Pyroclastic density currents (PDCs) are among the most dangerous volcanic phenomenaand can be important mechanisms of sediment supply in volcanic- affected basins, and for this are extensively studied to address the associated issues in hazard assessment and in hydrocarbon exploration. Several ancient volcanic edifices of the lower Cretaceous are well preserved in the Yingcheng Coal Mine area of Jiutai, Jilin Province, and contain deposits of PDCs. Based on detailed description of the lithology textures and sedimentary structures of the pyroclastic rocks, this paper systematically analyzes the sedimentation process of PDCs from the perspectives of material source, transport mechanism and emplacement pattern, by taking the clasts microscopic characters and grain size distribution into account. The sedimentary mechanisms of PDCs with different particle concentrations are discussed in the light of new theoretical progress in volcanology and sedimentology. The pyroclastic rocks in the study area can be categorized into five microfacies: (1) massive welded lapilli tuffs; (2) disorganized blockbearing lapilli tuffs; (3) inversely graded or doubly graded lapilli tuffs; (4) normally graded lapilli tuffs; and (5) rhythmically bedded tuffs. The type (1) with highgrade welding fabrics were formed by column collapse and emplaced at relatively high temperatures. The latter four types with normal pyroclastic structures were formed by lateral blasts and emplaced at moderate temperatures. The PDCs that deposited massive welded lapilli tuffs are inferred to have similar rheological characteristics to cohesive debris flows and come to rest en mass. The PDCs that formed disorganized blockbearing lapilli tuffs and reverse grading or double grading lapilli tuffs had rheological similarities to noncohesive grain flows and also came to an abrupt halt. The PDCs with normal grading lapilli tuffs and rhythmic bedding tuffs were analogous to turbulent flows in which sediments were deposited by progressive aggradation. Although PDCs encompass a continuous spectrum of particle concentration, there is a possibility of abrupt jumps in current behavior. The flow boundary zone approach is reasonable for explaining the depositional mechanism of dilute PDCs; however, the laminar flow model (debris flow or grain flow) is more suitable for very concentrated PDCs.