河西走廊早新生代红层次生剩磁及其对原生剩磁影响评价  

The secondary remanent magnetization in the Early Cenozoic redbed of Huoshaogou Formation and its influence on the stability and reliability of primary NRM

作　　者：戴霜[1] 方小敏[2] Mark Dekkers 程彧[1] 唐玉虎[1] 朱强[1] 

机构地区：[1]兰州大学西部环境教育部重点实验室和资源环境学院,兰州730000 [2]中国科学院青藏高原研究所,北京100085 [3]Paleomagnetism laboratory of Fort Hoofddijk,Utrecht university,Utrecht 3584,Netherlands

出　　处：《地球物理学进展》2007年第6期1760-1766,共7页Progress in Geophysics

基　　金：国家自然科学项目(40571017;40334038;40421101);国家重点基础研究发展计划项目(2005CB422001);甘肃省自然科学基金项目(3ZS051-A25-008)联合资助

摘　　要：系统研究了河西走廊火烧沟组陆相红层200个采点岩石的热退磁行为和17个代表性样品的岩石磁学特征,结果表明有102个采点可以分离出A、B、C三个剩磁分量,有82个采点只有一个分量(C分量),16个采点只能分离出A、B分量.A、B分量分别由针铁矿和磁赤铁矿携带,C分量在砂岩中由磁铁矿携带,在泥质砂岩和泥岩中由磁铁矿和赤铁矿共同携带.A、B分量剩磁方向随机分布,不能获得置信水平的古地磁平均方向,为次生剩磁.它们的存在并不影响岩石原生剩磁的分离,也不影响原生剩磁信号的稳定性和获得的古地磁数据的可靠性.16个砂岩采点中不能分离出C分量,是由于后生的赤铁矿彻底改变了由磁铁矿携带的原生剩磁组分,在高密度采样的情况下剔除这些采点并不影响古地磁极性柱的构建和解释.Analysis on the thermal demagnetization behavior and systematic rock magnetism measurement（IRM acquisition and back field measurement, hysteresis loop, thermal demagnetization behavior of three axes components IRM and temperature-dependent susceptibility） show that, three components remanent magnetization （marked A, B, C）, only one components （C） and two components A and B can be isolated from 102, 82 and 16 sampling sites of total 200 sampling sites for Cenozoic red_beds of Huoshaogou Formation in the Hexi Corridor. The A and B components rema- nent magnetization were loaded by goethite and maghemite respectively, the C component remanent magnetization was carried by the magnetite in the sandstones and were loaded conjunctly by the magnetite and hematite in the mudstones and muddy sandstones. The random directions of the A and B components remanent magnetization and absence of the reliable mean direction from theses samples indicates that they are secondary remanent magnetization, which are not derived from the remagnetozation. The appearance of these components remanent magnetization may not change the stability of the primary remanent magnetization and should not affect the reliability of the paleomagnetic data acquired. In a few of sandstone samples without the C components, rock magnetism measurements show that there exists new authi genic hematite and changes the primary remanent magnetization carried by the magnetite. That these samples were cancelled when constructed the geomagnetic polarity chrons do not weaken our magnetostratigraphic interpretation because of high-resolution sampiing.

关 键 词：次生剩磁 岩石磁学 红层 火烧沟组 河西走廊 

分 类 号：P318[天文地球—固体地球物理学]