晚奥陶世生物大灭绝后第一个腕足动物群:来自滇东北镇雄奥陶系顶部硅化腕足类的证据  

The first brachiopod fauna following Late Ordovician Mass Extinction:evidence from late Hirnantian brachiopods of Zhenxiong,Yunnan,SW China

作　　者：戎嘉余[1] 黄冰[1] RONG Jia-yu;HUANG Bing(State Key Laboratory of Palaeobiology and Stratigraphy,Nanjing Institute of Geology and Palaeontology,Chinese Academy of Sciences,Nanjing 210008,China)

机构地区：[1]中国科学院南京地质古生物研究所,现代古生物学与地层学国家重点实验室,南京210008

出　　处：《古生物学报》2023年第1期1-29,共29页Acta Palaeontologica Sinica

基　　金：中国科学院战略性先导科技专项(B类)(XDB26000000)资助。

摘　　要：首次记载云南镇雄奥陶系顶部尾坝层(赫南特晚期)硅化腕足类,命名其为幼始准携螺贝群落(Eospirigerina putilla Community)。将它与贵州毕节、仁怀观音桥层的德姆贝-褶窗贝群落(Dalmanella–Plectothyrella Community)[赫南特早中期赫南特贝动物群(Hirnantia Fauna)碳酸盐相浅水代表]比较表明,两者面貌差异显著。确认尾坝层腕足类化石群与中国黔北、赣东北和浙西,以及美国、加拿大、瑞典、挪威、俄罗斯、澳大利亚等地赫南特晚期至鲁丹期的化石同属于晚奥陶世大灭绝后第一个动物群,即埃吉伍德-华夏动物群(Edgewood–Cathay Fauna)。它与Hirnantia动物群在组成、多样性、优势度、生态分异、生物地理及共生生物等区别很大。大灭绝第一幕发生后,显生宙历时最短、源自高纬海域、适应冷凉水环境的“机会主义者”——赫南特贝动物群“如鱼得水”,广布全球,却在第二幕降临后,整体灭绝,成为两幕之间海洋底栖生物群演化的一个鲜明标志。此后,诞生了埃吉伍德-华夏动物群,它以世界性、延限历程长的减缩型(含复活型)属种占优势,新生属很少,体现了大灭绝后幸存动物群的基本特征。华南产该动物群的地层经常超覆在凯迪期地层之上,这是赫南特期海平面先大幅骤降、再快速上升的产物,也是浙赣边区缺失典型Hirnantia动物群的主因。上述两大动物群的更迭发生在赫南特中晚期之交,而不在奥陶-志留纪交界之时。本文还简论两幕灭绝间的动物群演变、产埃吉伍德-华夏动物群的地层对比、赫南特期全球环境变化等问题。Calcareous fossils from the upper part of the Weiba Bed(grainstone)at the Dagala section,Zhenxiong County,northeastern Yunnan(Fig.1)have been extensively silicified and are extracted through glacial acetic acid(5%–12%)dissolution,after high temperature deacidification from carbonate matrix.More than 2000 specimens are obtained.The Weiba Bed is conformably overlain by the Lungmachi Formation(Rhuddanian)and is disconformably underlain by the Daduhe Formation(upper Katian).The basal part of the Lungmachi Formation yields graptolites,suggesting the Akidograptus ascensus Biozone.Thus,the Weiba Bed is postulated as late Hirnantian in age(Wang et al.,2022).The brachiopods,making up approximately 95%of all specimens in this unit,dominate the benthic biota(Fig.2).A preliminary investigation of the silicified brachiopods is herein presented for the first time.Based on this study,more than 20 taxa are recognized,including Eospirigerina putilla(Hall and Clarke)[=E.praemarginalis(Savage)](predominant),Hesperorthis cf.orientalis Rong et al.,Dalmanella sp.(relatively common),Cathaysiorthis cf.yushanensis(Zeng and Hu),Mendacella sp.,Epitomyonia cf.subquadrata Rong et al.,Brevilamnulella cf.thebesensis(Savage),Hindella crassa(Sowerby)(rare),along with undetermined species of the genera Paracraniops,Fardenia,Triplesia,Leptaena,Eostropheodonta,Eoplectodonta,Platystrophia,Glyptorthis,Thebesia,Hallina?and Eospirifer(rare,very or extremely rare)(Figs.3 and 4),as well as a few undetermined taxa of orthide,rhynchonellide and atrypide.These taxa,representing far more genera than expected,belong to 9 orders,15 superfamilies,and 20 families,suggesting a relatively abundant and highly diverse brachiopod assemblage established in the aftermath directly following the Late Ordovician Mass Extinction(LOME).Wide-ranging groups of marine benthic organisms are associated with the brachiopods,signifying both autotropic and heterotrophic organisms,including calcareous algae,bryozoans,crinoids,gastropods,rugose corals,stromatoporoids(sponges),tabul

关 键 词：晚奥陶世大灭绝 腕足动物群大演替 埃吉伍德-华夏动物群 赫南特贝动物群 群落生态 气候剧变 

分 类 号：Q915[天文地球—古生物学与地层学]