Late Wisconsinan McConnell glaciation (ca. 24-11 ka) occurred in four phases in the Pelly Mountains of southern Yukon. Phase 1 marked the onset of ice accumulation in cirques above 1524 m above sea level (a.s.l.). These local glaciers expanded and fed valley glaciers that extended into the surrounding lowlands (after 26.3 ka). At glacial maximum or phase 2, the development of ice-divides to the east and south of the Pelly Mountains permitted Cordilleran ice lobes to invade the lesser glaciated Pelly Mountains, which resulted in up-valley ice-flow. This ice-flow arrangement continued into early deglaciation (phase 3), a period characterized by re-advances of the invading ice lobes. Following retreat of the ice lobes from the Pelly Mountains, some local cirque glaciers above 1600 m a.s.l. resumed limited down-valley flow (phase 4). For drift prospecting purposes, the dominant glacial dispersion trajectory in these high relief areas is controlled by the last phases of ice-flow (either phase 3 or 4).

Ice accumulations in the Coast Mountains of southwestern Yukon and the Cassiar Mountains of south-central Yukon during the late Wisconsinan were responsible for glaciation of the Whitehorse area. Cirques in the Coast Mountains likely supported the first glaciers that advanced out of the mountain valleys ahead of the more distal Cassiar accumulation. Glacial maximum is characterized by topographically unconstrained ice flow trending northwesterly over most of the map area. Ice thickness over the city of Whitehorse exceeded 1350 m during full glacial conditions. Deglaciation is characterized by frontal retreat punctuated by periods of dynamic equilibrium and readvances. Differential retreat of the Cassiar and Coast Mountain ice lobes enabled the Cassiar lobe to penetrate, and at times readvance, up-gradient into Coast Mountain valleys. This pattern of deglaciation created ice dams and a series of proglacial lakes that submerged valleys under as much as 300 m of meltwater.

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The Allan Creek section was identified and briefly described during reconnaissance mapping of the Watson Lake map area (NTS 105A) several decades ago and provides southeastern Yukon’s most complete known record of glaciation. The region supported ice sheets during multiple Quaternary glaciations, with landforms in Liard Lowland recording the ice flow toward the southeast during the Last Glacial Maximum (LGM). Inference of earlier ice-flow patterns requires sedimentologic characterization of glacial deposits underlying Liard Lowland. We expand macro-scale descriptions of the sequence of four diamict units exposed in the Allan Creek section to provide further insight on paleo-ice flow in southeastern Yukon. Pebble fabrics were measured from each diamict unit to compare with known LGM ice-flow directions and previously reported clast orientations. Three of the diamict units record ice-flow along the NW-SE trend of Liard Lowland. The second highest diamict in the sequence may record ice-flow directions both parallel and transvers to the basin’s trend. Only the lowest diamict unambiguously indicates unidirectional ice-flow; it suggests southeastward paleo-flow during early glaciation of southeastern Yukon, similar to that during the LGM.

Glacial history reconstructions and geomorphic mapping in the North McQuesten River, Dublin Gulch, and Keno Hill map areas indicate a succession of less extensive glaciations. From oldest to youngest, the main glacial episodes are the pre-Reid (multiple glacial episodes), Reid and McConnell glaciations. The surficial geology of the study area is dominated by deposits of the Reid and McConnell glaciations. Pre-Reid glacial deposits are mostly confined to infrequent erratics on plateau areas above the Reid glacial limit. Glacial limit mapping indicates that ice flow patterns were similar in both the Reid and McConnell glaciations. Valleys aligned parallel with glacial ice flow are broad and U-shaped with significant glacial deposits in valley bottoms. In contrast, valleys aligned transverse to glacial ice flow are narrower and have a more V-shaped morphology. This relationship appears to be a controlling factor on the distribution of placers in the study area. Numerous drainages were analyzed for their placer potential in each of the three map areas. Their potential was based on geomorphic evaluations, glacial history, geochemistry, bedrock geology, and historic records. A concentration of potential placer creeks were identified in the Keno Hill/Mayo Lake area. Fewer prospective creeks were identified in the Dublin Gulch and North McQuesten River map areas.

