Timing and controls on the delivery of coarse sediment to deltas and submarine fans on a formerly glaciated coast and shelf
Notice bibliographique
Résumé
The evolution of deltas and submarine fans is often envisioned as largely controlled by relative sea-level (RSL) variations. However, in some cases, RSL can have less effect on delta and submarine fan activity than sediment supply and shelf geomorphology. In order to document the relative importance of these three factors on deltaic and submarine fan evolution in a former glaciated environment, this presentation documents the delivery of coarse sediment to the Laurentian Channel (eastern Canada). The well-constrained stratigraphic and geomorphological framework of both the glacio-isostatically uplifted deltas and the modern Laurentian Channel fans allow us to document and contrast the evolution of river-fed deltas, river-fed canyon/fan systems and longshore drift-fed fans during deglacial and postglacial times. The evolution of these different types of fans can be divided into three phases. The first phase is characterized by delta progradation on the shelf while RSL was at its maximum, although already falling, and the ice-margin gradually retreated inland. The second phase is characterized by the delivery of deltaic sediment in the deep realm of the Laurentian Channel, permitted by the supply of large amounts of glaciogenic sediments derived from the retreating ice margin and the lowering of the RSL. At the same time, sediment instability along the steep Laurentian Channel formed small incisions that evolved into submarine canyons where the narrow shelf allowed the trapping of longshore sediment. The third phase is characterized by the withdrawal of the ice-margin from the watershed of the main rivers and the drastic decrease in sediment supply to the deltas. Consequently, the delta fronts experienced strong coastal erosion, even though RSL was still lowering in some cases, and the eroded sediments were transferred onto the shelf and to adjacent bays. This transfer of coastal sediments allowed the continued activity of longshore drift-fed canyons. The retreat of the ice margin from the watersheds thus controlled the supply of sediment and induced a change in delta type, passing from river-dominated to wave-dominated. This presentation highlights the role of the type of sediment supply (ice-contact, glaciofluvial and longshore drift) in the timing and activity of submarine fans in high-latitude environments. It proposes a conceptual model for high-latitude shelves where sediment delivery to submarine fans is mostly controlled by structural inheritance (watershed area and shelf geomorphology) rather than RSL fluctuations. Therefore, although RSL fell during delta progradation, this study demonstrates that it was not the main contributor to delta and submarine fan growth. This has wider implications for the extraction of sea-level information from stratigraphic successions.
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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 | 0,001 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,001 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| 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 ».