2000 Vol. 18, No. 1
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Display Method:
2000, 18(1): 1-6.
Abstract:
The formation of channel patterns and its characteristics are important aspects in modern and ancient fluvial system studies, and thus become the main concern for hydraulic engineers, geomorphologists and sedimentologists. So far, there are still some questions not clear in this area, for example, the classification of channel patterns, formation cause of anastomosing fluvial rivers, critical conditions of evolution of some fluvial channel patterns, and further studies are still needed. Another problem related to channel pattern is the transformation of the patterns. In the present paper, four ordinary patterns are discussed, which include the braided, meandering, anabranched (in which include the anastomosing) and straight patterns. Comprehensive study to the spatial transformation of above channel patterns has significance not only for management of modern river and prevention of flood,but also for prospect and exploitation for hydrocarbon and some mineral resources in ancient fluvial depositional systems. The spatial longitudinal variations of river patterns not only show the characteristics of individual channel patterns, but also the transformation between the patterns. The different transformation will shadow different characteristics and consenguencies, but the same transformation has definite general characters and analogous controlling factors. In this paper, the spatial transformation models of fluvial channel patterns and its influences are discussed. Five conceptual models for the spatial transformation of river channel patterns are presented, which include the models of "Braided-Meandering", "Straight-Meandering", "Meandering-Braided", "Meandering-Anabranched" and "Anabranched-Straight". Although the possible spatial transformations among the braided, meandering, anabranched and straight fluvial channel patterns possibly occur in nature, the others except above five in 12 possible transformations have not been observed so far. Furthermore, each one of the five models has different occurring frequency, the model of "Braided-Meandering" occurs generally in larger frequency. The 5 types of transformations are elucidated and interpreted in terms of various examples. The driven factors that control the trend of transformation are also discussed in details. In general, the transformations determined by the integration of geotectonics, climate, vegetation, river valley slope, bank sediment composition and hydraulic factors, but their influence to each type of the models are different.
The formation of channel patterns and its characteristics are important aspects in modern and ancient fluvial system studies, and thus become the main concern for hydraulic engineers, geomorphologists and sedimentologists. So far, there are still some questions not clear in this area, for example, the classification of channel patterns, formation cause of anastomosing fluvial rivers, critical conditions of evolution of some fluvial channel patterns, and further studies are still needed. Another problem related to channel pattern is the transformation of the patterns. In the present paper, four ordinary patterns are discussed, which include the braided, meandering, anabranched (in which include the anastomosing) and straight patterns. Comprehensive study to the spatial transformation of above channel patterns has significance not only for management of modern river and prevention of flood,but also for prospect and exploitation for hydrocarbon and some mineral resources in ancient fluvial depositional systems. The spatial longitudinal variations of river patterns not only show the characteristics of individual channel patterns, but also the transformation between the patterns. The different transformation will shadow different characteristics and consenguencies, but the same transformation has definite general characters and analogous controlling factors. In this paper, the spatial transformation models of fluvial channel patterns and its influences are discussed. Five conceptual models for the spatial transformation of river channel patterns are presented, which include the models of "Braided-Meandering", "Straight-Meandering", "Meandering-Braided", "Meandering-Anabranched" and "Anabranched-Straight". Although the possible spatial transformations among the braided, meandering, anabranched and straight fluvial channel patterns possibly occur in nature, the others except above five in 12 possible transformations have not been observed so far. Furthermore, each one of the five models has different occurring frequency, the model of "Braided-Meandering" occurs generally in larger frequency. The 5 types of transformations are elucidated and interpreted in terms of various examples. The driven factors that control the trend of transformation are also discussed in details. In general, the transformations determined by the integration of geotectonics, climate, vegetation, river valley slope, bank sediment composition and hydraulic factors, but their influence to each type of the models are different.
2000, 18(1): 13-17.
Abstract:
Organic carbon content in lake sediment is often used to indicate the lake paleoprimary productivity.The main sources of organic carbon include autochthonous lake organism and allochthonous terrestrial plant,and there is complex degradation after deposition.Therefore the total organic carbon in lake sediments only can offer rough information about lake paleoprimary productivity. Compared with organic carbon, pigments are more table and have close relationship with lake temperature,water depth,salinity,trophic status.Recently pigments are used as an effective environment index in the study of lake environmental evolution. According to the contents and assemblages of pigments and other environmental multiproxy from the sediments core of S1 Core in East Juyanhai in Inner Mongolia, this paper mainly deals with the climatic and environmental changes during the past 2 600 years of this area.The characteristics of climate assemblages have the feature with the process of warm wet(2 540～2 650 aB.P.)→lake shrink, warm dry (2 360～2 540 aB.P.)→warm wet,lake expand(2 150～2 360 aB.P.)→cold wet to cold dry,lake shrink(1 630～2 150 aB.P.)→warm wet,lake expand(600～1 630 aB.P.)→cold wet to warm dry(600 aB.P.～present).In the meantime, the authors also try to contribute the pigment and other environmental index to evaluate the paleoprimary productivity,and to distinguish the human activities in lake records.The natural climate change played an important role in the process of environmental evolution in the area of Juyanhai Lake during the past 2 600 years, and human activities affected the lake environment greatly only in a special period.
Organic carbon content in lake sediment is often used to indicate the lake paleoprimary productivity.The main sources of organic carbon include autochthonous lake organism and allochthonous terrestrial plant,and there is complex degradation after deposition.Therefore the total organic carbon in lake sediments only can offer rough information about lake paleoprimary productivity. Compared with organic carbon, pigments are more table and have close relationship with lake temperature,water depth,salinity,trophic status.Recently pigments are used as an effective environment index in the study of lake environmental evolution. According to the contents and assemblages of pigments and other environmental multiproxy from the sediments core of S1 Core in East Juyanhai in Inner Mongolia, this paper mainly deals with the climatic and environmental changes during the past 2 600 years of this area.The characteristics of climate assemblages have the feature with the process of warm wet(2 540～2 650 aB.P.)→lake shrink, warm dry (2 360～2 540 aB.P.)→warm wet,lake expand(2 150～2 360 aB.P.)→cold wet to cold dry,lake shrink(1 630～2 150 aB.P.)→warm wet,lake expand(600～1 630 aB.P.)→cold wet to warm dry(600 aB.P.～present).In the meantime, the authors also try to contribute the pigment and other environmental index to evaluate the paleoprimary productivity,and to distinguish the human activities in lake records.The natural climate change played an important role in the process of environmental evolution in the area of Juyanhai Lake during the past 2 600 years, and human activities affected the lake environment greatly only in a special period.
2000, 18(1): 22-28.
Abstract:
The sediments that accumulate in an estuarine environment recorded the information about the history of changes in the source of the material, the rate of deposition and the influence of man. Man's influences on Victoria Harbour are significant. To create flat land and cope with the rapid development in Hong Kong, reclamation activities have taken place about every 10～20 years in Victoria Harbour began from a few decades ago. And to maintain the navigation channel, get fill material for reclamation, many dredging activities were carried out in the Harbour. These activities changed the coastline seaward and also complicated the recent sedimentation process in the Harbour. To study the extent and history of man's influence on the sediments and recent sedimentation process in the Harbour, four vibrocores were collected in three designated locations within Victoria Harbour, Hong Kong in 1996. Sampling locations were chosen from a range of settings where reclamation or construction is planned or taking place. Each of the cores was 76 mm in diameter and 6 m in length. The sediment type and colour were describe from visual and photographic observations and by matching Munsell(R) Soil Color Charts. The 210Pb activities for the sediments were determined by210 Pb method and ICP-AES was employed for the determination of Zn, Cu, while FAAS for that of Pb concentrations. Sedimentation rates in Victoria Harbour have been determined to be about 0.3～2 cm/a in open areas based on 210Pb dating and heavy metal distributions. This value can represent the natural sedimentation rates in the Harbour. Since reclamation activities have changed the coastline and affect the sedimentation process in the Harbour, sediments have been contributed by effluent discharge, materials lost from dredging and reclamation work. In some nearby enclosed coastal port and dumping areas, the rates were found to be somewhat higher in these areas, in the range 3～5 cm/a. This result, that the sedimentation rates are high in some places in the Harbour, is also in keeping with the more serious heavy metal pollution in these places and reflects man's influence on the Harbour. This means that changes in the coastline caused by reclamation may have a significant effect on siltation in the Harbour.
The sediments that accumulate in an estuarine environment recorded the information about the history of changes in the source of the material, the rate of deposition and the influence of man. Man's influences on Victoria Harbour are significant. To create flat land and cope with the rapid development in Hong Kong, reclamation activities have taken place about every 10～20 years in Victoria Harbour began from a few decades ago. And to maintain the navigation channel, get fill material for reclamation, many dredging activities were carried out in the Harbour. These activities changed the coastline seaward and also complicated the recent sedimentation process in the Harbour. To study the extent and history of man's influence on the sediments and recent sedimentation process in the Harbour, four vibrocores were collected in three designated locations within Victoria Harbour, Hong Kong in 1996. Sampling locations were chosen from a range of settings where reclamation or construction is planned or taking place. Each of the cores was 76 mm in diameter and 6 m in length. The sediment type and colour were describe from visual and photographic observations and by matching Munsell(R) Soil Color Charts. The 210Pb activities for the sediments were determined by210 Pb method and ICP-AES was employed for the determination of Zn, Cu, while FAAS for that of Pb concentrations. Sedimentation rates in Victoria Harbour have been determined to be about 0.3～2 cm/a in open areas based on 210Pb dating and heavy metal distributions. This value can represent the natural sedimentation rates in the Harbour. Since reclamation activities have changed the coastline and affect the sedimentation process in the Harbour, sediments have been contributed by effluent discharge, materials lost from dredging and reclamation work. In some nearby enclosed coastal port and dumping areas, the rates were found to be somewhat higher in these areas, in the range 3～5 cm/a. This result, that the sedimentation rates are high in some places in the Harbour, is also in keeping with the more serious heavy metal pollution in these places and reflects man's influence on the Harbour. This means that changes in the coastline caused by reclamation may have a significant effect on siltation in the Harbour.
2000, 18(1): 36-42.
