沧东凹陷孔二段混合细粒沉积岩相特征及形成环境

Lithofacies Characteristics and Formation Environments of Mixed FineGrained Sedimentary Rocks in Second Member of Kongdian Formation in Cangdong Depression, Bohai Bay Basin

沧东凹陷孔二段页岩层系广泛发育混合细粒沉积岩.混合细粒沉积岩的岩石类型划分和沉积环境分析是其成因研究的重要组成部分,有助于总结混合细粒沉积岩的沉积规律,寻找有利勘探目标.通过岩心与薄片观察、二维XRF(X射线荧光光谱)扫描,结合XRD(X射线衍射)、元素地球化学测试等资料,以矿物成分和沉积构造为主要依据,将孔二段混合细粒沉积岩划分为21种岩相;通过Sr/Cu、Mg/Ca、Sr/Ba、V/(V+Ni)、Al、Ti含量、Fe/Mn和(Fe+Al)/(Ca+Mg)等地球化学指标的垂向变化及岩相分析沉积环境演化.沧东凹陷孔二段混合细粒沉积岩主要发育在气候干旱、微咸水-咸水相、水体贫氧、陆源输入较强的半深湖-深湖环境中;岩相类型的发育同时受到水体的高盐度和陆源输入的影响,均一细粒沉积岩分布最广,其次为灰云细粒沉积岩,黏土细粒沉积岩不发育.

Mixed fine-grained sedimentary rocks are widely developed in the shale formation of the second member of the Kongdian Formation(Ek2)in the Cangdong depression,Bohai Bay basin.A proper classification of rock types and sedimentary environment analysis of the mixed fine-grained sedimentary rocks are crucial for understanding their genesis,which is helpful to summarize the deposition law of mixed fine-grained sedimentary rocks and find favorable exploration targets.On the basis of detailed examination of cores and thin sections,XRF(X-ray fluorescence spectrometer)images,combined with XRD(X-ray diffraction),element geochemical measurement data,the mixed fine-grained sedimentary rocks in Ek2 are subdivided into 21 lithofacies based on mineral compositions and sedimentary structures.The evolution of sedimentary environments is revealed by lithofacies and changes of geochemical indexes such as Sr/Cu,Mg/Ca,Sr/Ba,V/(V+Ni),Al and Ti contents,Fe/Mn and(Fe+Al)/Ca+Mg)ratios.The mixed fine-grained sedimentary rocks in Ek2 were mainly developed under an arid climate in a semi-deep to deep lake,with brackish and anoxic water with strong terrestrial input.The lithofacies was developed under the influence of high saline water and the input of terrestrial sediments.Homogeneous fine-grained sedimentary rocks are the most widely distributed,which is followed by lime-dolomite fine-grained sedimentary rocks,while clayey fine-grained sedimentary rocks are not well developed.