Abstract:

Xihu depression is a sub-depression of Donghai basin, China. Pinghu Formation developed in late faulting-subsiding period is a suit of coal-bearing series, and the most important source rock in Xihu depression. On the basis of comprehensive analysis of seismic, drilling, logging and core data,three long-term and ten mid-term base level cycles are recognized. The main sedimentary environment developing coal seam are tide influencing delta plain, interdistributary bay of tide influencing delta front, supralittoral zone, and interdistributary bay of braided delta front. These long-term base level cycles are mainly positions where coal seam growth, and the long-term base level cycle LSC2 is the most developing place of coal seam. The place of coal seam in short-term base level cycle was controlled by size of accommodation space. Coal seams were mainly developed in middle-upper part of decreasing short-term base level cycle on the background of high accommodation space; whereas coal seams were mainly developed in the maximum accommodation space of short-term base level cycle on the background of low accommodation space.

Key words: Pinghu Formation, sequence stratigraphy, soal seam, accommodation, base level cycle