SHRIMP U-Pb zircon age of Late Mesozoic tuff(lava) in Luanping basin, northern Hebei, and its implications

The recently discovered bedded tuff and tuffaceous sandstone within the Dabeigou Formation in Luanping basin of northern Hebei were dated by SHRIMP zircon U-Pb technique at 133.9±2.5 Ma and 130.1± 2.5 Ma respectively. The SHRIMP zircon U-Pb age of 135.4±1.6 Ma for the top tufflava of the Zhangjiagou Formation at eastern Jingshang Village was also obtained. A comprehensive study indicates that a complete Jehol biota-bearing succession is deposited in Luanping basin of northern Hebei, and that 135 Ma is the lowest chronohorizon from which Jehol biota appeared. The authors hold that the boundary between Dabeigou Formation and Dadianzi Formation is 130 Ma in age, the data is helpful to the study of the boundary between Jurassic and Cretaceous.