天山北麓黄土沉积粒度及磁化率的差异性研究

本文分析了天山北麓不同海拔高度的两个黄土剖面粒度、磁化率特征及其古气候意义的差异性。结果表明,位于海拔2074m的鹿角湾剖面与海拔527m处的大佛寺剖面黄土粒度特征比较相近,但鹿角湾剖面黄土整体细于大佛寺黄土,并且其细颗粒分布范围也大于大佛寺剖面,而粗颗粒的则相反。鹿角湾剖面中全新世以来地层磁化率与成壤作用相关,显示成壤增强模式,其下末次冰期地层磁化率及大佛寺剖面磁化率与粗颗粒沉积相关,显示风速论模式。造成两个剖面粒度及磁化率差异的原因主要是地形导致的沉积颗粒分选及降水量不同引发的成壤作用差异。全新世中期以来大佛寺剖面记录的气候整体处于干旱状态,而鹿角湾剖面同时期地层受地形影响则记录了相对湿润的气候。

Differences in Grain Size and Magnetic Susceptibility of Loess Deposition in Northern Slope of the Tianshan Mountains, China

In this paper, loess grain size and magnetic susceptibility from two loess sections at different altitudes in northern slope of the Tianshan Mountains, China were analyzed. Differences in grain size and magnetic susceptibility were discussed and paleoclimatic significance was also analyzed in this paper. Results indicate that grain size characteristics of Lujiaowan(LJW) section at the altitude of 2074 m are similar to that of Dafosi(DFS) section at the altitude of 527 m. However, particle of loess from LJW section is finer than that from DFS section. Specifically, fine particle distribution range of LJW is wider than that of DFS, while coarse particle is the opposite. Magnetic susceptibility of Holocene palaeosoil layer in LJW section is positive correlated with pedogenesis, suggesting pedogenesis model. However, magnetic susceptibility from the last glacial loess layer in LJW and Holocene loess in DFS is positive correlated with coarse particles, suggesting wind model. In this area, topography and altitude between two sections are responsible for their difference in grain size and magnetic susceptibility. The reason is that high altitude brings about finer particle accumulation, more precipitation and stronger pedogenesis in northern slope of the Tianshan Mountains, especially comparing with lower elevations. Climate during the Holocene recorded in DFS is drought and stable. Contemporary climate recorded in LJW is relative humid due to the influence of topography.