Multistage evolution of intracontinental basins: the case of the Lusitanian Basin
Bibliographic record
Abstract
The Newfoundland-Iberia rift, which includes the Lusitanian Basin (LB), has been considered the archetype of a magma-poor rift, but its main steps are still debated. The new data reported here indicate that the LB’s eastern border comprises two contrasting types of contact between continental sediments and Variscan basement: major angular unconformity and master bounding fault. The unconformable contact could mean a pre-rift sag basin, or a syn-rift half-graben with flexural boundary in the E. However, given that newly recognized master NW-SE to NNW-SSE bounding faults displace the red continental deposits and basal unconformity by hundreds of meters, we infer that the master bounding fault is Alpine and displaces the base of a previous sag basin. In the case of unconformable contact and sag basin, the age of the red continental deposits would be older than the currently attributed Late Triassic age, and represent the missing Late Variscan denudation molasse. It seems therefore that the LB could be a rift basin underlain by an older and smaller sag basin. Later, Pangaea rifting produced a full graben, the LB, bounded to the east by a newly mapped master fault reactivating a major Variscan shear zone in the northern half of the Lusitanian Basin. A similar development of composite basins can be found in NE Brazil, where some Mesozoic intracontinental basins also show evidence of two-stage basin formation, an early sag (Palaeozoic) and a later rift (Mesozoic).
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".