济阳坳陷泥页岩细粒沉积体系

Lacustrine shale fine-grained sedimentary system in Jiyang depression

泥页岩细粒沉积体系是当前沉积学研究的前沿之一。以济阳坳陷沙河街组四段(沙四段)上亚段—沙河街组三段(沙三段)下亚段的细粒泥页岩为例,应用岩心描述、薄片观察和地球化学测试等方法研究了湖相泥页岩的细粒沉积体系,认为济阳坳陷沙四段上亚段—沙三段下亚段的泥页岩为相对稳定水体环境下的机械—生物化学混积作用的产物。基于沙四段上亚段—沙三段下亚段泥页岩的组分主要由他生盆外陆源碎屑岩和自生盆内碳酸盐岩构成的特点,先以物质来源为主要依据,将细粒沉积体系划分为外源相、混源相和内源相;进而以沉积动力和岩相的有序组合为主要依据,结合古地形,将外源相划分为斜坡边缘亚相和外斜坡亚相、混源相划分为内斜坡亚相和深洼亚相、内源相划分为水下隆起亚相和浅洼亚相。沉积体系在纵向上受沉积环境的演化控制,随着气候由干旱向潮湿演化,物源注入增强,由下至上依次发育内源相、混源相和外源相;横向上,盆地短轴方向受碎屑物源对称供给的影响,沉积相具有对称分布的特征,从缓坡至陡坡带依次发育外源相—混源相—内源相—混源相—外源相;平面上,受古物源、古盐度和古水深等控制,沉积相大致以盆地几何中心为核心呈环带状分布,内源相主要分布在水下隆起和浅洼区,混源相主要发育在半深湖区,外源相主要分布在粗碎屑沉积体系的边缘。

The study on fine sedimentary system of mud shale is the frontier of sedimentology.Taking the fine-grained mud shale from the upper submember of Member 4 and lower submember of Member 3 of Shahejie Formation in Jiyang depression as an example,using core description,thin section observation,geochemical tests and other methods,this paper investigates the fine-grained sedimentary system of lacustrine shale.It is considered that the mud shale from the upper submember of Member 4 and lower submember of Member 3 of Shahejie Formation in Jiyang depression is a product of the combined action of mechanical and biochemical mixed sedimentation under the relatively stable water environment.Based on the basic characteristics of mud shale in this study area mainly composed of allogenic terrestrial clastic rocks outside the basin and authigenic carbonate rocks inside the basin,the sedimentary facies are divided to exogenous facies,hybrid-source facies and the endogenous facies according to the material sources.Furthermore,mainly based on the orderly combination of sedimentary dynamics and lithofacies,in combination with the paleo-topography,the exogenous facies is divided into slope edge subfacies and outer slope subfacies;the hybrid-source facies is divided into inner slope subfacies and deep sag subfacies;the endogenous facies is divided into underwater bulge subfacies and panland subfacies.The sedimentary system is controlled by the evolution of sedimentary environment vertically.As the climate evolves from drought to moisture,the material source injection is enhanced.From bottom to top,endogenous facies,hybrid-source facies,and exogenous facies are developed.In the lateral direction,due to the symmetric supply of material source along the short axis of the basin,the sedimentary facies are characterized by symmetric distribution.From the gentle slope to the steep slope,the exogenous facies,hybrid-source facies,endogenous facies,hybid-source facies,exogenous facies are developed successively.In plane view,controlled by paleo-provenance,paleo-salinity and paleo water depth,the sedimentary facies is roughly distributed around the geometric center of the basin and distributed in a ring-like shape.The endogenous facies is mainly distributed in the underwater bulge and panland,the hybrid-source facies is mainly developed in the semi-deep lake area,and the exogenous facies is mainly distributed on the edge of coarse clastic rock system.