The Chenghai fault zone is located in the Sichuan–Yunnan rhombus block,which is surrounded by the Honghe River,Xianshuihe–Xiaojiang,and Jinsha River fault zones.As a mid-continental active fault,it is one of the mos...The Chenghai fault zone is located in the Sichuan–Yunnan rhombus block,which is surrounded by the Honghe River,Xianshuihe–Xiaojiang,and Jinsha River fault zones.As a mid-continental active fault,it is one of the most important seismogenic fractures in the southeast margin of the Tibetan Plateau.Geological seismic study is an important supplement to the historical seismic record;therefore,identification of paleoearthquake events in this region is of great significance to reveal the pattern and mechanism of earthquake development.In this study,detailed investigation has been carried out on the earthquake traces that formed in the Quaternary sediments in the Jinsha River section of the Chenghai fault zone,and samples for dating chronology testing were also collected.Many paleoearthquake traces were discovered in the field,including earthquake fissions,dammed lake sediments and landslides,earthquake-generated rock falls,seismic faults,and sand liquefaction veins.The collected samples were tested using optically stimulated luminescence,electron-spin resonance,and U-series methods.A total of 68 chronological samples were dated,combined with the results of field investigations,and 10 large paleoearthquake events were discovered in this region since 500 ka,which are at approximately 450,400,345,300,250,190,155,105,75,and 25 ka.Ten tectonic activity periods that produced multiple paleoearthquake events were identified since 500 ka.This study identifies paleoearthquake events in longer scales,larger spaces,and more extensive sediments,which provides new perspectives and new ideas for paleoearthquake research.展开更多
Multi-parameter studies (stable isotopes in carbonate and or ganic matter, pigment, organic carbon and nitrogen contents) from a 660-yr cont inuous sediment core from Lake Chenghai, a closed, eutropic lake in southern...Multi-parameter studies (stable isotopes in carbonate and or ganic matter, pigment, organic carbon and nitrogen contents) from a 660-yr cont inuous sediment core from Lake Chenghai, a closed, eutropic lake in southern Chi na, provide information on lake historical eutrophication. During the last 660 y ears, great changes have taken place in productivity and eutrophication of Lake Chenghai in response to human activities. In 1690, the productivity of the lake began to increase as Lake Chenghai became closed from agriculture in the lake’s watershed. In 1942, Lake Chenghai evolved to eutrophic state, marked by an incr ease in organic carbon, nitrogen, CaCO\-3, pigment contents and obvious negative values of stable isotopes, which is more or less simultaneous with the large-s cale population immigration during the period. In 1984, intensive human activiti es induced modern lacustrine productivity and eutrophic level. Human-induced tr ophic changes during the past few decades have affected the Lake Chenghai ecosys tem to such an extent that it has never experienced before in the last 660 years .展开更多
The carbon isotopic composition of organic matter from lake sediments has been extensively used to infer variations in productivity. In this paper, based on the study of the contents and δ13C values of organic matter...The carbon isotopic composition of organic matter from lake sediments has been extensively used to infer variations in productivity. In this paper, based on the study of the contents and δ13C values of organic matter in different types of lakes, it has been found that δ13C values of organic matter have different responses to lake productivity in different lakes. As to the lakes dominated by aqutic macrophytes such as Lake Caohai, organic matter becomes enriched in 13C with increasing productivity. As to the lakes dominated by aquatic algae such as Lake Chenghai, δ13C values of organic matter decrease with increasing productivity, and the degradation of aquatic algae is the main factor leading to the decrease of δ13C values of organic matter with increasing productivity. Therefore, we should be cautious to use the carbon isotopic composition of organic matter to deduce lake productivity.展开更多
