云南中甸纳帕海湖泊沉积物的磁化率及环境意义  

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

作　　者：殷勇[1] 方念乔[2] 王倩[1] 聂浩刚[2] 秦尊丽[2] 

机构地区：[1]南京大学海岸与海岛开发教育部重点实验室,南京210093 [2]中国地质大学海洋地学研究中心,北京100083

出　　处：《地理科学》2002年第4期413-419,共7页Scientia Geographica Sinica

基　　金：国家自然科学基金 (批准号 :49672 13 5 ) ;国家重大基础研究项目 (编号 :G19980 40 80 0 )

摘　　要：研究区母岩特性、搬运距离和搬运营力决定了磁性矿物主要赋存在砂砾级颗粒中。纳帕海湖泊沉积物的磁化率与颗粒粒径、沉积相和有机质含量存在密切的相关关系。滨浅湖环境中砂砾级颗粒含量增加以及波浪淘洗对磁性矿物的富集作用 ,磁化率较高 ;浅湖环境中粉砂增多 ,砂砾减少 ,磁化率较之滨浅湖有所降低 ;在低能的半深湖 /深湖环境中 ,由于缺乏磁性矿物的输入 ,磁化率再次降低 ;有机质含量很高的湖岸湖沼环境由于有机质的稀释作用磁化率值最低 ,磁化率等环境替代指标以及和北半球气候变化阶段、深海氧同位素阶段的对比 ,将纳帕海近 6ka年来划分成 6个主要的环境演化阶段 ,32kaB .P .(14 .99m)和 15kaB .P .(6 .0 6m)分别是环境和气候变化的重要转折点。 32～ 15kaB .P .期间出现的高湖面表明 ,虽然大气温度下降但有效湿度增加 ,全新世湖泊的急剧萎缩预示在大气温度增加的同时有效湿度降低 ,暖偏干构成了研究区全新世气候演化的特色。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

关 键 词：云南 磁化率 粒度 沉积相 相关性 古环境 古气候 中甸纳帕海 

分 类 号：P531[天文地球—古生物学与地层学] P532[天文地球—地质学]