Early-Middle Palaeozoic biogeography of Asian terranes derived from Gondwana

Abstract

Abstract Contiguity of the Shan-Thai Terrane and NW Australia is suggested for Cambro-Ordovician times by the close faunal affinities seen in Late Cambrian trilobites, Ordovician molluscs, stromatoporoids, brachiopods and conodonts. Taxa such as Spanodonta and Georgina are found only on these two blocks whilst others have a Shan-Thai North China, Australian distribution. This, with a re-evaluation of early Palaeozoic palaeomagnetism, places Shan-Thai against NW Australia, N China against N Australia, S China against the western Himalayan-Iran region with Indo-China and Tarim lying between S China and Shan-Thai. A palaeomagnetically required anticlockwise rotation of this greater Gondwana from the Early Cambrian to the Middle Ordovician satisfactorily accounts for the changing biogeographic patterns, in particular the differences between North and South China during the Ordovician. Recent studies on micro vertebrates and conodonts suggest that Shan-Thai was still very close to Australia in the Middle Devonian, as seen by similar turiniform thelodont species from western Yunnan, northern Thailand, and South Australia, as well as the polygnathid P. labiosus lineage, species of which have recently been found in Thailand. Continental fish faunas were highly endemic in South China from Silurian through to Early and Middle Devonian, indicating prolonged isolation of this terrane and separation of South China from Gondwana probably in the Silurian. In the Late Devonian, shared biotic assemblages between North China and South China (endemic Zhongning/Wuting plant flora; endemic antiarch placoderm and polybranchiaspid agnathan fishes); and between these Chinese terranes and Australia (sinolepid antiarchs, earlier appearances of certain antiarchs) indicate close continental proximity of these three major regions. New palaeomagnetic data for Ningxia, together with biogeographic data suggests that this region may have constituted a separate 'Hexizoulang Terrane'.