Devonian–Carboniferous extension and Eurekan inversion along an inherited WNW–ESE-striking fault system in Billefjorden, Svalbard
Bibliographic record
Abstract
Background: The Billefjorden area in central Spitsbergen hosts thick Lower–lowermost Upper Devonian, late–post-Caledonian collapse deposits presumably deformed during the Late Devonian Svalbardian Orogeny. These rocks are juxtaposed against Proterozoic basement rocks along the Billefjorden Fault Zone and are overlain by uppermost Devonian–early Permian deposits of the Billefjorden Trough, a N–S-trending Carboniferous rift basin bounded by the Billefjorden Fault Zone. Methods: We interpreted seismic reflection (also depth-converted), bathymetric, and exploration well data. Results: The data show abundant Early Devonian, WNW–ESE-striking (oblique-slip) normal faults segmenting the Billefjorden Trough, and a gradual decrease in tectonic activity from the Early Devonian (collapse phase) to early Permian (post-rift phase). Early Devonian–Middle Pennsylvanian WNW–ESE-striking faults were mildly reactivated and overprinted and accommodated strain partitioning and decoupling in the early Cenozoic. This resulted in intense deformation of Lower Devonian sedimentary rocks and in the formation of bedding-parallel décollements, e.g., between the Lower Devonian Wood Bay and the uppermost Pennsylvanian–lowermost Permian Wordiekammen formations. This suggests that intense deformation within Devonian rocks in Dickson Land can be explained by Eurekan deformation alone. Eurekan deformation also resulted in the formation of WNW–ESE- and N–S- to NNE–SSW-trending, kilometer-wide, open folds such as the Petuniabukta Syncline, and in inversion and/or overprinting of Early Devonian to Early Pennsylvanian normal faults by sinistral-reverse Eurekan thrusts. WNW–ESE-striking faults merge at depth with similarly trending and dipping ductile shear zone fabrics in Proterozoic basement rocks, which likely formed during the Timanian Orogeny. Conclusions: A NNE-dipping shear zone, which is part of a large system of Timanian thrusts in the Barents Sea, controlled the formation of WNW–ESE-striking Devonian–Mississippian normal faults and syn-tectonic sedimentary rocks in Billefjorden. Eurekan strain partitioning and decoupling suggest that the Svalbardian Orogeny did not occur in Svalbard.
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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 | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".