2012 Vol. 30, No. 3
Display Method:
2012, 30(3): 405-421.
Abstract:
FengxianTaibai sedimentary basin could be the Paleozoic pullapart basin which might be controlled by obliquedirected subduction and collision of the Qinling and Yangtze Plates based on new research methods, i.e., reconstruction and restoration of geotectonicpaleogeographic position and tectonic lithofacies. During the initial stage of the Middle Devonian period, FengxianTaibai sedimentary basin was enclosed and separated by marginal vertical baseuplifting, and dynamics of basin was controlled by four groups of synsedimentary faults, resulted in continual migrations of subsidence and sedimentary centers in the Late Paleozoic basin. During the middle stage of the Middle Devonian period, subsidence and sedimentary centers trending northwestdirected might be located in north part of FengxianTaibai basin while subsidence and sedimentary centers trending northwestdirected shrink in the center part of FengxianTaibai pullapart basin during the Late Devonian period. However, the Carboniferous subsidence and sedimentary centers were migrated from the center to the zones of marginal synfaults of FengxianTaibai pullapart basin, and the Carboniferous to the Early Triassic wedgeshaped sedimentfilling bodies related to zone of the plate subduction and collision was located at the southern part the Shangdan suture in the northern margin of FengxianTaibai pullapart basin. Finally, formation and evolution of FengxianTaibai pullapart basin might have been controlled by the NW, NNE, NS and NWtrending synsedimentary faults in the FengxianTaibai Devonian pullapart basin. The west part of Shangdan, the middle part of LixianFengxianFengzhenShanyang, and the west part of JiujianliangZhenanBanyanzhen synsedimentary faults were of most important controls not only in the formation of the FengxianTaibai Devonian pullapart basin but also in the evolution of the Carboniferous period to the Early Triassic pullapart basin. Tectonic inversion of synsedimentary faults controlled subsidence and sedimentary centers during the evolution of the basin from the Carboniferous period to the Early Triassic period. The FengxianTaibai Paleozoic pullapart basin can be divided into three different level basin based on the study of basin dynamics and tectonic lithofacies. The secondlevel, Fengxian basin is mineralization concentrated area of goldpolymetallic deposits in the west part of FengxianTaibai pullapart basin while the secondlevel, Taibai basin is mineralization concentrated area of gold deposits in the west part of FengxianTaibai pullapart basin. In the thirdlevel, BafangshanYinmushi basin, Bafangshan and Yinmushi polymetallic deposits and Baguamiao gold are the mineralization zoning at the scale of orefield and of deposits, which might be controlled by threelevel basin, synsedimentary faults, hydrothermal sedimentary lithofacies, and superimposed lithofacies of tectonic hydrothermal fluids. In the north and east part of the Paleozoic pullapart basin, formation of gold source beds and preliminary enrichment might be related to albiteite lithofacies and albitehydrothermal sedimentary lithofacies, and they may be superimposed by albitecarbonate breccia and Fedolomitealbite breccia formed by the Carboniferous tectonic hydrothermal fluids while the Triassic hydrothermal cherts and layered dacitic tuffs hosted Carlintype gold deposits in Wenjiangsi area in the south part of the Paleozoic pullapart basin. SEDEXtype leadzinc deposits may mainly related to chertic lithofacies and sideriteferrodolomitite lithofacies.
FengxianTaibai sedimentary basin could be the Paleozoic pullapart basin which might be controlled by obliquedirected subduction and collision of the Qinling and Yangtze Plates based on new research methods, i.e., reconstruction and restoration of geotectonicpaleogeographic position and tectonic lithofacies. During the initial stage of the Middle Devonian period, FengxianTaibai sedimentary basin was enclosed and separated by marginal vertical baseuplifting, and dynamics of basin was controlled by four groups of synsedimentary faults, resulted in continual migrations of subsidence and sedimentary centers in the Late Paleozoic basin. During the middle stage of the Middle Devonian period, subsidence and sedimentary centers trending northwestdirected might be located in north part of FengxianTaibai basin while subsidence and sedimentary centers trending northwestdirected shrink in the center part of FengxianTaibai pullapart basin during the Late Devonian period. However, the Carboniferous subsidence and sedimentary centers were migrated from the center to the zones of marginal synfaults of FengxianTaibai pullapart basin, and the Carboniferous to the Early Triassic wedgeshaped sedimentfilling bodies related to zone of the plate subduction and collision was located at the southern part the Shangdan suture in the northern margin of FengxianTaibai pullapart basin. Finally, formation and evolution of FengxianTaibai pullapart basin might have been controlled by the NW, NNE, NS and NWtrending synsedimentary faults in the FengxianTaibai Devonian pullapart basin. The west part of Shangdan, the middle part of LixianFengxianFengzhenShanyang, and the west part of JiujianliangZhenanBanyanzhen synsedimentary faults were of most important controls not only in the formation of the FengxianTaibai Devonian pullapart basin but also in the evolution of the Carboniferous period to the Early Triassic pullapart basin. Tectonic inversion of synsedimentary faults controlled subsidence and sedimentary centers during the evolution of the basin from the Carboniferous period to the Early Triassic period. The FengxianTaibai Paleozoic pullapart basin can be divided into three different level basin based on the study of basin dynamics and tectonic lithofacies. The secondlevel, Fengxian basin is mineralization concentrated area of goldpolymetallic deposits in the west part of FengxianTaibai pullapart basin while the secondlevel, Taibai basin is mineralization concentrated area of gold deposits in the west part of FengxianTaibai pullapart basin. In the thirdlevel, BafangshanYinmushi basin, Bafangshan and Yinmushi polymetallic deposits and Baguamiao gold are the mineralization zoning at the scale of orefield and of deposits, which might be controlled by threelevel basin, synsedimentary faults, hydrothermal sedimentary lithofacies, and superimposed lithofacies of tectonic hydrothermal fluids. In the north and east part of the Paleozoic pullapart basin, formation of gold source beds and preliminary enrichment might be related to albiteite lithofacies and albitehydrothermal sedimentary lithofacies, and they may be superimposed by albitecarbonate breccia and Fedolomitealbite breccia formed by the Carboniferous tectonic hydrothermal fluids while the Triassic hydrothermal cherts and layered dacitic tuffs hosted Carlintype gold deposits in Wenjiangsi area in the south part of the Paleozoic pullapart basin. SEDEXtype leadzinc deposits may mainly related to chertic lithofacies and sideriteferrodolomitite lithofacies.
2012, 30(3): 422-430.
Abstract:
The Devonian barite deposits located in Zhenning County, Guizhou Province have proved reserves of 33.02×106 t, belonging to largescale ore deposits. Research on sedimentation structures and tectonic characteristics related to the barite deposits reveal the coexistence of a variety of structures like laminar structures, baritebanded structure, brecciated structure, baritefragmental structure and massive structure, etc., which are similar to those of the TianzhuDahebian barite deposit, the hydrothermal barite rocks of Gutan in Guangxi Province and the hydrothermal water sedimentary barite rocks of Erlangping Group from north Qinling Mountains. Several types of sedimentary characteristics, such as hydrothermal venting channel phases formed in submarine hydrothermal venting, unitary hydrothermal lithofacies and hydrothermally mixed synsedimentary phases, were identified widely in barite orebeds in Zhenning, Guizhou. Similar to Devonian hydrothermal sedimentary rocks (deposits) from Qinling, those sedimentary phases and lithofacies features found in Zhenning characterize a hydrothermal turbidity current sedimentation phase. Sedimentary structures, constructions and lithofacies features of the orebed record well the information of submarine hydrothermal venting and its evolution, the sedimentation rhythm characteristics reveal the intensity of hydrothermal ventingflowing was weakstrongweak. Hence, barite deposits in Zhenning were formed in submarine hydrothermal venting sedimentation, and the hydrothermal sedimentary structures, constructions and hydrothermal lithofacies features make them ideal places for research on ancient hydrothermal venting diagenesis, metallogenesis and hydrothermal lithofacies categorization.
The Devonian barite deposits located in Zhenning County, Guizhou Province have proved reserves of 33.02×106 t, belonging to largescale ore deposits. Research on sedimentation structures and tectonic characteristics related to the barite deposits reveal the coexistence of a variety of structures like laminar structures, baritebanded structure, brecciated structure, baritefragmental structure and massive structure, etc., which are similar to those of the TianzhuDahebian barite deposit, the hydrothermal barite rocks of Gutan in Guangxi Province and the hydrothermal water sedimentary barite rocks of Erlangping Group from north Qinling Mountains. Several types of sedimentary characteristics, such as hydrothermal venting channel phases formed in submarine hydrothermal venting, unitary hydrothermal lithofacies and hydrothermally mixed synsedimentary phases, were identified widely in barite orebeds in Zhenning, Guizhou. Similar to Devonian hydrothermal sedimentary rocks (deposits) from Qinling, those sedimentary phases and lithofacies features found in Zhenning characterize a hydrothermal turbidity current sedimentation phase. Sedimentary structures, constructions and lithofacies features of the orebed record well the information of submarine hydrothermal venting and its evolution, the sedimentation rhythm characteristics reveal the intensity of hydrothermal ventingflowing was weakstrongweak. Hence, barite deposits in Zhenning were formed in submarine hydrothermal venting sedimentation, and the hydrothermal sedimentary structures, constructions and hydrothermal lithofacies features make them ideal places for research on ancient hydrothermal venting diagenesis, metallogenesis and hydrothermal lithofacies categorization.
2012, 30(3): 431-442.
Abstract:
The Zanda Basin is a Neogene rifted basin in South Tibet. On the basis of previous vertebrate palaeontology, palynology, magnetostratigraphy, and ESR dating research, the age interval can be bracketed between ~9.2 and 1 Ma through strata correlation. Based on lithology, paleocurrent measurements and provenance analysis, this paper studies sedimentological succession of the Neogene Basin, and three sedimentological phases are identified: initial rift filling phase(9.2~7.8 Ma), stable subsidence phase(7.8~2.6 Ma) and subduction phase(2.6~1.7 Ma). During 9.2~7.8 Ma, the braided river lithofacies with an SWS paleocurrent predominates in the Lower Tuolin Formation, and the sediment sources are mainly in the northesatern side of the basin, the sedimentary centrer is located at the southside of the basin. Then, the lacustrine lithofacies dominates in the basin, accompanied by lakedelta lithofacies, with a basincentric paleocurrent in the Upper Tuolin Formation from 7.8 Ma to 2.6 Ma, the lake area reach to maximum, and the source of the sedimentary basin comes from mountains surrounding the basin margin. During 2.6~1.7 Ma, the alluvialfan lithofacie dominates, with a SES paleocurrent in Xiangz Formation, implying the the source material are from southwestern side of the basin, and the facies change from fine lacustrine to coarse alluvial fan rapidly. The Pleistocene Gongba Formation is in angular unconformity with the underlying Xiangz Formation, implying end of the sedimentary basin. In summary, the lithofacies compose of braided river, lacustrine and alluvialfan, dominated by lacustrine lithofacies. Paleocurrent directions change from SW (lower part) to SE (upper part), with a basincentric direction in the middle part. Furthermore, regional geography changes from northeast high, southwest low to northwest high, southeast low, and the sedimentary central is located at the south margin of the basin. After 1.7 Ma, the Pleistocene Gongba Formation appears and implies disappearance of the basin. It indicates that the riftsag basin in southern Tibet rises firstly, forming a paleolake, and then falls abruptly, dating eastwest extensional tectonic evolvement when the plateau attains its maximum elevation.
