1.38 Ga Four‐Layer Tuff Marker Horizon in North China black Shales as a Chronostratigraphic Boundary for the Pre‐Ediacaran Geological Timescale
Bibliographic record
Abstract
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.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".