255 / 2025-04-15 21:32:59

The Great Unconformity in the Eastern North China Craton

North China Craton, Great Unconformity, Getun Formation, Chuaria-Tawuia assemblage, Detrital zircon

Theme 3: Earth-Life Co-evolution Through Time > Session 3a: Precambrian Earth and Life Co-evolution

The Great Unconformity, a discontinuous sedimentary contact between the Precambrian and Cambrian sequences typified in the Grand Canyon of North America, is widely distributed across many continents. Understanding its formation requires precise delineations on the unconformity type and scale of sedimentary hiatus for each local occurrence. The eastern margin of the North China Craton (NCC) preserves thick Neoproterozoic to early Cambrian strata, providing a critical window for studying the Great Unconformity. However, the specific stratigraphic position and scale of sedimentary hiatus associated with the Great Unconformity in the Dalian area of the eastern NCC remain unclear. Furthermore, the similarities and differences in the stratigraphic position, contact type, and scale of stratigraphic gaps across regions of the eastern NCC (e.g., southern Jilin, western Shandong, Huaibei, and Huainan) require further investigation. To address these questions, this study conducted systematic biostratigraphic and detrital zircon U-Pb geochronological analyses on the Getun Formation in the Dalian area. Detrital zircon analyses of a sandstone sample from the lower part of the Getun Formation reveal the youngest U-Pb zircon age of 960.3 ± 17 Ma. In addition, mudstone from the upper part of the formation yields abundant carbonaceous compression macrofossils, including Chuaria and Tawuia. These findings indicate that the Getun Formation is likely Tonian (~1000–720 Ma) in age. Thus, the Great Unconformity in Dalian area lies between the Getun Formation and the overlying Cambrian Dalinzi Formation, representing a stratigraphic gap of 200–300 million years. Regional stratigraphic correlation across the eastern NCC further demonstrate that the Great Unconformity in these areas is characterized by parallel unconformities. The sedimentary gap of the Great Unconformity in eastern NCC is mostly of 200–300 million years except the case in the Huainan region, at which the Fengtai conglomerate underlying the early Cambrian Houjiashan Formation represents late Ediacaran tillite (570–550 Ma), indicating a much shorter gap of <50 million years in this region. Therefore, the Great Unconformity in eastern NCC differs significantly from that of the Grand Canyon in North America in terms of contact type and scale of stratigraphic gap. Even within the NCC, the heterogeneity in stratigraphic gap across regions challenges a unified explanation for the occurrence of the Great Unconformity. Future studies should focus on high-precision stratigraphic correlations across cratons and criteria for identifying isochronous surfaces to unravel the mechanisms underlying the Great Unconformity.