The Proterozoic Qinggouzi microfossil assemblage and its biostratigraphic constraints on the Great Unconformity in northeastern North China Craton

The Great Unconformity at the Precambrian-Cambrian boundary has been recognized on several continents and may provide critical insights into the environmental context of the Cambrian explosion. However, the geodynamic drivers, geochronological duration, and paleogeographic extent of the Great Unconformity remain unconstrained in many cases. Recently, a major depositional gap of varying magnitudes has been reported around the Precambrian-Cambrian boundary in several regions of North China, leading to the interpretation that the Great Unconformity may have been widespread but diachronous across the North China Craton. However, the magnitude of the Great Unconformity remains unknown in northeastern North China, largely because of the poor age constraints on the thick Proterozoic–Cambrian successions in this region. Here we use biostratigraphic data to constrain the depositional age of Proterozoic strata below the Great Unconformity in northeastern North China. We report a diverse organic-walled microfossil assemblage from the Qinggouzi Formation in southern Jilin Province, northeastern margin of the North China Craton. Typical late Mesoproterozoic to early Neoproterozoic microfossils, including Trachyhystrichosphaera aimika and Proterocladus antiquus, are present in Qinggouzi assemblage, providing a solid biostratigraphic constraint on the Qinggouzi Formation. Given that the overlying Shuidong Formation contains typical early Cambrian small shelly fossils, our new data indicate that the Great Unconformity in northeastern North China represents a major depositional gap of >200 Myr. Thus, the new data, along with other available biostratigraphic and geochronological data from over the world, provide robust constraints on the paleogeographic extent, chronostratigraphic duration, and diachronous nature of the Great Unconformity.