Biostratigraphic constraints on the age of Neoproterozoic glaciation in North China
Xin Wang, Xingliang Zhang, Wei Liu
Abstract
Neoproterozoic glacial deposits commonly serve as important stratigraphic markers at interregional scales and provide significant insights into our understanding of the extreme climate during this period. More importantly, these glacial deposits are probably related to the breakup of the Rodinia supercontinent and, consequently, are tectonically significant. The Neoproterozoic sedimentary sequence along the southwestern margin of the North China Craton (NCC) typically contains a unique glacial deposit, named the Luoquan Formation, but this deposit is poorly documented for its age. Here, we report new occurrences of the late Ediacaran index fossil Shaanxilithes from the Dongpo Formation along the southwestern margin of the NCC, which not only extends the palaeogeographic distribution of Shaanxilithes but also provides convincing evidence for the late Ediacaran age of the Dongpo Formation. Hence, the conformably underlying glacial deposits of the Luoquan Formation is constrained to pre-Shaanxilithes in age. In both the NCC and Qaidam Block, the Shaanxilithes-bearing marine siliciclastic rocks consistently disconformably underlie the Cambrian (Stage 3) phosphoric deposits and conformably overlie the characteristic Neoproterozoic glacial deposits that are unconformably underlain by the Mesoproterozoic successions. From this perspective, we re-evaluate the potential tectonic affinity of these Precambrian tectonic units as mentioned above.