In the East Asian monsoon region, eolian deposits widely distributed in the middle-lower reaches of the Yantgze River are among the best materials available for studies on Quaternary climate change in the subtropical ...In the East Asian monsoon region, eolian deposits widely distributed in the middle-lower reaches of the Yantgze River are among the best materials available for studies on Quaternary climate change in the subtropical zone of Southern China. Typical eolian deposits in this region include upper Xiashu Loess (XL) and underlying Vermiculated Red Soil (VRS) layers. In this paper, chronological and paleoclimatic studies are conducted on an eolian deposit sequence near Jiujiang (J J) city in northern Jiangxi province. A magnetostratigraphic study, combined with optically stimulated luminescence (OSL) dating, is conducted on the JJ section and provides further evidence that eolian deposits in the middle-lower reaches of the Yangtze River have been formed since the late Early Pleistocene, and that the boundary age between the XL and VRS layers is about 300-400 kaBP. In grain-size records of the JJ section, the median grain-size and content of the 〉30μn size fraction increase sharply after 300-400 kaBP, representing an East Asian winter monsoon intensification event. Further pollen analysis reveals differing pollen assemblages before and after 300-400 kaBP: there is an evident increase in plants adapted to grow in a warm humid environment after 300-400 kaBP, implying an increase in precipitation caused by intensification of the East Asian summer monsoon. Global ice volume and uplift of the Tibet Plateau (TP) are regarded as crucial factors influencing variations of the East Asian monsoon on a long-term scale. The deep-sea JlSO record, which reflects variations in global ice volume, shows no obvious change after 300-400 kaBP. Moreover, the influence of global ice volume changes on the East Asian summer and winter monsoons is inverse; the global ice volume increase (decrease) implies a strengthened (weakened) winter monsoon and weakened (strengthened) summer monsoon. We therefore interpret the coupled intensifications of the East Asian summer and winter monsoons at about 300-400 kaBP to the uplift of the TP in the Middle Pleistocene. This climate event is also documented in eolian deposits from the southern margin of the Chinese Loess Plateau (CLP) and from the desert-loess transitional belt. However, it is not recorded in the loess-paleosol sequences from the central part of the CLP, thereby indicating differing climate responses to TP uplift in different regions, which requires further study.展开更多
In this study Chengdu Red Earth (CRE) from the Chengdu Plain (CP),Sichuan province,was analyzed for its elemental (major and trace elements) and isotopic (Sm-Nd) geochemistry and compared with Pleistocene loes...In this study Chengdu Red Earth (CRE) from the Chengdu Plain (CP),Sichuan province,was analyzed for its elemental (major and trace elements) and isotopic (Sm-Nd) geochemistry and compared with Pleistocene loess and paleosol samples from the Chinese Loess Plateau (CLP) in Northern China.The geochemical composition of CRE is similar to north China loess,and also resembles the average UCC.This indicates that CRE,as loess deposits in Northern China,was derived from well-mixed sedimentary protoliths that have undergone numerous upper crustal recycling processes.However,obvious differences in the geochemical characteristics of CRE and the north China loess are also revealed in our results.For chemically stable elements,CRE has higher Ti,Zr,Hf and lower ΣREE,Ba contents in comparison with loess samples from the CLP.Further analysis shows that CRE has higher TiO2/Al2O3,SiO2/Al2O3,Ba/Rb and lower Ce/Yb,Eu/Yb,LaN/YbN and ΣLREE/ ΣHREE ratios.In Sm-Nd isotopic geochemistry,Sm and Nd content and the εNd(0) value in CRE are significantly higher than those in north China loess.The higher TiO2 content in CRE coincided with a high background concentration of Ti in the Sichuan Basin and the surrounding regions.The lower ΣREE and higher Sm,Nd,εNd(0) values are related to the wide distribution of basalt in the southwest Sichuan Basin.The elemental and isotopic geochemistry of CRE indicates that eolian materials in the CP predominantly come from the Sichuan Basin and the surrounding regions,which differs from loess deposits in the CLP.展开更多
The Neogene eolian deposits in the Xining Basin are valuable archive for studying the evolution of the Asian monsoon system and geomorphic processes of Northwest China. The Neogene eolian deposits that paleomagnetical...The Neogene eolian deposits in the Xining Basin are valuable archive for studying the evolution of the Asian monsoon system and geomorphic processes of Northwest China. The Neogene eolian deposits that paleomagnetically dated at about 14 Ma probably were sourced from the middle and west Qinghai-Tibetan Plateau(QTP) as indicated by elemental compositions and magnetic properties. This study provides the Sr-Nd-Pb isotopic ratios of different sediments(gravels from the river terraces, Neogene eolian deposits and Quaternary loess) in the Xining Basin. The results show that:(1) Sr-Nd isotopic compositions of terrace gravels are different from those of the Neogene and Quaternary eolian deposits, although the Nd isotope ratios of gravel on the 10 th terrace(T10) and eolian deposits are similar.(2) Pb isotopic compositions of river gravels are obviously different from the eolian deposits in the Xining Basin. However, Pb isotopic compositions of eolian deposits in the basin are similar to those of eolian deposits in the central Chinese Loess Plateau.(3) Sr-Nd-Pb isotope results indicate that the Neogene eolian deposits in the Xining Basin were probably sourced from remote areas outside of the basin by long-distance transportation. The Qaidam Basin is probably an important source area for the eolian deposits in the Xining Basin.展开更多
