Zircon U-Pb dating on tuff bed from Gaoyuzhuang Formation in Yanqing, Beijing: Further constraints on the new subdivision of the Mesoproterozoic stratigraphy in the northern North China
北京延庆高于庄组凝灰岩的锆石U-Pb定年研究及其对华北北部中元古界划分新方案的进一步约束

A tuff bed in the upper horizon of Gaoyuzhuang Formation has been newly discovered in Yanqing County, Beijing. Two almost identical precise zircon U-Pb ages, 1559±12Ma (SHRIMP) and 1560±5Ma (LA-MC-ICPMS), have been obtained for the tuff bed, which indicates that the Gaoyuzhuang Formation in the northern North China Craton was formed in the early stage of Mesoproterozoic Calymmian Period (1600~1400Ma). Combining with the available zircon U-Pb age data (1622~1625Ma) for the volcanics from the upper part of Dahongyu Formaiton, the lower boundary age of Gaoyuzhuang Formation could be accurately positioned at 1600Ma. Moreover, with the newly determined SHRIMP U-Pb age (~1440Ma) of the K-bentonite in Tieling Formation, the authors therefore propose again that the basal boundary of Gaoyuzhuang Formation should be taken as the lower boundary of Mesoproterozoic Jixian System. The voluminous carbonate succession from Gaoyuzhuang Formation to Tieling Formation with time span of 1600Ma to 1400Ma comprises the Jixian System, almost identically comparable with the international Mesoproterozoic Calymmian System. The new achievement in dating on the tuff of the Gaoyuzhuang Formation provides strong age constraints on the Meso- to Neoproterozoic stratigraphic subdivision and other relevant important scientific issues in the northern North China Craton.