渤海南部莱州湾Lz908孔沉积物的岩石磁学性质  

Rock magnetic properties of the Lz908 borehole sediments from the southern Bohai Sea,eastern China

作　　者：李倩[1] 易亮[1,2] 刘素贞[1] 于洪军[3,4] 陈燕萍[5] 徐兴永[3] 李萍[3] 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 [2]中国科学院三亚深海科学与工程研究所,三亚572000 [3]国家海洋局第一海洋研究所海洋沉积与环境地质重点实验室,青岛266061 [4]国家深海基地管理中心,青岛266061 [5]国家海洋局第二海洋研究所工程海洋学重点实验室,杭州310012

出　　处：《地球物理学报》2016年第5期1717-1728,共12页Chinese Journal of Geophysics

基　　金：国家自然科学基金项目(41106062;41402153);国家重点基础研究发展计划(973计划)项目(2012CB821900);中国博士后基金项目(2013T60164)联合资助

摘　　要：亚洲大陆边缘海和陆表海在区域的物质和能量交换以及区域气候与环境演化过程中扮演了关键角色.磁性地层学和环境磁学方法是建立年代框架和环境演变序列的有效手段,但是,由于该地区边缘海和陆表海沉积物中磁性矿物来源十分复杂,磁性地层学和环境磁学研究的重要基础是要精细地解译沉积物的岩石磁学性质.为此,本文利用渤海南部莱州湾Lz908孔与钻孔附近的现代沉积物样品进行了详细的岩石磁学对比研究.结果显示,渤海南部沉积物中的磁性矿物主要是较粗颗粒(较大的准单畴至多畴)磁铁矿,还有少量磁赤铁矿,部分沉积物还含有赤铁矿和针铁矿,其中磁铁矿是特征剩磁的主要载体;莱州湾现代河流-海洋沉积物和钻孔样品之间的磁性特征无显著差异,说明莱州湾沉积物堆积之后尚未经历明显的沉积后期改造.Marginal seas and epicontinental seas in eastern Asia play an important role in moderating material and energy flux linkages between Asia and Northwest Pacific andsubsequently have a profound climatic and environmental impact. Magnetostratigraphy and environmental magnetism have been proven to be useful in the establishment of chronostratigraphic framework and paleoenvironmental processes,respectively.However,due to the complexities of magnetic mineralogy,magnetic grain size and magnetic concentration for the sediments in marginal and epicontinental seas of eastern Asia,it is necessary to carry out detailed rock magnetic studies using multiple parameters before magnetostratigraphic and enviromagnetic analyses.The Bohai Sea is part of the epicontinental seas in eastern China,and the Bohai Basin is one of the Cenozoic extensional basins in this area.In this study,we have carried out detailed rock magnetic investigations on the sediments from the Lz908 borehole sedimentary sequence of the southern Bohai Sea and the modern fluvial/marine sediments from the adjacent areas.The Lz908 core was drilled to a depth of 101.3mbelow the surface.The upper 54.3mof the core contains dominantly marine and coastal silts,sandy silts and fine-grained sands,and the lower 47.0m consists mainly of lacustrine and fluvial silts.The rock magnetic measurements include temperaturedependent magnetic susceptibility（-Tcurves）,hysteresis loops and associatedΔMand dΔM/dB curves,isothermal remanent magnetization（IRM）acquisition curves and backfield curves of IRM,first order reversal curve（FORC）diagrams,and stepwise thermal and alternating field demagnetization.The multiparameter rock magnetic measurements indicate that the sediments consist of a mixture of different magnetic minerals with variable grain size or concentration.The behaviors of-Tcurves suggest the presence of magnetite and maghemite in the sediments and the dominant contribution to susceptibility by magnetite.The combination of hysteresis loops and associatedΔM and dΔ

关 键 词：岩石磁学 渤海 莱州湾 

分 类 号：P318[天文地球—固体地球物理学]