冲绳海槽中部17000a以来沉积物中微量元素的组成特征及其对古环境的指示

Trace elements geochemistry composition and paleoenvironmental reflections of central Okinawa Trough over last 17000 years

基于加速器质谱仪AMS14C高精度定年,以及应用电感耦合等离子体质谱仪（ICP-MS）对S10孔岩芯沉积物进行微量元素测试,对冲绳海槽中部沉积物的微量元素组成及其记录的物源和古环境信息展开研究。研究结果显示,稀土元素、Th、Nb和Ta元素反映陆源碎屑混合矿物的化学组成特征,Zr和Hf元素指示锆石矿物的化学组成,锆石主要为火山来源,Sc元素可能与铁镁物质有关。稀土元素分析表明沉积物主要由陆源和火山源物质组成,陆源物质主要来自长江和黄河,不同时期,各源区物质贡献量不同：16 500~11 600 a,长江、黄河为沉积物的主要物质来源;11 600~7 750 a,长江物质贡献减少,黄河物质为主;7 750~6 450 a,K-Ah火山物质为主,长江、黄河物质供给骤减;6 450~3 900 a,长江、黄河陆源物质输入增加,4 000 a左右受火山作用影响;3 900~1 900 a,长江、黄河陆源物质输入持续增多;1 900 a以来长江、黄河物质仍有增加,且以黄河物质为主。此外,物源判别公式研究显示台湾物质输入量不能有效反映黑潮演变,而长江、黄河物质输入量对17 000 a以来东亚冬季风的强弱变化有很好的指示,可作为东亚冬季风演变的新证据。这些研究结果表明,冲绳海槽中部微量元素研究可得到海槽17 000 a以来物源及东亚冬季风的演化情况,有助于重建全新世以来沉积物物源及古环境的演变历史。

Based on precise AMS14 C dating and trace element data analyzed by ICP-MS, this paper examines the trace elements＇ composition and the sediment provenances and paleoenvironment information recorded in the Core S10 sediments from Central Okinawa Trough over the past 17 000 years. Our results indicate that rare earth elements and other trace elements（Th, Nb, and Ta）, reflect chemical compositions of mixed terrigenous detrital minerals. Zr and Hf show volcanic zircon geochemical features, whereas Sc might correlate with matic materials. REE analysis results indicate that sediments in the Central Okinawa Trough mainly comprise terrigenous sediments and volcanic materials. The terrigenous sediments predominantly came from the Yangtze River and the Yellow River; however, the contribution of these two provenances varied during the sediment periods. During the 16 500~11 600 a period, sediments were mainly terrigenous sediments, from the large rivers（the Yangtze River and the Yellow River） in East China. In the 11 600~7 750 a period, the contribution of the Yangtze River decreased and the Yellow River became the major sediment provenance. During the 7 750~6 450 a period, sediments were predominately volcanic materials which might be attlributed to K–Ah ash layer, while terrigenous sediments decreased dramatically. From 6 450 to 3 900 a, terrigenous sediments from the Yangtze River and the Yellow River increased and volcanic materials decreased except in the approximate year of 4 000, when another volcanic eruption intruded. In the 3 900~1 900 a period, terrigenous sediments from the Yangtze River and the Yellow River increased continuously. Since 1 900 a, terrigenous sediments from the Yellow River have predominated in the Core S10 sediments. Discriminant function（DF） investigation of the sediment provenance shows that Taiwan＇s DF data does not reflect the Kuroshio Current evolution, whereas DF data of the Yangtze River and the Yellow River may provide new evidence regarding the evolution of the East Asian Winter Monsoon.