冀北滦平盆地侏罗系——白垩系岩石地层研究新进展

Advances in the study of the Jurassic-Cretaceous lithostratigraphy in the Luanping basin,north ern Hebei

冀北滦平盆地火斗山乡张家沟大北沟组和大店子组剖面,是至今找到的出露良好、沉积连续和古生物丰富的好剖面。依据滦平盆地研究新成果及大北沟组和大店子组的区域分布特征,将原义的大北沟组划分为狭义的大北沟组和大店子组。阐明正常沉积岩层的出现并取代凝灰岩成为主要的岩层,是划分大北沟组与张家口组界线的标志;以“蜂窝梁砾岩”或与之相当的粗碎屑岩层之底界为大北沟组与大店子组的界线更为合理,并便于实际操作;大店子组的顶界,也就是西瓜园组的底界,应划在上营剖面第35层——“拉海梁砾岩”层的底面,将铃铛木沟和李营—西台子一带玄武安山岩层之上保留的残积砾岩划归西瓜园组。

The section of the Dabeigou and Dadianzi formations at Zhangjiagou,Huodoushan Township,in the Luanping basin,northern Hebei,is a well exposed section with successive deposits and rich fossils.Based on the regional distribution of the Dabeigou and Dadianzi formations and latest results obtained in the study of the Luanping basin,the original Dabeigou Formation is subdivided into the Dabeigou Forma-tion and Dadianzi Formation sensu stricto.The author suggests that the boundary of two formations is marked by the first appearance of ordinary sedimentary strata and their replacement of tuff,and that it is more reasonable and simpler to operate to take the base of “Fengwoliang conglomerate”or its coarse clastic equivalent as the boundary of the two formations.The top of the Dadianzi Formation,i.e.,the base of the Xiguayuan Formation,should be placed at bed35,i.e.,the base of the“Lahailiang conglomerate”,in the Shangying section,and the residual conglomerate above basaltic andesite in the vicinity of Lingdangmu ,Liying and Xitaizi is assigned to the Xiguayuan Formation.The redefined Dadianzi Formation in the paper also includes the Third and Fourth members of the Dadianzi Formation at the Zhangjiagou section,basaltic andesite(or called member)at Donggou,Lahailiang and Dabeigou of Dadianzi,as well as calcareous mud-stone-shale with marl intercalations overlapping on the basaltic andesite layer.