长江口外CX21柱样的磁性特征及其影响因素

以长江口外、长340 cm的CX21柱样为对象，在磁性特征、地球化学和粒度分析的基础上，结合前期对Y7柱样的研究，探讨粒度、早期成岩作用和物源变化对沉积物磁性特征的影响.研究结果表明，该柱样磁性特征和粒度垂向变化显著.磁性参数χ、SIRM、χ_fd和χ_fd%与 2~4 μm、4~8 μm粒级含量呈相对较弱的正相关, 而χ_ARM、χ_ARM/SIRM和χ_ARM/χ与16 μm以下的各细颗粒组分有较强的正相关，表明CX21柱样沉积物磁性特征受到粒度变化的影响.利用BCR方法进行的铁的形态分析结果表明，CX21柱样170 cm深度以下具有较强的还原环境，磁性矿物受到较强的早期成岩作用影响.氧化还原不敏感元素Ti的垂向变化指示了物源变化，Ti向表层的增加与χ和SIRM向表层的增强具有同步性，说明物源变化也是CX21沉积物磁性特征影响的重要因素.尽管粒度组成和沉积速率不同，CX21与Y7柱样的磁性特征在垂向上具有相似性，表明磁性特征可作为长江口外沉积物地层对比的工具之一.

Magnetic properties of the core CX21 off the Yangtze Estuary and its influencing factors

Core CX21（122°30’ E,30°00’ N） is 340 cm in length,obtained off the Yangtze Estuary, China.In this study,magnetic,geochemical and particle size analyses were conducted on sediments from the core CX21 to determine the major factors（including early diagenesis,particle size and sediment provenance） that control the down-core variations of magnetic properties.Re- suits indicate that there are strong positive relationships betweenχ_Arm,χ_arm/SIRM andχ_arm/χand the fractions finer than 16μm.χ,SIRM,χ_fd andχ_fd%display relatively weak,but positive correlations with the finer fractions（2—4μm and 4—8μm）.This suggests that particle size plays an important role in the variation of magnetic properties.Iron species analysis using the BCR method indicates that sediments below 170 cm experienced more reducing environment than that above,which is consistent with the phenomena of stronger reductive diagenesis of magnetic minerals.Ti,an element insensitive to redox conditions,reveals sediment provenance changes in the core CX21.The increase of Ti toward the surface is accompanied by an increase of concentration related magnetic parameters（χand SIRM）,suggesting that sediment source is also a main factor influencing magnetic properties.In spite of the difference in sedimentation rate and particle size composition,CX21 and the previously studied core Y7 show similar down core variations of magnetic properties,implying that magnetic properties can be used as a tool for core correlation in area off the Yangtze Estuary.