Abstract:The sequence cycle of the transgressive stage of lower to middle Wumishan Formation in the YanshanLiaoning area is characterized by symmetrical facies sequences and fabrics, but no detailed study has been paid on the sequence cycle of the regressive process of the upper Wumishan Formation. For this purpose, a systematic research about sedimentary microfacies, sedimentary facies sequences, sequences stratigraphy and chemical stratigraphy of the fourth member of the Wumishan Formation at Zhuanghuwa section, Yongding river valley, western Beijing, was carried out to restore sedimentary facies and classify parasequence type. Carbon and oxygon isotopic compositions and relevant data analyses were also performed to verify the evolution process of the ancient environment. Nine lithofacies have been identified in the Zhuanghuwa section, indicating different depths of water, topography, and biological conditions, which are also confirmed by corresponding δ13C and δ18O values. Generally, with the paleotemperature T increasing, the values of δ18O and paleosalinity Z decrease, reflecting sea level rise; conversely, reflecting sea level drop. Our research shows the sequences cycle of the regressive process is characterized by asymmetrical facies sequences and fabrics, its parasequence fabrics becomes gradually simple from supratidal zone to subtidal zone, and the minisequence of superimposed patterns evolves from 1∶4 to 1∶2. Therefore, facies sequences and fabrics of the fourth member of Wumishan Formation is distinctively different from the typical “Sequence Cycle of Wumishan Formation”, and this is probably related to the tectonic evolution from aulacogen to epeiric sea at the north margin of North China Platform in the Mesoproterozoic.