As one of the lakes on the Yunnan-Guizhou plateau, Lake Chenghai, which is a typical closed lake with the precipitation accounting for one-third or more of the annual water input, has a high total salinity (almost lik...As one of the lakes on the Yunnan-Guizhou plateau, Lake Chenghai, which is a typical closed lake with the precipitation accounting for one-third or more of the annual water input, has a high total salinity (almost like a saline lake).The inorganic C,O isotopic composition of lake sediments bears much sensitive information about environmental change in the catchment, while their correlations revealed the hydrological conditions under which the lake was closed. Their compositional variations are controlled by temperature, precipitation, photosynthesis, dissolving equilibrium of the carbonate system and hydrological condition. According to our research on inorganic C, O isotopic composition of Lake Chenghai sediments, we investigated the environmental change of this catchment several decades ago. The results showed that Lake Chenghai has kept good hydrological closing conditions in the past several decades, as indicated by the good correlation of inorganic C, O isotopic composition of sediments; and that the environmental change in this catchment shows a tendency of periodical evolution on a 10\+\{-11\}-years scale, although the signal noise is relatively high at the bottom of the sediment core. And we also can extend C, O isotopes, a sensitive environmental indicator, to nearly saline lake environments with a high degree of mineralization.展开更多
Lacustrine sediments can provide potential information about environmental changes in the past. On the basis of high-resolution multi-proxy analysis including carbon and nitrogen contents of organic matter, C/N ratios...Lacustrine sediments can provide potential information about environmental changes in the past. On the basis of high-resolution multi-proxy analysis including carbon and nitrogen contents of organic matter, C/N ratios, inorganic carbon contents, and carbon and oxygen isotopic composition of carbonate, together with precise 137Cs dating, the environmental evolution of Lake Chenghai, Yunnan Province, during the past 100 years has been investigated. It is shown that the carbonate in Lake Chenghai is authigenic, and the organic matter is mainly derived from aquatic plants and algae, instead of terrestrial-source materials. The environmental evolution of Lake Chenghai can be diverged into three periods with the contrasting characteristics during the past 100 years. Before 1940, the stable carbon and oxygen isotope values, the poor correlation between them and the lower carbon and nitrogen contents of organic matter suggested that Lake Chenghai was open, and the lake water was oligotrophic during that period. During 1940-1993, the negative δ13C values and the gradual increase of carbon and nitrogen contents of organic matter and C/N ratios indicated that the eutrophication was aggravated. The closeness of Lake Chenghai and human activities may be responsible for this eutrophication. After 1993, notable increases in carbon and oxygen isotopic values of carbonate, carbon and nitrogen contents of organic matter, C/N ratios and inorganic carbon contents demonstrated that the increase of lacustrine productivity and the serious eutrophication were resulted from strong human activities. Therefore, the multi-proxy in Lake Chenghai sediments has reliably recorded the natural environmental evolution and the impacts from human activities.展开更多
The fundamental assumption of 210Pbsediment dating is the stable flux of 210Pbse, which was derived from atmosphere and then transferred into sediments via lake water. When the sedimentation rate is relatively constan...The fundamental assumption of 210Pbsediment dating is the stable flux of 210Pbse, which was derived from atmosphere and then transferred into sediments via lake water. When the sedimentation rate is relatively constant, the 210Pbse activity in sediments will be exponentially reduced with sedimentation age. 210Pbse in lake water is incorporated into sediments mainly via organic particulates. If the sedimentation flux of organic matter in lake water is suddenly in- creased, 210Pbse will be significantly deposited and then transferred into sediments. On the one hand such sudden purification effect is obviously unfit for the fundamental assumption of 210Pbse dating; on the other hand, the sudden enhancement of 210Pbse flux would be indicative of the conspicuous variation of primary productivity of lake water. This problem will be discussed in accordance with the variation trend of 210Pbex in the vertical profile of recent sediments of Lake Chenghai, Yunnan Province. The sediment