1996 Vol. 14, No. 1
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Display Method:
1996, 14(1): 1-11.
Abstract:
Shujiaba Formation in the northern belt of Qinling mountains belongs to the Middle-late Devonian epoch with a total thickness over 2000 m. With the exception of the upper carbonate rock section, the middle and lower part of the Formation are composed of extremely thick clastic depositional sequence, which is the host rock measure of minutely-disseminated gold ore deposits. The paper focuses on the study of depositional environment and factes characteristics of the elastic rock sequence.The sequence is lack of any indicators of shallow depositional environment,instead, some bethyal-abyssal factes are discovered, which are described as follows:1. The elastic sequence consists of proximal turbidite, thin-bedded turbidite and abyssal mudstone. And the latter two are well developed. No conglomerate, gravel grit and factes such as olistostrome etc. are found in the sequence.2. Contourite is frequently associated with the turbidite.3. On the surface of turbidite measure and abyssal mudstone, "Nereites",a trace-fossil facies relevant to abyssal turbidity, is found. The trace-fossil factes are composed of 41 ichnogenera,of which near 80% are the typical "deep water" ones,e. g.,Cosmorhaphe, Helicolithus,Helminthoida, Nereites, Palendictyon, Spirophycus, Taphrhelmiothoida,Taphrhelminthopsis. Subphylloch orda. and so on.Based on the above features, the authors believe that the Shujiaba Formation coas deposited in a bathyal-abyssal environment. Combining the distribution of water depth showed by the typical "deep water" ichnogenera,a maximum water depth of the sedimentation of the Formation is inferred to be 2000 m.In addition, on the basis of the analyses on the vertical sequence, lithofacies characteristics and paleocurrent data, we propose a non-sea-floor fan model for the Shu Jiaba Formation.
Shujiaba Formation in the northern belt of Qinling mountains belongs to the Middle-late Devonian epoch with a total thickness over 2000 m. With the exception of the upper carbonate rock section, the middle and lower part of the Formation are composed of extremely thick clastic depositional sequence, which is the host rock measure of minutely-disseminated gold ore deposits. The paper focuses on the study of depositional environment and factes characteristics of the elastic rock sequence.The sequence is lack of any indicators of shallow depositional environment,instead, some bethyal-abyssal factes are discovered, which are described as follows:1. The elastic sequence consists of proximal turbidite, thin-bedded turbidite and abyssal mudstone. And the latter two are well developed. No conglomerate, gravel grit and factes such as olistostrome etc. are found in the sequence.2. Contourite is frequently associated with the turbidite.3. On the surface of turbidite measure and abyssal mudstone, "Nereites",a trace-fossil facies relevant to abyssal turbidity, is found. The trace-fossil factes are composed of 41 ichnogenera,of which near 80% are the typical "deep water" ones,e. g.,Cosmorhaphe, Helicolithus,Helminthoida, Nereites, Palendictyon, Spirophycus, Taphrhelmiothoida,Taphrhelminthopsis. Subphylloch orda. and so on.Based on the above features, the authors believe that the Shujiaba Formation coas deposited in a bathyal-abyssal environment. Combining the distribution of water depth showed by the typical "deep water" ichnogenera,a maximum water depth of the sedimentation of the Formation is inferred to be 2000 m.In addition, on the basis of the analyses on the vertical sequence, lithofacies characteristics and paleocurrent data, we propose a non-sea-floor fan model for the Shu Jiaba Formation.
1996, 14(1): 22-32.
Abstract:
the Ordovician weathering crust (O1ma51－4)is a major gas-bearing stratum of the Zhongbu gasfield in central Ordos Basin. 24 types of microfacies with different and abundant pores have respectively been recognized according to their mineral,texture,structure, diagenesis, geochemistry and petrophysics features. They were genetically reorganized into 8 MF associations. The table (below) shows the main characters of the MF associations.The main factors which control the characteristics of the reservoir are distribution character of the sedimentary factes (belts) and their MF associations, diagenesis, succeeding tification and tectonic movement.Sedimentary factes and their MF associations are the basic controlling factors. They control the regional strike and general distribution of the reservoir. The MF associations are the material foundation of the succeeding processes, which have direct strategic significance in guiding the petroleum exploration. The microfacies study results indicate that, for one thing the difference between the MF associations leads to the reservoir heterogeneity and, for another,the favourable microfacies have a very high proportion vertically in every well district and good continuity laterally, esp. in each section of O1ma51,the porportion of the narrowly distributed unfavourable micro factes is very low. The succeeding processes(including diagenesis,karstification and tectonic movement) determine the specific distribution patterns of the effective pore space and fvourable reservoir bodies, which has the most actual significance in directing the development.
the Ordovician weathering crust (O1ma51－4)is a major gas-bearing stratum of the Zhongbu gasfield in central Ordos Basin. 24 types of microfacies with different and abundant pores have respectively been recognized according to their mineral,texture,structure, diagenesis, geochemistry and petrophysics features. They were genetically reorganized into 8 MF associations. The table (below) shows the main characters of the MF associations.The main factors which control the characteristics of the reservoir are distribution character of the sedimentary factes (belts) and their MF associations, diagenesis, succeeding tification and tectonic movement.Sedimentary factes and their MF associations are the basic controlling factors. They control the regional strike and general distribution of the reservoir. The MF associations are the material foundation of the succeeding processes, which have direct strategic significance in guiding the petroleum exploration. The microfacies study results indicate that, for one thing the difference between the MF associations leads to the reservoir heterogeneity and, for another,the favourable microfacies have a very high proportion vertically in every well district and good continuity laterally, esp. in each section of O1ma51,the porportion of the narrowly distributed unfavourable micro factes is very low. The succeeding processes(including diagenesis,karstification and tectonic movement) determine the specific distribution patterns of the effective pore space and fvourable reservoir bodies, which has the most actual significance in directing the development.
1996, 14(1): 40-46.
