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

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.