273 samples from Ocean Drilling Program (ODP) Site 1146 in the northern South China Sea (SCS) were analyzed for grain-size distributions using grain-size class vs. standard deviation method and end-member modeling alg...273 samples from Ocean Drilling Program (ODP) Site 1146 in the northern South China Sea (SCS) were analyzed for grain-size distributions using grain-size class vs. standard deviation method and end-member modeling algorithm (EMMA) in order to investigate the evolution of the East Asian monsoon since about 20 Ma. 10–19 μm/1.3–2.4 μm, the ratio of two grain-size populations with the highest variability through time was used to indicate East Asian winter monsoon intensity relative to summer monsoon. The mass accumulation rate of the coarsest end member EM1 (eolian), resulting from EMMA, can be used as a proxy of winter monsoon strength and Asian inland aridity, and the ratio of EM1/(EM2+EM3) as a proxy of winter monsoon intensity relative to summer monsoon. The combined proxies show that a profound enhancement of East Asian winter monsoon strength and winter monsoon intensity relative to summer monsoon occurred at about 8 Ma, and it is possible that the summer monsoon simultaneously intensified with winter monsoon at 3 Ma. Our results are well consistent with the previous studies in loess, eolian deposion in the Pacifc, radiolarians and planktonic foraminifera in the SCS. The phased uplift of the Himalaya-Tibetan Plateau may have played a significant role in strengthening the Asian monsoon at 8 Ma and 3 Ma.展开更多
＂Ejin Section＂ found in a typical vegetation-covered sand dune in Ejin Oasis was investigated. In this study, 263 samples were taken from the section for grain-size analysis, 25 for chemical analysis, 11 for ^14C da...＂Ejin Section＂ found in a typical vegetation-covered sand dune in Ejin Oasis was investigated. In this study, 263 samples were taken from the section for grain-size analysis, 25 for chemical analysis, 11 for ^14C dating and 6 for scanning electron microscope （SEM）. The results of the study indicate that 3 types of the sediments in the section can be identified, YS, LS and ST. YS, homogeneous yellow-brown dune sands, is equal to those of inland deserts, LS, loess-like sandy soils, is the same as the sandy loess in the middle Yellow River and modem falling dusts, and ST, sandy sediments interbeded with the deadwood and defoliation of Tamarix spp, represents the depositional process of the section interrupted by abrupt changes in climate. The Ejin Section has recorded the repeated dust-storms or sandstorms since 2500 yr BP and the peak periods of the dust-storms or sandstorms revealed by the section are consistent with the records of ＂dust rains＂ in historical literatures, indicating that the change of climate is a key factor to increase sandstorms or dust-storms, whereas, ＂artificial＂ factor may only be an accelerating one for desertification.展开更多
The grain-size distribution characteristics and grain-size parameters of sediment in two vertical sections of Daniugou peatland in the Changbai Mountains were systematically investigated.A comparative analysis of the ...The grain-size distribution characteristics and grain-size parameters of sediment in two vertical sections of Daniugou peatland in the Changbai Mountains were systematically investigated.A comparative analysis of the sediment granularity using a discriminative function with Hongyuan peat,red clay,loess-paleosol,fluvial deposit as well as lacustrine deposit was also conducted.It turns out that the vertical section of Daniugou peat ash is primarily constituted by clay and silt particles,and the content of sand is relatively small.Grain-size frequency curves generally show a single-peak modality while a bimodal pattern is detected in the upper layer.The grain-size component and peak pattern of grain-size frequency curves also illustrate that peat ash materials were transported to the peatland by long-range aeolian dust during the deposition process,while there existed short-distance dust influence in peat deposition of the upper layer.Comparisons of grain-size parameters and the discriminative Y-value of Daniugou peat ash with those of typical aeolian sediments show close similarities,suggesting the possibility that atmospheric dust transport processes were involved in the accumulation of peat again.Moreover,the variations of grain-size distribution suggest the local environmental deterioration which is just the driving force of local dust elevation.Grain-size analysis of peatland sediment is demonstrated to be one effective method to extract information about regional and global environmental evolution,and more attention should be paid to current local ecological environment and to seeking a balance between economic development and environmental protection in Northeast China.展开更多
The loess accumulation process has great potential to record patterns of atmospheric circulation change,paleoclimate,and paleoenvironmental evolution.South-eastern Xizang is a climatically sensitive region and here,we...The loess accumulation process has great potential to record patterns of atmospheric circulation change,paleoclimate,and paleoenvironmental evolution.South-eastern Xizang is a climatically sensitive region and here,we analyze a loess profile at Ranwu in order to explore the processes and interactions of dust transport and paleoclimate evolution in the region.Based on parametric grain size end-member analysis,optically stimulated luminescence(OSL)dating,and environmental proxies we show that the Ranwu loess profile comprises five end members(EMs).EM1 represents the fine silt fraction transported by high-altitude westerly winds over long distances;EM2 represents the medium silt fraction accumulated by glacier winds;EM3 is the coarse silt fraction transported by local dust storms under the action of strong glacier winds;EM4 represents the very fine sand fraction transported by strong local dust storms,different wind strengths controls the relative proportion of EM3 and EM4 over time.EM5 is the coarse sand fraction formed from the product of strong weathering of gravels.OSL dating shows loess sedimentation at Ranwu started around 11.16 ka.The prevailing climate was generally warm and wet between 11.6 and 4.2 ka,with four cooling events at 10.50,9.18,7.85,and 6.37 ka.Extensive paleosol development between 8.2 and 4.2 ka,a change to dry and cold climate conditions was favorable for loess formation after 4.2 ka.The palaeoenvironmental changes and abrupt climate events recorded in the Ranwu loess sequence are consistent with Holocene global environmental changes.展开更多
基金National Natural Science Foundation of China (Grant Nos. 90411014 and 40576032)
文摘273 samples from Ocean Drilling Program (ODP) Site 1146 in the northern South China Sea (SCS) were analyzed for grain-size distributions using grain-size class vs. standard deviation method and end-member modeling algorithm (EMMA) in order to investigate the evolution of the East Asian monsoon since about 20 Ma. 10–19 μm/1.3–2.4 μm, the ratio of two grain-size populations with the highest variability through time was used to indicate East Asian winter monsoon intensity relative to summer monsoon. The mass accumulation rate of the coarsest end member EM1 (eolian), resulting from EMMA, can be used as a proxy of winter monsoon strength and Asian inland aridity, and the ratio of EM1/(EM2+EM3) as a proxy of winter monsoon intensity relative to summer monsoon. The combined proxies show that a profound enhancement of East Asian winter monsoon strength and winter monsoon intensity relative to summer monsoon occurred at about 8 Ma, and it is possible that the summer monsoon simultaneously intensified with winter monsoon at 3 Ma. Our results are well consistent with the previous studies in loess, eolian deposion in the Pacifc, radiolarians and planktonic foraminifera in the SCS. The phased uplift of the Himalaya-Tibetan Plateau may have played a significant role in strengthening the Asian monsoon at 8 Ma and 3 Ma.
