Froese, D.G., 2002, Eastern Beringian paleoclimate from fluvial and eolian deposits, Plio-Pleistocene middle Yukon River, central Yukon and Alaska: Calgary, Alberta, Canada, University of Calgary, Ph.D. dissertation, 134 p.
Stratigraphic, sedimentologic, geomorphic and geophysical investigations were made of a 1000 km reach of the unglaciated middle Yukon River between central Yukon and Alaska. The purpose is to examine the record of a large northern latitude river's response to climate change over the last 3 million years. Permafrost first appears in the Yukon basin, and its first known occurrence in North America, in the form of ice-wedge casts in the Klondike area at 3.2 Ma. The first Cordilleran glaciation of Yukon follows prior to 2.6 Ma showing a strong synchroneity with North Pacific ocean core records. This extensive glaciation is associated with diversion of a south-flowing paleo-Yukon River northwest into central Alaska. Near the mouth of Charley River, there is a record of multiple outburst flood rhythmites during oxygen isotope stages (MIS) 18 and 16 (ca. 720-600 kyr). These outburst flood deposits are associated with the most extensive Quaternary glaciation of the Yukon-Tanana Upland. Late glacial and early Holocene eolian deposits are common on the Yukon River floodplain. Sandsheets were active during the Younger Dryas (and perhaps the Older Dryas). Sandy loess accumulated during the Holocene indicates periods of stability interrupted by rapid eolian sedimentation. The timing of these eolian accumulation events is synchronous with North Atlantic climate oscillations, suggesting an atmospheric connection of the climate signal during the late glacial and early Holocene. Shallow geophysical characterization of the middle Yukon River indicates that valley-fill depths are comparable to depths of active scour holes above and below the Yukon Flats Sedimentary Basin, with increased valley-fill depths in the latter associated with sediment compaction underlying Yukon River. These data, together with recent terrace chronology, indicate the middle Yukon River has been in a state of mass-balance equilibrium over the last 10 000 years, providing a reference study of the Holocene 'interglacial' Yukon River. The results of this dissertation, examining changes in the Yukon basin at different temporal and geographic scales indicate the floodplain environment is sensitive to subtle changes in climate, while channel characteristics and valley-fills are relatively poor recorders of Quaternary and Holocene climate changes on large rivers without sealevel influence.
Theses and Dissertations