The Zanda Basin is a Neogene rifted basin in South Tibet. On the basis of previous vertebrate palaeontology, palynology, magnetostratigraphy, and ESR dating research, the age interval can be bracketed between ~9.2 and 1 Ma through strata correlation. Based on lithology, paleocurrent measurements and provenance analysis, this paper studies sedimentological succession of the Neogene Basin, and three sedimentological phases are identified: initial rift filling phase(9.2~7.8 Ma), stable subsidence phase(7.8~2.6 Ma) and subduction phase(2.6~1.7 Ma). During 9.2~7.8 Ma, the braided river lithofacies with an SWS paleocurrent predominates in the Lower Tuolin Formation, and the sediment sources are mainly in the northesatern side of the basin, the sedimentary centrer is located at the southside of the basin. Then, the lacustrine lithofacies dominates in the basin, accompanied by lakedelta lithofacies, with a basincentric paleocurrent in the Upper Tuolin Formation from 7.8 Ma to 2.6 Ma, the lake area reach to maximum, and the source of the sedimentary basin comes from mountains surrounding the basin margin. During 2.6~1.7 Ma, the alluvialfan lithofacie dominates, with a SES paleocurrent in Xiangz Formation, implying the the source material are from southwestern side of the basin, and the facies change from fine lacustrine to coarse alluvial fan rapidly. The Pleistocene Gongba Formation is in angular unconformity with the underlying Xiangz Formation, implying end of the sedimentary basin. In summary, the lithofacies compose of braided river, lacustrine and alluvialfan, dominated by lacustrine lithofacies. Paleocurrent directions change from SW (lower part) to SE (upper part), with a basincentric direction in the middle part. Furthermore, regional geography changes from northeast high, southwest low to northwest high, southeast low, and the sedimentary central is located at the south margin of the basin. After 1.7 Ma, the Pleistocene Gongba Formation appears and implies disappearance of the basin. It indicates that the riftsag basin in southern Tibet rises firstly, forming a paleolake, and then falls abruptly, dating eastwest extensional tectonic evolvement when the plateau attains its maximum elevation.
2012, 30(3): 443-450.
Abstract:
It is difficult to estimate paleobathymetry in sedimentary study. The modes of "indicatorpaleowater depth" have been used as qualitative or semiquantitative methods, but with challenges from hard samples requirement and low predicting precision. A new geometric approachshoreline trajectory for quantitatively paleobathymetric analysis has been proposed based on the study of Dongying delta, middle part of third member of Paleogene Shahejie Formation (Es32) in the Donying depression. Shoreline trajectory is used to obtain the variation principle of accommodation and sediment supply under a point sediment supply. Backstripping and forwarding methods are combined to acquire the initial sediment thickness and the increment of accommodation in the top layer of each unit, respectively. The water depth in undercompensation areas in deltaic front facies can be expressed as the value of sediment thickness subtracted by accommodation. Both differential tectonic subsidence and sediment supply tendency are considered in this method, making it an accurate approach to predict waterdepth variation in deltaic areas. This method is successfully applied in Dongying deltaic areas of Es32 where nine sets of progradation are developed, showing that the deepest water occurs in t3 with the maximum water depth up to 180 m. This method reveals the variation of water depth in deltaic area in detail, providing an effective way for quantitatively predicting the Spatial distribution of sediment.
It is difficult to estimate paleobathymetry in sedimentary study. The modes of "indicatorpaleowater depth" have been used as qualitative or semiquantitative methods, but with challenges from hard samples requirement and low predicting precision. A new geometric approachshoreline trajectory for quantitatively paleobathymetric analysis has been proposed based on the study of Dongying delta, middle part of third member of Paleogene Shahejie Formation (Es32) in the Donying depression. Shoreline trajectory is used to obtain the variation principle of accommodation and sediment supply under a point sediment supply. Backstripping and forwarding methods are combined to acquire the initial sediment thickness and the increment of accommodation in the top layer of each unit, respectively. The water depth in undercompensation areas in deltaic front facies can be expressed as the value of sediment thickness subtracted by accommodation. Both differential tectonic subsidence and sediment supply tendency are considered in this method, making it an accurate approach to predict waterdepth variation in deltaic areas. This method is successfully applied in Dongying deltaic areas of Es32 where nine sets of progradation are developed, showing that the deepest water occurs in t3 with the maximum water depth up to 180 m. This method reveals the variation of water depth in deltaic area in detail, providing an effective way for quantitatively predicting the Spatial distribution of sediment.
2012, 30(3): 451-460.
Abstract:
The Liwan area is located in the east edge of the deep waters of the Baiyun sag，belonging to the most development block of the Zhujiang Formation submarine fan sedimentary system in Pearl River Mouth Basin, which has very superior petroleum geological conditions. The research of diagenesis and diagenetic phase is one of the most important basic researches about the reservoir of the submarine fan and accumulation characteristics. But there is no systematic research about the relationship of diagenesis and high quality sandstone reservoir development in submarine fan. According to the results of analysis from thinsection, scanning electron microscope and stable carbon and oxygen isotopic composition. This paper comprehensively analyzes the diagenesis and evolutionary sequences in Zhujiang Formation of submarine fan in Pearl River Mouth Basin, sum up the diagenetic phase characteristics to play the role of predicting and evaluating the high quality of sandstone reservoir in deepwater fan. Firstly, based on the materials of the drilling cores, outcrop, rock slice identification and grain size analysis, etc, the author has made a study on the pearl river groups about the type of sandstone, the maturity of composition and the pore types.Then, the author concludes that the sandstone in pearl river groups consists of detrital feldspathic sandstone primarily and feldspathic litharenite secondly, and in which the sandstone is mainly dominated by primary intergranular pores and the intergranular pores after compaction and cementation, with few solution pores and organism cavity pores. Secondly, according to the core description, scanning electron microscope and casting thin sections, the author concludes that the diagenesis of deepwater fan sandstone reservoirs in Pearl River group is relatively weak, of which the compaction, cementation, filling of authigenic mineral and metasomatism is not conducive to formation and evolution of reservoir space, but the compression effect comes from early silica cementation and later dissolution are beneficial to the formation and evolution of the reservoir space. In addition, based on the analysis of the Xray diffraction, vitrinite reflectance, the illitemontmorillonite mixedlayer, smectite content, the author divides the diagenesis of pearl river group into three evolutionary stages and five substages in accordance with the national standard of diagenetic stage. The three evolutionary stages are penecontemporaneous stage, early diagentic stage, and middle diagenetic stage. The diagenesis of Pearl River group were mainly in middle diagenetic stage A, and some of them in burial part entered the middle diagenetic stage B. Finally, on the basis of analysis of diagenesis and diagenetic series and according to the rule of combination and distribution for the diagenesis of deepwater fan sedimentary system in Pearl River group, the author concludes that the lithofacies assemblages may be divided into four phases : weak compactionweakly cementedstrong dissolution diagenetic phase, medium compactionweakly cementedmedium dissolution phase, weak compactionweak solutionstrong carbonate cementation diagenetic phase and compactioncementation diagenetic phase. Especially, the sandbody physical property in the middle weak compactionweakly cementedstrong dissolution phase is the best, and the sandbody of deepwater fan channel in Pearl River group is dominated by this kind.
The Liwan area is located in the east edge of the deep waters of the Baiyun sag，belonging to the most development block of the Zhujiang Formation submarine fan sedimentary system in Pearl River Mouth Basin, which has very superior petroleum geological conditions. The research of diagenesis and diagenetic phase is one of the most important basic researches about the reservoir of the submarine fan and accumulation characteristics. But there is no systematic research about the relationship of diagenesis and high quality sandstone reservoir development in submarine fan. According to the results of analysis from thinsection, scanning electron microscope and stable carbon and oxygen isotopic composition. This paper comprehensively analyzes the diagenesis and evolutionary sequences in Zhujiang Formation of submarine fan in Pearl River Mouth Basin, sum up the diagenetic phase characteristics to play the role of predicting and evaluating the high quality of sandstone reservoir in deepwater fan. Firstly, based on the materials of the drilling cores, outcrop, rock slice identification and grain size analysis, etc, the author has made a study on the pearl river groups about the type of sandstone, the maturity of composition and the pore types.Then, the author concludes that the sandstone in pearl river groups consists of detrital feldspathic sandstone primarily and feldspathic litharenite secondly, and in which the sandstone is mainly dominated by primary intergranular pores and the intergranular pores after compaction and cementation, with few solution pores and organism cavity pores. Secondly, according to the core description, scanning electron microscope and casting thin sections, the author concludes that the diagenesis of deepwater fan sandstone reservoirs in Pearl River group is relatively weak, of which the compaction, cementation, filling of authigenic mineral and metasomatism is not conducive to formation and evolution of reservoir space, but the compression effect comes from early silica cementation and later dissolution are beneficial to the formation and evolution of the reservoir space. In addition, based on the analysis of the Xray diffraction, vitrinite reflectance, the illitemontmorillonite mixedlayer, smectite content, the author divides the diagenesis of pearl river group into three evolutionary stages and five substages in accordance with the national standard of diagenetic stage. The three evolutionary stages are penecontemporaneous stage, early diagentic stage, and middle diagenetic stage. The diagenesis of Pearl River group were mainly in middle diagenetic stage A, and some of them in burial part entered the middle diagenetic stage B. Finally, on the basis of analysis of diagenesis and diagenetic series and according to the rule of combination and distribution for the diagenesis of deepwater fan sedimentary system in Pearl River group, the author concludes that the lithofacies assemblages may be divided into four phases : weak compactionweakly cementedstrong dissolution diagenetic phase, medium compactionweakly cementedmedium dissolution phase, weak compactionweak solutionstrong carbonate cementation diagenetic phase and compactioncementation diagenetic phase. Especially, the sandbody physical property in the middle weak compactionweakly cementedstrong dissolution phase is the best, and the sandbody of deepwater fan channel in Pearl River group is dominated by this kind.
2012, 30(3): 461-468.
