新疆塔城地区黄土沉积的磁学特征及其对古环境变化的指示

摘要/Abstract

摘要：

西风区黄土沉积序列的磁化率变化特征比较复杂,磁化率与成壤强度之间的相关性在不同的区域环境中具有一定的差异。选取塔城地区黄土剖面作为研究对象进行较为系统的磁学特征分析。结果显示,塔城剖面的磁性矿物主要为磁铁矿、磁赤铁矿等亚铁磁性矿物,同时含有一定量的反铁磁性矿物和顺磁性矿物,磁畴状态主要是多畴（MD）和假单畴（PSD）。成壤作用影响单畴（SD）颗粒磁性矿物的相对含量,而对超顺磁（SP）颗粒的贡献有限。影响地层磁学性质的因素比较复杂,粒度与磁学参数的变化与区域的气候波动具有一定的对应关系。古土壤中磁性矿物浓度的降低以及钙积现象可能反映了成壤时期温暖干燥的气候条件,磁性矿物浓度的变化在一定程度上或许是对区域相对湿度状况的反映。

关键词: 黄土, 相对湿度, 磁性矿物, 粒度

Abstract:

The environmental magnetic parameters have been widely used in the paleoclimate studies for decades. It was reported that the magnetic susceptibility of loess and paleosol sequences were positively correlated with the pedogenic intensity in the Chinese Loess Plateau and Central Europe. However, there was a negative correlation between magnetic susceptibility and pedogenic intensity observed in Alaskan and Siberian loess deposits. The magnetic properties of the loess/paleosol sequences are complex in westerly region of Xinjiang, China. Based on the fundamental of environmental magnetism, we conducted a systematic study on the loess deposits in Tacheng District, Xinjiang Uygur Autonomous Region, China. Results indicate that the ferrimagnetic minerals such as magnetite and maghemite hold a dominant position within the magnetic minerals of the investigation profile, meanwhile, a certain amount of antiferromagnetic minerals and superparamagnetic minerals are also discovered. The multidomain(MD) and pseudo-single domain(PSD) are the main magnetic grain size. The further analysis shows that the pedogenesis may have some effects on the contents of the single domain(SD) magnetic grains but it doesn't obviously contribute to the increase of ultrafine-superparamagnetic domain particles. Moreover, the relatively warm and dry conditions during the pedogenic period are probably responsible for the decrease of the ferrimagnetic minerals and the calcium carbonate deposition in the palaeosol units. Consequently, the distribution of magnetic minerals concentration might represent the change of relative humidity condition. To some extent, the grain size and magnetic parameters of the investigative profile contain some information about the regional paleoclimate change of the study area.

Key words: loess, relative humidity, magnetic minerals, grain size

中图分类号:

P539.3

李冠华1, 夏敦胜1,2, 赵爽1, 刘现彬1, 贾佳1, 魏海涛1. 新疆塔城地区黄土沉积的磁学特征及其对古环境变化的指示[J]. 中国沙漠, 2012, 32(6): 1565-1575.

LI Guan-hua1, XIA Dun-sheng1,2, ZHAO Shuang1, LIU Xian-bin1, JIA Jia1, WEI Hai-tao1. Magnetic Properties and Palaeoclimatic Implication of the Loess Deposits in Tacheng, Northwest China[J]. JOURNAL OF DESERT RESEARCH, 2012, 32(6): 1565-1575.

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