The geomorphic evolution of northwestern China during the Cenozoic has been a subject of much geological interest because of its link with the uplift of the Himalayan-Tibetan complex.Much information about these chang...The geomorphic evolution of northwestern China during the Cenozoic has been a subject of much geological interest because of its link with the uplift of the Himalayan-Tibetan complex.Much information about these changes is recoverable from the sedimentary sequences of the region.We report here on the thick eolian deposits mantling the Huajialing Mountains,a relatively flat mountain range in the western Loess Plateau.Correlation of magnetic susceptibility stratigraphy with the QA-I Miocene eolian sequence dates a 134.7 m section(NL-VII) for the interval from 18.7 to 11.8 Ma,as confirmed by micro-mammalian fossils.These eolian deposits demonstrate a much wider distribution of the Miocene eolian deposits,and also indicate that the topography contrasts in the western Loess Plateau,including the uplifts of the Huajialing Mountains and the bedrock highlands in the Qinan region,were formed by the early Miocene.The near-continuous Miocene eolian sequence from 18.7 to 11.8 Ma indicates that the substratum of Huajialing had not experienced any intense tectonic changes during this time interval,which suggests further,the relative tectonic stability of the nearby Tibetan Plateau.展开更多
The Qaidam Basin is one of the main areas where the desert of the Qinghai-Xizang Plateau is distributed.According to the envirotunment records and the age of stratigraphy in Xiaxitai section in southeast part of Qaida...The Qaidam Basin is one of the main areas where the desert of the Qinghai-Xizang Plateau is distributed.According to the envirotunment records and the age of stratigraphy in Xiaxitai section in southeast part of Qaidam Basin,this paper reached the following conclusions: the desert development, formation of the cold-dry climate, evolution of natural environment and their reverse changes occurred frequently since the late glacial. In eolian sand deposits, the YoungerDryas event clearly appeared, which manifesed a dry-cold climatic period. Now there are two different opinions about theclimatic effect of Younger Dryas. According to the predecessors’ research and the field work of the authors, it is considered that the Younger Dryas event not only exists in different climatic zones of China, but the manifests the unitary drycold climatic effect.展开更多
基金supported by the National Department Public Benefit Research Foundation of China(grant no. 201211077)the Mineral Resources Investigation and Appraisal Project of the Ministry of Land and Resources (grant no.12120114001501)the Fundamental Research Funds for the Central Universities(grant no. 53200859557)
文摘In the East Asian monsoon region, eolian deposits widely distributed in the middle-lower reaches of the Yantgze River are among the best materials available for studies on Quaternary climate change in the subtropical zone of Southern China. Typical eolian deposits in this region include upper Xiashu Loess (XL) and underlying Vermiculated Red Soil (VRS) layers. In this paper, chronological and paleoclimatic studies are conducted on an eolian deposit sequence near Jiujiang (J J) city in northern Jiangxi province. A magnetostratigraphic study, combined with optically stimulated luminescence (OSL) dating, is conducted on the JJ section and provides further evidence that eolian deposits in the middle-lower reaches of the Yangtze River have been formed since the late Early Pleistocene, and that the boundary age between the XL and VRS layers is about 300-400 kaBP. In grain-size records of the JJ section, the median grain-size and content of the 〉30μn size fraction increase sharply after 300-400 kaBP, representing an East Asian winter monsoon intensification event. Further pollen analysis reveals differing pollen assemblages before and after 300-400 kaBP: there is an evident increase in plants adapted to grow in a warm humid environment after 300-400 kaBP, implying an increase in precipitation caused by intensification of the East Asian summer monsoon. Global ice volume and uplift of the Tibet Plateau (TP) are regarded as crucial factors influencing variations of the East Asian monsoon on a long-term scale. The deep-sea JlSO record, which reflects variations in global ice volume, shows no obvious change after 300-400 kaBP. Moreover, the influence of global ice volume changes on the East Asian summer and winter monsoons is inverse; the global ice volume increase (decrease) implies a strengthened (weakened) winter monsoon and weakened (strengthened) summer monsoon. We therefore interpret the coupled intensifications of the East Asian summer and winter monsoons at about 300-400 kaBP to the uplift of the TP in the Middle Pleistocene. This climate event is also documented in eolian deposits from the southern margin of the Chinese Loess Plateau (CLP) and from the desert-loess transitional belt. However, it is not recorded in the loess-paleosol sequences from the central part of the CLP, thereby indicating differing climate responses to TP uplift in different regions, which requires further study.
