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  

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

作　　者：葛淑兰[1] 石学法[1] 吴永华[1] 李德贵 熊应乾[1] SAITO Yoshi 

机构地区：[1]海洋沉积与环境地质国家海洋局重点实验室 [2]台湾地球科学研究所 [3]日本地质调查所

出　　处：《海洋学报》2005年第6期56-64,共9页

基　　金：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)

摘　　要：以2～4cm为间隔，对冲绳海槽北部的CSH1孔岩心（17．36m）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50ka．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50ka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．A detailed rock magnetic investigation was undertaken at 2-4 cm interval for the long core CSH1 （17.36 m） from the northern Okinawa Trough. 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 tephras 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 post-depositonal 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.

关 键 词：冲绳海槽北部 CSH1孔 岩石磁学特征 火山灰层 早期成岩作用 

分 类 号：P318.41[天文地球—固体地球物理学] P588.2[天文地球—地球物理学]