Abstract:
The Quaternary eolian deposits in Lanzhou,west of the Loess Plateau,is the thickest area in China as aresult of the geographic position and the topographic conditions.Investigation show that Lanzhou is also a dust-storm frequent area in the present time.Both provides us possibilities to form a grain size distribution model of the eolian deposits,and to identify deposits formed in different climatic conditions through researches of their grain composition. 180 samples are taken from newly dug 45m-deep loess well section at Gaolanshan near Lanzhou at a depth of 3 100cm to 4 000 cm,including stages LOMSS-4,5a,5b,5c,5d,5e and LOMSS-6 according to the magnetic susceptibility curve (LOMSS means loess magnetic susceptibility stage,and is basically corresponding to MIS).To conduct a very careful laboratory work of grain size analysis,the measuring range of grain diameter is set as 4.00-10.00Φ with step of 0.25Φ on the SKC-2000 Grain Size Analytical System. Studies show that the eolian deposits formed in different climatic stages are much similar to each other in grain size composition,leading to an establishment of grain size distribution model.They are characterized by four features：(a) badly sorted with particles more than 4Φ in diameter(mean diameter 6.4Φ);(b) named as a silty heavy clayey or typical loess with fine sand 2.6%,silt 77.8% and clay 19.6%;(c) mono-peaked and positively skewed frequency curve;(d) nearly the same in quantity for both long-term and short-term suspended particles according to Pye's eolian deposition model.Fortunately,these four features can also be seen from the present dust-storm deposits collected in the spring of 1993 in Lanzhou area.It shows that the eolian deposits are transported matinly by manner of dust stroms.This model can be used as a diagnosis model of the eolian deposits within the area of Lanzhou. Differences of grain size composition among the eolian deposits are noted too with regard to climate changes though it is not so big.Different time-scales of climatic change may cause changes in content of differnt grain size.For example,the content of＜5.50Φ particles in the deposits formed under the glacial climate is obviously higher than that under the interglacial,and the content of 4.5-6.75Φ particles formed under the stadial higher than under the interstadial.It implies a complex and delicate relationship between grain size composition and the winter monsoon.But we still recognize that two grain-size parameters(GSP)from the Lanzhou eolian deposits are of significance to the paleoclimate.GSP1(content of＜5.75Φ,＞5.75Φ or ＜5.75Φ/ ＞5.75Φ)can be used to reveal changes of winter monsoon on the scale of glacial-interglacial climate.GSP2(content of 4.5-6.75Φ,＞6.75Φ or 4.5-6.75Φ/＞6.75Φ)tends to reveal changes on the scale of stadial-interstadial climate
The Quaternary eolian deposits in Lanzhou,west of the Loess Plateau,is the thickest area in China as aresult of the geographic position and the topographic conditions.Investigation show that Lanzhou is also a dust-storm frequent area in the present time.Both provides us possibilities to form a grain size distribution model of the eolian deposits,and to identify deposits formed in different climatic conditions through researches of their grain composition. 180 samples are taken from newly dug 45m-deep loess well section at Gaolanshan near Lanzhou at a depth of 3 100cm to 4 000 cm,including stages LOMSS-4,5a,5b,5c,5d,5e and LOMSS-6 according to the magnetic susceptibility curve (LOMSS means loess magnetic susceptibility stage,and is basically corresponding to MIS).To conduct a very careful laboratory work of grain size analysis,the measuring range of grain diameter is set as 4.00-10.00Φ with step of 0.25Φ on the SKC-2000 Grain Size Analytical System. Studies show that the eolian deposits formed in different climatic stages are much similar to each other in grain size composition,leading to an establishment of grain size distribution model.They are characterized by four features：(a) badly sorted with particles more than 4Φ in diameter(mean diameter 6.4Φ);(b) named as a silty heavy clayey or typical loess with fine sand 2.6%,silt 77.8% and clay 19.6%;(c) mono-peaked and positively skewed frequency curve;(d) nearly the same in quantity for both long-term and short-term suspended particles according to Pye's eolian deposition model.Fortunately,these four features can also be seen from the present dust-storm deposits collected in the spring of 1993 in Lanzhou area.It shows that the eolian deposits are transported matinly by manner of dust stroms.This model can be used as a diagnosis model of the eolian deposits within the area of Lanzhou. Differences of grain size composition among the eolian deposits are noted too with regard to climate changes though it is not so big.Different time-scales of climatic change may cause changes in content of differnt grain size.For example,the content of＜5.50Φ particles in the deposits formed under the glacial climate is obviously higher than that under the interglacial,and the content of 4.5-6.75Φ particles formed under the stadial higher than under the interstadial.It implies a complex and delicate relationship between grain size composition and the winter monsoon.But we still recognize that two grain-size parameters(GSP)from the Lanzhou eolian deposits are of significance to the paleoclimate.GSP1(content of＜5.75Φ,＞5.75Φ or ＜5.75Φ/ ＞5.75Φ)can be used to reveal changes of winter monsoon on the scale of glacial-interglacial climate.GSP2(content of 4.5-6.75Φ,＞6.75Φ or 4.5-6.75Φ/＞6.75Φ)tends to reveal changes on the scale of stadial-interstadial climate
2000, 18(1): 50-56.
Abstract:
According to the data of rock cores, well loggings and seismic interpretations, three order base-level cycles are recognized from Penglaizhen Formation in Xinchang area, which consist of 45-47 short-term base-level cycles, 5 mid-term base-level cycles, 2 long-term bsae-level cycles and their structural types, stacking patterns and distributing models are deeply discussed by using high-resolution sequence stratigraphic theory and methods. On the basis of single-well analysis, higher-accuracy isochronostratigraphic correlation is done at the thrree order base-level cycles in Penglaizhen Formation, and the relative stratigraphic frameworks are built, meanwhile one-dimensional information about single-well is converted to three-dimensional information in gasfield. According to the analysis on characteristics of stratigraphic response course of sedimentary dynamics, favorable reservoir sands' sedimentary facies, association, occurrence, controls, and relationship with physical property in the course of mid-term and short-term base-level cycles are discussed. A table of the influence of the ratio of the accommodation and the sediment supply flux to the reservoir sands is also made in this paper. It clearly shows that the delta systems in the slowly ascent or descent process of the long-term base-level cycles are the necessary background for the favorable reservoir sands, and the main element of controlling the distribution in the time and space for the sedimentary system is the mid-term base-level cycles. The best reservoir sands are on the sides of the sequencesur face of the mid-term base-level cycles. So one of the important token of reservoir forecast is the sequence surface of the mid-term base-level cycles.
According to the data of rock cores, well loggings and seismic interpretations, three order base-level cycles are recognized from Penglaizhen Formation in Xinchang area, which consist of 45-47 short-term base-level cycles, 5 mid-term base-level cycles, 2 long-term bsae-level cycles and their structural types, stacking patterns and distributing models are deeply discussed by using high-resolution sequence stratigraphic theory and methods. On the basis of single-well analysis, higher-accuracy isochronostratigraphic correlation is done at the thrree order base-level cycles in Penglaizhen Formation, and the relative stratigraphic frameworks are built, meanwhile one-dimensional information about single-well is converted to three-dimensional information in gasfield. According to the analysis on characteristics of stratigraphic response course of sedimentary dynamics, favorable reservoir sands' sedimentary facies, association, occurrence, controls, and relationship with physical property in the course of mid-term and short-term base-level cycles are discussed. A table of the influence of the ratio of the accommodation and the sediment supply flux to the reservoir sands is also made in this paper. It clearly shows that the delta systems in the slowly ascent or descent process of the long-term base-level cycles are the necessary background for the favorable reservoir sands, and the main element of controlling the distribution in the time and space for the sedimentary system is the mid-term base-level cycles. The best reservoir sands are on the sides of the sequencesur face of the mid-term base-level cycles. So one of the important token of reservoir forecast is the sequence surface of the mid-term base-level cycles.
2000, 18(1): 63-67.
Abstract:
It is well known that integrated use of outcrop, well-logging and seismic data is the key to sequence stratigraphy. Therefore, how to identify the sequence boundary by well-logging in the lacustrine sediments which are lack in the unconformity is critical step to sequence stratigraphic analysis. With an example of sequencestratigraphy of Quaternary in well Jinda1, Qaidam basin, this paper presents the basic procedures of new approach for a stratigraphic subdivision of well logs into sequences by reconstruction of paleobathymetric curve. After the log facies analysis, six kinds of lithofacies have been recognized in Quaternary which are dark-grey shale, brown shale, grey silty shale, carbargillite, shaly siltstone and siltstone. For each Lithofacies association a sedimentologically coherent paleoenvironmental interpretation has to be established. Hence, a distinct paleobathymetric range is assigned to each lithofacies unit. Based on this relative paleo-waterdepth, paleobathymetric curve of Quaternary in well Jinda1 has been established from a vertical succession of lithofacies. This water-depth curve helps to identify stratigraphic sequence of different scales.This approach is based on the identification of bathymetry turnaround trends in the lithofacies succession. The maximum regressive surface is placed at the lowest waterdepth values on the smoothed bathymetry curve. The maximum regressive surface is identical to the sequence boundary. The maximum flooding surface is placed at the deepest bathymetry as the closest approximation. This horizon separates underlying transgressive half cycle from overlying regressive half-cycle. Based on the rules above, four sequences are identified in the Quaternary sediment of Jinda1 Well. Each sequence consists of two systems tracts separated by maximum flooding surface. It is clear that there are two scales of waterdepth cycle in the bathymetry curve. More frequent fluctuation in the bathymetry curve can be considered as the response to the high order stratigraphic sequence. At last, the prospective source rock, favorable reservoir and potential caprock have been predicted.
It is well known that integrated use of outcrop, well-logging and seismic data is the key to sequence stratigraphy. Therefore, how to identify the sequence boundary by well-logging in the lacustrine sediments which are lack in the unconformity is critical step to sequence stratigraphic analysis. With an example of sequencestratigraphy of Quaternary in well Jinda1, Qaidam basin, this paper presents the basic procedures of new approach for a stratigraphic subdivision of well logs into sequences by reconstruction of paleobathymetric curve. After the log facies analysis, six kinds of lithofacies have been recognized in Quaternary which are dark-grey shale, brown shale, grey silty shale, carbargillite, shaly siltstone and siltstone. For each Lithofacies association a sedimentologically coherent paleoenvironmental interpretation has to be established. Hence, a distinct paleobathymetric range is assigned to each lithofacies unit. Based on this relative paleo-waterdepth, paleobathymetric curve of Quaternary in well Jinda1 has been established from a vertical succession of lithofacies. This water-depth curve helps to identify stratigraphic sequence of different scales.This approach is based on the identification of bathymetry turnaround trends in the lithofacies succession. The maximum regressive surface is placed at the lowest waterdepth values on the smoothed bathymetry curve. The maximum regressive surface is identical to the sequence boundary. The maximum flooding surface is placed at the deepest bathymetry as the closest approximation. This horizon separates underlying transgressive half cycle from overlying regressive half-cycle. Based on the rules above, four sequences are identified in the Quaternary sediment of Jinda1 Well. Each sequence consists of two systems tracts separated by maximum flooding surface. It is clear that there are two scales of waterdepth cycle in the bathymetry curve. More frequent fluctuation in the bathymetry curve can be considered as the response to the high order stratigraphic sequence. At last, the prospective source rock, favorable reservoir and potential caprock have been predicted.
2000, 18(1): 73-79.
Abstract:
The study area,Jinmuda,Rangtang county, Sichuan province is located in the southeast of Aba Mass. During the early period of Late Triassic, deep water detrital sediments, which can be divided into Zhuwo Formation and Xinduqiao Formation, deposited in this area.The area is one part of Songpan-Ganze trough. For the first time,plenty of trace fossils have been discovered in Late Triassic Zhuwo Formation and Xind uqiao Formation in Riji Gully of Jinmuda area. After determination, these trace fossils have been classified into 38 ichnogenera and 63 ichnospecies.Most of them belong to deep water trace fossil. According to their composition, the relative abundance in different stratigraphic horizons and distribution features, five ich- noassemblages have been established, namely： (1) Helminthopsis-Paleodictyon ichnoassemblage, (2) Paleodictyon-Neonereites ichnoassemblage, (3) Megagrapton-Imponoglyphus ichnoassemblage, (4) Paleodictyon -Phycosiphon ichnoassemblage, (5) Megagrapton-Helminthoida ichnoassemblage. Based on detailed study it,turns out that all these five ichnoassemblages belong to Nereites ichnofacies. In order to analyze depositional environment, habit classification, characteristics and ichnofacies of trace fossils have been adopted. This paper concludes that each ichnoassemblage represents different depositional environment,ie. the first ichnoassemblage represents bathyal middle-lower slope environment, the second repre- sents abyssal basin margin environment,the third represents bathyal lower slope environment, the fourth repre sents abyssal basin and the fifth represents bathyal lower slope environment. Therefore it could be concluded that the sea level of Late Triassic Zuwo Formation in Riji Gully of Jinmuda area occurred secondary fluctuation with the general tendency of ascent, while from the top part of Zuwo Formation to Xinduqiao Formation, sea level began to descend. Thus, early Late Triassic depositional environment in Jinmuda area experienced the evolution of lower slope-abyssal basin margin-middle-lower slope-abyssal basin-lower slope. The study of deep water trace fossil brings another evidence for clarifying sedimentary water depth and eustatic fluctuation of the study area. Besides, it also provides new evidence for restoring paleogeography of the study area. In the study area,there are many gold deposits occurred in the turbidite of Late Triassic Xinduqiao Formation. Based on the study on trace fossils, the host strata of gold deposit,Xinduqiao Formation,was fomed in lower slope. So the study of trace fossil has a certain significance for searching for gold deposit and studying the formation environment of gold deposit.
