南海西部54万年以来元素地球化学记录及其反映的古环境演变  

Elemental Geochemical Records in the Western South China Sea since 540 ka and Their Paleoenvironmental Implications

作　　者：贺子丁[1] 刘志飞[1] 李建如[1] 谢昕[1] 

机构地区：[1]同济大学海洋地质国家重点实验室,上海200092

出　　处：《地球科学进展》2012年第3期327-336,共10页Advances in Earth Science

基　　金：国家自然科学基金项目"南海陆源碎屑沉积物的源区;搬运和沉积"(编号:40925008);"南海东北部底层海流和沉积搬运过程的观测研究"(编号:91128206)资助

摘　　要：通过对南海西部上升流区MD05-2899孔开展高分辨率碳酸盐地层学和XRF岩芯扫描元素地球化学分析,重建了晚第四纪54万来以来东亚夏季风的演化历史,探讨海平面升降对南海西部陆源碎屑供应量的影响。研究选用了ln(Ba/Al)作为该海区古生产力的指标,ln(Br/Al)作为有机物的指标,ln(Ti/Al)作为陆源碎屑供应量的指标。研究结果显示,东亚夏季风在过去54万年以来强度不断增强,具有明显的冰期—间冰期旋回特征,在间冰期强盛和冰期减弱,是控制该海区有机物含量变化的主要因素。东亚夏季风不断强盛可能直接导致了南海周边陆地降雨增强,河流径流量加大,使得南海西部上升流区域的陆源碎屑供应量在间冰期明显高于冰期。研究发现,当相对海平面低于-60 m的时候,大面积暴露的巽他陆架可能向南海西部深水区输入大量陆源碎屑物质,造成研究站位的陆源碎屑供应量在冰盛期出现高值。因此,晚第四纪的东亚夏季风演化和海平面升降共同控制了南海西部上升流区陆源碎屑物质供应量的变化。High-resolution carbonate stratigraphy and XRF core-scanning elemental geochemistry were ana- lyzed at Core MD05-2899 in the upwelling area of the western South China Sea to reconstruct the evolution history of the East Asian Summer Monsoon （EASM） over the past 540 ka in the late Quaternary and to study the effect of sea level change on terrigenous material supply to the western South China Sea. Three proxies of elemental ratios were chosen for indicating paleoenvironmental changes： ln（Ba/A1） for the paleoproductivity, ln（Br/A1） for the organic matters, and ln（Ti/A1） for the terrigenous material supply. Our results show that the EASM has been continually enhanced over the past 540 ka and presents strong glacial-interglacial cyclicity with strengthened intensity during in- terglacials and vice versa. The EASM could be the major factor controlling the variation pattern of organic matters inthe western South China Sea. The strengthened EASM could directly enhance the precipitation on lands surrounding the South China Sea, increase the runoff of their drainage basins, and finally produce higher terrigenous material supply during interglacial than glacial periods in the western South China Sea. However, when the relative sea level was lower than -60 m during glacial periods, the broad part of the Sunda Shelf was exposed and enormous amount of terrigenous materials could be eroded and then transported far to the western South China Sea, resulting in the strong terrigenous material supply during glacial maximum periods at Core MD05-2899. Therefore, we suggest that the late Quaternary EASM and sea level change could jointly control the variation of terrigenous material supply in the upwelling area in the western South China Sea.

关 键 词：碳酸盐地层 XRF岩芯元素扫描 东亚夏季风 海平面变化 晚第四纪 南海 

分 类 号：P722.7[天文地球—海洋科学] P736