The Tuktoyaktuk Coastlands consist of a thick wedge of Pleistocene marine and fluvial sediments that contain much ground ice and have been modified by glaciation and thermo karst. East of Nicholson Peninsula the Stanton Sediments, consisting of a basal clay member, lower complex member, thinly bedded member, and an upper sandy member, represent Middle Pleistocene deposition in marine and alluvial environments. West of Nicholson Peninsula, Kendall sediments and Hooper clay of marine origin underline the Kidluit Formation of alluvial origin. Kidluit Formation is overlain by the Kittigazuit Formation, a thick fine grained deltaic sand of likely glaciofluvial origin. Northwesterly moving continental (Laurentide) ice defined a glacial limit on Cape Bathurst peninsula around unglaciated terrain to the north during the Mason River Glaciation of Middle Pleistocene age. Major strandlines marking marine limits were formed in this area during the Horton and Harrowby marine episodes (seas) of Middle Pleistocene age. Also in this region low marine benches, some inset into glaciated terrain, are likely Sangamonian in age as they contain organicbearing deposits (Ikpisugyuk Formation) indicative of interglacial climate. Northwesterly flowing continental ice again covered most of the area during the Toker Stade of Early Wisconsinan age. Sediments were glacially deformed in peripheral areas; till (Toker Point Member) and outwash (e.g., Turnabout Member, Garry Island Member, and Cape Dalhousie Sands) grading to relatively high sea levels were deposited. During the likely equivalent Franklin Bay Stade, westerly moving ice from Amundsen Gulf impinged on the eastern coast of Cape Bathurst peninsula. Ground ice, common to most of the area, was formed during deglaciation. During the Sitidgi Stade of Late Wisconsinan age, Laurentide ice persisted in the southern Mackenzie Delta and Sitidgi Lake areas and deposited till (Sitidgi Member). Sediments of a large proglacial valley train (Portage Point Sands) and a large proglacial lake (Eskimo Lakes Member) formed in the unglaciated Eskimo Lakes area during this stade. Extensive thermokarst activity during the Holocene produced thermokarst deposits (Parsons Lake Formation) and resulted in the formation of the ice-cored topography. During Late Wisconsinan and Holocene, valleys that had been eroded during the Wisconsinan were drowned and filled with thick fine grained alluvium. The Mackenzie Delta, consisting mainly of fine sand and silt (Aklavik Formation) and characterized by many thermokarst lakes, was formed. Rapid retreat of exposed coastlines has occurred. Periglacial processes and minor eolian activity and peat accumulate on continued throughout the Holocene. Ground ice and subsidence resulting from its thaw represent major hazards to development as does flooding of low-lying areas. Sand fill is a common resource, but coarser aggregate is only locally available.

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New I4C ages date the eruptions that produced the White River and Bridge River tephras, two important Holocene marker beds in western Canada. The 14C ages were obtained on trees in growth position buried in coarse tephra and a pyroclastic flow near the source vents. The mean calendric age of the White River eruption, based on four I4C ages, is 1147 cal years BP (calibrated years, approximately equivalent to calendric years) or AD 803 (the 2a age range, obtained from the two most precise 14C ages, is 1014-1256 cal years BP or AD 694-936). The mean age of the Bridge River eruption, determined both from (i) the single most precise outer-ring I4c age and (ii) the weighted mean of six outer-ring I 14C ages is 2360 cal years BP or 411 BC (20 age range = 2349-2704 cal years BP or 755-400 BC).

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Two late Pleistocene limits of glaciation were delineated in the Snag-Klutlan area. Radiocarbon dates, surficial characteristics of its drift, and the palynology of overlying sediments imply the older glaciation (Mirror Creek) is early Wisconsin in age; the younger glaciation (Macauley) is late Wisconsin in age and culminated c. 13,700 B.P. The stratigraphy of depositswithin the Macauley glacial limit implies that deglaciation between the two glaciations was minimal.R ~S U M É . Glaciations finî-pléistocènes dans la région de Snag-KIutlan, Territoire du Yukon. On a retracé dans la région de Snag-Klutlan deux limites fini-pléistodnes de glaciation. Les datations au radiocarbone, les caractéristiques superficielles de sa moraine et la palynologie des sédiments de recouvrement impliquent que la plus ancienne glaciation (Mirror Creek) est d'âge wisconsinien ancien; la glaciation plus récente (Macauley) est d'âge hi-wisconsinien et a culminé vers 13,700 A.P. La stratigraphie des dépôts englobés par la limite glaciaire de Macauley laisse supposer que la déglaciation interglaciaire a été minime. PESIOME. lIo3tlwnneümnoqeuoeoe onetleutenuee pa&ne Cnaa -K d y m a u (K)xox).