内蒙古宁城道虎沟地区侏罗纪地层划分及时代探讨

Stratigraphic division of the Jurassic in the Daohugou area,Ningcheng,Inner Mongolia

最近在内蒙古宁城道虎沟村新发现了一些翼龙、蝾螈等重要化石,有关道虎沟化石层的地层层序和时代归属产生了较大的争论。笔者根据野外调查结果和生物地层学资料,讨论了道虎沟化石层的地层层序和时代归属。详尽的区域地层踏勘和实测地层剖面充分显示,道虎沟化石层归属于中侏罗世九龙山组,而不是所谓的义县组;道虎沟化石层与下伏太古宙马鞍山片麻岩而不是土城子组呈角度不整合接触。

Recent discoveries of pterosaurs and other fossils at Daohugou Village near Ningcheng County,Inner Mongolia,raise the question regarding the age and stratigraphic sequence of the fossil beds.Some authors assigned the fossil beds in the Daohugou area to the Early Cretaceous Yixian Formation based on the purported occurrence of such fossils as Lycoptera,Peipiaosteus and Ephemeropsis and asserted that the fossil beds are underlain unconformably by the Jurassic"Tuchengzi"Formation;while Other authors con-sidered the fossil beds to be of Middle or Late Jurassic with uncertainty based on the simultaneous occur-rence of the long-tailed rhamphorhynchoid pterosaurs and short-tailed pterodactyloid pterosaurs with primi-tive feathers in the fossil beds.On the basis of the important results from field investigations of the bios-tratigraphy of the Daohugou area,this paper discusses the age and stratigraphic sequence of the fossil beds in the area.Detailed reconnaissance coupled with measurements of geological section reveals the undeniable evidence showing that the Daohugou fossil beds are of the Middle Jurassic Jiulongshan Formation,rather than the so-called Yixian Formation.The fossil beds are unconformably underlain by the Archaean gneiss,rather than the so-called Tuchengzi Formation.Lycoptera fossils are absent in the fossil beds of this area,and the so-called Ephemeropsis fossils are actually misidentified Mesoneta.The Daohugou beds yield no el-ements of the Johel biota,while the insect assemblage and lithostratigraphic evidence clearly indicate that the Daohugou fossil beds belong to the Middle Jurassic Jiulongshang Formation.