中国帕米尔地区黄土磁化率特征及其影响因素

摘要/Abstract

摘要： 通过对地处西风区的中国境内帕米尔剖面进行磁化率的研究，并与研究区剖面其他常用气候替代指标粒度、色度、CaCO₃（%）和TOC等进行对比分析，初步探讨了帕米尔黄土磁化率增强机制的差异性。研究表明：帕米尔黄土剖面磁化率的平均值低于黄土高原典型剖面。粒度组成以粉砂（4～63 μm）为主，磁化率与细颗粒物质呈负相关，与粗颗粒物质呈正相关。色度a^*，b^*，L^*及磁化率的关系表明该区由于所受控的物质种类不同，使磁化率同红度a^*呈负相关，而与亮度L^*呈正相关关系；碳酸钙和有机质对磁化率影响较小，贡献微弱；由于沉积环境、气候等多种因素对磁化率产生不同程度的影响，使该区磁化率增强机制存在着空间差异性。

关键词: 磁化率, 粒度, 色度, 帕米尔, 增强机制

Abstract: Loess-paleosol sequences in the Chinese Loess Plateau reflect glacial/interglacial environmental changes,and have been regarded as the most detailed and continuous terrestrial records of past environmental change in the Quaternary. These records have been correlated to the changes in past climate found in the marine and ice core oxygen isotope curves. Similar to the loess in the Chinese Loess Plateau,the loess deposits in the Pamir of Central Asia arid area also play an important role in understanding the climate and environmental changes. As a substitute indicator for climate,magnetic susceptibility has been widely used for paleoclimatic and paleoenvironmental studies. However,there exist ambiguities and complexity when accurately interpreting this mineral magnetic proxy. To figure out the enhancement mechanisms behind magnetic susceptibility appears to be of vital significance. Based on the above analysis,combined with grain size,chroma,calcium carbonate and organic matter proxies,this paper analyzed the magnetic susceptibility features and discussed the differences in the enhancement mechanism of magnetic susceptibility in the Pamir loess dominated by the westerlies. Results show that the average value of magnetic susceptibility,27.72×10^-8 m³·kg^-1,was lower in the Pamir loess than that in typical loess on the loess plateau,and the frequency dependence(x_fd%) of which the average value was 0.27% also showed low value as it intended to estimate the relative contribution of fine viscous grains at the border between superparamagnetic and signal domain to the total ferromagnetic assemblage,suggesting that the study area had a weak pedogenic environment. Coarse silt(4~63 μm) was the dominant component of the section,accounting for 67.71%~85.48%,and magnetic susceptibility was positively correlated with coarse particles,however negatively with fine particles whose content were about 5.78%~19.92%. Meanwhile,magnetic susceptibility and L^* showed a positive correlation,for a^*,it showed a negative correlation;this is due to the fact that the dominant matter is different. Analysis of correlation between calcium carbonate,organic matter and magnetic susceptibility manifested that these two indexes made trivial contributions to magnetic susceptibility. From what has been discussed above,we can see that magnetic susceptibility features are complicated in this area due to the influence of various factors,such as sedimentary environment and climate,and the enhancement mechanism of magnetic susceptibility in the Pamir loess has spatial discrepancy. Conducting the relevance analysis between magnetic susceptibility and other climatic proxies is just a fundamental research;as to the influential proportion to magnetic susceptibility,much research work will still be needed in the future,such as the determination of the magnetic mineral content and so on.

Key words: magnetic susceptibility, grain size, chroma, Pamir enhancement mechanism

中图分类号:

P539.3

陈杰, 杨太保, 曾彪, 何毅, 王琳栋. 中国帕米尔地区黄土磁化率特征及其影响因素[J]. 干旱区地理, 2016, 39(4): 761-769.

CHEN JIE, YANG Tai-bao, ZENG BIAO, HE YI, WANG Lin-dong. Magnetic susceptibility features and influencing factors in Pamir,China[J]. , 2016, 39(4): 761-769.

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