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TitleLithalsa Formation and Holocene Lake-Level Recession, Great Slave Lowland, Northwest Territories
AuthorWolfe, S A; Morse, P D
SourcePermafrost and Periglacial Processes vol. 28, 3, 2017 p. 573-579,
Alt SeriesNatural Resources Canada, Contribution Series 20182010
Mediapaper; on-line; digital
File formatpdf
ProvinceNorthwest Territories
NTS85E; 85F; 85G; 85H; 85I; 85J; 85K; 85L; 85M; 85N; 85O; 85P; 75E; 75L; 75M
AreaGreat Slave Lowland
Lat/Long WENS-120.0000 -110.0000 64.0000 61.0000
Subjectsgeochemistry; hydrogeology; permafrost; ground ice; lakes; cores; Holocene; alluvial deposits; lithalsas; Quaternary
Illustrationslocation maps; photographs; tables; plots; histograms
ProgramClimate Change Geoscience, Permafrost
Released2016 06 03
AbstractLithalsas (ice-cored permafrost mounds) are common within silty clay sediments of the Great Slave Lowland, a low-relief bedrock plain extending to about 50m above Great Slave Lake, Northwest Territories. Following retreat of the Laurentide Ice Sheet, sediment deposition in the lowland accompanied inundation by glacial Lake McConnell between about 12 700 and 9300 cal BP, and continued subsequently in ancestral Great Slave Lake. Lake-level recession has occurred locally at about 5mm· a 1 for the last 8000 years, due primarily to isostatic rebound. Maximum limiting ages of permafrost and lithalsas in the lowland are elevation-dependent, being least near the modern shoreline and greater at higher elevations. Many lithalsas, which are up to 8m high and several hundred metres wide, are less than 3000 years old. They are abundant in alluvium of the Yellowknife River deposited within the last 2000 years, with permafrost aggradation and lithalsa formation continuing in historical time.
Summary(Plain Language Summary, not published)
The Great Slave Lowland occupies the north shore of Great Slave Lake. After glaciation, it was inundated by glacial Lake McConnell and ancestral Great Slave Lake. Holocene lake-level recession around Yellowknife is determined from accelerator mass spectrometer ages from peat and detrital organics. In the last 8000 years, recession occurred at about 5 mm/year, and permafrost is youngest near the modern shoreline and older at higher elevations. Silty-clay sediments are abundant, and lithalsas (ice-rich permafrost mounds) occurring within 40 m above the present lake level are less than 6000 years old. They are common on Yellowknife River alluvium deposited within the last 3000 years. Lithalsas on this surface probably developed as permafrost aggraded into saturated sediments, and ground ice has formed within the last 250 years.