Impact Ejecta at the Mistastin Lake Impact Structure, Labrador, Canada
Bibliographic record
Abstract
Introduction: One of the principal characteristics of impact events is the formation and emplacement of ejecta deposits. The compositional and physical characteristics of ejecta provide fundamental information about the shocked nature of target rocks and thus can provide one of the best and most accessible pieces of evidence for an impact origin of a structure [1] and provide a unique way to sample the sub-surface [2]. Impact ejecta is defined here as any target material, regardless of its physical state, that is transported beyond the rim of the transient cavity [2]. The original transient cavity reaches its maximum size during the excavation stage of crater formation, before rim collapse begins in the modification stage [3]. In complex craters, during the modification stage, rocks around the periphery of the bowl-shaped transient crater collapse downward and inward to form a series of terraces along the outer margin of the crater structure [1]. Most of the ejected material is deposited near the initial transient crater rim and can thus be found within the terraced region and beyond. Impact ejecta deposits, typically poorly preserved on Earth due to post-impact erosional processes, were recently identified in the rim region of the Mistastin Lake impact structure and are the focus of this study. Mistastin Lake Impact Structure: This impact structure, located in northern Labrador, Canada (55°53’N; 63°18’W), represents an intermediate-size, complex crater (28 km diameter) formed by a meteorite impact ~36 million years ago. The original crater has been differentially eroded; however, a subdued rim and distinct central uplift are still observed [4]. The inner portion of the Mistastin Lake impact structure is covered by the Mistastin Lake and the surrounding area is locally covered by soil/glacial deposits and vegetation. The topography directly surrounding the lake is slightly elevated in plateaus extending up to 5 km away from the shoreline. The crystalline target rocks of the Mistastin Lake region are dominated by granodiorite, mangerite, and anorthosite. Locally, allochthonous impactite units including impact melt and breccias are unevenly distributed around the lake and on Horseshoe Island (Fig. 1). Previous studies of the Mistastin Lake impactites have primarily focussed on the melt rocks (e.g., [4], [5]). This project builds on these studies and further evaluates the suite of impactite rocks in terms of their context within the crater structure and origin of their components. Fig. 1: Geology map (modified from [4], [5], and [6]).
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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 | 0.003 |
| Science and technology studies | 0.003 | 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) | 0.006 | 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".