A review of the lithology, sedimentary structures and palaeontology, supplemented by original investigations, suggests that the Triassic system in the Canning Basin can be subdivided into four broad environmental episodes. The sequence records a slow transgression culminating in the Smithian, when the riverine plain in the southeastern Fitzroy Graben was drowned. The resulting shallow embayment in the Fitzroy Graben supported a much impoverished marine biota, made up of species tolerant of reduced saline conditions caused by substantial run-off of fresh water from surrounding streams. A regression began in the Spathian and continued throughout the later Triassic, although there were minor transgressions with marine incursions: the environment evolved into a low-relief coastal alluvial plain, with meandering streams and lakes. A general trend to increasing aridity is evident, with an increase red beds, and is correlated with the withdrawal of the Blina Sea. Finally in Ladinian time the region became an area of non-deposition and remained so until the early Jurassic.