The study area,Jinmuda,Rangtang county, Sichuan province is located in the southeast of Aba Mass. During the early period of Late Triassic, deep water detrital sediments, which can be divided into Zhuwo Formation and Xinduqiao Formation, deposited in this area.The area is one part of Songpan-Ganze trough. For the first time,plenty of trace fossils have been discovered in Late Triassic Zhuwo Formation and Xind uqiao Formation in Riji Gully of Jinmuda area. After determination, these trace fossils have been classified into 38 ichnogenera and 63 ichnospecies.Most of them belong to deep water trace fossil. According to their composition, the relative abundance in different stratigraphic horizons and distribution features, five ich- noassemblages have been established, namely： (1) Helminthopsis-Paleodictyon ichnoassemblage, (2) Paleodictyon-Neonereites ichnoassemblage, (3) Megagrapton-Imponoglyphus ichnoassemblage, (4) Paleodictyon -Phycosiphon ichnoassemblage, (5) Megagrapton-Helminthoida ichnoassemblage. Based on detailed study it,turns out that all these five ichnoassemblages belong to Nereites ichnofacies. In order to analyze depositional environment, habit classification, characteristics and ichnofacies of trace fossils have been adopted. This paper concludes that each ichnoassemblage represents different depositional environment,ie. the first ichnoassemblage represents bathyal middle-lower slope environment, the second repre- sents abyssal basin margin environment,the third represents bathyal lower slope environment, the fourth repre sents abyssal basin and the fifth represents bathyal lower slope environment. Therefore it could be concluded that the sea level of Late Triassic Zuwo Formation in Riji Gully of Jinmuda area occurred secondary fluctuation with the general tendency of ascent, while from the top part of Zuwo Formation to Xinduqiao Formation, sea level began to descend. Thus, early Late Triassic depositional environment in Jinmuda area experienced the evolution of lower slope-abyssal basin margin-middle-lower slope-abyssal basin-lower slope. The study of deep water trace fossil brings another evidence for clarifying sedimentary water depth and eustatic fluctuation of the study area. Besides, it also provides new evidence for restoring paleogeography of the study area. In the study area,there are many gold deposits occurred in the turbidite of Late Triassic Xinduqiao Formation. Based on the study on trace fossils, the host strata of gold deposit,Xinduqiao Formation,was fomed in lower slope. So the study of trace fossil has a certain significance for searching for gold deposit and studying the formation environment of gold deposit.
2000, 18(1): 89-94.
Abstract:
The Honggucheng Formation lies in the Upper Lower Cretaceous in the Minghe basin, which is like multistory type and cyclic sequences resulting from multiple flood processing deposition. It is characterized by the interchange of structure underwater and exposure structure. The scales of early and later flooding exist difference,which shows that they were formed in depositional environments of shore lake and depression on banks.Combined with the analysis of environment-facies and process-facies, the features of deposition and tectonic background of the Honggucheng Formation are studied deeply,which illustrates that Hongguchenng Formation is the result of the basin's accelerated shrinking period during basin evolution. The environment facies and process-facies are two important contents of the nonmarine basin analysis.
The Honggucheng Formation lies in the Upper Lower Cretaceous in the Minghe basin, which is like multistory type and cyclic sequences resulting from multiple flood processing deposition. It is characterized by the interchange of structure underwater and exposure structure. The scales of early and later flooding exist difference,which shows that they were formed in depositional environments of shore lake and depression on banks.Combined with the analysis of environment-facies and process-facies, the features of deposition and tectonic background of the Honggucheng Formation are studied deeply,which illustrates that Hongguchenng Formation is the result of the basin's accelerated shrinking period during basin evolution. The environment facies and process-facies are two important contents of the nonmarine basin analysis.
2000, 18(1): 100-106.
Abstract:
The Carboniferous strata outcropped in Maanqiao and northern Baluntai area in Middle Tianshan include Maanqiao Formation (late Datang stage) and Sangshuyuan Formation (Weining stage).The strata belong to the mixed sediments of carbonate and clastic rocks. Maanqiao Formation, most of which is carbonate tidal-flat facies, consists of two depositional cycles. Cycle one shows peritidal cycle, but cycle two shows intertidal-subtidal cycle, which indicate a deepening of sea water from cycle one to cycle two. The Sangshuyuan Formation is composed of three depositional cycles, which mainly show subtidal cycles. The fluvial and lacustrine facies on the top of Sangshuyuan Formation indicates the retreating of sea water. The trace element composition shows that the depth of sea water is very shallow, but the major element composition indicates that most samples fall into the region of island arc. The QFL , QmFLt and QpLvLs diagrams for Carboniferous sandstones give the same results as the major element composition plots. It can be seen that the source area of the Carboniferous strata is from underlying middle Tinshan microplate composed of a great deal of volcanic rocks of island arc type and intermediate-acid granite. So, the Carboniferous strate are formed in the foreland basin resulting from the collision between middle Tianshan microplate and southern Tianshan back-arc basin. The evolution of Tianshan microplate shows that the opening of paleo-Tianshan Ocean starts from Sinian-early Ordovician. With the opening of paleo-Tianshan Ocean, the middle Tianshan microplate shifts from the Tarim plate. The opening of southern Tianshan back-arc basin results from the subduction and collision in the northern margin of middle Tianshan microplate. The collision between Tarim plate and middle Tianshan microplate results in the closure of the southern Tianshan back-arc basin. The collision ,also called as soft collision ,does not make the southern Tianshan uplift abruptly. The sea water in the research area and southern Tianshan does not retreat until the early Carboniferous. So, there is devoid of sediments during the early Yanguan stage. With the transgression of Carboniferous, southern Tianshan accepts the sedimentation during the late Yanguan stage , but the research area during the late Datang stage. After a short time of sedimentation , the research area uplifts.
The Carboniferous strata outcropped in Maanqiao and northern Baluntai area in Middle Tianshan include Maanqiao Formation (late Datang stage) and Sangshuyuan Formation (Weining stage).The strata belong to the mixed sediments of carbonate and clastic rocks. Maanqiao Formation, most of which is carbonate tidal-flat facies, consists of two depositional cycles. Cycle one shows peritidal cycle, but cycle two shows intertidal-subtidal cycle, which indicate a deepening of sea water from cycle one to cycle two. The Sangshuyuan Formation is composed of three depositional cycles, which mainly show subtidal cycles. The fluvial and lacustrine facies on the top of Sangshuyuan Formation indicates the retreating of sea water. The trace element composition shows that the depth of sea water is very shallow, but the major element composition indicates that most samples fall into the region of island arc. The QFL , QmFLt and QpLvLs diagrams for Carboniferous sandstones give the same results as the major element composition plots. It can be seen that the source area of the Carboniferous strata is from underlying middle Tinshan microplate composed of a great deal of volcanic rocks of island arc type and intermediate-acid granite. So, the Carboniferous strate are formed in the foreland basin resulting from the collision between middle Tianshan microplate and southern Tianshan back-arc basin. The evolution of Tianshan microplate shows that the opening of paleo-Tianshan Ocean starts from Sinian-early Ordovician. With the opening of paleo-Tianshan Ocean, the middle Tianshan microplate shifts from the Tarim plate. The opening of southern Tianshan back-arc basin results from the subduction and collision in the northern margin of middle Tianshan microplate. The collision between Tarim plate and middle Tianshan microplate results in the closure of the southern Tianshan back-arc basin. The collision ,also called as soft collision ,does not make the southern Tianshan uplift abruptly. The sea water in the research area and southern Tianshan does not retreat until the early Carboniferous. So, there is devoid of sediments during the early Yanguan stage. With the transgression of Carboniferous, southern Tianshan accepts the sedimentation during the late Yanguan stage , but the research area during the late Datang stage. After a short time of sedimentation , the research area uplifts.
2000, 18(1): 119-126.
Abstract:
The timing and duration of quartz cementation in sandstones have been mainly inferred from diagenetic texture, relationship between pore filling minerals, fluid inclusions and isotopic data. Fluid inclusion temperatures from North Sea reservoir sandstones indicate that most of the quartz cement forms at temperature exceeding 90℃ and is continually proceeding after oil emplacement, based on the fluid inclusion temperatures in quartz overgrowth which is approaching the bottom-hole temperatures. The duration of quartz cement after oil emplacement depends upon the saturation of porewater and the distribution of pore water film and the property of water-wet or oil-wet of the reactants. The leaching of K-feldspar by meteoric water requires pore water flow to move the released potassium and sodium and silica out the solution, which suggests the mechanism does not appear to be a major source of silica for quartz cementation. The quartz cementation coincidence with the compaction and pressure solution suggests the major source of silica. The alteration of feldspar by illitization of kaolinite may serve as another important source of silica at deep burial depth. External sources are not need to call on for illustrating the quartz cementation, because there is no evidences for large scale convection of pore water flow occurred in the burial history of reservoir sandstones of middle Jurassic in the North Sea.
The timing and duration of quartz cementation in sandstones have been mainly inferred from diagenetic texture, relationship between pore filling minerals, fluid inclusions and isotopic data. Fluid inclusion temperatures from North Sea reservoir sandstones indicate that most of the quartz cement forms at temperature exceeding 90℃ and is continually proceeding after oil emplacement, based on the fluid inclusion temperatures in quartz overgrowth which is approaching the bottom-hole temperatures. The duration of quartz cement after oil emplacement depends upon the saturation of porewater and the distribution of pore water film and the property of water-wet or oil-wet of the reactants. The leaching of K-feldspar by meteoric water requires pore water flow to move the released potassium and sodium and silica out the solution, which suggests the mechanism does not appear to be a major source of silica for quartz cementation. The quartz cementation coincidence with the compaction and pressure solution suggests the major source of silica. The alteration of feldspar by illitization of kaolinite may serve as another important source of silica at deep burial depth. External sources are not need to call on for illustrating the quartz cementation, because there is no evidences for large scale convection of pore water flow occurred in the burial history of reservoir sandstones of middle Jurassic in the North Sea.
2000, 18(1): 133-138.
