A New Cathaysiorthis Brachiopod Fauna from the Shiqian Bed (Uppermost Ordovician to Lowermost Silurian) in South China and Its Palaeoecological Significance

The Late Ordovician mass extinction (LOME) caused an intense global biotic turnover. In South China, the Edgewood-Cathay (EC) fauna replaced the cool-water Hirnantia fauna. The Cathaysiorthis fauna, an important representative of the EC fauna, was mainly reported from southeastern China. Based on 1224 brachiopod specimens from the “Shiqian Bed (upper Hirnantian-lower Rhuddanian)” in Meitan County, northern Guizhou, Southwest China, this study documents the first rich Cathaysiorthis fauna from this region of the South China palaeoplate. It includes 13 genera, with Eospirigerina, Hindella, and Cathaysiorthis as its dominant constituents, and represents one of the earliest known post-LOME recovery benthic communities developing during the transition from the survival to the early recovery interval. Palaeoecological analysis shows a deepening upward trend from the Eospirigerina–Hindella association (BA2) to the Eospirigerina–Cathaysiorthis association (BA3). This provides ecological evidence for a sea-level rise caused by global warming after the second pulse of the LOME. Comparison shows that the brachiopod fauna in northern Guizhou is very similar to that of eastern China and may represent an earlier recovery stage than the Cathaysiorthis fauna in Xichuan, Henan Province, Central China. This finding extends the known palaeogeographical range of the fauna and provides key information for understanding the earliest recovery and palaeoenvironmental background after the LOME. Furthermore, the contemporaneous “Wulipo Bed” and Weiba Formation are herein synonymized as junior synonyms of the Shiqian Bed.