedral rhombohedral crystal forms. 3 ) very good ordering degree and low CaCO3 mole content, 4 ) low δ18O values and 5 ) dull intensity of cathodoluminescence. Second type of dolomite, distributed in middle part of Guanwushan Formation, is characterized as follow: 1 ) containing few fossils but a lot of pyrite, 2 ) 5-60μm in size, dominantly xenomorphic granular crystal form, 3 ) poor ordering degree and high CaCO3mole content, 4 ) relatively high 618O values and 5 ) bright intensity of cathodoluminescence. Third type of dolomite distributed in the upper part of Guanwushan Formation, is characterized as follow: 1 ) containing some fossils, 2 ) 40-200μm in size, dominantly hypidiomorphic granular crystal form, 3 ) very good ordering degree and lower CaCO3 mole content, 4 ) relatively low δ18O values, low δ13Cvalues and 5 ) medium intensity of cathodoluminescence. The micrite dolomite in the lagoon resulted from the dolomitization by the solution having a high Mg2+/Ca2+ ratio during penecontemporaneous stage. The medium crystalline dolomite in biostrome and the fine crystalline dolomite in tidal flat resulted from the dolomitization by meteoric ground waters mixing with sea water during the early diagenetic stage.
The Guanwushan Formation consists of three types of dolomite; medium crystal line dolomite which occurred in biostrome environment, micrite dolomite in lagoon and fine crystalline dolomite in tidal flat. The first type of dolomite, distributed in the lower part of Guanwushan Formation, is characterized as follow: 1 ) containing abundant reef-forming organisms and other fossils, 2 ) 100-500μm in size, euhedral rhombohedral crystal forms. 3 ) very good ordering degree and low CaCO3 mole content, 4 ) low δ18O values and 5 ) dull intensity of cathodoluminescence. Second type of dolomite, distributed in middle part of Guanwushan Formation, is characterized as follow: 1 ) containing few fossils but a lot of pyrite, 2 ) 5-60μm in size, dominantly xenomorphic granular crystal form, 3 ) poor ordering degree and high CaCO3mole content, 4 ) relatively high 618O values and 5 ) bright intensity of cathodoluminescence. Third type of dolomite distributed in the upper part of Guanwushan Formation, is characterized as follow: 1 ) containing some fossils, 2 ) 40-200μm in size, dominantly hypidiomorphic granular crystal form, 3 ) very good ordering degree and lower CaCO3 mole content, 4 ) relatively low δ18O values, low δ13Cvalues and 5 ) medium intensity of cathodoluminescence. The micrite dolomite in the lagoon resulted from the dolomitization by the solution having a high Mg2+/Ca2+ ratio during penecontemporaneous stage. The medium crystalline dolomite in biostrome and the fine crystalline dolomite in tidal flat resulted from the dolomitization by meteoric ground waters mixing with sea water during the early diagenetic stage.
1988, 6(4): 33-43.