Abstract:
The geochemical characters of 13 Jurassic source rock samples in the eastern Qaidam basin are studied by means of Rock-Eval, GC-MS, GC-MS-MAT and so on Based on the comprehensive analyses of the organic carbon content, the content and conversion ratio of organic matter, parameters of pyrolysis, organic petrology parameters, biomarker characters of saturated hydrocarbon and stable carbon isotope composition of individual hydrocarbon, the organic matter's abundance, type and maturity are studied, and the potential of generation hydrocarbon are evaluated.1．Abundance of the organic matter：The variety range of the organic carbon content is wide, which is 0.20%～42.41%. Of which, the coal samples' organic carbon content is bigger than shale samples'. And only 31% samples' organic carbon content is less than 1.0%.The variation range of the soluble organic matter's content and total hydrocarbon is 0.0045%～1.0326% and 12.1×10-6～5 443.9×10-6 respectively, only 53.8% samples' soluble organic matter content exceeds 0.015%, 46.2% samples' total hydrocarbon exceeds 50×10-6, and have commonly low values. The conversion ratio of organic matter ("A"/TOC% and HC/TOC%) have also low values. Of which, the largest "A"/TOC% value is 4.20%, and only one sample's HC/TOC% is larger than 1.00%. 2．Type of the organic matter：According to the result of pyrolysis analysis, the variety range of IH、IO and S2/S3 is 25～1 700mg/gTOC、4～1 350mg/gTOC and 0.29～42.96 respectively. According to the organic petrology analysis of the maceral the major part is vitrinite, ranging from 17% to 80%, averaging being 65%. The second part is inertinite, ranging from 16% to 81%, averaging being 27%. The smallest part is exinite, ranging from 25% to 21%, averaging being 8%. 3．Maturity of the organic matter：Except three samples whose Tmax is above 512℃, all other samples'Tmax is 411～481℃,being the stage of lower-maturity to maturity. According to the vitrinite reflectance Ro, which is from 0.694 to 0.865, the organic matter is also lower-maturity to maturity stage, most of the source rocks being the highest stage of generating hydrocarbon. 4.Biomarker characteristics of saturated hydrocarbon：The characteristic of normal alkane are, from the TIC, the saturated hydrocarbon's dominant form is latter single peak, part of them is double peak or front single peak , having common features with other coal-bearing sedimentary basin. The isoprene's characteristics are that, the Pr/Ph of 54% samples is more than 1.0, which show that the Jurassic source rocks are not completely from the typical marsh environment, but much like the lake-beach and shallow lake depositional environment. CPI and OEP of the source rocks are more than 1.0, of which, CPI from 1.19 to 2.62, OEP from 1.05 to 2.40. ∑C+21/∑C_21 of the samples are lower. All these, on the one hand, show that the source rocks come from continental higher plants, on the other hand, show that the maturity of the source rocks is not high. The existence of bicyclic sesquiterpanes and diterpenoids show the source rocks have the characteristics of coal-measure formation.The characteristics of tricyclic terpanes and hopanes of Jurassic samples are the amount of the tricyclic terpanes is less than hopanes, in which, commonly C29 and C30the is major part, C27(Tm or Ts) is second part, the C32+ homohopanes' amount is low, and gammacerane can't be checked. The characteristics of steranes are that C29-steranes is major part, C27-steranes is second part, C27-steranes is lowest, which forming non-symmetrical V shape. The maturity parameters of steranes and hopanes doesn't reach the equilibrium point of evolution. 5．Stable carbon isotope of individual hydrocarbon：This feature is that δC13 of the coal samples is high, ranging from -23.2‰ to -33‰, mostly in -24‰～-27‰. The δC13 of shale and mudstone is less than coal samples, however, the δC13 of shale and mudstone is bigger than other areas, mostly in -20‰～-27‰. The variation of individual hydrocarbon isotope is obvious, and the curve has a jaggy shape. With the increase of carbon numbers, δC13 has a decreasing tendency. The distribution curve of shale is below that of mudstone, and that of mudstone is below the curve of coal-measure rocks. The δC13 of different samples have bigger difference. Above features show that the depositional imentary environment of the source rocks with their different bio-input being continental higher plants are marsh lake-beach and shallow lake, and the maturity of the source rocks is low. Summing up above all the characteristics, the following results are obtained： (1) The Jurassic source rocks have relatively high content of organic carbon, and most of the samples belong to medium-good source rock. (2) Most of the organic matters are of type Ⅲ,few of them are of typeⅠor type Ⅱ.(3) The organic matter is at low-maturity to maturity stage. (4) The sedimentary environment of the source rocks with their bio-inputs being continental higher plants were marsh, lake-beach and shallow lake, and the source rocks possess the characters of coal-measure rocks. (5)There is a hydrocarbon generation potentials with the Jurassic source rocks in some areas in the basin.
The geochemical characters of 13 Jurassic source rock samples in the eastern Qaidam basin are studied by means of Rock-Eval, GC-MS, GC-MS-MAT and so on Based on the comprehensive analyses of the organic carbon content, the content and conversion ratio of organic matter, parameters of pyrolysis, organic petrology parameters, biomarker characters of saturated hydrocarbon and stable carbon isotope composition of individual hydrocarbon, the organic matter's abundance, type and maturity are studied, and the potential of generation hydrocarbon are evaluated.1．Abundance of the organic matter：The variety range of the organic carbon content is wide, which is 0.20%～42.41%. Of which, the coal samples' organic carbon content is bigger than shale samples'. And only 31% samples' organic carbon content is less than 1.0%.The variation range of the soluble organic matter's content and total hydrocarbon is 0.0045%～1.0326% and 12.1×10-6～5 443.9×10-6 respectively, only 53.8% samples' soluble organic matter content exceeds 0.015%, 46.2% samples' total hydrocarbon exceeds 50×10-6, and have commonly low values. The conversion ratio of organic matter ("A"/TOC% and HC/TOC%) have also low values. Of which, the largest "A"/TOC% value is 4.20%, and only one sample's HC/TOC% is larger than 1.00%. 2．Type of the organic matter：According to the result of pyrolysis analysis, the variety range of IH、IO and S2/S3 is 25～1 700mg/gTOC、4～1 350mg/gTOC and 0.29～42.96 respectively. According to the organic petrology analysis of the maceral the major part is vitrinite, ranging from 17% to 80%, averaging being 65%. The second part is inertinite, ranging from 16% to 81%, averaging being 27%. The smallest part is exinite, ranging from 25% to 21%, averaging being 8%. 3．Maturity of the organic matter：Except three samples whose Tmax is above 512℃, all other samples'Tmax is 411～481℃,being the stage of lower-maturity to maturity. According to the vitrinite reflectance Ro, which is from 0.694 to 0.865, the organic matter is also lower-maturity to maturity stage, most of the source rocks being the highest stage of generating hydrocarbon. 4.Biomarker characteristics of saturated hydrocarbon：The characteristic of normal alkane are, from the TIC, the saturated hydrocarbon's dominant form is latter single peak, part of them is double peak or front single peak , having common features with other coal-bearing sedimentary basin. The isoprene's characteristics are that, the Pr/Ph of 54% samples is more than 1.0, which show that the Jurassic source rocks are not completely from the typical marsh environment, but much like the lake-beach and shallow lake depositional environment. CPI and OEP of the source rocks are more than 1.0, of which, CPI from 1.19 to 2.62, OEP from 1.05 to 2.40. ∑C+21/∑C_21 of the samples are lower. All these, on the one hand, show that the source rocks come from continental higher plants, on the other hand, show that the maturity of the source rocks is not high. The existence of bicyclic sesquiterpanes and diterpenoids show the source rocks have the characteristics of coal-measure formation.The characteristics of tricyclic terpanes and hopanes of Jurassic samples are the amount of the tricyclic terpanes is less than hopanes, in which, commonly C29 and C30the is major part, C27(Tm or Ts) is second part, the C32+ homohopanes' amount is low, and gammacerane can't be checked. The characteristics of steranes are that C29-steranes is major part, C27-steranes is second part, C27-steranes is lowest, which forming non-symmetrical V shape. The maturity parameters of steranes and hopanes doesn't reach the equilibrium point of evolution. 5．Stable carbon isotope of individual hydrocarbon：This feature is that δC13 of the coal samples is high, ranging from -23.2‰ to -33‰, mostly in -24‰～-27‰. The δC13 of shale and mudstone is less than coal samples, however, the δC13 of shale and mudstone is bigger than other areas, mostly in -20‰～-27‰. The variation of individual hydrocarbon isotope is obvious, and the curve has a jaggy shape. With the increase of carbon numbers, δC13 has a decreasing tendency. The distribution curve of shale is below that of mudstone, and that of mudstone is below the curve of coal-measure rocks. The δC13 of different samples have bigger difference. Above features show that the depositional imentary environment of the source rocks with their different bio-input being continental higher plants are marsh lake-beach and shallow lake, and the maturity of the source rocks is low. Summing up above all the characteristics, the following results are obtained： (1) The Jurassic source rocks have relatively high content of organic carbon, and most of the samples belong to medium-good source rock. (2) Most of the organic matters are of type Ⅲ,few of them are of typeⅠor type Ⅱ.(3) The organic matter is at low-maturity to maturity stage. (4) The sedimentary environment of the source rocks with their bio-inputs being continental higher plants were marsh, lake-beach and shallow lake, and the source rocks possess the characters of coal-measure rocks. (5)There is a hydrocarbon generation potentials with the Jurassic source rocks in some areas in the basin.
2000, 18(1): 146-150.
Abstract:
The indigenous characteristcs of organic matter in carbonate hydrocarbon source rock directly influences the precise evaluation of its hydrocarbon generation capability especially on marine carbonate rock with low organic matter abundance and high thermal evolution.The paper discusses that migration bitumen distribute widely in carbonate hydrocarbon source rock,meanwhile,all methods to distionguish primary or secondary organic matter in rocks are introduced in this paper.Finally,a series of measures to determine indigenous characteristics of organic matter carbonate source rock are proposed on the basis of the analyses of carbonate source rock of Lower Paleozoic in Ordos Basin. The so-called recognition of indigenous characteristics of hydrocarbon sources rock deals with two aspects：the first is the recognition of indigenous characteristics of organic matter so as to distinguish sources rock and reservoir and then determine the effective sources rock.The second is the recognition of indigenous characteristics of geochemical parameters and firsthand information so as to choose them which could really reflect the characteristics of sources rock. The carbonate rock has the dual propertes of source rock and reservoir,and the later alteration and tectonic action could make it become reservoir,especially the tectoclass or microcracks usually being the migration route or the detained space of bitumen,this phenomenon is widely distributed in the high-over mature carbonate source rock ,such as Sichuan Basin,Tarim Basin and Eerduosi Basin.The existence of migration bitumen will result in three kinds of influence on the evaluation of capability of hydrocarbons generation of organic matter in carbonate rock：First,the content of organic matter tends to be high.Second,maturation of organic matter is difficult to be determined and evaluated.In addition,it is difficult to determine the type and quality of organic matter.Therefore,the recognition of indigenous characteristics of organic matter in carbonate rock is the basis and prerequisite of all the geochemical research. On the whole,all the existed methods studying the indigenous characteristics of source rock lay particular emphasis on theory.Hence,this paper begins with rock type information as well as common used the pyrolysis data.Based on the pyrolysis principle and hydrocarbon generation theory,this paper established a series of measures that simply and practically determine the indigenous characteristics of organic matter in the carbonate source rock 1.Recognition of rock type：The carbonate source rocks usually exist in low energy environment.Due to water body being relatively quite.the rock is fine and close,mud content is high,colour is relatively dark and the rock is relatively rich in organic matter.For the water body is turbulent,the rock grain is coarse, mud content is low,the rock is relatively poor in organic matter,and the rock type is dominated by coarse-grain carbonate rock.This kind of carbonate rock could be used as reservoir but non-source rock,whose geochemical analyticd data should be removed. 2.Rock pyrolysis parameter：On the basis of pyrolysis principle and parameter,taking Ordos Basin as an example,the authors observe and measure a great deal of pyrolysis data.It is discovered that the abnormal samples whose pyrolysed hydrocarbons S2 is not proportional with the content of organic carbon resulted from filled migration bitumen and solid bitumen.They leads to high content of organic carbon and very low pyrolysed hydrocarbons S2,which is typical features of non-indigenous source rock. Thus,ws could appraise the indigenous characteristics of organic matter in source rock and geochemical parameters by the means of combining rock type with primary pyrolysis data. Though this method might be affected by organic matter type,its practical; effect is good in these areas widely coverde by marine carbonate rock.
