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Abstract:

<p>Thick and regionally extensive, mainly fluvial, detritus was deposited unconformably across the Canadian Shield at approximately 1.7-1.6 Ga and again from 1.0-0.9 Ga. Detrital zircon provenance and sedimentological studies of the preserved remnants of these deposits suggest that they were derived from erosion of extensive mountain belts represented by the ca. 1.9 -1.7 Ga Hudsonian orogeny and the ca 1.2 - 1.0 Ga Grenvillian orogeny, respectively. The Hudsonian and Grenvillian orogenies represent the main constructional phases of the Nuna and Rodinia supercontinents, so it is hypothesized that these terrestrial deposits are the sedimentary record of supercontinent assembly. Erosion and transport of detritus was aided by a lack of vegetation and dynamic climatic and atmospheric conditions that favored vigorous continental weathering. Sediment was transported by extensive, contemporaneous river systems that drained northwestward across Laurentia and deposited into huge intracontinental basins. The distal parts of the river systems are preserved in strata exposed in the northern Canadian Cordillera, which represent remnants of these basins left behind on the trailing edge of Laurentia after supercontinent disaggregation. Our recent work shows that large, deeply channeled, perennial rivers were developed, despite the lack of sediment-stabilizing vegetation. The width:depth of fluvial channel forms match those of p counterparts with sedimentology pointing to low discharge variability. Our studies also indicate that Proterozoic river systems were significantly more extensive than today's largest river systems such as the Amazon, Nile and Brahmaputra.</p>

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