Abstract:
The characteristic parameters of sedimentary microfacies are extracted by using well logs and geological parameter curves.The digital well logmicrofacies model of the Chengdao oil field is established by means of the principal component analysis and fuzzy K-A average cluster method. The software of automatically and continuously discriminating microfacies based on the above-mentioned method has been developed. The well logging data of several wells located in the Chengdao oilfield have been processed by this software. The results well coincide with the micro factes that are determined by geologists. It has been demonstrated that the suggested methods are successful, the software is feasible. This paper presents the results of processing well log data in Well CB 20-1.
The characteristic parameters of sedimentary microfacies are extracted by using well logs and geological parameter curves.The digital well logmicrofacies model of the Chengdao oil field is established by means of the principal component analysis and fuzzy K-A average cluster method. The software of automatically and continuously discriminating microfacies based on the above-mentioned method has been developed. The well logging data of several wells located in the Chengdao oilfield have been processed by this software. The results well coincide with the micro factes that are determined by geologists. It has been demonstrated that the suggested methods are successful, the software is feasible. This paper presents the results of processing well log data in Well CB 20-1.
1996, 14(1): 59-68.
Abstract:
At the third and fourth members of Quantou Group,Middle Cretaceous in the east of the neighbouring area of the Daqing oilfield, it is revealed that the element abundances and their ratios of mudstones in a lacustrine-deltaic (subaqueous)depositional pakage are controlled by basin-in factors(reducing F1, acidity F2) and basin-out factors (protolith F3, colloid input F4)while the general geochemical rules of the element behaviours are combined with R-mode factor,Q-mode cluster, Q-mode factor analyses and other geologic features, which are expressed conspicuously in correlations of Sr/Ca positive to reducing and acidity, CaO/MgO negative to acidity, Ni/Co negative to reduction, Ti/V negative to influence of basic protolith,Sr/Ba negative to colloid input. The mode cluster demonstrates that the mudstones are devided into four types, which with intercalated siltstones(spread flow genetic units)construct the subaqueous channal periphery fine sedimentary associations(SPF),coastal-shallow lake sedimentary associations(CSL),prodelta sedimentary associations(PDT) and deeper lake sedimentary associations(DPL) in an increasing depositional depth with water chemistry changing gradually from alkali and strongly oxidative to weakly alkali and oxidative. The basic protolith influences more strongly on the SPF and PDT than on the CSL and sometimes intensely on the DPL because of the gravity flows derived from the delta front. The colloid inputs are of not striking differences among all of the associations.
At the third and fourth members of Quantou Group,Middle Cretaceous in the east of the neighbouring area of the Daqing oilfield, it is revealed that the element abundances and their ratios of mudstones in a lacustrine-deltaic (subaqueous)depositional pakage are controlled by basin-in factors(reducing F1, acidity F2) and basin-out factors (protolith F3, colloid input F4)while the general geochemical rules of the element behaviours are combined with R-mode factor,Q-mode cluster, Q-mode factor analyses and other geologic features, which are expressed conspicuously in correlations of Sr/Ca positive to reducing and acidity, CaO/MgO negative to acidity, Ni/Co negative to reduction, Ti/V negative to influence of basic protolith,Sr/Ba negative to colloid input. The mode cluster demonstrates that the mudstones are devided into four types, which with intercalated siltstones(spread flow genetic units)construct the subaqueous channal periphery fine sedimentary associations(SPF),coastal-shallow lake sedimentary associations(CSL),prodelta sedimentary associations(PDT) and deeper lake sedimentary associations(DPL) in an increasing depositional depth with water chemistry changing gradually from alkali and strongly oxidative to weakly alkali and oxidative. The basic protolith influences more strongly on the SPF and PDT than on the CSL and sometimes intensely on the DPL because of the gravity flows derived from the delta front. The colloid inputs are of not striking differences among all of the associations.
1996, 14(1): 80-85.
Abstract:
Study on the characteristics of capillary pressure curves of direct argillaceous cap rocks for natural gas from paleozoic in shanganning Basin was carried out in this paper. The parameters,which have been obtained in the process of experiment, show that the direct argillaceous cap rock has above medium power to seal natural gas. Those parameters are the pore throat median diameter, median pressure, change coefficient of the frequency distribution of pore throat and the pemeability contribution. The results also show that the pore throat median diameter is proportional to the maximum mercury saturation, but disproportional to the median pressure and the change coefficient.
Study on the characteristics of capillary pressure curves of direct argillaceous cap rocks for natural gas from paleozoic in shanganning Basin was carried out in this paper. The parameters,which have been obtained in the process of experiment, show that the direct argillaceous cap rock has above medium power to seal natural gas. Those parameters are the pore throat median diameter, median pressure, change coefficient of the frequency distribution of pore throat and the pemeability contribution. The results also show that the pore throat median diameter is proportional to the maximum mercury saturation, but disproportional to the median pressure and the change coefficient.
1996, 14(1): 93-102.
Abstract:
This paper includes a systematic analysis and correlation study on the sporo-pollen assemblage, stratigraphic sequence and geochronology of the Siwangou red bed section in Yaojie,Gansu. The following sporo-pollen assemblages may be recongnized in the Siwangou section (in ascending order ):① Pinuspollenites-Inaperturopollenites-Taxodiaceaepollenites-Quercoidites-Lygodioisporites assemblage,which may be assigned to Early Oligocene;② Betu laceoipollenites- Quercoidites-Chenopodipollis -Lygodioisporites assemblage,which belongs to Middle Oligocene. The results of this study show that, the geological age of the red bed section belongs to Eocene-Middle Oligocene; the Eocene sporo-pollen assemblages of Yaojie are approximately similar to those of the east region and the west region of China,which indicate a subtropical broadleaf and deciduous forest, mainly composed of the subtropical and warm temperate taxa, and a burning hot climate; from Late Eocene to Early Oligocene, the vegetation of Yao ne evolved to warm temperate mixed broadleaf and needleaf forests, mainly composed of the warm broadleaf and deciduous plants, presumably associated with warm and humid conditions; the Middle-Oligocene sporo-pollen records of Yaojie reflect comparatively warm and wet climates, which indicate that temperate broadleaf and deciduous forests are mainly constituted by Betulaceoipollenites and Quercoidites. The region correlation analysis shows that since Early Oligocene a trend toward difference of vegetation and climate has been on the increase between east and west region of China. Early Oligocene may be an important age of neotectonic movement in China.
