Organic Bioherms and Their Forming Models of Changxing Formation in ManyueGanquan Section of Kaixian, Northeast Sichuan

Key words: 
• bioherm /
• biohermforming model /
• Changxing Formation /
• Northeast Sichuan

Abstract: Two phases of bioherms are respectively developed in the middleupper of two descending cycles in the forepart of Changxing Formation in ManyueGanquan section of Kaixian, northeastern Sichuan. By the outcrop surveying, observation by microscope and diffraction of Xray, the composition of bioherms is researched in detail. It is found that the first phase of bioherm in which the biohermbuilding organisms are dominated by cyanobacteria and the lithology includes micrites and dolomitised limestone is composed of biohermbottom and biohermcore. The second phase of bioherm in which the biohermbuilding organisms are dominated by algae primarily and types of sponges and corals later and the lithology includes micrites with partly dolomitation is composed of biohermbottom, biohermcore and biohermtop and turns to reef finally. Based on that, the biohermforming models of two bioherms are discussed: the former which develops on the platform margin shoalslope is low energy bioherm and has two phases of evolvement, while the latter which develops on the platformmargin shoal and reef is high energy bioherm and has four phases of evolvement.