Volcanic ash and lignite of the Lower Cretaceous Chaswood Formation, central Nova Scotia
Bibliographic record
Abstract
Lignites and coals, because of their low sedimentation rates of terrigenous detritus, commonly preserve a record of the input of volcanic ash. A reconnaissance study has been made of lignite from the Lower Cretaceous Chaswood Formation of the Elmsvale basin, central Nova Scotia in order to identify whether volcanic ash is present, and if it is, whether it could be used to correlate the poorly dated terrestrial rocks with better dated marine successions offshore. The bulk mineralogy and geochemistry of lignite and lignitic mudstones has been determined by X-ray diffraction (XRD) and whole-rock geochemical analysis of ashed samples; in addition, selected samples have been examined by electron microprobe (EMP) and scanning electron microscope (SEM). Lignites from the Chaswood Formation have several features indicating the presence of volcanic ash: unusual abundance of high-field-strength elements (HFSE) such as Nb, Ta and Hf; the presence of augite in EMP and XRD analyses; the rare presence of euhedral quartz; and aluminophosphate-sulphate minerals that appear to pseudomorph volcanic ash. Wood or charcoal fragments appear mineralized and diagenetic talc is present. Much of the terrigenous component of the lignites consists of background detrital sediments (characterized by detrital illite) and most of any ash component has been altered to kaolinite. Bulk composition of ash is inferred to range from basaltic to rhyolitic. Ash beds are present in both the lower and the middle member of the Chaswood Formation, but our sampling density was insufficient to correlate single beds from one borehole to another. Several ash beds may be present in a single lignite unit. The closest sources of ash are the early Albian volcanic rocks within the lower Cree Member of the Orpheus graben, in a stratigraphic interval that has been previously correlated with the middle member of the Chaswood Formation, and Berriasian to Barremian volcanic rocks on the SW Grand Banks and Fogo Seamounts. These rocks show similar abundances of HFSE to the Chaswood Formation lignites. Distinctive REE patterns with low La/Nd ratios are found in many lignites from the middle member of the Chaswood Formation. They likely result from concentration in organic matter of relatively unfractionated REE in ash of similar composition to Albian volcanic rocks to the southeast.
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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 | 0.000 |
| 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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".