Unraveling the Complexities of Deltaic Strata in the Lowermost Nikanassin Group, NW Alberta: Insights into Reservoir Architecture and Palaeogeography
Bibliographic record
Abstract
Deposits of the Jurassic–early Cretaceous Nikanassin Group represent the initial coarse-grained pulse of sedimentation into the evolving Mesozic foreland basin in northwest Alberta (Miles et al. 2009). The lowermost formation in the Nikanassin Group, the Monteith, consists of three distinct coarsening upwards packages separated by regionally correlatable flooding surfaces, herein referred to as the lower, middle and upper allomember. Each of the allomembers in the Monteith Formation was deposited by a series of prograding deltaic complexes flanking the foreland trough; facies associations indicate that fluvial and storm processes were significant influences on deposition, with tidal influence also notable locally. Deducing the complex interplay between waves, tides, fluvial input and storms during deposition of the delta from an extensive core and wireline log database provides valuable insight into reservoir architecture and the palaeogeography of this interval. Coarsening upwards deltaic complexes of the Monteith Formation are capped by regionally correlatable flooding surfaces. A facies association attributed to deposition in a prodelta setting characterizes the basal fine portion of each succession. This prodelta association consists of thin normally graded sandy to muddy beds representative of hyperpycnal flow deposits interbedded with hummocky cross stratified sandstones (up to 75 cm thick) interpreted to represent tempestites. Salinity stresses associated with the influx of fresh water via hyperpycnal plumes are interpreted, based on the presence of impoverished trace fossil assemblages dominated by opportunistic forms and abundant syneresis cracks. A delta front/mouth bar facies association sharply overlies the prodelta assemblage with minimal evidence for incision. The sharp contact is interpreted to be autocyclic in origin associated with rapid progradation of the delta during storm events and/or lobe switching. The delta front facies association is characterized by current rippled and cross stratified sandstone attributed to channel mouthbar sedimentation; however, a number of intervals contain massive sandstones with fluid escape structures. Bank collapse in deltaic distributary channels triggered by storm events is speculated to play a role in the origin of these massive units. Overlying the delta front/mouthbar facies association are facies with a more terrestrial signature including deposits of fluvial channels, tidal channels, brackish embayments, and delta plain lakes.
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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 | 0.001 |
| 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".