南海西沙海槽83PC柱状沉积物组成特征及其古环境意义

为了解南海北部末次间冰期以来的沉积环境演化,分析了西沙海槽83PC柱状沉积物的浮游有孔虫氧碳同位素、碳酸钙、有机碳和粒度组成。浮游有孔虫的δ18 O值具有冰期-间冰期旋回特征,记录了海平面的升降和古气候的变化,而海平面变化控制了沉积物的碳酸钙和有机碳含量。冰期,海平面下降,陆源物质输入增多,带来了大量的碎屑物质和陆源有机质,沉积物具有低碳酸钙含量和高有机碳含量;间冰期,海平面上升,陆源物质输入减少,碎屑物质的稀释作用减弱,沉积物具有高碳酸钙含量和低有机碳含量。南海北部83PC柱状沉积物记录了末次间冰期以来的多次海平面升降旋回,还记录了气候变冷事件以及低碳酸钙沉积事件,其中,150、510、660和740cm处的低碳酸钙含量和相对重δ18 O值记录了全球性气候变冷事件,而冰后期的低碳酸钙沉积事件,则主要反映了季风降雨的增强,出现了洪水高发期,陆源碎屑物质对碳酸钙沉积的稀释作用明显增强。

THE COMPONENT CHARACTERISTICS AND PALEOENVIRONMENTAL SIGNIFICANCES FOR SEDIMENTS IN CORE 83PC FROM THE XISHA TROUGH,SOUTH CHINA SEA

In order to understand the paleo-environmental evolution in the northern South China Sea(SCS) since the last interglacial,the compositions of C-O isotope,calcium carbonate,total organic carbon(TOC) and grain size for sediments in Core 83PC derived from the Xisha trough were investigated.The results showed that the δ18O and δ13C values of planktonic foraminifer exhibited significant glacial-interglacial cycles,controlled by the sea level fluctuation and climate change.The input of terrestrial materials increased during glacial sea level fall,and the sediments had lower carbonate content and higher TOC content;however,it decreased during interglacial sea level rise,and the sediments had higher carbonate content and lower TOC content.The chemical composition of sediments in core 83PC indicates climatic instability in late Pleistocene;and rapid climate changes and low carbonate sedimentation could be identified.The low carbonate contents at depth of 150 cm,510 cm,660 cm and 740 cm is thought to be an evidence for the occurrence of global cooling events.And a rapid decrease in carbonate content during early-middle post-glacial period might be resulted from the changes in rainfall.Erosion would be intensified wile heaop rain,and the dilution effect to carbonate wap thus enhanced.