末次冰消期以来东海内陆架沉积物地球化学特征及其古环境意义

Geochemical characteristics of sediments on the inner shelf of the East China Sea:Implications for paleoenvironment since the last deglaciation

尝试对末次冰消期以来东海内陆架沉积物地球化学特征及其蕴含的古环境、古气候信息进行探讨。对位于浙-闽沿岸泥质沉积中心附近的EC2005孔岩性、粒度、常量元素、矿物以及AMS14C测年数据进行了综合分析,得出以下主要结论:(1)东海内陆架沉积物不同常量元素与TiO2的比值具有不同的环境、气候意义,SiO2、Na2O与TiO2的比值可以用来反映沉积水动力条件的强弱,Al2O3、Fe2O3、MgO、K2O、MnO以及下部湖相沉积层中的CaO、P2O5与TiO2的比值则主要反映了沉积物源区的变化以及与风化程度相关的源区气候变化。(2)研究区自17.3kaBP以来沉积环境经历了剧烈变化,岩芯底部60.20m至41.00m(17.3～13.1kaBP)为湖泊三角洲沉积序列,海水自13.1kaBP开始侵入研究区,形成了41.00m的海相沉积地层。自12.3kaBP研究区受到沿岸流影响,7.3kaBP以来稳定的泥质沉积体开始形成。(3)自末次冰消期初期至末期,气候总体向暖湿方向发展,新仙女木事件、8.2ka冷事件在本孔中有明显的记录,显示出全球性重要气候事件在中纬度浅海陆架海域的区域性响应。

This contribution studied the geochemical characteristics of sediments since the last deglaciation from the East China Sea （ECS）, aim to reveal records of paleoenvironment and paleoclimate. Based upon analysis of lithology, grain-size, geochemical and mineral compositions, and AMS^14C dating for Core EC2005, located in the depocenter of Zhejiang-Fujian mud wedge on the inner shelf of the ECS, some principal results and conclusions are summarized as follows. （ 1 ） TiO2-normalized values of different major elements of the ECS inner shelf sediment have dirt）rent environmental and climatic significances. The variation of TiO2-normalized values of SiO2, Na2O can be used as proxies to reconstruct the hydrodynamic conditions. The varied TiO2-normalized values of Al2O3, Fe2O3, MgO, K2O, MnO of the whole core sediment, as well as CaO and P2O5 in the lacustrine sedimentary environment can be used as proxies to reconstruct the sediment sources and climatic changes in the source regions, reflecting the intensity of weathering. （2） The paleoenvironment dramatically changed within the study area since 17.3 ka BP. A lacustrine delta developed from the bottom 60.20 m to 41.00 m （ 17.3 - 13.1 ka BP）. The sea water arrived at the study area at 13.1 ka BP and a 41 m thick marine sediment fomled from then on. From 12.3 ka BP, the study area was influenced by Zhejiang-Fujian Coastal Current （ZFCC） . Since 7.3 ka BP, the sedimentary environment is dominated by the ZFCC, and the homogeneous mud deposit began to form. （3） From the beginning to the end of the last deglaciation, the overall climate changed towards warm and wet. Worldwide climatic events such as the Younger Dryas episode and the 8.2 ka event were well recorded in the core, indicating a regional response to important global climatic events at the shallow continental shelf area in the middle latitudes.