Abstract:
Sedimentary Environments of the Toutunhe Formation in Southern Changji Prefecture,Xinjiang,have been systematically investigated by field observetion and using the techniques of thin-section examination,X-ray diffraction,scanning electronic-microscopy,cathodoluminescone micros-copy,stable isotope analysis,grain-size analysis,methematical statistics, etc.From southern to northern part of the studied area,Toutunhe Formation is represented by a succession of fluvial,deltaic and lacustrine deposits.At the Sulphur Valley section,the fluvial facies-association comprises four cycles each of which consists of a lower coarse member and an upper fine member. 11 lithofacies havebeen distinguished from these cyclic sediments: (1) Massive conglomerate facies (Gm),for which thicker beds situating at lower part of the cycle and streching laterally in a distance more than 10m are referred to lag deposits and thinner conglomerates laying in the scour hole on top of large-sea le tabular cross-bed sandstones are assumed to be chute fill.(2) Tabular cross-bed conglomerate (Gp) is produced by lateral migration of point-bar. (3) Large-scale cross-bed sandstone facies (St)- those with multiple cetts might be produced by the migration of sinuous-ridge dunes at the upper part of point bar and those with solitary set by filling-up of scour hole. (4) Large-scale tabular cross-bed sandstone facies (Sp) are produced by sand bar or scrollbar. (5) -cross-bedding sandstone facies (ε) with four-grade boundaries,It is evidence of lateral accretion of point bar. (6) Smallscalc cross-bed fine-sandstone facies (S1). (7) Ripple-bedded siltstonc facies (Sr) occur at the top of point-bar,on natural lavee and in oxbow lakes. (8) C-hannel plug silty mudstone facies (Cp). (9) Chute plug facies (Ccp) and (11) Pa-leosol facies (Psc) of mottled mudstone is intercalated with low-quality coal seams.The vertical facies-relationship and facies-model have been worked out by us-eing Selley's (1970) technique of transform matrix.The model is similar to that of the Old Red Sands-tone (Allen,1963) but even more complex.Inside the sand-bodies of Toutunhe Formation no simple upwards-fining sequence is found, instead, up- wards-coarsening often occurring on the basal scour surface of the conglomerate lenses. The presence of tabular cross bedds at upper part of the coarse m-embers and the occurrence of e-cross bedds suggest typical meandering river depo-its. Besides, the rapid facies-change, frequent scour structures and abundant conglomerate and mudstone lenses might suggest that the corresponing rivers were characterized by shallow water, high flow-velocity, unstable currents and ample detritus supplies. The Paleocurrent directions from measurements of cross-bedds, oblate gravels and loggs show a preferred azimuth between 260° and 61° which coincides well with the regional transport-direction North to Tien- Shan Mountain. Parameters of channelgeomorphology and hydraulics for cycle 1-3 have been worked out by employing the equations of Schumm (1960, 1963, 1968), Cotter (197 1), Eicher (1969) and Hack (1957). They suggest that during the period of cycle 1 to that of cycle 3, the corresponding rivers were getting deeper and broader and their channel sinuosity, length and curvature radius getting greater, but the channel slope getting smaller. These implicate a tendancy of increasing river scale, channel stability, annual mean discharge and suapended-load and decreasing flow velocity and bed-load. It is obvious that the rivers of cycle 3 were approching more to the lower reach than that of cycle 1 and 2, owing to the influence of climates and tectonic movements. But the innercycle-3 rivers evoluted in an opposite way, i.e., from former to later stage, the rivers were decreased in scale sinnosity and suspended-load but increased in slope and bed-load, which might be explained by an uplifting source area and a drier climate. It is presumed that the ancient Tou-tunhe river is similar to the modern Dane River in Great Britain. Both are of m-ixed-load channel types.
Sedimentary Environments of the Toutunhe Formation in Southern Changji Prefecture,Xinjiang,have been systematically investigated by field observetion and using the techniques of thin-section examination,X-ray diffraction,scanning electronic-microscopy,cathodoluminescone micros-copy,stable isotope analysis,grain-size analysis,methematical statistics, etc.From southern to northern part of the studied area,Toutunhe Formation is represented by a succession of fluvial,deltaic and lacustrine deposits.At the Sulphur Valley section,the fluvial facies-association comprises four cycles each of which consists of a lower coarse member and an upper fine member. 