Characteristics of Striae and Clast Shape in Glacial and Non-Glacial Environments
Notice bibliographique
Résumé
Linear abrasion features on rock surfaces are produced by interacting rock particles in relative motion. The most common examples are striae produced by temperate glaciers, and as a consequence, striae have long been used as a means of identifying the passage of past glaciers. However, there are many non-glacial processes that can produce striae. These have been sporadically documented in the geological literature but have failed to make a lasting impression on the wider Earth Sciences community. These non-glacial processes include tectonic deformation, meltwater flow, non-glacial ice, wind action, volcanic blasting, mass movements of rock debris, among many others. Many produce coarse-grained deposits similar in character to glacial tills and there are several instances where non-glacial deposits and striae have been misinterpreted as glacial in origin. This thesis examines linear abrasion features (mostly striae) from five different environments, three glacial (temperate, polythermal and cold) and two non-glacial environments (mass movement and tectonic) to characterise the striae from different origins. The aim was to assess if there are readily observable and measurable differences in striae character between environments and to develop field-based criteria that allow a sound judgement of their origin in the geological record. Over 760 measurements of individual striae were made (orientation and size) on around 20 representative clasts and characteristic features of about 50 striated clasts from the various environments are illustrated in an "Atlas of linear abrasion features". In addition clast shape and striae occurrence were measured on 1260 clasts from deposits and about 100 bedrock linear abrasions from a cold-based glacier were recorded. The results show that some striae are diagnostic of certain environments but a combination of clast shape and striae characteristics is the most reliable method of correctly interpreting coarse-grained deposits with striated clasts. Results also highlight the wide range of striae characteristics within each environment and the importance of lithology in striae generation. This is evident even within the well-known temperate glacial environment where there is a marked contrast between striae formed within a thick debris layer and those formed in thin debris-rich basal ice. There appears to be little difference in striae formed by temperate and polyhermal glaciers, but glacial striae are readily distinguishable from striae found in various mass movement deposits or tectonically deformed conglomerates. Glacial striae tend to be sub-parallel to the clast long axes and show a high density on individual surfaces, whereas those in non-glacial origin typically show a lower density of slightly shorter, wider striae and show either no preferred orientation or weak grouping. The survivability of glacial abrasion features of clasts once they have entered a fluvial system has been assessed in a small South Island glacier fed river. This has provided a basis for estimating the proximity of a glaciofluvial deposit to the glacier front. Striae are found to survive only 1 to 2 km and glacial facets are mostly removed within 6 km. The study has also documented previously undescribed linear abrasion features from a cold-based glacier in Antarctica. This discovery is a significant advance in understanding cold glacial processes, and has provided new criteria for recognising the passage of cold-based glaciers in polar areas or regions where cold-based ice may have existed in the past.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,001 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,002 | 0,001 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,001 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».