Abstract:  Sensitive High Resolution Ion Microprobe (SHRIMP) U-Pb dating was carried out using zircons from tuffs in the Ermaying and Tongchuan formations of Shanxi, China. The results show weighted mean ages of 245.9±3.2 Ma for a sample from Member II of the Ermaying Formation, 243.1±3.9 Ma for a sample from Member I of the Tongchuan Formation, and 238.6±2.6 Ma and 234.6±6.5 Ma for two samples from the upper part of Member II of the Tongchuan Formation. These ages indicate that the lower part of the Ermaying Formation, which contains the Shaanbeikannemeyeriaassemblage, is mostly likely Lower Triassic in age, whereas, the Tongchuan Formation is likely late Anisian to Ladinian, Middle Triassic.