满洲里—新巴尔虎右旗地区满克头鄂博组形成的时限与古气候环境

大兴安岭西侧满洲里—新巴尔虎右旗地区广泛分布的满克头鄂博组缺乏古生物化石和年代学方面的系统研究,因此地层形成时代上存在争议,形成的古气候环境不明。本次在野外地质调查中,在满克头鄂博组发现了Nestoria(尼斯托叶肢介)化石和Cedripites-Piceaepollenites-Psophosphaera孢粉组合,其形成时代为晚侏罗世晚期,也指示了其形成的古气候环境为亚热带、半湿润-湿润气候。在该组中上部流纹岩中获得锆石LA-ICP-MS U-Pb年龄为156.61±0.96Ma,结合古生物化石年代学特征,确定满克头鄂博组形成于晚侏罗世中晚期;同时,满克头鄂博组中流纹岩的锆石U-Pb年龄(156.61±0.96Ma)指示以Nestoria为代表的叶肢介化石带时限为启莫里阶。

Forming age and paleoclimate of Manketouebo Formation in Manzhouli- Xinbarhuyouqi area

The Manketouebo formation widely distributing in Manzhouli- Xinbaerhuyouqi area in the west of Daxinganling mountains is lack of system paleontology and chronology research, which lead to a controversy of its forming age and uncertain climate in its forming age.Through field geological investigation, Nestoria fossil and Cedripites- Piceaepollenites- Psophosphaera fossil assemblage is found in the Manketouebo formantion. and they lived in the late stage of the late Jurassic epoch. They also reflect it was a subtropical and semi- humid to humid climate in their living age. The zircon U- Pb age of the rhyolite in the upper part of Manketouebo formation is 156.61±0.96Ma, Combined with paleontology chronology result, It is determined that the Manketouebo formation was formed in the middle and late stage of the late Jurassic epoch. On the other hand, The zircon U- Pb age of the rhyolite(156.61±0.96Ma) also indicates that the time limit of the fossil zone, represented by Nestoria, is the Kimmeridgian.