Impact-Related Deformation Features in Cherts from Terrestrial Impact Structures
Bibliographic record
Abstract
Introduction: Cherts, rocks predominantly made up of microto cryptocrystalline silica that formed during the diagenetic SiO2 replacement of the sedimentary host rock, are commonly found associated with limestones and sulfates [1;2]. Among the microto cryptocrystalline, microfibrous varieties of silica, chalcedony sensu stricto (‘length-fast chalcedony’) and quartzine (‘length-slow chalcedony’) [3;4] are widespread in sedimentary-diagenetic cherts. Impacts into limestone targets might, therefore, cause specific impact-related deformation in chert. However, with the exception of the report of shocked recrystallized chert from the Slate Islands impact structure (Canada) [5], there is sparse data on the petrography and shockmetamorphic behavior of such rocks at terrestrial impact sites. A preliminary review of impact-induced and potentially impact-related microdeformation features in cherts from a number of sedimentary-hosted terrestrial impact structures is presented. Cherts from Terrestrial Impact Structures and Associated Microdeformation Features: Jebel Waqf as Suwwan, Jordan. The investigation of a shocked, chalcedony-, quartzine-, and quartzbearing allochthonous (Upper Cretaceous) chert nodule recovered from wadi gravels in the central uplift of the ~6 km Jebel Waqf as Suwwan impact structure [6] revealed new potential shock indicators in microfibrous-spherulitic silica, in addition to well-defined shock-metamorphic effects [7] in coarser-crystalline quartz. Apart from the macroscopic overall brecciation of the chert, the microcrystalline silica groundmass exhibits a dendritic-suborthogonal fracture pattern (Fig. 1) commonly associated with thin silica ‘recrystallization bands’ that intersect the diagenetic chert fabric. Fibrous aggregates of quartzine spherulites in chalcedony-quartzine-quartz veinlets locally have shattered appearance and show conspicuous microscopic ‘curved fractures’ perpendicular to the quartzine fiber direction (parallel to the basal plane; Fig. 2); the curved fractures commonly trend subparallel to planar fractures (PFs) in neighboring shocked quartz. Quartz exhibits PFs, feather features [8], and mainly single sets of planar deformation features (PDFs) parallel to the basal plane (0001) (Brazil twins) [7;9] with rare additional PDFs parallel to {1013}. In contrast, autochthonous Eocene cherts from the weakly shocked uplifted rim of the Jebel Waqf as Suwwan impact structure lack PFs and PDFs in quartz, as well as quartzine and curved fractures therein [10]. Fig. 1: Polished section of shocked chert from the Jebel Waqf as Suwwan impact structure, Jordan, showing a distinct dendritic-suborthogonal fracture network.
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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 | 0.001 |
| 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) | 0.001 | 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".