Sedimentary Characteristics And Coal-accumulation Patterns Of The Middle And Lower Part Of Jurassic In Yili Basin

Yili basin located in the Yili—mi d-Ti anshan mi cro-plots of mi d-Tianshanuplift zone, which is in the south-eastern section of the Kazakhstan plate.As there areUranium and Oil—gas reservoirs, has caused the attention of geologists at homeand abroad. Shuixigou Group is the main coal-bearing stra tum in Yili basin. theprevious have done some research, and obtain the corresponding results, but the lackof systematic integrity. Based on the analyses of data about drilling, loggings,outcrops and palaeophytes, this paper studied the sequence stratigraphy of ShuixigouGroup in Yili basin. Five sequences, the lower part of Badaowan formation （SQ₁）、the top part of Badaowan formation （SQ₂）、 the Sangonghe formation （SQ₃）、the lower part of Badaowan formation （SQ₄）and the top part of Badaowan formation（SQ₅）, were identified with the classic sequence stratigraphy method. And fourteensystem tracts were subdivided according to the superposition style of strata andsedimentation cycle. The characteristics of sedimentary evolution of Shuixigou Groupwere also defined through analyzing the sedimentary environments. In sequence SQ₁、SQ₂and SQ₄, a river-dominated （fan） delta was developed; a stable peat swamp wasformed in the lake edge and flood plain area and stable thick coal seams were alsoformed after a long-time and wide-range intense coal accumulation. In sequence SQ₃a Lacustrine was developed,as in reduction environment,it is not conducive to formecoal seams; In sequence SQ₂, owing to the tectonic transformation, the strongdenudation and insufficient data, the coal accumulation and the sedimentarycharacteristics need to further study. The result provided the basis for furtherexploration of coal resources in Xishanyao Formation in Yili basin.