A Highly Diverse Olenekian Brachiopod Fauna from the Nanpanjiang Basin, South China, and Its Implications for the Early Triassic Biotic Recovery

SIMPLE SUMMARY: Brachiopods have been thought to be in very low diversity in the Early Triassic for a long time. There are only several Olenekian brachiopod fauna reported worldwide, all of which are in very low diversity. This paper reports the most diverse Olenekian brachiopod fauna so far, containing 14 species with nine genera. Among them, three new species are proposed, and six genera are found in the Early Triassic for the first time. This diverse fauna indicates that the diversity of Olenekian brachiopod fauna has been underestimated. Based on precise age constrained by conodont biostratigraphy and quantitative data of brachiopod, it can be inferred that brachiopod recovery in the studied section occurred in the latest Spathian rather than the Smithian when the environment started to ameliorate. Global brachiopod data also indicates that the initial recovery of brachiopods happened in the Spathian. ABSTRACT: As one of the predominant benthic organisms in the Palaeozoic, brachiopod was largely eliminated in the Permian–Triassic boundary mass extinction, and then highly diversified in the Middle Triassic. Since fossil data from the Early Triassic are rarely reported, the recovery patterns of Early Triassic brachiopods remain unclear. This study documents a well-preserved fauna that is the most diverse Olenekian brachiopod fauna so far (age constrained by conodont biostratigraphy) from the Datuguan section of ramp facies in South China. This fauna is composed of 14 species within nine genera, including six genera (Hirsutella, Sulcatinella, Paradoxothyris, Dioristella, Neoretzia and Isocrania) found in the Early Triassic for the first time and three new species, including Paradoxothyris flatus sp. nov., Hirsutella sulcata sp. nov. and Sulcatinella elongata sp. nov. The Datuguan fauna indicates that the diversity of Olenekian brachiopod fauna has been underestimated, which can be caused by a combination of reduced habitats (in geographic size and sedimentary type) compared with the end-Permian, great bed thickness making it difficult to find fossils and most species in the fauna having low abundance. Based on the faunal change in the Datuguan section and environmental changes in South China, it can be inferred that brachiopod recovery in the studied section occurred in the latest Spathian rather than the Smithian when the environment started to ameliorate. Global brachiopod data also indicates that the initial recovery of brachiopods happened in the Spathian, and many genera that widely occurred in the Middle or Late Triassic had originated in the Olenekian.