This paper includes a systematic analysis and correlation study on the sporo-pollen assemblage, stratigraphic sequence and geochronology of the Siwangou red bed section in Yaojie,Gansu. The following sporo-pollen assemblages may be recongnized in the Siwangou section (in ascending order ):① Pinuspollenites-Inaperturopollenites-Taxodiaceaepollenites-Quercoidites-Lygodioisporites assemblage,which may be assigned to Early Oligocene;② Betu laceoipollenites- Quercoidites-Chenopodipollis -Lygodioisporites assemblage,which belongs to Middle Oligocene. The results of this study show that, the geological age of the red bed section belongs to Eocene-Middle Oligocene; the Eocene sporo-pollen assemblages of Yaojie are approximately similar to those of the east region and the west region of China,which indicate a subtropical broadleaf and deciduous forest, mainly composed of the subtropical and warm temperate taxa, and a burning hot climate; from Late Eocene to Early Oligocene, the vegetation of Yao ne evolved to warm temperate mixed broadleaf and needleaf forests, mainly composed of the warm broadleaf and deciduous plants, presumably associated with warm and humid conditions; the Middle-Oligocene sporo-pollen records of Yaojie reflect comparatively warm and wet climates, which indicate that temperate broadleaf and deciduous forests are mainly constituted by Betulaceoipollenites and Quercoidites. The region correlation analysis shows that since Early Oligocene a trend toward difference of vegetation and climate has been on the increase between east and west region of China. Early Oligocene may be an important age of neotectonic movement in China.
1996, 14(1): 110-116.
Abstract:
Systematic classification for natural gases is not only a foundation for development of natural gas geological theory, but also very siginificant in exploration of natural gases. Based on a great deal of geological and geochemical data obtained from many years of academic research of our group and others, a new classification for natural gases was put forward under the guidence of "multi-source complex and multi-stage continuity". In this classification, natural gases were classified into the biogenic and abiogenic substantially,the biogenic natural gas was further divided into oil type gas and coal type gas according to its source organic matter.Natural gases were also classified dynamically as microbial gas, biothermo-catalytic transitional gas, thermo-catalytic decompositional gas, and high temperature decomposition gas. Different types of natural gases often show different geochemical behavoirs for the reason of variation in organic input, source rocks and thermal maturity. These geochemical properties provide indicators for classification of natural gases. The indicators include chemical compositional related ones: CH4 Index,C1 /C1-5, C2+, C2/C3,and Hg abundance; isotopic compositional ones: δ13C1, δ13C2,δ13C3,δ13C4,40Ar/36 Ar; the companying liquid hydrocarbon indices:paraffin index,heptane index, alkane/aromatics index; and their internal relations.
Systematic classification for natural gases is not only a foundation for development of natural gas geological theory, but also very siginificant in exploration of natural gases. Based on a great deal of geological and geochemical data obtained from many years of academic research of our group and others, a new classification for natural gases was put forward under the guidence of "multi-source complex and multi-stage continuity". In this classification, natural gases were classified into the biogenic and abiogenic substantially,the biogenic natural gas was further divided into oil type gas and coal type gas according to its source organic matter.Natural gases were also classified dynamically as microbial gas, biothermo-catalytic transitional gas, thermo-catalytic decompositional gas, and high temperature decomposition gas. Different types of natural gases often show different geochemical behavoirs for the reason of variation in organic input, source rocks and thermal maturity. These geochemical properties provide indicators for classification of natural gases. The indicators include chemical compositional related ones: CH4 Index,C1 /C1-5, C2+, C2/C3,and Hg abundance; isotopic compositional ones: δ13C1, δ13C2,δ13C3,δ13C4,40Ar/36 Ar; the companying liquid hydrocarbon indices:paraffin index,heptane index, alkane/aromatics index; and their internal relations.
1996, 14(1): 127-134.
Abstract:
Based on the hydrous pyrolysis simulation experiments of low-mature mud limestone,the characteristics of gas. liquid and solid products, especially the liquid products(including expelled oil. bitumen A and bitumen C) are discussed systematically in this paper.During thermal evolution, the vitrinite reflectance value of kerogen changes from 0.64 % (original sample)to 1. 76 % (360℃ /72 ) and the evolution route of kerogen elements on Van Krevelen's model is in line with the evolution path of type- I kerogen. These reflect that the process of the artificial simulation evolution is similar to that of natural evolution.The characteristics of gas products are that the yield of methane and hydrogen increases,while that of heavy hydrocarbon series(C2- C5) and alkene gases Increases at first, then decreases later, The value of δ13C of methane becomes lighter at the early stage and heavier at the late stage.The light oil (C2- C14) plays an important role in the expelled oil. The relative contentsof light oils are from the large to samll then to large in the process of thermal evolution, reflecting the process of hydrocarbon generation and expulsion. The accurate measurement of light oils provides an important parameter for evaluating the quantity of oil generation.The characteristics of geochemistry of bitumen C are different from those of bitumen A of the host rock, the former contains more aromatic hydrocarbons and the most of ratio values of saturated hydrocarbons and aromatic hydrocarbons are smaller than 1, but that of the latter are larger than 1. The results of component analyses and GC analyses on expelled oil, bitumen A and bitumen C as well as the correlation of their characteristics show that the different existing forms of organic matter have their special hydrocarbon expulsion ways and make different contribution to hydrocarbon generation during each evolution stage; the thermal degradation of a large amount of kerogen is in the leading role during mature stage, but in high mature stage,the hydrocarbon generation and expulsion(or release) of inclusion organic matter play an important role because the inclusion organic matter begins to be overally pyrolysed.
