西太平洋特定海域沉积物的地磁场相对强度研究

IOCAS-IR > 海洋环流与波动重点实验室

	西太平洋特定海域沉积物的地磁场相对强度研究
其他题名	GEOMAGNETIC RELATIVE PALEOINTENSITY RECORDS OF SEDIMENTS FROM THE WEST PACIFIC OCEAN
	孟庆勇
学位类型	博士
	2009-05-23
学位授予单位	中国科学院海洋研究所
学位授予地点	海洋研究所
关键词	地磁场相对强度菲律宾海东海还原成岩岩石磁学
摘要	沉积物可以提供连续的地磁场相对强度（RPI）记录，这些记录在全球范围内的对比具有一致性。目前RPI记录越来越多地在布容极性期内作为千年尺度高精度的地层对比手段，但由于构建RPI所需的岩石磁学标准较高，总体来说，RPI数据还相对缺乏，尤其是太平洋地区连续的RPI记录更是相对较少。本文以西太平洋特定海域沉积物为研究对象，进行了古地磁和岩石磁学方面等多个参数的综合测量，通过归一化天然剩磁得到了地磁场相对强度变化曲线，为RPI研究提供了新的记录，为研究区测年提供了新的手段。西菲律宾海的Ph05孔沉积物的岩石磁学和古地磁研究表明，岩芯中的载磁矿物比较单一，以低矫顽力的磁铁矿为主，χ、ARM及SIRM等参数指示的磁性矿物的含量变化不大。磁性矿物的颗粒以准单畴为主，粒度指示参数χARM/χ具有冰期-间冰期旋回变化。通过交变退磁可得到稳定的特征剩磁，32-38 cm及108-110 cm处发现负倾角，并伴随着RPI的低值。谱分析检验后选择ARM作为归一化参数，通过ARM归一化天然剩磁获得了200 ka以来的地磁场相对强度记录。重建的RPI记录与综合曲线Sint-200有良好对比，可以反映全球性的信号。基于RPI建立的年代模型与氧碳同位素年代模型相似，可以作为独立的定年手段。对东菲律宾海帕里西维拉海盆西侧F090102孔柱样沉积物进行了系统的古地磁和岩石磁学分析，结果表明样品适合进行相对强度研究。根据功率谱分析结果，选择非磁滞剩磁作为归一化的参数，得到约2 Ma以来的地球磁场相对强度变化曲线。该曲线与SINT-2000曲线可详细对比，比如呈比较典型的锯齿状特征，布容期内的记录与800 ka以来的SINT-800曲线相符。布容/松山极性转换期呈单强度降低的特征，在极性转换期和极性漂移期，相对强度曲线表现为显著低值。对东海内陆架泥质区沉积物EC2005孔的磁学研究表明，岩芯在110 cm即受到还原成岩作用的影响；110-600 cm经历了铁氧化物还原阶段，样品中磁性矿物以PSD磁铁矿为主，随深度增加，其含量快速减少，其间随着硬磁矿物含量的波动，磁学参数也呈现出峰谷变化；600 cm向下岩芯经历硫酸盐还原阶段，各磁学参数都维持在很低的水平，顺磁性颗粒增加，并出现黄铁矿。早期成岩作用及重磁化作用使得古地磁信号被削弱和改造。
其他摘要	The possibility of retrieving relative intensity variations of the Earth’s magnetic field from sediments allows the documentation of continuous geomagnetic paleointensity variations back in time, and these records show a mutual good agreement to the global scale field. At present, RPI curves have been increasingly used as global, millennial-scale correlation and stratigraphic tool. Despite such importance, data constraining the past intensity of the planetary body remain relatively scarce, especially in the Pacific Ocean. In this study, we present the details of a paleomagnetic and rock magnetic study carried out on the sediments from the West Pacific Ocean. The aim of this study is to document the relative paleointensity data by normalizing the natural remanent magnetization, which would provide a new approach for regional stratigraphic division and correlation. A detailed rock magnetic analysis has been conducted on core Ph05 from the West Philippine Sea. Rock magnetic results demonstrate that the core preserve a strong, stable remanent magnetization and meet the magnetic mineral criteria for relative paleointensity (RPI) analyses. The magnetic minerals in the sequence are dominated by pseudosingle-domain magnetite, and the concentration of magnetic minerals are at the same scale. Both the conventional normalizing method as well as the pseudo-Thellier method were used in conjunction with the examination of the rock magnetic properties and natural remanent magnetization. Susceptibility (χ), anhysteretic remnant magnetization (ARM) and saturation isothermal remnant magnetization (SIRM) were used as the natural remanent magnetization normalizer. However, coherence analysis results indicate that only ARM is more suitable for paleointensity construction .The age model of core is established based on oxygen isotope data and AMS14C data, which is consistent with the age model estimated from RPI records. The relative paleointensity data provide a continuous record of the intensity variation during the last 200 ka, which correlates well with the global references RPI stacks. Several prominent low paleointensity values are identified and correlate to the main RPI minima in the SINT-200 record, it suggests that the sediments have recorded the real changes of geomagnetic field. The rock magnetic measurements of core F090102 suggested that the cores preserve a strong, stable remanent magnetization and meet the magnetic mineral criteria for reliable paleointensity analyses. χ, ARM and SIRM were used as the natural remanent magnetization normalizer. The relative paleomagnetic intensity record over the past about 2 Ma was obtained and was further compared to previously published stack records, SINT-800 and SINT-2000. Our new RPI record exhibits asymmetrical saw-tooth pattern of the geomagnetic field intensity and some major declines in paleointensity (DIP) at reversal boundaries as well as geomagnetic excursions. The Brunhes/Matuyama polarity transition was characterized by a single-DIP but not a double-DIP, it may be due to the low sedimentation accumulation rates. The record can be used to refine the chronological framework of the sediment in this region. The results of core EC2005, located in the mud area in the inner shelf of the East China Sea, demonstrate that the upper 110 cm sediments are little affected by reductive diagenesis; The 110-600 cm sediments are within the stage of iron oxide reduction, PSD magnetite mainly contributes to sediments of this section, with less abundant and coarser grains downcore. The magnetic parameters vary along with the fluctuation of the content of hard magnetic phases; The 600-2800 cm sediments are within the stage of sulphate reduction. Values of magnetic parameters, such as x, SIRM, and HIRM, drop sharply in this section, with little fluctuation. Paramagnetic minerals contribute to sediments of this section, including pyrites. The reductive diagenesis and post-depositonal alteration have weaken and destroyed the original magnetic signals.
页数	160
语种	中文
文献类型	学位论文
条目标识符	http://ir.qdio.ac.cn/handle/337002/1471
专题	海洋环流与波动重点实验室
推荐引用方式 GB/T 7714	孟庆勇. 西太平洋特定海域沉积物的地磁场相对强度研究[D]. 海洋研究所. 中国科学院海洋研究所,2009.

条目包含的文件
文件名称/大小	文献类型	版本类型	开放类型	使用许可
10001_20061800681206（4101KB）			限制开放	--	浏览