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《Marine Geology & Quaternary Geology》 2018-05
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Holocene variations of paleomagnetic characteristics along the loess section of Ansai and their controlling factors

LU Caichen;JIA Jia;GAO Fuyuan;XIA Dunsheng;Key Laboratory of Western China Environmental Systems,Ministry of Education,Lanzhou University;  
The loess in west China is widely recognized as one of the most important continental records of Quaternary paleoclimate and paleoenvironment.Numerous studies have been devoted to the reconstruction of the histories of Asian monsoon,atmospheric circulation,and uplifting of the Tibetan Plateau.Magnetic susceptibility is one of the most important paleoclimatic proxies.As previous studies suggest,pedogenesis may produce a large amount of fine-grained particles with strong magnetism to enhance the magnetic susceptibility of soil units,and as the result from a sequence characterized by alternated sequence of paleosol layers of higher magnetic susceptibility and loess layers of lower magnetic susceptibility.However,the main factors controlling over the formation of the magnetic particles are still in debate.In this paper,the Holocene loess section in Ansai of the central Chinese Loess Plateau,is investigated for the variation in magnetic characteristics,and the main controlling factors over the formation of secondary magnetic particles discussed upon the basis.The results show that during the time of 10000-8500 a,the concentrations of ferrimagnetic minerals were low upon an increasing trend;while during the period from8000-3000 a,the concentrations of ferrimagnetic minerals were high.It reached its peak in 7000-5000 a.Then,the ferrimagnetic minerals concentrations turned to a decreasing trend with the lowest value after 3000 a.All of the magnetic parameter curves have three rapid changes,a sharp increase in ferrimagnetic minerals concentrations at~6500 a and two sharp decreases at~4500 a and~2700 a,respectively.By comparing the magnetic susceptibility with the records of paleoprecipitation and temperature in Holocene,it is proposed that precipitation is the key climatic factor controlling the concentration variation of secondary ferrimagnetic minerals.Hot weather may limit the formation of secondary magnetic minerals owing to the decrease in effective moisture in soil.However,the relatively cool weather can not either help to increase the concentration of strong magnetic minerals in loess soils.It is also found that the variation in magnetic minerals concentrations responds slowly to climate improvement,but rapidly to the deterioration of climate.
【Fund】: 国家自然科学基金项目“黄土记录的新疆地区全新世有效湿度变化历史研究”(41401046);; 兰州大学中央高校基本科研业务费专项资金“中亚黄土记录的晚第四纪气候不稳定性研究”(lzujbky-2016-167)
【CateGory Index】: P532;P534.632
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