Transtensional deformation of the western Moncton Sub-basin, southern New Brunswick
Bibliographic record
Abstract
The Maritimes Basin of Atlantic Canada contains deformed late Paleozoic sedimentary rocks. Major dextral strike-slip deformation produced complex structural geometries and stratigraphic relationships. Large strike-slip faults separate smaller sub-basins from basement uplifts; these sub-basins display similar stratigraphy and deformation histories. The Moncton Sub-basin in southern New Brunswick contains the unconformity-bounded, Late Devonian to Early Mississippian Horton Group. The Albert Formation within this group is host to the productive onshore McCully gas field, roughly 2.5 km below the surface. This member is up to 800 m thick and comprises interbedded sandstone, siltstone, and mudstone rocks. Wellbore and 2- and 3-dimensional seismic data from the McCully gas field was combined with outcrop data to investigate the 3D geometry of the Horton Group in the western Moncton Sub-basin. Kinematic parameters were calculated using the geometrical observations of faults and folds that deform the Frederick Brook and Hiram Brook members. At McCully, the subsurface data display large curved ESE-WNW-striking extensional faults within the upper Horton Group, with less common contractional faults and folds. Vertical seismic sections perpendicular to the normal faults show horizontal extension in the range of 12 to 16%, contrasted with vertical seismic sections parallel to the extensional faults that show smaller amounts of horizontal shortening. Analogous outcrop-scale structures are observed within the Albert Formation, 13 km from the seismic data location, along the general strike of the structural pattern. 3-dimensional outcrop mapping reveals a complex relationship of these structures. Relative orientations between extensional and contractional structures, as well as the orientations of the structures relative to the Kennebecasis Fault, indicates that major dextral strike-slip deformation has produced significant clockwise rotation of structures (upwards of 60° for extensional faults). Subsurface measurements, combined with outcrop observations, of the bulk strain suggest that the basin deformed in a transtensional setting with a large angle of divergence (59°) early in its history; however, variations in the apparent stretch and orientation of the faults across the shear zone indicate that the basin deformed heterogeneously in space and time, in addition to asynchronous development of structural features. Towards the SE, the apparent stretch decreases and the orientation of the faults relative to the shear zone boundary increases, resulting in a gradual decrease in α across the shear zone. It is possible to explain the SW-directed concave curvature of the extensional faults by using these variations in the kinematic parameters.
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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 | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| 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".