Major end moraines of Younger Dryas age on Wollaston Peninsula, Victoria Island, Canadian Arctic: implications for paleoclimate and for formation of hummocky moraine: Discussion

Abstract

Discussion In referring to several large moraine belts n Arctic Canada, Dyke and Savelle (2000) state “a consensus is emerging that these moraines are cored by glacier ice” (p. 615). They further state that ice-cored morainal belts in Arctic Canada “would resemble southern areas of hummocky moraine were they to lose their ice cores” (p. 617). More investigation and research is required before these statements can be accepted in lieu of theories proposed by other investigators for the origin of ice within hummocky Arctic topography and for the evolution of this topography. The claimed consensus is that of Dyke et al. (1992), Sharpe (1992), and St-Onge and McMartin (1995). Dyke et al. (1992) stated that many of the moraines present on Prince of Wales Island consist of buried glacier ice. Sharpe (1992) reported exposures of relatively debris-free ice containing a few debris-rich bands underlying up to 2m of diamicton within areas of hummocky moraine. He noted the contact between the diamicton and ice as abrupt. St-Onge and McMartin (1995) reported icy sediments overlain by bouldery diamicton with a sharp and subhorizontal contact; reticulate ice was noted in the diamicton near the contact. All contacts between till and ice appear characteristic of segregation ice developing in the base of and under a finetextured soil (Mackay and Dallimore 1992). In addition, the above sequences are the reverse of the normal continental glacier sequence, where relatively clean glacier ice overlies debris-rich glacier ice. St-Onge and McMartin believed (i) the hydrogeochemistry and isotopic values of reticulate ice, ice-wedge ice, and the observed icy sediments and (ii) the slope of the co-isotope plot from their icy sediment samples support a glacial origin for the icy sediments. The latter is the strongest argument for a glacial origin of the icy sediments as the slope is similar to that for meteoric water (Lorrain and Demeur 1985). However, differentiation of segregation ice and glacial ice by co-isotope relation has since been seriously questioned (French and Harry 1990; Mackay and Dallimore 1992). The hydrogeochemistry and isotope values reported by St-Onge and McMartin (1995) for the different ice types simply confirm different origins of the ice types and do not necessarily indicate a glacial origin for the icy sediments. Dyke and Savelle’s (2000) analysis of ice-cored topography excluded the mainland west of the Amundson Gulf, where a hummocky belt of topography on the Tuktoyaktuk Peninsula and adjacent areas (Fig. 1) was studied in detail by Mackay (cf. 1963, 1971, 1973, 1983) and his colleagues (Mackay and Stager 1966, Rampton and Mackay 1971, Rampton 1974, Rampton and Bouchard 1975, Gell 1976, Rampton 1988a, 1988b, Dallimore and Wolfe 1988, Mackay and Dallimore 1992). They concluded that the ice cores found within hummocky morainal topography along the Tuktoyaktuk Peninsula and Yukon Coastal Plain (Rampton 1982, Pollard and Dallimore 1988, Harry et al. 1988) are intrasedimental ice. The conclusion is based on evidence summarized in Rampton (1988a) and Mackay and Dallimore (1992), namely — similar geochemistry and isotope values for massive ice and ice within the underlying sandy sediments in numerous profiles, indicating a common water source and downward freezing; isotope plots having linear trends through ice and underlying interbedded sand and ice and co-isotope plots showing a linear trend down through till, ice, and sand, both trends suggesting downward freezing; petrographic data from massive ice indicative of a segregation origin; the common presence of reticulate ice within the till immediately over the massive ice (reticulate ice develops in fine-grained sediments as permafrost aggrades); the asso-