云南点苍山冰川湖泊沉积物磁化率的影响因素及其环境意义

文章通过对点苍山海拔3820m冰水沉积剖面的粒度参数、磁化率、氧化铁含量和有机质含量的综合实验分析,并讨论了这些指标的相互关系及其环境意义。实验结果表明,磁化率的强度与粗砂组分的含量成正相关,而与粘土等细粒组分含量成负相关;同时与有机质含量成负相关,与氧化铁含量成正相关。矿物组分分析实验表明,沉积物主要磁性来源于磁化铁。根据以上结果,结合冰川湖泊流域面积小、高寒环境的特点,其磁化率的影响因素与一般湖泊不同,认为冰川湖泊沉积中,因为物源较近导致外源磁性矿物主要赋存于粒度较粗的碎屑颗粒中,而高寒的环境条件使得有机质对沉积物的磁性矿物起到了稀释的作用,而很难有积极的贡献。根据磁化率的环境意义,恢复了全新世以来点苍山的古气候,从中可以划分6个不同的气候阶段:11.5～10.6kaB.P.,10.6～8.9kaB.P.,8.9～5.5kaB.P.,5.5～3.3kaB.P.,3.3～0.8kaB.P.和0.8kaB.P.至今,代表了末次冰期结束以后湖泊从产生至消亡的全过程。根据与其他相关地区的对比,分析了西南季风演变的一些规律。

THE INFLUENCING FACTORS AND ENVIRONMENTAL SIGNIFICANCE OF MAGNETIC SUSCEPTIBILITY IN THE GLACIO-LACUSTRINAL SEDIMENTS ON THE DIANCANG MOUNTAINS,YUNNAN PROVINCE

The Diancang Mountains, reaching an attitude of 4 122m, is located at the south western margin of the Qinghai Xizang Plateau. Towards the south is the low relief area of southeast Asia. To the north the Indian Ocean monsoon prevails and vertical climatic zoning is clear here. The Diancang Mountains is climatically situated between south subtropics and mid subtropics and the climate changes on the mountain are affected by the combined effects of vertical and horizontal climatic zones. Continental glaciers and glaciations were well developed during the Quaternary period. The Diancang Mountains is a typical region for studies on a diversity of biological species, evolution of ecological conditions and vegetation migration due to its special physical characteristics. A continuous record of climatic changes is recovered from a glacio lacustrinal sedimentary profile. The age of the oldest sediments, 11.5kaB.P. recorded climatic changes during the Holocene period and indicats that the lake formed after the last glaciation. Studies of the sediments were carried out by analysing magnetic susceptibility, grain size, organic material content and the contents of Fe 2O 3 and FeO. The results show that the magnetic susceptibility is positive proportional to the content of coarse sand and Fe 2O 3 and FeO, and reversal proportional to the contents of fine sand and organic materials. X ray diffraction indicates that the most magnetic susceptibility should be attributed to magnetite. The late glacial environmental changes, particularly during the Holocene period, have been reconstructed based on the analysis of grain size, environmental susceptibility and geochemistry in the stratigraphical profile. According to the experimental data, a warm stage is established during 11.5～10.6kaB.P. after the late glaciation. It became humid from 10.6kaB.P., and dried up from 8.9kaB.P. to 5.5kaB.P. It became cold and humid again after 5.5kaB.P., and warm and dry again from 3.3 to 0.8 kaB.P. It was humid from 0.8 to the preent.