Superimposition of ribbed moraines on a palaeo‐ice‐stream bed: implications for ice stream dynamics and shutdown
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Bibliographic record
Abstract
Abstract The sediments and landforms preserved on palaeo‐ice‐stream beds can provide important information about their subglacial conditions and flow mechanisms, and the processes accompanying their shutdown. In this paper, detailed observations of an intriguing subglacial landform assemblage of ribbed moraines superimposed on glacial lineations on the Dubawnt Lake Ice Stream bed (north‐west Canadian Shield) are presented, including their morphometry, internal structure (from ground penetrating radar (GPR) surveys and from glaciogeological analysis) and sedimentological characteristics (from sediment architecture and lithofacies analysis). The observations suggest an abrupt change in ice dynamics that correlates with two phases of glacial landform development. This hypothesis is based on evidence from a deformed lodgement till, which subsequently underwent brittle deformation and developed prominent thrust (shear) structures and tension fractures. Tension fractures are observed in a sediment exposure and thrust structures are observed in GPR surveys, where they occur most prominently in the ribbed moraine ridge crests. The presence of the fractures, and their association with a population of clasts in the till that are orientated with their a‐ axes transverse to the inferred ice flow direction, suggests a compressional flow regime. It is therefore inferred that the glacial lineations were formed under an extensional flow regime during ice stream activity, but that at some point patches of till under the ice stream stiffened through dewatering. The subsequent increase in basal shear stress resulted in compressional flow and the development of subglacial thrusting and the building of ribbed moraines. We therefore suggest that ribbed moraines may form in areas of compressional flow under ice streams, i.e. sticky spots, and/or at the transition between slow and fast ice flow along parts of an ice stream. The general absence of ribbed moraines on most other palaeo‐ice‐stream beds suggests that either these ice streams continued operating during deglaciation or processes other than the development of localized compressional flow (sticky spots) led to their shutdown (e.g. ice depletion). Copyright © 2008 John Wiley & Sons, Ltd.
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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) | 0.000 | 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 it