苏北东台坳陷古新统阜宁组三段微量、稀土元素地球化学特征及其地质意义

沉积岩的微量、稀土元素对沉积环境的水介质变化有着较高的敏感度,对于研究古环境、沉积物源性质和构造背景方面具有重要的意义。前人对于东台坳陷元素地球化学方面的研究相对薄弱,利用元素地球化学资料解释古环境和源区性质方面的研究尚属空白。本文以苏北东台坳陷古新统阜宁组三段20件泥岩样品为研究对象,对其进行微量、稀土元素测定,并分析其地球化学特征及所揭示的地质意义。结果表明:(1)Sr含量、Sr/Cu、Rb/Sr、La_n/Yb_n比值指示干热气候;Li、Sr、Ni、Ga微量元素含量和Sr/Ba比值均指示淡水—半咸水的水体环境,整体以淡水环境为主,偶有咸水注入盆地,局部为半咸水环境;而V/(V+Ni)、V/Cr、Ni/Co、U/Th、δCe指示氧化—弱还原的水体环境。(2)Co/Th—La/Sc、La/Th—Hf判别图解和稀土元素配分模式,表明阜宁组三段沉积岩应来自于上地壳的长英质物质。(3)La—Th—Sc、Th—Co—Zr/10和Th—Sc—Zr/10构造背景判别图解反映了大陆岛弧与活动大陆边缘的构造背景,且与Bhatia不同构造背景杂砂岩的微量、稀土元素特征值的对比分析结果一致。

Geochemical characteristics of trace and rare earth elements in the 3rd Member of Paleocene Funing Formation in Dongtai Depression,North Jiangsu Basin,and their geological significance

Objectives:The trace elements and rare earth elements in sedimentary rocks are highly sensitive to changes in the water medium of the sedimentary environment,and are of great significance to the study of the paleoenvironment,sediment source properties and tectonic background.Previous studies on the element geochemistry of the Dongtai Depression,North Jiangsu Basin(Subei Basin),are relatively weak,and the use of element geochemical data to explain the paleoenvironment and provenance is blank to now.Methods:The paper takes 20 mudstone samples from the 3rd Member of the Paleocene Funing Formation in Dongtai Depression as the research object,carries on the determination of trace elements and rare earth elements,and analyzes their geochemical characteristics and the geological significance revealed.Results and Conclusions:(1)Sr,Sr/Cu,Rb/Sr,La_n/Yb_n indicate dry and hot climates,and Li,Sr,Ni,Ga,Sr/Ba indicate freshwater—brackish water environment.V/(V+Ni),V/Cr,Ni/Co,U/Th,andδCe indicate oxidation—weakly reducing water environment.The overall water environment is mainly freshwater,occasionally saltwater is injected into the basin,and local is brackish water.(2)Co/Th—La/Sc,La/Th—Hf discriminant diagrams and rare earth elements distribution patterns reflect the original sedimentary materials from the upper crust.(3)La—Th—Sc,Th—Co—Zr/10,and Th—Sc—Zr/10 discrimination diagrams generally reflect the tectonic setting of continental island arcs and active continental margins.The comparison results between the characteristics of the trace elements and rare earth elements in the sandstones of different structural backgrounds listed by Bhatia and the samples in the study area also reached the same conclusion.