西藏米林地区湖积物的磁性特征及其古气候意义

米林地区雅鲁藏布江三级河流阶地上发育厚达52.2m的晚更新世晚期深-浅湖相和滨-浅湖相沉积物, 显示当时米林地区存在一个规模较大的古堰塞湖.为了探讨该套湖积物记录的古气候、古环境信息, 在米林机场剖面采集了259块定向样品进行环境磁学测试和分析.其中, 磁组构分析表明86%的样品具有原生磁组构, 它们的最大磁化率主轴κ₁指示米林古堰塞湖的物源经历了由南、北方向到西、北东再至西向这一大致顺时针方向变化的趋势, 可能与该区的差异隆升作用有关.研究剖面的天然剩余磁化强度 (NRM) 和体积磁化率 (κ) 变化曲线与沉积物的粒度、沉积相关系密切, 反映该区晚更新世晚期至少经历了4次显著的气候波动;同时, NRM、κ波动曲线能够很好地对应于格陵兰冰心GISP2的δ18O曲线IS1-IS6和IS8, 并记录了新仙女木事件 (YD) 和3次Heinrich事件 (H1, H2, H3) , 表明米林地区晚更新世晚期的气候变化受到全球气候系统影响. 

Magnetic Properties of Lacustrine Sediments and Implications for Paleoclimate in Milin Area, Tibet

There are 52.2 m deep-low lacustrine facies and littoral-low lacustrine facies sediments developed at the later stage of late Pleistocene distributed on the third terrace of Yarlung Zangbo river, Milin region, southeast Tibet, indicating that there was a large ancient dammed lake in the Milin region at that time. In order to discuss the paleoclimate and paleoenvironment of this area, we measured some magnetic parameters of 259 directed samples collected from the Milin airport section. The results indicated that most of the samples have original magnetic fabric, and their κ₁ axis indicated the direction of provenance of the Milin ancient dammed lake changed from south and north directions to west and northeast directions, and then to west direction, i. e. a clockwise changing, the changes probably are related to the change in denudation rate induced by differential uplifting of the studied region. The natural remanent magnetization (NRM) and bulk susceptibility (κ) of Milin section have close relationship with particle size and sedimentary facies, which revealed that there are at least four times obvious fluctuates of paleoclimate during later stage of late Pleistocene. The NRM & κ curves of Milin section correspond to IS1-IS6 and IS8 stages of Greenland GISP2 δ18O ice record and also clearly record the Younger Dryas (YD) event and Heinrich events (H1, H2, H3) , indicating that the climate of Milin region was influence by the global climate system.