湖北松滋早奥陶世生物礁

EARLY ORDOVICIAN ORGANIC REEFS IN SONGZI,HUBEI

湖北松滋早奥陶世生物礁为笔者首次发现。可分为藻岩隆礁、叠层石层礁和灰泥岩隆礁。最有代表性的藻岩隆礁由一系列丘状、面包状和似层状礁体组成。单个礁体高1.5—22m,宽6—50m,高/宽比变化于1∶3.6—1∶4.5间。原地生长的主要造礁生物为蓝绿藻、托盘藻、古钵海绵和少量苔藓虫、钙质海绵。附礁生物为头足类、腕足类、三叶虫、海百合、瓣鳃类、介形虫等。一个完整的礁体由礁基、礁核、礁盖层和礁间沉积物组成。礁核从底到顶可分出三个微相:(1)粘结岩,(2)障积-粘结岩,(3)粘结-障积岩。与此相应,礁体存在三个发展期:奠基期、发育期和衰亡期。

Early Ordovician organic reefs in Songzi were firstly discovered by the authors.Thereefs can be divided into algal buildup reef,stromatolite beded reef and lime-mud buildupreef,of which the algal buildup reef is best represented and composed of a series ofmound,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,receptaculitid 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 ofthe reef bodies can be divided into three periods:foundation stage,development stage anddecline stage.