基金National Basic Research Program of China, No.2004CB720206 Knowledge Innovation Project of CAS, No.KZCX2-SW-118
文摘＂Ejin Section＂ found in a typical vegetation-covered sand dune in Ejin Oasis was investigated. In this study, 263 samples were taken from the section for grain-size analysis, 25 for chemical analysis, 11 for ^14C dating and 6 for scanning electron microscope （SEM）. The results of the study indicate that 3 types of the sediments in the section can be identified, YS, LS and ST. YS, homogeneous yellow-brown dune sands, is equal to those of inland deserts, LS, loess-like sandy soils, is the same as the sandy loess in the middle Yellow River and modem falling dusts, and ST, sandy sediments interbeded with the deadwood and defoliation of Tamarix spp, represents the depositional process of the section interrupted by abrupt changes in climate. The Ejin Section has recorded the repeated dust-storms or sandstorms since 2500 yr BP and the peak periods of the dust-storms or sandstorms revealed by the section are consistent with the records of ＂dust rains＂ in historical literatures, indicating that the change of climate is a key factor to increase sandstorms or dust-storms, whereas, ＂artificial＂ factor may only be an accelerating one for desertification.
基金Under the auspices of National Natural Science Foundation of China (No 40871089, 40830535)State Key Laboratory of Loess and Quaternary Geology,Institute of Earth Environment, Chinese Academy of Sciences (No SKLLQG0910)
文摘The grain-size distribution characteristics and grain-size parameters of sediment in two vertical sections of Daniugou peatland in the Changbai Mountains were systematically investigated.A comparative analysis of the sediment granularity using a discriminative function with Hongyuan peat,red clay,loess-paleosol,fluvial deposit as well as lacustrine deposit was also conducted.It turns out that the vertical section of Daniugou peat ash is primarily constituted by clay and silt particles,and the content of sand is relatively small.Grain-size frequency curves generally show a single-peak modality while a bimodal pattern is detected in the upper layer.The grain-size component and peak pattern of grain-size frequency curves also illustrate that peat ash materials were transported to the peatland by long-range aeolian dust during the deposition process,while there existed short-distance dust influence in peat deposition of the upper layer.Comparisons of grain-size parameters and the discriminative Y-value of Daniugou peat ash with those of typical aeolian sediments show close similarities,suggesting the possibility that atmospheric dust transport processes were involved in the accumulation of peat again.Moreover,the variations of grain-size distribution suggest the local environmental deterioration which is just the driving force of local dust elevation.Grain-size analysis of peatland sediment is demonstrated to be one effective method to extract information about regional and global environmental evolution,and more attention should be paid to current local ecological environment and to seeking a balance between economic development and environmental protection in Northeast China.
基金supported by the National Natural Science Foundation of China(Grant No.41807448).
文摘The loess accumulation process has great potential to record patterns of atmospheric circulation change,paleoclimate,and paleoenvironmental evolution.South-eastern Xizang is a climatically sensitive region and here,we analyze a loess profile at Ranwu in order to explore the processes and interactions of dust transport and paleoclimate evolution in the region.Based on parametric grain size end-member analysis,optically stimulated luminescence(OSL)dating,and environmental proxies we show that the Ranwu loess profile comprises five end members(EMs).EM1 represents the fine silt fraction transported by high-altitude westerly winds over long distances;EM2 represents the medium silt fraction accumulated by glacier winds;EM3 is the coarse silt fraction transported by local dust storms under the action of strong glacier winds;EM4 represents the very fine sand fraction transported by strong local dust storms,different wind strengths controls the relative proportion of EM3 and EM4 over time.EM5 is the coarse sand fraction formed from the product of strong weathering of gravels.OSL dating shows loess sedimentation at Ranwu started around 11.16 ka.The prevailing climate was generally warm and wet between 11.6 and 4.2 ka,with four cooling events at 10.50,9.18,7.85,and 6.37 ka.Extensive paleosol development between 8.2 and 4.2 ka,a change to dry and cold climate conditions was favorable for loess formation after 4.2 ka.The palaeoenvironmental changes and abrupt climate events recorded in the Ranwu loess sequence are consistent with Holocene global environmental changes.
