莱州湾7000年以来沉积地球化学记录及其地质意义

Variation of Geochemical Records and Geological Significance of the Sediments in the Laizhou Bay Since 7000 a B.P.

在建立年代框架的基础上,通过分析435孔沉积物粒度和常微量元素组成随时间的变化特征,探讨了其主控因素并重建了莱州湾地区7 000年来的沉积环境演化历史。结果表明,435孔中Al_2O_3、CaO等常量元素以及大部分微量元素含量随埋深增加呈现高-低交替变化模式,而SiO_2、Na_2O则呈现相反模式;常微量元素含量变化主要受细粒陆源碎屑(以Al_2O_3为代表)、粗粒陆源碎屑(以TiO_2为代表)和生源碎屑(以Sr为代表)3个因子控制;莱州湾7 000年以来的沉积环境演变可划分为5个阶段,其中,阶段V、IV和III(7 000~1 800aB.P.)中K/Na比值、CIA指数呈现高-低交替变化的趋势,Si/Al比值呈现低-高交替变化的趋势,揭示了古气候由温湿到干冷的环境演变,阶段IV、II和I(5 800~5 200aB.P.,1 800~0aB.P.)中黄河物源指数PI、CIA指数或Sr/Ba比值呈现减小趋势,揭示了黄河历史改道对莱州湾沉积环境的影响。

Based on the chronological framework,the element composition variations with time and grain size of sediments in Core 435 were analyzed to explore its main controlling factors for element composition and reconstruct the evolution of sedimentary environment in Laizhou Bay since 7 000 a B.P..The results showed that the content of Al 2O 3,CaO and other constant elements and most of the trace elements in Core 435 showed a high-low alternation pattern with the increase of the depth,while SiO 2 and Na 2O showed the opposite pattern.Changes in major and trace elements were mainly controlled by fine-grained terrigenous debris(represented by Al 2O 3),coarse-grained terrigenous debris(represented by TiO 2)and biological debris(represented by Sr).The evolution of sedimentary environment of Laizhou Bay since 7 000 a B.P.were divided into five stages.The K/Na ratio and CIA index showed a high-low alternation trend,while the Si/Al ratio showed a low-high alternation trend,revealing that the paleoclimate climate evolved from warm and humid to dry and cold in the stage V,IV and III(7 000~1 800 a B.P.).The Yellow River Provenance Index(PI),CIA index or the Sr/Ba ratio in the stages IV,II and I(5 800~5 200 a B.P.,1 800~0 a B.P.)showed a decreasing trend,which revealed the influence of the Yellow River diversion on the sedimentary environment of Laizhou Bay.