The carbon isotope δ 13C value of dispersed organic matter in the Upper Triassic sediments in the Ordos basin is （-24.5 to -26.6） ×10^-3 with the carbon being derived from C3-1ike pleustons. The paleoclimate o...The carbon isotope δ 13C value of dispersed organic matter in the Upper Triassic sediments in the Ordos basin is （-24.5 to -26.6） ×10^-3 with the carbon being derived from C3-1ike pleustons. The paleoclimate of the Late Triassic, especially during the deposition of the Chang 7 member, was characterized by a hot and humid climate. It underwent four small climate cycles from humid and warm to humid and hot.展开更多
A 6.2 m thick core of Gucheng Lake sediment provided a 3600 years record of climate change. The contents of the TOC in the core changed from 2.63% to 8.48%, and the δ13C values of organic matter were from - 21.54% to...A 6.2 m thick core of Gucheng Lake sediment provided a 3600 years record of climate change. The contents of the TOC in the core changed from 2.63% to 8.48%, and the δ13C values of organic matter were from - 21.54% to - 27.3%. The TOC/TN ratios indicated that the organic materials in sediments were from lake plankton and land-derived plants.The 2.9-22 m core interval with high TOC/TN ratios, low δ13C values and low contents of TOC indicated a cold climate Stage. The 6.2-5.5 m and 0.4-0.1 m intervals were characterized by low TOC/TN ratios, highδ13C values and high contents of TOC and reflcted temperate climate stages.展开更多
Fine-grained disseminated carbonate was found in Holocene sediments in a core taken from the northern basin of Lake Baikal. The core had two distinct facies. a terrigenous blue-clay overlain by a diatomaceous silt. Ox...Fine-grained disseminated carbonate was found in Holocene sediments in a core taken from the northern basin of Lake Baikal. The core had two distinct facies. a terrigenous blue-clay overlain by a diatomaceous silt. Oxygen and carbon stable isotope analyses, combined with SEM , X-ray diffraction and .palynology, show that the carbonate in the blue-clay layer is pedogenic in origin, rather than biogenic or authigenic . The S C values in the blue clay suggest that the carbonate is derived from a single source , while the carbonate in the diatom-rich layer might be transported by winds from different sources. On the assumption that the carbonate was formed during the post-glacial age and was transported primarily by river runoff, the 18O isotopic values suggest that the annual temperature in the northern Baikal drainage area was about 3℃ warmer during the middle Holocene (8500-7000 a, B. P.) than during the early Holocene (11 000-8 500a, B.P.) when the blue clay was being deposited . This interpretation展开更多
Study on the organic compounds and stable isotope composition of a sediment section in Dabusu Lake revealed that the organic materials in the sediments came mainly from terrestrial plants brought into the lake by runo...Study on the organic compounds and stable isotope composition of a sediment section in Dabusu Lake revealed that the organic materials in the sediments came mainly from terrestrial plants brought into the lake by runoff. The δ 13 C of the organic materials had high values during warm-dry climatic stages and decreased in cold-wet stages. Analysis of data on carbonate content and 14 C age showed that the lake basin had experienced several wet-cold and warm-dry climatic cycles since 15000 a BP. Since 6700 a BP, the climate reached a relatively stable warm-dry stage, so that the lake water was gradually condensed and finally a saline lake was formed.展开更多
We firstly present the description of the river terrace at Tangjia（唐家） Village in Lhasa,Tibet,collect soil samples,and select the climate indicators including δ13C,total organic carbon（TOC）,and the Rb/Sr ratios...We firstly present the description of the river terrace at Tangjia（唐家） Village in Lhasa,Tibet,collect soil samples,and select the climate indicators including δ13C,total organic carbon（TOC）,and the Rb/Sr ratios to study its paleoclimate in this area.Ancient climate changes have been recon-structed since the last glacier period.The results show that the δ13C,TOC,and the Rb/Sr ratio are good indicators of ancient climate fluctuations.Paleoclimatic evolution in the Lhasa Tangjia region could be divided into seven stages.In stages II（11.7-10.2 kaB.P.） and IV（8.1-6.1 kaB.P.）,δ13C was positive and TOC was high,indicating that the climates in these two stages were relatively warm and humid.In stages III（10.2-8.1 kaB.P.） and V（6.1-4.9 kaB.P.）,δ13C showed cyclical fluctuations,but TOC exhibited less change,suggesting that the climates displayed variation on the millennial scale.Moreover,the cli-matic variations were on a century-long scale during the later Middle Holocene.Compared with δ13C from Sumxi Co（松木希错） and δ18O from the Guliya（古里雅） ice core,the study confirmed that four cold events occurred during the Holocene（9.4,8.2,5.4,and 4.2 kaB.P.）.The climate indicators were limited to the river terrace based on the geological characteristics of the Lhasa region.Unexpectedly,δ13C was a sensitive indicator of climate change.展开更多
