Mid-Carboniferous rugose corals from Xinjiang, Northwest China: Evolutionary and palaeogeographical implications

The mid-Carboniferous represents a key transition in the evolution of rugose corals, but the evolutionary pattern has been scarcely studied due to the lack of consecutive carbonate succession caused by Hercynian orogeny and Gondwana glaciation. In this study, seventeen rugose coral species belonging to fourteen genera are described from the late Visean to Bashkirian strata in the Suguersu section, northern Xinjiang, Northwest China. The late Visean is distinguished by large dissepimented solitary coral species, such as Haplolasma sp., Palaeosmilia murchisoni, and colonial coral Lithostrotion decipiens. Coral diversity dramatically decreased during the Serpukhovian, with only one species present. During the Bashkirian, rugose corals gradually recovered with the increased diversity and abundance, as evidenced by the occurrence of colonial coral Petalaxis kitakamiensis. This evolutionary pattern is consistent with that from South China and Russia, represented by the replacement of the Mississippian large solitary corals by the Pennsylvanian colonial corals. The Suguersu coral assemblage is composed of endemic taxa in Xinjiang and Qinghai regions of Northwest China, South China and Japan in northeastern Palaeotethys, as well as a few cosmopolitan elements across the Palaeotethys. This suggests that the Suguersu coral assemblage is biogeographically endemic, with occasional exchanges with other palaeo-oceans during the mid-Carboniferous period.