对河南省二郎坪群层序及时代的新认识

对二郎坪群的层序划分及时代归属问题,长期以来存在较大分歧。作者根据在南召地区1:5万区域地质调查工作,重新厘定了该群的层序,由下而上划分为小寨组、火神庙组,大庙组,各组之间均为整合接触关系.同时,在火庙组新发现一批丰富的头足及腹足类等古生物化石,结合区域地质构造特征及同位素地质年龄资料,作者认为二郎坪群不可能属于三叠纪或早—中元古代,其形成时代主要应为中奥陶世时纪的沉积.

NEW RECOGNITION OF THE STRATIGRAPHIC SEQUENCE AND AGE OF THE ERLANGPING GROUP IN HENAN PROVINCE

Divergent views have long existed as to the stratigraphic division and ageof the Erlangping Group in Henan Province.On the basis of the new resultsof the 1:50000 regional surveys conducted in the Nanzhao area,the authorshave redefined the sequence of this group.From below upwards it is dividedinto the Xiaozhai and Huoshenmiao Formations which show conformable contactrelationships.The group is in fault contact with the underlying KuanpingGroup and is in turn unconformably overlain by the Triassic strata.Meanwhile,in the light of a group of cephalopod,gastrpod and brachiopod fossils collectednewly from the Damiao Formation coupled with regional structural features andisotopic ages,the authors consider that the Erlangping Group is impossible tobe of Triassic or early-middle Proterozoic age and that it was mainly formedin the Middle Ordovician.