Refined U-Pb zircon age of the Kusandong Tuff: A key stratigraphic marker for Cretaceous arc magmatism in northeast Asia
Bibliographic record
Abstract
The Kusandong Tuff is a prominent stratigraphic unit within the Gyeongsang Basin, the largest Cretaceous sedimentary basin on the Korean Peninsula in East Asia. Extending approximately 200 km in a north–south direction, it serves as a key marker bed within the basin. Located in the upper part of the Hayang Group, the Kusandong Tuff records the onset of subduction-related arc magmatism that followed extension-related volcanism in the Gyeongsang Basin. Overlying the Hayang Group with Kusandong Tuff, the Yucheon Group in the eastern basin reflects the development of the Gyeongsang Arc System through subduction. The Kusandong Tuff thus represents an initial phase of subduction-related volcanism prior to Yucheon deposition. Despite its significance, establishing the precise eruption age of the tuff has been challenging, with previous zircon U-Pb dating studies reporting ages ranging from approximately 97 Ma to 103–104 Ma. These discrepancies have hindered consistent stratigraphic correlations and geological interpretations. In this study, we analyzed five samples from different outcrops using three zircon U-Pb dating methods to refine the eruption age. The results confirmed that the tuff erupted during the late Albian of the Early Cretaceous, approximately 103 Ma. These findings provide a refined temporal framework for understanding the tectonic evolution, stratigraphy, and volcanic activity of the Cretaceous in northeast Asia, and enhance the stratigraphic correlation within the Gyeongsang Basin.
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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) | 0.000 | 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".