The project is supported by the National Natural Science Foundation of China (No. 40972019), the S&T plan projects of Hubei Provincial Education Department (No. 03Z0105), the Project of Scientific and Technologic Development Planning of Jingzhou (No. 20101P031-5) and the Innovative Experimenting Plan of Undergraduate Students of China (No. 091048934). The authors are grateful to Yi Xiaowei, Lu Jun, Gan Yuqing and Ding Jing for their help.
XIAO Chuantao
1 Key Laboration of Exploration Technologies for Oil and Gas Resources (Yangtze University), Ministry of Education, Jingzhou, Hubei 434023, China; 2 Gas Geology Department of Langfang Branch Research Institute of Petroleum Exploration and Development, CNPC Langfang, Hebei 065007, ChinaLI Meng
1 Key Laboration of Exploration Technologies for Oil and Gas Resources (Yangtze University), Ministry of Education, Jingzhou, Hubei 434023, China; 2 Gas Geology Department of Langfang Branch Research Institute of Petroleum Exploration and Development, CNPC Langfang, Hebei 065007, ChinaYANG Wei
1 Key Laboration of Exploration Technologies for Oil and Gas Resources (Yangtze University), Ministry of Education, Jingzhou, Hubei 434023, China; 2 Gas Geology Department of Langfang Branch Research Institute of Petroleum Exploration and Development, CNPC Langfang, Hebei 065007, ChinaHU Mingyi
1 Key Laboration of Exploration Technologies for Oil and Gas Resources (Yangtze University), Ministry of Education, Jingzhou, Hubei 434023, China; 2 Gas Geology Department of Langfang Branch Research Institute of Petroleum Exploration and Development, CNPC Langfang, Hebei 065007, ChinaLI Chao
1 Key Laboration of Exploration Technologies for Oil and Gas Resources (Yangtze University), Ministry of Education, Jingzhou, Hubei 434023, China; 2 Gas Geology Department of Langfang Branch Research Institute of Petroleum Exploration and Development, CNPC Langfang, Hebei 065007, ChinaThe project is supported by the National Natural Science Foundation of China (No. 40972019), the S&T plan projects of Hubei Provincial Education Department (No. 03Z0105), the Project of Scientific and Technologic Development Planning of Jingzhou (No. 20101P031-5) and the Innovative Experimenting Plan of Undergraduate Students of China (No. 091048934). The authors are grateful to Yi Xiaowei, Lu Jun, Gan Yuqing and Ding Jing for their help.
The Early Ordovician System 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 0.5 m to 11.5 m and lengths varying from 1 m to 130 m. The reef-building organisms include Archaeoscyphia, Recepthaculitids, Batostoma, Cyanobacteria and Pulchrilamina. Through the research of characteristics of the reef-bearing strata of the Early Ordovician in the Yichang area, four sorts of biofacies are recognized, which are (1) shelly biofacies: containing Tritoechia-Pelmatozans community and Tritoechia-Pomatotrema community; (2) reef biofacies: including the Batostoma, Calathium-Archaeoscyphia, Pelmatozoa-Batostoma, Archeoscyphia and Calathium-Cyanobacteria communities; (3) standing-water biofacies: including the Acanthograptus-Dendrogptus and Yichangopora communities; and (4) allochthonous biofacies: containing Nanorthis-Psilocephlina taphocoense community. The analysis of sea-level changes indicates that there are four cycles of sea-level changes 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 growth of accommodation space. The authors hold that reefs were mostly formed in the high sea level periods. Because of the development of several subordinate cycles during the sea-level rising, the reefs are characterized by great quantity, wide distribution, thin thickness and small scale, which are similar to that of Juassic reefs in northern Tibet. The research on the evolution of communities shows that succession and replacement are the main forms. The former is favorable to the development of reefs and the latter indicates the disappearance of reefs.
The Early Ordovician System 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 0.5 m to 11.5 m and lengths varying from 1 m to 130 m. The reef-building organisms include Archaeoscyphia, Recepthaculitids, Batostoma, Cyanobacteria and Pulchrilamina. Through the research of characteristics of the reef-bearing strata of the Early Ordovician in the Yichang area, four sorts of biofacies are recognized, which are (1) shelly biofacies: containing Tritoechia-Pelmatozans community and Tritoechia-Pomatotrema community; (2) reef biofacies: including the Batostoma, Calathium-Archaeoscyphia, Pelmatozoa-Batostoma, Archeoscyphia and Calathium-Cyanobacteria communities; (3) standing-water biofacies: including the Acanthograptus-Dendrogptus and Yichangopora communities; and (4) allochthonous biofacies: containing Nanorthis-Psilocephlina taphocoense community. The analysis of sea-level changes indicates that there are four cycles of sea-level changes 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 growth of accommodation space. The authors hold that reefs were mostly formed in the high sea level periods. Because of the development of several subordinate cycles during the sea-level rising, the reefs are characterized by great quantity, wide distribution, thin thickness and small scale, which are similar to that of Juassic reefs in northern Tibet. The research on the evolution of communities shows that succession and replacement are the main forms. The former is favorable to the development of reefs and the latter indicates the disappearance of reefs.
XIAO Chuantao, LI Meng, YANG Wei, HU Mingyi, LI Chao.2011. Paleoecology of Early Ordovician Reefs in the Yichang Area, Hubei: a Correlation of Organic Reefs Between Early Ordovician and Jurassic[J]. ACTA GEOLOGICA SINICA(English edition),85(5):1003~1015
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