The indigenous characteristcs of organic matter in carbonate hydrocarbon source rock directly influences the precise evaluation of its hydrocarbon generation capability especially on marine carbonate rock with low organic matter abundance and high thermal evolution.The paper discusses that migration bitumen distribute widely in carbonate hydrocarbon source rock,meanwhile,all methods to distionguish primary or secondary organic matter in rocks are introduced in this paper.Finally,a series of measures to determine indigenous characteristics of organic matter carbonate source rock are proposed on the basis of the analyses of carbonate source rock of Lower Paleozoic in Ordos Basin. The so-called recognition of indigenous characteristics of hydrocarbon sources rock deals with two aspects：the first is the recognition of indigenous characteristics of organic matter so as to distinguish sources rock and reservoir and then determine the effective sources rock.The second is the recognition of indigenous characteristics of geochemical parameters and firsthand information so as to choose them which could really reflect the characteristics of sources rock. The carbonate rock has the dual propertes of source rock and reservoir,and the later alteration and tectonic action could make it become reservoir,especially the tectoclass or microcracks usually being the migration route or the detained space of bitumen,this phenomenon is widely distributed in the high-over mature carbonate source rock ,such as Sichuan Basin,Tarim Basin and Eerduosi Basin.The existence of migration bitumen will result in three kinds of influence on the evaluation of capability of hydrocarbons generation of organic matter in carbonate rock：First,the content of organic matter tends to be high.Second,maturation of organic matter is difficult to be determined and evaluated.In addition,it is difficult to determine the type and quality of organic matter.Therefore,the recognition of indigenous characteristics of organic matter in carbonate rock is the basis and prerequisite of all the geochemical research. On the whole,all the existed methods studying the indigenous characteristics of source rock lay particular emphasis on theory.Hence,this paper begins with rock type information as well as common used the pyrolysis data.Based on the pyrolysis principle and hydrocarbon generation theory,this paper established a series of measures that simply and practically determine the indigenous characteristics of organic matter in the carbonate source rock 1.Recognition of rock type：The carbonate source rocks usually exist in low energy environment.Due to water body being relatively quite.the rock is fine and close,mud content is high,colour is relatively dark and the rock is relatively rich in organic matter.For the water body is turbulent,the rock grain is coarse, mud content is low,the rock is relatively poor in organic matter,and the rock type is dominated by coarse-grain carbonate rock.This kind of carbonate rock could be used as reservoir but non-source rock,whose geochemical analyticd data should be removed. 2.Rock pyrolysis parameter：On the basis of pyrolysis principle and parameter,taking Ordos Basin as an example,the authors observe and measure a great deal of pyrolysis data.It is discovered that the abnormal samples whose pyrolysed hydrocarbons S2 is not proportional with the content of organic carbon resulted from filled migration bitumen and solid bitumen.They leads to high content of organic carbon and very low pyrolysed hydrocarbons S2,which is typical features of non-indigenous source rock. Thus,ws could appraise the indigenous characteristics of organic matter in source rock and geochemical parameters by the means of combining rock type with primary pyrolysis data. Though this method might be affected by organic matter type,its practical; effect is good in these areas widely coverde by marine carbonate rock.
2000, 18(1): 157-161.
Abstract:
Based on the study of factors influencing the dissolution ability of gas in formation water, this paper analyses the geological conditions for gas to release from water,and points out that the decrease of temperature and pressure, increase of mineralization degree are the main causes to bring out the release of gas from water. Based on this cognition and using the relation among the amount of gas dissolved in water,and temperature and pressure conditions,the paper establishes a calculation method to study the amount of gas released from water.By analysing the losing of gas released from water on the way of migration due to diffusion and adsorption,the paper has put forward the concept of effective amount of gas released from water ,and established a research method , finally applied it in Alaxin and Erzhan gas fields in the north part of Songliao Basin.Through study on the effective amount of gas released from water of the first member of Nenjiang Formation in Qijia-Gulong Sag, it can be seen that the amount is about 8.60×108m3, which is about 18.64% of geological reserves in two gas fields ,indicating that the gas released from water is the important part for gas to accumulate and form gas pool.
Based on the study of factors influencing the dissolution ability of gas in formation water, this paper analyses the geological conditions for gas to release from water,and points out that the decrease of temperature and pressure, increase of mineralization degree are the main causes to bring out the release of gas from water. Based on this cognition and using the relation among the amount of gas dissolved in water,and temperature and pressure conditions,the paper establishes a calculation method to study the amount of gas released from water.By analysing the losing of gas released from water on the way of migration due to diffusion and adsorption,the paper has put forward the concept of effective amount of gas released from water ,and established a research method , finally applied it in Alaxin and Erzhan gas fields in the north part of Songliao Basin.Through study on the effective amount of gas released from water of the first member of Nenjiang Formation in Qijia-Gulong Sag, it can be seen that the amount is about 8.60×108m3, which is about 18.64% of geological reserves in two gas fields ,indicating that the gas released from water is the important part for gas to accumulate and form gas pool.
2000, 18(1): 7-12.
Abstract:
On the delta during Yellow River in zero,there developed a great number of slump structures,which might be formed near the edge of point bar and channel bar or in the channel developed whithin the point bar or channel bar,as well as in the river course.Slump may result in three products:one is slump wall and/or slump crack;the second is slump body,and the third is slump deformation basement.The slump wall and/or slump crack could be divided into two types according to the dynamic mechanics：one is of extension and the other of shearing.They has different sizes:the largest has more than ten meters in length and the smaller is not beyond three to five centimeters in length.The slump body is also defferent in sizes,and the largest may have one meter high and two or three meters long.and the smaller is a few centimeters in height and length.The observation indicates that the slump has been caused by wave and/or runing water washing and not by earthquake and/or sliding on slope. Interrupting of the Yellow River flow results in forming small ‘lake'in some lower courses and the water in the ‘lake'is blown by wind to forming wave.The wave-washing causes the wall of point bar and channel bar collapse,forming a series of slump structures.Interrupting of the Yellow River flow,meanwhile,makes almost all the point bar and channel bar exposed wholly and the rainfall in Yellow River delta is concentrated to form small runoff in the bar surface,which scours walls of the bar,resulting in forming a series of slump structures.Some of slump structures are buried by wind-induced sand and easily preserved,and the wind-induced sand filling in the slump fissures will become sand walls by diagenesis.
On the delta during Yellow River in zero,there developed a great number of slump structures,which might be formed near the edge of point bar and channel bar or in the channel developed whithin the point bar or channel bar,as well as in the river course.Slump may result in three products:one is slump wall and/or slump crack;the second is slump body,and the third is slump deformation basement.The slump wall and/or slump crack could be divided into two types according to the dynamic mechanics：one is of extension and the other of shearing.They has different sizes:the largest has more than ten meters in length and the smaller is not beyond three to five centimeters in length.The slump body is also defferent in sizes,and the largest may have one meter high and two or three meters long.and the smaller is a few centimeters in height and length.The observation indicates that the slump has been caused by wave and/or runing water washing and not by earthquake and/or sliding on slope. Interrupting of the Yellow River flow results in forming small ‘lake'in some lower courses and the water in the ‘lake'is blown by wind to forming wave.The wave-washing causes the wall of point bar and channel bar collapse,forming a series of slump structures.Interrupting of the Yellow River flow,meanwhile,makes almost all the point bar and channel bar exposed wholly and the rainfall in Yellow River delta is concentrated to form small runoff in the bar surface,which scours walls of the bar,resulting in forming a series of slump structures.Some of slump structures are buried by wind-induced sand and easily preserved,and the wind-induced sand filling in the slump fissures will become sand walls by diagenesis.
2000, 18(1): 18-21.
Abstract:
The stufy of loess-paleosol sequence reveals the magnetic susceptibility is of indexical significance in identifying loess-paleosol and their progression in the loess section,but also in simulating the changes of paleoenvironment.The magnetic susceptibility is also of indexical significance to Xiashu loess.Therefore,we gathered 595 sample blocks for the study in Zhenjiang Dagang section,which is located in the lower reaches of the Changjiang River. On the basis of systematic testing,we obtain a magnetic susceptibility curve of Dagang section.Compared with the other Xiashu Loess sections in this area,the magnetic suscreptibility curve of Xiashu Loess indicates that the loess-paleosol sequence of Dagang section represented 7 large climatic cycles since the Middle-Pleistocene.It is similar to that disclosed from the other Xiashu sections and the loess-paleosol sequence in north China,reflecting that the middle and lower Changjiang River regions have undergone the same course of the paleoclimate changes in the north China since the Middle-Pleistocene.Comparative study also demonstrates that the extent of the paleoclimate changes is much smaller than that in the loess area in north China.There are frequently minor undulations of climate in both the warm period and the cold period,comparable to the δ18O stage of deep sea.The study also found the sedimentation rate and the depositional environment of Xiashu Loess varied in different area in the middle and lower Changjiang River region. The study of the magnetic susceptibility curve indicates there were a small quantites of aeolian accumulation in the interglacial warm period. S1 and S2 in the magnetic susceptibility curve of Dagang section can be divided into S1a, S1b, S1c and S2a, S2b, S2c respectively. S1a, S1b and S1c of S1 correspond to 5a,5b and 5c of the δ18O stage of deep sea,supporting that the climate changes of the middle and lower Changjian River region are largely affected by the ocean. Climate changes of the middle and lower Changjiang River region are quite sensitive to global changes.
The stufy of loess-paleosol sequence reveals the magnetic susceptibility is of indexical significance in identifying loess-paleosol and their progression in the loess section,but also in simulating the changes of paleoenvironment.The magnetic susceptibility is also of indexical significance to Xiashu loess.Therefore,we gathered 595 sample blocks for the study in Zhenjiang Dagang section,which is located in the lower reaches of the Changjiang River. On the basis of systematic testing,we obtain a magnetic susceptibility curve of Dagang section.Compared with the other Xiashu Loess sections in this area,the magnetic suscreptibility curve of Xiashu Loess indicates that the loess-paleosol sequence of Dagang section represented 7 large climatic cycles since the Middle-Pleistocene.It is similar to that disclosed from the other Xiashu sections and the loess-paleosol sequence in north China,reflecting that the middle and lower Changjiang River regions have undergone the same course of the paleoclimate changes in the north China since the Middle-Pleistocene.Comparative study also demonstrates that the extent of the paleoclimate changes is much smaller than that in the loess area in north China.There are frequently minor undulations of climate in both the warm period and the cold period,comparable to the δ18O stage of deep sea.The study also found the sedimentation rate and the depositional environment of Xiashu Loess varied in different area in the middle and lower Changjiang River region. The study of the magnetic susceptibility curve indicates there were a small quantites of aeolian accumulation in the interglacial warm period. S1 and S2 in the magnetic susceptibility curve of Dagang section can be divided into S1a, S1b, S1c and S2a, S2b, S2c respectively. S1a, S1b and S1c of S1 correspond to 5a,5b and 5c of the δ18O stage of deep sea,supporting that the climate changes of the middle and lower Changjian River region are largely affected by the ocean. Climate changes of the middle and lower Changjiang River region are quite sensitive to global changes.
2000, 18(1): 29-35.
