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| 环境磁学反映的藏南沉错地区1300年来冷暖变化 | |
| 引用本文： | 朱立平,陈玲,张平中,李炳元.环境磁学反映的藏南沉错地区1300年来冷暖变化[J].第四纪研究,2001,21(6):528-539. |
| 作者姓名： | 朱立平 陈玲 张平中 李炳元 |
| 作者单位： | 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 |
| 基金项目： | 国家自然科学重点基金项目 (批准号 :4 9732 0 90 )，国家科技部“九五”科技攻关项目 (编号 96 -91 3-0 7-0 1 )资助 |
| 摘 要： | 塔里木西缘帕米尔-西昆仑山北麓和西南天山南麓前陆盆地中巨厚的晚新生代磨拉石建造在岩石地层上包括阿图什组、西域组、乌苏组和戈壁组.通过对这套磨拉石建造及其中生长地层和生长不整合的野外观测,结合磁性地层年代学,初步研究了西域砾岩(即西域组)和西域运动的起始年代以及西域运动可能的演化阶段,得到如下初步认识:1)研究区西域砾岩开始沉积于3.5～4 6 Ma B.P.之前,其底界具有穿时性,其年代从山体向前陆盆地一般逐渐变新;2)在上述前陆盆地分布着4～6排由晚新生代磨拉石建造组成的逆断层-褶皱带.各排褶皱带均发育有生长地层及生长不整合,生长地层的开始沉积指示了该排褶皱和相应生长不整合的开始形成.从最靠山体一排褶皱带生长地层开始沉积的年代,初步判定西域运动的起始年代在西昆仑山叶城附近约为3.6 Ma B.P.,在西南天山喀什附近显然早于2.4 Ma B P.此后该运动可能经历了4～6个活动阶段,每一阶段又由若干个相对活跃期和相对稳定期组成.它们可通过各排褶皱带内生长地层的产状、组成和年代测定来确定.本文还探讨了生长地层和生长不整合形成过程中构造变形与侵蚀-剥蚀和沉积作用间的相互关系. |
| 关 键 词： | 磁学参数 环境变化 湖芯 沉错 |
| 收稿时间： | 2001-08-31 |
| 修稿时间： | 2001年8月31日 |
COLD/WARM FLUCTUATIONS OF THE LAST 1 300 YEARS REFLECTED BY ENVIRONMENTAL MAGNETISM IN THE CHEN CO AREA, SOUTHERN TIBET |
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| Institution: | 1. Institute of Geographical Sciences and Natural Resources Research,Chinese Academy of Sciences,Beijing 100101; 2. Lanzhou Institute of Geology,Chinese Academy of Sciences,Lanzhou 730000 |
| Abstract: | 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 other research results from sediment core, ice core and historic documents. |
| Keywords: | Western Tarim Late Cenozoic molasses Xiyu Conglomerate growth strata growth unconformity |
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