滇东泥盆系几个含鱼层的时代和对比

从鱼化石的角度对滇东泥盆系下述含鱼地层进行了分析,并认为:1)曲靖地区下泥盆统徐家冲组与坡松冲组或四川的平驿铺组、广西的那高岭组层位相当,时代为布拉格期;其层位低于含 duyunolepids-Kueichowlepis鱼类组合的贵州乌当组或舒家坪组,后者时代为埃姆斯期。2)滇东中泥盆统含两个不同时期的含鱼层,其中含Yinosteus-Wudinolepis鱼类组合的武定地区旧城组属中泥盆统早期,该鱼类组合现仅知分布于武定地区。而中泥盆统晚期含鱼地层,在曲靖地区由下而上包括穿洞组、上双河组和海口组三个岩石组;其中穿洞组＋上双河组与武定的鱼子甸组对比,而海口组与曲靖组为同时异相;武定茶花箐组与曲靖组对比。3)文中时上述地层中的某些鱼化石的层位或鉴定作了评述或厘定。

THE AGE AND CORRELATION OF SOME DEVONIAN FISH-BEARING BEDS OF EAST YUNNAN, CHINA

1 The age and correlation of Xujiachong FormationIn Qujing region the Lower Devonian rocks are commonly divided into four members: Xishancun Formation, Xitun Formation, Gujiatun Formation and Xujiachong Formation, and the last formation was traditionally considered to conformably underlie the Middle Devonian strata. However, the author put forward a proposal in 1985 that Xujiachong Formation could be as early as Pragian and a depositional break could exist between this formation and the Middle Devonian sequence. Since then the proposal has been strengthened due to the increase of the discovery of the fish fossils. Up to now, the fishes found from this formation include huananaspid galeaspids Sanchaspis magolarostrata and Gantarostraspis geni; eugaleaspid galeaspids Eugaleaspis xujiachongensis and Ptergonaspis yuhaii; arthrodire Szelepis sp. ; petalichthyid Neopetalichthys sp. and antiarchs Yunnanolepis chii and Chuchinolepis gracilis . Among the forms listed above the most significant in biostratigraphic correlation are the huananaspids and Neopetalichthys, for the others, except Pterogonaspis found only from Xujiachong Formation, either as species or as genera also occur in the lower strata, such as Xitun Formation or Xishancun Formation. As to Neopetalichthys , as it was originally found from Pingyipu Formation of Sichuan, it should be taken as an evidence of the correlation of Xujiachong Formation to Pingyipu Formation.As for huananaspids, Huananaspiformes is an endemic order of Galeaspida in South China, which in this paper there are 11 genera to be referred to ( table 1 ) . With the exception of Wumengshanaspis from the early Middle Devonian, all the genera occur in the Lower Devonian, known from Xujiachong Formation and Posongchong Formation of Yunnan Province, from Pingyipu Formation of Sichuan Province and from Nagaoling Formation of Guangxi Province. In the current literatures the last three formations are considered to correlate with each other and are dated as Siegenian or Pragian. Now that Xujiachong Formation shares Gantarostraspis and Neopetalichthys with Posongchong and Pingyipu formations respectively, it should correlate to these two formations and Nagaoling Formation in addition. Thus, on the basis of the available information it can be considered that the huananaspids appeared and greatly developed during Pragian time. 2 The correlation and age of the Middle Devonian Bothriolepis- bearing bedsThe Middle Devonian so-called Bothriolepis- bearing beds widely spread in East Yunnan and were traditionally named as Haikou Formation ( s. 1.) . In fact the Haikou Formation (s. s.) in Kunming region, including the type locality Haikou nearby Kunming City, is usually about 10 meters in thickness, consisting of sandstone and shale. It rests upon pre-Devonian rocks and conformably underlies Zaige Formation yielding early Late Devonian corals Disphyllum cylindricum and Hunanophrentis aff. H. zaphrentoides in its lower part. But in other regions Haikou Formation (s. l.) is much thicker, generally over 100 meters, sometimes even more than 500 meters. It usually rests upon the Devonian rocks of various times and may conformably underlie Zaige Formation but mostly underlies the Middle Devonian Stringocephalus- bearing beds, such as Qujing Formation or the beds corresponding to Qujing Formation. Consequently the age and correlation of the Middle Devonian Bothriolepis- bearing beds in East Yunnan have been debated for a long time.In this paper the attention is mainly paid to the Bothriolepis- bearing beds of Qujing and Wuding regions because of their abundance of fish fossils and well-developed stratigraphicsequences.As to Qujing region, the Bothriolepis-bearing beds disconformably overlay the Lower Devonian Xujiachong Formation and underlie the Upper Devonian Zaige Formation. They are currently subdivided into three members ascendingly: Chuandong Formation, Shangshuanghe Formation and Haikou Formation (table 2) , or Shangshuanghe Formation is merged into Haikou Formation because of the similarity of the florae in these t