Abstract
The latest Ordovician Hirnantia Fauna is distributed worldwide including South China, but with very few records from the western margin of the Yangtze Platform. A silicified Hirnantia Fauna from the uppermost Tiezufeike Formation in the Laoga section, Butuo County, southwestern Sichuan, enriches the fauna’s record and warrants the recognition of the upper part of the Tiezufeike Formation as the Kuanyinchiao Bed. Etching bulk limestone samples from this level with acetic acid yielded 275 specimens of Dalmanella testudinaria, Plectothyrella crassicosta, and Hindella crassa. The population dynamics are analyzed for three successive populations in the section. Size-frequency histograms and survivorship curves indicate gradual improvement of the palaeoenvironments during the end of the Late Ordovician glaciation. The low-diversity brachiopod assemblages recognized in our study are assigned to the Dalmanella-Plectothyrella Community (DP Community) according to their dominant species. It is comparable with two other examples of DP communities, one from the neighboring Guizhou Province of Southwest China, and the other from the Baltica Region.
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