The Biocommunity Evolution and Depositional Environment Transition of the Lower Ordovician Fenxiang Formation in the Western Hubei Aera
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摘要: 鄂西地区下奥陶统分乡组生物群按其生态特征划分为3个生态组合,10个化石群落或埋藏群:(1)壳相组合:Tritoechia-Pelmatozan群落?Tritoechia-Pomatotrema群落;(2)礁相组合:Archaeoscyahia群落?Ar-chaeoscyphia-Calathium群落?Batostoma-pelmatoxoan群落?Batostoma群落?Calathium-蓝绿藻群落;(3)静水相组合:Acanthograptus-Dendrograptus群落?Nanorthis-Psilocephalina埋藏群?Yichangopora?群落?它们之间随环境变化显示出由壳相组合→礁相组合→静水相组合→壳相?礁相组合的演化序列,造礁生物之间也存在着一定的演替和取代?群落演化特征反映了研究区分乡期至红花园期沉积环境演变过程是一个海水不断加深复又变浅的海侵—海退旋回,这与早奥陶世特马豆克晚期至阿伦尼格早期世界性海平面升降过程是完全一致的Abstract: The fossils in Fenxiang Formation of the Lower Ordovician could be subdivided into three ecologicassemblages and ten communities: (1), shelly facies assemblage: Tritoechia-Pelmatozoan community, Tri-toechia-Pomatotrema community;(2) Reef facies assemblage: Archaeoscyphia community, Archaeoscyphia-Calathium community, Batostoma- pelmatozoan community,Calathium-Bluegreen algae community, and(3), stll water facies assemblage: Acanthograptus- Dendrograptus community, Nanorthis-Psilocephalinacryptocoenosis, Yichangopora? community.Among these assemblages, evolutionary successions could beobserved in the transition cycle of (1) to (2) to (3)and then back to (1) and (2).Similarly, certain succes-sion events and faunal replacements took place between the reef-building communities.The communityevolution indicated that a transgression and regression cycle led to progressive increase and decrease inwater depth, and such a process might have extended over the middle Yangtze platform and be consistentto the eustatic change of sea level during the late Tremadocian to the Early Arenigian time.
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