New data on the biostratigraphy of the Early Devonian "Spirifer" tonkinensis brachiopod fauna in South China and adjacent region

Conodont and brachiopod biostratigraphic studies have been conducted at the Mode and Poyuan sections, Guangxi Province, South China. Combining these with seven previously studied sections, it is suggested that the appearance of the Spirifer tonkinensis Fauna in different areas of South China and adjacent areas is diachronous, showing an evident chronological trend from south to north. This trend is consistent with the northeastward transgression during the Early Devonian in South China. The Spirifer tonkinensis fauna may originate from northern Vietnam and then spread northwards into the South China Block. The persistence of the Early Devonian transgression resulted in the disappearance of favourable biotopes of the Spirifer tonkinensis Fauna (i.e. the near-shore, shallow marine environment with muddy substratum and plentiful terrigenous input), due to either a deepening of seawater or the development of a carbonate platform. This might ultimately have triggered the extinction of the fauna.