摘要
瓶筐石(Calathium)是早-中奥陶世期间常见的重要的造礁生物之一,与菌藻类、海绵以不等丰度相聚集共同组成位于浅海区的礁丘群落。早期阶段(特马道克期-弗洛期早期)以瓶筐石-海绵-菌藻类礁群落为主,其后因海绵丰度减弱而逐渐演替为瓶筐石-菌藻群落,达瑞威尔期以瓶筐石为群落主体的礁丘分布已趋于局限,中奥陶世晚期伴随着珊瑚-层孔虫造礁群落的崛起,瓶筐石礁丘骤然衰减。瓶筐石在礁丘建造过程中主要是障积生屑,因而有利于形成海底正向地貌隆起,所形成点礁的生长阶段和群落的更替过程易于识别。一般分为定殖期生屑滩型的礁基,至拓殖期和泛殖期的礁核部位则多为瓶筐石和/或海绵构成的障积岩和菌藻类形成的粘结岩,与礁间相和/或礁翼相界线多显现清晰边界。经过一定距离搬运的瓶筐石也可与其他生屑颗粒共同堆积成展布宽泛的生物滩。
The receptaculitid genus Calathium is an extinct genus of sessile organisms of uncertain systematic position but which has most often been attributed to sponge or calcareous Green algae,having a somewhat similar appearance to dasyclads-which still survive at the present day.Calathium ranges in stratigraphic age from Ordovician to Silurian and is particularly notable because it played a major role in reef building during the Early and Middle Ordovician.The base of the Early Ordovician saw the initiation of a major new phase in composition of reefs within shallow marine carbonate settings-in which the mud mounds previously dominantly constructed by microbes became joined in varying proportions by Calathium and by a limited diversity of metazoans,mainly sponges-particularly siliceous lithistid sponges.The ＇microbes＋Calathium＋sponges＇ assemblage was particularly common in shallow marine carbonate environments of the Tremadocian to Floian（Early Ordovician）.However in the succeeding Dalpingian Stage（early Middle Ordovician） the sponge component declined in relative abundance so that reef mounds then became dominated by ＇microbes＋Calathium＇ only.In the Darriwilian Stage（late Middle Ordovician）,this kind of reef was very limited in temporal and spatial distribution,and only occurred in the Tarim Block.Finally,reefs with Calathium-dominated eventually vanished in the Late Ordovician,at the same time as the innovation occurred of significantly more diverse metazoan reef communities including corals and stromatoporoid sponges-leading to still more developed and complex reef systems.The habit,or ＇framework profile＇,of Calathium was favourable for entrapment of bioclastic and clastic debris,which enhanced the positive profile of reef mounds.Generally speaking,Calathium reef mounds formed patch reefs.The reef base was formed at the stabilization stage,followed by the reef core at the early stages of colonization and diversification-represented mainly by Calathium and/or sponge bafflestones and microbial bindstones.Profiles of reef core facies,inter reef facies and/or reef flank facies are clearly differentiated.Allochthonous fragments of Calathium also sometimes formed organic shoals over a wider area.
出处
《古生物学报》
CAS
CSCD
北大核心
2011年第1期132-140,共9页
Acta Palaeontologica Sinica
基金
国家自然科学基金(Nos.40872078
41072002)
中国科学院南海海洋研究所知识创新工程领域前沿项目(LYQY200806)
中国科学院知识创新工程方向性项目(Nos.KZCX2-YW-Q05-01
KZCX2-YW-122)联合资助
关键词
瓶筐石
礁丘
演化
古生态学
奥陶纪
Calathium
reef mounds
evolution
palaeoecology
Ordovician
