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

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.