The Indochinese Province: A Potential Bioprovince in the Permian of the Eastern Palaeotethys

The Indochina Peninsula remains ‘Terra Incognita’, an underexplored region in Asian geosciences. Once a focal point for geological and palaeontological surveys during the French colonial period, research in this area diminished during the subsequent civil wars. The Indochina block, along with its arc in the Malay Peninsula, the East Malaya block, is thought to be one of the Devonian terranes that separated from Gondwana, alongside the South China and North China blocks. The Early–Middle Permian of Indochina features the Tethyan ‘tropical trio’: Verbeekinidae/Neoshwagerinidae (large fusulinids), Waagenophyllidae (rugose corals), and Alatoconchidae (giant bivalves). The general affinity to the palaeo-equatorial Cathaysian biota is evident through the Permian gigantopterid flora and rich Permo-Carboniferous warm-water Asian faunas present. In contrast, cool-water or anti-tropical elements, such as Vjalovognathus, Monodiexodina, and Gondwanan-type brachiopods or molluscs, are absent from Indochina. Unlike South China, the late Palaeozoic positioning of Indochina is not well defined. Traditionally, Indochina has been arbitrarily positioned either as attached to or adjacent to South China, or as intermediate between South China and the Cimmerian continent in palaeogeographic reconstructions. Available palaeomagnetic data from the Permo-Carboniferous of Indochina (s.l.) suggest a positioning within a southerly low-latitudinal zone (ca. 15°S–25°S), although some data are derived from the Simao block, a northern extension of Indochina. Further investigations of pre-Jurassic magnetisation within the Indochina block (s.s.) are essential to confirm whether these findings represent the primary magnetisation of Indochina proper. Fusulinids and conodonts are prevalent in Permian carbonate deposits of Indochina. They exhibit no provincialism but are predominantly warm-water Tethyan taxa. While Permian brachiopods in Indochina and East Malaya superficially resemble those of South China, many appear to be endemic, and some demonstrate Cimmerian linkage. Other fossil groups, including smaller foraminifers and corals, also exhibit distributions shared with Cimmeria but did not extend into equatorial South China, implying possible subtropical conditions. A collection of Cambodian fossils made by the late Dr Derek Gobbett before the civil war has now aided in reconfirming long-forgotten endemic taxa. The following points can be articulated: 1) The Permian of the Indochina block and its arc terranes comprises warm-water Tethyan or Cathaysian biota while exhibiting endemism: this constitutes the Indochina bioprovince. 2) This bioprovince includes genera and species that were also distributed in Cimmeria but were absent from or rare in equatorial South China; thus, they are atypical of the Cathaysian biota and are classified as ‘extra-Cathaysian elements’. 3) The palaeobiogeographic provincialism of Indochina is most pronounced in the Kungurian–Capitanian (late Early–Middle Permian) period.