Based on the data of organic carbon stable isotope ratios and magnet ic susceptibility, climate evolution in the past 5 kaB.P. in Poyang Lake plain (in Jiangxi Province) has been reconstructed. The results of the re...Based on the data of organic carbon stable isotope ratios and magnet ic susceptibility, climate evolution in the past 5 kaB.P. in Poyang Lake plain (in Jiangxi Province) has been reconstructed. The results of the research indicate that the climate evolution can be divided into nine stages in the past 5 kaB.P.. Comparisons of different regional environmental records suggest that the intens ity and the temporal spatial changes of monsoon in China mainly controlled the climate evolution.展开更多
The Qaidam Basin is. a tectonically controlled depression at 2700 m altitude on the northern margin of the Tibet Plateau. A succession of Neogene clastic sediments indicates lake depocentre migration from NW to SE. To...The Qaidam Basin is. a tectonically controlled depression at 2700 m altitude on the northern margin of the Tibet Plateau. A succession of Neogene clastic sediments indicates lake depocentre migration from NW to SE. Towards late Pliocene, evaporative conditions developed with formation of gypsum, halite, celestite, mirabilite and bloedite. Continued deformation through Pleistocene developed a series of NW- SE trending domes and troughs. This setting continued to exert a controlling influence on basin and brine evolution and the progressive development of sulfate to chloride brines as, dry conditions intensified in late Pleistocene, at the end of which, extensive flat floors were formed in Dalangtan, Qarhan and other playas.The, model, which was set up based on the synthetic analyses, divides the fluctuating palaeoclimate since 750ka,B. P. into 11 warm and humid stages and 10 dry and cold stages. The water of the lakes evaporated during the dry-cold periods and were freshened during the warm-humid展开更多
Study on the carbonate content and oxygen isotope of a sediment section in Dabusu Lake revealed that this region has experienced several cold wet and warm dry climatic cycles since 15400 a BP. It was about 6740 a BP w...Study on the carbonate content and oxygen isotope of a sediment section in Dabusu Lake revealed that this region has experienced several cold wet and warm dry climatic cycles since 15400 a BP. It was about 6740 a BP when the climate in the region reached a relatively stable warm stage, so that the lake water was gradually condensed and finally a saline lake was formed.展开更多
The stable carbon isotope composition(δ13 C) of lacustrine sediments, which can record changes in past environmental conditions such as the C4/C3 terrestrial vegetation composition, has been widely used for the recon...The stable carbon isotope composition(δ13 C) of lacustrine sediments, which can record changes in past environmental conditions such as the C4/C3 terrestrial vegetation composition, has been widely used for the reconstruction of terrestrial ecosystems and global climate changes. It has also been widely used in paleolimnological studies in arid northwestern China. In recent years, however, an increasing number of studies have enriched the environmental significance reflected by the stable carbon isotope geochemistry of lakes;therefore, the interpretation of lake δ13 C variations in paleoenvironmental reconstructions should be carefully evaluated from various aspects. In this paper, previous studies from the past several decades on the lacustrineδ13 C variations in arid northwestern China were reviewed, and the possible mechanisms of the δ13 C variations were discussed.Our study will provide a reference for the application of carbon isotope geochemistry in paleoenvironmental reconstructions.展开更多
文摘The carbon isotope δ 13C value of dispersed organic matter in the Upper Triassic sediments in the Ordos basin is （-24.5 to -26.6） ×10^-3 with the carbon being derived from C3-1ike pleustons. The paleoclimate of the Late Triassic, especially during the deposition of the Chang 7 member, was characterized by a hot and humid climate. It underwent four small climate cycles from humid and warm to humid and hot.
文摘A 6.2 m thick core of Gucheng Lake sediment provided a 3600 years record of climate change. The contents of the TOC in the core changed from 2.63% to 8.48%, and the δ13C values of organic matter were from - 21.54% to - 27.3%. The TOC/TN ratios indicated that the organic materials in sediments were from lake plankton and land-derived plants.The 2.9-22 m core interval with high TOC/TN ratios, low δ13C values and low contents of TOC indicated a cold climate Stage. The 6.2-5.5 m and 0.4-0.1 m intervals were characterized by low TOC/TN ratios, highδ13C values and high contents of TOC and reflcted temperate climate stages.
