2009 Portland GSA Annual Meeting (18-21 October 2009)

Paper No. 14
Presentation Time: 11:15 AM

PLEISTOCENE STRATIGRAPHY AND PALEOENVIRONMENTS OF THE WHITE RIVER, YUKON


TURNER, Derek G.1, WARD, Brent C.1, BOND, Jeffrey D.2, JENSEN, Britta J.L.3, FROESE, Duane G.3, TELKA, Alice4, BIGELOW, Nancy H.5 and ZAZULA, Grant D.6, (1)Earth Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada, (2)Energy Mines and Resources, Yukon Geological Survey, P.O. Box 2703, Whitehorse, YT Y1A 0C2, Canada, (3)Earth and Atmospheric Sciences, University of Alberta, 1-26 Earth Sciences Building, Edmonton, AB T6G 2E3, Canada, (4)Paleotec Services, 1-574 Somerset Street West, Ottawa, ON K1R 5K2, Canada, (5)Alaska Quaternary Center, Univ of Alaska Fairbanks, P.O. Box 755940, Fairbanks, AK 99775-5940, (6)Yukon Palaeontology Program, P.O. Box 2703 L2A, Whitehorse, YT Y1A 2C6, Canada, dgturner@sfu.ca

Exposures examined along the White River in southwest Yukon Territory contain thick accumulations of glacial and non-glacial sediment from the middle to late Pleistocene. The White River sections are located beyond the limit of marine oxygen isotope (MIS) stage 2 glaciation and contain deposits from MIS 4 and MIS 6 glaciations. The non-glacial deposits contain up to ten metres of re-worked loess, lacustrine silt and clay, peat and gravel with tephra beds, paleosols, plant and insect macrofossils and large mammal fossils. The presence of organics with finite and non-finite ages, and Dawson (25 300 14C yr BP) and Woodchopper Creek (between 77.8 ± 4.1 ka and 131 ± 11 ka) tephras provide a chronologic framework for these deposits. These data combined with pollen and macrofossil analysis are used to reconstruct the glacial and non-glacial history of the White River area. A thick, likely MIS 6 aged till forms the bottom unit in all the sections. Above this, two MIS 5 age (sensu lato) peat units containing beaver-chewed wood represent a shallow depression with mostly birch shrubs growing near a shoreline within a white spruce forest in a climate as warm or warmer than present. This contrasts with another MIS 5 aged sequence of organic-rich pond sediments containing abundant birch but no conifers, suggesting that an open birch tundra existed at some point before MIS 4 glacial advance. Till deposited during MIS 4 is observed at several sections. Late MIS 3 to early MIS 2 deposits above this till are identified by finite-aged (30.9 ± 0.3 and 39.8 ± 0.6 ka 14C BP) bison and mammoth bones and Dawson tephra. During this time the environment was treeless, dry and dominated by Artemisia and grasses. The presence of interstratified glacial and organic non-glacial deposits allow the reconstruction of environmental change along the White River for much of the past 190 000 years.