Based on the hydrous pyrolysis simulation experiments of low-mature mud limestone,the characteristics of gas. liquid and solid products, especially the liquid products(including expelled oil. bitumen A and bitumen C) are discussed systematically in this paper.During thermal evolution, the vitrinite reflectance value of kerogen changes from 0.64 % (original sample)to 1. 76 % (360℃ /72 ) and the evolution route of kerogen elements on Van Krevelen's model is in line with the evolution path of type- I kerogen. These reflect that the process of the artificial simulation evolution is similar to that of natural evolution.The characteristics of gas products are that the yield of methane and hydrogen increases,while that of heavy hydrocarbon series(C2- C5) and alkene gases Increases at first, then decreases later, The value of δ13C of methane becomes lighter at the early stage and heavier at the late stage.The light oil (C2- C14) plays an important role in the expelled oil. The relative contentsof light oils are from the large to samll then to large in the process of thermal evolution, reflecting the process of hydrocarbon generation and expulsion. The accurate measurement of light oils provides an important parameter for evaluating the quantity of oil generation.The characteristics of geochemistry of bitumen C are different from those of bitumen A of the host rock, the former contains more aromatic hydrocarbons and the most of ratio values of saturated hydrocarbons and aromatic hydrocarbons are smaller than 1, but that of the latter are larger than 1. The results of component analyses and GC analyses on expelled oil, bitumen A and bitumen C as well as the correlation of their characteristics show that the different existing forms of organic matter have their special hydrocarbon expulsion ways and make different contribution to hydrocarbon generation during each evolution stage; the thermal degradation of a large amount of kerogen is in the leading role during mature stage, but in high mature stage,the hydrocarbon generation and expulsion(or release) of inclusion organic matter play an important role because the inclusion organic matter begins to be overally pyrolysed.
1996, 14(1): 149-155.
Abstract:
The δ18O change and the age of the stalagmite of the Tiane cave in Ninghua, Fujian Province, are corresponding to that of the V28-238 core of the deep sea. The growth period of the stalagmite began (1.8-25)×104 years ago and belonged to the Middle Pleistocene Epoch. The paleoclimate change in Ninghua area, Fujian, synchronizes with that in the globe and is the same as that in the Taiwan strait and the South China sea.
The δ18O change and the age of the stalagmite of the Tiane cave in Ninghua, Fujian Province, are corresponding to that of the V28-238 core of the deep sea. The growth period of the stalagmite began (1.8-25)×104 years ago and belonged to the Middle Pleistocene Epoch. The paleoclimate change in Ninghua area, Fujian, synchronizes with that in the globe and is the same as that in the Taiwan strait and the South China sea.
1996, 14(1): 162-166.
Abstract:
Heavy-mineral suites have frequently been used in studies of parent rocks, but it is usually hampered by the depletion of intrastratal solution and other factors. While in the provenance analysis, the study of garnet compositions by microprobe analysis is superior and has its own originality, which reduces the effects of hydroynamism and diagenesis to a minimum. In this paper, We analyzed the composition of detrital garnets from Bobal Basin. The results indicate that the garnet of Bobal Basin is mainly of low grossular content and different source areas have different garnet associations, which also proves that provenance analysis of the early stage IS correct.
Heavy-mineral suites have frequently been used in studies of parent rocks, but it is usually hampered by the depletion of intrastratal solution and other factors. While in the provenance analysis, the study of garnet compositions by microprobe analysis is superior and has its own originality, which reduces the effects of hydroynamism and diagenesis to a minimum. In this paper, We analyzed the composition of detrital garnets from Bobal Basin. The results indicate that the garnet of Bobal Basin is mainly of low grossular content and different source areas have different garnet associations, which also proves that provenance analysis of the early stage IS correct.
1996, 14(1): 12-21.
Abstract:
The Middle-Late Triassic Huanmaqing Group in the Lower Yangtse area is characteristic of lacustrine factes deposits. The Huangmaqing sedimentary basin, extending in NE-direction and developing perfect northwestern peripheral factes deposits, are bounded on the northwest by the NNE-striking Tanlu fault zone, a great strike-slip fault zone in East China. However,there develops a marine basin extending in the same direction and in the same space. The evolution of the marine basin was lasting from Late Devonian to the end of Early-Middle Triassic.Significantly, there did not exist northwestern peripheral factes deposits of the marine basin.They used to be appear, but have already disappeared in this area just since Middle-Late Triassic. It is obvious that the occurrence of the Huanmaqing basin and the tectonical erosion of the pre-Huangmaqing basin are controlled by the activity of the Tanlu fault zone, a transform-type boundary following the docking of Yangtse Plate and North China Plate in Early-Middle Triassic. Therefore, the formation of Huangmaqing basin must be closely related to the docking event of these two plates not only in time but also in space.Sedimentary conglomerates occur at the base of the Huangmaqing Group, extending discontinuously along boundary faults of the basin, as a series of subaqueous deposit fans, and overlying always unconformably on underlying strata. This shows that the earth crust of this area began to suffer from significantly tectonical deformation with folding and faulting, and established a base for the formation of the Huangmaqing basin during the early stage of plate docking.Sandstones, as a main portion of the Huangmaqing Group are composed of a large number of elastics derived from metamorphic rocks and tectonites. Detrital minerals derived from a high pressure metamorphic zone, such as phengite, corindon etc. are also discovered in the sandstones. These facts mean that Dabie Massive and Zhangbalin Uplift composed of old metamorphic rocks and located respectively at both sides of the Tanlu fault zone are the main source areas of the Huanmaqing deposits. In fact, the characteristics of heavy mineral association contained in the sandstones are coincident with that of the rocks composing the Susong formation in Dabie Massive and the Zhangbalin formation in Zhangbalin Uplift.Research on geochemistry of rare earth elements, rare elements and main elements in the sandstones shows that the Huangmaqing basin genetically belongs to a strike-slip basin related to an uplifted basement with thick earth curst. The discrimination result is completely coincident with the geological setting of the lower Yangtse area and the above-mentioned geological facts.
