末次冰期以来日本海陆源沉积的地球化学记录及其对海平面和气候变化的响应

GEOCHEMICAL RECORD OF TERRIGENOUS SEDIMENTS FROM THE SEA OF JAPAN SINCE LAST GLACIAL AND ITS RESPONSE TO SEA LEVEL AND CLIMATE CHANGE

通过对日本海Ulleung盆地KCES-1岩心中的主微量元素、稀土元素及粒度的综合分析,探讨了沉积物来源及其控制因素。结合地层年代模型,恢复了研究区48ka以来的古环境记录。结果显示,日本海Ulleung盆地沉积物以陆源碎屑为主,沉积物中主微量元素(Al、K、Fe、Mg、Na、Ti、Th、Sc、Rb、Sr、Cr、Co、Hf、Zr)含量普遍低于平均页岩。稀土元素丰度(ΣREE)为80～213μg/g,与长江、黄河及中国黄土接近,高于日本上地壳。球粒陨石标准化显示,沉积物中轻稀土显著富集,有显著的Eu负异常(0.6～0.8),Ce异常不显著。元素比值(La/Th、Th/Sc)及La/Th-Hf物源性质判别分析显示,研究区沉积物主要来源于上地壳,母岩落入长英质源岩区。在11～18ka,主微量元素的分布特征与11～0ka及48～18ka有显著差异。海平面和全球气候变化是控制主微量元素时空分布的重要因素。化学蚀变指数CIA(45～61)显示沉积物源区化学风化程度较弱,18ka以前风化程度低于18ka以后风化程度,暗示气候由干冷向暖湿转移。这与全球气候变化和东亚夏季风强度变化趋势一致。

We analyzed major,trace,and rare earth element chemistry,and grain sizes for KCES-1 piston core sediments from the Ulleung basin in the Sea of Japan to determine the sediment provenance and factors controlling the composition of the sediments.Based on the stratigraphic age model,a 48 ka record for paleoenvironmental change was retrieved.The results show that,the composition of sediments is dominated by terrigenous matter.In general,the concentrations of major and minor elements（Al,K,Fe,Mg,Na,Ti,Th,Sc,Rb,Sr,Cr,Co,Hf,Zr）are less than average shale.REE total abundances（ΣREE）which are closed to those reported previously for the Yangtze,Yellow River,and Chinese Loess,but are much higher than the upper crust composition of Japan Island,range between 80 and 213 μg/g.Chondrite-normalized REE patterns with distinct negative Eu（0.6～0.8）anomalies and a strong light-REE enrichment were seen throughout the data.Cerium anomaly is not distinct.Elemental ratios and La/Th-Hf discrimination diagram of source rocks show that sediments in the study area mainly originate from upper crust and the parent rocks are feldspar-quartzose.During 11～18 ka,the abundances of major,minor,and rare earth elements are different from those during 0~11 ka and 18~48 ka.The factors controlling the elements distributions are related to sea-level and climate changes.The Chemical Index of Alteration（CIA）（45～61）indicates that the intensity of chemical weathering in the sediment source is weak.The weathering intensity is much higher after 18ka,indicating climate changes from cold and dry to warm and wet conditions.The weathering trend is very similar to global climate change and to the intensity of the East Asian summer monsoon.