Palaeoecology and taphonomy of two brachiopod shell beds from the Anisian (Middle Triassic) of Guizhou, Southwest China: Recovery of benthic communities from the end-Permian mass extinction

Two brachiopod shell beds are documented from the Anisian Qingyan Formation at Qingyan, Guizhou province, southwest China. Taphonomic evidence indicates that the shell bed from the Yingshangpo Member of the Qingyan Formation, namely the Madoia sp. (M) assemblage, represents an autochthonous assemblage. This assemblage may have inhabited a low-energy, calm environment and the shells have been transported very little but undergone a long-term off burial after death. Another shell bed preserved in the Leidapo Member of the Qingyan Formation is termed the Rhaetina angustaeformis (R) assemblage, which represents either a parautochthonous assemblage or a residual and sorted but in situ assemblage living in a high-energy habitat. The M assemblage might be one of the recovery benthic communities following the end-Permian mass extinction because it not only has a much greater diversity, lower dominance, and higher evenness than the Early Triassic brachiopod assemblages, but it also shares similarities with the Changhsingian communities in terms of diversity indices. The Anisian brachiopod assemblage is also similar to the early Wuchiapingian recovery fauna in all diversity indices, but lacks distinctive Lazarus, surviving and generalist taxa, which are characteristic of the recovery shelly faunas following the end-Guadalupian mass extinction. This is probably responsible for the different faunal radiations after the biotic recovery following the end-Permian and end-Guadalupian mass extinctions, respectively. Brachiopod faunas rapidly diversified and proliferated in the middle-late Wuchiapingian, but patchily diversified in the Anisian in South China.