【作者】 张可；

【导师】 冯庆来；

【作者基本信息】 中国地质大学 ， 地质学， 2018， 硕士

【摘要】 奥陶纪海侵广泛,海生动物空前发育,晚奥陶世凯迪期-赫兰特期是奥陶纪海洋生物多样性急剧增长的重要时期,保存有丰富的化石记录,其中,宏体生物如三叶虫、笔石动物、腕足动物、棘皮动物等引起学者的广泛关注,然而同时期微体动物(如有孔虫、放射虫、介形虫等)的生物面貌研究则相对较少。本文在前人研究基础上,对晚奥陶世微体化石进行系统古生物学研究,旨在补充该时期微体古生物资料,并从微体化石角度探讨研究区沉积环境。本人对湖北秭归西陵峡剖面上奥陶统宝塔组、临湘组瘤状灰岩和五峰组硅质岩中的微体化石进行了详细研究,发现丰富的微体化石生物群,其中,牙形石共鉴定14属20种(含6个未定种),介形虫共鉴定14属26种(含16个未定种)。另外,产自宝塔组、五峰组的单房室胶结壳有孔虫和球形放射虫系华南首次报道,包括有孔虫Lagenammina sp.1、Lagenammina sp.2、Amphitremoida sp.、放射虫Armstrongisphaera sp.。宝塔组和临湘组的牙形石动物群属于Hamarodus–Dapsilodus-Scabbardella(HDS)相,代表深凉水型牙形石动物群;介形虫动物群以Planoria,Fenxiangia,Schmidtella和Aparchites为优势属,可与苏格兰西南部Craighead Limestone组和加拿大上奥陶统Esbataottine组开阔台地相或较深水相报道的介形虫动物群进行对比,有孔虫和放射虫丰度和分异度均较低,壳体为中薄壳,壳体形态保存较为完整,反映较低能的水动力环境。五峰组放射虫具高丰度低分异度,壳体中等偏大,呈球形,通常报道于深水相沉积环境中。研究区微体动物群总体属于较深水相的偏凉水动物群。本人在西陵峡剖面发现的微体化石构成研究区的深水相生物组合,补充了研究区晚奥陶世微体生物资料。研究区晚奥陶世放射虫和有孔虫系华南区首次报道,为后续探讨原生生物早期骨骼演化提供生物资料。根据微体化石生物群特征,再综合学者对上奥陶统岩性特征研究资料,认为宝塔组至临湘组属于较深水、低能的陆棚相沉积环境,五峰组属于深水相沉积环境。更多还原

【Abstract】 Extensive transgression events occurred during the Ordovician and the sea-level rise in the Late Ordovician was quite high.Marine creatures were developed and evolved rapidly during this period,especially Arthropods,Echinodermats,Mollusks,Vertebrates,etc.However,microfossils such as foraminifers,radiolarians and ostracods were rarely reported.Thus we collected loads of microfossils to do systematic palaeontology research in order to enrich the diversity of microbiota from the Upper Ordovician and discuss the contemporary sedimentary environment in the study area.The Upper Ordovician strata,including the Pagoda Formation,the Linhsiang Formation and the Wufeng Formation,from the Xilingxia Section in Zigui,Hubei Province yieded various and aboundant microfossils.After detailed identification,conodonts of 14 genus and 20 species(6 undetermind species),ostracods of 14 genus and 26 species(16 undetermined species)were recognized.Moreover,agglutinated foraminifers and spherical radiolarians were first reported from the Pagoda Formation and the Wufeng Formation in South China,namely Lagenammina sp.1,Lagenammina sp.2,Amphitremoida sp.,Armstrongisphaera sp.The conodont assemblage from the Pagoda Formation and the Linhsiang Formation was characterized by the HDS biofacies,which belong to relatively deep and cold water assemblage.The ostracod assemblage,dominated by Planoria,Fenxiangia,Schmidtella and Aparchites,could be compared with that from the Upper Ordovician Craighead Limestone Formation in southwest Scotland and the Esbataottine Formation in Canada,which indicate deeper marine environment.Spherical radiolarians from the Wufeng Formation,with low aboundance and diversity,were relatively well preserved and usually reported from the deeper water envieonment.Accordingly,the microfossils from the study area belong to deeper and colder water assemblage.The microfossils found in the Xilingxia Section constitute a deep-water biofacies of the Late Ordovician in the study area.In addition,foraminifers and radiolarians,first reported in South China,provide more paleontological data for the discussions of the early evolution of protist skeletons.According to the characteristic of microfossil assemblage as well as lithology,the Pagoda Formation and the Linhsiang Formation were considered as low energy and relatively deep shelf marine environment,the Wufeng Formation were thought as deep water environment.更多还原