冲绳海槽北部CSH1孔岩石磁学特征及其早期成岩作用的影响

葛淑兰; 石学法; 吴永华; 李德贵; 熊应乾; SAITOYoshi

冲绳海槽北部CSH1孔岩石磁学特征及其早期成岩作用的影响

1.
海洋沉积与环境地质国家海洋局重点实验室山东青岛 266061;国家海洋局第一海洋研究所山东青岛 266061中国科学院地质与地球物理研究所北京100029
2.
海洋沉积与环境地质国家海洋局重点实验室山东青岛 266061
3.
台湾地球科学研究所台湾台北
4.
日本地质调查所筑波 306-8567

基金项目: 国家自然科学基金重点资助项目(40431002);国家海洋局青年基金资助项目(2004303)

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出版历程
- 收稿日期: 2005-03-22
- 修回日期: 2005-06-13

The rock magnetic behavior og gravity core CSH1 from the northern Okinawa Trough and the effect of early diagenesis

1.
Marine Sedimentation and Environmental Geology Key Laboratory of State Oceanic Administration, Hangzhou 310012, China;First Institute of Oceanography, State Oceanic Administration, Qingdao 266061, China;Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
2.
Marine Sedimentation and Environmental Geology Key Laboratory of State Oceanic Administration, Hangzhou 310012, China
3.
Institute of Earth Sciences, Taipei, China
4.
Geology Survey of Japan, Tsukuba 306-8567, Japan

摘要

摘要: 以2~4 cm为间隔,对冲绳海槽北部的CSH1孔岩心(17.36 m)进行了岩石磁学研究.根据岩心上部的两个特征火山灰层和浮游有孔虫组合分析建立了钻孔的时间框架,沉积物底部年龄可能为50 ka.除了在三个火山灰层和近表层向下的快速降低外,整个钻孔磁学参数的变化甚小,未能反映出50 ka来的气候变化.与大多数沉积物不同,该钻孔大多数层位的S值(S=-IRM-0.3T/SIRM,它代表了低矫顽力磁性矿物的含量)小于0.9,指示钻孔沉积物中存在相当比例的高矫顽力磁性矿物.代表性沉积物样品的磁化率-温度(K-T)曲线除了存在580℃磁铁矿的居里温度之外,还显示200~350℃的居里温度,指示样品中存在铁硫化物(胶黄铁矿-磁黄铁矿).这与加热过程中有刺鼻的臭味、加热后的沉积物变黑对铁硫化物的指示相吻合.自生成因的铁硫化物的存在以及表层磁性参数的快速降低,都明确表明沉积物遭受了早期成岩作用.除了三个火山灰层以外钻孔的其他层位无特征磁学变化,表明沉积物后来受到的改造作用强烈,磁学参数所蕴含的原始气候信号被破坏.在这一系列氧化-还原过程中消耗了沉积物中的有机质和水溶液中的硫酸盐,造成了沉积物中铁、锰元素的重新溶解和沉淀等.
- 冲绳海槽北部 /
- CSH1孔 /
- 岩石磁学特征 /
- 火山灰层 /
- 早期成岩作用
Abstract: A detailed rock magnetic investigation was undertaken at 2~4 cm interval for the long core CSH1 (17.36 m) from the northern Okinawa T rough.A time scale of the core was constructed by two characteristic tephras and foraminferal assemblages,indicating an age of 50 ka for the bottom of the core.Except for three tephr as and abrupt decrease in surface,there are little changes in all kinds of rock magnetic parameters that can be correlated to the climate change for the last 50 ka.Being different from the common sediments,most of S value (S= -IRM_-0.3T/SIRM) for the sediments are smaller than 0.9,which implies substantial amount of magnetic minerals with high coercivity.Representative susceptibility-temperature (K-T) curves show 200~350℃ Curie temperature in addition to 580℃ of magnetite which reveals the existence of iron sulphide (greigite or pyrrhotite).This is also consistent with awful smell during heating and dark heating product which indicates the existence of iron sulphide.Both the occurrence of authigenic iron sulphide and quick decrease of magnetic parameters at the surface clearly show that sediments from Core CSH1 have undergone early diagenesis.The featureless magnetic changes of the whole core except for the three tephras mean that the postdepositonal alteration is so strong that most original signals have been destroyed.For the same reason,the organic matter in sediment and sulphate in pore water have been consumed,and iron,manganese dissolution and precipitation happen during the redox processes.Great caution must be taken when using these altered chemical parameters for the interpretation of climatic changes.
- northern Okinawa Trough /
- gravity core of CSH1 /
- rock magnetic behavior /
- tephra sequences /
- early diagenesis

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参考文献(37)

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