杜婧, 鲁瑞洁, 刘小槺, 吕志强, 陈璐. 青海湖湖东沙地全新世风成沉积物磁化率特征及其环境意义[J]. 海洋地质与第四纪地质, 2018, 38(2): 175-184. DOI: 10.16562/j.cnki.0256-1492.2018.02.018
引用本文: 杜婧, 鲁瑞洁, 刘小槺, 吕志强, 陈璐. 青海湖湖东沙地全新世风成沉积物磁化率特征及其环境意义[J]. 海洋地质与第四纪地质, 2018, 38(2): 175-184. DOI: 10.16562/j.cnki.0256-1492.2018.02.018
DU Jing, LU Ruijie, LIU Xiaokang, LV Zhiqiang, CHEN Lu. Magnetic susceptibility of aeolian sediments deposited since Holocene in the East of Qinghai Lake and its environmental implications[J]. Marine Geology & Quaternary Geology, 2018, 38(2): 175-184. DOI: 10.16562/j.cnki.0256-1492.2018.02.018
Citation: DU Jing, LU Ruijie, LIU Xiaokang, LV Zhiqiang, CHEN Lu. Magnetic susceptibility of aeolian sediments deposited since Holocene in the East of Qinghai Lake and its environmental implications[J]. Marine Geology & Quaternary Geology, 2018, 38(2): 175-184. DOI: 10.16562/j.cnki.0256-1492.2018.02.018

青海湖湖东沙地全新世风成沉积物磁化率特征及其环境意义

Magnetic susceptibility of aeolian sediments deposited since Holocene in the East of Qinghai Lake and its environmental implications

  • 摘要: 在亚洲季风控制区,黄土-古土壤序列中的磁化率能够很好地反映土壤成壤强度和区域沉积环境变化,但在风成砂-古土壤序列中磁化率的古气候意义仍有待研究。选取青海湖湖东沙地典型风成砂-古土壤序列,基于AMS14C和光释光测年结果,结合土壤学中传统的土壤发育指标,对沉积物的磁化率特征及环境意义进行分析。研究表明在青海湖盆地风成砂-古土壤序列里,磁化率与成壤强度密切相关:(1)剖面磁化率总体表现为古土壤层最高、弱发育古土壤层次之和风成砂层最低的规律。相较低频磁化率χlf,频率磁化率χfd%能够更好、更细致地反映沉积环境的变化;(2)剖面中磁化率与成壤强度有关(正相关),因成壤作用对两剖面原始物源各粒级组分的改造程度不同,磁化率与黏粒和粉砂正相关;(3)基于剖面磁化率以及粒度特征的综合分析,将青海湖湖东沙地全新世以来气候环境划分为3个阶段:10kaBP以前气候冷干,成壤作用微弱;10~4kaBP气候暖湿,成壤作用显著;4kaBP至今,气候逐渐趋于冷干,成壤作用渐弱。

     

    Abstract: Magnetic susceptibility is an efficient indicator to the intensity of pedogenesis and depositional environment for a loess-palaeosol sequence under the Asian monsoon. However, its paleoclimatic implications still need to be revealed for an aeolian-sand-palaeosol sequence. Within the time framework established by AMS 14C and OSL dating, we studied the magnetic susceptibility characteristics of the aeolian deposits to the east of the Qinghai Lake. Taking the traditional pedogenetic indicators used in soil sciences as references, we found that the magnetic susceptibility is closely related to the intensity of soil development in the sandy land to the East of Qinghai Lake. The results show that: (1) The highest magnetic susceptibility occurs in the palaeosol layer, followed by the weakly developed palaeosol and the aeolian sand. Compared to χlf, χfd% is more efficient to reflect environmental changes; (2) The variation in magnetic susceptibility exhibits a positive correlation with pedogenesis, and is positively correlated with the content of clay and silt; (3) On the basis of comprehensive analysis, the climatic change in Qinghai Lake since Holocene could be divided into three main phases as follows: Before 10kaBP, the climate was cold and dry and the weathering process weaker. In the period of 10~8.5 kaBP, the climate turned to warm and wet. Optimum period took place from 8.5 kaBP to 4 kaBP, while the climate was warm and humid and the aeolian activity was weakened and pedogenesis became stronger. The climate was colder and drier between 4 to 1.3 kaBP. There possibly existed an abrupt climate cooling event during 3.1~2.4 kaBP. Since1.3 kaBP, the climate became colder and drier further and similar to the modern climate.

     

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