The Reexamination of Late Mesoproterozoic-Tonian Chuaria–tawuia Assemblage and Its Biostratigraphical and Paleogeographical Significance

Chuaria and Tawuia are two types of carbonaceous compression macrofossils that were widely distributed from the Precambrian to the early Cambrian. Previous studies have proposed that their co-occurrence (Chuaria–Tawuia assemblage) may serve as a biostratigraphic marker for Late Precambrian strata on a global scale. However, their biostratigraphic significance remains controversial due to the broad temporal range of solely Chuaria and Tawuia and the lack of systematic research and supporting evidence. Here, we provide a detailed morphological definition of the Chuaria–Tawuia assemblage from the exceptionally preserved fossil layer of the Liulaobei Formation, and conduct systematic comparisons with Chuaria–Tawuia assemblages from various regions and geological intervals worldwide. The results demonstrate that the Chuaria–Tawuia assemblages from the Late Mesoproterozoic to the Tonian Period of the Neoproterozoic exhibit a specific set of morphological features that clearly distinguish them from assemblages that occur before the Late Mesoproterozoic and after the Tonian. These findings suggest that Chuaria–Tawuia assemblages exhibiting similar morphological traits to those from the Liulaobei Formation can serve as potential biostratigraphic markers for strata of Late Mesoproterozoic to Tonian age. In comparison to other contemporaneous microfossils with biostratigraphic significance, such as Cerebrosphaera and vase-shaped microfossils, the Chuaria–Tawuia assemblage spans a longer stratigraphic range. However, its geographic distribution is restricted to specific cratonic blocks, including the North China, South China, Indian, Siberian, Laurentian blocks, and East Svalbard terrane, indicating a regionally constrained pattern. This non-global distribution may reflect the presence of paleogeographic barriers in the Proterozoic oceans or suggest connectivity and isolation among different paleocontinents during that time. This study provides new evidence supporting the biostratigraphic significance of the Chuaria–Tawuia assemblage and offers important insights into the paleogeographic configuration and paleobiogeographic patterns of the Mesoproterozoic–Neoproterozoic transition.