四川长宁下、中奥陶统的三叶虫序列  

EARLY-MIDDLE ORDOVICIAN STRATIGRAPHY AND TRILOBITE SUCCESSION IN CHANGNING,SOUTHERN SICHUAN,SOUTHWEST CHINA

作　　者：魏鑫[1,2] 袁文伟[1] 

机构地区：[1]现代古生物学和地层学国家重点实验室,中国科学院南京地质古生物研究所,南京210008 [2]中国科学院大学,北京100049

出　　处：《古生物学报》2015年第4期453-464,共12页Acta Palaeontologica Sinica

基　　金：国家自然科学基金委员会基金项目(41221001,41290260);现代古生物学和地层学国家重点实验室;IGCP 591项目(早-中古生代重大变革)的阶段成果

摘　　要：四川长宁位于奥陶纪华南陆块西部,临近奥陶纪康滇古陆,早及中奥陶世充足的陆源供应和局部快速沉降,在该区沉积了一套浅海相的陆源碎屑岩。长宁双河剖面早奥陶世晚期及中奥陶世地层共发现有三叶虫6科8属18种,根据共生笔石,初步建立区内大官山组(弗洛期—达瑞威尔最早期)和大沙坝组(达瑞威尔期)的三叶虫序列。除Asaphidae科的Liomegalaspides的分布几乎贯通两组的始终(filiformis-murchisoni带)外,Nileidae科的Psilocephalina和Psilocephalops分布局限于approximatus-eobifidus带;Taihungshaniidae科的Taihungshania高度分异,共有4种之多,分布于approximatus-hirundo带;Calymenidae科的Neseuretus也有4种之多,分布于hirundo-clavus带和intersitus带;Trinucleidae科的Hanchungolithus sp.分布于clavus-austrodentatus带;Leiostegiidae科的Pseudocalymene包括2种,分布于intersitus-murchisoni带,Annamitella sp.分布于murchisoni带。基于Zhou等(2011)对大官山组的三叶虫相所做研究,根据各层段三叶虫的组成、优势分子和分异度,认为approximatus-filiformis带的三叶虫属于Psilocephalina相(白云质泥岩),eobifidus-suecicus带三叶虫属于Taihungshania相(页岩、粉砂质页岩),hirundo带三叶虫属于Neseuretus相(粉砂质页岩),clavus-austrodentatus带三叶虫属于Liomegalaspides相(钙质页岩),大沙坝组(intersitus-murchisoni带)主体层段的三叶虫仍以Liomegalaspides占优,三叶虫相类型应与下伏地层(clavus-austrodentatus带)相同。长宁地区弗洛期—达瑞威尔期的岩相和生物相指示了向上逐渐加深的浅水内陆棚环境,但是即使在大坪期和达瑞威尔期的较大海侵期,水深仍应在70m以内。长宁双河的三叶虫多样性在hirundo带达到一个峰值,以Neseuretus(Calymenidae)和Hanchungolithus(Trinucleidae)为代表的Whiterock动物群在剖面中首次出现。In Changning area （ Fig. 1 ）, paleogeographically in the western marginal area of the South China Block close to the Kangdian Land, the lower-middle Ordovician is complete consisting of a set of thick shallow water clastic deposits such as sandstones, siltstones and shales. Trilobites from the Daguanshan and Dashaba formations of Shuanghe, southern Changning, southern Sichuan comprise 18 species of 8 genera and 6 families. The associated fossils include graptolites, brachiopods, bivalves, gastropods, etc. Biostratigraphic analysis of graptolites and the trilobite succession （Figs. 2-3 ） confirm the age of each lithostratigraphic unit： the Daguanshan Formation from Floian to the earliest Darriwilian and the Dashaba Formation mainly Darriwilian. Except for the Asaphidae Liomegalaspides （including 3 species）, which ranges almost throughout the two formations （ filiformis-murchisoni zones ）, the Nileidae Psilocephalops and Psilocephalops are restricted in the approximatus-eobifidus zones,the Taihungshaniidae Taihungshania （including 4 species ） in the approximatus-hirundo zones, the Calymenidae Neseuretus （ 4 species ） in the hirundo-clavus and intersitus zones, the Trinucleidae Hanchungolithus in the clavus-austrodentatus zones, and the Leiostegiidae Pseudocalymene in the intersitus-murchisoni zones and the Annarnitella in the murchisoni zones. According to the composition, diversity and predominant constituents of different horizons, four trilobite biofacies were recognized from the Daguanshan Formation by Zhou et al. （2011） ascendingly the Psilocephalina Biofacies （dolomitic mudstone） （approximatus-filiformis zones）, the Taihungshania Biofacies （shale and silty shale ） （ eobifidus-suecicus zones ）, the Neseuretus Biofacies （silty shales） （hirundo zones） and the Liomegalasides Biofacies （ calcareous shale ） （ clavus-austrodentatus zones ）. The Dashaba Formation consists mainly of calcareous shale yielding trilobites mainly Liomegalasides. Therefore, the

关 键 词：三叶虫序列 地层 早、中奥陶世 四川长宁 

分 类 号：Q915[天文地球—古生物学与地层学]