The Middle-Late Triassic Huanmaqing Group in the Lower Yangtse area is characteristic of lacustrine factes deposits. The Huangmaqing sedimentary basin, extending in NE-direction and developing perfect northwestern peripheral factes deposits, are bounded on the northwest by the NNE-striking Tanlu fault zone, a great strike-slip fault zone in East China. However,there develops a marine basin extending in the same direction and in the same space. The evolution of the marine basin was lasting from Late Devonian to the end of Early-Middle Triassic.Significantly, there did not exist northwestern peripheral factes deposits of the marine basin.They used to be appear, but have already disappeared in this area just since Middle-Late Triassic. It is obvious that the occurrence of the Huanmaqing basin and the tectonical erosion of the pre-Huangmaqing basin are controlled by the activity of the Tanlu fault zone, a transform-type boundary following the docking of Yangtse Plate and North China Plate in Early-Middle Triassic. Therefore, the formation of Huangmaqing basin must be closely related to the docking event of these two plates not only in time but also in space.Sedimentary conglomerates occur at the base of the Huangmaqing Group, extending discontinuously along boundary faults of the basin, as a series of subaqueous deposit fans, and overlying always unconformably on underlying strata. This shows that the earth crust of this area began to suffer from significantly tectonical deformation with folding and faulting, and established a base for the formation of the Huangmaqing basin during the early stage of plate docking.Sandstones, as a main portion of the Huangmaqing Group are composed of a large number of elastics derived from metamorphic rocks and tectonites. Detrital minerals derived from a high pressure metamorphic zone, such as phengite, corindon etc. are also discovered in the sandstones. These facts mean that Dabie Massive and Zhangbalin Uplift composed of old metamorphic rocks and located respectively at both sides of the Tanlu fault zone are the main source areas of the Huanmaqing deposits. In fact, the characteristics of heavy mineral association contained in the sandstones are coincident with that of the rocks composing the Susong formation in Dabie Massive and the Zhangbalin formation in Zhangbalin Uplift.Research on geochemistry of rare earth elements, rare elements and main elements in the sandstones shows that the Huangmaqing basin genetically belongs to a strike-slip basin related to an uplifted basement with thick earth curst. The discrimination result is completely coincident with the geological setting of the lower Yangtse area and the above-mentioned geological facts.
1996, 14(1): 33-39.
Abstract:
The study on sea-level change in geological history is one of the most important aspects in sedimentology and paleooceanography, and it is also the theoretical basis and key content of sequence stratigraphy. With the development of geoscience toward system science,the study of global sea level change has become an important frontier problem. In the study of sedimentology, we used to discuss the sea level change with the relative change of water depth in outcrop section, but the evidence from the study of seismic stratigraphy and sedimentology of Cambrian in northern Tarim Basin indicates that the relative change of water depth in outcrop section is quite different from the relative change of coastal onlap reflecting the relative sea level change. The relative change of coastal onlap got from the seismic stratigraphic research shows steady rising in Cambrian, but the relative change of water depth in outcrop section is gradually falling. Thus, it can be seen that although the relative change of water depth got from the study of outcrop section has a great deal to do with sea level change, it can not stand for sea level change completely. The reason is that the relative change of water depth is not only controlled by sea level change, and it is also controlled by basement subsidence and sediment supply, so under the condition of the same sea level change, the relative change of water depth will be quite different in the different site with different velocity of basement subsidence and sediment supply. Even if the basement subsidence is uniform in the basin, it will also change from place to place because of the different velocities of sediment supply (or productivities).Computer simulating results confirm that it is entirely possible that whether sea level is rising or falling, the water depth will decrease on the very shallow carbonate platform where the basement subsidence is relatively slow. This is because the carbonate productivity is very high and the production of carbonate sediments can keep pace with the increase of accommodation at all time, and even can exceed it at some time. As a result, the keeping-up carbonate system will generate,resulting in the decrease of water depth. In order to understand the rule of sealevel change from the outcrop section, the tendency of sea-level change has been reconstructed with the mathematical method and the developed Fischer Plot, and the results show that the reconstructed tendency of sea-level change is the same as that of the change of coastal onlap reflecting the relative change of sea-level change, which proves that the sea-level change has an important control over depositional sequences, but it is difficult to evaluate the sealevel change only on the relative change of water depth from outcrop section. It is only after removing the effects of basement subsidence and sediment productivity that the correct information of sea-level change can be obtained from the outcrop section.
The study on sea-level change in geological history is one of the most important aspects in sedimentology and paleooceanography, and it is also the theoretical basis and key content of sequence stratigraphy. With the development of geoscience toward system science,the study of global sea level change has become an important frontier problem. In the study of sedimentology, we used to discuss the sea level change with the relative change of water depth in outcrop section, but the evidence from the study of seismic stratigraphy and sedimentology of Cambrian in northern Tarim Basin indicates that the relative change of water depth in outcrop section is quite different from the relative change of coastal onlap reflecting the relative sea level change. The relative change of coastal onlap got from the seismic stratigraphic research shows steady rising in Cambrian, but the relative change of water depth in outcrop section is gradually falling. Thus, it can be seen that although the relative change of water depth got from the study of outcrop section has a great deal to do with sea level change, it can not stand for sea level change completely. The reason is that the relative change of water depth is not only controlled by sea level change, and it is also controlled by basement subsidence and sediment supply, so under the condition of the same sea level change, the relative change of water depth will be quite different in the different site with different velocity of basement subsidence and sediment supply. Even if the basement subsidence is uniform in the basin, it will also change from place to place because of the different velocities of sediment supply (or productivities).Computer simulating results confirm that it is entirely possible that whether sea level is rising or falling, the water depth will decrease on the very shallow carbonate platform where the basement subsidence is relatively slow. This is because the carbonate productivity is very high and the production of carbonate sediments can keep pace with the increase of accommodation at all time, and even can exceed it at some time. As a result, the keeping-up carbonate system will generate,resulting in the decrease of water depth. In order to understand the rule of sealevel change from the outcrop section, the tendency of sea-level change has been reconstructed with the mathematical method and the developed Fischer Plot, and the results show that the reconstructed tendency of sea-level change is the same as that of the change of coastal onlap reflecting the relative change of sea-level change, which proves that the sea-level change has an important control over depositional sequences, but it is difficult to evaluate the sealevel change only on the relative change of water depth from outcrop section. It is only after removing the effects of basement subsidence and sediment productivity that the correct information of sea-level change can be obtained from the outcrop section.
