【作者】 李萍；

【导师】 李培英； 傅命佐；

【作者基本信息】 中国海洋大学 ， 环境工程， 2005， 博士

【摘要】 本文选取东海陆架至冲绳海槽槽底平原的代表性沉积样品110个和已有研究基础的DH180岩心样品,通过颗粒分离、磁性矿物分析、趋磁细菌培养、浮游有孔虫δ¹⁸O测定、AMS¹⁴C测年、多种磁学参数测量（包括磁化率、等温剩磁、x-T热磁曲线、磁滞回线、非磁滞剩磁和饱和等温剩磁等）等试验手段,分析探讨了不同粒级沉积物对磁性的贡献、沉积物磁性与物质来源及环境的内在联系、短期古海洋事件的环境磁学表现等科学问题。主要研究结果和认识如下: 1.根据不同沉积环境中沉积物的磁滞回线、等温剩磁曲线、热磁曲线等磁性特征和磁性矿物的分析结果,认为从陆架外缘到冲绳海槽槽底平原沉积物的磁性矿物以磁铁矿为主,磁性矿物的粒度以准单畴为主,存在少量超顺磁颗粒。 2.不同沉积环境中沉积物对磁性矿物富集的粒级不同,不同粒级沉积物对磁化率的贡献存在差异。陆架外缘粗颗粒沉积物对磁化率的贡献大,西陆坡和西槽底平原细颗粒沉积物对磁化率的贡献大,而东槽底平原因含有火山物质,粗细粒级对磁化率贡献相当。 3.根据各沉积环境中不同粒级沉积物对磁化率的贡献、磁性矿物的成分、磁畴状态、磁滞回线及等温剩磁曲线和热磁曲线变化的幅度和趋势,认为各沉积环境中磁性矿物的来源和成因不同。从陆架外缘到东槽底平原,在磁性矿物来源上既有一定的联系,又受不同环境因素（如火山作用）的制约,表现出不同的磁性特征和环境特点。 4.冲绳海槽东槽底平原沉积物含有较多的火山物质,磁学特征与其它沉积环境有明显差异,各磁性参数特征值也明显较强。 5.CaCO₃含量与磁性参数没有明显的相关性,但在高含量区,可能对沉积物磁性矿物的含量具有稀释作用,沉积物磁学性质相对减弱。 6.根据DH180岩心沉积物的磁学性质的变化特征,认为冲绳海槽中部曾发生过两次火山事件和一次短期气候变冷事件（新仙女木事件）。两次火山事件发生时代分别距今约12.6ka和6.2ka,最近一次火山喷发的年代与K-Ah火山喷发的年代基本一致;在新仙女木事件发生时期,DH180岩心磁化率（x）曲线明显减小,SIRM/x和ARM/x比值有稍微增大的波动特征。更多还原

【Abstract】 Multiple experiments such as grain-sized separation , magnetic mineral analysis, magnetic parameters measurement were made on 110 surface samples and 64 samples of the 180 core sediment taken from the shelf of the East China Sea to abyssal plain of the Okinawa Trough. The magnetic parameters measurement include magnetic susceptibility, saturation remanent magnetization, x(T) curve , hesteresis loop, anhysteresis remanent magnetazation and so on. Based on the measured results, some science problems such as the contribution of the grain size to the magnetic susceptibility, correlation in sediment magnetic characteristic and material provenance with different sedimentary environments, magnetic exhibition of plaoleoceanography event were discussed. The main results and conclusions are presented as following:1 The properties of hesteresis loop、 isothermal remanent magnetization and x(T) curve show that the magnetic mineral is dominated by magnetite with a small amount of hematite.The granulometry of magnetic fractions in samples is primarily in pseudo-single-domain state, possibly existing a small amount of superparamagnetic (sp) particles.2 The magnetic minerals exist as different grain-sized particles that contribute magnetic susceptibility in different proportion to bulk sediments from different sedimentary environment. For example, the coarse grain-sized particles contribute much magnetic susceptibility to bulk sediments from the continental shelf edge of the East China Sea, while the fine grain-sized particles contribute much magnetic susceptibility to bulk sediments from the continental slope of the East China Sea and western abyssal plain of the Okinawa Trough. The sediments from eastern abyssal plain of the Okinawa Trough contain some volcanic materials and thus their totalmagnetic susceptibility is both from coarse and fine grain-sized particles.3 According to grain-size contribution to total magnetic susceptibility of bulk sediments, magnetic mineral, magnetic domain state and hystersis properties and the width and height of magnetic parameters curve changes different degree and trend in different sediment environment. That indicates that there are different provenance and formation in different sediment environments. It is concluded that sediments from different environments, continental slope of the East China Sea, western and eastern abyssal plain of the Okinawa Trough, are correlated each other in material source. Other local environment factors, such as turbidity current and volcanic activity, have also impacted on sediments and made them showing different magnetic properties and environmental characteristics.4 According of east abyssal plain of the Okinawa Trough with some volcanic materials, it show strong magnetic characteristics different from other sediment environments.5 There are no evidently correlation between CaCO3 and magnetic parameters, but magnetic feature tends to become weaker with the content of CaCO3 increase. Being as biologic index, CaCO3 possibly dilute the content of magnetic minerals of sediments to affect on magnetic characteristics of sediments .6 It have verified that two Volcano Ejecting events and Younger Dryas event had happened in the Okinawa Trough from the magnetic information contained in sediments of the typical core. The time of Volcano Ejecting events happened at 12.6ka and 6.2ka respectively, and the time of the last Volcano Ejecting event is consistent with K-Ah Volcano Ejecting events. Where the Younger Dryas event happened in 180 core, the magnetic susceptibility curve markedly decrease. At the same time SIRM/x and ARM/x curve little increase. It record the characteristic of environmental magnetism at the Younger Dryas event.更多还原