core was collected from the deep-water area of Lake Chenghai in June 1997. The vertical profile of 137 Cs activity is characterized by a tree-peak pat- tern. This profile gave reliable ages, and also showed the stability of sediment accumulation in the recent ten years. The vertical profile of210Pbse activity displays a specific distribution of peaks, and is similar to the vertical profile of Corg. This phenomenon seems to be related to the mecha- nism of constraining the transfer of 210Pbse into lake sediments. The average atomic ratios of Horg/Corg and Corg/Norg in Lake Chenghai sediments are 5.51 and 7.04, respectively, indicating that the organic matter was predominantly derived from the remains of endogenic algae. In terms of the three-stage evolutionary characteristics of organic matter in sediments, i.e., “deposition-de- composition-accumulation”, the sedimentation fluxes （F（Corg）） of organic carbon （Corg） since 1970 were calculated by modeling. The sedimentation fluxes of 210Pbse (F(210Pbse)) in different years display good synchronous relations with the sedimentation flux of organic carbon （F（Corg））, es- pecially in the years of 1972─1974 and 1986─1989. The variation of F（Corg） led to the variation of F(210Pbse); the variation of F（210Pbex） reflects, to some extent, the historical variation of lake pro- ductivity.展开更多
Investigating the formation and evolution of coarse-grained deposits in modern lakes and the relevant controlling conditions is indispensable to the prediction of reservoir sandbodies, disaster prediction,and limnolog...Investigating the formation and evolution of coarse-grained deposits in modern lakes and the relevant controlling conditions is indispensable to the prediction of reservoir sandbodies, disaster prediction,and limnological research. The source-to-sink system of coarse-grained deposits in Lake Chenghai, a deep,scarped Late Quaternary lake, was investigated in this study based on 62 outcrops, Advanced Land Observing Satellite(ALOS) digital elevation model(DEM) data, and regional geological survey data. The findings include the following:(1) the source areas of coarse-grained deposits in Lake Chenghai were lithologically classified into carbonate source areas, basaltic source areas and siliciclastic source areas, and were geomorphically categorized as scarp type or confluence type. Subaqueous colluvial aprons have formed downstream of the carbonate source areas and scarp-type basaltic source areas, while Gilbert-type deltas have formed downstream of siliciclastic source areas and confluence-type basaltic source areas.(2) The formation and evolution of coarse-grained deposits are controlled by the sediment flux that evolves in synchrony with the geomorphic evolution of the source areas and the sink regimes. Scarps represent the initial landform of the source areas.Source material rolls off or slides down scarps or forms small-scale debris flows before entering the lake. The source material initially formed subaqueous colluvial apron(synonymous with subaqueous fans) where sufficient space was present to accommodate sediments and the basement angle exceeded than the natural angle of repose. As weathering and denudation have progressed, the initial scarps have transformed into confluencetype slopes, and the source material has formed medium-and large-scale debris flows that have entered the lake, resulting in an increase in sediment flux. Consequently, the subaqueous colluvial aprons have rapidly grown and developed subaerial deposits, which have evolved into larger-scale Gilbert-type deltas that overlie the initial aprons.(3) The morphology and distribution of coarse-grained deposits vary in response to differences in quantity and composition of materials from different source areas, which resulting from different rates of weathering and denudation and different sediment input regimes. Firstly, the size and surface slope angle of a subaqueous colluvial apron from a carbonate source are smaller than those of a subaqueous colluvial apron of basaltic origin. Secondly, a Gilbert-type delta from a basaltic source features a greater slope angle and a thicker topset than does a Gilbert-type delta of siliciclastic origin, and the latter exhibits a longer foreset and a thicker bottomset than in the former. Thirdly, the sizes of subaqueous colluvial aprons are not strongly correlated with the sizes of the source areas, while the sizes of Gilbert-type deltas are.展开更多
