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Based on the detailed observations of the whole core, bulk of organic geochemical analysis, and combined with regional geological characteristics, the evolution of depositional environments and enrichment pattern of organic matter of mudstone of the Meihe Formation in the Meihe Basin was studied, and this will be enriched the theory of oil shale and coal metallogenic mechanism of the Meihe Basin. Three types of sedimentary facies were identified in the Meihe Formation including alluvial fan, fan-delta and lake facies. Mid-fan subfacies of alluvial fan is developed in the bottom of Sandy-Conglomerate Member, and fan delta deposited in the Lower Coal-bearing Member. In the middle Mudstone Member, the mainly depositional environment is semi deep-deep lake. Lacustrine bog and shallow lake are developed in the Upper Coal-bearing Member and the Green-rock Member separately. It should be noted that, oil shale developed in the semi deep to deep lake, and coal layers deposited in the swamp. The organic matter content in mud-stone shows a decreasing trend after increasing upward, meanwhile the type of kerogen changes from type III to II2 and II1, then becomes to type III, and this caused the organic facies changes from E to A, and becomes E finally. Comprehensive studies show that, the base level, depositional environment evolution, organic matter supply and preservation conditions caused by tectonic and paleoclimate evolution result in different types and abundance of organic matter in mudstone. Due to the limit terrestrial debris supply, good preservation condition and explosion of higher plants, it is favorable for coal seam to occur in the stable shallow water area in the mid-stage of initial subsidence and the beginning of the basin shrinkage stage. While with the high lake productivity and good preservation conditions, oil shale deposited in the stable deep water area during the largest basin subsidence stage. [ABSTRACT FROM AUTHOR]

Clay mineral and inorganic geochemical characteristics of Eocene Huadian formation in Huadian basin have been found through X-ray diffraction, scanning electron microscopy and inorganic geochemical element tests. Clay minerals of Huadian formation of the study area contain montmorillonite, kaolinite and illite. The content of montmorillonite is the highest, and illite/smectite mixed layer is rare. Mn, Sr, P, Cd, Sr/Cu, B/Ga, Sr/Ba and Ca/(Ca+Fe) change with an exactly similar trend vertically, and Cu, Cs, Rb/Sr, V/(V+Ni) and 8Ce change with another similar trend. Clay minerals and inorganic geochemical evidence reveal the characteristics of paleoclimate and paleolimnology:the upper section containing coal and the lower section containing pyrite of Huadian formation belong to terrestrial sedimentary environment under the condition of warm and humid climate and low salinity ; the middle section containing oil shale belongs to frequently alternating freshwater and saltwater environment, alternating humid and drought climate. The largest expansion phase of lacustrine basin which was under reduction condition with alternating humid and drought climate and salinity stratification developed semi-deep lake and deep lake facies which formed oil shale; the shrinkage phase of lacustrine basin with warm and humid climate developed delta plain with peat swamp which formed coal. [ABSTRACT FROM AUTHOR]