PALEOECOLOGY OF CODIALES FOSSILS IN LATE PERMIAN LIMESTONE FROM CILI, HUNAN PROVINCE

A total of three genera and seven species are identified from the Upper Permian Changhsingian of the Xiamidong section in Cili, Hunan Province, which include Anchicodium, Gymnocodium, Permocalculus of Codiaceae. This shows an obvious upward change from a Codiales flora to a Dasycladales flora. The fossils previously assigned to the family Gymnocodiaceae are recommended to be assigned to the family Codiaceae based on morphological structure and mineral fabric. Here, for the first time, the matrix micrite content of the rocks is used to determine paleo-water depth. It is found that the Codiales occurred in deeper water environment; and Codiales fossils mainly occur in wackestones and packstones with high matrix micrite content, while Dasycladales fossils mainly in the sparite grainstones in the interval with low matrix micrite content, indicating that Codiales live in a low-energy environment and the Dasycladales in a high-energy environment. We conclude that Late Permian Codiales generally lived in deep-water, low-energy environment within the photic zone of a water depth of about 20–80 meters. The Dasycladales generally live in shallow-water, high-energy environment above the wave base and the wa-ter depth is < 20 m. It is believed that the main controlling factor for the succession of the Codiales flora to the Dasycladales flora is the water depth becoming shallow.

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