Paleoproterozoic Stark Formation, Athapuscow Basin, Northwest Canada: Record of Cratonic-Scale Salinity Crisis
Notice bibliographique
Résumé
Abstract The Paleoproterozoic Stark Formation, a thick breccia unit, formed during the transition from marine to non-marine foreland basin fill in the Athapuscow Basin, Northwest Territories, Canada. Four types of breccia occur in the Stark Formation: (1) bedded breccias at the base of the unit, overlying the basinal facies of the underlying Pethei Group, are interpreted as debris flows, (2) massive chaotic breccias occur in the lower part of the Stark Formation throughout the basin and these are interpreted to be evaporite-collapse breccias; (3) siltstone and mudstone breccia occurs in the upper part of the Stark Formation and is also interpreted as evaporite collapse breccia, though much less evaporite was involved in its formation than the underlying chaotic breccia; and (4) laminar accretionary breccia consisting of laminar carbonate clasts, commonly with flat bottoms and convex-up upper surface geometries; these clasts occur in lenticular pods and are interpreted to form in caves following dissolution of evaporites or carbonates. The widespread presence and abundance of evaporite pseudomorphs (especially halite) in all breccia types, the stratigraphic restriction of the Stark Formation, and irregular filling above this unit indicates that all but the bedded breccia formed by the dissolution and collapse of evaporites. Chaotic breccia directly above underlying Pethei Group shallow-water and deep-water carbonates indicates the evaporates formed across the platform and adjacent deep basin. Foundered megaclasts (up to 1.5 km long and 40 m thick) in basinal settings suggest cumulative evaporite thicknesses on the order of a few tens to a few hundreds of meters. Carbonate clasts in all the breccias contain abundant wave ripples, planar laminations, stromatolites, and ooids. These structures along with a paucity of subaerial exposure features indicates nearly all carbonate deposition in the Stark was subaqueous. Thus, by inference the evaporites in the Stark Formation were also partially subaqueous. Displacive halite pseudomorphs are common throughout all facies in the Stark Formation. Silicified and dolomite-filled halite pseudomorphs are common along the contact between the evaporite-collapse breccia and underlying carbonate platform (Pethei Group) and surrounding large clasts in basinal settings. Silicified hopper crystal casts within deep-water rhythmites of the uppermost Pethei Group indicate precipitation of halite over deep waters. Gypsum pseudomorphs are exceedingly rare, and anhydrite pseudomorphs were not observed. The dominance of halite features in this basin and two penecontemporaneous basins (Kilihigok Basin and Wopmay Orogen) surrounding the Slave Craton suggests that, relative to the present day, seawater at ∼ 1.9 to 1.8 Ga was oversaturated with respect to calcium carbonate, had higher HCO3− concentration, and possibly was depleted in SO42−. The dearth of extensive, thick-bedded marine gypsum in the Archean and early Paleoproterozoic can be explained by low atmospheric oxygen content prior to ∼ 2 Ga in conjunction with increased carbonate saturation before ∼ 1.6 Ga.
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 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 | 0,003 | 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 | 0,001 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,001 |
| 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 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 ».