PALEOENVIRONMENTAL CHARTS FOR TERRESTRIAL IMPACT STRUCTURES - A SIMPLE TOOL TO TEST IMPACT AGES AND MARINE/CONTINENTAL IMPACT CONDITIONS.
Bibliographic record
Abstract
Introduction and Background: Most of the ~175 impact structures currently known on Earth are still insufficiently dated [1-2]. At buried or deeply eroded impact structures that lack material suitable for isotopic dating, stratigraphic methods provide the only con-straints for the timing of crater formation; in many cases, only the maximum age (the actual age of the shocked target rock) is given in the literature and in terrestrial impact crater listings [3]. In addition to isotopic and stratigraphic dating, paleogeographic considerations may help to test and refine poor and/or equivocal impact ages as recently done for PuchezhKatunki (Russia) and Obolon (Ukraine) [4]. Paleogeographic studies are, furthermore, an essential tool to discriminate between impact structures that formed in continental or marine environments. Only a small number (~25) of marine terrestrial impact structures have been reported so far [5]. Structural and sedimentological investigations (e.g., the recognition of submarine resurge breccia deposits) helped to reveal some additional marine impact structures, such as Obolon (Ukraine) [6]. However, further efforts need to focus on the recognition of marine impact structures on Earth. Data: Combining recent paleogeographic maps of North America (provided by Ron Blakey, Northern Arizona University [7]) with impact ages available in the literature [3; 8-14], we present a preliminary set of paleoenvironmental charts for some selected North American impact structures (USA: Ames, Oklahoma; Avak, Alaska; Crooked Creek, Missouri; Newporte, North Dakota; Sierra Madera, Texas; Upheaval Dome, Utah; Wells Creek, Tennessee; Canada: Carswell, Saskatchewan; Charlevoix, Quebec; Pilot, Northwest Territories; Steen River, Alberta; Fig. 1). Interpretation and Results: In accordance with [7], given that both the paleogeographic maps and impact ages can include uncertainties, the paleoenvironmental charts suggest that Newporte (~500 Ma [8]) and Steen River (91 ± 7 Ma [9]) formed under marine conditions and that Ames (>470 Ma [10]), Avak (~93-88 Ma [11]), Charlevoix (~450-480 Ma [12]), and Carswell (115±10 Ma [13]) are probably marine impact structures. The Pilot (445±2 Ma [13]) event was obviously a continental impact scenario, as most likely was the Wells Creek (200±100 Ma [14]) impact. Charts exhibit transitions in environmental conditions for Crooked Creek (320±80 Ma [14]), Upheaval Dome (<170 Ma [3]), and Sierra Madera (<100 Ma [14]). New field studies and the detection of structural and sedimentological features diagnostic for marine or continental impact, respectively, might strongly narrow the age windows for these structures.
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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) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.003 | 0.004 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.031 | 0.004 |
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".