1996, 14(1): 47-58.
Abstract:
Based on multidisciplinary analyses of sedimentology,environmental magnetism,ichnology, mineralogy and geochemistry, it is found that,in the reddish- grey lamination in rhythmic deposits,there are various features about flocculent deposits with high susceptibility , high contents of total Fe and free Fe, and higher grades of bioturbation,showing that changes with chemical sedimentation caused by climatic cycles are the main controlling factor on the rhythmic beddings, and bioturbation could accelerate changes in micro-chemical environment on surface between water and sediments.Results from spectral analysis on time sequences show that the reddish-grey rhythmic deposits were controlled by decade-or century-level climatic periods which might be related to several astronomic cycles,such as sunspot or solar magnetic field. The influence of these astronomic factors on climatic changes is not likely very strong, but this kind of rhythmic bedding could be visible,probably resulting from the sensitive response of chemical sedimentation to climatic cycles ,and or the lacustrine chemical environment was nearby the sedimentary threshold for flocculation during the period in the upper and middle member of Shahejie Formation.
Based on multidisciplinary analyses of sedimentology,environmental magnetism,ichnology, mineralogy and geochemistry, it is found that,in the reddish- grey lamination in rhythmic deposits,there are various features about flocculent deposits with high susceptibility , high contents of total Fe and free Fe, and higher grades of bioturbation,showing that changes with chemical sedimentation caused by climatic cycles are the main controlling factor on the rhythmic beddings, and bioturbation could accelerate changes in micro-chemical environment on surface between water and sediments.Results from spectral analysis on time sequences show that the reddish-grey rhythmic deposits were controlled by decade-or century-level climatic periods which might be related to several astronomic cycles,such as sunspot or solar magnetic field. The influence of these astronomic factors on climatic changes is not likely very strong, but this kind of rhythmic bedding could be visible,probably resulting from the sensitive response of chemical sedimentation to climatic cycles ,and or the lacustrine chemical environment was nearby the sedimentary threshold for flocculation during the period in the upper and middle member of Shahejie Formation.
1996, 14(1): 69-79.
Abstract:
It is important to recover ancient pressures for the research of the He generation and expulsion process of source rocks and He migration, accumulation and forming pools. Nakayama (1981) recovered ancient pressures of abnormal compaction strata by using the math matical models put forward by Rubey (1959) and Chapman (1972) when they made basin modelling research. However, when researching the abnormal compaction strata in Songliao Basin, this paper found that the abnormal compaction factor varies with geological conditions of stratigraphic thickness, depth and the permeability of surrounding rocks, etc.. Based on it, this paper puts forward a statistics modelling method of recovering pressures of abnormal compaction strata. This method overcomes the shortcomings that the abnormal compaction factor was not to be changed in the buried process of strata considered by Nakayama. This paper uses it in researching the ancient pressures of abnormal compaction strata in Songliao Basin. The application results are identical with the drilling results in the basin. It indicates that the method is feasible and effective.
It is important to recover ancient pressures for the research of the He generation and expulsion process of source rocks and He migration, accumulation and forming pools. Nakayama (1981) recovered ancient pressures of abnormal compaction strata by using the math matical models put forward by Rubey (1959) and Chapman (1972) when they made basin modelling research. However, when researching the abnormal compaction strata in Songliao Basin, this paper found that the abnormal compaction factor varies with geological conditions of stratigraphic thickness, depth and the permeability of surrounding rocks, etc.. Based on it, this paper puts forward a statistics modelling method of recovering pressures of abnormal compaction strata. This method overcomes the shortcomings that the abnormal compaction factor was not to be changed in the buried process of strata considered by Nakayama. This paper uses it in researching the ancient pressures of abnormal compaction strata in Songliao Basin. The application results are identical with the drilling results in the basin. It indicates that the method is feasible and effective.
1996, 14(1): 86-92.
Abstract:
The early Triassic deposits consist of chaotic megabreccias,conglomerates, slump deposits,turbidites, deep-water limestones and calcareous mudstones.From bottom to top, sediments show four sedimentary cycles controlled by tectonic process. A single sedimentary cycle is composed of chaotic megabreccias, conglomerates,turbidite, slump deposits,deep-water limestone and calcareous mudstones upward. Based on the directional structures of turbidite and slump deposits, continental margin slope dipping to the west-south, the palaeocurrent direction ranges from 220°to 260°.This indicates that on the north plate margin existed an extensional tectonic setting along Luqu-Chenxian in Early Triassic, which is related to the rollback caused by the subduction of the Yangtze plate towards the north.The subduction causing the roll-back process made the north plate margin form a series of normal faults. This also made the early formed shallow water platform factes break,collapse and slide along the steep slope,at last they deposited in the deep water basin and formed the chaotic megabreccias,conglomerates deposits which slid and slumed at the later,and the turbidite,at the relatively stable period, formed the deep water limestone and calcareous mudstone.In another tectonic active period,the similar sediments deposited in the deep water basin.So,the early Triassic deposits were obviously controlled by the tectonic process.
