Turonian (Upper Cretaceous) lithostratigraphy and biochronology, southern Gulf Islands, British Columbia, and northern San Juan Islands, Washington State
Bibliographic record
Abstract
Clastic strata preserved on Sidney Island, Barnes Island, and adjacent islands of the southernmost Gulf Islands of British Columbia and the northern San Juan Islands of Washington State are assigned to new stratigraphic units: the Sidney Island Formation and the Barnes Island Formation. The Sidney Island Formation consists of basal conglomerate and sandstone that grades upward through planar-stratified sandstone into hummocky cross-stratified sandstone and siltstone, all of which are deposited in relatively shallow-marine environments. The Barnes Island Formation, in contrast, consists of deep-marine conglomerate, sandstone, and mudstone that was deposited in a submarine-fan setting. Mollusk fossils from the Sidney Island Formation are of Early to Middle Turonian age, whereas ammonites and foraminifers from the Barnes Island Formation indicate a Late Turonian age. The Sidney Island Formation thus records initial marine transgression and inundation of basement rocks, followed by basin deepening that is transitional to the deep-marine submarine-fan deposits of the Barnes Island Formation. Sidney Island Formation strata have been considered previously as derived from uplift along the nearby San Juan thrust system in mid-Cretaceous time. However, the shallow-marine strata are internally well organized, and the facies succession is persistent across the formation's outcrop area. In addition, the formation lacks the distinctive detrital metamorphic mineral assemblages that are characteristic of older rocks of the San Juan Islands. These observations suggest that strata of the Sidney Island Formation did not accumulate immediately adjacent to active thrusting but rather in a more distal setting relative to the thrust system.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| 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 teacher head, 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".