Proposed new karst reserves in the arctic and sub-arctic Northwest Territories of Canada
|Location||International Geological Congress,oslo 2008|
|Holding Date||08 September 2008|
At present, arctic and sub-arctic karst terrains are little represented in the UNESCO World Heritage Natural Sites and International Geopark programmes. Karst is well developed in the Western Interior Lowlands, Franklin and Mackenzie Mountains physiographic regions north of Lat. 60 N in the Northwest Territories of Canada. Most of this vast area was glaciated repeatedly by Laurentide continental or cordilleran glaciers but, due to Ice Age aridity, there was an ice-free corridor through the central Mackenzies. The postglacial climate includes a summer warm season but mean annual temperatures everywhere are below 0 C and precipitation is generally only 250 - 600 mm. Permafrost is widespread to continuous in the lowlands, continuous in the mountains.
At Lats. 61-62 N in the Mackenzie Mountains, South Nahanni River National Park Reserve (one of the first World Heritage natural sites) is proposed for expansion to ~34.000 km2 to include the watershed of the River plus that of Ram River to its north. The Nahanni North Karst, an ancient karst invaded by ice-margin scabland floods, straddles both basins. At the surface it includes the most accentuated karst topography (sinkholes, poljes, solution corridors) known in northern regions, while underground there is well integrated karstic flow through massive limestones and dolomites, at proven rates exceeding 5 km/day that indicate that permafrost conditions imposes little restraint at these latitudes.
East and west of the Mackenzie River between Lats. 65 and 67 N there are extensive spreads of platformal dolomites of Cambrian-Silurian age, underlain by redbeds and salt and overlain by the remarkable Bear Rock Fm (Devonian), a re-cemented dolomite-gypsum solution breccia that outcrops over some thousands of km2. A sample transect of the Mackenzie Mountain karst in these strata is being proposed for a new International Geopark. It begins at 1600 m asl on dolomite plateaus in the ice-free corridor, where felsenmeere and patterned ground dominate at the surface but karst groundwater circulation via taliks produces elegant steephead valleys (reculées) that were locally adapted to host small cirque glaciers. Descending to the east, a large polje of tectonic origin and a striking dry canyon in the dolomites are succeeded by foundered terrains over the salt. Entering the glaciated zone at 1000 m asl, glacier-scoured dolomites display the greatest extent of solutional pavement reported from arctic regions, succeeded by a possibly unique "dissolution-drape" karst of sinkholes, dry valleys, lakes, natural bridges, caves and scablands on the breccia.
In the Interior Lowlands extensive dolomite plateaus exhibit well-organised karst drainage via >1000 sinkholes and many large turloughs. An outcrop of the breccia has captured the drainage of a 450 km2 lake underground via a lengthy ridge created by the hydration of gypsum along a local front of the Laurentide Ice Sheet.