1.38 Ga Four‐Layer Tuff Marker Horizon in North China black Shales as a Chronostratigraphic Boundary for the Pre‐Ediacaran Geological Timescale

Abstract Boundaries in the Phanerozoic chronostratigraphic scale are mainly precisely defined and dated, and many correspond to environmental catastrophes induced by the emplacement of LIPs. The pre‐Ediacaran geological timescale is currently subdivided by approximate absolute ages. Here we identified a unique four‐layer tuff sequence within the Xiamaling Formation black shales, North China Craton, that can be traced over a large area ∼400 km long by ∼100 km wide, and represents a synchronous marker horizon formed by air fall tuffs from distant volcanic eruptions. High‐precision U‐Pb geochronology shows that the tuff sequence span a short duration of 0.21 Myr at 1380.41 ± 0.99 Ma. The tuff layers match the age of widely distributed ∼1,380 Ma LIPs found on multiple cratons in supercontinent Columbia/Nuna. Based on climate circulation models, the specific inferred source for the tuff sequence is the Mashak LIP in Baltica. We suggest that the four‐layer tuff marker horizon represents a unique chronostratigraphic marker for the Calymmian/Ectasian boundary at 1380.41 ± 1.20 Ma.