Abstract: Coal and oil shale occur alternatively and cyclically in the Paleogene Huangxian faulted Basin. The oil shale, lack of bedding structure, is mostly brown black, brownishblack in colour and appears as compact, rigid masses. The content of organic materials is up to 45% and consists mainly of kerogen of I type. Reconstruction of the Palaeoecology in the Paleogene Huangxian faulted Basin indicates that periodical marine invasion dominated. Oil shale was formed in semisaline or saline water environments caused by commixture of sea water (salty water) with fresh water. While the salt water is mixed up by the fresh water, gelatinous function related to the mixing of two waters resulted in the formation of the oil shale. When the base of the basin subsided quickly with marine invasion, oil shale was deposited. When the subsiding of the basin base became slow down, no marine invasion was found and the basin was dominated by a peat swamp environment in which coal beds were deposited. The cyclic sedimentation of the coal and oil shale was caused by changing subsiding rates of the basin, periodical aggression and retrogression of seawater.

Key words: Huangxian, faulted basin, oil shale, gelatinous function, formation mechanism