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.