中上扬子上奥陶统五峰组含放射虫硅质岩与古环境

Radiolarian siliceous rocks and palaeoenvironmental reconstruction for the Upper Ordovician Wufeng Formation in the middle-upper Yangtze area

关键词:  放射虫  硅质岩  五峰组  古环境  抓抓岩  雷波

Key words:  radiolarias  siliceous rock  Wufeng Formation  palaeoenvironment  Zhuazhuayan  Leibo

摘要:

四川雷波抓抓岩五峰组上部硅质岩含丰富的放射虫化石,表明晚奥陶世五峰期富硅质海水随着第二次海侵进入到扬子克拉通,进而证明了扬子西缘康滇古陆与川中古隆起间存在水道与巴颜喀拉海相通。在分析抓抓岩剖面五峰组沉积序列的基础上,通过含放射虫硅质岩的区域对比,清理了该时期各地区岩性岩相组合及地层接触关系,恢复了中上扬子地区晚奥陶世五峰期的古环境。

Abstract:

Abundant radiolarian fossils were discovered in the siliceous rocks from the Wufeng Formation in Zhuazhuayan,Leibo,Sichuan.This discovery indicates that the silica-rich sea water once entered into the Yangtze craton in response to the second phase of marine trangressions during the Wufengian of the Late Ordovician,resulting in the deposition of radiolarian siliceous sediments.It also implys that there once existed the channels connected the Bayan Har Sea with the Xikang-Yunnan old land and the central Sichuan palaeo-uplift on the western margin of the Yangtze craton.The palaeoenvironments are reconstructed in this study for the middle-upper Yangtze area during the Wufengian of the Late Ordovician on the basis of depositional sequences,regional correlation,lithologic associations and stratigraphic contacts in the Wufeng Formation in the Zhuazhuayan section,Leibo,Sichuan.