Lithalsa Formation and Holocene Lake-Level Recession, Great Slave Lowland, Northwest Territories

Lithalsas (ice-cored permafrost mounds) are common within silty clay sediments of the Great Slave Lowland, a low-relief bedrock plain extending to about 50 m 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 5 mm.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 8 m 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. Copyright (c) 2016 John Wiley & Sons, Ltd.