BIOSTRATIGRAPHIC IMPORTANCE OF THE NEW CA-TIMS U-PB GEOCHRONOLOGY FOR THE BELLY RIVER GROUP AT DINOSAUR PROVINCIAL PARK (CAMPANIAN, ALBERTA, CANADA)
Bibliographic record
Abstract
Dinosaur Provincial Park (DPP; southern Alberta) yields a well-preserved and uniquely-diverse assemblage of late Campanian dinosaur fossils. Because the assemblage plays a central role in documenting Late Cretaceous peak-dinosaur-diversity, a chronostratigraphic framework for DPP’s fossils has evolutionary and paleoecological significance that extends beyond DPP’s boundaries. Here we employ high-precision CA-TIMS U-Pb zircon geochronology to constrain the ages of five bentonites that are semi-evenly spaced through the exposed bedrock section. Weighted mean 206Pb/238U dates for the bentonites range from 76.7 Ma to 74.3 Ma (with 2σ internal errors of ≤30 kyr), indicating that the section is younger than previously understood and that it encompasses a longer time span (2.4 Myr). Combined with biostratigraphic data, these results confirm a previous hypothesis that the Oldman–Dinosaur Park formation contact becomes younger toward southeastern Alberta. A significantly lower sediment accumulation rate near the Oldman-Dinosaur Park formation contact suggests the presence of a ~230 kyr hiatus (or stacked hiatuses) near the contact. Coincident first occurrences of five palynomorph taxa—that otherwise show stratigraphically staggered first occurrences in southeastern Alberta—support an interpretation that the hiatus is limited to the uppermost few meters of the Oldman Formation. Previously amassed sedimentological and stratigraphic data suggest that the hiatus may be a consequence of overall lower rates of sediment accumulation and interrupted sedimentation along the northern edge of the Oldman sedimentary lobe. Rates of sediment accumulation stay largely constant through the Dinosaur Park Formation, but may decline upwards into the Bearpaw Formation. Applying a currently accepted ammonite biochronology to DPP’s age-calibrated strata correlates the bottom of the section with the middle of the Baculites scotti Zone, and the top of the section with the approximate base of the Baculites compressus Zone. Four previously recognized dinosaur-assemblage zones at DPP are also calibrated and show durations of approximately 600–700 kyr, similar to those of ammonite biozones.
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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 | 0.001 | 0.001 |
| 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) | 0.001 | 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".