CGRG Bibliography of Canadian Geomorphology
Search Results
Author : Brooks, G.R.
Date : 2002.
Title : Holocene lateral channel migration of the Red River, near St. Jean Baptiste, Manitoba.
Publication : Geological Association of Canada and Mineralogical Association of Canada Joint Annual Meeting, May 27 - 29, 2002. Saskatoon, Saskatchewan.
Issue :
Page(s) :
Abstract
The evolution of the Red River floodplain was investigated at two successive river meanders near St. Jean Baptiste, Manitoba. A transect of five boreholes was sited across the floodplain at each meander to approximately follow the path of lateral channel migration, as revealed by a ridge and swale topography visible on aerial photographs. The alluvium in the ten cores ranges from 15.3 to 21.6 m thick, and is composed of primarily silt. Twenty four wood and charcoal samples collected from 9 cores were selected for AMS radiocarbon dating. The dates from the lower half of the alluvium in each core were calibrated and averaged, and are interpreted to represent the age of the primary phase of lateral floodplain accretion at the borehole sites. The averaged ages along the two transects increase progressively from 0.92 to 7.85 ka cal BP and 1.01 to 8.09 ka cal BP, respectively, from the proximal to distal portions of the floodplain. This indicates that a continuous record of post-Lake Agassiz lateral channel migration is represented by the floodplain deposits along each meander. The temporal pattern of channel migration, reconstructed from the borehole floodplain ages and the pattern of the ridge and swale topography, reveals that the rate of lateral channel migration along both meanders was greatest prior to about 6 ka. At the upstream meander, the average rate of channel migration was initially 0.35 m/yr between 7.9 and 7.4 ka cal BP, then decreased to 0.18 m/yr between 7.4 and 6.2 ka cal BP, and varied between 0.04 and 0.08 m/yr since 6.2 ka cal BP. The pre-6 ka interval of higher channel migration occurred when climate was warmer than present, but was also drier than at any other time in the Holocene on the Canadian prairies. The factor controlling the temporal variation of lateral channel migration is hypothesized to be a long-term decrease in sediment supply through the study reach. Sediment supply likely was initially high following the drop in baselevel during the final recession of glacial Lake Agassiz as the river system extended northwards and became established on the former lake bed in southern Manitoba and northern North Dakota and Minnesota.
Bibliography of Canadian Geomorphology