甘肃平凉上奥陶统牙形石和笔石生物地层  

Upper Ordovician conodont and graptolite biostratigraphy of Pingliang,Gansu Province,China

作　　者：樊茹[1,2] 马雪莹 吕丹 卢远征[1,2] 张学磊[1] 张元动[3] 邓胜徽[1,2] 谭聪 宋昊南 张凤廉 李鑫[1,2] 张师本[1] 段文哲[5] FAN Ru;MA Xueying;Lü Dan;LU Yuanzheng;ZHANG Xuelei;ZHANG Yuandong;DENG Shenghui;TAN Cong;SONG Haonan;ZHANG Fenglian;LI Xin;ZHANG Shiben;DUAN Wenzhe(Research Institute of Petroleum Exploration&Development,PetroChina,Beijing,100083;State Key Laboratory for Enhanced Oil Recovery of China,Beijing,100083;Nanjing Institute of Geology and Palaeontology,Chinese Academy of Sciences,Nanjing,210008;Harbin Center for Integrated Natural Resources Survey,Harbin,150086;School of Earth Sciences and Resources,China University of Geosciences,Beijing,100083)

机构地区：[1]中国石油勘探开发研究院,北京100083 [2]中国石油天然气集团公司油气储层重点实验室,北京100083 [3]中国科学院南京地质古生物研究所,南京210008 [4]中国地调局哈尔滨自然资源综合调查中心,哈尔滨150086 [5]中国地质大学,北京100083

出　　处：《地质学报》2020年第11期3213-3227,共15页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号41702031);国家十三五油气重大专项(编号2017ZX05001001-003)资助的成果。

摘　　要：在经典的平凉官庄剖面附近的一个采石场内,出露一套新鲜的奥陶纪地层。为了确定其精确层位,在灰岩和页岩层段分别密集地采集了牙形石和笔石样品并获得丰富的化石标本。鉴定结果显示,牙形石动物群存在不同生物地理区化石属种混生的现象,其中北美中大陆型的以Belodina compressa(Branson et Mehl,1933)、Erismodus typus Branson et Mehl,1933和Plectodina aculeatus(Stauffer,1930)等属种为代表,北大西洋型的以Pygodus anserinus Lamont et Lindstr9m,1957、Periodon aculeatus Hadding,1913和Protopanderodus varicostatus(Sweet et Bergstrom,1962)等属种为代表。Belodina compressa系北美中大陆生物地理区重要的且常见的带化石,在本次获得的所有牙形石属种中其指示的层位最高。据此,判定研究剖面的牙形石动物群属于Belodina compressa牙形石带。本次研究的笔石动物群以带化石Climacograptus bicornis(Hall,1847)的出现为主要特征,与之伴生的其它重要的属种包括Nemagraptus gracilis(Hall,1847)、Normalograptus brevis(Elles et Wood,1906)、Dicranograptus brevicaulis Elles et Wood,1904以及Archiclimacograptus meridionalis(Ruedemann,1947)等,共计14属20种。显然,该动物群对应Climacograptus bicornis笔石带。Belodina compressa牙形石带和Climacograptus bicornis笔石带同为晚奥陶世桑比期全球广布性的重要的化石带。这表明两类生物地层研究结果高度吻合、统一,研究剖面的地层时代为晚奥陶世桑比期晚期,对比官庄剖面(标准剖面)平凉组的顶段。不同生物地理区牙形石属种混生的现象,反映了研究区在这一地质历史时期发生过令水体加深、水温下降的古构造活动事件。The Ordovician sequence outcrops in a quarry,not far from the well-known Guanzhuang section in Pingliang,Gansu Province.A large number of specimens of conodont and graptolite are recovered from the sequence.The conodont fauna is characterized by a particular taxa mixture.The North American Midcontinent fauna including Belodina compressa(Branson et Mehl,1933),Erismodus typus Branson et Mehl,1933,Plectodina aculeatus(Stauffer,1930)et al.,co-occurs with the North Atlantic fauna such as Pygodus anserinus Lamont et Lindstr9 m,1957,Periodon aculeatus Hadding,1913,Protopanderodus varicostatus(Sweet et Bergstrom,1962).The presence of the late Sandbian index fossil,Belodina compressa indicates the sequence corresponds to the eponymous conodont biozone.The graptolite fauna recovering 20 species of 14 genera,is represented by Climacograptus bicornis(Hall,1847),Nemagraptus gracilis(Hall,1847),Normalograptus brevis(Elles et Wood,1906),Dicranograptus brevicaulis Elles and Wood,1904 and Archiclimacograptus meridionalis(Ruedemann,1947).It shows the feature of the Climacograptus bicornis biozone,which is consistent with the biostratigraphic result of the conodont.It suggests that the sequence is of the late Sandbian and correlates well with the uppermost part of the Pingliang Formation in the Guanzhuang section.The particular conodont taxa-mixture phenomenon reveals that tectonic events during this period deepen the water and make it much cooler in the study area.

关 键 词：桑比期晚期 平凉组 官庄剖面 鄂尔多斯盆地 古生物地理区 

分 类 号：Q911.2[天文地球—古生物学与地层学]