Abstract:
In the research of many geological problems about weathered eluvial zone, the conten theory is widely adpoted, which is based on content of chemical composition. Although the content is very important to resolve lots of geological problems, this theory is not perfect because the content of chemical composition is easily effected by the weathering process. In order to remedy the defect of traditional content theory and reveal the law of nature, it is necessary to establish anew theory. During the investigation of paleosol and weathered eluvial zone in the Loess Plateau, the author found unsuccessive illuviation, thick layer or multi-layer illuviation of CaCO3 and other chemical composition-a special geological phenomenon. In the paper, the author established a new theory on depth of CaCO3 illuvial horizon of weathered zone combining with CaCO3 content analysis and penetrating experiment, this theory is very effetive to study paleosol, weathering crust, paleoenvironment and many geological problems of weachered eluvial zone. The theory reveals that the more precipitation is, the bigger the movement depth of CaCO3 illuvial horizon is, though the eluvial process is very short; the less the precipitation is, the shallower the movement depth of CaCO3 illurial horizon is, though eluvial process is very long. Because the process in which CaCO3 moves to the illuvial horizon is very short, the influence of time could be neglected. So the moved depth of CaCO3 illuvial horizon is reliable basis for studying many geological problems about weathered eluvial zone. Since CaCO3 belongs to dissoluble salt, the illuviation process of the salts such as NaCl, CaSO4, which are more dissoluble than CaCO3, is much shorter, and the illuvial theory on the depth of CaCO3 can be applied to them. The movement of colloid material such as Fe2O3 and Al2O3 is influenced clearly by time factor, however, as long as their illuvial horizons form, that is to say, the process needed in which they move to the illuvial horizon have been met. So their illuvial depth can also be regarded as areliable foundation for studying the geological problem of weathered eluvial zone. There are three reasons why the movement time of CaCO3 to illuvial depth is very short. The first is that CaCO3 can move under the condition of basicity. Movement and illuviation can occure in the early period of soil-forming processes. The second is that a part of CaCO3 comes from precipitation and CaCO3 can illuviate at the bottom of soil as long as eluvial occurs. The third is that CaCO3 exists in the form of Ca2+and HCO-3 in the water. The two ions will follow the penetrating water whereever it goes. According to the quantitative correlation (y=305x+168.5) between mean annual precipitation (y) and depth of CaCO3 illuvial horizon(x), the mean annual precipitation in the developmental period of paleosol and weathering crust can be calculated quantitatively and provides a basis for determining the formula on precipitation of rainy season. The author can draw three deductions in accordance with the illuvial theory on depth of CaCO3 and the types of CaCO3 illuvial horizon. Deduction 1：when movement depth of CaCO3 illuvial horizon exceeds the thickness of clay-grouting layer of soil, it can be seen that the soil is the neutral or acid soil of leaching type. Deduetion 2： When moved depth of CaCO3 illuvial horizon exceeds the thickness of developing zone of soil (about 2 m) , it can be determined that the soil is changing to weathering crust. Deduction 3： when two, three layers or unusually thick CaCO3 illuvial horizon exists under the same paleosol or weathering profile, it indicates that there are two or more soil-forming periods and corresponding climate change at that time.
In the research of many geological problems about weathered eluvial zone, the conten theory is widely adpoted, which is based on content of chemical composition. Although the content is very important to resolve lots of geological problems, this theory is not perfect because the content of chemical composition is easily effected by the weathering process. In order to remedy the defect of traditional content theory and reveal the law of nature, it is necessary to establish anew theory. During the investigation of paleosol and weathered eluvial zone in the Loess Plateau, the author found unsuccessive illuviation, thick layer or multi-layer illuviation of CaCO3 and other chemical composition-a special geological phenomenon. In the paper, the author established a new theory on depth of CaCO3 illuvial horizon of weathered zone combining with CaCO3 content analysis and penetrating experiment, this theory is very effetive to study paleosol, weathering crust, paleoenvironment and many geological problems of weachered eluvial zone. The theory reveals that the more precipitation is, the bigger the movement depth of CaCO3 illuvial horizon is, though the eluvial process is very short; the less the precipitation is, the shallower the movement depth of CaCO3 illurial horizon is, though eluvial process is very long. Because the process in which CaCO3 moves to the illuvial horizon is very short, the influence of time could be neglected. So the moved depth of CaCO3 illuvial horizon is reliable basis for studying many geological problems about weathered eluvial zone. Since CaCO3 belongs to dissoluble salt, the illuviation process of the salts such as NaCl, CaSO4, which are more dissoluble than CaCO3, is much shorter, and the illuvial theory on the depth of CaCO3 can be applied to them. The movement of colloid material such as Fe2O3 and Al2O3 is influenced clearly by time factor, however, as long as their illuvial horizons form, that is to say, the process needed in which they move to the illuvial horizon have been met. So their illuvial depth can also be regarded as areliable foundation for studying the geological problem of weathered eluvial zone. There are three reasons why the movement time of CaCO3 to illuvial depth is very short. The first is that CaCO3 can move under the condition of basicity. Movement and illuviation can occure in the early period of soil-forming processes. The second is that a part of CaCO3 comes from precipitation and CaCO3 can illuviate at the bottom of soil as long as eluvial occurs. The third is that CaCO3 exists in the form of Ca2+and HCO-3 in the water. The two ions will follow the penetrating water whereever it goes. According to the quantitative correlation (y=305x+168.5) between mean annual precipitation (y) and depth of CaCO3 illuvial horizon(x), the mean annual precipitation in the developmental period of paleosol and weathering crust can be calculated quantitatively and provides a basis for determining the formula on precipitation of rainy season. The author can draw three deductions in accordance with the illuvial theory on depth of CaCO3 and the types of CaCO3 illuvial horizon. Deduction 1：when movement depth of CaCO3 illuvial horizon exceeds the thickness of clay-grouting layer of soil, it can be seen that the soil is the neutral or acid soil of leaching type. Deduetion 2： When moved depth of CaCO3 illuvial horizon exceeds the thickness of developing zone of soil (about 2 m) , it can be determined that the soil is changing to weathering crust. Deduction 3： when two, three layers or unusually thick CaCO3 illuvial horizon exists under the same paleosol or weathering profile, it indicates that there are two or more soil-forming periods and corresponding climate change at that time.
2000, 18(1): 43-49.
Abstract:
Different types of meter-scale cyclic sequences in stratigraphical records are the outcomes of episodic accumulation of strata related to Milankovitch cycles. They are marked by particular features of facies-successions resulted from different sediment source and sedimentary dynamics in different paleogeographic background, which become the fundmental rule on the division of meter-scale cyclic sequences. The widespread development in stratigraphic records and the regularly vertical stacking-patterns in long-term sequence, the evolution characters of earth-history and the genetic types reflected by particular fabric features of facies-succession in different paleogeography background, all of these features shows that meter-scale cyclic sequences are not only the fundmental working-unit on stratigraphy and sedimentology but also the replenish and extention of parasequence in sequence stratigraphy.There are generally two kinds of facies-succession for meter-scale cyclic sequcence in neretic-facies strata of carbonates as well as clastic rock, which are normal grading succession mainly formed by tidal sedimentation and inverse grading succession mainly made by wave sedimentation, both of them constitutes generally upward shallowing succession, the thickness of succession is from several tens centimeters to several meters. In terms of fabric features of facies-succession,it can be made the division of genetic types for meter-scale cyclic sequences. Carbonate meter-scale cyclic sequences could be divided into four types,which are L-M type, deep-water asymmetrical type, subtidal type and peritidal type. Clastic meter-scale cyclic sequences could be divided into two types, which are tidal-dynamictype and wave-dynamic type. The boundaries of meter-scale cyclic sequence are marked by instantaneous punctuated surface formed by non-deposition resulted from high-frequence sea-level changes, which include instantaneous exposed punctuated surface and drowned punatuated surface as well as their correlative surface. The development of instantaneous punctuated surface used as the boundary of meter-scale cyclic sequence lead to the limiting of Walthers Law that is used to explain facies distribution in time and space, and reaffirm the importance of Sander's Rule on analysis of stratigraphical records. These noncontinue surfaces could be traced in long distance and some be correlative in same basin range. The study on meter-scale cyclic sequences and their regularly vertical stacking patterns in long-term sequence indicate that the research on cyclicity of stratigraphic records is a useful way to get more regularity from stratigraphic records that are frequently complex as well as non-integratd.
Different types of meter-scale cyclic sequences in stratigraphical records are the outcomes of episodic accumulation of strata related to Milankovitch cycles. They are marked by particular features of facies-successions resulted from different sediment source and sedimentary dynamics in different paleogeographic background, which become the fundmental rule on the division of meter-scale cyclic sequences. The widespread development in stratigraphic records and the regularly vertical stacking-patterns in long-term sequence, the evolution characters of earth-history and the genetic types reflected by particular fabric features of facies-succession in different paleogeography background, all of these features shows that meter-scale cyclic sequences are not only the fundmental working-unit on stratigraphy and sedimentology but also the replenish and extention of parasequence in sequence stratigraphy.There are generally two kinds of facies-succession for meter-scale cyclic sequcence in neretic-facies strata of carbonates as well as clastic rock, which are normal grading succession mainly formed by tidal sedimentation and inverse grading succession mainly made by wave sedimentation, both of them constitutes generally upward shallowing succession, the thickness of succession is from several tens centimeters to several meters. In terms of fabric features of facies-succession,it can be made the division of genetic types for meter-scale cyclic sequences. Carbonate meter-scale cyclic sequences could be divided into four types,which are L-M type, deep-water asymmetrical type, subtidal type and peritidal type. Clastic meter-scale cyclic sequences could be divided into two types, which are tidal-dynamictype and wave-dynamic type. The boundaries of meter-scale cyclic sequence are marked by instantaneous punctuated surface formed by non-deposition resulted from high-frequence sea-level changes, which include instantaneous exposed punctuated surface and drowned punatuated surface as well as their correlative surface. The development of instantaneous punctuated surface used as the boundary of meter-scale cyclic sequence lead to the limiting of Walthers Law that is used to explain facies distribution in time and space, and reaffirm the importance of Sander's Rule on analysis of stratigraphical records. These noncontinue surfaces could be traced in long distance and some be correlative in same basin range. The study on meter-scale cyclic sequences and their regularly vertical stacking patterns in long-term sequence indicate that the research on cyclicity of stratigraphic records is a useful way to get more regularity from stratigraphic records that are frequently complex as well as non-integratd.
2000, 18(1): 57-62.
Abstract:
A sedimentary organic facies is defined as a stratigraphic unit, in which there are the similar characteristics of depositional environment, biological assemblage, diagenetic environment, reduction-oxidation condition, and the genetic type of organic matter. As the distribution of sedimentary organic facies is controlled by sequence stratigraphic framework in sedimentary basin, sequence sedimentary organic facies analysis can become a very useful tool to determine and predict the distribution of source rocks. Based on the analysis of sequence stratigraphy and sedimentary organic facies, Majiagou Formation of Lower Ordovician in Ordos basin is divided into three sequences and the distribution of sedimentary organic facies in each sequence is discussed in this paper. The results indicate that the distribution of sedimentary organic facies in sequence stratigraphic framework of Majiagou Formation present a certain regularity. In the western and southern part of the basin, the sedimentary organic facies of deeper- water sequence are mainly composed of open platform C facies from bottom to top, in which the content of organic carbon is 0.08% ～ 0.18 %. In the middle of the basin, the sedimentary organic facies of transgressive system tract of shallow- water sequence are mainly composed of open platform C facies and restricted platform D facies, in which the content of organic carbon is 0.12% ～ 0.25 %, whereas the sedimentary organic facies of highstand system tract are composed of restricted platform D facies and evaporation platform E facies, in which the content of organic carbon is 0.17% ～ 0.49 %.The best source rocks are mostly distributed over highstand system tract of shallow- water sequence in the middle of the basin
A sedimentary organic facies is defined as a stratigraphic unit, in which there are the similar characteristics of depositional environment, biological assemblage, diagenetic environment, reduction-oxidation condition, and the genetic type of organic matter. As the distribution of sedimentary organic facies is controlled by sequence stratigraphic framework in sedimentary basin, sequence sedimentary organic facies analysis can become a very useful tool to determine and predict the distribution of source rocks. Based on the analysis of sequence stratigraphy and sedimentary organic facies, Majiagou Formation of Lower Ordovician in Ordos basin is divided into three sequences and the distribution of sedimentary organic facies in each sequence is discussed in this paper. The results indicate that the distribution of sedimentary organic facies in sequence stratigraphic framework of Majiagou Formation present a certain regularity. In the western and southern part of the basin, the sedimentary organic facies of deeper- water sequence are mainly composed of open platform C facies from bottom to top, in which the content of organic carbon is 0.08% ～ 0.18 %. In the middle of the basin, the sedimentary organic facies of transgressive system tract of shallow- water sequence are mainly composed of open platform C facies and restricted platform D facies, in which the content of organic carbon is 0.12% ～ 0.25 %, whereas the sedimentary organic facies of highstand system tract are composed of restricted platform D facies and evaporation platform E facies, in which the content of organic carbon is 0.17% ～ 0.49 %.The best source rocks are mostly distributed over highstand system tract of shallow- water sequence in the middle of the basin
2000, 18(1): 68-72.
