Sedimentary geochemistry properties of rare earth elements from the continental lower slope of the northeastern South China Sea over the last 20 ka and its implication for provenance
本文通过对南海东北部STD235沉积柱状样品稀土元素(REE)分布模式及特征参数的分析,结合主量元素分析结果,探讨了STD235柱状样沉积物REE指示的物质来源及其纵向变化与环境之间的关系。研究结果表明: 20 ka以来STD235站位的沉积物具有基本相同的物质来源,以陆源物质输入为主。通过与周边河流沉积物的对比分析发现,STD235柱状样沉积物REE上地壳标准化的配分模式及其特征参数分布与台湾东南部河流沉积物具有密切的亲缘关系,表明该站位陆源物质主要来源于台湾东南部河流输入,进一步的分析表明台西南河流沉积物对该站位也有所贡献,沉积物的搬运过程主要受到了北太平洋深海流及黑潮的影响。沉积物中REE和主量元素的纵向变化指示20 ka以来南海东北部下陆坡的沉积物源区在冰期时风化作用较弱,间冰期则相对增强。该变化与沉积物源区的气候环境变化有关,指示了20 ka以来台湾地区气候由相对冷干向暖湿转变,由此推测20 ka以来台湾岛和华南地区应该受相同环境因素的制约,东亚季风系统是控制该区域环境变化的主因。此外,在约16~13 ka BP的末次冰消期期间,STD235柱状样沉积物中的各项指标都发生了显著的变化,并都指示了风化作用的逐渐增强,代表了该阶段沉积物源区逐渐向暖湿的气候环境转变。
英文摘要:
Rare earth elements (REEs) and major elements in Core STD235 sediments from the northeastern South China Sea (SCS) were analyzed. Combined with the results,the sediment provenance and the relationship between the vertical variations of REE parameters and climate change were discussed. REE chemical characteristics showed that the sediments in the investigated site had the same main provenance and were dominated by the terrestrial contribution during the last 20 ka. The UCC-normalized REE pattern and REE parameters of sediments from Core STD235 are close to sediments from southeastern Taiwan Rivers,indicating that sediments were primarily derived from the southeastern Taiwan rivers. Further analysis implied that the southwestern Taiwan rivers might also make contribution to the core STD235. The sediments might be transported by the North Pacific Deep Water and Kuroshio through the Luzon Strait into SCS. Synthetically analysis potentially denotes the climatic environment variations should be the main factor causing the vertical variations of REE indexes. The analysis indicated the stronger chemical weathering intensity during the last interglacial period than that during the last glacial period on the source areas of the sediment, implying a warmer and wetter climate in Taiwan during the last interglacial period. The variations of chemical weathering intensity recorded in sediments might be associated with changes of environment and climate on the source areas. It is speculated that the controlling factors of environment and climate on Taiwan Island were similar to the south China, and the East Asian monsoon system might be the primary cause of the regional environment and climate changes. In addition,abrupt changes in almost of all proxies of the Core STD235 sediments from about 16 ka BP to 13 ka BP occurred and indicated a stronger chemical weathering,which implied the environmental and climatic condition on source area changed to warm and humid climate during that period.