LATE QUATERNARY HISTORY OF THE MACKENZIE-BEAUFORT REGION, ARCTIC CANADA, FROM MODELING OF PERMAFROST TEMPERATURES .2. THE MACKENZIE DELTA-TUKTOYAKTUK COASTLANDS

In the Mackenzie-Beaufort region, maximum permafrost thickness is 750 m in the Pleistocene Tuktoyaktuk Coastlands, less than 100 m in the Ho locene Mackenzie Delta, and 500 m and anomalously warm in the Big Lake Delta Plain between the two areas. Numerical modelling has been used to derive surface temperature histories that fit ground temperatures a nd permafrost conditions at 12 wells in the Unipkat, Kumak, and Taglu hydrocarbon fields. The models indicate that the present Holocene Mack enzie Delta was built by fluvial processes into a submarine trough. Th e delta front passed a site presently some 20 km from the coast about 4.5 ka, and subsequently 58 m of ice-bonded permafrost has aggraded. I n contrast, the Big Lake Delta Plain was a subaerial platform for much of the Wisconsinan. It experienced several thousand years of inundati on in the Holocene, probably due to widespread development of thermoka rst lakes. At sites 8-12 km from the coast, the present subaerial cond itions were established 0.5-1.5 ka through lake drainage and fluvial-d eltaic deposition.