南海北部DSH-1C柱状样晚更新世以来沉积物磁性特征及其环境意义

对取自南海北部陆坡"海洋四号沉积体"的DSH-1C柱状样,进行了沉积学和磁学分析,结合相关资料探讨了该柱状样沉积物磁性特征的纵向变化及其与该区沉积环境变化的关系。结果表明:DSH-1C柱状样自上而下共划分为3个岩性单元,表层沉积物为全新世氧同位素1期(MIS1)以粘土质粉砂为主的深海-半深海沉积;中部含数层重力流沉积夹层为晚更新世氧同位素2期(MIS2)沉积;底部为晚更新世氧同位素3期(MIS3)粘土质粉砂。该柱状样磁化率(χ)平均值为1.72×10-7m3/kg。所有样品的等温剩磁(IRM)均已达到饱和等温剩磁(SIRM)的80%以上,S300的最小值为0.605。该柱状样沉积物中的磁性矿物极少,以低矫顽力矿物为主;在陆源物质输入较多的间冰期(MIS1和MIS3期),其磁性参数值较高;反之,在MIS2其磁性参数值较低,可能与冰期该区陆源物质减少有关。此外,该岩心柱中富含有孔虫壳体或双壳碎屑的重力流层沉积物的磁性参数值低,与这些逆磁性碳酸盐组分的增加有关。

Magnetic Properties of Late Pleistocene Sediments in Core DSH-1C from Northern South China Sea and Their Environment Significance

A study of magnetic properties of sediments at the piston core DSH-1C from deep sea area of Dongsha,the South China Sea was carried out.The 626 cm-core was subdivided into three lithologic units as follows: Holocene clayey silt(Unit I,MIS1) at the top interval of the core,Late Pleistocene turbidity sequences characterized by 3 to 4 major sand layers in the middle interval(Unit II,MIS2),and the lowest sequences composed by clayey silt interbedded with thin silty sand or silt layers(Unit III,MIS3).The average value of the χ of the sediments is 1.72×10-7m3/kg,and all samples show high values of IRM,over 80% of SIRM,while the minimum of S300 for all samples is 0.605.According to magnetic properties obtained,it was inferred that sediments from the core contained very rare magnetic minerals.Lowest values of magnetic properties(χ,NRM and SIRM) were observed in the intervals of Unit II,where turbidity layers containing abundant calcareous foraminifera shells occurred,indicating the dilution of carbonate in these sediment layers.On the other hand,higher values of those parameters were seen in the interglacial period(MIS1 and MIS3),probably owing to terrigenous of debris input during warm periods in this area.