Physics
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmgp33a0096n&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #GP33A-0096
Physics
1520 Magnetostratigraphy, 1535 Reversals: Process, Timescale, Magnetostratigraphy, 1560 Time Variations: Secular And Longer, 1616 Climate Variability (1635, 3305, 3309, 4215, 4513)
Scientific paper
As part of an NSF-funded Research Experience for Undergraduates (REU) program at the University of Alaska Fairbanks, samples were collected from the Gold Hill Loess 3 km southwest of Fairbanks, Alaska. Previous studies of the magnetostratigraphy of the Gold Hill Loess show the outcrop studied as extending uninterrupted from 1.9 Ma to at least 3 Ma (Westgate et al., Geology, 1990), although unconformities with inferred time gaps are reported higher in the section. Our goal was to assess the reproducibility and increase the resolution of the earlier study of the older part of the section. Oriented cubes and cylindrical cores were collected from two sections of the loess starting from the prominent PA Tephra and extending down to 3.7 m and 2 m. The tephra has a recently published age of 2.02 +/- 0.14 Ma (Westgate et al., Quat. Res., 2003). The remnant magnetization of the samples was measured using a cryogenic magnetometer. Both alternating field and thermal demagnetization techniques were employed. Our results show that the section is predominantly reversed polarity, as expected in the Matuyama Reversed Chron, with two thin horizons of normal polarity at 0.7 m and 3.1 m below the PA tephra. The previously published magnetostratigraphy shows the same pattern of polarity changes; however, there are discrepancies in the vertical distribution of these changes between sampling areas that are less than 10 m apart. This calls into question the lateral continuity of the loess section, an observation that should be taken into account in any future studies. Our lower polarity change coincides with a normal event previously correlated with the 2.14 Ma Reunion Subchron, while our upper reversal was not seen by Westgate et al. (1990), either due to the fact that it was not preserved in their section or was too thin to be seen with their 10 cm sampling interval. However, the proximity of this reversal to the PA tephra suggests that this, not the lower one, is the Reunion Subchron. The lower reversal then would correlate to the Matuyama - Gauss Boundary, making the section significantly older than previously believed. We also see correlations between magnetic susceptibility data from the loess, the marine oxygen isotope record (Horng et al., Earth, Planets, Space, 2002) and the onset of Pleistocene glaciation.
Beget James E.
Domeier Mathew
Fallon J. F.
Layer Paul W.
Naibert T. J.
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