Abstract: Preliminary results from the Stewart River stratigraphy and surficial mapping suggest a minimum of four glaciations and two interglacial periods. Methods of stratigraphy, paleomagnetics, soil analysis, tephra chronology, and relative geomorphic preservation are employed to differentiate and describe Quaternary events. Glaciations, from oldest to youngest, are the pre-Reid (multiple early to mid Pleistocene glaciations), Reid (> 200 000 years), and McConnell (14 000 - 29 600 years). Interglacials are represented by organic deposits from Stirling Bend and Ash Bend, in addition to Wounded Moose and Diversion Creek paleosols preserved on pre-Reid and Reid surfaces.

During their maximum extent, pre-Reid ice sheets inundated the study area leaving isolated nunataks on Klondike Plateau and the northern part of Stewart Plateau near Syenite Range. North trending intervalley channels on Stewart Plateau represent confined ice flow in Stewart and McQuesten River valleys from ice obstructions in Tintina Trench. Undifferentiated pre-Reid surficial materials are thick in the lowlands of Klondike Plateau and Tintina Trench, areas proximal to the terminus of multiple pre-Reid glaciations. Reid ice terminated at Reid Lakes in the Tintina Trench. The McConnell ice sheet impinged into the east boundary of the study area, terminating approximately 20 km northeast of Stewart Crossing.

Petrographic analysis of woody material from the oldest pre-Reid deposit at Stirling Bend (unit A), suggests a late Tertiary age. Paleomagnetic measurements from overlying loess (unit B) and glaciofluvial sediments (unit C) have undetermined polarity. Remaining pre-Reid glacial and interglacial units from Stirling Bend have normal polarities and represent deposits from either a subchron within the Matuyama reversed chron or early Bruhnes normal chron. Reid deposits underlie Sheep creek tephra at Ash Bend suggesting a minimum age of 200 000 years. McConnell deposits are late Wisconsin age.

The distribution of surficial materials, related to multiple glaciations, physiography, and fluvial order contrasts, may govern the distribution of placer occurrences in McQuesten map area. Placer deposits occur anomalously in areas around Klondike Plateau, coinciding with the terminus of pre-Reid glaciations, Further exploration in pre-Reid ice terminal environments may yield significant placers through a better understanding of sediment distribution and genesis.

Authors: Bond, J.D.

Map Scale: 1 : 0

NTS Mapsheet(s): 115P

Citation: Bond, J.D., 1996. Quaternary history of McQuesten map area, central Yukon. In: Yukon Quaternary Geology - Volume 1 - 1996, LeBarge, W.P. (ed), Indian & Northern Affairs Canada/Department of Indian & Northern Development: Exploration & Geological Services Division, p. 27-46.

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