Influence of channelized-flow density structure on the stratal architecture of deep-marine levee deposits
Notice bibliographique
Résumé
ABSTRACT Deep-water channel and levee deposits are common depositional elements on modern and ancient continental slopes. Unlike their channel counterparts, the spatial and temporal evolution of levee stratigraphy is much less well understood, in part because of the typically more recessive nature of levee deposits in the ancient sedimentary record, and sparse, widely spaced core control or seismic images of insufficient resolution in the modern. Moreover, it is generally inferred that levee development, at least in part, precedes the main phase of channel filling, the reasons for which remain largely unknown. In the Isaac Formation of the Windermere Supergroup (Neoproterozoic) of east-central British Columbia, Canada, well-exposed levee deposits are divided vertically into packages, each consisting of a sand-rich lower part overlain sharply by a mud-rich upper part. The lower part (3–10 m thick) consists mostly of medium- to thick-bedded, upper medium- to coarse-grained, lower-division turbidites intercalated with thin-bedded, fine-grained, upper-division turbidites. Along depositional strike away from channel-fill margins, the thickness of lower-division turbidites exhibit a distinctive thickening and then thinning over a few hundreds of meters that results in a similar thickening and thinning of the entire lower part of a package. The upper part (3–16 m thick) consists mostly of thin-bedded, fine-grained, upper-division turbidites intercalated with uncommon medium- to thick-bedded, medium-grained, lower-division turbidites. Significantly, the thickness of very thin- and thin-bedded turbidites in the upper part generally decreases stratigraphically upward whereas the thickness of intercalated medium- and thick-bedded turbidites changes little. The lateral and vertical changes in these deposits suggest that channelized flows were initially coarse grained and moderately well-sorted, causing them to exhibit negligible density stratification, and therefore high flow efficiency. We interpret that the velocity maximum occurred above the height of the incipient channel margins, thereby allowing the lower, coarse-grained, dense part of flows to easily overspill and deposit thick-bedded, coarse-grained turbidites in the lower part of each package. The sharp contact with the upper part of each package marks the point when relief from channel floor to levee crest exceeded the height of the velocity maximum in average throughgoing turbidity currents. Above this height, density of the flow decreased abruptly and consisted of significantly finer-grained sediment that overspilled to form the upper, finer-grained part of each package. Later the makeup of the sediment supply changed to a more polydispersed grain-size distribution, which caused the throughgoing currents to be more density stratified. This enhanced near-bed stratification and concentration effects, which in addition to intense interfacial mixing, resulted in rapid kinetic energy loss, and promoted deposition in the channel.
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Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,001 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,001 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,001 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,004 | 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 tête enseignante, 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 ».