环境磁学反映的藏南沉错地区1300年来冷暖变化  

COLD/WARM FLUCTUATIONS OF THE LAST 1 300 YEARS REFLECTED BY ENVIRONMENTAL MAGNETISM IN THE CHEN CO AREA, SOUTHERN TIBET

作　　者：朱立平[1] 陈玲[1] 张平中[2] 李炳元[1] 

机构地区：[1]中国科学院地理科学与资源研究所,北京100101 [2]中国科学院兰州地质研究所,兰州730000

出　　处：《第四纪研究》2001年第6期520-527,共8页Quaternary Sciences

基　　金：国家重点基础研究规划项目 (批准号 :G1 9980 4 0 8);中科院知识创新方向项目 (批准号 :KZCX2 -31 4 -2 );中科院地理科学与资源研究所知识创新项目 (批准号 :CXIOG -A1 -0 2 )资助

摘　　要：通过藏南沉错湖芯的2 10 Pb和13 7Cs的测试 ,获得湖芯的平均沉积速率为 0 .1 6cm a。根据湖芯长度和分样间距 ,获得平均分辨率为 6～ 7年 ,长达 1 3 5 0年的连续湖芯环境序列。对湖芯样品磁学指标的低频磁化率 (χlf)、等温剩磁 (IRM)、饱和等温剩磁 (SIRM)、非滞后剩磁(ARM)等指标及其比值的测试 ,划分了 6 5 0A .D .以来沉错湖区的冷暖变化阶段和相对强度。结果表明 ,6 90～ 86 0A .D .和 1 1 2 0～ 1 3 2 0A .D .分别出现两个相对集中的暖期 ,每个暖期中间又具有相对寒冷时段。1 5 2 0～ 1 6 5 0A .D .出现寒冷时段之后 ,1 82 0A .D .左右直至现在环境又逐渐进入转暖时期。在 3个暖期中 ,以 1 2 2 0A .D .前后的温暖程度最强 ,而冷期中以 1 6 1 0～1 6 5 0A .D .达到最盛。沉错湖区冷暖环境的演变得到了其他资料的很好验证。Chen Co, situated at 28°54′～28°59′N,90°34′～90°39′E, is a closed lake with 148 km 2 of drainage area and 40 km 2 of water area. It is mainly supplied by glacier melting water and atmospheric precipitation. For seeking the sequence of environmental change during the past 2 000 years, a 216 cm long lake sediment core was drilled at a site with 8 m of water depth, 800 m far from the lake bank and 1.5% of the bottom slope degree in this lake. The sediment core was taken by PISTON sampler and was cut in 1 cm interval in laboratory. By 210Pb dating, an average sedimentary rate of 0.16 cm/a was obtained, and it was confirmed by 137Cs dating. Magnetic analyses such as the low-frequency dependent susceptibility (χ lf), the isothermal remanent magnetism (IRM), the saturation isothermal remanent magnetism (SIRM), the anhysteretic remanent magnetism (ARM) were performed for the sediment core. The low-frequency dependent susceptibility (χ lf) can reflect the environmental conditions, but it can not fully reveal the magnetic features in the real circumstance. This had been proved by the testing of saturation of the isothermal remanent magnetism (IRM) under different magnetic intensities. The log(SIRM/χ lf) has much more information to reveal environmental changes. ARM/χ lf might be more sensitive to reflect the local environmental conditions because it can well indicate the grain-size fluctuation of magnetic particles. Thus, the three peak stages (690～860A.D., 1 120～1 320A.D., 1 320～ 1 480A.D.), one fluctuated increasing stage (1 720A.D.～ present) and two valley stages (860～ 1 120A.D., 1 520～1 650A.D.) were divided by ARM/χ lf. In the past 1 300 years, the concentrated warm periods occurred in 690～860A.D. and 1 120～1 320A.D. After a cold period of 1 520～1 650A.D., the environment began to warm since 1 820A.D. The warmest occurred around 1 220A.D. and the coldest between 1 610～ 1 650A.D. This result might be compared with many o

关 键 词：磁学参数 环境变化 湖芯 沉错 沉积速率 古气候 环境磁学 

分 类 号：P532[天文地球—古生物学与地层学] P318[天文地球—地质学]