Biostratigraphic constraints on the age of Neoproterozoic glaciation in North China

Abstract

Neoproterozoic glacial deposits are important stratigraphic markers for correlation of the Neoproterozoic successions in both regional and interregional scales due to their worldwide distribution and rightfully isochronous nature. Importantly, numerous studies have suggested that Neoproterozoic glaciations are closely related to the breakup of the Rodinia supercontinent and, consequently, provide an important clue for discussing the tectonic affinity of those Precambrian continents as well. Typically, the Neoproterozoic sedimentary sequence along the southwestern margins of the North China Craton contains a unique glacial deposit, named the Luoquan Formation, but this deposit is poorly documented for its age. Shaanxilithes is an important index fossil for late Ediacaran due to its limited stratigraphic in terminal Neoproterozoic with wide distribution on a global scale. Here, we report the new occurrences of the late Ediacaran index fossil Shaanxilithes from the Dongpo Formation along the southwestern margin of North China Craton, which not only extends the palaeogeographic distribution of Shaanxilithes but also provide the convincing evidence for determining the late Ediacaran age of the Dongpo Formation. Hence the conformably underlying glacial deposits of Luoquan Formation is constrained to pre- Shaanxilites in age. On the NCC and Qaidam Block, Ediacaran Glacial deposits and related Shaanxilithes- bearing marine siliciclastics always disconformably overlie Mesoproterozoic successions and disconformably contact with the overlying Cambrian (Stage 3) phosphorict rocks. These common tectonostratigraphic characteristics and unconformities allow us to suggest that the Qaidam Block share close tectonic affinities with the NCC during the Neoproterozoic–Cambrian period. • New occurrences of Shaanxilithes expand its palaegeographic distribution and biostratigraphic utility. • The Dongpo Formation is late Ediacaran in age, and the underlying Luoquan diamictite must be older. • The Qaidam Block shared a closer tectonic affinity with the North China Craton during the Neoproterozoic-Cambrian period. 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.