ABSTRACT: Surficial geology of the area around Illisarvik, Richards Island, Northwest Territories.

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Permafrost studies have been in progress at Illisarvik since 1978. Surficial geology mapping was undertaken to provide a geologic framework within which to interpret the results of the studies that are underway and proposed at this important experimental site. Illisarvik is situated some 60 km west of Tuktoyaktuk, N.W.T. Physiographically, the study area comprises sections of both the Modern Delta and Pleistocene Coastlands (Tununuk and Kittigazuit Low Hills subdivisions). The stratigraphy of the former consists of a thick sequence of alluvial silt and fine sand, locally veneered by organics or recent marine deposits. Fine to medium sand, of marine-deltaic origin, occurs throughout the Pleistocene Coastlands. On ridges and uplands, it is overlain by diamicton (till and/or mudflow debris), in depressions by organics and recent lacustrine material. With a mean annual ground temperature in the range -7 to -9°C, permafrost is continuous and in excess of 600 m thick in the Pleistocene Coastlands. It is discontinuous and thinner in the Modern Delta. Active layer thicknesses range from 30 cm to greater than 100 cm, depending on lithology and vegetation cover. Ground ice type and distribution are variable and often related to lithology, ranging from pore and vein ice, through ice wedges, to massive ground ice. Pingos are abundant in the Tununuk Low Hills. Active geomorphic processes are associated with fluvial erosion and deposition, permafrost and ground ice, and marine processes. Permafrost-related activities include downslope movement by soil creep, ground ice formation and ice wedge growth, and pingo growth and decay. All contribute significantly to shaping of the present-day landscape in the area. Coastline change at Illisarvik has been significant, and is related to: retreat of coastal bluffs, erosion of tidal flats, and expansion of flats and spits. Erosion of tidal flats is apparently the dominant process; retreat rates of up to 50 m/yr are indicated locally. Pleistocene marine-deltaic sand is the oldest unit exposed within the area. Together with the till that overlies it (laid down by a Laurentide ice-sheet that moved down the Mackenzie Valley and fanned out into the Beaufort Sea), the sand is beyond the range of radiocarbon dating. Both are considered, however, to be pre mid-Wisconsin in age. Since the ice sheet retreated (prior to 40 000 B.P.) periods of thermokarst activity (generally short) have led to landscape modification as massive ice thawed and the present hummocky topography developed. Since about 3600 B.P., the climate has deteriorated and thermokarst activity has been much reduced. Aside from continuing lake drainage, leading to pingo development, marine and alluvial erosion and deposition are now dominant in the Illisarvik area. The terrain at Illisarvik is similar to that in areas of Richards Island where construction is considered in connection with onshore and offshore hydrocarbon development. Engineering concerns have been identified relating to the occurrence of ice-rich and saline permafrost soils, the potential for flooding in low-lying areas, and the ongoing coastline changes.

Bibliography of Canadian Geomorphology