Palaeobiogeographically, the Permian marine faunas of East and NE Asia are assigned to four major provinces: Verkolyman, Sino-Mongolian–Japanese, Cathaysian and Panthalassan provinces, on the basis of their palaeogeographical distribution patterns and characteristics of faunal assemblages. Of these, the Sino-Mongolian–Japanese Province has considerable significance for regional palaeogeographical, plate tectonic and palaeoceanographical reconstructions during the Middle Permian, because of its conspicuously mixed cool- and warm-water marine biota. The origin of this biogeographically mixed marine biota is interpreted to have resulted from a combination of some key factors, including the increased tectonic convergence between the Bureya–Jiamusi Terrane and the Sino-Korean Platform during the Permian and the intermingling of both warm- and cold-water ocean currents off the eastern coastal areas of the Bureya–Jiamusi Terrane and the Sino-Korean Platform during the Middle Permian.