地球化学在高分辨率层序界面识别中的应用

粘土矿物、微量元素普遍存在于各种沉积物中,它们对环境的变化极为敏感,它们的沉积分异、组合特征、矿物成分及其含量都从不同的角度记录了环境的变化。东营凹陷胜北断层下降盘沙河街组三段—沙河街组四段高分辨率层序地层单元中岩石地球化学标型参数的研究表明,在古气候驱动下的湖平面变化旋回中,沉积岩中的矿物成分(粘土矿物和胶结物)、化学成分(微量元素)等皆发生周期性变化。高分辨率层序界面上、下,伊利石+伊/蒙混层含量及高岭石+绿泥石含量表现出截然不同的变化趋势;界面上、下古盐度也具有完全不同的特征,水进体系中,从下往上高岭石相对含量增加,蒙脱石则相应地减少,古盐度值逐渐降低,水退体系则正好相反,反映不同的水进、水退序列。界面处白云质胶结物含量呈现相对较高值,并对应着较低值的钙质胶结物和泥质胶结物。

APPLICATION OF GEOCHEMICAL METHODS IN THE RECOGNITION OF HIGH-RESOLUTION SEQUENCE BOUNDARY

Clay minerals and trace elements are widely distributed in the different types of sediments,which are so sensitive to environment change.The characteristics of clay minerals (sedimentary differentiation,mineral assemblages, and mineral composition and contents) has provided the information of environment change during their formation process.After studying the typical lithogeochemical parameters of high-resolution sequence units in the 3rd and 4th of Shahejie Fm in the fall-wall of Shengbei fault,Dongying depression,it has been found that mineral composition (including clay minerals and cements),chemical constituents (trace elements) would be periodically changed with the pace of change cycle of lake surface controlled by paleoclimate.The contents of illite + mixing-stratified illite/semectite and kaolinite +chlorite as well as paleosalinity show distinct change features above and below high-resolution sequences boundary.In the water transgressive system, the content of kaolinite is increased but the content of semectite and value of paleosalinity are gradually reduced from bottom to top.However these characteristics in water regressive system would be opposite. On the sequence boundary under different transgressive and regressive water systems,the contents of dolomitic cement is relatively high,while the contents of calcitic and mixing cements is relatively low.