黄土高原西部白草塬剖面L_1和S_1记录的古地磁场特征  

PALEOMAGNETISM OF THE LOESS/PALEO～SOL COUPLET L_1/S_1 AT THE BAICAOYUAN SECTION,WESTERN LOESS PLATEAU

作　　者：邓成龙[1] 

机构地区：[1]中国科学院地质与地球物理研究所岩石圈演化国家重点实验室,北京100029

出　　处：《第四纪研究》2008年第5期854-865,共12页Quaternary Sciences

基　　金：国家自然科学基金项目(批准号:40674032和40221402);中国科学院创新团队计划项目资助

摘　　要：文章详细介绍了黄土高原西部白草塬剖面L1和S1的高精度岩石磁学和古地磁学结果,讨论了白草塬剖面记录古地磁场的特征,从古地磁学角度探讨白草塬剖面黄土沉积的连续性。白草塬剖面黄土沉积物中,磁铁矿和磁赤铁矿是主要的亚铁磁性矿物,粗粒的碎屑磁铁矿是其天然剩磁和特征剩磁的主要载体。白草塬剖面L1和S1没有记录任何地磁漂移。其中,L1没有记录MonoLake或Laschamp地磁漂移的原因可归结于黄土沉积物堆积过程的不连续性和/或粗颗粒载磁矿物的重磁化,但前者是主要原因,而堆积过程的不连续性是导致S1没有记录Blake地磁漂移的主要原因。因此,白草塬剖面的L1和S1分别存在约2000年和4000～6000年的沉积不连续。High-resolution paleomagnetic investigation was conducted on the Baicaoyuan loess-paleosol sequence since the last interglacial in the western Chinese Loess Plateau. Magnetite and maghemite are the main ferrimagnetic minerals, indicated from temperature-dependent magnetic susceptibility measurements. Coarse-grained magnetite of eolian origin was identified as the main carrier for the natural remanent magnetization（NRM） and the characteristic remanent magnetization （ChRM） by stepwise thermal demagnetization of the NRM and low-temperature demagnetization of the NRM and the ChRM. The paleomagnetic results reveal the absence of any short-lived geomagnetic excursions in the Baicaoyuan section. This absence could be interpreted by two alternative mechanisms,magnetic overprinting and discontinuous sedimentation. The absence of the Mono Lake and Laschamp geomagnetic excursions in the last glacial loess L1 is probably due to the viscous overprinting of the remanence carried by coarse-grained magnetite of eolian origin and/or to the episodic nature of loess accumulation during the last glacial period. However, discontinuous sediment accumulation may more likely lead to the absence of the Blake geomagnetic excursion in the last interglacial soil S, as well as of the Mono Lake and Laschamp excursions in the last glacial loess L1 at the Baicaoyuan section. The finding probably indicates the discontinuous nature of loess accumulation in the western Chinese Loess Plateau,where sedimentation of the last glacial loess L1 may be episodic at the timescale equivalent to the duration of the Mono Lake or Laschamp geomagnetic excursions（ca. 2ka）, and sedimentation of the last interglacial soil S1 may be episodic at the timescale equivalent to the duration of the Blake geomagnetic excursion（4 - 6ka）.

关 键 词：黄土高原 末次冰期-间冰期旋回 古地磁学 岩石磁学 

分 类 号：P318.44[天文地球—固体地球物理学] P941.74[天文地球—地球物理学]