LATE PERMIAN ORGANIC REEFS FROM SOUTHERN CHINA

The Late Permian organic reefs are exposed dominantly in the Upper Yangtze area, southern China, including two parts: the eastern Sichuan—western Hubei region and the Nanpanjiang region. Reef development commences from east to west. The reef horizons are uplifted progressively while the degree of reef development decreases gradually. Five types of reefs are recognized from shoreline basinwards: patch reefs, barrier reefs, platform margin reefs, platform margin and slope knoll reefs and isolated platform margin reefs, and sedimentary facies associations are divided into four facies, eight subfacies and twenty microfacies which constitute distintct sectional structures. The sedimentary model for the organic reefs from the eastern Sichuan—western Hubei region differs from that for the Nanpanjiang region. As for the former, the organic reefs are formed within the facies change zone of the blocking-controlled platform, whereas as for the latter, the organic reefs are developed in the facies change zone between the platform and turbidite basin. The main reef-building organisms consist of sponges, hydrozoans and bryozoans. The binding organisms are dominated by the bluegreen algae. Framestones composed mainly of massive and columnar sponges are formed in the high-energy environments while the bindstones and bafflestones consisting of the fir-tree and kidney-shaped sponges are generated in the low-energy environments.