Abstract:
Based on a large amount of drill, core and seismic data from the eastern Baiyun Sag, by the analysis of seismic attributes, seismic facices as well as drilling sedimentary facies, it is proved that in Baiyun Sag there is not only the north provenance but also the eastern depositional system which is derived from the Dongsha Uplift in early Miocene, and this discovery will lead to the expansion of the exploration scope for the deepwater clastic deposits of Baiyun Sag.The Eastern Depositional System is mainly developed in SQ23.8, with the bottom boundary SB23.8. Previous studies reported that the “Baiyun Movement” occurred in 23.8 Ma B.P. results in tremendous changes of Baiyun sag, causing the thermal subsidence of the sag, making the shelf neritic environment transform into slope deepwater environment, and SB23.8 is the interface of the shelf break belt migrating from the south of Baiyun sag to north. In 23.8 Ma B.P. the relative sea level fell to the lowest, which made the Panyu Low Uplift in the north and the Dongsha Uplift in the east be in a state of exposure. The formers' study has confirmed that the Panyu Low Uplift provides debris for the deep water of Baiyun sag, and then, whether the Dongsha Uplift which was also exposed in SQ23.8 can serve as the provenance for Baiyun sag is the breakthrough point of this paper.The erosion area of Dongsha uplift during early Miocene is about 20 000 km2, which is close to Baiyun sag, and considering such a great erosion area the uplift should provide materials for Baiyun sag. Besides, on the image of 3D seismic RMS amplitude slices present an abnormally high amplitude in the east of Baiyun sag, and the graph of sandstone/strata contour of SQ23.8 also presents high values in the east. In addition, on seismic, a wedgeshaped progradational reflection configuration with the direction from Dongsha Uplift to Baiyun sag in SQ23.8 is developed. Therefore, according to the above analysis, it is concluded that the Dongsha Uplift is one of the provenances of Baiyun sag during the period of SQ23.8 deposition.On seismic, the deposits characterized by wedgeshaped progradational reflection configuration are interpreted as the deposits of deltas for their developed location, and the deposits in front characterized by highamplitude, good continuity, progradational reflection on the trend seismic profile, a hummocky bidirectional progradation configuration on the cross profile, are interpreted as the submarine fan. Through observation of the core it is found that the carbonate content is fairly high in the core of SQ23.8, indicating that the sediments come from Dongsha Uplift, because during the period of SQ23.8 deposition,only Dongsha Uplift developed carbonate, also, again confriming the viewpoint that Dongsha Uplift is the provenance of Baiyun sag. Besides, a variety of gravity flow sedimentary structures are found in the core, such as normal graded bedding, Bouma sequence and slumpdeformation bedding and so on, indicating a kind of gravity flow deposits in bathyal environment.The sediments of the core are identified as submarine fan deposits.Based on the sequence division result by integrating well and seismic data, SQ23.8 can be divided into three system tracts: LST, TST and HST. Combining the sequence stratigraphic analysis and the study of the sedimentary facies, the sedimentary and evolution model of the eastern sedimentary system has been established. In this depositional system, the lowstand system tracts (LST) are represented by submarine fans, and the trangressive system tracts (TST) are dominated by the mixed deposits of clastic and carbonate rock, while in the highstand system tracts (HST) the deltaic deposits are well developed. The deposits and sedimentary model are mainly controlled by the change of relative sea level and material supply.
Based on a large amount of drill, core and seismic data from the eastern Baiyun Sag, by the analysis of seismic attributes, seismic facices as well as drilling sedimentary facies, it is proved that in Baiyun Sag there is not only the north provenance but also the eastern depositional system which is derived from the Dongsha Uplift in early Miocene, and this discovery will lead to the expansion of the exploration scope for the deepwater clastic deposits of Baiyun Sag.The Eastern Depositional System is mainly developed in SQ23.8, with the bottom boundary SB23.8. Previous studies reported that the “Baiyun Movement” occurred in 23.8 Ma B.P. results in tremendous changes of Baiyun sag, causing the thermal subsidence of the sag, making the shelf neritic environment transform into slope deepwater environment, and SB23.8 is the interface of the shelf break belt migrating from the south of Baiyun sag to north. In 23.8 Ma B.P. the relative sea level fell to the lowest, which made the Panyu Low Uplift in the north and the Dongsha Uplift in the east be in a state of exposure. The formers' study has confirmed that the Panyu Low Uplift provides debris for the deep water of Baiyun sag, and then, whether the Dongsha Uplift which was also exposed in SQ23.8 can serve as the provenance for Baiyun sag is the breakthrough point of this paper.The erosion area of Dongsha uplift during early Miocene is about 20 000 km2, which is close to Baiyun sag, and considering such a great erosion area the uplift should provide materials for Baiyun sag. Besides, on the image of 3D seismic RMS amplitude slices present an abnormally high amplitude in the east of Baiyun sag, and the graph of sandstone/strata contour of SQ23.8 also presents high values in the east. In addition, on seismic, a wedgeshaped progradational reflection configuration with the direction from Dongsha Uplift to Baiyun sag in SQ23.8 is developed. Therefore, according to the above analysis, it is concluded that the Dongsha Uplift is one of the provenances of Baiyun sag during the period of SQ23.8 deposition.On seismic, the deposits characterized by wedgeshaped progradational reflection configuration are interpreted as the deposits of deltas for their developed location, and the deposits in front characterized by highamplitude, good continuity, progradational reflection on the trend seismic profile, a hummocky bidirectional progradation configuration on the cross profile, are interpreted as the submarine fan. Through observation of the core it is found that the carbonate content is fairly high in the core of SQ23.8, indicating that the sediments come from Dongsha Uplift, because during the period of SQ23.8 deposition,only Dongsha Uplift developed carbonate, also, again confriming the viewpoint that Dongsha Uplift is the provenance of Baiyun sag. Besides, a variety of gravity flow sedimentary structures are found in the core, such as normal graded bedding, Bouma sequence and slumpdeformation bedding and so on, indicating a kind of gravity flow deposits in bathyal environment.The sediments of the core are identified as submarine fan deposits.Based on the sequence division result by integrating well and seismic data, SQ23.8 can be divided into three system tracts: LST, TST and HST. Combining the sequence stratigraphic analysis and the study of the sedimentary facies, the sedimentary and evolution model of the eastern sedimentary system has been established. In this depositional system, the lowstand system tracts (LST) are represented by submarine fans, and the trangressive system tracts (TST) are dominated by the mixed deposits of clastic and carbonate rock, while in the highstand system tracts (HST) the deltaic deposits are well developed. The deposits and sedimentary model are mainly controlled by the change of relative sea level and material supply.
2012, 30(3): 469-476.
Abstract:
Yinggehai Basin is a Cenozoic marine sedimentary basin with total sediment of 17 km, occupying an area of 11 104 km2, located in the continental shelf of South China Sea. The basin is structurally composed of Yingdong Slope, Yingxi Slope and Central Depression. Due to the existence of the overpressures and the movements of geothermal fluids, there are various unusual geological phenomena in Yinggehai Basin. There exist three types of clay mineral transformations in the basin, normal transformation, faster transformation and slower transformation. The Cenozoic group in Yingdong Slope develops hydrostatic pressure, and the clay minerals transform regularily. With the increase of buried depth and temperature, smectite transforms into illite by illite/smectite mixed layer, and smectite layer content S% in illite/smectite mixed layer decreases gradually. There exist overpressures in the Cenozoic group of Central Depression. DST measured pressure coefficient even reaches 2.4 in LD3011A well district located in the southeast of the depression. As the measured S% in I/S data show that the overpressures retard the transformation of clay minerals,the clay minerals transform more slowly in the overpressure formation , and the S% in I/S mixed layer is 10%～30% higher than that of formations with a hydrostatic pressure at the same depth in Yingdong Slope. Overpressure’s retardation also resulted in the putoff of the expulsion of H+, interlayer water and various cations, which lead the dissolution and cementation of the contiguous reservoirs to be weakened. The cements of Cenozoic group reservoirs in LD3011A well are lower 50% than that of Yingdong Slope at the same depth. During Neocene, a large scale of diapirism developed, and geothermal fluids richer in CO2 with a temperature of 200℃were active in Central Depression. The activity of geothermal fluids accelerated the transformation of clay minerals. The S% in I/S mixed layer jumped to zone R2 or R3 from zone R0 abruptly, without going through zone R1. Meanwhile, chlorite turned to kaolinite unusually in the acid environment, which is confirmed by the Gibbs free energy increment computations. The quick transformation of clay minerals lead to a large amount of such cations as Na+,Ca2+,Mg2+,Fe3+,Si4+ expelled from the mudstones. These cations entered the adjacent sandstones and precipitated to form siderite, ankerite, dolomite and ferrocalcite, which filled the pores of the reservoirs and reduced the porosity of the reservoirs.
Yinggehai Basin is a Cenozoic marine sedimentary basin with total sediment of 17 km, occupying an area of 11 104 km2, located in the continental shelf of South China Sea. The basin is structurally composed of Yingdong Slope, Yingxi Slope and Central Depression. Due to the existence of the overpressures and the movements of geothermal fluids, there are various unusual geological phenomena in Yinggehai Basin. There exist three types of clay mineral transformations in the basin, normal transformation, faster transformation and slower transformation. The Cenozoic group in Yingdong Slope develops hydrostatic pressure, and the clay minerals transform regularily. With the increase of buried depth and temperature, smectite transforms into illite by illite/smectite mixed layer, and smectite layer content S% in illite/smectite mixed layer decreases gradually. There exist overpressures in the Cenozoic group of Central Depression. DST measured pressure coefficient even reaches 2.4 in LD3011A well district located in the southeast of the depression. As the measured S% in I/S data show that the overpressures retard the transformation of clay minerals,the clay minerals transform more slowly in the overpressure formation , and the S% in I/S mixed layer is 10%～30% higher than that of formations with a hydrostatic pressure at the same depth in Yingdong Slope. Overpressure’s retardation also resulted in the putoff of the expulsion of H+, interlayer water and various cations, which lead the dissolution and cementation of the contiguous reservoirs to be weakened. The cements of Cenozoic group reservoirs in LD3011A well are lower 50% than that of Yingdong Slope at the same depth. During Neocene, a large scale of diapirism developed, and geothermal fluids richer in CO2 with a temperature of 200℃were active in Central Depression. The activity of geothermal fluids accelerated the transformation of clay minerals. The S% in I/S mixed layer jumped to zone R2 or R3 from zone R0 abruptly, without going through zone R1. Meanwhile, chlorite turned to kaolinite unusually in the acid environment, which is confirmed by the Gibbs free energy increment computations. The quick transformation of clay minerals lead to a large amount of such cations as Na+,Ca2+,Mg2+,Fe3+,Si4+ expelled from the mudstones. These cations entered the adjacent sandstones and precipitated to form siderite, ankerite, dolomite and ferrocalcite, which filled the pores of the reservoirs and reduced the porosity of the reservoirs.
2012, 30(3): 477-489.
