南海东北部深海盆末次冰盛期以来陆源碎屑粒度特征及影响因素

Grain size characteristics and influencing factors of terrigenous sediment in the deep-sea basin of the northeastern South China Sea since the Last Glacial Maximum

南海东北部深海盆底流演变受多种因素控制,但目前对末次冰盛期以来底流的敏感指标、演变过程及其控制因素还缺乏深入认识。本文选取南海东北部深水区16ZBS11岩心开展陆源碎屑粒度测试和年龄测定,通过粒级-标准偏差法提取环境敏感因子,并计算底流强度及搬运能力。研究结果表明,研究区陆源碎屑主要由粉砂和粘土组成,砂组分仅在部分层位出现。南海东北部深海沉积环境经历了3个演化阶段,第Ⅰ阶段为22.39~16.02ka BP,第Ⅱ阶段为16.02~9.58ka BP,第Ⅲ阶段为9.58ka BP至今,各阶段粘土和粉砂组分均呈反相演变过程。海平面变化是深海沉积和海洋过程的重要影响因素,末次冰盛期以来南海东北部深海盆底流强度和搬运能力逐渐减弱并呈同步变化,16ka BP、11.5ka BP后南海分别与印度洋、台湾海峡连通,影响了南海北部的海洋过程。特别是9.58ka BP以来南海北部海洋混合方式和强度的改变,深刻影响着深海陆源碎屑的输运及沉积演化。本文研究结果为深入认识南海北部底流活动演变和南海深海过程提供了新证据。

A number of factors control the evolution of deep-sea currents in the northeastern South China Sea(SCS),but there is still a lack of deep understanding of sensitive indicators,evolution processes and controlling factors of the bottom currents since the Last Glacial Maximum(LGM).We selected the 16ZBS11 core in the deep-sea basin of the northeastern SCS to analyze the grain size and age of the terrigenous sediment.The environmental sensitivity factors were extracted by the grain size-standard deviation method;at the same time,the bottom current intensity and transport capacity were calculated.Our results show that the terrigenous debris in the study area are mainly composed of silt and clay;sandy components only appear in a few layers.The deep-sea sedimentary environment evolution in the northern SCS has gone through three stages:stageⅠ:22.39~16.02 ka BP;stageⅡ:16.02~9.58 ka BP;stageⅢ:9.58 ka BP to present.Interestingly,the components of clay and silt in each evolution stage evoluted in reverse phase.The intensity and transport capacity of the bottom current have decreased gradually since the LGM and changed synchronously.At about 16 ka BP and 11.5 ka BP,the SCS was connected with the Indian Ocean and the Taiwan Strait,respectively,which affected the oceanic processes in the northern SCS.In particular,the changes of mixing patterns and intensities in the northern SCS since 9.58ka BP,profoundly affected the deep-sea terrigenous sediment transport and sedimentary evolution.Our results provide a new understanding of the evolution of bottom current activities in the northern SCS,and new evidence for deep-sea processes in the SCS.