Electromagnetic and geological transect across permafrost terrain, Mackenzie River delta, Canada

Abstract

Abstract The time-domain electromagnetic (TDEM) method provides a surface geophysical technique suitable for interpreting deep permafrost conditions. This paper describes profiles collected in early spring in a transitional area of the Mackenzie Delta, Arctic Canada, with differing permafrost conditions and surficial geology. These data augment previously published profiles and allow the construction of a 30-km-long TDEM transect from the Holocene-age Mackenzie Delta in the southwest to the Pleistocene-age Tuktoyaktuk Coastlands in the northeast. The geoelectric section produced from the TDEM data is interpreted in terms of permafrost distribution. This interpretation provided a basis for inferring lithologic changes. Unconsolidated, non-ice-bonded (unfrozen) sediment has resistivities less than 10 ohm-m. Partially ice-bonded sediment ranges in resistivity from 10 to 40 ohm-m. Ice-bonded (frozen) sediment has resistivities from 30 to 300 ohm-m. Bedrock has low resistivities (from 5 to 15 ohm-m). Interpretation of the geoelectric section derived from both the shallow (<200 m) and deep (>500 m) TDEM data suggests that the main body of permafrost increases in thickness from 50 to 500 m over a few kilometers. A horizontally persistent unfrozen zone (talik) is situated from 50 to 100 m in depth within the main body of permafrost. Ice-bonding models derived from the TDEM surveys provide constraints on the geologic history of the Mackenzie Delta.