Quaternary periglacial aeolian processes in Canada
DOI:
https://doi.org/10.26485/BP/1973/22/4Keywords:
wind action, quartz-grain abrasion, pre-Quaternary eolisationAbstract
Article in French.
ORIGINAL TITLE: Éolisations périglaciaires Quaternaires au Canada
In Canada and (or) the northern United States (Table I), rounded and smoothened dull quartz sand grains (RM), 0,5 to 1 mm in length, due to wind-wearing, are very numerous (60 to 95%) in the Precambrian, Cambrian and Ordovician loose sandstones studied, less numerous (O to 30%, mean: 6%) in the Cretaceous sands.
In Canada, in the Quaternary and Recent deposits (Table Il, about 300 samples studied), such RM grains are more abundant in dunes, eolian covers, loesses and sands with ventifacts (median value: 19%) than in the drift, fluvial, lacustrine or marine deposits (5%), which is not surprising. In Southern Canada, as almost anywhere else in the World, they are very scarce (average: 2 to 6%) in the mountains (Appalachians, Cordilleras) and on the Precambrian Shield, both regions where non-worn grains NU are highly prevailing (average: 78 te 94%). In full contrast, in the Prairies, the non-worn grains are minimal (average: 47%) and clean wind-worn ones attain their maxima] averages: 22% in Manitoba, 35% in Saskatchewan, 47% in Alberta.
Since elsewhere rehandling of older, prequaternary wind-worn grains (RS) is recognizible, and furnishes, outside the Prairies, only small percentages (average: 4 to 12%) the strong wind-wearing detected in the Prairies must be of Quaternary age. The classical Quaternary of Medicine Hat confirms it clearly (Table V): at the bottom, resting on Cretaceous sands, only 7% of wind-worn RM, against 70% at the top.
Certainly, the wind-action has been enhanced, in the Prairies, since at least the-Eocene and until now by the well-known continentality and relative aridity. But its renewed outbreak in the Quaternary requires other favouring factors: most probably, during the cold phases, the low temperature and frost, which thwarted the vegetal cover and let the ground freely exposed to the strong winds. This periglacial explanation is supported by the association, in the Quaternary of Edmonton, of high percentages of wind-worn grains, to unequivocable signs of cold cilmate, such as involutions, pseudomorphoses of typical ice-wedges, sand-wedges ... etc., testifying of mean annual temperatures of at least -2° t.o -6°C, against +2 to +4°C presently.
The criterion (shape of sand grains) on which this paper is principally based has been more fully exposed and discussed in English in Cailleux (1969).
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