STUDY ON SEQUENCE STRATIGRAPHY OF HUANGHUA DEPRESSION IN NORTH CHINA:TAKING Es_1-Nm STRATA IN BAISHUITOU-TANGJIAHE AREA AS EXAMPLES

Based on the theory of sequence stratigraphy and through comprehensive analyses of geologic, drilling, logging, and seismic data, the first member of Shahejie Formation (Es1)-the Minghuazhen Formation (Nm) in Baishuitou-Tangjiahe area in Huanghua depression are divided into 2 first-order and 4 second-order sequences. They are successively, from the bottom to the top, the sequence Ⅰwhich corresponds to the first member of Shahejie Formation, the sequence Ⅱ which corresponds to the Dongying Formation, the sequence Ⅲ which corresponds to the Guantao Formation, and sequence Ⅳ which corresponds to the Minghuazhen Formation. Of these second-order sequences, the sequence Ⅰ and Ⅱ are of lacustrine facies, and can be divided into 3 depositional system tracts, including lowstand system tract (LST), lake expanding system tract (EST) and highstand system tract (HST). While the sequence Ⅲ and Ⅳ are of fluvial facies and can be divided into a base level ascending and a base level descending system tracts. Based on sequence division and stratigraphic correlation, sedimentary features of lacustrine facies sequence and fluvial facies sequence are analyzed, and a sequence stratigraphic model is built in the study area. It is believed that the HST of sequence Ⅰ, LST of sequence Ⅱ and base-level ascending system tract of sequence Ⅲ are the most favorable exploration targets in the study area. The HST of sequence Ⅰ is dominated by stratigraphic unconformity traps, the base-level ascending system tract of sequence Ⅲ is dominated by structural-lithologic traps, and the sequence Ⅳ is dominated by lithologic traps.