Thermokarst sediments and sedimentary structures, Tuktoyaktuk Coastlands, western Arctic Canada

• Published in: Global and Planetary Change
• Main Author: Murton, Julian B
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier 2001
• Subjects: G0001 Geography (General); Arctic; Canada; Tuktoyaktuk; Ice; permafrost; Thermokarst; wedge*
• Online Access: http://sro.sussex.ac.uk/id/eprint/11034/; https://doi.org/10.1016/S0921-8181(00)00072-2

Abrupt climate warming during glacial–interglacial transitions promotes regional thermokarst activity in areas of ice-rich permafrost. The ensuing thaw-related processes of melt-out, soft-sediment deformation and resedimentation may produce widespread thermokarst sediments and sedimentary structures. Examples of the most distinctive thermokarst sediments and sedimentary structures from the Tuktoyaktuk Coastlands, western Arctic Canada, comprise: (1) soft-sediment deformation structures (thermokarst involutions) in a palaeoactive layer; (2) ice-wedge casts and composite-wedge casts; (3) peaty to sandy diamicton deposited mainly by debris flows in retrogressive thaw slumps; and (4) a basal unit of diamicton and/or impure sand in some thermokarst-basin sequences, deposited by progradation of resedimented materials in thermokarst lakes. Many of the thermokarst sediments and sedimentary structures in the Tuktoyaktuk Coastlands formed as a result of rapid climate warming during the last glacial–interglacial transition, although some continue to form at present due to local (non-climatic) factors. Identification of thermokarst sediments and sedimentary structures in the geological record requires evidence for the thaw of excess ice. Direct evidence for the former occurrence of excess ice includes: (1) ice-wedge casts; (2) composite-wedge casts; (3) lenticular platy microstructures in frost-susceptible sediment; (4) certain near-surface brecciation of frost-susceptible bedrock; and (5) ramparted depressions attributed to the decay of frost mounds. Indirect evidence for former excess ice results where thaw consolidation initiates soft-sediment deformation or gelifluction.