On April 26,the China Foundation for Peace and Development(CFPD),in collaboration with the Shenzhen Foundation for International Exchange and Cooperation(SFIEC),the Shenzhen Ye Chenghai Charity Foundation and the Chin...On April 26,the China Foundation for Peace and Development(CFPD),in collaboration with the Shenzhen Foundation for International Exchange and Cooperation(SFIEC),the Shenzhen Ye Chenghai Charity Foundation and the China-Myanmar Economic Cooperation and Development Promotion Association(Myanmar),held a handover ceremony at Yangon Airport to donate five tons of medicine to the disasterstricken areas of Myanmar.展开更多
基金supported by Geological Survey Program(Grant No.12120114001501,DD20160306 and DD20160268)the National Natural Science Foundation of China(Grant No.41772383 and 41571013)。
文摘The Chenghai fault zone is located in the Sichuan–Yunnan rhombus block,which is surrounded by the Honghe River,Xianshuihe–Xiaojiang,and Jinsha River fault zones.As a mid-continental active fault,it is one of the most important seismogenic fractures in the southeast margin of the Tibetan Plateau.Geological seismic study is an important supplement to the historical seismic record;therefore,identification of paleoearthquake events in this region is of great significance to reveal the pattern and mechanism of earthquake development.In this study,detailed investigation has been carried out on the earthquake traces that formed in the Quaternary sediments in the Jinsha River section of the Chenghai fault zone,and samples for dating chronology testing were also collected.Many paleoearthquake traces were discovered in the field,including earthquake fissions,dammed lake sediments and landslides,earthquake-generated rock falls,seismic faults,and sand liquefaction veins.The collected samples were tested using optically stimulated luminescence,electron-spin resonance,and U-series methods.A total of 68 chronological samples were dated,combined with the results of field investigations,and 10 large paleoearthquake events were discovered in this region since 500 ka,which are at approximately 450,400,345,300,250,190,155,105,75,and 25 ka.Ten tectonic activity periods that produced multiple paleoearthquake events were identified since 500 ka.This study identifies paleoearthquake events in longer scales,larger spaces,and more extensive sediments,which provides new perspectives and new ideas for paleoearthquake research.
文摘Multi-parameter studies (stable isotopes in carbonate and or ganic matter, pigment, organic carbon and nitrogen contents) from a 660-yr cont inuous sediment core from Lake Chenghai, a closed, eutropic lake in southern Chi na, provide information on lake historical eutrophication. During the last 660 y ears, great changes have taken place in productivity and eutrophication of Lake Chenghai in response to human activities. In 1690, the productivity of the lake began to increase as Lake Chenghai became closed from agriculture in the lake’s watershed. In 1942, Lake Chenghai evolved to eutrophic state, marked by an incr ease in organic carbon, nitrogen, CaCO\-3, pigment contents and obvious negative values of stable isotopes, which is more or less simultaneous with the large-s cale population immigration during the period. In 1984, intensive human activiti es induced modern lacustrine productivity and eutrophic level. Human-induced tr ophic changes during the past few decades have affected the Lake Chenghai ecosys tem to such an extent that it has never experienced before in the last 660 years .
基金supported by the National Basic Research Program of China (Grant No. 2006CB403201)the National Natural Science Foundation of China (Grant No. 40673068)
文摘The carbon isotopic composition of organic matter from lake sediments has been extensively used to infer variations in productivity. In this paper, based on the study of the contents and δ13C values of organic matter in different types of lakes, it has been found that δ13C values of organic matter have different responses to lake productivity in different lakes. As to the lakes dominated by aqutic macrophytes such as Lake Caohai, organic matter becomes enriched in 13C with increasing productivity. As to the lakes dominated by aquatic algae such as Lake Chenghai, δ13C values of organic matter decrease with increasing productivity, and the degradation of aquatic algae is the main factor leading to the decrease of δ13C values of organic matter with increasing productivity. Therefore, we should be cautious to use the carbon isotopic composition of organic matter to deduce lake productivity.
