| Title | Highly variable Precambrian fluvial style recorded in the Nelson Head Formation of Brock Inlier (Northwest Territories, Canada) |
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| Author | 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 |
| Image |  |
| Year | 2016 |
| Alt Series | Earth Sciences Sector, Contribution Series 20150282 |
| Publisher | Society for Sedimentary Geology |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf |
| Province | Northwest Territories; Nunavut |
| NTS | 96; 97; 98; 86; 87; 88 |
| Area | Nelson Head Formation |
| Lat/Long WENS | -128.0000 -112.0000 76.0000 64.0000 |
| Subjects | general geology; sedimentology; regional geology; Nature and Environment; deltaic sediments; fluvial deposits; fluvial systems; fluvial processes; fluvial transport; sedimentary environment; sedimentary
rocks; sedimentary petrology; sedimentary structures; braided channels; mudstones; sandstones; carbonates; Plants; Precambrian |
| Illustrations | geological maps; sketch maps; location maps; photographs; cross-sections; cross-sections, stratigraphic; photomicrographs; tables |
| Program | GEM2: Geo-mapping for Energy and Minerals Mackenzie Corridor, Shield to Selwyn |
| Released | 2016 03 22 |
| Abstract | 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. |
| Summary | (Plain Language Summary, not published)
The Nelson Head Formation is a ~1 billion year-old fluvial to shallow-marine sandstone deposit exposed at several sites in the western Canadian Arctic.
Spectacular canyon exposures along the modern Brock River, Northwest Territories, offer a rare opportunity to study the deposits of rivers, which existed before the appearance of land plants on Earth. We analyze the sedimentology, 3D architecture and
depositional evolution of 16 stacked river-channel deposits at this site, demonstrating a variability in fluvial depositional style much greater than that previously portrayed for Precambrian rivers. |
| GEOSCAN ID | 297265 |
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