CGRG Bibliography of Canadian Geomorphology
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Author : Froese, D.; Westgate, J.; Preece, S.; and Sandhu, A.
Date : 2001.
Title : Mid-Pliocene permafrost and the first Cordilleran Ice Sheet in Yukon Territory.
Publication : Canadian Quaternary Association/ Association canadienne pour l'etude du Quaternaire, Annual Meeting 2001. Whitehorse, Yukon Territory, August 20 – 24, 2001.
Issue :
Page(s) :
Abstract
Arctic regions are especially sensitive to changes in climate. At no time has this been more apparent than during the intense climate shifts of the late Pliocene that led to the onset of extensive northern hemisphere glaciation. Fluvial deposits of the Klondike goldfields, central Yukon, are of particular interest since these sediments immediately precede and follow the onset of glaciation in the Pliocene. Stratigraphic and sedimentologic investigations of these deposits, coupled with fission track ages and paleomagnetic data, provide a basis for assessing Pliocene environmental change in eastern Beringia. The first ice-wedge casts known in North America occur in the upper White Channel gravel. At the Dago Hill site, a fission track age on the Dago Hill tephra indicates aggradation began by 3.18 Ma and slightly earlier evidence of permafrost is found in the reversely magnetized sediments at Jackson Hill. An ice-wedge cast at the Jackson Hill site suggests discontinuous permafrost, with a mean annual temperature no warmer than present (MAT –5.1º C), existed by the Mammoth sub-chron (3.22-3.33 Ma). At the Quartz Creek site, an ice-wedge cast infill includes the Quartz Creek tephra which has an 40Ar-39Ar age on hornblende of 2.6± 0.24 Ma, which agrees with the minimum age of the L-shaped spectrum of 2.71 Ma- the step least likely to contain extraneous argon. A weighted mean isothermal plateau fission track age on this tephra of 2.97± 0.3 Ma is consistent with a normal polarity (Gauss >2.6 Ma). The first evidence of glaciation in Yukon is recorded by the Klondike gravel, an extensive glaciofluvial outwash derived from the first Cordilleran ice sheet advance in the region. The lower portion of the Klondike gravel interbeds with the White Channel in the Klondike valley and is also magnetically normal, indicating an equivalent magnetostratigraphic unit. Based on the close association of the Klondike gravel with the first evidence of permafrost in the upper White Channel gravel and Quartz Creek tephra (2.6±0.24 Ma) we think the first glaciation also occurred within the Gauss chron (>2.6 Ma), suggesting large ice volumes in the northern Cordillera at the onset of northern hemisphere glaciation.
Bibliography of Canadian Geomorphology