文摘As one of the lakes on the Yunnan-Guizhou plateau, Lake Chenghai, which is a typical closed lake with the precipitation accounting for one-third or more of the annual water input, has a high total salinity (almost like a saline lake).The inorganic C,O isotopic composition of lake sediments bears much sensitive information about environmental change in the catchment, while their correlations revealed the hydrological conditions under which the lake was closed. Their compositional variations are controlled by temperature, precipitation, photosynthesis, dissolving equilibrium of the carbonate system and hydrological condition. According to our research on inorganic C, O isotopic composition of Lake Chenghai sediments, we investigated the environmental change of this catchment several decades ago. The results showed that Lake Chenghai has kept good hydrological closing conditions in the past several decades, as indicated by the good correlation of inorganic C, O isotopic composition of sediments; and that the environmental change in this catchment shows a tendency of periodical evolution on a 10\+\{-11\}-years scale, although the signal noise is relatively high at the bottom of the sediment core. And we also can extend C, O isotopes, a sensitive environmental indicator, to nearly saline lake environments with a high degree of mineralization.
基金financially supported jointly by the National Basic Research Program of China (Grant No. 2006CB403201)the National Natural Science Foundation of China (Grant No. 40673068)
文摘Lacustrine sediments can provide potential information about environmental changes in the past. On the basis of high-resolution multi-proxy analysis including carbon and nitrogen contents of organic matter, C/N ratios, inorganic carbon contents, and carbon and oxygen isotopic composition of carbonate, together with precise 137Cs dating, the environmental evolution of Lake Chenghai, Yunnan Province, during the past 100 years has been investigated. It is shown that the carbonate in Lake Chenghai is authigenic, and the organic matter is mainly derived from aquatic plants and algae, instead of terrestrial-source materials. The environmental evolution of Lake Chenghai can be diverged into three periods with the contrasting characteristics during the past 100 years. Before 1940, the stable carbon and oxygen isotope values, the poor correlation between them and the lower carbon and nitrogen contents of organic matter suggested that Lake Chenghai was open, and the lake water was oligotrophic during that period. During 1940-1993, the negative δ13C values and the gradual increase of carbon and nitrogen contents of organic matter and C/N ratios indicated that the eutrophication was aggravated. The closeness of Lake Chenghai and human activities may be responsible for this eutrophication. After 1993, notable increases in carbon and oxygen isotopic values of carbonate, carbon and nitrogen contents of organic matter, C/N ratios and inorganic carbon contents demonstrated that the increase of lacustrine productivity and the serious eutrophication were resulted from strong human activities. Therefore, the multi-proxy in Lake Chenghai sediments has reliably recorded the natural environmental evolution and the impacts from human activities.
基金supported by the National Natural Science Foundation of China(Grant Nos.40373038 and 49773207)the Natioual Key Basic Research Project(Grant No.2002CB412300)the Nat ional Science Foundation of USA(Grant No.NSF 82-50).
文摘The fundamental assumption of 210Pbsediment dating is the stable flux of 210Pbse, which was derived from atmosphere and then transferred into sediments via lake water. When the sedimentation rate is relatively constant, the 210Pbse activity in sediments will be exponentially reduced with sedimentation age. 210Pbse in lake water is incorporated into sediments mainly via organic particulates. If the sedimentation flux of organic matter in lake water is suddenly in- creased, 210Pbse will be significantly deposited and then transferred into sediments. On the one hand such sudden purification effect is obviously unfit for the fundamental assumption of 210Pbse dating; on the other hand, the sudden enhancement of 210Pbse flux would be indicative of the conspicuous variation of primary productivity of lake water. This problem will be discussed in accordance with the variation trend of 210Pbex in the vertical profile of recent sediments of Lake Chenghai, Yunnan Province. The sediment core was collected from the deep-water area of Lake Chenghai in June 1997. The vertical profile of 137 Cs activity is characterized by a tree-peak pat- tern. This profile gave reliable ages, and also showed the stability of sediment accumulation in the recent ten years. The vertical profile of210Pbse activity displays a specific distribution of peaks, and is similar to the vertical profile of Corg. This phenomenon seems to be related to the mecha- nism of constraining the transfer of 210Pbse into lake sediments. The average atomic ratios of Horg/Corg and Corg/Norg in Lake Chenghai sediments are 5.51 and 7.04, respectively, indicating that the organic matter was predominantly derived from the remains of endogenic algae. In terms of the three-stage evolutionary characteristics of organic matter in sediments, i.e., “deposition-de- composition-accumulation”, the sedimentation fluxes （F（Corg）） of organic carbon （Corg） since 1970 were calculated by modeling. The sedimentation fluxes of 210Pbse (F(210Pbse)) in different years display good synchronous relations with the sedimentation flux of organic carbon （F（Corg））, es- pecially in the years of 1972─1974 and 1986─1989. The variation of F（Corg） led to the variation of F(210Pbse); the variation of F（210Pbex） reflects, to some extent, the historical variation of lake pro- ductivity.
