In the northern Yukon there is a significant group of limestone caves in an area that was not glaciated during the Quaternary. Permafrost appears to have played an important role in restricting calcite speleothem deposition in the caves. U/Th dating and stable isotopic studies indicate that the deposits form two distinct groups, a first group younger than 350 ka, and a second group older than the 350 ka BP limit of the conventional U/Th alpha spectrometric dating method. Two large samples from the second group yield sequences of magnetic declinations and inclinations with reversed and normal polarity, perhaps from the Tertiary. The pollen content of five speleothems, the modes of calcite deposition, and stable isotopic analyses indicate that the speleothems were deposited under a cold regime. It is suggested that the ancient speleothems were deposited at a time when permafrost was absent, during the later Tertiary or at the beginning of the Quaternary period. The establishment and maintenance of permafrost throughout the Quaternary has prevented the formation of younger speleothems, except at a few cave entrances where the active layer may have deepened during interglacials.
ABSTRACT. Saiga antelopes (Saiga tatarica), presently confined to Central Asia, spread westward to England and eastward to the Northwest Territories of Canada during the late Pleistocene. Two saiga cranial fragments from the Yukon Territory and the Northwest Territories have yielded radiocarbon dates of 13 390 ± 180 and 14 920 ± 160 B.P. respectively. Thus, saigas occupied the easternmost part of their known Pleistocene range toward the close of the Wisconsinan glaciation. Saigas probably died out between 13 000 and 10 000 years ago in North America because of rapid changes in climate and plantscapes occurring about that time, as former steppe-like terrain was replaced by spruce forest and tundra.Key words: saiga antelope, Saiga tatarica, Yukon Territory, Northwest Territories, late Pleistocene, vertebrate fossils RÉSUMÉ. La saïga, ou antilope des steppes (Saiga tatarica), qu'on ne trouve actuellement qu'en Asie centrale, couvrait pendant le pléistocène tardif un territoire s'étendant vers l'ouest jusqu'à l'Angleterre et vers l'est jusqu'aux Territoires du Nord-Ouest du Canada. Deux fragments de crâne de saïga venant du Territoire du Yukon et des Territoires du Nord-Ouest ont donné par radiodatation un âge de 13 390 ± 180 et de 14 920 ± 160 BP respectivement. La saïga occupait donc la région la plus orientale de son territoire connu au pléistocène, vers la fin de la glaciation du Wisconsin. La saïga a probablement disparu il y a environ 13 000 à 10 000 ans en Amérique du Nord en raison des changements rapides dans le climat et les paysages végétaux qui se produisirent à cette époque, alors que la pessière et la toundra remplacèrent le terrain steppique.
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