Depositional record of late Wisconsin Glacial Lake Mackenzie, Northwest Territories, Canada: Implications for permafrost degradation in a warming climate.

摘要

In the Northwest Territories of Canada, Glacial Lake Mackenzie developed as the Laurentide Ice sheet retreated away from the Cordillera sometime after 10, 000 14C ybp. Glaciolacustrine deposits of Lake Mackenzie extend over some 21, 000 km2 of the Mackenzie Valley. Detailed sedimentological study of large outcrops created by postglacial fluvial down cutting through glacial sediments in a 11 250 km2 area of the basin reveals the depositional history of Glacial Lake Mackenzie. A regionally extensive till sheet provides a stratigraphic marker throughout the basin recording the maximum extent of the Laurentide Ice Sheet sometime between and 35, 000 and 22, 000 14C ybp. The overlying glaciolacustrine basin fill can be divided into six facies associations.; Integration of outcrop and map data shows that parent glacial sedimentary facies closely control the distribution of permafrost. In particular, the widespread presences of wet, fine-grained mud facies promoted the growth of ground ice when exposed by lake drainage. There is an excellent spatial relationship between glaciolacustrine mud facies and thaw lakes that identify terrain subsidence that was initiated by the melting of permafrost during a period of mid-Holocene warming. Unconventional gas reservoirs likely exist in the Glacial Lake Mackenzie basin given the presence of coal-bearing Mesozoic source rock strata and coarse-grained reservoir fan-delta deposits preserved below thick and extensive glaciolacustrine muds.