黄土高原与伊犁黄土磁学特征对比及启示  

THE COMPARISON BETWEEN LOESS PLATEAU AND ILI LOESS MAGNETIC PROPERTIES AND THEIR IMPLICATIONS

作　　者：贾佳[1] 夏敦胜[1,2] 王博[1] 李冠华[1] 赵爽[1] 刘现彬[1] 

机构地区：[1]兰州大学西部环境与气候变化研究院,西部环境教育部重点实验室,兰州730000 [2]中国科学院寒区旱区环境与工程研究所沙漠与沙漠化重点实验室,兰州730000

出　　处：《第四纪研究》2012年第4期749-760,共12页Quaternary Sciences

基　　金：国家重点基础研究发展规划项目(973项目)(批准号:2010CB950202);国家自然科学基金项目(批准号:40871090和41071125);高等学校博士点基金项目(批准号:20100211110001)共同资助

摘　　要：近30年来世界黄土磁学性质及其古气候意义研究取得了重大进展,并提出了"成壤说"和"风速论"两种主要的磁化率增强模式。由于两种模式是针对特定地区黄土地层的磁学性质变化规律提出的,其应用范围有限,然而模型描述的影响磁化率的增强因素是否可能普遍适用于黄土地层?近些年来的研究结果倾向于肯定这种假设。本研究选取黄土高原和伊犁地区黄土进行磁学分析进一步探讨这个假设存在的可能性。磁化率测量结果发现伊犁地区的古土壤/黄土层与x_(lf)曲线的峰/谷对应关系不明确,且分布范围和平均值的差别小,区别于黄土高原。岩石磁学分析结果表明黄土高原和伊犁地区黄土/古土壤地层的磁学性质受磁铁矿(和磁赤铁矿)控制,细粒磁性矿物和低矫顽力矿物对地层总体磁性的贡献与成壤强度呈正相关关系;区别在于黄土高原黄土的磁性矿物含量与地层成壤强度呈现良好正相关关系,伊犁黄土中磁性矿物含量与成壤强度无明确相关关系,且总体高于黄土高原黄土。后者的细粒磁性矿物和低矫顽力矿物百分比含量显著高于伊犁黄土。研究结果表明两种磁化率增强因素在黄土中是普遍存在的,在不同环境下两种因素对磁化率的贡献不同,因此磁化率在不同的环境下具有不同的环境指示意义,磁化率作为降水量的代用指标并不适用于所有黄土剖面。相比较而言,反映细粒磁性矿物和低矫顽力矿物百分比含量的磁学参数以及反映粗粒磁性矿物含量的磁学参数更适合于古气候研究。Recent 30yrs, environmental magnetism of loess deposit had been achieved rapid progress. Two magnetic susceptibility enhancement mechanisms,＂ pedogenesis＂ and ＂wind intensity＂ ,which presented to aim at explaining the magnetic susceptibility variation in Loess Plateau and Alaskan loess deposit, had been observed as two successful achievements. Due to loess deposit displayed opposite relationship between magnetic susceptibility and pedogenesis intensity in these two regions, the above mentioned two mechanisms had been applied to explain paleoclimate variation history in specific regions. Actually, pedogenesis process and wind sorting are dominant factors to influence the magnetic susceptibility variation in two mechanisms, respectively. Do these two factors influence magnetic susceptibility in all loess deposit？ More and more researches tend to confirm this hypothesis. In this study, we choose the loess sequences depositing Ili area （AXK and KS loess-paleosol sequences）and Loess Plateau （YX and JZT loess-paleosol sequences）to analysis the possibility of the hypothesis. AXK site is located close to Xinyuan（43°32＇N, 83°19＇E; altitude 860m）which is a town in east of Ili Basin of Xinjiang province and the thickness of which is about 18m. KS site is located east of AXK（43°32＇N, 83°25＇E; altitude 1400m）. Altitude of KS is obviously higher than former and the thickness of which is much smaller. YX site is located in south of Loess Plateau about 120kin to the north of Xi＇an city and in the rural area of Yaozhou city（34°53＇N, 108°45＇E; altitude 880m）. The sequences expose 5m loess deposition. We collected samples in the top 4m depth. JZT site is located west of Loess Plateau, on the north of Lanzhou city （36°03＇N, 103°50＇E ; altitude 2066.8m）. JZT loess-paleosol sequences presents more than 300m in thickness. In this study,we just sampled in upper layer about 3.5m. Samples were collected at 2cm intervals in AXK, KS, and YX loess-paleosol sequences, and 5cm in JZT.

关 键 词：黄土高原 伊犁地区 黄土沉积物 磁学特征 

分 类 号：P318.41[天文地球—固体地球物理学] P941.74[天文地球—地球物理学]