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TitleDeeply channeled Precambrian rivers depicted in the 1.9 Ga Burnside [River] Formation of Kilohigok Basin (Nunavut, Arctic Canada)
AuthorIelpi, A; Rainbird, R HORCID logo
SourceMargins through time: GAC-MAC 2016; Geological Association of Canada-Mineralogical Association of Canada, Joint Annual Meeting, Programs with Abstracts vol. 39, 2016 p. 38 Open Access logo Open Access
LinksOnline - En ligne (complete volume - volume complet, PDF, 1.3 MB)
Alt SeriesNatural Resources Canada, Contribution Series 20190440
PublisherGeological Association of Canada
MeetingGAC-MAC 2016; Whitehorse, YK; CA; June 1-3, 2016
Mediaon-line; digital
File formatpdf
Subjectssedimentology; Science and Technology; Nature and Environment
ProgramGEM2: Geo-mapping for Energy and Minerals Rae Province, Chantrey-Thelon
Released2016 06 01
AbstractWe present outcrop evidence for deeply channeled fluvial drainage in the 1.9 Ga Burnside River Formation of Kilohigok Basin (Nunvaut, Arctic Canada), a feature that contrasts with the dominant sheet-like geometry observed in many ground-based studies of Precambrian fluvial sandstones. In the Burnside River Formation, sheeted sandbodies with ubiquitous cross-bedding observed at the outcrop scale are at first consistent with classic, unconfined depositional models. However, satellite and oblique-aerial imagery of sections up to 15 km wide and 500 m thick reveals the occurrence of incised paleovalleys hosting clustered, km-scale, channel bodies with attached large foreset bars, sand sheets with width to thickness ratio > 2500, and scattered eolian intervals. The association of these architectural elements points to the coexistence of fluvial piedmonts generated by braidplain channels, at time wind-winnowed, and weakly-sinuous channel belts up to 25 m deep. Channel geometries comparable to those of late Paleozoic to modern braided channels disprove the inference that all Precambrian streams readily widened in response to increased discharge. The current facies models for large-scale Precambrian sheetdominated fluvial sandstones did not include large channel forms because the latter could not be resolved by ground-based observations alone. Based on the abundance of architectural elements with very high width to thickness ratio, and on their limited geomorphic variability in fluvial style, we recommend that large sheet-braided fluvial systems should still be considered a separate entity from post-Silurian (i.e., vegetated) and modern braided rivers. Parallels between sheet-braided and modern dryland rivers do not reconcile with the deep and perennial channelized morphodynamics evident from the Burnside River Formation. On the other hand, the distal and sand-bed reaches of modern humid sandur plains bear possible analogies to Precambrian sheetbraided rivers. This conclusion contradicts the assumption that all Precambrian rivers simulated seasonal behaviors independently from their original climate regime.

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