Abstract:
The seismites emerge in the first and sencond members of Lower Triassic Feixianguan Fm. in Baimiaozi section, Beibei, Chongqing, China and in the second member of Lower Triassic Jialingjiang Fm. in Longdongwan, Xuyong county, the southern Sichuan province, China,as well as in the same stratigraphic sequences in Xingwen county, Sichuan province and Xishui county, Guizhou province. There are some macroscopic and microscopic sedimentary structures of seismic events in the outcrops, drilling cores and thin sections including the following basic types could be observed: Softsediment liquefied deformation structures include curled deformation (sliding deformation structure, "sausage structure") and microscopic folds (laminated plastic deformation). In the first member of Feixianguan Fm. at Beibei, Chongqing. Microscopic folds (lamina plastic deformation) are found in the second member of Feixianguan Fm. at Longdongwan, and microscopic folds emerge in laminated thinlayer limestone, presenting slight folds in laminated thinlayer limestone and their low radian with undulation. In addition to study areas, some softsediment deformation structures such as convolute beddings, microscopic folds and so on are developed in the first member of Feixianguan Fm. at Jichang, Xuanhan county, Sichuan province,China, and may be related to paleoearthquake activities. The tabularpebbles with differentsize diameters are developed in the lower part of the second member of Feixianguan Fm., interbedded with laminated thinlayer micritic limestone of normal sequences. The sedimentary characteristics of tabular gravel layers are also comparable with those in the second member of Feixianguan Fm. at Beibei, Chongqing. The gravels are developed with different size, shape and psephicitie in the first member of Feixianguan Fm. in Baimiaozi , Beibei Chongqing, and the second member of Jialingjiang Fm. in Longdongwan, Xuyong ,Sichuan province, the shape being irregular mass, nearly spherical or tabular, the size ranging from 0.5 to 25cm, the lithology being grey or grey white thickbedding massive micrite, some of which have certain psephicities. The intraformational microscopic faults are developed in the first and second member of Feixianguan Fm.at Beibei, Chongqing, they are limited to develop intraformationally, and don't cut through the upper and lower beds with short slip of fault and slow angle of fault plane. Some welldeveloped microscopic seismites can also be discovered in some thin sections of the second member of Jialingjiang Fm. at Longdongwan, Xuyong county,and Jianshe,Dali,Chengdong, Wenxin county ,Sichuan province, Huangmuping ,Xishui county , Guizhou province,including the following basic types:microscopic liquefied curled deformation structure;microscopic tabularpebbles layer;microscopic slip and microscopic flame structure. Seismites developed in the lower Triassic in Sichuan Basin have not only wide transverse distribution, but also are distributed longitudinally.Some seismites with volcanic debris sediments of Early Triassic have been found in other places of Sichuan basin besides research area. The author argues that the Sanjiang tectonic belt represented by the evolution of Yidun arc in the western Sichuan had strong activities at the west margin of the upper Yangtze plate, which may be related to the formation of seismites in the early Triassic. At the west margin of the upper Yangtze plate, the strongest tectonic deformation and metamorphism occurred in the early Triassic emerge between YiDui arc and Qiangtang mass, representing the subduction of the PaleoTethys. Magmatic and volcanic activities occur when the paleoTethyan oceanic crust subducts eastward along Litangbatang volcanic arc and westward along Jinsha River suture zone. In the early Triassic, seismic activities and volcanic eruption can be triggered in large areas with plate collision and ocean crust subduction. The author speculates that Yidui arc is the major cause of formation of seismites in Sichuan Basin that emerge in the early Triassic.
The seismites emerge in the first and sencond members of Lower Triassic Feixianguan Fm. in Baimiaozi section, Beibei, Chongqing, China and in the second member of Lower Triassic Jialingjiang Fm. in Longdongwan, Xuyong county, the southern Sichuan province, China,as well as in the same stratigraphic sequences in Xingwen county, Sichuan province and Xishui county, Guizhou province. There are some macroscopic and microscopic sedimentary structures of seismic events in the outcrops, drilling cores and thin sections including the following basic types could be observed: Softsediment liquefied deformation structures include curled deformation (sliding deformation structure, "sausage structure") and microscopic folds (laminated plastic deformation). In the first member of Feixianguan Fm. at Beibei, Chongqing. Microscopic folds (lamina plastic deformation) are found in the second member of Feixianguan Fm. at Longdongwan, and microscopic folds emerge in laminated thinlayer limestone, presenting slight folds in laminated thinlayer limestone and their low radian with undulation. In addition to study areas, some softsediment deformation structures such as convolute beddings, microscopic folds and so on are developed in the first member of Feixianguan Fm. at Jichang, Xuanhan county, Sichuan province,China, and may be related to paleoearthquake activities. The tabularpebbles with differentsize diameters are developed in the lower part of the second member of Feixianguan Fm., interbedded with laminated thinlayer micritic limestone of normal sequences. The sedimentary characteristics of tabular gravel layers are also comparable with those in the second member of Feixianguan Fm. at Beibei, Chongqing. The gravels are developed with different size, shape and psephicitie in the first member of Feixianguan Fm. in Baimiaozi , Beibei Chongqing, and the second member of Jialingjiang Fm. in Longdongwan, Xuyong ,Sichuan province, the shape being irregular mass, nearly spherical or tabular, the size ranging from 0.5 to 25cm, the lithology being grey or grey white thickbedding massive micrite, some of which have certain psephicities. The intraformational microscopic faults are developed in the first and second member of Feixianguan Fm.at Beibei, Chongqing, they are limited to develop intraformationally, and don't cut through the upper and lower beds with short slip of fault and slow angle of fault plane. Some welldeveloped microscopic seismites can also be discovered in some thin sections of the second member of Jialingjiang Fm. at Longdongwan, Xuyong county,and Jianshe,Dali,Chengdong, Wenxin county ,Sichuan province, Huangmuping ,Xishui county , Guizhou province,including the following basic types:microscopic liquefied curled deformation structure;microscopic tabularpebbles layer;microscopic slip and microscopic flame structure. Seismites developed in the lower Triassic in Sichuan Basin have not only wide transverse distribution, but also are distributed longitudinally.Some seismites with volcanic debris sediments of Early Triassic have been found in other places of Sichuan basin besides research area. The author argues that the Sanjiang tectonic belt represented by the evolution of Yidun arc in the western Sichuan had strong activities at the west margin of the upper Yangtze plate, which may be related to the formation of seismites in the early Triassic. At the west margin of the upper Yangtze plate, the strongest tectonic deformation and metamorphism occurred in the early Triassic emerge between YiDui arc and Qiangtang mass, representing the subduction of the PaleoTethys. Magmatic and volcanic activities occur when the paleoTethyan oceanic crust subducts eastward along Litangbatang volcanic arc and westward along Jinsha River suture zone. In the early Triassic, seismic activities and volcanic eruption can be triggered in large areas with plate collision and ocean crust subduction. The author speculates that Yidui arc is the major cause of formation of seismites in Sichuan Basin that emerge in the early Triassic.
2012, 30(3): 490-500.
Abstract:
Previously considered the Dashuitang Formation in the Upper Triassic series in Baoshan Area was shallow marine sedimentary environment. This paper argues that the background deposition of the Dashuitang Formation in the Upper Triassic series in Baoshan area subject to a calcareous turbidite by 1∶〖KG-*2〗50000 regional geological survey of Jinji Village site.It is mainly composed of the A, E segment that sandwiched thinbedded chert in central folder(Hunger deposition),accompanied by slump rock blocks,being classified for slopebasin environment, and is a part of the Yongde Montenegro Rift Valley(Trough). For the first time, the author found the seismites in the Dashuitang Formation that including vibration liquefaction deformation structures, microfault with the micro deposition, liquefied micritic veins, seismic unconformity, fissure, liquefied breccia, liquefied eyeball, and sliding(Flowing) sedimentary rocks, slip (flow) folds, slump rock blocks of liquefied sediment flow of the earthquake. It is very poor that the regularity of combination of these phenomena. Only a small amount of them with vertical combination sequence that shows features of endemic species. MicroFault with the micro deposition and liquefied micritic veins are almost filled the whole process of the deposition.It can emit a very strong smell of oil when the rock was struck, that shows the good characteristics of hydrocarbon source rocks. Therefore, the study on the distribution and formation of seismites, Dashuitang Formation has very important practical significance that for the ancient paleogeographic environment of the Dashuitang Formation in the Upper Triassic series and the search for hydrocarbon source rocks.
Previously considered the Dashuitang Formation in the Upper Triassic series in Baoshan Area was shallow marine sedimentary environment. This paper argues that the background deposition of the Dashuitang Formation in the Upper Triassic series in Baoshan area subject to a calcareous turbidite by 1∶〖KG-*2〗50000 regional geological survey of Jinji Village site.It is mainly composed of the A, E segment that sandwiched thinbedded chert in central folder(Hunger deposition),accompanied by slump rock blocks,being classified for slopebasin environment, and is a part of the Yongde Montenegro Rift Valley(Trough). For the first time, the author found the seismites in the Dashuitang Formation that including vibration liquefaction deformation structures, microfault with the micro deposition, liquefied micritic veins, seismic unconformity, fissure, liquefied breccia, liquefied eyeball, and sliding(Flowing) sedimentary rocks, slip (flow) folds, slump rock blocks of liquefied sediment flow of the earthquake. It is very poor that the regularity of combination of these phenomena. Only a small amount of them with vertical combination sequence that shows features of endemic species. MicroFault with the micro deposition and liquefied micritic veins are almost filled the whole process of the deposition.It can emit a very strong smell of oil when the rock was struck, that shows the good characteristics of hydrocarbon source rocks. Therefore, the study on the distribution and formation of seismites, Dashuitang Formation has very important practical significance that for the ancient paleogeographic environment of the Dashuitang Formation in the Upper Triassic series and the search for hydrocarbon source rocks.
2012, 30(3): 501-510.
Abstract:
The evolution of the New Tethys has been attracting the interest of many geologists around the world for it separated Eurasia and Gondwana during the Mesozoic era. In addition to creating the AlpsHimalayan orogenic system, the diminishing and closing of the New Tethys may have played a major role in changing the Cenozoic global climate and causing the Asian inland aridity. The Tarim Basin is one of the few areas in China where MesoCenozoic marine strata are exposed. In this study, Kuzigongsu section of Late Cretaceous to Oligocene strata is selected to investigate the lithology and biological assemblage， particle composition and substrate type as well as sedimentary structure of the Late Cretaceous to Oligocene marine stratum by means of sedimentary microfacies analysis. Focusing on carbonate rocks, nine main types of carbonatefacies in the section canbe recognized, including debris cryptocrystal limestone, cryptocrystal limestone, microcrystalline (cryptocrystalline) dolomite, bird's eye cryptocrystal limestone, microcrystalline oosparite dolomite, bioclastic limestone, microcrystalline spherulite dolomite, biolimestone, and sparite oosparite limestone. Combining with sedimentary characteristics of the section，we identify five sedimentary facies (supratidal zone, intertidal zone, sublittoral zone, shallow of platform edge, and reefs) and restore the sedimentary evolution process from the late Cretaceous to Oligocene in the section. Based on the distribution of sedimentary facies and the regional information, there are five cycles of marine transgression along the northwestern margin of Tarim Basin from the Cretaceous to Paleogene. Three largescale transgression are found in Kukebai group , Qimugen group and Kalataer group and two smallscale transgression are found in Yigeziya group and the late of Bashenbulake group. No numerous marine paleontology fossils are found in the strata lying above the oyster layer in the uppermost part of Bashenbulake Formation, which implicate that the New Tethys finally retreat from the northwestern margin of Tarim Basin in Oligocene at the top of Bashibulake Formation. Thus，these will surely provide some references for finding out evolution of the Tethys Ocean from the Cretaceous to Oligocene and reconstructing regional paleoenvironment of Tarim Basin.
