Allostratigraphy of the Lower Colorado Group (Cretaceous) in south-west Alberta
Bibliographic record
Abstract
Clastic, upper Albian-lower Cenomanian strata were deposited in a low-accommodation backbulge depozone of the Western Canada Foreland Basin in SW Alberta. These strata are lithologically very heterogeneous and encompass a spectrum of depositional environments along an alluvial to offshore transect. These rocks are assigned, in subsurface, to the Lower Colorado Group, and in outcrop to the upper Blairmore Group. Lithological heterogeneity, as a result of rapid lateral facies changes, resulted in diverse nomenclature that obscured genetic relationships between time-equivalent strata. The present study integrates wireline log, core, and outcrop data to establish a high-resolution allostratigraphic framework which allowed recognition of the Basal Colorado, Joli Fou, Viking and Westgate alloformations, in ascending order. Each alloformation comprises several allomembers and parasequences. The Basal Colorado alloformation is a NE thinning wedge that progressively onlaps lower Albian Mannville Group strata. Deposition took place in a brackish-water embayment open to the south. Basal Colorado strata correlate with the Lynx Creek Member of the Mill Creek Formation in outcrop. The Joli Fou and Viking alloformations have a broadly sheet-like geometry. Both alloformations comprise three allomembers, composed of a complex array of river-dominated and mixed-influence deltaic successions. The location of successive deltas was strongly influenced by differential compaction of underlying deltas. Sandstone-rich Joli Fou rocks pass northward into offshore mudstone. To the south and west, marine Joli Fou and Viking deposits grade laterally into alluvial facies. Only the upper part of the Westgate alloformation extends into SW Alberta. Tectonic tilting is indicated by the lowermost (alluvial) and uppermost (marine) Westgate parasequences, which are SW and NE thickening wedges, respectively. Paleo-valleys, typically ~20 m deep, are incised into the top surface of most allomembers. Different examples of valley incision and fill can be attributed to both sea-level changes, and also to climatically-controlled changes in the sediment load to discharge ratio. Two pulses of thrust-induced loading and a long term (>1 myr) eustatic cycle provided the overall control on stratal architecture, whereas climate-controlled cycles in the ~400 and 100 kyr band exerted an important control on the development of allomembers and parasequences. Eustatic changes are estimated to have been ~20 – 30 m.
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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 | 0.000 |
| 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".