BIOSTRATIGRAPHIC CONSTRAINT ON TONIAN SUCCESSIONS IN EASTERN NORTH CHINA BLOCK

Neoproterozoic is a critical era for the early evolution of life and its environment on the Earth. Neoproterozoic successions are widely distributed on the eastern margin of North China Block, including Shandong, southern Liaoning, northern Anhui, and northern Jiangsu provinces (also known as the Jiao-Liao-Xu-Huai region). These successions are important for their abundant geobiological records and their key role in filling out a complete Neoproterozoic of China. However, the exact depositional ages of these successions have long been debated and were variously interpreted as Tonian (~1000–720 Ma), Cryogenian (~720–635 Ma), Ediacaran (~635–541 Ma), and even Cambrian. This is largely because the paleontological record of these strata is poorly documented and diagnostic Neoproterozoic fossils are rare. Recently, the biostratigraphy of Tonian has seen significant progress with several taxa proposed as diagnostically Tonian fossils, including the acanthomorphic acritarch Trachyhystrichosphaera aimika, Vase-Shaped Microfossils (VSM), and carbonaceous compression macrofossils of the Chuaria-Tawuia-Pararenicola-Protoarenicola association. Therefore, it is important to critically reassess the paleontological record of the Neoproterozoic successions in Jiao-Liao-Xu-Huai region. Our investigation, using low manipulation maceration technique and combined optical and electron microscopy, has revealed important Tonian fossils from these successions, including T. aimika from the Tumen Group and VSM from the Penglai Group in Shandong Province. Integrated with previously reported Tonian assemblages from the Huainan and Feishui groups in northern Anhui Province, the Huaibei Group in northern Jiangsu and northern Anhui provinces, and the Jinxian Group in southern Liaoning Province, our data suggest that the Neoproterozoic successions in the Jiao-Liao-Xu-Huai region are mainly Tonian deposits. This is consistent with the available geochronological and chemostratigraphic data from these successions, which are overlain by Cambrian strata, with a >200 myr break in between.