Revisiting the Liantuo Formation in Yangtze Block, South China: SIMS U-Pb zircon age constraints and regional and global significance

The age and stratigraphic correlation of the Liantuo Formation in the Yangtze Block have been controversial. Disputes diverge on whether it is correlative with the Xieshuihe Formation, the Fulu Formation, the Chang'an Formation or the Banxi Group. Some radiometric dates have been obtained from the Liantuo Formation but they suffer from inheritance. In this paper, we carried out a detailed SIMS U-Pb zircon examination of the Liantuo Formation. Radiometric dates from six tuff/tuffaceous siltstone beds within the Liantuo Formation suggest it was deposited in a time interval of ca. 780-714 Ma, indicating its correlation with the Banxi Group. New ages not only coordinated the age-paleopole contradictions in the Liantuo and Nantuo formations for exploring the evolution history of Yangtze Block during the breakup of Rodinia supercontinent, but also strengthened the viewpoint that the Sturtian glaciation occurred at ca. 715 Ma in at least three paleocontinents of Arabia-Nubia, Laurentia, and South China. Some zircon grains in samples YC20 and 13YCB develop bright domains of ca. 690-680 Ma. These domains have lower total REE, lower trace element contents, and lower Th/U ratios than cores. However, both the bright domains and cores show similar delta O-18 values lower than the normal mantle zircon values. These characteristics suggest that these domains were possibly formed by post-depositional recrystallization. (C) 2015 Elsevier B.V. All rights reserved.