11 lithofacies havebeen distinguished from these cyclic sediments: (1) Massive conglomerate facies (Gm),for which thicker beds situating at lower part of the cycle and streching laterally in a distance more than 10m are referred to lag deposits and thinner conglomerates laying in the scour hole on top of large-sea le tabular cross-bed sandstones are assumed to be chute fill.(2) Tabular cross-bed conglomerate (Gp) is produced by lateral migration of point-bar. (3) Large-scale cross-bed sandstone facies (St)- those with multiple cetts might be produced by the migration of sinuous-ridge dunes at the upper part of point bar and those with solitary set by filling-up of scour hole. (4) Large-scale tabular cross-bed sandstone facies (Sp) are produced by sand bar or scrollbar. (5) -cross-bedding sandstone facies (ε) with four-grade boundaries,It is evidence of lateral accretion of point bar. (6) Smallscalc cross-bed fine-sandstone facies (S1). (7) Ripple-bedded siltstonc facies (Sr) occur at the top of point-bar,on natural lavee and in oxbow lakes. (8) C-hannel plug silty mudstone facies (Cp). (9) Chute plug facies (Ccp) and (11) Pa-leosol facies (Psc) of mottled mudstone is intercalated with low-quality coal seams.The vertical facies-relationship and facies-model have been worked out by us-eing Selley's (1970) technique of transform matrix.The model is similar to that of the Old Red Sands-tone (Allen,1963) but even more complex.Inside the sand-bodies of Toutunhe Formation no simple upwards-fining sequence is found, instead, up- wards-coarsening often occurring on the basal scour surface of the conglomerate lenses. The presence of tabular cross bedds at upper part of the coarse m-embers and the occurrence of e-cross bedds suggest typical meandering river depo-its. Besides, the rapid facies-change, frequent scour structures and abundant conglomerate and mudstone lenses might suggest that the corresponing rivers were characterized by shallow water, high flow-velocity, unstable currents and ample detritus supplies. The Paleocurrent directions from measurements of cross-bedds, oblate gravels and loggs show a preferred azimuth between 260° and 61° which coincides well with the regional transport-direction North to Tien- Shan Mountain. Parameters of channelgeomorphology and hydraulics for cycle 1-3 have been worked out by employing the equations of Schumm (1960, 1963, 1968), Cotter (197 1), Eicher (1969) and Hack (1957). They suggest that during the period of cycle 1 to that of cycle 3, the corresponding rivers were getting deeper and broader and their channel sinuosity, length and curvature radius getting greater, but the channel slope getting smaller. These implicate a tendancy of increasing river scale, channel stability, annual mean discharge and suapended-load and decreasing flow velocity and bed-load. It is obvious that the rivers of cycle 3 were approching more to the lower reach than that of cycle 1 and 2, owing to the influence of climates and tectonic movements. But the innercycle-3 rivers evoluted in an opposite way, i.e., from former to later stage, the rivers were decreased in scale sinnosity and suspended-load but increased in slope and bed-load, which might be explained by an uplifting source area and a drier climate. It is presumed that the ancient Tou-tunhe river is similar to the modern Dane River in Great Britain. Both are of m-ixed-load channel types.
1988, 6(4): 62-71.
Abstract:
The studied area is situated in Tianba mining area ( Yangchang Syncline in Eastern Yunnan) and Tuchen mining area (Panxian Syncline in Western Guiz- ou ). The Late Permian coal measures, which is divided into three members ( tipper, middle and lower), is a shallow water delta complex in this area. The upper member of the coal measures, which is 80-120 metre thick, and compares to the Changxingian, is the main coal-bearing section representing the deposits of destructive period of the delta complex. A great quantities of facies analysis data shows that the sedimentary environments of this area belongs to a shallow water delta of invasion type behind a barried bar. Tianba area is covered by river sediments, in which the sand bodies are banded in shape along N-S or S-E directions. In Tuchen area, sedimentation is characterized by both river and tidal actions under the influence of alongshore current. The wave action is very weak. Sand bodies are lobe, bird's feet and mat in shapes mostly along S-E direction. The river inflows into the studied area from northwest and bifuractessin Tianba mining area, where the environment begins to change into upper delta plain from alluvial plain. There are always 1-2 distributary channels flowing by the Tianba Coal Mine, and after entering the Tuchen mining area, the environments begin to change into the upper-lower delta transitional zone till the lagoon-ba trier system. There are 4 rather stably developed distributary channels passing by each area ( Datianba, Tuchen Coal Mine, Songhe and Xiasuzuo ). These flu-viation-dominated sand bodies and the barrier bod ies