基金supported by the National Department Public Benefit Research Foundation of China (grant no. 201211077)the Mineral Resources Investigation and Appraisal Project of the Ministry of Land and Resources (grant nos. 41212011087118 and 1212010914041)
文摘In this study Chengdu Red Earth (CRE) from the Chengdu Plain (CP),Sichuan province,was analyzed for its elemental (major and trace elements) and isotopic (Sm-Nd) geochemistry and compared with Pleistocene loess and paleosol samples from the Chinese Loess Plateau (CLP) in Northern China.The geochemical composition of CRE is similar to north China loess,and also resembles the average UCC.This indicates that CRE,as loess deposits in Northern China,was derived from well-mixed sedimentary protoliths that have undergone numerous upper crustal recycling processes.However,obvious differences in the geochemical characteristics of CRE and the north China loess are also revealed in our results.For chemically stable elements,CRE has higher Ti,Zr,Hf and lower ΣREE,Ba contents in comparison with loess samples from the CLP.Further analysis shows that CRE has higher TiO2/Al2O3,SiO2/Al2O3,Ba/Rb and lower Ce/Yb,Eu/Yb,LaN/YbN and ΣLREE/ ΣHREE ratios.In Sm-Nd isotopic geochemistry,Sm and Nd content and the εNd(0) value in CRE are significantly higher than those in north China loess.The higher TiO2 content in CRE coincided with a high background concentration of Ti in the Sichuan Basin and the surrounding regions.The lower ΣREE and higher Sm,Nd,εNd(0) values are related to the wide distribution of basalt in the southwest Sichuan Basin.The elemental and isotopic geochemistry of CRE indicates that eolian materials in the CP predominantly come from the Sichuan Basin and the surrounding regions,which differs from loess deposits in the CLP.
基金supported by NSFC (Nos. 41402314, 41472313)Natural Science Foundation of Qinghai Province (No. 2012-Z-933Q)+2 种基金KLSLRC (No. KLSLRC-KF-13-DX-11)Youth Guidance Foundation of ISL-CAS (Nos. Y460261051, Y360441058)China Geological Survey (No. 12120113033029)
文摘The Neogene eolian deposits in the Xining Basin are valuable archive for studying the evolution of the Asian monsoon system and geomorphic processes of Northwest China. The Neogene eolian deposits that paleomagnetically dated at about 14 Ma probably were sourced from the middle and west Qinghai-Tibetan Plateau(QTP) as indicated by elemental compositions and magnetic properties. This study provides the Sr-Nd-Pb isotopic ratios of different sediments(gravels from the river terraces, Neogene eolian deposits and Quaternary loess) in the Xining Basin. The results show that:(1) Sr-Nd isotopic compositions of terrace gravels are different from those of the Neogene and Quaternary eolian deposits, although the Nd isotope ratios of gravel on the 10 th terrace(T10) and eolian deposits are similar.(2) Pb isotopic compositions of river gravels are obviously different from the eolian deposits in the Xining Basin. However, Pb isotopic compositions of eolian deposits in the basin are similar to those of eolian deposits in the central Chinese Loess Plateau.(3) Sr-Nd-Pb isotope results indicate that the Neogene eolian deposits in the Xining Basin were probably sourced from remote areas outside of the basin by long-distance transportation. The Qaidam Basin is probably an important source area for the eolian deposits in the Xining Basin.
基金supported by National Natural Science Foundation of China (Grant No. 40730104)Chinese Academy of Sciences (Grant Nos. KZCX2-YW-Q1-15 and KZCX2-YW-117)
文摘The geomorphic evolution of northwestern China during the Cenozoic has been a subject of much geological interest because of its link with the uplift of the Himalayan-Tibetan complex.Much information about these changes is recoverable from the sedimentary sequences of the region.We report here on the thick eolian deposits mantling the Huajialing Mountains,a relatively flat mountain range in the western Loess Plateau.Correlation of magnetic susceptibility stratigraphy with the QA-I Miocene eolian sequence dates a 134.7 m section(NL-VII) for the interval from 18.7 to 11.8 Ma,as confirmed by micro-mammalian fossils.These eolian deposits demonstrate a much wider distribution of the Miocene eolian deposits,and also indicate that the topography contrasts in the western Loess Plateau,including the uplifts of the Huajialing Mountains and the bedrock highlands in the Qinan region,were formed by the early Miocene.The near-continuous Miocene eolian sequence from 18.7 to 11.8 Ma indicates that the substratum of Huajialing had not experienced any intense tectonic changes during this time interval,which suggests further,the relative tectonic stability of the nearby Tibetan Plateau.
文摘The Qaidam Basin is one of the main areas where the desert of the Qinghai-Xizang Plateau is distributed.According to the envirotunment records and the age of stratigraphy in Xiaxitai section in southeast part of Qaidam Basin,this paper reached the following conclusions: the desert development, formation of the cold-dry climate, evolution of natural environment and their reverse changes occurred frequently since the late glacial. In eolian sand deposits, the YoungerDryas event clearly appeared, which manifesed a dry-cold climatic period. Now there are two different opinions about theclimatic effect of Younger Dryas. According to the predecessors’ research and the field work of the authors, it is considered that the Younger Dryas event not only exists in different climatic zones of China, but the manifests the unitary drycold climatic effect.