Interference folding and orocline implications: A structural study of the Ponga Unit, Cantabrian orocline, northern Spain
Bibliographic record
Abstract
The origin of the Cantabrian orocline of the Variscan orogen in NW Iberia remains a topic of debate. We present a structural study of the Ponga Unit, a Cambrian to Carboniferous tectonostratigraphic package within the West European Variscan belt foreland fold-and-thrust belt that lies within the core region of the orocline. Our primary goal was to determine if W-plunging folds of the fold-and-thrust belt are attributable to formation of the Cantabrian orocline, or if they reflect lateral ramps in the underlying Variscan thrust faults. The major lithologic units of the Ponga Unit are the rheologically competent Lower Ordovician Barrios quartzite, and the less-competent, Carboniferous Barcaliente limestone and Beleno shale and sandstone formation. Our mapping and structural analysis within the Ponga Unit focused on the Laviana, Rioseco, and Campo de Caso thrust sheets, and associated bounding thrusts. Over 800 structural orientation measurements were collected across the study area. These data, coupled with data compiled from regional geological maps, allow for analysis of the crustal structure. West-plunging folds of the Laviana, Rioseco, and Campo de Caso thrust sheets form kilometer-scale anticline-syncline pairs, producing a complex fold interference pattern that is characteristic of the Ponga Unit. Our analysis shows that: (1) the geometry of the W-plunging folds is inconsistent with a lateral ramp model; (2) the map pattern defines a mushroom-type fold interference pattern, indicating two distinct deformational events characterized by principal compressive stresses oriented at a high angle (perpendicular) to one another; and (3) paleomagnetic data from the study area are consistent with the secondary model of orocline formation and indicate that there was a short window of time between the end of Variscan orogenesis and the onset of oroclinal buckling. Our results indicate that early N-S–trending folds, which resulted from Variscan orogenesis, were refolded during a post-Variscan orogen-parallel compression event attributable to formation of the Cantabrian orocline.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 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".