Allostratigraphy of the Cretaceous, Lower Colorado Group in SE Alberta: Tectonic and eustatic controls on depositional cyclicity
Bibliographic record
Abstract
The Lower Colorado Group is a Cretaceous, shallow marine, clastic succession, 150-200 m thick, deposited in the Western Canada Foreland Basin during the Late Albian and Early Cenomanian (c. 105-100 Ma). High-resolution allostratigraphy based on marine flooding surfaces allowed recognition of four alloformations: Basal Colorado, Joli Fou, Viking, and Westgate, in ascending order. Alloformations can be similarly divided into allomembers and sequences.\nThe Basal Colorado alloformation, comprising five allomembers, thickens southward and records active thrust loading to the south. The overlying Joli Fou and Viking alloformations are broadly sheet-like and record tectonic quiescence, and even uplift of the Cordillera, as suggested by the westward thinning of the Viking alloformation. At this time, depocentres were laterally offset from one another, and progressively shift seaward, to the NE, as a result of very limited accommodation and progressive filling of up-dip accommodation.\nA brief pulse of tectonic loading is inferred from Westgate sequence WCa that is of alluvial facies, and thickens to the SW. Sheet-like, sandy deltaic facies of Westgate sequences WCb to WCe prograde to the NE and suggest tectonic quiescence. The overlying, mudstone-dominated sequences WCf to WCj onlap westward but thicken to the SE. This reflects eustatic rise and subsidence of the intracratonic Williston Basin.\nAbrupt thickness and lateral facies changes in parts of the Joli Fou, Viking and Westgate alloformations define linear belts that suggest syn-depositional fault movement that localized the position of deltas. Faults may be related to deep-seated structures in the Precambrian basement, and may have been active at times of low in-plane stress.\nThe Basal Colorado plus Joli Fou record a long-term (> 1 Myr) tectono-eustatic sea-level rise when the basin was flooded from both north and south, whereas the Viking alloformation records eustatic fall and regression. The Westgate records a second long-term eustatic rise, with transgression from the north. Higher-frequency sea-level cycles of ?10-20 m are superimposed on these long-term cycles, with allomembers and their internal sequences apparently spanning c. 500 and c. 100 kyr, respectively, possibly reflecting long and short orbital eccentricity cycles that modulated climate, driving sea-level change through aquifer eustasy and/or glacio-eustasy.
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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 | 0.003 | 0.003 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".