Petrology and potential tectonic significance of a K-bentonite in a Taconian shale basin (eastern Ontario, Canada), northern Appalachians
Bibliographic record
Abstract
A 6 cm thick K-bentonite, herein defined as the Russell Bed, occurs in an Upper Ordovician deep-basin shale succession in eastern Ontario, Canada, forming part of the distal Taconic foreland in eastern North America. The bed lies within the pygmaeus graptolite Biozone, which is about 451 to 452 Ma in age. Although some bentonites are reported from this interval in eastern North America, we are reporting the first set of compositional data for a bentonite of this age. Gamma-log correlation identifies a potential minimum distribution area of <2×10 5 km 2 for the K-bentonite, covering part of southern Quebec, New York State and eastern Ontario. The deposit coincides with the first influx of distal turbdites into this shale basin, associated with Taconic flysch, and simultaneous abrupt ventilation of the once anoxic deep-water basin, which had formed initially after foundering of the Upper Ordovician carbonate platform. Concurrent intrabasinal extinction of several graptolite species suggests that change in sedimentation, palaeoceanography and volcanism were linked to a regional external process. Compositionally, the bentonite is distinct from the older Ordovician platform deposits in eastern North America. The deposit contains abundant titaniferous phlogopite with 1.6% BaO, fluoroapatite with 2.5% F, and dynamically shaped glass spherules now altered to clay. The spherules and clay matrix constitute 45% of the bed and, compositionally, define an illite (>90%)–smectite (I/S) structure with about 7.5% K 2 O%. Age-dating by Ar–Ar analysis of the phlogopite crystals yielded a younger than expected (440–445 Ma) age. This difference, along with evidence of localized chloritization of phlogopite, likely reflects known post-Ordovician hydrothermal activity within the basin. On the basis of several geochemical proxies, the magmatic source of the Russell K-bentonite falls within the trachyandesite field and was Ba-enriched. Comparison of geochemistry and mineralogy with older, Middle to Late Ordovician and younger Early Silurian K-bentonites within the Taconic orogen along eastern Laurentia and Baltica reveals that the potential source magma for the Russell Bed was more mafic, more alkaline, and less fractionated than sources typical of older (platform) bentonites. Instead, it is more similar to the younger Llandovery bentonites of Scandinavia and Scotland. It remains uncertain if it signals local or regional compositional change in volcanic source in the northern Appalachians.
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 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 | 0.000 | 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 | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.017 | 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".