Early history of the Midcontinent Rift inferred from geochemistry and sedimentology of the Mesoproterozoic Osler Group, northwestern Ontario
Bibliographic record
Abstract
The Mesoproterozoic 1108–1105 Ma Osler Group, a 3 km thick succession of basaltic flows and sedimentary units on the north shore of Lake Superior, is among the oldest expressions of the Midcontinent Rift. Basal sediments of the Simpson Island Formation (new name) deposited by braided fluvial systems record westward transport of debris eroded from local Archean and Proterozoic rock units. Strata deposited by this fluvial system are intercalated with, and overlain by, ocean-island basalt (OIB)-like basalts, which become increasingly contaminated up section (εNd(1100Ma) = +0.3 to –5.3). The light rare-earth element (LREE) enriched (La/Smn = 1.5–3.9) and heavy REE (HREE) fractionated (Gd/Ybn = 1.5–3.7) subaerial flows are divisible into two units that correlate with other sections of the Osler Group to the east, but simple correlations with more distant sequences are difficult. The volcanic rock dominated portion of the succession is overlain by a thin (25 m thick) conglomerate–sandstone assemblage representing southeast progradation of an alluvial fan in a semi-arid climatic setting. Clast lithologies and geochemistry indicate no extra-rift detritus was delivered from the hinterland of the fan. Various lines of evidence in both volcanic and sedimentary rocks support a scenario where early, pre-1108 Ma, subsidence along a north–south axis from the western arm of the rift to the Nipigon Embayment was replaced by subsidence along the east–west rift axis between 1108 and 1105 Ma.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".