南海北部陆坡30 ka以来的沉积环境演变

Sedimentary environmental evolution for the past 30 ka of the northern continental slope of the South China Sea

南海是西太地区最大的边缘海,汇集了周边陆地大量碎屑物质。这些陆源碎屑通过复杂的洋流系统经陆坡大量的输送到南海深海海盆中,使陆坡成为研究深海沉积物源汇体系不可缺少的重要环节。但陆坡区域水深变化大,洋流体系复杂,加之冰期间冰期海平面升降和季风的变化,使陆坡沉积环境一直成为研究的难点。为了研究陆坡沉积环境的演变过程,本文选用了南海北部陆坡中部和底部的两个重力柱开展元素地球化学方面的研究,探讨陆坡区域近三万年以来的沉积环境特征。研究发现海平面和季风是影响区域沉积环境的两个重要因素:(1)海平面变化是控制陆坡陆源物质/深海钙质碎屑变化的主要因素;(2)研究区域地层发育有“碳酸盐稀释事件”与东亚夏季风在全新世初期(11.5~8.5 kaBP)增强有关。

The South China Sea is the largest marginal sea in the Western Pacific,which receives massive sediments from the surrounding landmasses.Terrestrial sediments are transported into the deep basin via a complex ocean current system,with the continental slope as a key component of the source-to-sink process.However,past changes in sedimentary environment of the continental slope remain rarely understood,because of the drastic variations in water depth and complicated current systems in addition to sea level changes induced by glacial-interglacial cycles and the changes in trade wind.In this research,two gravity cores collected from the northern South China Sea are used to study the sedimentary environmental evolution of the continental slope.One is located in the middle of the slope,and the other at the lower part of the slope.According to the results of element geochemistry,it is revealed that:1)the sea level change is the key factor which controls the changes in the ratio of terrigenous to biogenic components of the sediments;2)a carbonate dilution event is found related to the intensification of the East Asian Summer Monsoon during the early Holocene from 11.5 to 8.5 kaBP.