Abstract:
The Qilang Formation of Middle Ordovician in northwest Tarim basin is composed of laminae marl and laminae limestone with abundance graptolites and trilobites.This kind of marl and limestone thin alternation is typical L-M (limestone-marl) cycle.There are about thirty beds of distal calcareous tempestites in Middle-Upper Qilang Formation.In the plane and bottom of the tempestites ten trace fossils were found and they are： Belorhape, Circulichnus, Dendrichnus,Gordia, Granularia,Megagrapton,Phycodes,Planolites,Protopaleodictyon and Rhabdoglyphas. Because of abundance of Phycodes and Magagrapton,these trace fossils can be named Phycodes-Magagrapton assemblage which are predominant in fodinichnia and shape of ramification,and belong to Zoophycos ichnofacies proposed by Seilacher.This assemblage represent quiet lower energy sedimentary environments under main storm wave level.Based on the fact that event deposition has close relation to the trace fossils,it is believed that Phycodes-Megagrapton assemblage can be a fine auxiliary marker to judge distal tempestite and to differentiate the e vent and normal limestone.
The Qilang Formation of Middle Ordovician in northwest Tarim basin is composed of laminae marl and laminae limestone with abundance graptolites and trilobites.This kind of marl and limestone thin alternation is typical L-M (limestone-marl) cycle.There are about thirty beds of distal calcareous tempestites in Middle-Upper Qilang Formation.In the plane and bottom of the tempestites ten trace fossils were found and they are： Belorhape, Circulichnus, Dendrichnus,Gordia, Granularia,Megagrapton,Phycodes,Planolites,Protopaleodictyon and Rhabdoglyphas. Because of abundance of Phycodes and Magagrapton,these trace fossils can be named Phycodes-Magagrapton assemblage which are predominant in fodinichnia and shape of ramification,and belong to Zoophycos ichnofacies proposed by Seilacher.This assemblage represent quiet lower energy sedimentary environments under main storm wave level.Based on the fact that event deposition has close relation to the trace fossils,it is believed that Phycodes-Megagrapton assemblage can be a fine auxiliary marker to judge distal tempestite and to differentiate the e vent and normal limestone.
2000, 18(1): 80-88.
Abstract:
One hundred sixty-three species of fossil spores and pollen referred to 83 genera extracted from 44 crude oil samples collected from the Tarim Basin were recorded. Based on the investigations of the characteristics of the petroleum sporo-pollen assemblages, the geological ages and formations of the petroleum source rocks of the North Tarim, Kuqa, Kashi, and Yecheng petroliferous regions were discussed. According to the colors of spore and pollen fossils, the organic thermal maturity of the petroleum source rocks of the mentioned petroliferous regions was identified. The results of this study indicate that the Carboniferous, the Triassic, and the Jurassic petroleum source rocks all belong to mature phase of liquid petroleum generation. In addition, the method used to extract fossil spores, pollen, and algae from crude oils was introduced in detail in this paper.
One hundred sixty-three species of fossil spores and pollen referred to 83 genera extracted from 44 crude oil samples collected from the Tarim Basin were recorded. Based on the investigations of the characteristics of the petroleum sporo-pollen assemblages, the geological ages and formations of the petroleum source rocks of the North Tarim, Kuqa, Kashi, and Yecheng petroliferous regions were discussed. According to the colors of spore and pollen fossils, the organic thermal maturity of the petroleum source rocks of the mentioned petroliferous regions was identified. The results of this study indicate that the Carboniferous, the Triassic, and the Jurassic petroleum source rocks all belong to mature phase of liquid petroleum generation. In addition, the method used to extract fossil spores, pollen, and algae from crude oils was introduced in detail in this paper.
2000, 18(1): 95-99.
Abstract:
Fan-shaped depositional bodies are those mainly composed of terrigenous coarse deposits and fan-shaped in morphology, including alluvial fan, fan delta, delta and subaqueous fan and so on. They are important exoil-gas targets in oil and gas-bearing basins in Mesozoic and Cenozoic interior and offshore in China, which are the problems deeply concerned with by oil-gas exploration department to show quantitatively the features of their morphological distribution and inner structure parameters. Recent researches on fan-shaped bodies are results combining static, qualitative and megascopic methods with dynamic, quantitative and microscopic approaches. Great efforts were made in quantitative modeling and in simulating of structural parameters of sedimentary bodies, but there have been still few of published documents about how to build morphological and simulating models of sedimentary bodies up to now. With fractal theory applied widely to sedimentology , it may be considered from a new point of view to solve the problems. The growing of fan-shaped depositional bodies is a complex nonlinear dynamics process and a fractal. Fractal dimension may reflect the complexity of their outer morphology and inner structure, and predict some information about tectonic and depositional setting. It will be one of the most important ways to realize nonlinear dynamics building models and simulation of depositional bodies combined fractal with chaos theory. On the bases of analyses of sedimentological features of more than twenty faulted basins at home and abroad, the paper probes the growing dynamic process of fan-shaped depositional bodies, summarizes their fractal features, and establishes the model of shape fractal growing and structural fractal. The structural fractal box dimensions are determined. Simulations of morphologies of the fan-shaped bodies are made by fractal, and of their structures by fractal-Kringing. The main conclusions are as follows： 1.Fan-shaped sedimentary bodies are complex nonlinear systems. Their forming processes are both a depositional dynamics of growing, crevassing, abandoning and a complex stochastic, nonlinear dynamics. Crevasses can be viewed as a kind of bifurcation and fluctuation; the choice of branches and the interaction of the fluctuation quantities are the important causes to form the complex and various morphological features and inner structures of fan-shaped bodies. 2.The box dimension of morphology fractal of a fan-shaped body is generally 1.1-1.4, that of structure fractal is generally 1.25-1.45. 3.The different box dimensions show different tectonic and depositional setting. Fractal dimensions represents the structural anisotropism of sedimentary bodies. 4.Fractal-Kriging proves to be useful method for modeling morphology and inner structures of sedimentary bodies, it can better reveal the local features and anisotropic change in the bodies by adjusting fractal dimension D, horizontal and vertical range.
Fan-shaped depositional bodies are those mainly composed of terrigenous coarse deposits and fan-shaped in morphology, including alluvial fan, fan delta, delta and subaqueous fan and so on. They are important exoil-gas targets in oil and gas-bearing basins in Mesozoic and Cenozoic interior and offshore in China, which are the problems deeply concerned with by oil-gas exploration department to show quantitatively the features of their morphological distribution and inner structure parameters. Recent researches on fan-shaped bodies are results combining static, qualitative and megascopic methods with dynamic, quantitative and microscopic approaches. Great efforts were made in quantitative modeling and in simulating of structural parameters of sedimentary bodies, but there have been still few of published documents about how to build morphological and simulating models of sedimentary bodies up to now. With fractal theory applied widely to sedimentology , it may be considered from a new point of view to solve the problems. The growing of fan-shaped depositional bodies is a complex nonlinear dynamics process and a fractal. Fractal dimension may reflect the complexity of their outer morphology and inner structure, and predict some information about tectonic and depositional setting. It will be one of the most important ways to realize nonlinear dynamics building models and simulation of depositional bodies combined fractal with chaos theory. On the bases of analyses of sedimentological features of more than twenty faulted basins at home and abroad, the paper probes the growing dynamic process of fan-shaped depositional bodies, summarizes their fractal features, and establishes the model of shape fractal growing and structural fractal. The structural fractal box dimensions are determined. Simulations of morphologies of the fan-shaped bodies are made by fractal, and of their structures by fractal-Kringing. The main conclusions are as follows： 1.Fan-shaped sedimentary bodies are complex nonlinear systems. Their forming processes are both a depositional dynamics of growing, crevassing, abandoning and a complex stochastic, nonlinear dynamics. Crevasses can be viewed as a kind of bifurcation and fluctuation; the choice of branches and the interaction of the fluctuation quantities are the important causes to form the complex and various morphological features and inner structures of fan-shaped bodies. 2.The box dimension of morphology fractal of a fan-shaped body is generally 1.1-1.4, that of structure fractal is generally 1.25-1.45. 3.The different box dimensions show different tectonic and depositional setting. Fractal dimensions represents the structural anisotropism of sedimentary bodies. 4.Fractal-Kriging proves to be useful method for modeling morphology and inner structures of sedimentary bodies, it can better reveal the local features and anisotropic change in the bodies by adjusting fractal dimension D, horizontal and vertical range.
2000, 18(1): 114-118.
Abstract:
There were cyclothems consisted of evaporite rocks,deep color mudstones or shales and deep water turbidity sediments of Peleogene Sha-4 member in Dongying sag,which was salt lake sedimentary assemblage with more than 1000m in thickness.The evaporite rocks consisted of halite and anhydrite rocks mainly existed in north and centre of Dongying sag where the deep fractures developed.The fossil assemblage indicated that the climate was semi-dry and semi-moist in Paleogene Sha-4 member in Dongying sag.Analyzed the sedimentary characteristics and depositional conditions,the authors considered that the brine in deep water was the substance basis of the salt sediment,the salt in deep strata was the source of brine and the deep fractures in the north of the sag were the paths where the salt substance entered the developing sag.The deep water genesis model of salt lake in Dongpu sag which can be compared with that of Lake Kivu,was put forward after the discussion.The new field in subsalt strata exploration can be found on the basis of the lithofacies assemblage of source rock and evaporite rock.
There were cyclothems consisted of evaporite rocks,deep color mudstones or shales and deep water turbidity sediments of Peleogene Sha-4 member in Dongying sag,which was salt lake sedimentary assemblage with more than 1000m in thickness.The evaporite rocks consisted of halite and anhydrite rocks mainly existed in north and centre of Dongying sag where the deep fractures developed.The fossil assemblage indicated that the climate was semi-dry and semi-moist in Paleogene Sha-4 member in Dongying sag.Analyzed the sedimentary characteristics and depositional conditions,the authors considered that the brine in deep water was the substance basis of the salt sediment,the salt in deep strata was the source of brine and the deep fractures in the north of the sag were the paths where the salt substance entered the developing sag.The deep water genesis model of salt lake in Dongpu sag which can be compared with that of Lake Kivu,was put forward after the discussion.The new field in subsalt strata exploration can be found on the basis of the lithofacies assemblage of source rock and evaporite rock.
2000, 18(1): 127-132.
