HR: 0800h
AN: ED51D-0040    [Abstracts]
TI: Paleomagnetic Investigation of the East Palisades, Yukon River Valley, Alaska
AU: * Opalka, S
EM: S\_Opalka@hotmail.com
AF: Hobart and William Smith Colleges, Department of Geosciences, Geneva, NY 14456
AU: Graf, G J
EM: Grafg72@uwosh.edu
AF: University of Wisconsin-Oshkosh, Department of Geology, Oshkosh, WI 54901
AU: Dorff, D M
EM: daniel.dorff@mnsu.edu
AF: Minnesota State Univesity Mankato, Department of Geology and Geography, Mankato, MN 56001
AU: Bowman, D R
EM: dbowman@depauw.edu
AF: DePauw University, Department of Geosciences, Greencastle, IN 46135
AU: Stone, D B
EM: dstone@gi.alaska.edu
AF: Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK 99775
AU: Layer, P W
EM: player@gi.alaska.edu
AF: Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK 99775
AB: The East Palisades is a ~60 m high erosional cut-bank bluff that reveals loess, tephra, silt, clay, peat horizons, and ice wedges along the Yukon River, 55 km southwest of Tanana, Alaska. Matheus et al. (2003) concluded through geochemical analysis of tephras, that the bluff spans $\sim$2 Ma of Pliocene/Pleistocene time. Using this stratigraphy, the Bruhnes-Matuyama Normal/Reversal boundary (0.78 Ma) should be present within the outcrop. Paleomagnetic analyses of oriented samples from five selected sections indicate a stable, normal polarity component with a dispersion of declination and inclination consistent with secular variation. Rock magnetic experiments show similar magnetic carriers throughout all samples. These include a broad spectrum of coercivities and blocking temperatures indicative of single and multi-domain magnetic carriers, and high field remagnetization indicative of small amounts of hematite. Our expectations were to see the Normal/Reversed boundary, however, our investigations indicate no magnetic reversals are present through the sampled section. We were able to find a tephra high in the section that correlates with the Old Crow tephra (140,000 years) as described by Matheus et al. (2003), however no older tephras were found. Our results conflict with the previous correlations of tephras, and call into question the lateral continuity of the published stratigraphy. Other causes for this discrepancy could be sediment slumping due to permafrost melting or the effects of activity along the Kaltag Fault, $<$ 1 km northeast of the cliffs, causing uplift, and/or tectonic rotations. Matheus, P., Beget, J., Mason, O., and Gelvin-Reymiller, C., 2003, Quat. Res. 60, 33-43.
DE: 1520 Magnetostratigraphy
DE: 1522 Paleomagnetic secular variation
DE: 1535 Reversals (process, timescale, magnetostratigraphy)
DE: 1540 Rock and mineral magnetism
SC: Education and Human Resourcese [ED]
MN: 2004 AGU Fall Meeting