南海陆坡晚第四纪沉积物磁化率的对比及其古海洋学意义

对南海西沙群岛附近陆坡、南海南部陆坡以及东沙群岛附近陆坡晚第四纪磁化率变化特征进行了综合对比,并初步分析了磁化率与碳酸钙百分含量之间的关系。就磁化率变化特征而言,西沙群岛附近陆坡和南海南部陆坡可归为一个单元,东沙群岛附近陆坡划为另一单元,其中,前一单元晚第四纪磁化率曲线的共性表现为深海氧同位素期次的奇数期向偶数期过渡时期以磁化率峰值为特点,偶数期向奇数期过渡时期以磁化率谷值为特点;后一单元晚第四纪磁化率曲线的共性表现为磁化率曲线大致平行于有孔虫氧同位素曲线。上述两个单元内的磁化率曲线共性都具有地层学意义,但这两个单元内部某些部位的晚第四纪磁化率变化具有地方局限性,不宜当作大范围地层对比的工具。南海陆坡磁化率曲线和碳酸钙百分含量曲线的关系存在镜像和平行两大基本类型,但这两种对应关系未必意味着磁化率和碳酸钙百分含量之间存在着直接的因果联系。南海陆坡磁化率变化的原因很可能与冰期旋回中南海陆源物质通量的变化密切相关,另外,局部海域磁化率还可能严重受沉积物早期成岩作用的影响。

COMPARISON OF MAGNETIC SUSCEPTIBILITY OF LATE QUATERNARY SEDIMENT DERIVED FROM SLOPES IN THE SOUTH CHINA SEA AND IMPLICATION FOR PALEOCEANOGRAPHY

Based on the comparison of the magnetic susceptibility variations of late Quaternary sediment derived from slopes neighboring the Xisha Trough, Dongsha Islands, and southern slope in the South China Sea, we preliminarily analyze the relationship between magnetic susceptibility and calcium carbonate percentage. According to the characteristics of magnetic susceptibility changes, the slope neighboring the Xisha Trough and southern slope should be regarded as one unit, and the slope neighboring the Dongsha Islands another unit. While the late Quaternary magnetic susceptibility curves from the former unit is characterized by peaks during the transitions from marine isotope odd stage to marine isotope even stage, and by valleys during the transitions from marine isotope even stage to marine isotope odd stage, the late Quaternary magnetic susceptibility curves from the latter unit is parallel with the foraminifera oxygen isotope curve. In each unit, the common characters of magnetic susceptibility can be used for stratigraphic division and correlation, but some magnetic susceptibility during the late Quaternary fluctuated locally, and therefore its curve is not a tool for regional stratigraphic correlation. There are two kinds of relationships between magnetic susceptibility and calcium carbonate percentage curves, i.e., mirror type and parallel type, but the relationships do not mean a necessary link between magnetic susceptibility and calcium carbonate percentage. The causes of sediment susceptibility changes in the slopes seem related with the changes in terrigenous flux in the glacial-interglacial cycles.The sediment susceptibility in some local area is probably influenced severely by early diagenesis.