| Titre | Highly variable Precambrian fluvial style recorded in the Nelson Head Formation of Brock Inlier (Northwest Territories, Canada) |
| Auteur | Ielpi, A; Rainbird, R H |
| Source | Journal of Sedimentary Research vol. 86, no. 3, 2016 p. 199-216, https://doi.org/10.2110/jsr.2016.16 |
| Année | 2016 |
| Séries alt. | Secteur des sciences de la Terre, Contribution externe 20150282 |
| Éditeur | SEPM |
| Document | publication en série |
| Lang. | anglais |
| DOI | https://doi.org/10.2110/jsr.2016.16 |
| Media | papier; en ligne; numérique |
| Formats | pdf |
| Province | Territoires du Nord-Ouest; Nunavut |
| SNRC | 96; 97; 98; 86; 87; 88 |
| Lat/Long OENS | -128.0000 -112.0000 76.0000 64.0000 |
| Sujets | sédiments deltaïques; dépôts fluviaux; systèmes fluviaux; processus fluviaux; transport fluvial; milieu sédimentaire; roches sédimentaires; pétrologie du sediment; structures sédimentaires; chenaux
anastomosés; mudstones; grès; carbonates; géologie générale; sédimentologie; géologie régional; Précambrien |
| Illustrations | geological maps; sketch maps; location maps; photographs; cross-sections; cross-sections, stratigraphic; photomicrographs; tables |
| |
| Programme | Bouclier à Selwyn du corridor de Mackenzie, GEM2 : La géocartographie de l'énergie et des minéraux |
| Résumé | (disponible en anglais seulement)
Spectacular canyon exposures of the ~ 1 Ga Nelson Head Formation along the modern Brock River, Northwest Territories, provide a rare opportunity to assess the
deposits of pre-vegetation, braided to sinuous-channelized fluvial systems. We analyze the sedimentology, architecture, and depositional evolution of 16 stacked fluvial-channel belts at this site, demonstrating greater variability in sedimentary
style and morphodynamics than is typically interpreted for Precambrian rivers. Inferences on fluvial planview based on integrated analysis of depositional architecture and paleoflow reveal complex patterns of channel-planform evolution, and four
depositional stages are recognized: (1) floodbasin-splay progradation with bounding episodes of eolian reworking; (2) deposition in wandering-channel belts characterized by deep anabranches and prominent lateral accretion; (3) progressive shift
towards shallow, braided-channel belts confined within alluvial valleys and dominated by downstream accretion; and (4) deposition by marine-influenced braided-channel belts with mixed downstream, lateral, and upstream accretion.
Overall, the
studied fluvial-channel belts point to significant morphodynamic complexity and geomorphic variability, challenging the assumption that all pre-Silurian rivers shared poor channelization and low sinuosity. Observed channel bodies also have
width:thickness ratios strongly overlapping with those of rivers postdating the rise of vegetation. In both wandering- and braided-channel belts, complex patterns of channel migration, bar accretion, and dissection were the result of co-acting
processes such as development of transverse-velocity zones within the channels, local paleoflow disturbance induced by depositional topography, and avulsion. In concert with the regional extent and paleoflow, and increasingly distal character of
correlative stratigraphic units towards the northwest, the magnitude of the observed trunk-fluvial channels is consistent with a mature drainage capable of transecting the Laurentian craton over thousands of kilometers. |
| Résumé | (Résumé en langage clair et simple, non publié)
La Formation de Nelson Head est constituée de grès d'origine fluviatile à épicontinentale, datant d'environ un milliard d'années, qui affleure à
plusieurs endroits dans l'ouest de l'Arctique canadien. Des affleurements spectaculaires dans des canyons le long de l'actuelle rivière Brock, dans les Territoires du Nord-Ouest, offrent une rare occasion d'étudier les dépôts de cours d'eau qui
existaient avant l'apparition de plantes terrestres sur la Terre. Nous présentons, pour ce site, une analyse de la sédimentologie, de l'architecture 3D et de l'évolution sédimentaire de 16 dépôts de chenaux fluviatiles empilés, démontrant ainsi une
variabilité du style sédimentaire fluviatile beaucoup plus grande que les descriptions antérieures ne le laissaient supposer pour les cours d'eau du Précambrien. |
| GEOSCAN ID | 297265 |
|
|