【摘要】 宜昌地区下奥陶统主要为一套台地相碳酸盐沉积,间夹页岩,其中的特征沉积为发育有较多的生物礁。造礁生物主要有海绵类、瓶筐石类、有柄棘皮类、苔藓虫及蓝细菌和Pulchrilamina等。在下奥陶统含礁层系中识别出四种生物相:(1)壳类生物相:发育有Tritoechia-Pelmatozans群落和Tritoechia-Pomatotrema群落;(2)礁生物相:包括Batostoma群落、Calathium-Archaeoscyphia群落、Pelmatozoans-Batostoma群落、Archeoscyphia群落和Gzlathium-Cyanobacteria群落;(3)静水生物相:发育有Acanthograptus-Dendrogptus群落和Yichangoporu群落;(4)异地生物相:产有异地埋藏群,即Nanorchis-Psilocephlina埋藏群。含礁层系存在四个海平面变化旋回,生物礁的发育明显受海平面的升降速率与容纳空间增长速率的控制。生物礁多形成于高海平面时期。由于本区的海平面在上升过程中存在多个次一级旋回,致使生物礁具有数量多、分布广以及厚度薄和规模小等特点。造礁群落存在着演替和取代两种形式,前者有利于生物礁的发育,后者则表现为礁体的衰亡。更多还原

【Abstract】 The Lower Ordovician is composed mainly of a series of carbonate platform deposits interbedded with shale and is especially characterized by a large number of organic reefs or buildups that occur widely in the research area. The reefs have different thicknesses ranging from 0.5m to 11.5m and lengths varying from 1 m to 130 m, and the most important is that the reefs are characterized by a great quantity, wide distribution, thin thickness and small scale. The reef-building organisms are Archaeoscyphia, Recepthaculitids, Batostoma, Cyanobacteria, Pulchrilamina and so on. Through the study of the characteristics of the reef-bearing strata of the Lower Ordovician in the Yichang area, four sorts of Biofacies are recognized, which are (1) Shelly Biofacies: containing Tritoechia-Pelmatozans community and Tritoechia-Pamatotrema community; ( 2 ) Reef Biofacies: including Batostoma community, Calathium-Archaeoscyphia community, Pelmatozoans-Batostoma community, Archeoscyphia community and Calathium-Cyanobacteria community; ( 3 ) Standing-water Biofacies : including Acanthograptus-Dendrogptus community and Yichangopora community; and (4) Allochthonous Fades: containing Nanorthis-Psilocephlina taphocoense. The analysis of sea-level changes indicate that there are four cycles of sea-level change during the period when reef-bearing strata were formed in this area, and the development of reefs is obviously controlled by the velocity of sea-level changes and the growing velocity of accommodation space. The authors hold that reefs mostly formed in the period of high sea level. Because of the development of several subordinate cycles while the sea-level rising, the reefs are characterized by a great quantity, wide distribution, thin thickness and small scale. The research of evolution of community shows that succession and replacement are the main forms. The former is favourable to the development of reefs and the latter indicates the disappearance of reefs.更多还原