Abstract：Aiming at making clear the issues that existed in the exploration about the types of sedimentary facies, a series of study was carried out. Based on the detailed core observation, a series of phenomenon can be seen in Shanxi formation of Hangjinqi area, in combination with regional geological data, logging, well log and particle size data. The content and maturity of stable minerals tend to be increased gradually from the north to south. The grain-size accumulative probability curve is characterized by bidirectional current. The sedimentary structures such as wedge-shaped cross-bedding, wave bedding, sand grain cross-bedding and mudstone ripup, reflect the stable-agitated high-energy water environment. The change of mud color draws the sedimentary outline of a transitional zone from subaqueous to subaerial deposit. In consideration of a series of evidences concerned above, it draws an conclusion that the braided river delta is developed in the Shanxi formation and the study area has experienced the evolution from braided river delta front to braid-river delta plain, and the lake range has moved the south from Shan-1 formation to Shan-2 formation, which shows that the Shanxi formation developed the sedimentary system of braided river delta characterized by “deposits progradation and lacustrine regression ”. The microfacies of a distributary mouth bar develop little and underwater distributary channel dominates the distribution of depositions. The thick sand bodies of the super-compensation braided river delta, which can be acted as reservoir and hydrocarbon migration channel, have developed much in the study area. The carbonaceous mudstone in the tributary bay provides favorable conditions for the formation of coalformed gas and coal.

Keyword：braided river delta;sedimentary evolution;Shanxi formaion;