Abstract

The Yukon Territory contains a complex record of multiple glaciations and ice sources dating from Pliocene to Late Pleistocene (Yakataga Formation,4.2- 4.7 Ma). The oldest glaciations are recorded only in southwest Yukon, and are correlative to those documented in southeast Alaska. These events ultimately relate to uplift of the coastal mountains beginning ca. 4 Ma and climatic cooling at about 10 Ma. Glaciation followed regional erosion and renewed uplift. The earliest glaciation of west-central Yukon occurred between 2.6 and 2.9 Ma, forming a continuous carapace of ice connecting all the mountain ranges except a small part of the Dawson Range,which remained free of ice. This first glaciation was also the most extensive to occur in the region, and resulted in the Yukon River being diverted northwest into Alaska by the Cordilleran Ice Sheet. A series of glaciations extending from Mid Pliocene-Early Pleistocene have been documented in the stratigraphy of the Tintina Trench, north of Dawson. The limits of all of these glaciations have been mapped on the basis of glacial landforms and the distribution of erratics. Although morphological features of the older glaciations (Pliocene to Early Pleistocene) are generally not well preserved, there is relatively good control on the distribution of glacial erratics related to these events. Morphological evidence of glacial limits for the last two Cordilleran glaciations (Middle and Late Pleistocene) are well defined in most areas, with those of the Late Pleistocene having the sharpest features. Continental (Laurentide) ice only reached the Yukon ca. 30 ka BP, with associated features and limits also well defined. The Laurentide Ice Sheet occupied the eastern and northern slopes and foothills of the northern Cordillera as well as the Mackenzie Delta area, extending along the Yukon Coastal Plain to the vicinity of Herschel Island. Retreat from this ice limit integrated all the drainages of the eastern flanks of the northern Cordillera to form the Mackenzie River, the largest glacially-diverted river system in the world.