冀北围场一带张家口组同位素测年研究及地层学意义

Isotopic Dating and Stratigraphic Significance of Zhangjiakou Formation in Weichang Area of Northern Hebei Province

冀北围场县山湾子一带张家口组火山—沉积地层发育,由下、中、上3套岩性组合组成。为了确定张家口组的地质时代,正确建立岩石地层单位,对3套岩性组合分别开展了同位素测年研究。测年成果确定下部、中部岩性组合形成时代为晚侏罗世,上部岩性组合形成时代为早白垩世。该成果对河北省内张家口组地层划分以及与邻省中生代火山—沉积地层划分对比具有重要的意义。

The volcanic-sedimentary strata of the Zhangjiakou Formation in the Shanwanzi area of Weichang County,northern Hebei Province are developed and consist of three sets of lower,middle and upper lithological combinations.In order to determine the age of the Zhangjiakou Formation and correctly es⁃tablish the lithostratigraphic unit,the three sets of lithological assemblages were respectively studied for isotope dating.The dating results determined that the lower and central lithological assemblages were formed in the Late Jurassic,and the upper lithological assemblages were formed in the Early Cretaceous.This result has important significance for the stratigraphic division of the Zhangjiakou Formation in Hebei Province and the comparison with the Mesozoic volcanic-sedimentary stratigraphic division of neighboring provinces.