湘西-鄂西中-晚奥陶世头足类动物群

Middle-Late Ordovician cephalopod faunas from western Hunan and Hubei provinces,South China

湘西–鄂西地区具有中–晚奥陶世连续过渡、出露良好的地层序列,并产出大量头足类化石。我们选择了位于该地区的湖北宜昌陈家河剖面和湖南桃源茅草铺剖面开展头足类研究工作,采集化石标本1000余块,鉴定出了24属46种。本文描述了其中6个新种,归属于3目3科5属。在中–晚奥陶世头足类动物群研究基础上,本文在湖北宜昌陈家河剖面宝塔组和临湘组自下而上识别出Sinoceras chinense带和Richardsonoceras simplex带两个头足类化石带;在湖南桃源茅草铺剖面牯牛潭组、大田坝组和宝塔组下部识别出4个头足类化石带,自下而上分别是Proterovaginoceras incognitum带、Ancistroceras undulatum带、Cyclolituites带以及Sinoceras chinense带。在此基础上,结合前人已发表的数据,本文厘定了中扬子地区牯牛潭组到宝塔组的5个头足类化石带,自下而上分别是:Proterovaginoceras incognitum带、Meitanoceras–Ancistroceras带、Lituites–Cyclolituites带、Sinoceras chinense带和Richardsonoceras simplex带,为该地区生物地层划分对比提供了头足类信息。

In the middle Yangtze region,continuous and well-exposed Middle to Upper Ordovician strata yield abundant cephalopod fossils.This paper describes the systematic palaeontology and biostratigraphy of cephalopods of the Middle–Late Ordovician age based on specimens from the Kuniutan,Datianba/Miaopo,Pagoda and Linhsiang formations at the Chenjiahe section in Yichang,Hubei Province,and the Maocaopu section in Taoyuan,Hunan Province.From a collection of more than 1000 specimens,46 species in 24 genera have been identified.Among them,six new species belonging to five genera have been systematically described here,and their biostratigraphy has been discussed and redefined.In light of the Middle–Late Ordovician cephalopod faunas,two cephalopod biozones,in ascending order,the Sinoceras chinense and the Richardsonoceras simplex biozones,have been recognized in the Pagoda and Linhsiang formations at the Chenjiahe section.Four biozones,including the Proterovaginoceras incognitum,the Ancistroceras undulatum,the Cyclolituites and the Sinoceras chinense biozones,have been defined in the Kuniutan,Datianba and the lower part of the Pagoda formations at the Maocaopu section.Based on the new results and redefinition of the previously established biozones,a total of five cephalopod biozones in the Dawan(middle part),Kuniutan,Datianba(or Miaopo),Pagoda and Linhsiang formations in South China are proposed.These are,in ascending order,the Proterovaginoceras incognitum,the Meitanoceras–Ancistroceras,the Lituites-Cyclolituites,the Sinoceras chinense,and the Richardsonoceras simplex biozones.