滇西保山地块中部寒武纪双地麦群的特征及其时代重新厘定

Characteristics and redefining of the Cambrian Shuangmaidi Group in the middle part of the Baoshan block of western Yunnan Province

在进行云南l∶5万板桥幅区域地质调查的过程中,对该区保山地块中前人划分的双麦地群进行了详细研究。结果发现,该区的双麦地群实为一套细碎屑板岩夹大理岩和安山质、玄武质火山岩组合,并在其中首次发现了晚寒武世崮山期Blackwelderia带的三叶虫化石分子Blackwelderia baoshanensis Luo,Blackwelderia sp.,Parashengia elongata Luo等,且具明显的底栖-浮游的混生现象,从而确定该套地层应属寒武系上统核桃坪组,而非寒武系下—中统双麦地群。该套地层岩石组合及其时代的确定,为进一步深入了解保山地块的构造属性、构造单元划分和发展演化提供了新的证据。

On the basis of the latest data obtained from 1∶50000 regional geological survey of the Banqiao Sheet,the authors redefined the Early-Middle Cambrian Shuangmaidi Group as the Late Cambrian Hetaoping Formation.The lithologic association is composed of microclastic rocks and marbles with some basalts and andesitic basalts.The authors discovered for the first time the Late Cambrian trilobites Blackwelderia baoshanensis Luo,Blackwelderia sp.,Parashengia elongata Luo,revealing the loss of Early and Middle Cambrian sediments.It is interesting that the bottom-living and planktonic trilobites lived together in mixture.This study will be of great significance in the study of tectonic property,evolution and unit subdivision in Baoshan block.