上扬子北缘寒武纪早期后生动物礁特征及古环境意义  

Sedimentary Characteristics and Paleoenvironmental Significance of Early Cambrian Metazoan Reefs in Northern Margin of Upper Yangtze Block

作　　者：李杨凡 李飞 王夏[3] 李翔 李怡霖 王曾俊[1] 李雅兰 易楚恒 曾伟 Li Yangfan;Li Fei;Wang Xia;Li Xiang;Li Yilin;Wang Zengjun;Li Yalan;Yi Chuheng;Zeng Wei(School of Geosciences and Technology,Southwest Petroleum University,Chengdu 610500,China;Natural Gas Geology Key Laboratory of Sichuan Province&National Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Southwest Petroleum University,Chengdu 610500,China;Institute of Sedimentary Geology,Chengdu University of Technology,Chengdu 610059,China;PetroChina Research Institute of Petroleum Exploration and Development-Northwest,Lanzhou 730020,China)

机构地区：[1]西南石油大学地球科学与技术学院,四川成都610500 [2]西南石油大学天然气地质四川省重点实验室和油气藏地质及开发工程全国重点实验室,四川成都610500 [3]成都理工大学沉积地质研究院,四川成都610059 [4]中国石油勘探开发研究院西北分院,甘肃兰州730020

出　　处：《地球科学》2023年第11期4321-4334,共14页Earth Science

基　　金：国家自然科学基金项目(Nos.42172136,41872119).

摘　　要：作为一种海洋高等级生态系统,生物礁在前寒武‒寒武纪过渡时期经历了重要转变,特别是后生动物礁的大规模出现对寒武纪早期生命与环境协同演化具有重要意义.以上扬子北缘多个寒武系仙女洞组含古杯生物礁剖面为例,开展了系统的沉积学特征分析.结果显示古杯动物既可以单独成礁,也可以与钙质微生物联合造礁,或者作为附礁生物保存于钙质微生物礁内部.古杯礁大部分具有低缓的外部形貌,障积结构发育且古杯化石保存较好,部分具亮晶胶结特征,以在正常浪基面附近和滩间环境发育最为典型.钙质微生物‒古杯礁与含古杯钙质微生物礁既可以单独发育,也可以在潮下带形成多个叠置状复合体;内部可见古杯被微生物黏附包绕或结壳,但礁胶结物少见.高能环境生物礁中古杯动物具有破碎状、异地搬运等特征,其原因可能与其个体较小,以及较薄的钙质骨骼还无法适应强水动力条件有关.另一方面,由于研究区滨海环境经常性陆源输入带来的较高营养条件更有利于微生物主导的生物礁发育,古杯在与其竞争过程中可能处于劣势.As a complex marine ecosystem,reefs underwent a significant change in the composition of major builders during the Precambrian-Cambrian transition.The wide distribution of reef-building metazoans was likely a response to the co-evolution of life and oceans in the Early Cambrian.In this study,it performed a systematic sedimentological analysis on the archaeocyath-bearing reefs of the Xiannüdong Formation in the northern margin of the Upper Yangtze block.Petrological evidence indicates that the archaeocyaths may have contributed to the formation of the reefs individually or in combination with calcimicrobes.In some situations,archaeocyaths acted only as inhabitants of large thrombolitic reefs.The archaeocyathdominated reefs are characterized by low-relief morphological units and partially cemented internal structures,and are thought to have formed in mid-ramp and inter-shoal environments with relatively low hydrodynamic conditions.Archaeocyathcalcimicrobial reefs and archaeocyath-bearing microbial reefs can form separately or develop as multiple stacked complexes in depositional successions thought to have formed in subtidal environments.Within the reef complexes,some archaeocyaths are coated or crusted by calcified microbes and few reefal cements are visible.The lack of archaeocyath-dominated reefs in shallow,high-energy conditions may be related to their small body size and thin skeletal structures,which cannot withstand the washing and destruction of waves and storms during this period.In addition,the relatively high nutrient levels in coastal environments,possibly caused by increased terrigenous input,may be more conducive to the development of calcimicrobedominated reef systems than archaeocyath-dominated reefs due to the greater nutrient competitiveness of the microbes.

关 键 词：古杯动物 钙质微生物 仙女洞组 寒武纪第三期 汉南‒米仓山地区 沉积学 环境地质 

分 类 号：P588[天文地球—岩石学]