内蒙古中部中—晚志留世西别河组的划分和时代

Division and age of the Mid-Upper SilurianXibiehe Formation in central Inner Mongolia

华北板块北缘早古生代造山带的稳定盖层——西别河组是顶底清晰,下界不整合覆于早—中奥陶世岛弧建造之上,其上被下泥盆统查干哈布组、上石炭统阿木山组不整合覆盖的一套稳定的滨浅海相沉积建造。本次工作根据岩石地层特征划分了砂砾岩段、灰岩段、砂板岩段和巴特敖包礁4个填图单元;在生物地层工作的基础上分别划分了2个珊瑚、腕足化石组合带,确立了该组为中—晚志留世地层,即Wenlockian-Pridolian期的沉积。

The Xibiehe Formation is a stable littoral-neritic sequence in an Early Paleozoic orogenic belt on the northern margin of the North China plate. With a clear-cut top and base, it is unconformably underlain by an Early-Mid Ordovician island-arc sedimentary sequence and is in turn overlain unconformably by the Lower Devonian Qaganhebu Formation and Upper Carboniferous Amushan Formation. According to the lithostratigraphic features, four mapping units may be distinguished; they are the Sandstone-Conglomerate Member,Limestone Member,Sandstone-Slate Member and Bate Obo Reef. On the basis of the biostratigraphic study,two coral and brachiopod assemblage-zones are established. Thus this formation is determined to be Mid- Late Silurian strata, i.e. Wenlockian- Pridolian sediments.