The early Triassic deposits consist of chaotic megabreccias,conglomerates, slump deposits,turbidites, deep-water limestones and calcareous mudstones.From bottom to top, sediments show four sedimentary cycles controlled by tectonic process. A single sedimentary cycle is composed of chaotic megabreccias, conglomerates,turbidite, slump deposits,deep-water limestone and calcareous mudstones upward. Based on the directional structures of turbidite and slump deposits, continental margin slope dipping to the west-south, the palaeocurrent direction ranges from 220°to 260°.This indicates that on the north plate margin existed an extensional tectonic setting along Luqu-Chenxian in Early Triassic, which is related to the rollback caused by the subduction of the Yangtze plate towards the north.The subduction causing the roll-back process made the north plate margin form a series of normal faults. This also made the early formed shallow water platform factes break,collapse and slide along the steep slope,at last they deposited in the deep water basin and formed the chaotic megabreccias,conglomerates deposits which slid and slumed at the later,and the turbidite,at the relatively stable period, formed the deep water limestone and calcareous mudstone.In another tectonic active period,the similar sediments deposited in the deep water basin.So,the early Triassic deposits were obviously controlled by the tectonic process.
1996, 14(1): 103-109.
Abstract:
Exeperiments of dissolution for dolomite with and without gypsum (or anhydrite) have been made under different temperatures and pressures (40-130℃, normal atmospheric pressure-30MPa) of epigenesis and burial diagenesis conditions.The results show that the effect of presence of gypsum(or anhydrite) on dissolution of dolomite is positive when temperature is below 75℃ and pressure below 20MPa, but it is negative when temperature is higher than 75℃ and pressure higher than 20MPa. Based on the results we can predict that under the conditions of epigenesis and relatively shallow burial diagenesis the dissolution and formation of secondary porosity of dolomite with gypsum (or anhydrite) should be more common than that of dolomite without gypsum (or anhydrite), but under the deeper burial conditions the dissolution and formation of secondary porosity of dolomite without gypsum (or anhydrite) should be more common than that of dolomite with gypsum (or anhydrite).
Exeperiments of dissolution for dolomite with and without gypsum (or anhydrite) have been made under different temperatures and pressures (40-130℃, normal atmospheric pressure-30MPa) of epigenesis and burial diagenesis conditions.The results show that the effect of presence of gypsum(or anhydrite) on dissolution of dolomite is positive when temperature is below 75℃ and pressure below 20MPa, but it is negative when temperature is higher than 75℃ and pressure higher than 20MPa. Based on the results we can predict that under the conditions of epigenesis and relatively shallow burial diagenesis the dissolution and formation of secondary porosity of dolomite with gypsum (or anhydrite) should be more common than that of dolomite without gypsum (or anhydrite), but under the deeper burial conditions the dissolution and formation of secondary porosity of dolomite without gypsum (or anhydrite) should be more common than that of dolomite with gypsum (or anhydrite).
1996, 14(1): 117-126.
Abstract:
Hydrocarbon source rocks in Section Sha-1 and Sha-2 of the eastern depression in Liaohe Basin, dealt with in the present paper, are mainly in an immature stage and of which stereochemical parameters of steranes and terpanes in the soluble organic matter show an abnormal abundance of "geopolymer" isomers. Each parameter is generally over its corresponding threshold value and shows a systematical variation with depth roughly bounded by 2200m to 2300 m, 2500 m, 2700 m and 2770 m, respectively. Meanwhile, maturity parameters of phenanthrene, naphthalene, dibenzofuran and dibenzothiophene series are found to be similar in variation to those of steranes and terpanes. On the basis of the contrast study in detail and the integration of variations of infrared absorption parameters in the original soluble organic matter,the paper points out that variations of maturity parameters of steranes, terpanes and aromatics within the bio- thermocatalytic transition zone are dependent on the evolutionary features of the original soluble organic matter. The paper also qualitatively raises some geochemical identification markers for the bio-thermocatalytic transition zone of the eastern depression in Liaohe Basin. The present results can be applied to the identification of biothermocatalytic transition zone gases or immature and low-mature oils in other different areas.
Hydrocarbon source rocks in Section Sha-1 and Sha-2 of the eastern depression in Liaohe Basin, dealt with in the present paper, are mainly in an immature stage and of which stereochemical parameters of steranes and terpanes in the soluble organic matter show an abnormal abundance of "geopolymer" isomers. Each parameter is generally over its corresponding threshold value and shows a systematical variation with depth roughly bounded by 2200m to 2300 m, 2500 m, 2700 m and 2770 m, respectively. Meanwhile, maturity parameters of phenanthrene, naphthalene, dibenzofuran and dibenzothiophene series are found to be similar in variation to those of steranes and terpanes. On the basis of the contrast study in detail and the integration of variations of infrared absorption parameters in the original soluble organic matter,the paper points out that variations of maturity parameters of steranes, terpanes and aromatics within the bio- thermocatalytic transition zone are dependent on the evolutionary features of the original soluble organic matter. The paper also qualitatively raises some geochemical identification markers for the bio-thermocatalytic transition zone of the eastern depression in Liaohe Basin. The present results can be applied to the identification of biothermocatalytic transition zone gases or immature and low-mature oils in other different areas.
1996, 14(1): 135-142.
