LA-ICP-MS U-Pb dating of zircons from Tuchengzi Formation in Qianjiadian of North Beijing and its significance

Tuchengzi Formation is a widely distributed continental sedimentary stratum in northern Hebei and western Liaoning provinces. Since the 1980s, the stratigraphic age of this formation has attracted much attention and aroused heated debate among researchers. Through LA-ICP-MS U-Pb dating of zircons, the authors obtained two early Late Jurassic ages of this formation in Qianjiadian area. One of them is 157.6±0.7 Ma for the lower part, and the other is 157.1±1.0 Ma for the upper part. Combined with previous data, the ages of Tuchengzi Formation should be 163-130 Ma in the Yanshan area. During this period, Tuchengzi Formation showed mobility and intermittent sedimentary characteristics. The primary sedimentary ages of Yanshan area should be 146-137 Ma, and the contact relationship between Tiaojishan, Tuchengzi and Zhangjiakou formations are not in unconformity. The authors consider that they should be products of the same ectonic setting in most cases.