Sedimentary Mechanism in the Coal and Oil Shale Bearing Succession Graben Basins: The Comparision between Fushun and Huangxian Basins, Eastern China

The association of coal and oil shale had been a hot topic for a long time. Various types of association of coal and oil shale can be found in one basin, for instance, the coal can act as the roof or floor or interlayer of the oil shale, etc. The most crucial factor for the formation of oil shale is stratification and seasonal blooming of lower plankton, while the final formation of the coal still needs a hypoxia restored deposition environment. We take Huangxian and Fushun basins as typical examples to study the coal and oil shale sedimentary mechanisms controlled by the boundary fault. We found that the sedimentary mechanisms are different in different stages during the process of basin evolution. In the early stage, the association of coal and oil shale with thinner layers can be found. In the late part of early stage, thick layer coal seams and oil shale can be formed because of the relative stable faults. In the middle stage, thicker oil shale can be formed in deep lake and thicker coal seams can be formed in the lacustrine shore. In the late stage of basin evolution, the association of thickest coal seams and oil shale can be formed as the stable tectonic environment. Compared with the depression basin, more active fault and short cycle subsidence controlled by the episodic tectonic movements are the obvious characteristics. Higher rate of tectonic subsidence and a vast difference between sedimentary (peat-bearing) supply rate and accommodation space change rate are in favor of forming oil shale, and slower rate of tectonic subsidence is favor of forming coal. The study found that faulted structures obviously control the development, thickness and distribution characteristics of oil shale and coal. As mentioned above, the episodic tectonic movement of continental rift basin controls the types and filling and evolution of deposits.