DEPOSITIOAL CHARACTERISTICS OF SHANXI FORMATION IN ZHENGZHUANG BLOCK OF QINSHUI BASIN

The Shanxi Formation at the Zhengzhuang block is relatively thin and separated with upper and lower Formations by sandstone K₇ and K₈ and contains the No 3 main coal seam. It was formed in the transitional phase from an epicontinental sea to a land. A sequence of deltaic plain deposits, consisting of deltaic plain, distributary channel, interdistributary bay, natural levee, crevasse splay and swamp deposits, were developed in large area of the basin, even the delta front and prodelta deposits were not developed. According to the sedimentary environment, this paper divided the Formation into three sand groups (Ⅰ, Ⅱ, Ⅲ). Careful study has been made on the spatial distribution and evolution of micro-facies in this block. It is revealed that with the retreat of sea water, distributary channels become wider and more straight as bifurcates reduced and mouth bars gradually disappeared. Then the Formation changed into land facies at the upper part.