calendar Add meeting dates to your calendar.

 

Paper No. 6
Presentation Time: 2:55 PM

PLEISTOCENE STRATIGRAPHY AND PALEOENVIRONMENTS OF THE WHITE RIVER, SOUTHWEST YUKON TERRITORY


TURNER, Derek G.1, WARD, Brent C.1, BOND, Jeffrey D.2, JENSEN, Britta J.L.3, FROESE, Duane G.3, TELKA, Alice M.4, 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 with both glacial and non-glacial middle to late Pleistocene sediment constrain the glacial limits and reconstructed paleoenvironments in southwest Yukon. These sections contain two glacial limits beyond the marine oxygen isotope stage (MIS) 2 extent. The non-glacial deposits contain up to 30 m of loess, lacustrine silt and clay, peat and gravel with tephra beds, paleosols, pollen, plant and insect macrofossils and mammal fossils. Organics with finite and non-finite 14C ages, Dawson tephra (25 300 14C yr BP), Woodchopper Creek tephra (77.8 ± 4.1 ka to 124 ± 10 ka) and newly sampled tephras provide a chronologic framework for these deposits.

A thick, likely MIS 6 aged till forms the lowest unit. Moraine-dammed glaciolacustrine deposits above this till were deposited during the transition into MIS 5. Intercalated gravel and sand beds with Woodchopper Creek tephra suggest this lake drained before ~77 ka. MIS 5 age peat units containing beaver-chewed wood indicate a white spruce forest with a climate as warm or warmer than present developed, probably after MIS 5e. This contrasts with overlying organic-rich pond sediments with abundant birch but no conifers. The presence of the informally named Donjek tephra, found elsewhere in association with Woodchopper Creek tephra, below these pond deposits suggests that an open birch tundra existed before MIS 4. Glaciation during MIS 4 deposited till and locally glaciotectonized the underlying sediments. Late MIS 3 to early MIS 2 deposits are identified by Dawson tephra and finite-aged (30.9 ± 0.3 and 39.8 ± 0.6 ka 14C BP) steppe-bison and woolly mammoth bones. The environment at this time was characterized by open, steppe-tundra vegetation (sage, grasses and forbs). The White River sections allow dating of the maximum and penultimate limits of the St. Elias lobe of the northern Cordilleran Ice Sheet and reconstructions of environmental change for much of the past 190 ka.

Meeting Home page GSA Home Page