Abstract:

Based on field surveying on the outcrop and comprehensive laboratory study, combining with the fundamental principles and methods of sequence stratigraphy, the authors analyze the sedimentary characteristics of the Wumishan Formation occuring in the western Yanshan Mountains, which are mainly composed of tidal flat carbonate rocks and rich in stromatolite. The Qiangou section, the most complete section in study area, can be divided into 26 third-order sequences which can be combined into six second-order sequences (S.1-S.6). Every third-order sequence includes three parts, which are transgressive system tract, early highstand system tract, and late highstand system tract. By correlation of sequences in the study area, the sequence stratigraphic frameworks have been established. According to the distribution of sedimentary facies belts, the paleographic environment has been preliminarily reconstructed. During the deposition period of the Wumishan Formation, the paleographic environment of the First and Second Member was slow transgression. Up to the deposition period of the Third and Fourth Member, the paleo epicontinental sea reached maximum. After then, in the deposition period of Fifth and Sixth Member, the paleo sea regressed to the center of subsidence.