HR: 0830h
AN: GP31D-0771    [PDF]
TI: Late Quaternary Records of Magnetic Field Excursions From the Southern Hemisphere (ODP Leg 202 - Chilean Margin)
AU: * Lund, S
EM: slund@usc.edu
AF: Dept. of Earth Sciences, University of Southern California, Los Angeles, CA 90089-0740 United States
AU: Stoner, J
EM: stoner@Colorado.edu
AF: INSTAAR, University of Colorado, Boulder, CO 80309 United States
AU: Kleiven, H
EM: kikki@geol.uib.no
AF: Dept. of Geology, University of Bergen, Bergen, 5007 Norway
AU: Ninnemann, U
EM: ulysses@ldeo.columbia.edu
AF: Dept. of Geology, University of Bergen, Bergen, 5007 Norway
AU: Lamy, F
EM: flamy@uni-bremen.de
AF: Marine Studies, University of Bremen, Bremen, 28334 Germany
AU: McManus, J
EM: jmcmanus@whoi.edu
AF: Dept. of Geol. Geophys., Woods Hole Oceanographic Inst., Woods Hole, MA 02543 United States
AB: During ODP Leg 202, shipboard paleomagnetic measurements indicated the existance of three late Quaternary magnetic field excursions at Site 1233 (~41$\deg$S, Chilean Margin). Two were located in what was estimated to be Stage 3 and one was suspected to occur in early Stage 5. The `Stage 3' excursions were also identified at Site 1234 (~36$\deg$S, Chilean Margin). New u-channel measurements of replicate sections of the three excursions at Site 1233 verify their existence and clearly document their detailed directional and paleointensity variation. A single u-channel record from Site 1233 also indicates the presence of a fourth excursion above the two `Stage 3' excursions. Selected oxygen isotope data and AMS radiocarbon dates indicate that all three `Stage 3' excursions do occur in Stage Three and that the oldest excursion of the group is synchronous with the Laschamp Excursion (~40 ka), as documented in the North Atlantic Ocean/Europe. The youngest excursion (not yet replicated) is apparently synchronous with the Mono Lake excursion (~32 ka), and the last excursion occurs about half way between them (~36 ka). The Laschamp Excursion equivalent is distinctive in that it is a class II excursion (full polarity reversal, I and D variation in phase). All other excursions are Class I excursions (I and D variation near 90$\deg$ out of phase). This observation provides clear evidence that the Laschamp Excursion had both Class I and Class II excursions occurring at the same time in different parts of the world. The Class II excursions occurred closer to the poles (tangent cylinder) and the Class I excursions occurred closer to the equator. Overall, this is suggestive of an octupolar excursional state for the Laschamp Excursion itself with an extended (~10ky) period of subsequent instability. We will provide computer simulations to provide a unifying conceptual framework for this set of observations.
DE: 1507 Core processes (8115)
DE: 1513 Geomagnetic excursions
DE: 1521 Paleointensity
DE: 1522 Paleomagnetic secular variation
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting