Dolomites of the Boat Harbour Formation in the Northern Peninsula, western Newfoundland, Canada: Implications for dolomitization history and porosity control
Bibliographic record
Abstract
Abstract The Boat Harbour Formation constitutes the upper part of the Lower Ordovician St. George Group on the Northern Peninsula, western Newfoundland. It ranges in thickness from 140 m (459 ft) at Main Brook to 96 m (315 ft) at Daniel's Harbour. Dolomitization of the carbonate sequence is more pervasive in the lower 30 to 40 m (98 to 131 ft) at Main Brook, whereas at Daniel's Harbour, the section is entirely dolomitized. Petrography suggests that the Boat Harbour Formation has been affected by three phases of dolomitization. The earliest (near surface or synsedimentary) phase is D1 dolomicrite (4–55 μm), which exhibits dull to no luminescence. It commonly occurs as laminae-capping cycles and as breccias in the younger dolomite phases. It has low Sr (228 ± 30 ppm) and an average δ18O value of −6.0‰ ± 0.8‰ (Vienna Peedee belemnite [VPDB]) in the Main Brook section but more depleted signatures for δ18O of −8.8‰ ± 1‰ (VPDB) and lower Sr contents (45 ± 8 ppm) in the Daniel's Harbour section. The geochemical composition suggests that D1 was developed from fluids of a mixture of meteoric and marine waters. The midburial phase D2 dolomite consists of coarse planar subeuhedral crystals (30–400 μm) that show concentric cathodoluminescence zoning and are also crosscut by microstylolites. Its δ18O values range between −6.6‰ ± 1.3‰ (VPDB) at Main Brook and −9.0‰ ± 0.5‰ (VPDB) at Daniel's Harbour. This dolomite likely precipitated from fluids that circulated through crustal rocks with progressive burial (Th value of 114°C ± 11°C and salinity value of 23 ± 1.8 eq. wt. % NaCl). The late-stage D3 dolomite has large and coarse nonplanar crystals (125 μm–7 mm) that exhibit sweeping extinction under crossed polars, which is characteristic of saddle dolomite and also sometimes shows thin brightly luminescent rims. It was likely precipitated during deeper burial in pulses and from hot fluids (Th values of 148°C ± 19°C and 115°C ± 19.6°C and mean salinities of 23 ± 2 and 22 ± 2 eq. wt. % NaCl at Main Brook and Daniel's Harbour, respectively). This is also supported by their relatively more depleted δ18O (−11.1‰ ± 1.2‰ and −12.3‰ ± 1.4‰ VPDB, respectively) and low Sr contents (88 ± 36 and 38 ± 5.9 ppm, respectively). Porosity in the Boat Harbour Formation is mainly associated with the midburial D2 dolomite. Intercrystalline porosity is the dominant type, and it ranges in the formation from less than 1% to 8% at Main Brook and from 7% to 12% at Daniel's Harbour. Vugs are less common but are associated with D3 dolomite. The porous zone in the formation at Main Brook starts approximately 10 to 15 m (33 to 49 ft) below the lower Boat Harbour disconformity and extends down to the lower formational boundary, whereas porous zones in the formation at Daniel's Harbour are indiscriminately distributed throughout the section.
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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 | 0.003 | 0.003 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".