喀喇昆仑东段天神大坂-拉竹龙地区的奥陶系

本区奥陶系划分下统阿克萨依湖组,中统落石沟组(或兽形湖组),上统饮水河组。早奥陶世的腕足类、三叶虫及头足类的生物区系较复杂,与华北、藏南-滇西和扬子区关系较密切,属混生型。中晚奥陶世的头足类、三叶虫及腕足动物与藏南-滇西和扬子区接近,基本上属扬子区系。说明奥陶纪时亚洲大陆的海洋通道由早期南北向到中晚期近东西向的转变过程,即古特提斯海由早期萌发到中晚期雏形形成过程。

THE ORDOVICIAN SYSTEM IN THE TIANSHENDABAN-LAZHULONG DISTRICT OF THE EASTERN KALAKUNLUN

The Ordovician system in this area can be divided into four formations: the Akesayihu, Luoshigou(or Shouxinghu) and Yinshuihe. Early-Middle Ordovician fauna was represented by brachiopodous Aporthophyla, Syntrophina and trilobite Niobella, Il- laeaus, Isolelus and Cephalopoda Dideroceras. Both of them were characterized by the complex mixture of fauna from vari- ous regions. The phenomenon of fauna mixture indicated that the relations of Kalakunlun with the Yangtz Sea, West Yunnan, Himalayan and North China were not distinctive during the Early-Middle Ordovician, and the original Pale- otethys Ocean might be in embryo at the same time. The Middle-Upper Ordovician fauna is rich in Cephalopoda, trilobite, brachiopodous and conodonts. Most of Cephalopoda with straight shell and fine siphuncle such as Lituites, Michelioceras are also widly distributed in Southwest China. Mean while the trilobite Illaeus, Reedocolymene, Calymenesun, Eucrinuroides commonly ocurr in Yangtz, West Yunnan- South Xizang area. Although the fauna in both areas have some differences, they should belong to the same South China forms. Thus, it can be seen that the Eastern Kalakunlun Ocean more or less connected with the Yangtz and West Yunnan- South Xizang and the Paleotethys Ocean was in embryo during the Middle and Upper Ordovician.