U–Pb dating of zircons from tuff layer, sandstone and tillite samples in the uppermost Liantuo Formation and the lowermost Nantuo Formation in Three Gorges area, South China

Abstract Uranium-lead (U–Pb) dating was conducted on zircons in tuff layers and sandstone samples from the uppermost Liantuo Formation and in a tillite sample from the lowermost Nantuo Formation in Three Gorges area, South China, using SHRIMP and LA-ICP-MS techniques. Zircons from these samples yielded age spectrum (within 1000 Ma) of ∼890, ∼830, ∼780, ∼730, and 646 Ma. Zircons from the Liantuo tuffs have a weighted mean 206 Pb/ 238 U age of 734.1 ± 8.1 Ma (2σ, n  = 7, MSWD = 0.48), which was regarded as the best estimation of the upper boundary age of the Liantuo Formation. Combining with previous geochronologic data, the Liantuo Formation was proposed to be a pre-Chang′an glaciation unit, and it is comparable to the middle-upper Banxi/Danzhou Group in South China.