基金the National Natural Science Foundation of China (Grant No. 42172115,41972099, 42102153)the China Postdoctoral Science Foundation (Grant No. 2021M693500)the National Major Science and Technology Projects of China(Grant No. 2017ZX05009-002, 2017ZX05072-002)。
文摘Investigating the formation and evolution of coarse-grained deposits in modern lakes and the relevant controlling conditions is indispensable to the prediction of reservoir sandbodies, disaster prediction,and limnological research. The source-to-sink system of coarse-grained deposits in Lake Chenghai, a deep,scarped Late Quaternary lake, was investigated in this study based on 62 outcrops, Advanced Land Observing Satellite(ALOS) digital elevation model(DEM) data, and regional geological survey data. The findings include the following:(1) the source areas of coarse-grained deposits in Lake Chenghai were lithologically classified into carbonate source areas, basaltic source areas and siliciclastic source areas, and were geomorphically categorized as scarp type or confluence type. Subaqueous colluvial aprons have formed downstream of the carbonate source areas and scarp-type basaltic source areas, while Gilbert-type deltas have formed downstream of siliciclastic source areas and confluence-type basaltic source areas.(2) The formation and evolution of coarse-grained deposits are controlled by the sediment flux that evolves in synchrony with the geomorphic evolution of the source areas and the sink regimes. Scarps represent the initial landform of the source areas.Source material rolls off or slides down scarps or forms small-scale debris flows before entering the lake. The source material initially formed subaqueous colluvial apron(synonymous with subaqueous fans) where sufficient space was present to accommodate sediments and the basement angle exceeded than the natural angle of repose. As weathering and denudation have progressed, the initial scarps have transformed into confluencetype slopes, and the source material has formed medium-and large-scale debris flows that have entered the lake, resulting in an increase in sediment flux. Consequently, the subaqueous colluvial aprons have rapidly grown and developed subaerial deposits, which have evolved into larger-scale Gilbert-type deltas that overlie the initial aprons.(3) The morphology and distribution of coarse-grained deposits vary in response to differences in quantity and composition of materials from different source areas, which resulting from different rates of weathering and denudation and different sediment input regimes. Firstly, the size and surface slope angle of a subaqueous colluvial apron from a carbonate source are smaller than those of a subaqueous colluvial apron of basaltic origin. Secondly, a Gilbert-type delta from a basaltic source features a greater slope angle and a thicker topset than does a Gilbert-type delta of siliciclastic origin, and the latter exhibits a longer foreset and a thicker bottomset than in the former. Thirdly, the sizes of subaqueous colluvial aprons are not strongly correlated with the sizes of the source areas, while the sizes of Gilbert-type deltas are.
文摘On April 26,the China Foundation for Peace and Development(CFPD),in collaboration with the Shenzhen Foundation for International Exchange and Cooperation(SFIEC),the Shenzhen Ye Chenghai Charity Foundation and the China-Myanmar Economic Cooperation and Development Promotion Association(Myanmar),held a handover ceremony at Yangon Airport to donate five tons of medicine to the disasterstricken areas of Myanmar.
