Abstract: Taizhou Formation of Upper Cretaceous (K2t) in Hai'an Sag of Subei Basin is a set of clastic rocks developed in the early stage of sag formation, which vertically forms a normal sedimentary cycle from lower to upper. Comprehensive analysis of the mud log, log, and core data of more than 30 wells shows that types of depositional systems in the area mainly belong to braided delta depositional system in the early to middle period of the first member of Taizhou Formation, while normal delta depositional system in the late period of the member. It can be divided into five types of sedimentary subfacies and 11 types of sedimentary microfacies. The normal delta sedimentary system in the area typically belongs to retrogradation depositional system with clear multicyclicities with frequent movement up and down of the lake level. Comprehensive analysis of the distribution and evolution of depositional systems of the Formation shows that Liangduo-Anfeng-Haizhong region where sand bodies developed is favorable for forming petroleum reservoirs.

Key words: sedimentary facies, evolution, Taizhou Formation, Hai'an Sag, Subei Basin