Organic reefs of the Upper Triassic are well developed in Gaize County of Tibet. The reef-building organisms consist of hexacorallia, calcispongiae and calcareous algae, whereas the reef-inserted organisms consist of foraminifera, brachiopods, bivalves, gas-tropods, echinoderms and bryozoans. Biological sequence from the bottom to the top of a single reef was developed through five stages:calcareous algae, bivalves and gastropods→calcareous algae, bivalves and hexacorallia→hexacorallia→hexacorallia, calcispongiae and bryozoans→bioclast. Correspondingly, the lithological sequence from the bottom upward can also be divided into five members:bioclastic limestone→bafflestone→frame stone→bind stone→Bioclastic and intraclastic limestones. The development of platform mar-gin reef generally includes three cycles, each of which has the same structural composition and can be divided into reef base, reef core and reef cap from the bottom upward. It is shown that the history of organic reefs has experienced four evolutionary stages, i.e., reef foundation, early flourishing, prosperousness and reef declining. Cycle ⅠandⅡare at a large scale, and have complicated construc-tion, whereas CycleⅢis small and simple comparatively. All of the three cycles have formed the secondary prograde sequence under a transgressive background.%西藏改则地区上三叠统日干配错组发育有大量生物礁，造礁生物有六射珊瑚、钙质海绵和钙藻类，附礁生物为双壳类、有孔虫、苔藓虫、棘皮动物、腹足类、腕足类等。单个礁体的生物发育顺序可分为5个阶段，自下而上依次为：钙藻类+双壳类+腹足类→钙藻类+双壳类+六射珊瑚→六射珊瑚→六射珊瑚+钙质海绵+苔藓虫→生物碎屑。与此相对，各礁体岩性演化顺序也包括5段：生物碎屑灰岩→障积岩→骨架岩→粘结岩→生物碎屑和内碎屑灰岩。台地边缘生物礁的发育经历了3个旋回，各旋回组成结构相似，礁体均由礁基、礁核和礁顶构成，生物礁经历了生物礁奠基、初期繁盛、最大繁盛和生物礁衰亡4个演化阶段。旋回Ⅰ和旋回Ⅱ规模较大，内部构成复杂，旋回Ⅲ规模较小，内部构成较简单，自下而上构成一个海侵大背景下的次级进积序列。
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