HR: 0800h
AN: GP21A-0148    [Abstracts]
TI: Anisotropy of Magnetic Susceptibility Study of Lacustrine Sediments Recovered From the Deschutes River (Pringle Falls, Oregon) Area.
AU: Lau, J
AF: SOEST-HIG Petrofabrics and Paleomagnetics Laboratory, University of Hawaii at Manoa, 1680 East West Rd, Honolulu, HI 96822 United States
AU: * Herrero-Bervera, E
EM: herrero@soest.hawaii.edu
AF: SOEST-HIG Petrofabrics and Paleomagnetics Laboratory, University of Hawaii at Manoa, 1680 East West Rd, Honolulu, HI 96822 United States
AB: We have studied a total of 827 samples drilled from five widely spaced profiles sampled along the Deschutes river Oregon . The five profiles sampled recorded a high-resolution paleomagnetic record of the Pringle Falls magnetic polarity episode (ca. 218+/- 10 ka) and are characterized by diatomaceous lacustrine sediments. This lacustrine sedimentary sequence that was sampled was part of an extensive prehistoric fluvial and lacustrine complex that formed east of the Cascade Mountains during the last 1.0 Ma. The lake appears to have resulted from a late Pliocene/Pleistocene rise in the base level to the east of the of the sampling area near the western margin of the Basin and Range structural province and is related to the development of the extensive volcanism associated with the Newberry volcano. Present outcrops and subsurface distribution of these lakes are to the west and north of the volcano, and their distribution appears to have been influenced by the development of streams and rivers systems draining the Newberry volcanic center as well as the Cascades themselves. We have conducted anisotropy of magnetic susceptibility (AMS) measurements in order to investigate if the acquisition of their fabrics during their formation was primary or secondary and also the characteristics of such fabrics. We conducted low-field vs susceptibility analysis to determine the magnetic carriers of the sediments and we found that the main magnetic carrier is pure magnetite (Curie point 575 $^{o}$C). The magnetic grain size indicated SD-PSD magnetite. The magnetic fabrics of the 5 different profiles indicated that the sediments were deposited with the minima axes (Kmin) perpendicular to the bedding plane of the sediments. The sediments are also characterized by a strongly oblate fabric that is confined to the bedding plane of the sediments, in addition since the fabric is entirely foliated without a superimposed lineation then the sediments were deposited almost on a horizontal surface and quiet and calm water conditions (current less than 1 cm/s).
DE: 1518 Magnetic fabrics and anisotropy
DE: 1530 Rapid time variations
DE: 1535 Reversals (process, timescale, magnetostratigraphy)
DE: 1560 Time variations--secular and long term
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting