摘要
伊犁盆地位于亚洲中纬度内陆,其特殊的构造和地理位置,使得该区具有特殊的气候环境。分布在盆地内的黄土记录了该区气候环境的变化过程,但是由于受到区域气候、海拔及近地物源的影响,使得磁化率在该区的表现和环境意义与黄土高原黄土中的会有差异。为了较准确的应用磁化率指标表征气候环境意义,就必须理解磁化率变化所受到的制约因素。本文通过伊犁盆地近地表采取的38个黄土样品(相当于黄土高原马兰黄土顶层),应用粒度,磁化率,元素分析的方法,结合地形和气候因素,初步探讨了近地表黄土的磁性特征、地域分异和受控因素,指出了磁化率在伊犁古环境研究中需考虑的问题。结果表明,近地表黄土样品的磁化率与<2μm的粘粒含量、Fe_2O_3含量成负相关,与>63μm的粗粒级含量呈正相关关系;样品的频率磁化率与<2μm含量、Fe_2O_3含量呈正相关;成壤作用形成的超顺磁颗粒对磁化率的贡献有限,粗颗粒组分对磁化率贡献较大。近地表黄土磁化率与降水、海拔高度、局地物源等多种因子有关,在黄土古气候解译中需要综合考虑这些因子对磁化率变化的可能影响。
Located in the middle latitude of Central Asian, the Ili Basin has specific geology, geomorphicand geography characters, the moisture and warm water flow from the Atlantic Ocean, Caspian Sea,Balkhash Lake get into the region, thus the climate is very special in the Xinjiang. Because of theinfluence of the climate condition, the altitude and the nearby materials, there have some environmentsignificance differences of the loess between the Ili Basin and the CLP. Loess magnetic susceptibility（MS） in the Chinese Loess Plateau is usually regarded as an index of East Asian Summer Monsoonintensity; however, the paleoclimatic significance of loess MS value in Central Arid Asia is still unclear.In order to break through the barriers in the application of the MS in the paleoclimate research, we mustunderstand the constraints of the MS. Here the authors report the results of MS, sedimentology andgeochemistry of 38 near-surface loess samples from different geomorphological-climatic units of the IliBasin, Xinjiang, Central Asia, and discuss the possible effect factors of loess MS value, and point out afew remarks about the application of MS in the paleoenvironment research in the Ili basin. The resultsshow that the MS of the near-surface loess samples are negatively correlated to clay fractions （〈2 μm）and Fe2O3 content, but positively correlated to coarse fractions （〉63 μm）. Superparamagnetic particlesproduced by pedogensis and fine fractions have limited contribution to loess MS value and coarsefractions play important role on the enhancement of MS. There is a high degree of complexity of nearsurfaceloess susceptibility vary with temperature and precipitation in Ili basin. The loess in the Ili basinis near its dust source, the wind moving distance is shorter, resulting to the higher proportion of coarsegrain particles, which causes that the susceptibility is positively correlated to coarse fractions. There isa weak negative correlation between MS and altitude, a weak positive correlation between frequencydependentsusceptibility and altitude. The possible effector factors of loess MS such as the ratio of thedistal aeolian dust and regional sources, climatic conditions and altitude should be considered in thepaleoenvironmental interpretation.
出处
《地球环境学报》
CSCD
2014年第2期135-144,共10页
Journal of Earth Environment
基金
国家自然科学基金项目(41172166)
国家重点基础研究发展规划项目(2013CB955904)
中国科学院科技创新"交叉与合作团队"项目
关键词
黄土
磁化率
影响因素
伊犁盆地
loess
magnetic susceptibility, affecting factors
Ili Basin
