南海深海平原柱状样QD189磁化率、非磁滞剩磁、粒度、碎屑矿物丰度之间的主要关系

磁学可能是南海深海平原古环境研究取得突破的关键方面之一。众多磁学参数中,磁化率是最基本、最综合反映沉积物磁性矿物总体状况的参数,非磁滞剩磁对单畴颗粒含量敏感,而且单畴颗粒是剩磁的主要携带者,结合粒度、碎屑矿物丰度等数据探索南海深海平原柱状样QD189磁化率和非磁滞剩磁地质含义。在磁化率大于45×10-5层位和481 cm以浅的磁化率小于45×10-5的层段,磁化率、2~5粒级含量、ARM和ARM@20m T变化一致性较好,2~5粒级软磁性多畴颗粒含量变化可能是这些层位磁化率变化的主要原因。在808~488 cm层段内,小于45×10-5的磁化率与2~5粒级含量、ARM和ARM@20m T变化总体上一致性较差,磁化率变化机制有待进一步研究。2~5粒级是QD189重要的较粗粒级组分,大体上以深度350 cm为界具有下层段含量较高且粒度变化大、上层段含量较低且粒度变化小的特点。ARM@20m T比ARM更加真实地表示QD189单畴颗粒含量,除了单畴颗粒外,9~12粒级假单畴、多畴颗粒矿物对665~48 cm层段的ARM可能有一定贡献,其中,层段548~310 cm的ARM中可能还有6~9粒级多畴颗粒的贡献。通过碎屑矿物丰度、火山玻璃丰度和(或)磁化率异常峰值的对应关系识别出6次火山活动,火山玻璃丰度的分布特点还揭示出QD189中普遍发生生物扰动作用。

The Relationship among Magnetic Susceptibility,Grain Size,Anhysteretic Remanent Magnetization and Clastic Mineral Abundance in Core QD189 Retrieved from Abyssal Plain of the South China Sea

Magnetism is probably one of key disciplines for breakthrough of paleoenvironment studies in abyssal plain of the South China Sea. Magnetic susceptibility is the most basic and general parameter reflecting information of magnetic minerals in sediment, while ARM is sensitive to the concentration of singe domain particles which is main carrier of remanent magnetization. In this study, we explore the geological implications of magnetic susceptibility and Anhysteretic Remanent Magnetization (ARM) in core QD189 retrieved from abyssal plain of the South China Sea integrating the data of grain size and clastic mineral abundance. In the segments with magnetic susceptibility great than 45×10^-5 or the segments with depth less than 481 cm and magnetic susceptibility less than 45×10^-5, there are similar fluctuations among magnetic susceptibility, the contents of 2~5 ? grain size range, ARM, and ARM_@20mT , and the magnetic susceptibility changes in these segments is probably due to the fluctuations of contents of the soft magnetic multidomain grains within 2~5 ? grain size range. In the segments with depth from 808 cm to 488 cm and magnetic susceptibility less than 45×10^-5, the coherences among the changes of magnetic susceptibility, the contents of 2~5 ? grain size range, ARM, and ARM_@20mT are poor, and the mechanism of magnetic susceptibility changes is pending further research. 2~5 ? grain size range is an important coarse grain size component in QD189, and generally have a higher contents and bigger change ranges below the depth of 350 cm than above the depth of 350 cm. ARM_@20mT can more accurately indicate the concentration of singe domain particles in QD189 than ARM, and except single-domain particles, the particles of the pseudo-single-domain and multidomain within 9~12 ? grain size range probably make some indispensablet contributions to ARM in the segment with 665~48 cm depth, and a part of ARM in segment with 548~310 cm depth is also derived from multidomain within 6~9 ? grain size range. Six volcanic actions are recognized by the corresponds among the extreme peak values of clastic mineral abundance, volcanic glass abundance and magnetic susceptibility. The distribution pattern of volcanic glass abundance reveals the prevalence of bioturbation in QD189.