南海与台湾岛东部海域浅地层碳酸盐旋回

Carbonate cycle in sub-bottom strata in the South China Sea and the east sea area of Taiwan Island

前人提出南海晚第四纪碳酸钙含量变化存在“大西洋型”和“太平洋型”两种基本类型,本文利用δ18O、CaCO3含量、Al2O3含量、SiO2含量、浮游有孔虫丰度及钙质超微化石丰度,来表征南海与台湾东部海域13个柱状样的碳酸盐旋回特征。CaCO3含量和SiO2含量通常是表征碳酸盐旋回的良好指标,二者的变化常呈相互消长关系。研究区碳酸盐旋回包括“大西洋型”和“太平洋型”两种标准型式,但也存在不规则形态。“大西洋型”碳酸盐旋回与海平面冰期-间冰期升降旋回密切相关,本文研究的具有该旋回特征的柱状样主要分布在南海水深3000 m以浅区域,其中南海北部碳酸盐旋回很可能伴随着海平面下降(上升)期间富集陆源较粗(细)颗粒物的过程。“太平洋型”碳酸盐旋回在南海现今碳酸钙溶跃面上下很大水深范围都有分布,碳酸钙溶解作用旋回不是“太平洋型”碳酸盐旋回的根本原因。本文研究的台湾东部海域柱状样碳酸盐旋回既不属于大西洋型,也不属于太平洋型。研究区浅地层沉积速率变化与碳酸盐旋回的型式关系不大,主要受控于水深和冰期旋回中海平面变化。随着水深增大,沉积速率趋于增加。MIS2期平均沉积速率大约是MIS1期平均沉积速率的2倍多。

It was discovered that there existed two classic types of carbonate cycle,namely,Atlantic type and Pacific type,in the late Quaternary sediments in the South China Sea.In this paper,some characteristics of carbonate cycles in the South China Sea and the sea area southeast of Taiwan were discussed using the data ofδ18O,CaCO3 content,Al2O3 content,SiO2 content,planktonic foraminireral abundance,and calcareous nannofossil abundance.These data were derived from thirteen cores.Generally,CaCO3 content and SiO2 content are good proxies for the representation of carbonate cycles,and these two variables often display inverse relationship.In the study area,the types of carbonate cycle include not only the classic Atlantic and Pacific types,but also irregular forms.The Atlantic-type carbonate cycle is intimately related to sea level fluctuation in the glacial-interglacial cycle,and the studied cores with this type cycle are mainly located in the region whose water depth is less than 3000 m in the South China Sea.The Atlantic-type carbonate cycle on the north slope of the South China Sea was likely accompanied by the enrichment process of coarser(finer)particles during the periods of sea level descent(rise).The cores featured by Pacific-type carbonate cycle in the South China Sea are distributed within a big depth range across the modern calcite lysocline,which suggests that carbonate dissolution cycle was not the primary cause of the Pacific-type carbonate cycle.The carbonate cycle type of the studied core derived from the sea area east of Taiwan was neither Atlantic-type nor Pacific-type.The sedimentation rates of sub-bottom strata in the study area had little relationship with the types of carbonate cycle,but were deeply influenced by water depth and the glacialinterglacial sea level fluctuations.The sedimentation rates were increased with increasing water depth,and the average sedimentation rates during MIS2 was more than twice the ones during MIS1.