The origin of the Middle Permian Chihsia Formation from South China remains a puzzle for long, with its evident oxygen-deficient features associated with diverse benthos.

• 华南地区中二叠世栖霞组有机质丰富，出现多方面缺氧沉积特征，同时多门类底栖生物繁盛，其成因一直令人困惑。