武汉天兴洲近代沉积物的磁性特征及其环境意义  

Magnetic Properties of Recent Sediments at Tianxing Centralshoal of Wuhan:Implication for Sedimentary Environment Change in the Middle Reaches of the Yangtze River

作　　者：李永涛[1] 顾延生[2,3] 曲赞[1] 

机构地区：[1]中国地质大学地球物理与空间信息学院,湖北武汉430074 [2]中国地质大学(武汉)生物地质与环境地质教育部重点实验室,湖北武汉430074 [3]湿地演化与生态恢复湖北省重点实验室,湖北武汉430074

出　　处：《地球科学（中国地质大学学报）》2011年第4期779-788,共10页Earth Science-Journal of China University of Geosciences

基　　金：国家自然科学基金项目(Nos.41072261;40872202;40771213);中央高校基本科研业务费专项资金(No.CUG090103)

摘　　要：利用多磁性参数（包括质量磁化率、频率磁化率、饱和等温剩磁、退磁系数以及热磁曲线）及磁组构分析，以长江中游武汉天兴洲近代河流沉积物为研究对象，探讨了近100年以来沉积物磁性参数变化特征及其对长江中上游水文变化及气候环境的指示．结果表明，上部组合带（0．60～1．50m）和下部组合带（2．40～3．30m）沉积物的磁性载体以亚铁磁性矿物磁铁矿为主，同时存在少量较稳定的不完整反铁磁性物质，中部（1．50～2．40m）亚铁磁性矿物相对较少，且剖面上部沉积物的超顺磁（SP）颗粒对沉积物Х贡献较大．整个沉积剖面自下而上磁性矿物含量呈“C”字型变化，反映了“软”-“硬”-“软”的磁性特性．沉积物磁组构组合带研究显示，历史时期沉积环境水动力强度、颗粒排列有序化程度以及长江流速发生了明显的变化，沉积环境水动力强度经历了“不稳定”-“稳定”-“不稳定”的变化过程，反映了长江古水文状况的变化．近代沉积物磁性特征变化格局与1900年以来以来长江中上游“暖湿”-“温凉”-“暖湿”气候环境变化和“强降水”-“弱降水”-“强降水”以及长江汉口站流量变化过程相吻合．这一研究成果为深刻认识历史时期长江流域气候环境变迁其及对长江古水文和沉积环境的影响提供了重要的参考资料．Multi-proxy of environmental magnetism （such as mass susceptibility, frequency dependent susceptibility, saturation isothermal, demagnetizing factor and thermalmagnetic curve） and magnetic fabric parameters derived from the recent sediments at Tianxing Centralshoal of Wuhan are employed to reconstruct the history of paleo-hydrology and climate changes in the mid- upper reaches of the Yangtze River. The assemblage zones of multi-proxy of environmental magnetism indicate that both upper （0. 60-1.50 m） and lower （2.40-3. 30 m） zones are dominated by the ferromagnetic magnetite. The upper zone is marked by the superparamagnetic grains, which make greater contributions to the mass susceptibility. The percentage of antiferromagnetic minerals in the middle zone （1.50-2. 40 m） increases in inverse proportion to the percentage of the ferromagnetic. Therefore, the depth variation of the magnetic mineral contents is like letter C reflecting the magnetic characteristics of ＂SOFT＂, ＂hard＂ and ＂SOFT＂ throughout the section. The analysis on the magnetic fabric parameters demonstrates that hydrodynamic intensity of sedimentary environment, ordering degrees of particle arrangement, and flow velocity of the Yangtze River have undergone significant changes in the past 100 years, which is related to the paleo-hydrological change of the Yangtze River. Variation patterns of magnetic properties in the recent sediments are consistent with the climate change and discharge change at Hankou Station. Especially, hydrodynamic intensity of sedimentary environment has changed from unstable to stable, then unstable, cotresponding to the temperature and precipitation changes from hot-wet to cool-dry and hot-wet. Our research has provided significant evidence for further understanding the influence of climate change on the paleo-hydrology and sedimentary environment of the Yangtze River in the historical period.

关 键 词：沉积物 环境磁学 磁组构 地球物理 

分 类 号：P736.21[天文地球—海洋地质]