Upper Triassic reef coral fauna in the Renacuo area, northern Tibet, and its implications for palaeobiogeography

Abstract

Upper Triassic reef corals from the Riganpeicuo Formation in northern Tibet represent important scleractinian coral fauna that help explain the palaeobiogeography of the eastern Tethys region during the Late Triassic period. The corals were discovered in bedded limestone in patch reefs or biostromes of the Renacuo area. In this paper, 15 genera and 25 species are identified and categorized, the systematic composition of these corals and their relationships with other Triassic coral faunas are also discussed. The results show that these corals are composed of the typical elements of the western Tethys, with the following genera and species that are endemic to China: Radiophyllia cf. astylatus, Margarosmilia zogangensis and Conophyllopsis qamdoensis, and the genera Retiophyllia, Margarosmilia, Hydrasmilia, Procyclolites, Pamiroseris, Araiophyllum, Stylophyllopsis, Stylophyllum and Guembelastraea provide important links to the Tethys province. The coral fauna also highlights the connection between the Qiangtang terrane and the Songpan-Ganzi fold belt, but shows that the areas are distinct from the Himalayan terrane. It has been interpreted that the Qiangtang terrane and the Songpan-Ganzi fold belt were in the vicinity of the gradually-closed Paleo-Tethys Ocean, which resulted in the free transmigration of the benthonic organisms of these areas. On the other hand, the Himalayan terrane was separated from the Qiangtang terrane by a wide ocean–meso Tethys during the Late Triassic period, which made it impossible for the benthonic organisms on both flanks to freely migrate toward the opposite continental margins.