constitute the sedimentary rramework of Changxingian in studied area. According to the vertical sequences of the facies and their spacial dispositions fhe studied area can be divided into three major facies belts: 1. Upper delta plain facies belt: It is located in the western mining area (Tianba) and dominated by distributary channel facies, flood plain facies and lake facies. Lake-delta deposits can be seen in the roof of coal seams K2+1, K0 No animal fossils are found, but plant fossils and siderite nodules are common, also there are some erect tree stem and plenty worm boring in this area. 2. Upper-lower delta transitional zone facies belt: its location is from Tuchen mine field 1-2 to Datianba. Predelta consists of the lagoon ( freshed lagoon ) facies, Delta-front consists of the mouth bar facies and distributary-tidal channel facies. Delta plain consists of the distributary channel, flood plain and ind tcrdistributary bay deposits. The prodelta is small in thickness, and intercalated with 3-5 marine-brackish water animal fossils layers in this belt. 3,Lower delta plain facies belt:It is located from the Songhe mine field to the east Datianba. Delta complex is similar to the upper-lower delta transitional zone belt in structure, but the prodelta deposits is relatively thick and intercalated with 5-10 marine-brackish water animal remains layers. On the outside of the delta system, marine animal remains are common and lagoon facies, tidal flat facies and barrier facies are developed. They belong to a barier-lagoon system deposits which are distributed from Hetaozhai to the east of the studied area, as well as the upper strata of lower delta plain facies belt Coal-bearing characters have a close relationship with palcogeographic environments in this area.In the upper delta plain facies belt, coal seams are mainly formed in the flood plain. Because of the plenty supplement of terigenous elastics,the depositional area under the state of depositional over-compensation and as well as the frequent crevassing and changing the way of rivers, coal seams are often scoured, so most coal seams vary largely in thickness and bifurcate, pinch-out frequently with high ash and low s ;lphur. During the coal-forming period of coal seams K2+1, K6-K7 and K9, crustal subsidence is relatively large so that relatively long stable environments are kept, rather thick and stable coal seams are formed. In the upper-lower de
The studied area is situated in Tianba mining area ( Yangchang Syncline in Eastern Yunnan) and Tuchen mining area (Panxian Syncline in Western Guiz- ou ). The Late Permian coal measures, which is divided into three members ( tipper, middle and lower), is a shallow water delta complex in this area. The upper member of the coal measures, which is 80-120 metre thick, and compares to the Changxingian, is the main coal-bearing section representing the deposits of destructive period of the delta complex. A great quantities of facies analysis data shows that the sedimentary environments of this area belongs to a shallow water delta of invasion type behind a barried bar. Tianba area is covered by river sediments, in which the sand bodies are banded in shape along N-S or S-E directions. In Tuchen area, sedimentation is characterized by both river and tidal actions under the influence of alongshore current. The wave action is very weak. Sand bodies are lobe, bird's feet and mat in shapes mostly along S-E direction. The river inflows into the studied area from northwest and bifuractessin Tianba mining area, where the environment begins to change into upper delta plain from alluvial plain. There are always 1-2 distributary channels flowing by the Tianba Coal Mine, and after entering the Tuchen mining area, the environments begin to change into the upper-lower delta transitional zone till the lagoon-ba trier system. There are 4 rather stably developed distributary channels passing by each area ( Datianba, Tuchen Coal Mine, Songhe and Xiasuzuo ). These flu-viation-dominated sand bodies and the barrier bod ies constitute the sedimentary rramework of Changxingian in studied area. According to the vertical sequences of the facies and their spacial dispositions fhe studied area can be divided into three major facies belts: 1. Upper delta plain facies belt: It is located in the western mining area (Tianba) and dominated by distributary channel facies, flood plain facies and lake facies. Lake-delta deposits can be seen in the roof of coal seams K2+1, K0 No animal fossils are found, but plant fossils and siderite nodules are common, also there are some erect tree stem and plenty worm boring in this area. 2. Upper-lower delta transitional zone facies belt: its location is from Tuchen mine field 1-2 to Datianba. Predelta consists of the lagoon ( freshed lagoon ) facies, Delta-front consists of the mouth bar facies and distributary-tidal channel