LATE JURASSIC REEFS IN DONGQIAO AREA OF ANDO, XIZANG (TIBET)
Xiao Chuantao Li Yibin Hu Mingyi Gong Wenping Xiao Ancheng Lin Kexiang Zhang Cunshan (Jianghan Institute of Petroleum, Jingzhou, Hubei 434102)
Late Jurassic reefs are firstly discovered in Dongqiao area of Tibet, the reef building organisms are mainly composed of hexacorals and stromatoporoids which comprise dendritic, cylindric and massive forms. They were mostly preserved in place. Five types of microfacies can be distinguished according to the study on petrology of reefs, i.e. cylindric dendritic stromatoporoids bafflestone, dendritic stromatoporoids bafflestone, cylindric stromatoporoids bafflestone, cylindric massive stromatoporoids baffle framestone and cylindric stromatoporoids hexacorals baffle framestone. They formed five types of buildup, namely, cylindric dendritic stromatoporoids baffling buildup, dendritic stromatoporoids baffling buildup, cylindric stromatoporoids baffling buildup, cylindric massive stromatoporoids baffle frame buildup and cylindric stromatoporoids hexacorals baffle frame buildup. They all went through three stages:colonization, development and declination, which reflects the control of sedimentary environment and water energy on reef development.