ABSTRACT: Youngest hills in Axel Heiberg Island, Canadian Arctic Archipelago: Are the salt domes rising?

CGRG Bibliography of Canadian Geomorphology
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Since the 1960s, geologists have wondered whether some of the 46 exposed evaporite diapirs in Axel Heiberg Island (composed of allochthonous Carboniferous Otto Fiord Fm) have grown in the Holocene. These domal or narrow ridge structures form flat-topped hills less than one to several kilometres in horizontal diameter that rise hundreds of metres above the bottom of U-shaped glacial valleys. Their steep and freshly gullied flanks give them an alien appearance of “warts” in the landscape. Because they are composed of the relatively soft and soluble minerals gypsum, anhydrite and halite, they are unlikely candidates to have posed much resistance to glacial erosion; in some localities they are topographically higher, yet down-ice from very hard igneous bedrock that displays striations and roches moutonnées. Present day glaciers (e.g. Thompson Glacier) have no difficulty slicing through diapirs. In some localities diapirs appear to intrude young sediments and they disrupt the course of glacial streams. The fact that mountain building processes ceased after the Eurekan Orogeny in the Eocene, makes the case for actively growing salt domes hard to defend. Part of the surface swelling of the evaporite outcrops is caused by expansion during hydration of anhydrite, but the large topographic bulges formed by the diapirs still pose a problem. The best evidence for present-day growth is in the Stolz Diapir near Whitsunday Bay in SE Axel Heiberg Island. The Stolz Diapir has a diameter of 1.2 km and its irregular surface is pitted with solution sinkholes. Dissolution is caused by a seasonal stream which, obstructed by the diapir wall, penetrates into it and reappears down valley. House-size blocks of banded halite stumble down the steep flanks, and despite this obvious disintegration, the diapir towers over a hundred metres above the valley. In order to test the hypothesis that some diapirs are actively rising, an early attempt using RADARSAT-1 data from the Stolz Diapir indicated successive images are completely decorrelated, which we interpret to indicate the structure is moving, although the displacement cannot be quantified. In order to detect possible neotectonic movements, we placed radar corner reflectors on selected exposures of evaporite and “stable” bedrock reference areas near by in the region of Expedition Fiord. Data acquisition of RADARSAT-2 at 24 day intervals along the same orbit has been commissioned to accumulate data for a few years to build a suitable time series for more robust analysis.

Bibliography of Canadian Geomorphology