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Highly variable Precambrian fluvial style recorded in the Nelson Head Formation of Brock Inlier (Northwest Territories, Canada)

Alessandro Ielpi and Robert H. Rainbird
Highly variable Precambrian fluvial style recorded in the Nelson Head Formation of Brock Inlier (Northwest Territories, Canada)
Journal of Sedimentary Research (March 2016) 86 (3): 199-216

Abstract

Spectacular canyon exposures of the approximately 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.


ISSN: 1527-1404
EISSN: 1938-3681
Serial Title: Journal of Sedimentary Research
Serial Volume: 86
Serial Issue: 3
Title: Highly variable Precambrian fluvial style recorded in the Nelson Head Formation of Brock Inlier (Northwest Territories, Canada)
Affiliation: Laurentian University, Department of Earth Sciences, Sudbury, ON, Canada
Pages: 199-216
Published: 201603
Text Language: English
Publisher: Society for Sedimentary Geology, Tulsa, OK, United States
References: 100
Accession Number: 2016-083555
Categories: Sedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table, sketch maps
N69°20'20" - N69°20'60", W122°58'00" - W122°54'00"
Secondary Affiliation: Geological Survey of Canada, CAN, Canada
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by SEPM (Society for Sedimentary Geology), Tulsa, OK, United States
Update Code: 201640
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