DISTRIBUTION AND CHARACTERISTICS OF MIXED (TRANSITIONAL) MID-PERMIAN (LATE ARTINSKIAN-UFIMIAN) MARINE FAUNAS IN ASIA AND THEIR PALEOGEOGRAPHIC IMPLICATIONS

The Permian marine biogeography of the Asian region is characterised b y the development of three broad realms (Boreal, Tethyan and Gondwanan ). In the early Early Permian (Asselian to Early Artinskian), there se ems to have existed sharp biogeographical boundaries with no transitio nal zones between the realms, presumably due to the effect of Gondwana n glaciation and sharp climatic zonation. The mid-Permian (Late Artins kian to Ufimian) of the Asian region is distinguished by the rise of t wo broad transitional zones in which mixed marine faunas flourished. T he northern transitional zone (north and northeast China, Sikhote Alin , central and northeast Japan) is characterised by an admixture of bot h warm-water Cathaysian and cold temperate Boreal genera. The southern transitional zone (Arabian Peninsula, Iran, Afghanistan, the Karakoru m, southeast and central Pamir, Salt Range, central and northwest Tibe t, Shan-Thai terrane, Timer, and western Irian Jaya), on the other han d, is distinguished by incorporating faunal elements of both Gondwanan and Cathaysian origin. The mixed faunas of both transitional zones sh are several antitropically distributed genera (e.g., Monodiexodina, Ly tvolasma and Spiriferella) and are succeeded by palaeotropical Tethyan faunas of Late Permian age. It has been postulated that the mixed mid -Permian fauna of the northern transitional zone was probably formed i n an epicontinental sea which was connected to both the Asian Tethys a nd the Arctic, which facilitated the migration of Cathaysian and Borea l forms into the epicontinental sea and subsequent faunal mixing. The formation of the mixed faunas of the southern transitional zone, on th e other hand, is probably related to the breaking off of the Cimmerian blocks from northern Gondwana and subsequent drifting into a lower la titudinal zone with geographical proximity to both Gondwana and Cathay sia during the mid-Permian.