During retreat of the Cassiar lobe of the Cordilleran ice sheet from the last glacial maximum there was a large stagnation or re-advance near what is now the north end of Lake Laberge (Lower Laberge) in the south central Yukon. This stagnation generated a large moraine that would come to act as a sediment dam for Glacial Lake Laberge. As the retreat of the ice front resumed a lake formed between the ice front to the south, and the sediment dam to the north. With the ice front continually drawing further south, combined with incision of an outlet flow into the sediment dam, the geomorphology of Glacial Lake Laberge constantly changed. Throughout the history of Glacial Lake Laberge there has been a gradual decline in the lake level largely controlled by incision into the sediment dam near Lower Laberge, as is indicated from sets of fluvial terraces above the current outlet river (the Yukon River). This gradual decline has produced several sets of preserved shorelines rising above the present lake level. By surveying the shape, location, and elevation of these shorelines and outwash terraces, in combination of all other applicable data sets, a detailed glacial retreat and alluvial history can be examined.

Paleomagnetic results are presented for 154 specimens from 16 sites in the Late Cretaceous Seymour Creek stock, a small granodioritic intrusion emplaced into Paleozoic gneisses and schists of the Yukon-Tanana Terrane (YTT), west-central Yukon. Stepwise demagnetization of the specimens revealed steep characteristic remanent magnetization directions in 2 normal- and 14 reversed-polarity sites with a mean direction of declination D=65.0°, inclination I =-83.6° (alpha 95 = 4.3°, k =73.8). Geological relations suggest that the stock has not been tilted since its emplacement at 68.5 ± 0.2 Ma. The paleopole for the Seymour Creek stock at 55.2°N, 202.5°E (dp =8.3°, dm=8.5°), plots south of the North American apparent polar wander path. This suggests that the YTT has experienced a net 79° ± 36° counter-clockwise rotation, and a nonsignificant 2.4° ± 7.5° anti-poleward translation relative to North America since 68.5 Ma. This result does not agree with the previously reported large poleward translation and minimal rotation estimated for the YTT from paleomagnetism of the coeval Carmacks Group volcanic rocks.

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Nine pollen profiles were obtained along a broad latitudinal transect extending from the Upper Nisling Valley to the Ittlemit Lake and Bear Lakes areas in the southwest Yukon Territory. Radiocarbon dated fossil pollen records from these profiles provided evidence for the reconstruction of postglacial environmental history of the area. Surficial samples combined to aid the interpretation of the fossil data. Records of these sequences suggest that the post-glacial vegetation in the area exhibited a successional development. Immediately after the deglaciation, the area was covered by a sparse herb dominated tundra assemblage. Betula glandulosa invaded the area at about 10,000 yr BP, which initiated the replacement of herbaceous tundra by a dwarf birch shrub-tundra. Picea glauca invaded the Upper Nisling Valley in the northern part of the study area and the Ittlemit Lake Basin in the south at least around 9,000 yr BP, while 8,600 yr BP in the central Aishihik Basin, marked the establishment of forest-tundra environment in the area. Significant rise of Picea pollen at 7,500-8,000 yr BP in the north-central part of the study area indicate the establishment of a modern boreal forest, which is approximately 1,500-2,000 years earlier than that indicated by the Antifreeze Pond pollen diagram from the Snag area of the southwest Yukon. It is notable that the pollen spectra of two lacustrine sediments suggest a phase change of lakes into marsh occurring around 5,000-6,000 yr BP in the area, and change of bog conditions has also been recorded at almost the same time in the area. These events occurred simultaneously in the area and probably reflect the change of climatic conditions, which might have led to the development of permafrost in the region. The development of early post-glacial vegetation in the area exhibited an unstable pattern. This instability was primarily related to the sequential invasion and migration of taxa from late-glacial refugia. Stable vegetation associations were established in the area as a result of migrators reaching their limit of climatic tolerance during the middle Holocene. Post-glacial vegetation history in the Ittlemit Lake Basin area seems to have exhibited a different pattern.

Throughout the Pleistocene epoch, Yukon was repeatedly influenced by glacial ice originating from the Cordilleran Ice Sheet and independent alpine glaciers. The penultimate limit in Yukon has garnered controversy in recent years, as moraines in the central region of the territory were found to be older (MIS 6) than moraines in the southwest part of the territory and Alaska (MIS 4). The Ogilvie Mountains, located east of Dawson City, have proven especially problematic for chronological studies. This study will attempt to test a relatively new dating method on penultimate surfaces in the Ogilvie Mountains; Chapman Lake is the primary study area. Using a vertical sampling method to construct a cosmogenic depth versus concentration profile in outwash gravel, this research will determine whether Marine Isotope Stage 4 or 6 provided the conditions necessary for ice nucleation to build the penultimate glacial surface. The age calculated by the depth profile is supported by radiocarbon ages and macrofossil samples, optically stimulated luminescence ages, TCN boulder dating, as well as detailed stratigraphy of significant sites near the Chapman Lake moraine. The results will help determine the effects of climate forcing in this region and its relationship to the existing glacial framework of the territory.