SCIENTIA GEOGRAPHICA SINICA ›› 2002, Vol. 22 ›› Issue (4): 413-419.doi: 10.13249/j.cnki.sgs.2002.04.413

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Magnetic Susceptibility of Lacustrine Sediments and Its Environmental Significance: Evidence from Napahai Lake, Northwestern Yunnan, China

YIN Yong1, FANG Nian-qiao2, WANG Qian1, NIE Hao-gang2, QING Zun-li2   

  1. 1. Department of Geo and Ocean Sciences, Nanjing University, Nanjing, Jiangsu 210093;
    2. China University of Geosciences, Beijing 100083
  • Received:2001-07-18 Revised:2001-10-15 Online:2002-07-20 Published:2002-07-20

Abstract: Magnetic susceptibility measurements have been made on a long sediment core from Napahai, northwestern Yunnan, China. These results are set alongside those derived from total organic carbon and granulometric analysis to reconstruct the environmental and climatic processes recorded in the radiocarbon dated sediment column. It is shown that the variations of magnetic susceptibility in this sediment core are mainly the result of changes in size constitution, hydrological and sedimentological regimes and organic content, implying shifts in the sedimentary environment and climatic condition. Decided by the characterization of sediment source and proximal transport, the magnetic minerals, in this case, are mainly concentrated in coarser sand size fractions. The values of magnetic susceptibility in an organic-free shallow lake correlate positively with coarser sediment. The proportions of magnetic minerals are strongly linked to the increase of runoff around the catchment and high energy conditions in the environment. The magnetic minerals are mainly concentrated in silty sand in low energy conditions below wavebase and the values of magnetic susceptibility decrease due to the lack of coarser sediment, the major carrier of magnetic minerals. The magnetic susceptibility has no definitely link to a fixed grain-size fraction in lakeshore environment and extremely low values of magnetic susceptibility are encountered due to the dilution of organic matter. Six major environmental sages during the last 60,000 years from the core record have been identified on the basis of magnetic susceptibility. Two major environment shifts occurred in approximately 32 ka B. P. (14.99 m) and 15 ka B.P. (6.06 m) respectively, in response to climate change. Cold/moist and warm/dry assemblages dominated the area and a typical cold/moist climate occurred from 32 ka B. P. to 15 ka B. P. The incline of precipitation during this stage is due to an increased mass exchange between the cold/dry air of northern continent and the water vapor from the northern Indian ocean.

CLC Number: 

  • P534.63+2