阿西克剖面记录的西天山地区黄土磁学性质及古气候意义初探

Magnetic Property and Paleoclimatic Implication Recorded by AXK Sequence in West Tianshan Area

选取阿西克剖面作为研究对象,对伊犁地区末次间冰期以来的沉积的黄土地层的磁学特征进行分析。结果发现,伊犁地区黄土地层的磁性矿物有磁铁矿、磁赤铁矿、赤铁矿、针铁矿,磁学性质受亚铁磁性的磁铁矿(和磁赤铁矿)控制;MD和PSD是地层中亚铁磁性矿物的主要磁畤状态,随着成壤强度增加,地层中的SP和SD颗粒相对含量逐渐增加;亚铁磁性矿物含量与地层并不完全对应。对磁学参数控制机制的分析表明,本剖面磁学性质受控因素比较复杂,磁性矿物含量主要受控于物源的磁学性质,成壤作用对地层中细粒磁性矿物含量具有很大影响,还原作用可能对底部古土壤层的磁学性质造成一定影响,但对整个剖面的磁学性质影响相对较小。

The magnetic property of loess is widely used on paleoclimate research.In the Loess Plateau of China,it appears positive correlation with climate.This phenomenon also appears in European loess sediments.But,the magnetic significances of loess sediments in some areas don＇t correlate with climatic conditions,or negatively correlate with climate,such as in Yili area,Xinjiang of China.This paper chose the AXK loess sequence located in the east of Yili area as research object.The deposition of the thick loess sediments in this area started since the last interglacial period.Results showed that magnetite,maghemite,hematite and goethite were discovered in the loess sequence,and the property of magnetite and maghemite controlled magnetic property of the loess layer,so ferrimagnetism was the major magnetic mineral of the loess sequence.Further analysis showed multidomain and pseudo-single domains were the major sharp of ferrimagnetic particles,and the content of single domain and superparamagnetic domain increased with the increase of soil development level.But the content of ferrimagnetism didn＇t appear correlation with the soil development level.The analysis of mechanism of magnetic susceptibility enhancement showed that magnetic susceptibility was affected by many factors,such as magnetic property of origin,soil development level,oxidative-reductive environment,and so on.