facies. Delta plain consists of the distributary channel, flood plain and ind tcrdistributary bay deposits. The prodelta is small in thickness, and intercalated with 3-5 marine-brackish water animal fossils layers in this belt. 3,Lower delta plain facies belt:It is located from the Songhe mine field to the east Datianba. Delta complex is similar to the upper-lower delta transitional zone belt in structure, but the prodelta deposits is relatively thick and intercalated with 5-10 marine-brackish water animal remains layers. On the outside of the delta system, marine animal remains are common and lagoon facies, tidal flat facies and barrier facies are developed. They belong to a barier-lagoon system deposits which are distributed from Hetaozhai to the east of the studied area, as well as the upper strata of lower delta plain facies belt Coal-bearing characters have a close relationship with palcogeographic environments in this area.In the upper delta plain facies belt, coal seams are mainly formed in the flood plain. Because of the plenty supplement of terigenous elastics,the depositional area under the state of depositional over-compensation and as well as the frequent crevassing and changing the way of rivers, coal seams are often scoured, so most coal seams vary largely in thickness and bifurcate, pinch-out frequently with high ash and low s ;lphur. During the coal-forming period of coal seams K2+1, K6-K7 and K9, crustal subsidence is relatively large so that relatively long stable environments are kept, rather thick and stable coal seams are formed. In the upper-lower de
1988, 6(4): 81-92.
Abstract:
This paper introduces a new method, the Most Predictable Surface, which is used for quantitative study on sedimentary enviromcnt. It is known that some g-geological parameters and the geographical parameters are closely related. For the purpose of quantitative study on sedimentary environment the following mathematical model is set up: Where Zi is a value of the ith geological parameter,And ai is a coefficient of the ith geological parmeter which depemnds on the geographical parameters and characterizes the relationship between two groups of parameters. So U means a value of quantification of sedim-ntary environment. The coefficients (ai) may be obtained by means of the mathematical processing. As soon as Z and a are determined, we can get U in each section.Many values of U can be linked and formed contour map of quantitative sedimentary environments. Same values of U show the same properties of lithological paragenetic association, that is the same sedimentary environments.The form of contours shows the outlines of the sedimentary environments.The density of distribution of the contours means the degree of variation of the sedimentary environments. The denser sontours in a region shows acute sedimentary environments changeing, on the other hand, the steader. The sedimentary environments are researched in this paper as an example of the Upper Sinian Epoch phosphate bearing sequence in the South of China. The sequence consists of the phosphate rocks, dolomite rocks, clay and silica rocks. Depending on the relation between lithologies and sedimentary environments, the following five lithological states, five geological parameters, are determined, i.e., coarse-grained intraclastic rock (A),medium or mediumfine grained intra-poclastic rock (B),micritic dolomite rock (c), clay rocfc ( D ), and silica rock (E).Therefore, the lithologies from ( A ) to ( E ) are the different products de-osited in the different sedimentary environments that the hydrodynamical conditions are changed from strong to weak. The mathematical model is set up depending on the five geological parameters determined and the geographic positions, geographic parameters, in each section.The maps of the quantitative sedimentary environments, the contour maps of U, are made for the five sedimentary cycles in all period respectively. Depending on these maps the sedimentary environments of each cyclic period and the changing of the environments are researched. The researches show that the regions with positive values of U indicate a carbonate platform under the water, but the regions with negative values of U show a shllow sea basin,and the regions with dense U contours show the regions where the environments chauge acntely.The regions with zero contour and its neiphou-ring regions show the regions where two environments mentioned above transfer each other. In the study area, from beginning deposite in the wide area to the end of tipper Sinian Epoch, the basic framework of sedimentary environments is steady. The zones, i.e., Southwest Guizhou -Northeast Guizhou-Northwest Hunan-middle Hubei, are the trasitional zones between the carbonate platform and the shallow-sea basin, and the carbonate platform distributes mainly in the region to the northwest of the zones,bnt