文摘Fine-grained disseminated carbonate was found in Holocene sediments in a core taken from the northern basin of Lake Baikal. The core had two distinct facies. a terrigenous blue-clay overlain by a diatomaceous silt. Oxygen and carbon stable isotope analyses, combined with SEM , X-ray diffraction and .palynology, show that the carbonate in the blue-clay layer is pedogenic in origin, rather than biogenic or authigenic . The S C values in the blue clay suggest that the carbonate is derived from a single source , while the carbonate in the diatom-rich layer might be transported by winds from different sources. On the assumption that the carbonate was formed during the post-glacial age and was transported primarily by river runoff, the 18O isotopic values suggest that the annual temperature in the northern Baikal drainage area was about 3℃ warmer during the middle Holocene (8500-7000 a, B. P.) than during the early Holocene (11 000-8 500a, B.P.) when the blue clay was being deposited . This interpretation
文摘Study on the organic compounds and stable isotope composition of a sediment section in Dabusu Lake revealed that the organic materials in the sediments came mainly from terrestrial plants brought into the lake by runoff. The δ 13 C of the organic materials had high values during warm-dry climatic stages and decreased in cold-wet stages. Analysis of data on carbonate content and 14 C age showed that the lake basin had experienced several wet-cold and warm-dry climatic cycles since 15000 a BP. Since 6700 a BP, the climate reached a relatively stable warm-dry stage, so that the lake water was gradually condensed and finally a saline lake was formed.
基金financially supported by the China Geological Survey (No. 1212010818085)
文摘We firstly present the description of the river terrace at Tangjia（唐家） Village in Lhasa,Tibet,collect soil samples,and select the climate indicators including δ13C,total organic carbon（TOC）,and the Rb/Sr ratios to study its paleoclimate in this area.Ancient climate changes have been recon-structed since the last glacier period.The results show that the δ13C,TOC,and the Rb/Sr ratio are good indicators of ancient climate fluctuations.Paleoclimatic evolution in the Lhasa Tangjia region could be divided into seven stages.In stages II（11.7-10.2 kaB.P.） and IV（8.1-6.1 kaB.P.）,δ13C was positive and TOC was high,indicating that the climates in these two stages were relatively warm and humid.In stages III（10.2-8.1 kaB.P.） and V（6.1-4.9 kaB.P.）,δ13C showed cyclical fluctuations,but TOC exhibited less change,suggesting that the climates displayed variation on the millennial scale.Moreover,the cli-matic variations were on a century-long scale during the later Middle Holocene.Compared with δ13C from Sumxi Co（松木希错） and δ18O from the Guliya（古里雅） ice core,the study confirmed that four cold events occurred during the Holocene（9.4,8.2,5.4,and 4.2 kaB.P.）.The climate indicators were limited to the river terrace based on the geological characteristics of the Lhasa region.Unexpectedly,δ13C was a sensitive indicator of climate change.
文摘Based on the data of organic carbon stable isotope ratios and magnet ic susceptibility, climate evolution in the past 5 kaB.P. in Poyang Lake plain (in Jiangxi Province) has been reconstructed. The results of the research indicate that the climate evolution can be divided into nine stages in the past 5 kaB.P.. Comparisons of different regional environmental records suggest that the intens ity and the temporal spatial changes of monsoon in China mainly controlled the climate evolution.
文摘The Qaidam Basin is. a tectonically controlled depression at 2700 m altitude on the northern margin of the Tibet Plateau. A succession of Neogene clastic sediments indicates lake depocentre migration from NW to SE. Towards late Pliocene, evaporative conditions developed with formation of gypsum, halite, celestite, mirabilite and bloedite. Continued deformation through Pleistocene developed a series of NW- SE trending domes and troughs. This setting continued to exert a controlling influence on basin and brine evolution and the progressive development of sulfate to chloride brines as, dry conditions intensified in late Pleistocene, at the end of which, extensive flat floors were formed in Dalangtan, Qarhan and other playas.The, model, which was set up based on the synthetic analyses, divides the fluctuating palaeoclimate since 750ka,B. P. into 11 warm and humid stages and 10 dry and cold stages. The water of the lakes evaporated during the dry-cold periods and were freshened during the warm-humid
文摘Study on the carbonate content and oxygen isotope of a sediment section in Dabusu Lake revealed that this region has experienced several cold wet and warm dry climatic cycles since 15400 a BP. It was about 6740 a BP when the climate in the region reached a relatively stable warm stage, so that the lake water was gradually condensed and finally a saline lake was formed.
基金supported by the CAS Strategic Priority Research Program (Grant No. XDA05120400)
文摘The stable carbon isotope composition(δ13 C) of lacustrine sediments, which can record changes in past environmental conditions such as the C4/C3 terrestrial vegetation composition, has been widely used for the reconstruction of terrestrial ecosystems and global climate changes. It has also been widely used in paleolimnological studies in arid northwestern China. In recent years, however, an increasing number of studies have enriched the environmental significance reflected by the stable carbon isotope geochemistry of lakes;therefore, the interpretation of lake δ13 C variations in paleoenvironmental reconstructions should be carefully evaluated from various aspects. In this paper, previous studies from the past several decades on the lacustrineδ13 C variations in arid northwestern China were reviewed, and the possible mechanisms of the δ13 C variations were discussed.Our study will provide a reference for the application of carbon isotope geochemistry in paleoenvironmental reconstructions.
