The organic reefs and their reef-forming model for the Upper Permian Changxing Formation in northeastern Sichuan

The present paper gives a detailed description of the organic reefal outcrops represented by the (Panlongdong), Tiechanghe and Yanggudong organic reefs in northeastern Sichuan. The Panlongdong organic reefs are generally subjected to dolomitization and composed of extensive framestone, which is filled by organic (remains) and sandy fragments, with minor micritic mud, whereas the Yanggudong organic reefs are dominated by bafflestone with a small amount of bindstone, which consists of organic remains and calcitic mud, and are slightly dolomitized. The comparative study shows that the Panlongdong and Yanggudong organic reefs are not (contemporaneous); the latter is earlier than the former in age. On the whole, the organic reefs in the study area (exhibit) a trend of transition from a platform to a basin, and a ramp model of platform margin reefs-bank type.