The evolution of the New Tethys has been attracting the interest of many geologists around the world for it separated Eurasia and Gondwana during the Mesozoic era. In addition to creating the AlpsHimalayan orogenic system, the diminishing and closing of the New Tethys may have played a major role in changing the Cenozoic global climate and causing the Asian inland aridity. The Tarim Basin is one of the few areas in China where MesoCenozoic marine strata are exposed. In this study, Kuzigongsu section of Late Cretaceous to Oligocene strata is selected to investigate the lithology and biological assemblage， particle composition and substrate type as well as sedimentary structure of the Late Cretaceous to Oligocene marine stratum by means of sedimentary microfacies analysis. Focusing on carbonate rocks, nine main types of carbonatefacies in the section canbe recognized, including debris cryptocrystal limestone, cryptocrystal limestone, microcrystalline (cryptocrystalline) dolomite, bird's eye cryptocrystal limestone, microcrystalline oosparite dolomite, bioclastic limestone, microcrystalline spherulite dolomite, biolimestone, and sparite oosparite limestone. Combining with sedimentary characteristics of the section，we identify five sedimentary facies (supratidal zone, intertidal zone, sublittoral zone, shallow of platform edge, and reefs) and restore the sedimentary evolution process from the late Cretaceous to Oligocene in the section. Based on the distribution of sedimentary facies and the regional information, there are five cycles of marine transgression along the northwestern margin of Tarim Basin from the Cretaceous to Paleogene. Three largescale transgression are found in Kukebai group , Qimugen group and Kalataer group and two smallscale transgression are found in Yigeziya group and the late of Bashenbulake group. No numerous marine paleontology fossils are found in the strata lying above the oyster layer in the uppermost part of Bashenbulake Formation, which implicate that the New Tethys finally retreat from the northwestern margin of Tarim Basin in Oligocene at the top of Bashibulake Formation. Thus，these will surely provide some references for finding out evolution of the Tethys Ocean from the Cretaceous to Oligocene and reconstructing regional paleoenvironment of Tarim Basin.
2012, 30(3): 511-521.
Abstract:
With the application of well data from 1 800 exploration and development wells with the inter distance of 200 m , identification of lithology and analysis of logging facies, we compile sand thickness map and joint wells section of sand body in sandunitⅠ, third segment of Nengjiang Formation. By the semiquantitative analyses on sand bodies, we find that the interval of interest is deposited as the shallowwater deltas front and the main kind of sand body is subaqueous distributary channel deposition, witch extends over 20 km and evolves into three types processing to the end of delta front: the sand body of meandering channel, which is characterized as long pod ,with the width from 600 m to 900 m , and branch off after stretched 8~10 km ; the sand body of branching channel ,which is characterized as short pad , with the width from 500 m to 900 m , and branch off after stretched 2~3 km ,distribute as the symbol of ‘人’or rhombusshaped ; the sand body of reticulate channel, which is distribute as nets, with the width from 300 m to 500 m ,and branch off after stretched 0.5~1 km. The evolution of subaqueous distributary channel sand body associated with the change of superimposed styles and microfacies. The former changed from vertical superposition to dislocated superposition to dislocatedlevel composited superposition to levelly related joint to isolated dispersion; the latter changed from crevasse channel to interchannel deposits to mouth bar. All of the above association are the result of gentle sedimentary basement，rich sediment supply，steadily falling lake level，stable subsea natural barrier and the energy transformation between rivers and lakes.
With the application of well data from 1 800 exploration and development wells with the inter distance of 200 m , identification of lithology and analysis of logging facies, we compile sand thickness map and joint wells section of sand body in sandunitⅠ, third segment of Nengjiang Formation. By the semiquantitative analyses on sand bodies, we find that the interval of interest is deposited as the shallowwater deltas front and the main kind of sand body is subaqueous distributary channel deposition, witch extends over 20 km and evolves into three types processing to the end of delta front: the sand body of meandering channel, which is characterized as long pod ,with the width from 600 m to 900 m , and branch off after stretched 8~10 km ; the sand body of branching channel ,which is characterized as short pad , with the width from 500 m to 900 m , and branch off after stretched 2~3 km ,distribute as the symbol of ‘人’or rhombusshaped ; the sand body of reticulate channel, which is distribute as nets, with the width from 300 m to 500 m ,and branch off after stretched 0.5~1 km. The evolution of subaqueous distributary channel sand body associated with the change of superimposed styles and microfacies. The former changed from vertical superposition to dislocated superposition to dislocatedlevel composited superposition to levelly related joint to isolated dispersion; the latter changed from crevasse channel to interchannel deposits to mouth bar. All of the above association are the result of gentle sedimentary basement，rich sediment supply，steadily falling lake level，stable subsea natural barrier and the energy transformation between rivers and lakes.
2012, 30(3): 522-529.
Abstract:
Shape is the fundamental property of all objects, including sedimentary gravels. As one of the three elements of the shape, roundness of gravels can reflect their transportation history. Since it was brought up, researchers have paid close attention to it. However, the methods of defining gravel roundness in the field haven't made obvious progress. On one hand, the sedimentologists have not paid enough attention to the field outcrops, which causes the phenomenon that those methods are almost for threedimensional gravels and have no effect on the field outcrops, though there are various kinds of quantitative methods to work on gravel roundness. In the past, the terms to describe the roundness of gravel in the field are merely well rounded, rounded, subrounded, subangular, angular and very angular and some other qualitative descriptions. Furthermore, comparing the observed outlines of the gravels with visual comparator is also a way to describe the roundness which is confined in describing between qualitative and semiquantitative. On the other hand, quantifying the roundness of gravels in the field is quite difficult, for many outcrops can't be measured directly because of the topography, and the measuring is timeconsuming and field time is always limited. To get quantitative data of roundness of gravels, this paper proposes a new method, taking Permian Qixia Formation in Chaohu, Anhui Province for example. First, we take photos of conglomerates on field outcrops with a digital camera, and then deal these digital images with a variety of related computer software. The main steps including: determine the boundary between gravel and matrix, then outline the gravel; drawing the maximum inscribed circle of the contours and the inside circles of the corners on the counters, then obtaining the radius of curvature of the circles; putting the radius into the Wadell's (1932) formula and then we can know the value of roundness of the gravel. This method makes it possible to obtain the quantitative data of the roundness of gravel, which is more operable and efficient. What's more, we also use it to deal with the percentage composition of gravel and matrix. Therefore, our work not only provides new quantitative research methods and ideas for the roundness of gravel, but also is of significant meaning for describing the geometry characteristics of gravel. However, there are still many things for us to improve. For example, when we outline the gravels and determine the round corners, some subjective factors will be inevitably brought in. In this part, we need to do some new attempts, such as distinguishing boundary between gravel and matrix and obtaining more accurate corners radius using some sorts of graphical analysis software such as Arcgis.
Shape is the fundamental property of all objects, including sedimentary gravels. As one of the three elements of the shape, roundness of gravels can reflect their transportation history. Since it was brought up, researchers have paid close attention to it. However, the methods of defining gravel roundness in the field haven't made obvious progress. On one hand, the sedimentologists have not paid enough attention to the field outcrops, which causes the phenomenon that those methods are almost for threedimensional gravels and have no effect on the field outcrops, though there are various kinds of quantitative methods to work on gravel roundness. In the past, the terms to describe the roundness of gravel in the field are merely well rounded, rounded, subrounded, subangular, angular and very angular and some other qualitative descriptions. Furthermore, comparing the observed outlines of the gravels with visual comparator is also a way to describe the roundness which is confined in describing between qualitative and semiquantitative. On the other hand, quantifying the roundness of gravels in the field is quite difficult, for many outcrops can't be measured directly because of the topography, and the measuring is timeconsuming and field time is always limited. To get quantitative data of roundness of gravels, this paper proposes a new method, taking Permian Qixia Formation in Chaohu, Anhui Province for example. First, we take photos of conglomerates on field outcrops with a digital camera, and then deal these digital images with a variety of related computer software. The main steps including: determine the boundary between gravel and matrix, then outline the gravel; drawing the maximum inscribed circle of the contours and the inside circles of the corners on the counters, then obtaining the radius of curvature of the circles; putting the radius into the Wadell's (1932) formula and then we can know the value of roundness of the gravel. This method makes it possible to obtain the quantitative data of the roundness of gravel, which is more operable and efficient. What's more, we also use it to deal with the percentage composition of gravel and matrix. Therefore, our work not only provides new quantitative research methods and ideas for the roundness of gravel, but also is of significant meaning for describing the geometry characteristics of gravel. However, there are still many things for us to improve. For example, when we outline the gravels and determine the round corners, some subjective factors will be inevitably brought in. In this part, we need to do some new attempts, such as distinguishing boundary between gravel and matrix and obtaining more accurate corners radius using some sorts of graphical analysis software such as Arcgis.
2012, 30(3): 530-535.
Abstract:
The experimental results show that :(1) the sediment particles are vulnerable to be broken because of the brunt. When the propeller of the laser grainsize equipment rotates quickly, larger particles would be broken to smalls with grain size of 32~87 μm, at the same time, the ultrasonic disaggregating of the laser grainsize equipment would also shatter the sediment particles; therefore, the ultrasonic disaggregating of the laser grainsize equipment should not be available. (2) The sample shading degree would be influenced by the rotatespeed of the laser grainsize equipment. During the test, we found that the slower rotational speed of the equipment, the less instability of the measure result. But with the slowing rotatespeed, the differences of the shading degree and blue light shading degree of the samples become bigger. The sample shading degree is mostly stable when the rotational speed of the laser grainsize equipment is 500 r/min, but the water power is so inadequate that the larger particles can't be pumped into sample injector, hence the sample shading degree is lower, and the differences of the shading degree and blue light shading degree of the samples become bigger.(3) It would contribute to more serious damage of large particles if the rotational speed is too fast, on the contrary, the low speed would lead the sediment particles not to disperse equably in the solution. Analyses that accounted for the stability of measure results, the sample shading degree, the grain size changes and content changes during the test shows that the appropriate rotational speed is about 1 900~2 000 r/min. So the comprehensive analysis can be concluded is that the appropriate rotational speed of Mastersizer 2000 laser particle analyzer is about 1 900~2 000 r/min for the river arenaceous sediment, and the ultrasonic disaggregating of the laser grainsize equipment should not be available.
