Abstract:

Early Ordovician organic reefs in Songzi were firstly discovered by the authors.The reefs can be divided into algal buildup reef,stromatolite beded reef and lime-mud buildup reef,of which the algal buildup reef is best represented and composed of a series of mound,bread-like,beded-like reef bodies.Individual reef bodies are 1.5-22m high,6-50m wide,and the ratio of high/wide is 1:3.6-1:4.5.The main reef-building or-ganisms in situ are blue-green algae,recept aculitid algae,sponges and a few bryozoans.The accessory organisms are cephalopods (Hopecicoceras,Cameroceras),brachiopods,trilo-bites,echinoderms,bivalves,ostracods,etc.A complite reef body consists of reef base,reef core,reef cap,and interreef sedi-ments.The reef core can be divided into three microfacies from bottom to top:1.bind-stone,2.baffle-bindstone,3.bind-bafflestone.Correspondingly,the development of the reef bodies can be divided into three periods:foundation stage,development stage and decline stage.