Dissecting 20 million years of deep-water forearc sediment routing using an integrated basin-wide Bayesian chronostratigraphic framework
Bibliographic record
Abstract
Abstract Sedimentary deposits along convergent margins contain a record of sediment transfer and coupled tectonic processes. Deciphering the evolution of ancient convergent margins, both spatially and temporally, is challenging as their stratigraphic successions are often locally deformed, which makes it difficult to correlate stratigraphic units over large distances, and they may have limited age constraints. Here, we construct a novel Bayesian chronostratigraphic framework for Late Cretaceous–Paleocene units of the Nanaimo forearc basin in western British Columbia, Canada, which reveals unparalleled detail into long-term sedimentation processes along an active deep-water margin. The Upper Nanaimo Group outcrop belt features ~2000 m of forearc basin fill that includes the deposits of multiple submarine channel systems along a 160-km-long depositional strike-oriented cross section of the ancient continental margin. The age and longevity of individual slope-channel systems was determined by constructing a Bayesian Monte Carlo numerical model in which biostratigraphic and magnetostratigraphic measurements were used to further constrain 37 detrital zircon maximum depositional ages. Important context for the refined maximum depositional ages is provided by a detailed stratigraphic dataset composed of 2199 m of measured stratigraphic section and 4207 paleoflow measurements, which demonstrate the facies, architecture, distribution, and orientation of 12 slope-channel systems. In combination, our results reconstruct the spatio-temporal evolution of coarse-grained, deep-water sediment routing along the paleo-margin and enable the timing of sedimentation to be compared with hinterland and forearc processes. Our integrative approach demonstrates that submarine channel-system deposits of the upper Nanaimo Group cluster into three long-lived fairways (8–18 m.y.), each of which has a unique depositional history. Along-strike variations in the timing of sediment routing, channel-system architecture, and channel-system orientation are interpreted to be driven by local subsidence, magmatism, and subduction-related processes. We show, for the first time, how Bayesian age models can be applied at a basin-scale to produce robust chronostratigraphic frameworks for deciphering basin evolution that provide valuable insight into long-term geodynamic processes.
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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 | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.003 | 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) | 0.001 | 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".