Abstract:
This paper reports carbon isotopic compositions of individual n-alkanes and isoprenoids from crude oil and source rock samples in the Junggar Basin. Between nC11 and nC34 , the most part of isotopic compositions of n-alkanes originating from the Jurassic limnetic factes is-27.0‰, to-32.4‰,,heavier than that of the crude oil from the marine factes strata, characterized by 13C-rich isotope.The n-alkane δ13C values of the crude oil from the type Ⅱ A source rock are lighter than that of the type Ⅱ B oil, it suggests that n-alkane be richer in 12C relatively.If crude oils are derived from the same group of organism or,at least,from organism using the same carbon source, the δ13C values of these n-alkanes and isoprenoids have a similar distributional range and total variational trend. Therefore, these data can be used in the source rock/oil correlation.The isotopic compositions of individual n-alkanes of the oil from the Cainan oil field become similar to that from the lower Jurassic Sangonghe source rock, they show a variation from-26.0‰,to-32.0‰,in the nC11 to nC32 range, among the same carbon numbers, the δ13C differences is less than 2‰,especially the δ13C value of n-alkanes in the Cainan oil matches that in the saturated hydrocarbon fractions from the lower Jurassic Sangonghe source rock.In the Pencan-2 well, the δ13C values of crude oil n-alkanes coincide with that of the Badaowan source.The Du-71 well is located on the southern margin of the Junggar Basin, its productive strata are shallower.The δ13C values of C11 -C23 n-alkanes vary from heavier to lighter with increasing of the carbon number, ranging from - 25. 4‰, to - 33.0‰, These values have a similar trend to the Toutunhe source rock. Through the study on microbiology, it has been proved that there is a great amount of Methanococcus in the Toutunhe hydrocarbon source rock.Therefore, the origin of the Dushanzi oil is possibly related to archaeobacteria.
This paper reports carbon isotopic compositions of individual n-alkanes and isoprenoids from crude oil and source rock samples in the Junggar Basin. Between nC11 and nC34 , the most part of isotopic compositions of n-alkanes originating from the Jurassic limnetic factes is-27.0‰, to-32.4‰,,heavier than that of the crude oil from the marine factes strata, characterized by 13C-rich isotope.The n-alkane δ13C values of the crude oil from the type Ⅱ A source rock are lighter than that of the type Ⅱ B oil, it suggests that n-alkane be richer in 12C relatively.If crude oils are derived from the same group of organism or,at least,from organism using the same carbon source, the δ13C values of these n-alkanes and isoprenoids have a similar distributional range and total variational trend. Therefore, these data can be used in the source rock/oil correlation.The isotopic compositions of individual n-alkanes of the oil from the Cainan oil field become similar to that from the lower Jurassic Sangonghe source rock, they show a variation from-26.0‰,to-32.0‰,in the nC11 to nC32 range, among the same carbon numbers, the δ13C differences is less than 2‰,especially the δ13C value of n-alkanes in the Cainan oil matches that in the saturated hydrocarbon fractions from the lower Jurassic Sangonghe source rock.In the Pencan-2 well, the δ13C values of crude oil n-alkanes coincide with that of the Badaowan source.The Du-71 well is located on the southern margin of the Junggar Basin, its productive strata are shallower.The δ13C values of C11 -C23 n-alkanes vary from heavier to lighter with increasing of the carbon number, ranging from - 25. 4‰, to - 33.0‰, These values have a similar trend to the Toutunhe source rock. Through the study on microbiology, it has been proved that there is a great amount of Methanococcus in the Toutunhe hydrocarbon source rock.Therefore, the origin of the Dushanzi oil is possibly related to archaeobacteria.
1996, 14(1): 156-161.
Abstract:
In this work, samples of airborne particulates,vent gas and smog dust during heating and non-heating seasons were collected in the urban and suburban areas of Lanzhou. After extraction and separation, four kinds of components, such as saturated hydrocarbons, aromatics,non-hydrocarbons and asphaltenes, were obtained. According to the quantitative analysis, the results are shown as follows:(1)In the airborne particulates the concentration of organic matter during heating seasons is higher than that during non-heating ones.(2) According to the concentration comparisosn of four kinds of organic components among the smog dust, vent gas and airborne particulate in Lanzhou, industrial pollution, vent gas and smog dust are the main sources in Xigu, Panxuanlu and Tieluju, respectively.(3) In a word, the pollution in Lanzhou is mainly attributed to burning of coal, vent gas and indutrial release, which contribute different percentages depending on the particular seasons or areas.
In this work, samples of airborne particulates,vent gas and smog dust during heating and non-heating seasons were collected in the urban and suburban areas of Lanzhou. After extraction and separation, four kinds of components, such as saturated hydrocarbons, aromatics,non-hydrocarbons and asphaltenes, were obtained. According to the quantitative analysis, the results are shown as follows:(1)In the airborne particulates the concentration of organic matter during heating seasons is higher than that during non-heating ones.(2) According to the concentration comparisosn of four kinds of organic components among the smog dust, vent gas and airborne particulate in Lanzhou, industrial pollution, vent gas and smog dust are the main sources in Xigu, Panxuanlu and Tieluju, respectively.(3) In a word, the pollution in Lanzhou is mainly attributed to burning of coal, vent gas and indutrial release, which contribute different percentages depending on the particular seasons or areas.
1996, 14(1): 167-175.
Abstract:
Based on seismic,palaeontological, sedimentary and logging data, strata frequency of Shahejie formation in Qibei seg, Huanghua depression was studied by means of sequence stratigraphy,and the formation was divided into two sequences,Ⅰ(3rd member of the formation and Ⅱ(2nd and 1st members of the formation). Each sequence was further divided into three system tracts, low stand, transgressive and high stand system tracts. The characteristics of the system tracts were described in detail, and prospective factes tracts and zones for oil/gas accumulation in the seg were pointed out in the paper.
Based on seismic,palaeontological, sedimentary and logging data, strata frequency of Shahejie formation in Qibei seg, Huanghua depression was studied by means of sequence stratigraphy,and the formation was divided into two sequences,Ⅰ(3rd member of the formation and Ⅱ(2nd and 1st members of the formation). Each sequence was further divided into three system tracts, low stand, transgressive and high stand system tracts. The characteristics of the system tracts were described in detail, and prospective factes tracts and zones for oil/gas accumulation in the seg were pointed out in the paper.
