MAGNETOSTRATIGRAPHY OF CORE GX149 FROM THE WEST PHILIPPINE SEA
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摘要: 对取自西菲律宾海西部的GX149重力活塞柱状样沉积物进行系统的岩石磁学和古地磁学研究,结果表明:沉积物中主要载磁矿物为低矫顽力的磁铁矿,粒径以假单畴(PSD)为主。天然剩磁强度分布范围为(1.07~6.51)×10-7 Am2,平均值为3.33×10-7 Am2。经过0~80 mT交变场退磁后,几乎所有样品均可获得稳定的特征矢量方向,且磁倾角绝大部分为正值,表明整个GX149柱状样处于布容正极性期。样品的磁倾角普遍存在浅化现象,且从顶到底,磁倾角变浅程度逐渐增强,与沉积物的压实作用有关。通过与相邻海域柱状样的对比,估算出GX149柱状样的平均沉积速率在0.79~2.42 cm/ka之间,其底界年龄在256.2~781 ka之间。Abstract: Rock magnetic and paleomagnetic studies were carried out for the core GX149 taken from the western West Philippine Sea. The magnetic carrier in sediments is dominated by low coercivity magnetite within the pseudo-single-domain (PSD) in size. The natural remanent magnetization (NRM) of samples ranges from 1.07×10-7 to 6.51×10-7 Am2 with a mean of 3.33×10-7 Am2. Most samples could acquire well-defined, steadily characteristic remanence component after stepwise alternating field (AF) demagnetization upto 80mT. The geomagnetic inclinations of most samples are positive, suggesting that the whole core of GX149 falls in the Brunhes epoch. The shallowing of inclinations of the sediments are common in core GX149, and the degree of inclination bias increases from top to the bottom. The cause for the inclination bias is most likely the syn/post-depositional compaction of sediments. The sedimentation rate is estimated in a range of 0.79~2.42 cm/ka for the whole sequence. The maximum geochronological constraint for sedimentation duration of core GX149 is estimated 256.2~781ka by comparing with other sediment cores in adjacent areas.
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Key words:
- West Philippine Sea /
- piston core sediment /
- inclination bias /
- magnetostratigraphy /
- Brunhes epoch /
- sedimentary rate
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