the shallow-sea basin distributes mainly in the region to the eastsouth of the zones. In the transitional zone between two environments that is the favourable environment for P-deposits, because the environments change acutely in this zone, and the properties of the deposits and the hydro-dyn amical conditions change frequently with the change of environments.Specially, as there are closed or semi-closed basin or "gulf" under the water in the platform or in its borderland, it is more favourable environments where P-deposits are deposited. However,the size,thinkness and P-bearing grade of the P-deposits in the other environments can not be compared with those of P-deosits in the enviroments mentioned above. The results of this research have demonstrated that the Most Predictable Surface me
This paper introduces a new method, the Most Predictable Surface, which is used for quantitative study on sedimentary enviromcnt. It is known that some g-geological parameters and the geographical parameters are closely related. For the purpose of quantitative study on sedimentary environment the following mathematical model is set up: Where Zi is a value of the ith geological parameter,And ai is a coefficient of the ith geological parmeter which depemnds on the geographical parameters and characterizes the relationship between two groups of parameters. So U means a value of quantification of sedim-ntary environment. The coefficients (ai) may be obtained by means of the mathematical processing. As soon as Z and a are determined, we can get U in each section.Many values of U can be linked and formed contour map of quantitative sedimentary environments. Same values of U show the same properties of lithological paragenetic association, that is the same sedimentary environments.The form of contours shows the outlines of the sedimentary environments.The density of distribution of the contours means the degree of variation of the sedimentary environments. The denser sontours in a region shows acute sedimentary environments changeing, on the other hand, the steader. The sedimentary environments are researched in this paper as an example of the Upper Sinian Epoch phosphate bearing sequence in the South of China. The sequence consists of the phosphate rocks, dolomite rocks, clay and silica rocks. Depending on the relation between lithologies and sedimentary environments, the following five lithological states, five geological parameters, are determined, i.e., coarse-grained intraclastic rock (A),medium or mediumfine grained intra-poclastic rock (B),micritic dolomite rock (c), clay rocfc ( D ), and silica rock (E).Therefore, the lithologies from ( A ) to ( E ) are the different products de-osited in the different sedimentary environments that the hydrodynamical conditions are changed from strong to weak. The mathematical model is set up depending on the five geological parameters determined and the geographic positions, geographic parameters, in each section.The maps of the quantitative sedimentary environments, the contour maps of U, are made for the five sedimentary cycles in all period respectively. Depending on these maps the sedimentary environments of each cyclic period and the changing of the environments are researched. The researches show that the regions with positive values of U indicate a carbonate platform under the water, but the regions with negative values of U show a shllow sea basin,and the regions with dense U contours show the regions where the environments chauge acntely.The regions with zero contour and its neiphou-ring regions show the regions where two environments mentioned above transfer each other. In the study area, from beginning deposite in the wide area to the end of tipper Sinian Epoch, the basic framework of sedimentary environments is steady. The zones, i.e., Southwest Guizhou -Northeast Guizhou-Northwest Hunan-middle Hubei, are the trasitional zones between the carbonate platform and the shallow-sea basin, and the carbonate platform distributes mainly in the region to the northwest of the zones,bnt the shallow-sea basin distributes mainly in the region to the eastsouth of the zones. In the transitional zone between two environments that is the favourable environment for P-deposits, because the environments change acutely in this zone, and the properties of the deposits and the hydro-dyn amical conditions change frequently with the change of environments.Specially, as there are closed or semi-closed basin or "gulf" under the water in the platform or in its borderland, it is more favourable environments where P-deposits are deposited. However,the size,thinkness and P-bearing grade of the P-deposits in the other environments can not be compared with those of P-deosits in the enviroments mentioned above. The results of this research have demonstrated that the Most Predictable Surface me
1988, 6(4): 100-107.
