Newmarket Till aquitard: optimum grain packing with a pore-filling calcite-rich cement
Bibliographic record
Abstract
Newmarket Till is a stony, sandy (38%) silty (~47%) diamicton, which is of variable thickness (~1 - 69 m) and of widespread distribution in Southern Ontario. The Newmarket Till has unusually high densities (2.2 - 2.4 g/cm3); elevated seismic velocities (Vp ~2600 m/s) determined by downhole geophysical studies are characteristic and the Till can be traced across the region as a seismostratigraphic marker. As the Till is highly indurated and has low permeability, it forms a regional aquitard that confines underlying aquifers, and is also a basal aquitard for overlying aquifers (e.g. Oak Ridges Moraine). Given the high sand content of this diamicton, the low permeability and indurated nature is surprising, and could be resultant from over-consolidation due to glacial loading, presence of a secondary cement, or both processes. Recent observations from drill core and surficial sampling transects illustrate that Newmarket Till is not always cemented, but the observation of residual cement on pebbles indicates it was potentially formerly cemented. Our new studies indicate that the matrix of the Dummer moraine (adjacent to and south of the Shield - Paleozoic boundary and to the north of the Newmarket Till) is mineralogically and geochemically equivalent to Newmarket Till, and we thus suggest the Dummer Moraine is a very stone- to boulder-rich equivalent of the Newmarket Till. The matrix mineral assemblage of the Till (in decreasing abundance) is quartz, calcite, K-feldspar, plagioclase, dolomite, amphibole and clinopyroxene; these grains are comminuted and range in size from ~2000 ?m to ~2 ?m, leading to optimum packing, and potentially over-consolidation. The intra-grain matrix is exceptionally fine (<1 ?m, typically 0.25 - 0.50 ?m) and not resolvable by optical methods. Higher resolution SEM and FE-SEM backscattered electron and secondary electron images of the intra-grain matrix reveals a complex pore filling cement. The minerals comprising the secondary cement are a challenge to analyze due to their very fine grain size and composition. Semi-quantitative EDS analyses indicate a calcite (CaCO3) cement with minor phyllosilicates, as confirmed by XRD on the clay-silt and clay fractions. The calcite cements the silt- to sand-sized mineral grains and larger clasts, and result in the Newmarket Till being highly indurated and of low permeability. The timing and process of the initial cementation event is currently being evaluated; we also note that in the vadose zone the Till becomes uncemented (i.e. the original calcite cement dissolves out).
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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 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 0.001 |
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".