Abstract: Diamictite has gradually become an important type of oil and gas reservoir through exploration and development practice. But there are some basic and controversial problems during diamictite research, such as the concept of diamictite, which generally refers to the sedimentary mixing of terrigenous clasts and carbonate. In addition, can it still be defined as the diamictite after mixing pyroclastic rock or other lithologic components? A complex lithology was discovered during the process of studying Es1 member reservoir of a certain oilfield in Bohai Bay Basin, and it was consisted of terrigenous sedimentary glutenite, bioclastic dolomite of carbonate origin and sedimentary tuff of pyroclastic origin. So, it was determined as a generalized diamictite through petrological characteristics and genetic analysis, and its reservoir characteristics were studied from the aspects of reservoir physical properties and pore structure. The results show that the reservoir is characterized by low porosity and low permeability, but the diamictite reservoir heterogeneity is strong, so it could be a high-quality reservoir with locally developed desserts. The study on the definition of the diamictite name and reservoir characteristics in this paper is an effective expansion and supplement to the basic research of diamictite.