The experimental results show that :(1) the sediment particles are vulnerable to be broken because of the brunt. When the propeller of the laser grainsize equipment rotates quickly, larger particles would be broken to smalls with grain size of 32~87 μm, at the same time, the ultrasonic disaggregating of the laser grainsize equipment would also shatter the sediment particles; therefore, the ultrasonic disaggregating of the laser grainsize equipment should not be available. (2) The sample shading degree would be influenced by the rotatespeed of the laser grainsize equipment. During the test, we found that the slower rotational speed of the equipment, the less instability of the measure result. But with the slowing rotatespeed, the differences of the shading degree and blue light shading degree of the samples become bigger. The sample shading degree is mostly stable when the rotational speed of the laser grainsize equipment is 500 r/min, but the water power is so inadequate that the larger particles can't be pumped into sample injector, hence the sample shading degree is lower, and the differences of the shading degree and blue light shading degree of the samples become bigger.(3) It would contribute to more serious damage of large particles if the rotational speed is too fast, on the contrary, the low speed would lead the sediment particles not to disperse equably in the solution. Analyses that accounted for the stability of measure results, the sample shading degree, the grain size changes and content changes during the test shows that the appropriate rotational speed is about 1 900~2 000 r/min. So the comprehensive analysis can be concluded is that the appropriate rotational speed of Mastersizer 2000 laser particle analyzer is about 1 900~2 000 r/min for the river arenaceous sediment, and the ultrasonic disaggregating of the laser grainsize equipment should not be available.
2012, 30(3): 536-546.
Abstract:
The Horqin desert, intensely influenced by East Asian monsoon, is located in the desert-loess boundary belt and agricultural and animal husbandry interlaced zone in North China. The geographic setting suggests that the Horqin desert is very sensitive to the global climatic change, so it is an ideal zone for studying the response of global climatic change. Analysis on magnetic susceptibility, grain size and oxides and ratios of chemical elements from TL profile during the middle and late Holocene indicates that the regional climate is very unstable, which is classified into the following phases: ① From 6.0 ka BP to 4.2 ka BP, the summer monsoonal strength is continuously increased and dominated this region, the warm and humid climate is corresponding to the Holocene thermal maximum period, but exists climatic fluctuation on centennial scale, accompanying with weaker winter monsoon. During this period, the climate is warm and humid in 6.0~5.6 ka BP, 5.5~5.4 ka BP, 4.9~4.7 ka BP, 4.5~4.2 ka BP while it is relatively cold and dry in 5.6~5.5 ka BP, 5.4~4.9 ka BP, 4.7~4.5 ka BP. ② From 4.2 ka BP to 1.3 ka BP, compared with the former phase, the regional climate becomes relatively warm and humid but have smaller fluctuations, accompanying with the declined summer monsoonal strength. The climate is dominated by cold and dry in 4.2~3.63 ka BP, 3.57~3.4 ka BP while it is relatively warm and humid in 3.63~3.57 ka BP, 3.4~1.3 ka BP. ③ From 1.3 ka BP to 0.65 ka BP, the regional climate is frequently fluctuated and tends to warm and humid in the later stage. These climatic changes in Horqin desert are very coincident with the regional and global climatic change, reflecting the obvious consistency between them.
The Horqin desert, intensely influenced by East Asian monsoon, is located in the desert-loess boundary belt and agricultural and animal husbandry interlaced zone in North China. The geographic setting suggests that the Horqin desert is very sensitive to the global climatic change, so it is an ideal zone for studying the response of global climatic change. Analysis on magnetic susceptibility, grain size and oxides and ratios of chemical elements from TL profile during the middle and late Holocene indicates that the regional climate is very unstable, which is classified into the following phases: ① From 6.0 ka BP to 4.2 ka BP, the summer monsoonal strength is continuously increased and dominated this region, the warm and humid climate is corresponding to the Holocene thermal maximum period, but exists climatic fluctuation on centennial scale, accompanying with weaker winter monsoon. During this period, the climate is warm and humid in 6.0~5.6 ka BP, 5.5~5.4 ka BP, 4.9~4.7 ka BP, 4.5~4.2 ka BP while it is relatively cold and dry in 5.6~5.5 ka BP, 5.4~4.9 ka BP, 4.7~4.5 ka BP. ② From 4.2 ka BP to 1.3 ka BP, compared with the former phase, the regional climate becomes relatively warm and humid but have smaller fluctuations, accompanying with the declined summer monsoonal strength. The climate is dominated by cold and dry in 4.2~3.63 ka BP, 3.57~3.4 ka BP while it is relatively warm and humid in 3.63~3.57 ka BP, 3.4~1.3 ka BP. ③ From 1.3 ka BP to 0.65 ka BP, the regional climate is frequently fluctuated and tends to warm and humid in the later stage. These climatic changes in Horqin desert are very coincident with the regional and global climatic change, reflecting the obvious consistency between them.
2012, 30(3): 547-555.
Abstract:
Sediments in tidal deposits of the northern Hangzhou Bay are mainly supplied by fluvial discharge of the Yangtze River. In recent years, sediment discharge of the Yangtze River has declined dramatically. Therefore, the potential impact on tidal deposits of the Hangzhou Bay has attracted great attentions. Magnetic minerals, ubiquitous components of sediments, are sensitive to sediment source variations. As a result, magnetic methods have been widely used in provenance tracing of suspended matters and sediments in fluvial, marine, lacustrine and atmospheric environments. We have carried out magnetic measurements on surface tidal deposits collected daily from a fixed intertidal site at Luchaogang along the northern bank of the Hangzhou Bay during 2004 and 2005. It was found that particle size and magnetic properties exhibit significant seasonal changes. In general, during the accretion period of tidal flat, magnetic mineral concentrations are higher when sediments are finer, and vice versa. In this study, magnetic measurements and particle size analysis were carried out on tidal flat sediments, collected daily at the same site from 2007 to 2010. The purpose is to study the annual changes in sediment composition under a context of the declined fluvial sediment discharge of Yangtze River. The monthly and annual variation pattern of magnetic properties and its relationship with particle size were discussed. Magnetic parameters of sediments show similar monthly variations from 2007 to 2009. Magnetic susceptibility (χ), Susceptibility of anhystereric remnant magnetization (χARM), Saturation isothermal remnant magnetization (SIRM) and the ratio (χARM/ SIRM, show higher values in December to July and lower values in August to November, and S300 shows the opposite tend. Particle size analysis indicates that sediments are finer between December and July, and coarser between August and November in these three years, suggesting that ferrimagnetic minerals are enriched in finer sediments, which is similar to the previous results reported for samples collected in 2004 and 2005. Compared to samples collected in 20072009, it can be seen that magnetic mineral concentrations in sediments of 2010 decrease between December and July, and increase between August and November. As a result, the amplitude of monthly variation of magnetic properties becomes smaller. Meanwhile, sediments of 2010 become coarser between December and July, and finer between August and November. The relationship between magnetic properties and particle size is generally similar in the four years, which suggests that the monthly variation of particle size is the main factor for the monthly changes of magnetic properties in 2010. In general, χ, χARM, SIRM and χARM / SIRM are positively correlated with the <16 μm fraction and negatively with the >63 μm fraction. In contrast, S300 is negatively correlated with the <16 μm fraction and positively with the >63 μm fraction. It indicates that magnetic minerals are enriched in the <16 μm fraction, which is diluted by the >63 μm fraction. In 2010, the decreases of concentrationrelated magnetic parameters between December and July are caused by the decline of the <8 μm fraction. On the contrary, the increase of concentrationrelated magnetic parameters in the remaining months are caused by the increase of the <32 μm fraction. However, the above mentioned relationships between magnetic parameters and particle size weaken since 2009, which is especially significant in 2010. The factors for the observed relationship between magnetic properties and particle size in 2010, which is different from previous years, may include tides, winds, sediments flux, coast morphology and engineering works. Therefore, an integrated monitoring of hydrodynamics, meteorology, and topography is needed to address the mechanism. In addition, the potential impacts of decline sediment input of the Yangtze River on tidal flat sediment source, need to be assessed in future study. This study demonstrates that magnetic methods, with the virtue of being simple and sensitive, can provide valuable insights to environmental change through the analysis of sediment composition in a simple and nondestructive way.
Sediments in tidal deposits of the northern Hangzhou Bay are mainly supplied by fluvial discharge of the Yangtze River. In recent years, sediment discharge of the Yangtze River has declined dramatically. Therefore, the potential impact on tidal deposits of the Hangzhou Bay has attracted great attentions. Magnetic minerals, ubiquitous components of sediments, are sensitive to sediment source variations. As a result, magnetic methods have been widely used in provenance tracing of suspended matters and sediments in fluvial, marine, lacustrine and atmospheric environments. We have carried out magnetic measurements on surface tidal deposits collected daily from a fixed intertidal site at Luchaogang along the northern bank of the Hangzhou Bay during 2004 and 2005. It was found that particle size and magnetic properties exhibit significant seasonal changes. In general, during the accretion period of tidal flat, magnetic mineral concentrations are higher when sediments are finer, and vice versa. In this study, magnetic measurements and particle size analysis were carried out on tidal flat sediments, collected daily at the same site from 2007 to 2010. The purpose is to study the annual changes in sediment composition under a context of the declined fluvial sediment discharge of Yangtze River. The monthly and annual variation pattern of magnetic properties and its relationship with particle size were discussed. Magnetic parameters of sediments show similar monthly variations from 2007 to 2009. Magnetic susceptibility (χ), Susceptibility of anhystereric remnant magnetization (χARM), Saturation isothermal remnant magnetization (SIRM) and the ratio (χARM/ SIRM, show higher values in December to July and lower values in August to November, and S300 shows the opposite tend. Particle size analysis indicates that sediments are finer between December and July, and coarser between August and November in these three years, suggesting that ferrimagnetic minerals are enriched in finer sediments, which is similar to the previous results reported for samples collected in 2004 and 2005. Compared to samples collected in 20072009, it can be seen that magnetic mineral concentrations in sediments of 2010 decrease between December and July, and increase between August and November. As a result, the amplitude of monthly variation of magnetic properties becomes smaller. Meanwhile, sediments of 2010 become coarser between December and July, and finer between August and November. The relationship between magnetic properties and particle size is generally similar in the four years, which suggests that the monthly variation of particle size is the main factor for the monthly changes of magnetic properties in 2010. In general, χ, χARM, SIRM and χARM / SIRM are positively correlated with the <16 μm fraction and negatively with the >63 μm fraction. In contrast, S300 is negatively correlated with the <16 μm fraction and positively with the >63 μm fraction. It indicates that magnetic minerals are enriched in the <16 μm fraction, which is diluted by the >63 μm fraction. In 2010, the decreases of concentrationrelated magnetic parameters between December and July are caused by the decline of the <8 μm fraction. On the contrary, the increase of concentrationrelated magnetic parameters in the remaining months are caused by the increase of the <32 μm fraction. However, the above mentioned relationships between magnetic parameters and particle size weaken since 2009, which is especially significant in 2010. The factors for the observed relationship between magnetic properties and particle size in 2010, which is different from previous years, may include tides, winds, sediments flux, coast morphology and engineering works. Therefore, an integrated monitoring of hydrodynamics, meteorology, and topography is needed to address the mechanism. In addition, the potential impacts of decline sediment input of the Yangtze River on tidal flat sediment source, need to be assessed in future study. This study demonstrates that magnetic methods, with the virtue of being simple and sensitive, can provide valuable insights to environmental change through the analysis of sediment composition in a simple and nondestructive way.
