Abstract: Exemplified by the Aba Basin, the emphasis is placed on the evolution and environmental changes of the Cenozoic basins in northwestern Sichuan and southeastern Qinghai on the eastern margin of the Qinghai-Xizang Plateau. A number of biologic assemblages are established. The Quaternary glacial deposits are treated in detail, and the climato-stratigraphic units are tentatively constructed. The allopatric coral fossils are collected in the olistostromes of the Upper Triassic Zhuwo Formation in Mandi, Zamtang, and two biozones of Triassic bivalves are established. The sequences, rhythmic section structures and sedimentary structures are examined for three lithostratigraphic units such as the Zhuwo, Xinduqiao and Runian Formations. The Rb-Sr isochron ages are determined for the Ruomoke volcanic rocks (214±1 Ma) and Xiaoshitoushan granites (244±1 Ma).