adiaxial fibrous cement(RFC)developed in reefal framestone of Late Permian isolated carbonate platform in northeastern Sichuan Basin．Although the RFC has completely dolomitized，it still presents the typical characteristics of curved twin planes，undulose extinction and distal convergence，and also has the geochemical characteristics of high strontium and high natrium content and dark cathodoluminescence，showing marine fluid environment，as well as laminated cement an d internal deposition in cement．High magnesian calcite deposited in marine environment is the primary mineral of RFC，indicating that spongy reefs of Perm ian Changxing Form ation in northeastern Sichuan Basin developed in a steep platform margin，an d contacted with seawater for tens of millions of years．The internal deposition in RFC indicates that the process of cementation lasted very long and breaked in a short period．This depositional break is relevant to sea level drop in a short period，but as to the RFC development process，the sea level is rising，and the rate of organic reefs iS in accordan t with the rising amplitude of sea level．