Abstract:
Based on the analysis of compression pore evolution, fracture, mineral component and the study of effect of diagenesis stages on reservoirs, the physical base of effects of diagenesis stages on reservoirs is discussed by applying well logging information. These results indicate that the effect of diagenetic stages on reservoirs are available by means of well log information. The method include as fellows：(1) In Early diagenesis stage, the porosity and lithology well logging data are applied to analysis compression curve, and to determine the compression area. (2) In Middle diagenetic stage, first, it is used to analysis the secondary pores by means of acoustic porosity and density-neutron porosity. The crossplot technique is used to determine mineral component and the types of cementation and replacement. The mud content is able to be determined by means of mud indication log. The clay mineral can be studied by using the gamma spectrometry, special thorium, and potassium content. (3) In the late diagenetic stage, the distributions of secondary pore, fracture, grain component, grain content and clay mineral can be researched by logging. The above methods are tested in Th-Ha basin and show an ideal effect.
Based on the analysis of compression pore evolution, fracture, mineral component and the study of effect of diagenesis stages on reservoirs, the physical base of effects of diagenesis stages on reservoirs is discussed by applying well logging information. These results indicate that the effect of diagenetic stages on reservoirs are available by means of well log information. The method include as fellows：(1) In Early diagenesis stage, the porosity and lithology well logging data are applied to analysis compression curve, and to determine the compression area. (2) In Middle diagenetic stage, first, it is used to analysis the secondary pores by means of acoustic porosity and density-neutron porosity. The crossplot technique is used to determine mineral component and the types of cementation and replacement. The mud content is able to be determined by means of mud indication log. The clay mineral can be studied by using the gamma spectrometry, special thorium, and potassium content. (3) In the late diagenetic stage, the distributions of secondary pore, fracture, grain component, grain content and clay mineral can be researched by logging. The above methods are tested in Th-Ha basin and show an ideal effect.
2000, 18(1): 139-145.
Abstract:
The physical and chemical nature of petroleum changes with source rock and maturity,although the feature of oil and gas can also be influenced by local biodegadration or water washing.During the process of reservoir filling,some polar compound in crude oils,such as carbazoles which can interact relatively strongly with water,rock minerals and each other,and thus induce hetrogenous petroleum. Meanwhile, heterogenous migration pathways also influence the characteristics of oils. In the paper,authors discuss in detail the chemical nature of oil samples,which come from six oil fields in Jiuxi Basin.Among twelve oil samples,except one sample's carbon isotope(δ13Coil‰) of the whole liquid hydrocarbon (crude oil) is -30.5‰,the other's is about -31‰,whose absolute error is less than 0.2‰. Distillation mode of carbon isotope of N-alkane element series is also similar to each other.Based on GC and GC-MS analysis,seventeen conventional geochemical parameters are selected to calculate correlation coefficients between twelve oil samples,correlation coefficients of all samples are more than 0.86,most of them is up to 0.96.All of these parameters show that twelve oil samples come from the same source rock. Two star diagrams (multivariable plots in polar coordinates) have been developed to assess subtle chemical differences among oils.The diagrams are based on analysis of C7 hydrocarbon of crude oils separated by gas chromatography.The first C7 diagrams is used for distinguishing variation in oils caused by transformation,e.g. water washing,biodegradation and evaporation. The second C7-based diagram consists of four ratios composed of compounds that are very resistant to the effects of transformation.Two star diagrams of six oils representing different oil fields show water washing,biodegradation and other transformations are not the main factors to control heterogenous petroleum.Either is maturity,based on the molecular isomerization parameters of C29ααα sterane 20S/(20S+20R) as maturity parameter. At the end of the paper,pyrrolic nitrogen compound distrbutions of crude oil are studied.Pyrrolic nitrogen compounds in oil have been shoun to be very useful geotracers in predicting the direction and even the distance of oil secondary migration in the reservoirs.Alkylcarbazole series in the neutral pyrrolic nitrogen are just discussed,1,8-dimethylcarbazole/3,4-dimethylcarbazole,1,8-dimethylcarbazole/1,3-dimethylcarbzole,carbazole/methylcbazole and methylcarbazole/dimethylcarbzole are used as migration parameters.These parametes of different crude oils with similar other parameters have some changes.It is concluded that migration fractionation is the main factor to control heterogeneity of petroleum in Jiuxi Basin.At the same time,migration parameters verify that oils come from Qingxi sag and the direction of migration is from west to east.
The physical and chemical nature of petroleum changes with source rock and maturity,although the feature of oil and gas can also be influenced by local biodegadration or water washing.During the process of reservoir filling,some polar compound in crude oils,such as carbazoles which can interact relatively strongly with water,rock minerals and each other,and thus induce hetrogenous petroleum. Meanwhile, heterogenous migration pathways also influence the characteristics of oils. In the paper,authors discuss in detail the chemical nature of oil samples,which come from six oil fields in Jiuxi Basin.Among twelve oil samples,except one sample's carbon isotope(δ13Coil‰) of the whole liquid hydrocarbon (crude oil) is -30.5‰,the other's is about -31‰,whose absolute error is less than 0.2‰. Distillation mode of carbon isotope of N-alkane element series is also similar to each other.Based on GC and GC-MS analysis,seventeen conventional geochemical parameters are selected to calculate correlation coefficients between twelve oil samples,correlation coefficients of all samples are more than 0.86,most of them is up to 0.96.All of these parameters show that twelve oil samples come from the same source rock. Two star diagrams (multivariable plots in polar coordinates) have been developed to assess subtle chemical differences among oils.The diagrams are based on analysis of C7 hydrocarbon of crude oils separated by gas chromatography.The first C7 diagrams is used for distinguishing variation in oils caused by transformation,e.g. water washing,biodegradation and evaporation. The second C7-based diagram consists of four ratios composed of compounds that are very resistant to the effects of transformation.Two star diagrams of six oils representing different oil fields show water washing,biodegradation and other transformations are not the main factors to control heterogenous petroleum.Either is maturity,based on the molecular isomerization parameters of C29ααα sterane 20S/(20S+20R) as maturity parameter. At the end of the paper,pyrrolic nitrogen compound distrbutions of crude oil are studied.Pyrrolic nitrogen compounds in oil have been shoun to be very useful geotracers in predicting the direction and even the distance of oil secondary migration in the reservoirs.Alkylcarbazole series in the neutral pyrrolic nitrogen are just discussed,1,8-dimethylcarbazole/3,4-dimethylcarbazole,1,8-dimethylcarbazole/1,3-dimethylcarbzole,carbazole/methylcbazole and methylcarbazole/dimethylcarbzole are used as migration parameters.These parametes of different crude oils with similar other parameters have some changes.It is concluded that migration fractionation is the main factor to control heterogeneity of petroleum in Jiuxi Basin.At the same time,migration parameters verify that oils come from Qingxi sag and the direction of migration is from west to east.
2000, 18(1): 151-156.
Abstract:
Because both migration and accumulation of oil and gas proceeded within the pore space of reservoir,the porosity structures directly have an effect on the accumulation of oil and gas as well as the formation and distribution of oil and gas reservoirs. Based on pore microstructure,the microscopic process of hydrocarbon accumulation is quantitatively studied by proposing three stages and relevant concepts models,which inclueds early migration with resistance force,interim accumulation and late filling. Several models of hydrocarbon accumulation and distrbution are also presented respectively according to the related serial complex traps and simple traps that are composed of various porelevel heterogeneous reservoirs.In homogeneous reservoir hydrocarbon accumulation is similar to capillary pressure curve and the change of oil saturation in reservoir directly has something to do with depth or height of oil column,it is also to say that oil saturation on the bottom of reservoir(nearly from the oil-water conatct)is lower,while oil saturation on the top of reservior is higher. In heterogeneous reservoir,the features of hydrocarbon accumilation are very complex,and,sometimes, it has regular features that oil saturation on the bottom of reservoir (nearly from the oil-water contact) is lower,while oil saturation on the top of reservoir is higher,but sometimes it has contrary ones,because of characteristics of internal combination in reservior.In serial traps,hydrocarbon accumulation has something to do with lots of macroscopic factors of reservoir that includes intercalated beds,different graded combination of pore structure type,connectedness of reservoir and so on. The conclusion makes a good complement to the traditional theories of petroleum geology.The study is also proved a successful attempt in quatitative geology.
Because both migration and accumulation of oil and gas proceeded within the pore space of reservoir,the porosity structures directly have an effect on the accumulation of oil and gas as well as the formation and distribution of oil and gas reservoirs. Based on pore microstructure,the microscopic process of hydrocarbon accumulation is quantitatively studied by proposing three stages and relevant concepts models,which inclueds early migration with resistance force,interim accumulation and late filling. Several models of hydrocarbon accumulation and distrbution are also presented respectively according to the related serial complex traps and simple traps that are composed of various porelevel heterogeneous reservoirs.In homogeneous reservoir hydrocarbon accumulation is similar to capillary pressure curve and the change of oil saturation in reservoir directly has something to do with depth or height of oil column,it is also to say that oil saturation on the bottom of reservoir(nearly from the oil-water conatct)is lower,while oil saturation on the top of reservior is higher. In heterogeneous reservoir,the features of hydrocarbon accumilation are very complex,and,sometimes, it has regular features that oil saturation on the bottom of reservoir (nearly from the oil-water contact) is lower,while oil saturation on the top of reservoir is higher,but sometimes it has contrary ones,because of characteristics of internal combination in reservior.In serial traps,hydrocarbon accumulation has something to do with lots of macroscopic factors of reservoir that includes intercalated beds,different graded combination of pore structure type,connectedness of reservoir and so on. The conclusion makes a good complement to the traditional theories of petroleum geology.The study is also proved a successful attempt in quatitative geology.
2000, 18(1): 162-164.
Abstract:
Cave calcium has turned out to be a very important data-bank of paleoclimatic evolution.Stalagmite,flow stone and calcite veins in caves,like tree rings,ice cores,loess and lacustrine deposits,contain precise records of past environmental variation.Deciphering of these "codes" would contribute significantly to a better understanding of environmental changes on a global scale and would thereby enable us to make a better prediction of the future trend of climatic and environmental evolution. Highly precise dating is one of the problems in global change study and is recently considered as a hot point in the Quaternary geology.With high-sensitive and high-precision U-Th disequilibrium method,Quaternary geology age by thermal ionization mass spectrolmetry (TIMS) has been determined.This has obtained significant achievements in palaeoclimate,palaeoenvironment,palaeo-ocean,archaeology and modern volcanism-magmatism studies.In this paper,we have determined Chinese standard sample stalagmite (GBW4412,GBW4413) and international standare sample Cpra;s(RKM-4) By MAT-262 mass spectrometer.The measured U content,isotopic ration and age value comply with that of the standard sample very well,indicating that an ideal tool for precise timing,which is the TIMS method is analysis also of advantages such as rapid,high precision and low sample comsuption.
Cave calcium has turned out to be a very important data-bank of paleoclimatic evolution.Stalagmite,flow stone and calcite veins in caves,like tree rings,ice cores,loess and lacustrine deposits,contain precise records of past environmental variation.Deciphering of these "codes" would contribute significantly to a better understanding of environmental changes on a global scale and would thereby enable us to make a better prediction of the future trend of climatic and environmental evolution. Highly precise dating is one of the problems in global change study and is recently considered as a hot point in the Quaternary geology.With high-sensitive and high-precision U-Th disequilibrium method,Quaternary geology age by thermal ionization mass spectrolmetry (TIMS) has been determined.This has obtained significant achievements in palaeoclimate,palaeoenvironment,palaeo-ocean,archaeology and modern volcanism-magmatism studies.In this paper,we have determined Chinese standard sample stalagmite (GBW4412,GBW4413) and international standare sample Cpra;s(RKM-4) By MAT-262 mass spectrometer.The measured U content,isotopic ration and age value comply with that of the standard sample very well,indicating that an ideal tool for precise timing,which is the TIMS method is analysis also of advantages such as rapid,high precision and low sample comsuption.
