Christoph E. Geiss, Subir K. Banerjee, Univ. of Minnesota, 100 Union St. S.E., Minneapolis, MN 55455
Marith C. Reheis, U.S. Geol. Survey, MS-980, Federal Center, Denver, CO 80225 United States
We studied the mineral-magnetic properties of deposited dust from collectors generally downwind (south and east) of Owens (dry) Lake. Samples were collected between 1991 and 1998 to quantify the role of Owens (dry)Lake (OdL) as a local and regional dust source. Dusts collected directly on the lakebed are weakly magnetized, containing a low concentration of coarse grained (MD) magnetite. Thermal demagnetization curves of low-temperature isothermal remanence (IRM), acquired at 5 K, show the presence of Verwey transitions in all samples, indicating magnetite as the predominant magnetic mineral across the region. The concentration of magnetic minerals increases steadily up to a distance of approximately 50 km south of OdL. This increase is reflected in all concentration-dependent parameters, such as magnetic susceptibility, IRM, and saturation magnetization. IRM acquisition curves for these sites show only a magnetically soft component, which is saturated at fields < 300 mT. Sites farther southeast contain an additional magnetically hard component that cannot be saturated in a maximum field of 1.6 T. For these sites, concentration-dependent magnetic parameters also show no apparent influence of OdL dust. Hysteresis loops are dominated by the presence of coarse-grained magnetite and are poorly suited to distinguish between sites influenced by OdL and sites dominated by other local dust sources. The magnetic properties of samples close to Owens (dry) Lake ($<$ 50 km distant) are characterized by the influx of dust low in magnetite content from the dry lakebed that is progressively diluted by strongly magnetic dust derived from local sources, such as alluvial fans in Owens Valley. Magnetic minerals from other sources dominate samples farther than 50 km from the lakebed.The influence of OdL dust is most noticeable during years of high dust generation on the lakebed. In other years the magnetic properties of all sites are more similar, probably due to the presence of a well-mixed background dust component.
EOS suppl. v.81, p. F369, 2000
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