Zircon U-Pb age and stratigraphic significance of the tuff from the lowermost Liantuo Formation in the Dahongshan area of the northern Yangtze Block

The Liantuo Formation, exposed on the northern Yangtze Block, is one of the important Neoproterozoic stratigraphic units in South China. However, no consensus has been reached on its depositional period, regional correlation, depositional environment and paleogeographic characteristics so far. In this study, we obtained a zircon LA-ICP-MS U-Pb age of 798.4 ± 4.5 Ma (MSWD = 0.40, n = 13) for the tuff layer from the bottom of the Liantuo Formation in the Dahongshan area. Integrating the previous reported data, the depositional period of the Liantuo Formation was constrained to ca. 800–714 Ma. Regionally, the Liantuo Formation is comparable to the middle-upper part of the Banxi Group and its equivalent strata, as well as to the Xiuning Formation, Chengjiang Formation, Kaijianqiao Formation, Wudang Group and Suixian Group. The Liantuo Formation is a set of rift filling deposition, which rests on the Jinning orogeny unconformity and underlies the Nanhua Glacial Period deposition, representing a filling sequence while the rift basin fully opening and the depositional area rapidly expansion. The depositional sequence is mainly composed of alluvial fan, fluvial and littoral-neritic facies sediments. During the Liantuo Period, the northern Yangtze Block was a rift basin, which gradually deepened to the north. Meanwhile, the Liantuo Formation in the Dahongshan area represents an alluvial fan deposition that distributed around the Northern Hubei Paleo-uplift, and evolves to the littoral-neritic-bathyal deposition that represented by the Suixian Group.