2012, 30(3): 556-564.
Abstract:
High resolution records as lakes, peats, speleothems are reported to study the hydrological exhibition of 4.2 ka BP event in China in recent years. The terrigenous clastic matter in continental shelf could reveal sedimentary environment evolvement and paleoclimate. Sediment grain size, clay mineral, major elements, and benthic foraminifera of the Core C069 (113 49' E, 21 15' N, length: 2.1 m), which is from inner shelf of the northern South China Sea, have been investigated to reveal sedimentary environment evolvement and paleoclimate. The results indicate that sediments became finer and well from bottom to top. The frequency distribution curves of grain size in the lower segment (1.1~2.1 m) are poorly sorted with bimodal distribution, which display the strong hydrodynamic condition. However, in the upper segment (0~1.1 m) after 4.4 ka, the sediments have single peak frequency distribution curves. The coarse sediments derived from the Pearl River. The clay mineral assemblage consists dominantly of illite, lesser abundance of kaolinite and chlorite, with scare smectite. Kaolinite of the northern South China Sea is dominartly originated major origin from the Pearl River, predominant illite and chlorite from Taiwan, and principal smectite from the Luzon islands. The content of kaolinite decreases from 27% (1.1~2.1 m) to 18% (0~1.1 m), and illite crystallinity and illite chemistry index decrease similarily. The upper segment with more illite displays that more contribution of illite from Taiwan carried by surface currents, result in lower illite crystallinity and chemistry index. The results suggest that clay mineral assemblages in the inner shelf of the northern South China Sea are mainly controlled by provenance supply and downcore records do not bear contemporaneous paleoclimatic features. The benthic foraminifera dominant species in the lower segment are Ammonia becarii and Ammonia dominicana, which lived in brackish environment where the water was influenced by Pearl River diluted water. However, the benthic foraminifera dominant species changed with Cibicidoides subhaidingarii, Ammonia compressituta in the upper segment, which lived in normal shallow water environment. MgO/Al2O3 ratio increased from bottom to top due to the less terrigenous clastic matter transported to inner shelf of the northern South China Sea in extreme drycold after 4.2 ka. The lower segment sediments contain higher kaolinite content; lower MgO/Al2O3 ratio, with benthic foraminifera dominant species lived in brackish environment where the water was influenced by Pearl River diluted water in the Holocene Megathermal. However, the upper segment sediments contain lower kaolinite content, higher MgO/Al2O3 ratio in the upper segment, displaying that less Pearl River's contribution in extreme drycold time since 4.2 ka.
High resolution records as lakes, peats, speleothems are reported to study the hydrological exhibition of 4.2 ka BP event in China in recent years. The terrigenous clastic matter in continental shelf could reveal sedimentary environment evolvement and paleoclimate. Sediment grain size, clay mineral, major elements, and benthic foraminifera of the Core C069 (113 49' E, 21 15' N, length: 2.1 m), which is from inner shelf of the northern South China Sea, have been investigated to reveal sedimentary environment evolvement and paleoclimate. The results indicate that sediments became finer and well from bottom to top. The frequency distribution curves of grain size in the lower segment (1.1~2.1 m) are poorly sorted with bimodal distribution, which display the strong hydrodynamic condition. However, in the upper segment (0~1.1 m) after 4.4 ka, the sediments have single peak frequency distribution curves. The coarse sediments derived from the Pearl River. The clay mineral assemblage consists dominantly of illite, lesser abundance of kaolinite and chlorite, with scare smectite. Kaolinite of the northern South China Sea is dominartly originated major origin from the Pearl River, predominant illite and chlorite from Taiwan, and principal smectite from the Luzon islands. The content of kaolinite decreases from 27% (1.1~2.1 m) to 18% (0~1.1 m), and illite crystallinity and illite chemistry index decrease similarily. The upper segment with more illite displays that more contribution of illite from Taiwan carried by surface currents, result in lower illite crystallinity and chemistry index. The results suggest that clay mineral assemblages in the inner shelf of the northern South China Sea are mainly controlled by provenance supply and downcore records do not bear contemporaneous paleoclimatic features. The benthic foraminifera dominant species in the lower segment are Ammonia becarii and Ammonia dominicana, which lived in brackish environment where the water was influenced by Pearl River diluted water. However, the benthic foraminifera dominant species changed with Cibicidoides subhaidingarii, Ammonia compressituta in the upper segment, which lived in normal shallow water environment. MgO/Al2O3 ratio increased from bottom to top due to the less terrigenous clastic matter transported to inner shelf of the northern South China Sea in extreme drycold after 4.2 ka. The lower segment sediments contain higher kaolinite content; lower MgO/Al2O3 ratio, with benthic foraminifera dominant species lived in brackish environment where the water was influenced by Pearl River diluted water in the Holocene Megathermal. However, the upper segment sediments contain lower kaolinite content, higher MgO/Al2O3 ratio in the upper segment, displaying that less Pearl River's contribution in extreme drycold time since 4.2 ka.
2012, 30(3): 565-571.
Abstract:
In the latest decades it has been confronted with the enhanced flood risk in the Yinchuan plain reach of the Yellow River and occurred several large floods have induced much economic losing. Many researches concluded that these flood disasters were resulted from the three large reservoir (Qingtongxia, Liujiaxia and Longyangxia) construction in the upper Yellow River because of the operation of the reservoirs and the water derivation from the reservoirs and the main stream in the upper Yellow River induced the enhanced channel sedimentation rate in the studied river reach. However, many previous studies in the world have showen that large dam or reservoir construction could induce the enhanced channel erosion or decreasing sedimentation rate in the dwonstream reach below the dam or reservoir. The change trends of channel sedimentation rates in longtime scale which includes anthropogenic dominant period (e.g. last 50 years) and natural dominant period (e.g. 1 000 years ago) could be used to reveal the influences of human activities on the channel change in the last decades. The aims of this study are to reveal the variation trend of the channel sedimentation rates in the Yinchuan plain reach of the Yellow River since 0.9 Ma B.P. and to evaluate whether the human activities have led to increase the channel sedimentation rates during the last decades. The methods used in this study are mainly the caculation of the average rate of channel sedimentation in geomophological scale according to the chronological analysis of a bore core with depth about 300 m, correlation analysis in different time periods since 0.9 Ma B.P., and the comparison of channel bed variation according to the 9 channel cross-sections in the river reach measured in the two different years of 1993 and 2001 that could be uesed to assess the present channel sedimentation rate. The results indicate that the pulse function relationship between years and channel sedimentation rates obtained from the correlation analysis method can be used to estimate commendably the historical variation trend of the channel sedimentation rate in the study river reach in geomophological scale. The sedimentation rate has had an increase trend since 0.9 Ma B.P. as a whole, however, a decrease trend of channel sedimentation rates has occurred since 20 ka B.P. The peak value of 3.43 cm/a appeared in 20 ka B.P., it indictes that the maximum channel sedimentation rate was in 20 ka B.P. The average channel sedimentation rate since 0.04 Ma B.P. calculated from the pulse function is 3.16 cm/a. The present sedimentation rate estimated from this function is 0.51 cm/a which is close to the result of 0.3 cm/a caculated from the actual measurement of the channel cross-section variation. Obviously, the present channel sedimentation rate is far less the maximum sedimentation rate in the geomophological scale as well as the average channel sedimentation rate since 0.04 Ma B.P. The human activities, such as the water and soil conservation, large reservoir or dem constructions, and water derivation in the main stream of the upper Yellow River drainage basin, have decreased a lot of coarse sediment feeding to the Yinchuan plain reach of the upper Yellow river and decreased the channel sedimentation rate in the studied river reach.
In the latest decades it has been confronted with the enhanced flood risk in the Yinchuan plain reach of the Yellow River and occurred several large floods have induced much economic losing. Many researches concluded that these flood disasters were resulted from the three large reservoir (Qingtongxia, Liujiaxia and Longyangxia) construction in the upper Yellow River because of the operation of the reservoirs and the water derivation from the reservoirs and the main stream in the upper Yellow River induced the enhanced channel sedimentation rate in the studied river reach. However, many previous studies in the world have showen that large dam or reservoir construction could induce the enhanced channel erosion or decreasing sedimentation rate in the dwonstream reach below the dam or reservoir. The change trends of channel sedimentation rates in longtime scale which includes anthropogenic dominant period (e.g. last 50 years) and natural dominant period (e.g. 1 000 years ago) could be used to reveal the influences of human activities on the channel change in the last decades. The aims of this study are to reveal the variation trend of the channel sedimentation rates in the Yinchuan plain reach of the Yellow River since 0.9 Ma B.P. and to evaluate whether the human activities have led to increase the channel sedimentation rates during the last decades. The methods used in this study are mainly the caculation of the average rate of channel sedimentation in geomophological scale according to the chronological analysis of a bore core with depth about 300 m, correlation analysis in different time periods since 0.9 Ma B.P., and the comparison of channel bed variation according to the 9 channel cross-sections in the river reach measured in the two different years of 1993 and 2001 that could be uesed to assess the present channel sedimentation rate. The results indicate that the pulse function relationship between years and channel sedimentation rates obtained from the correlation analysis method can be used to estimate commendably the historical variation trend of the channel sedimentation rate in the study river reach in geomophological scale. The sedimentation rate has had an increase trend since 0.9 Ma B.P. as a whole, however, a decrease trend of channel sedimentation rates has occurred since 20 ka B.P. The peak value of 3.43 cm/a appeared in 20 ka B.P., it indictes that the maximum channel sedimentation rate was in 20 ka B.P. The average channel sedimentation rate since 0.04 Ma B.P. calculated from the pulse function is 3.16 cm/a. The present sedimentation rate estimated from this function is 0.51 cm/a which is close to the result of 0.3 cm/a caculated from the actual measurement of the channel cross-section variation. Obviously, the present channel sedimentation rate is far less the maximum sedimentation rate in the geomophological scale as well as the average channel sedimentation rate since 0.04 Ma B.P. The human activities, such as the water and soil conservation, large reservoir or dem constructions, and water derivation in the main stream of the upper Yellow River drainage basin, have decreased a lot of coarse sediment feeding to the Yinchuan plain reach of the upper Yellow river and decreased the channel sedimentation rate in the studied river reach.
2012, 30(3): 572-579.
