STRATIGRAPHICAL OCCURRENCES OF ORDOVICIAN TRILOBITES IN NORTHEASTERN YUNNAN
【Abstract in Chinese】 详细讨论滇东北奥陶纪的岩石地层和动物群特征,初步建立区内的三叶虫地层序列,据此可靠确定各有关岩组的时代。该地区除普遍缺失早奥陶世早期的沉积外,依次发育了红花园组(特马豆克末期—弗洛初期),湄潭组(弗洛期—达瑞威尔初期),风洞岗组(达瑞威尔早—晚期),十字铺组(达瑞威尔末期—桑比早期)、宝塔组(桑比晚期—凯迪早期),盐津组(晚凯迪早期)、五峰组(晚凯迪晚期)及观音桥组(赫南特期),岩相与黔北的相应岩组可作大致对比,而三叶虫动物群的组成和序列则大体与当时同属扬子陆块西部边缘的沉积区包括滇东、滇东南、黔北、川中、重庆、陕南及安徽和县等地区相似。共记述本区奥陶纪三叶虫计19属27种,分属14科。并对其中的一个新种Hungioides yanjinensis sp.nov.以及两个未命名的新种Abulbaspis sp.nov.和Plaesiacomiasp.nov.作系统描述。Abulbaspis过去仅报道于华北和哈萨克斯坦地区的达瑞威尔阶,而在本地区则产于桑比阶上部—凯迪阶下部;Plaesiacomia广泛分布于达瑞威尔阶—桑比阶西泛冈瓦纳地区,在滇东北的发现不但将该属的分布区域扩大到了东泛冈瓦纳地区,而且因其产出于大坪中期的层段,表明该属可能起源于东泛冈瓦纳,尔后才向西迁移的;这两属在扬子区的首次发现,对于进一步研究奥陶纪不同区块间的三叶虫动物群的扩散和交流具有重要意义。
【Abstract】 The Ordovician lithological characters and faunal associtions of northeastern Yunnan(Textfig.1)are reviewed.On the basis of previous records and new material,the trilobite succession established herein affords reliable evidence for the age determination of each of stratigraphic units:the Hunghuayuan Formation(latest Tremadocian-earliest Floian),Meitan Formation(early Floianearliest Darriwilian), Fengdonggang Formation(early-late Darriwilian), Shihtzupu Formation(latest Darriwilian-early Sandbian),Pagoda Formation(late Sandbian-early Katian),Yantsin Formation(early late Katian), Wufeng Formation(late late Katian),and Kuanyinchiao Formation(Hirnantian)(Text-fig.2).As a whole,the aspect and development of the lithofacies exhibited in the Ordovician of the study area is closely comparable with those of northern Guizhou,while the trilobite faunas share a large number of genera and species with the Ordovician sequences of eastern Yunnan,southeastern Yunnan,northern Guizhou,cetral Sichuan,Chongqin,southern Shaanxi,and Hexian of Anhui,all of which may have formed a then petrologic province along the western marginal areas of the Yangtze Block(see also Zhou et al.,2011).Twenty seven species belonging to 19 genera and 14 families are recorded in this paper,three of which are new,e.g.Hungioides yanjinensis sp.nov.and two other unnamed forms,Abulbaspis sp.nov.and Plaesiacomia sp.nov.that are fully described below.The appearance of the species Plaesiacomia and Abulbaspis in the Yangtze Block is of great significance in revealing the faunal exchanges within the Peri-Gondwanan terranes.The genus Plaesiacomia has been widely described in the Darriwilian-Sandbian of Wales,northwestern France,central Saudi Arabia,Spain,Portugal,Florida of USA and Czech Republic(Zhou and Dean,1986,p.133),for Fortey and Cocks(2003)all of which belong to the Ordovician western Peri-Gondwana.The discovery of the genus in northeasten Yunnan is regarded as the first record in the eastern PeriGondwana,and,as the new form occurs in the middle Dapingian,it is likely that Plaesiacomia may have originated in the Yangtze Block and then migrated into and got developed in the western Peri-Gondwana.Abulbaspis sp.nov.is described herein from a bed of upper Sandbian-lower Katian.According to Zhou and Zhou(2006),the distribution of Abulbaspis was restricted to the Darriwilian of North China and Kazakhstan. For Zhou and Zhen(2008a,b)the eastern Peri-Gondwanan terranes in China and neighbouring areas may further be separated into two subprovinces during the Floian-early Katian,both exhibited significant faunal differences,of which one comprises the Yangtze and the other North China and Kazakhstan among the rest.However,Zhou and Zhen also indicated that the deep-water facies trilobites had progressively become more unified from the middle Darriwilian to early Katian.The raphiophorid genus Abulbaspis,a typical slope-facies dweller, was eventually migrated onto the Yangtze Block just before the subprovinces eventually broke down by the late Katian.
【Key words】 Ordovician trilobites； stratigraphical occurrences； northeastern Yunnan；
- 【Source】 古生物学报 ,Acta Palaeontologica Sinica , Editorial E-mail ,2014(04)
- 【CLC code】Q915