Spatiotemporal Correlations Between Mid-Proterozoic Lips and Black Shales: Implications for Defining the Pre-Ediacaran Geological Timescale Boundaries

While the Phanerozoic and base of the Ediacaran in the international chronostratigraphic scale are each defined by a basal rock-based Global Stratotype Section and Point (GSSP) marked by “golden spikes” corresponding to environmental catastrophes induced by global events such as large igneous provinces (LIPs), the pre-Ediacaran geological timescale is formally subdivided by approximate absolute age due to a lack of rock-based GSSPs (Gradstein et al., 2020). Although the 'Boring Billion' (1800‒800 Ma) or Earth’s middle age (1750‒750 Ma) in the mid-Proterozoic is considered a stability era in Earth history (Cawood and Hawkesworth, 2014), LIPs and large volumes of black shales are common during this period (Ernst, 2014; Ernst et al., 2021; Zhang et al., 2021). Recent research revealed synchronous deposition of voluminous black shales across different cratons in the Columbia and Rodinia supercontinents and established spatiotemporal correlations between the mid-Proterozoic LIPs and black shales, especially those of ~1640 Ma, ~1380 Ma and ~1100 Ma ages (Zhang et al., 2018, 2021, 2024). Coeval LIPs and black shales can provide natural markers for the mid-Proterozoic geological timescale boundaries, such as the Statherian/Calymmian boundary at ~1640 Ma, the Calymmian/Ectasian boundary at ~1380 Ma (Zhang et al., 2018, 2024). These boundaries are located at special horizons within black shales that can be defined as rock-based GSSPs. We recently discovered a unique 4-layer tuff marker horizon in black shales of the Xiamaling Formation in the Yanliao Basin, northern North China Craton, which can be traced over a large area >400 km long by 100 km wide (Zhang et al., 2025). High-precision zircon CA-ID-TIMS U-Pb dating shows that the sequence of volcanic eruptions occurred over a very short duration of 0.21±0.04 Myr at 1380.41±0.99 Ma (Zhang et al., 2025). The 4-layer tuff marker horizon is likely related to the widely distributed ~1380 Ma LIPs and the source for the tuff sequence inferred by climate circulation models is the Mashak LIP in Baltica (Zhang et al., 2025). We proposed that the 4-layer tuff marker horizon in black shales of the Xiamaling Formation in the North China Craton represents a potential “golden spike” for the Calymmian/Ectasian boundary at 1380.41±1.20 Ma, and provides the world’s first “golden spike” and type section for the pre-Ediacaran geological timescale (Zhang et al., 2025). This research was financially supported by the National Natural Science Foundation of China (U2244213, 41920104004, 41725011) and the Fundamental Research Fund of Chinese Academy of Geological Sciences (JKYZD202320).