太湖平原西北部全新世古河道沉积特征及环境演变

粒度、磁化率定量数据分析在判明第四系沉积物的来源、识别沉积分异作用、解译古沉积相和环境方面有着重要作用。对太湖平原西北部卜弋桥ZK01钻孔上部全新统如东组进行了粒度和磁化率测试分析,结合该孔孢粉成果,揭示研究区全新世古河道沉积环境和气候明显经历了3个阶段:1)11000—9500cal.aBP,沉积物主要由粉砂组成,粒度证据表明水动力条件较强,孢粉证据显示该阶段气候较温暖湿润;2)9500—3900cal.aBP,沉积物砂组分含量大幅增加,粒度资料显示古河道水动力明显增强,孢粉植被表明该时期处于全新世大暖期,气候暖湿稳定;3)3900cal.aBP以来,粉砂组分在沉积物中占优势,粒度结果表明该阶段水动力显著减弱,孢粉资料和磁化率证据表明研究区自该阶段特别是后期以来逐步出现了明显的人类活动迹象。

SEDIMENTARY CHARACTERISTICS OF THE PALAEOCHANNEL AND ENVIRONMENT EVOLUTION DURING THE HOLOCENE IN THE NW TAIHU PLAIN,YANGTZE RIVER DELTA

A 8.0m long sediment core from Boyiqiao Town,NW Taihu Plain,Jiangsu Province,provides detailed information about changes in the palaeochannel and environment evolution during the Holocene based on combined analysis of multiple environmental proxies such as granularity,magnetic susceptibility and pollen.Evidences show that the Holocene palaeochannel and climate underwent three distinctive stages:1) 11 000—9 500 cal.aBP,granularity data show that the hydrodynamics of the palaeochannel was strong and the climate was warm and moist;2) 9 500—3 900 cal.aBP,the paleohydrodynamics of the river became much stronger,indicating the considerable rainfall related to the strong East Asia summer monsoon.The climate turned warm and wet corresponding to the Holocene Megathermal.Lowest values of magnetic susceptibility and higher amount of carbon particles possibly point to natural fire events around 7 500—7 000 cal.aBP;3) Since 3 900 cal.aBP,granularity evidence suggests the paleohydrodynamics of the ancient river in this stage became weak and was possibly disturbed by the growing anthropogenic activity shown by the magnetic susceptibility and pollen data.