Abstract:
The different grain size content range from 0.5~500 μm and magnetic susceptibility were measured to study the correlation between grain size and magnetic susceptibility, selected more 590 samples, in sediments from Core Changping. The results show that magnetic susceptibility of the profile is of some relationship with that of the content of different grain sizes, the correlation coefficient between susceptibility and the mean grain size is positive for the whole core. The magnetic minerals are mainly concentrated in fractions with coaster grains. Furthermore, the correlation between grain size and magnetic susceptibility is also affected by sediment source, the degree of sorting process and so on. The correlation coefficient of susceptibility with the content of 0.5~30 μm, especially 0.5~10 μm, is negative, and with the content of 65~500 μm is positive, dominated by large particles of magnetic minerals in the core. In addition, the correlation is different in various depth. Due to the different condition of lake and aggregation, the correlation between magnetic susceptibility and grain sizes should be analyzed depending on deferent sedimental environment. When the strong hydrodynamic, magnetic susceptibility are relatively large, and relatively weak, the magnetic susceptibility is relatively small. Therefore, the grain size and magnetic susceptibility changes to reflect the changes in hydrodynamic conditions, indicating that changes in the strength of the East Asian monsoon. Especially, the climate cycle from the Quaternary period, the to-and-fro of the glaciation and interglaciation, we concluded that data and magnetic susceptibility, particle size and get paleoclimate information of the drilling: 1100~800 ka B.P. is mainly cool and there is a small heating between them, 800~600 ka B.P. cool and warm alternate in temperature, 600~400 ka B.P. climate is prior to hot and humid, 400~200 ka B.P. climate is prior to cold and dry, 200~0 ka B.P. climate is priority to cool alternate fluctuation. Research shows that the core may reflect the 8~10 climatic cyclicities. The area of precipitation increases in humid climate period, with alluvial deposits containing more coarse particles and larger magnetic susceptibility. The fluctuations of susceptibility indicate the changes of paleoclimate.
The different grain size content range from 0.5~500 μm and magnetic susceptibility were measured to study the correlation between grain size and magnetic susceptibility, selected more 590 samples, in sediments from Core Changping. The results show that magnetic susceptibility of the profile is of some relationship with that of the content of different grain sizes, the correlation coefficient between susceptibility and the mean grain size is positive for the whole core. The magnetic minerals are mainly concentrated in fractions with coaster grains. Furthermore, the correlation between grain size and magnetic susceptibility is also affected by sediment source, the degree of sorting process and so on. The correlation coefficient of susceptibility with the content of 0.5~30 μm, especially 0.5~10 μm, is negative, and with the content of 65~500 μm is positive, dominated by large particles of magnetic minerals in the core. In addition, the correlation is different in various depth. Due to the different condition of lake and aggregation, the correlation between magnetic susceptibility and grain sizes should be analyzed depending on deferent sedimental environment. When the strong hydrodynamic, magnetic susceptibility are relatively large, and relatively weak, the magnetic susceptibility is relatively small. Therefore, the grain size and magnetic susceptibility changes to reflect the changes in hydrodynamic conditions, indicating that changes in the strength of the East Asian monsoon. Especially, the climate cycle from the Quaternary period, the to-and-fro of the glaciation and interglaciation, we concluded that data and magnetic susceptibility, particle size and get paleoclimate information of the drilling: 1100~800 ka B.P. is mainly cool and there is a small heating between them, 800~600 ka B.P. cool and warm alternate in temperature, 600~400 ka B.P. climate is prior to hot and humid, 400~200 ka B.P. climate is prior to cold and dry, 200~0 ka B.P. climate is priority to cool alternate fluctuation. Research shows that the core may reflect the 8~10 climatic cyclicities. The area of precipitation increases in humid climate period, with alluvial deposits containing more coarse particles and larger magnetic susceptibility. The fluctuations of susceptibility indicate the changes of paleoclimate.
2012, 30(3): 580-587.
Abstract:
The crude oils from Ordovician reservoir in TZ52 and TZ162 well have been analyzed, the results showed that there are some evident differences in the distributions and compositions of their biomarker from two kinds of the known marine oils in the middle zone of Tarim Basin. For example, it is firstly reported that its trycyclic terpane series is of special steplike model with C19>C20>C21>C23>C24>C25>C26 in relative abundance, C24 tetracyclic terpane is abnormally abundant and it relative abundance is much more than C26 tricyclic terpanes, which occurs in those source rocks and the crude oils deposited under fresh water swamp and shallow lacustrine facies. As for their triterpane series, the abundance of gammacerane is much less than C31 homohopanes, but the distributions of their sterane and hopane series are very similar to the marine oils derived from middle to middle-upper Ordovician source rocks such as with abnormally abundant pregnane and homopregnane, relatively lower C28 sterane in C27-29 steranes and more abundant C29 norhopane secondary to C30 hopane. In addition, their stable carbon isotope of whole oil is very light and their δ13Ｃ values are less than -30‰ like other marine oils, showing that this kind of crude oil is marine. Based on the biomarker data in the source rocks with abundant benthic marco-algae from 4-5 member of Lianglitage formation of upper Ordovician in TZ12 well, it is found that their distribution and the relative composition of its C19-26 tricyclic terpane, C24 tetracyclic terpane and gammacerane is very similar to this kind of crude oils, showing that there is a close relationship between this kind of novel crude oils and the source rocks. Therefore, it should pay much more attention to the source rocks and their exploration potential from Lianglitage Formation of upper Ordovician in Tarim Basin.
The crude oils from Ordovician reservoir in TZ52 and TZ162 well have been analyzed, the results showed that there are some evident differences in the distributions and compositions of their biomarker from two kinds of the known marine oils in the middle zone of Tarim Basin. For example, it is firstly reported that its trycyclic terpane series is of special steplike model with C19>C20>C21>C23>C24>C25>C26 in relative abundance, C24 tetracyclic terpane is abnormally abundant and it relative abundance is much more than C26 tricyclic terpanes, which occurs in those source rocks and the crude oils deposited under fresh water swamp and shallow lacustrine facies. As for their triterpane series, the abundance of gammacerane is much less than C31 homohopanes, but the distributions of their sterane and hopane series are very similar to the marine oils derived from middle to middle-upper Ordovician source rocks such as with abnormally abundant pregnane and homopregnane, relatively lower C28 sterane in C27-29 steranes and more abundant C29 norhopane secondary to C30 hopane. In addition, their stable carbon isotope of whole oil is very light and their δ13Ｃ values are less than -30‰ like other marine oils, showing that this kind of crude oil is marine. Based on the biomarker data in the source rocks with abundant benthic marco-algae from 4-5 member of Lianglitage formation of upper Ordovician in TZ12 well, it is found that their distribution and the relative composition of its C19-26 tricyclic terpane, C24 tetracyclic terpane and gammacerane is very similar to this kind of crude oils, showing that there is a close relationship between this kind of novel crude oils and the source rocks. Therefore, it should pay much more attention to the source rocks and their exploration potential from Lianglitage Formation of upper Ordovician in Tarim Basin.
2012, 30(3): 588-593.
Abstract:
Different structures and functional groups in organic matter have different carbon isotopic compositions. This kind of difference can be predicted by carbon isotopic thermodynamic factor (βfactor) of organic matter. In the simulation experiments, the carbon isotopic composition of CO2 is relatively heavy, which is related to that the thermodynamic carbon isotopic factor (β13C) of carboxyl is relatively large in kerogen. In hydrous experiments, part of methylene finally changes into CO2 by way of cleavage, hydrogen transfer and reaction with water. Because the β13C of methylene is relatively small, correspondingly the carbon isotopic composition of the increased CO2 is relatively light in hydrous experiments, so the carbon isotopic composition of CO2 in the two series of hydrous experiments is slightly lighter than that in anhydrous experiments. This phenomenon proves that water medium is involved in the chemical reaction of hydrocarbon generation. In the three series of experiments, the carbon isotopic composition of methane is relatively heavy in the low temperature phase (≤300℃), which may be related to that the carbon isotopic composition of methane precursor is heavier in this earlymature stage, such as methoxy group. The thermodynamic carbon isotopic factor of methoxy is relatively heavy, which causes that the isotopic composition of methane is relatively heavy in the low evolution stage. While the theory of isotope kinetic fractionation is developing at a high speed at present, we still can not neglect the isotope thermodynamic fractionation, which will be a great help to us in the further study on the mechanism of hydrocarbon generation.
Different structures and functional groups in organic matter have different carbon isotopic compositions. This kind of difference can be predicted by carbon isotopic thermodynamic factor (βfactor) of organic matter. In the simulation experiments, the carbon isotopic composition of CO2 is relatively heavy, which is related to that the thermodynamic carbon isotopic factor (β13C) of carboxyl is relatively large in kerogen. In hydrous experiments, part of methylene finally changes into CO2 by way of cleavage, hydrogen transfer and reaction with water. Because the β13C of methylene is relatively small, correspondingly the carbon isotopic composition of the increased CO2 is relatively light in hydrous experiments, so the carbon isotopic composition of CO2 in the two series of hydrous experiments is slightly lighter than that in anhydrous experiments. This phenomenon proves that water medium is involved in the chemical reaction of hydrocarbon generation. In the three series of experiments, the carbon isotopic composition of methane is relatively heavy in the low temperature phase (≤300℃), which may be related to that the carbon isotopic composition of methane precursor is heavier in this earlymature stage, such as methoxy group. The thermodynamic carbon isotopic factor of methoxy is relatively heavy, which causes that the isotopic composition of methane is relatively heavy in the low evolution stage. While the theory of isotope kinetic fractionation is developing at a high speed at present, we still can not neglect the isotope thermodynamic fractionation, which will be a great help to us in the further study on the mechanism of hydrocarbon generation.
2012, 30(3): 594-602.
Abstract:
Secondary hydrocarbon generation of source rocks included the residual kerogen pyrolysis evolution and thermal cracking of residual oil, two interrelated and completely different physical and chemical reactions. Based on simulation experiments of the natural maturity marine shale samples, used a phased continuouly progressive simulation experiment, and evaluated the residual hydrocarbon potential of kerogen and soluble organic matter into oil and gas residues potential, setd a quantitative evaluation method of secondary hydrocarbon generation of different maturity marine shale. And for the first time clearly put forward the kerogen oil source index KIo, kerogen gas index KIg, kerogen hydrocarbon index KIh and other hydrocarbon index of hydrocarbon source rock evaluation of the parameters of the potential, made up for the ROCKEVAL pyrolysis evaluation method of source rocks can not be evaluated separately in different evolutionary stages of hydrocarbon generation of the "oil" or "hydrocarbon gas" potential deficiencies.
Secondary hydrocarbon generation of source rocks included the residual kerogen pyrolysis evolution and thermal cracking of residual oil, two interrelated and completely different physical and chemical reactions. Based on simulation experiments of the natural maturity marine shale samples, used a phased continuouly progressive simulation experiment, and evaluated the residual hydrocarbon potential of kerogen and soluble organic matter into oil and gas residues potential, setd a quantitative evaluation method of secondary hydrocarbon generation of different maturity marine shale. And for the first time clearly put forward the kerogen oil source index KIo, kerogen gas index KIg, kerogen hydrocarbon index KIh and other hydrocarbon index of hydrocarbon source rock evaluation of the parameters of the potential, made up for the ROCKEVAL pyrolysis evaluation method of source rocks can not be evaluated separately in different evolutionary stages of hydrocarbon generation of the "oil" or "hydrocarbon gas" potential deficiencies.
