Structural and Paleomagnetic Evidence for Tertiary Bending of the Eastern Brooks Range Flexure, Alaska
Bibliographic record
Abstract
Paleozoic carbonate sedimentary rocks from northeastern Alaska have been sampled for a structural and paleomagnetic study of the relationship of the Porcupine Terrane to both cratonic North America and adjacent Brooks Range terranes. Major structural features investigated includes the Yukon Porcupine megashear and the Northeast Alaskan oroclinal flexure. Structural analysis of two well-exposed Paleozoic sections along the upper Porcupine River in northeastern Alaska yields estimates of shortening directions for two distinct phases of deformation. In the Upper Ramparts region of the Porcupine Terrane, north-south shortening (D1) occurs in Silurian-Devonian units. In the equivalent units of the Lower Ramparts northwest-southeast shortening occurs. A much younger deformational event (D2), presumably associated with the Late Cretaceous Brookian Orogeny, overprints these earlier pre-Permian (D1) structural elements. In the Upper Ramparts the orientation of this event is somewhat equivocal but appears to be oriented northwest-southeast with vergence to the southeast. The Lower Rampart Permian section is clearly deformed by the D2 event in an east-west sense with vergence to the west. The general trend between the D1 and D2 deformational events differ by 45 degrees in the Upper Rampart Region. A similar variance between D1 and D2 is observed in the Lower Ramparts, but the structural orientations differ by 45 degrees between the Upper and Lower Ramparts, suggesting large scale block rotations occurred after the D2 shortening event. The characteristic remanent magnetization postdates the latest phase of deformation (D2) and therefore represents an overprint. This overprint is presumed to be early to middle Tertiary, although the mean paleomagnetic pole lies off the expected apparent polar wander path (APWP) for North America. This paleomagnetic discordance is in declination only, and the sense and magnitude of rotation is clockwise approximately 45 to 90 degrees. It is proposed that the structural-grain of the Brookian Orogeny in northeastern Alaska was aligned with the northwest Canadian Cordilleran. Subsequent bending in the Tertiary produced the eastern Brooks Range orocline.
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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".