Investigation of high-level glaciofluvial terraces and re-evaluation of the established soil stratigraphy for Early and Middle Pleistocene surfaces, central Yukon, Canada

Palaeosols developed on the highest Yukon River glaciofluvial terraces were investigated in order to reconstruct the Plio-Pleistocene evolution of the river valley beyond Late Pleistocene glacial limits. A record of at least two pre-Reid (> 311 kyr) glaciations is chronicled by the presence of two populations of glaciofluvial terraces within the study area. The populations of pre-Reid terraces were identified based on their degree of soil development and elevation. Pre-Reid terraces 200–250 m above river level have preserved morphological and mineralogical features of the Wounded Moose palaeosol, a palaeosol previously associated with pre-Reid surfaces in central Yukon. Clay mineralogy and colour indicate that the Wounded Moose palaeosol developed in part during warm and sub-humid as well as temperate and humid interglacials. A second set of pre-Reid terraces between 110 and 30 m above river level are characterized by the presence of the less-developed Diversion Creek palaeosol, a palaeosol previously associated with only Reid-aged (< 311 kyr) surfaces in central Yukon. In contrast to the Wounded Moose palaeosol, the Diversion Creek palaeosol developed during comparatively cool and humid interglacial conditions. The presence of Diversion Creek palaeosols on pre-Reid outwash terraces suggests that a transition from dominantly warmer to cooler interglacial conditions occurred prior to 311 kyr in Yukon Territory. In addition, the presence of a Diversion Creek palaeosol cannot be used to differentiate stable Reid and stable pre-Reid surfaces across central Yukon.