Soil genesis in relation to glacial history, Central Yukon.

Upland soils formed in three different parent materials in the Lewes Plateau of the Central Yukon were studied: till from the McConnell (MIS 2) and penultimate (MIS 4 or 6) glaciations, and weathered bedrock beyond the penultimate limit. Soils at penultimate and McConnell sites have solum thicknesses of 50-75 cm and <50 cm respectively but other field and chemical observations did not identify differences in weathering patterns between age groups. The two groups have distinctive clay mineral assemblages, with smectite present in the youngest deposits. These results contrast with reconnaissance studies conducted in the 1970s and 1980s on low-elevation soils in the Klondike Plateau. My study shows that field criteria are insufficient for differentiating between McConnell and penultimate deposits in upland landscape positions in the Lewes Plateau and that the presence of smectite clay may be attributable to different parent materials and source areas for ice and into solely changing paleoclimatic conditions. Soils formed on weathered bedrock have characteristics consistent with both limited and significant weathering. These pedons have solum thicknesses that exceed the depth of the excavated pits (85-110 cm) as well as distinctive clay mineralogy, but chemical data suggest that only limited weathering has occurred. Sola are strongly cryoturbated despite the restricted occurrence of permafrost in the contemporary environment. Two scenarios for the genesis of these soils are proposed which favour either preservation of relict soil features beneath cold-based ice, or prolonged interglacial soil formation following erosion of till deposited by warm-based ice. Alternatively, the area may have remained ice-free throughout the Quaternary so that soil evolution was shaped by multiple glacial-interglacial climatic cycles. --P.ii.