Abstract:
In this paper,the authors measure the trace elements, such as B, Ga, Sr and Ba, from a total of 131 samples in 4 wells of Shahejie Formation of Lower Tertiary in the northern Dongying Basin with atomic absoption spectrophometer. Salinities of water as deposited in Shahejie Formation was specified qualitati-velybased on the content of boron with equivalent boron,the ratio of B/Ga as well as Sr/Ba.Paleosalinites have been calculated with the formulas Adans, T.D.and Walker,C.T. in accordance with the data of clay mineral analysis and the measure boron content.The results shows that salinity in some strata of the fourth member of Shahejie Formation in the northern Dongying Basin gets as high as 31‰, 24.3‰ in the lower part of the third member of Shahejie Formation, and 7‰ and 8.2‰ in the middle and npper part in the thirt member and in the second member respectively, whereas it run up to 15‰ in the first member, particularly in the lower part of the first member of Shahejie Formation.The study is of quite significance both to the determination of sedimentary enviroment and the evalu tion of the source rocks and reservoir in Lower Tertiary.
In this paper,the authors measure the trace elements, such as B, Ga, Sr and Ba, from a total of 131 samples in 4 wells of Shahejie Formation of Lower Tertiary in the northern Dongying Basin with atomic absoption spectrophometer. Salinities of water as deposited in Shahejie Formation was specified qualitati-velybased on the content of boron with equivalent boron,the ratio of B/Ga as well as Sr/Ba.Paleosalinites have been calculated with the formulas Adans, T.D.and Walker,C.T. in accordance with the data of clay mineral analysis and the measure boron content.The results shows that salinity in some strata of the fourth member of Shahejie Formation in the northern Dongying Basin gets as high as 31‰, 24.3‰ in the lower part of the third member of Shahejie Formation, and 7‰ and 8.2‰ in the middle and npper part in the thirt member and in the second member respectively, whereas it run up to 15‰ in the first member, particularly in the lower part of the first member of Shahejie Formation.The study is of quite significance both to the determination of sedimentary enviroment and the evalu tion of the source rocks and reservoir in Lower Tertiary.
1988, 6(4): 130-136.
Abstract:
A dickite with an elogated crystal habit in the direction of the a-axis occurs as pore fillings in coarse quartzite sandstone of Upper Permian Shiqian-feng Formation in Xuzhou coal basin,Jiangsu province.Scanning electron microscope micrographs of the dickite clearly show euhedral crystal outlines. The length of its plates is from 25 to 40μm and the width 4μm;The ratios of the length and width varies from 6:1to 10:1.Elogated pseudohexagonal flakes commonly stacked in book-like assemblages.Results of thin section observation, X-ray diffraction pathern,infrared spectrum and different thermal analysis confirm it as a dickite.It was precipitased from pore fluids after the overgrewths of quartz formed Log (Al ) -PH solubility diagram was constructed and indicated that the dickite was formed in acidic environment. The particular morphology with elogated crystal habit probably was caused by dilute porewater and slow crystalization.
A dickite with an elogated crystal habit in the direction of the a-axis occurs as pore fillings in coarse quartzite sandstone of Upper Permian Shiqian-feng Formation in Xuzhou coal basin,Jiangsu province.Scanning electron microscope micrographs of the dickite clearly show euhedral crystal outlines. The length of its plates is from 25 to 40μm and the width 4μm;The ratios of the length and width varies from 6:1to 10:1.Elogated pseudohexagonal flakes commonly stacked in book-like assemblages.Results of thin section observation, X-ray diffraction pathern,infrared spectrum and different thermal analysis confirm it as a dickite.It was precipitased from pore fluids after the overgrewths of quartz formed Log (Al ) -PH solubility diagram was constructed and indicated that the dickite was formed in acidic environment. The particular morphology with elogated crystal habit probably was caused by dilute porewater and slow crystalization.
