ABSTRACT: Aspects of Foreland Belt Thermal and Geological History in the Southern Canadian Cordillera from Fission-Track and Organic Maturity Data
Bibliographic record
Abstract
ABSTRACT Apatite fission-track (FT) data from the Lewis thrust sheet and environs exhibit systematic variations with elevation. Current elevation serves as a proxy for deformed structural position. Apatite FT ages decrease from ~70 Ma, at the highest elevations in the Lewis thrust sheet east of the Flathead Fault (> +2000 m), to ∼30 Ma below the Lewis Thrust (~ -1000 m). In this profile mean horizontal confined fission-track lengths (HCTL) exhibit a dog-leg, or piece-wise linear variation with elevation. Mean HCTL is >13 microns at the highest elevations and decreases to -12 microns at ~ +1400 m. At about +800 m mean HCTL is again about 13 microns, indicating the top of the second segment of the profile. At lower elevations mean HCTL decreases progressively to ∼11.5 microns at 7 km thick, deposited during the mid-Campanian to Maastrichtian, which is no longer preserved. The Lewis thrust sheet geothermal gradient at the time of peak temperature was significantly lower than that observed currently (17°C/km). In late Campanian-Maastrichtian time (~75 Ma), the Lewis thrust sheet exhibited a profound cooling and additional lowering of its geothermal gradient. This cooling indicates motion on the Lewis Thrust Fault. We infer that the peak temperature and coalification rank of rocks below the Lewis Thrust were achieved by tectonic burial below the cooling and eroding overthrusting sheet. The dog-leg in the HCTL and high vitrinite reflectance further substantiate this inference. Considering the short time interval for burial and the moderate thermal gradient indicated by the low coalification gradient, the maximum temperature below the Lewis thrust sheet inferred from both the apatite FT profile and the %Ro implies deep burial (i.e. a relatively thick overriding Lewis thrust sheet). In mid-Eocene time a second cooling affected the region east of the Flathead Fault. This indicates displacement on Flathead Fault and links thermal histories derived from apatite FT parameters with the formation of Flathead Basin and the epeirogenic uplift of the craton.
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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 | 0.004 | 0.006 |
| Science and technology studies | 0.002 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".