Achieving a thorough understanding of how primary sedimentary granularity drives considerable het-erogeneity in internal reservoir attributes of terrigenous fine-grained deposits is of great significance.We investigated the quantitative differentiation and its corresponding driving forces of physical reservoir properties and pore-structure characteristics of silty-mud sediments in the Upper Triassic Xujiahe For-mation (SW China) using a multi-method approach.The results show that the micro-mesopore volume and surface area of mudstones/shales are apparently higher than those of silty mudstones and a remarkable threefold rise in average permeability also presents.Extensively distributed bitumen pores occurring mostly along brittle mineral grains or forming clay-organic complexes make considerable contributions to shrinking microcracks.Furthermore,an evidently higher concentration of clay minerals in mudstone/shale reservoirs is primarily responsible for development of the two types of clay inter-crystalline pores distributed along grain aggregates and between well-oriented platelets.These two major causes facilitate the formation of micro-bedding fractures/non-bedding microfractures and con-nected fracture and pore-fracture networks,and also high-quality argillaceous reservoirs by strongly enhancing storage spaces and seepage capacities.Finally,a conceptual model is established for inter-preting a differential reservoir-forming mechanism and corresponding two-sided effects on petrophys-ical and reservoir quality properties for continental silty-mud sediments.