HR: 1330h
AN: OS22A-1150    [PDF]
TI: Exploration of the Humboldt Slide using Anisotropy of Magnetic Susceptibility - Comparison with the Gaviota Slide
AU: * Schwehr, K
EM: kdschwehr@ucsd.edu
AF: UCSD, MC-0208, La Jolla, CA 92093 United States
AU: Driscoll, N
EM: ndriscoll@ucsd.edu
AF: UCSD, MC-0208, La Jolla, CA 92093 United States
AU: Tauxe, L
EM: ltauxe@ucsd.edu
AF: UCSD, MC-0208, La Jolla, CA 92093 United States
AU: Lee, H J
EM: hjlee@usgs.gov
AF: USGS, 345 Middlefield Rod MS 999, Menlo Park, CA 94025 United States
AB: The origin of the "so-called" Humboldt Slide has raised much controversy. Some researchers argue that it is a slide deposit, while others interpret the deposit as a depositional feature mantling an old slide scar formed by down-slope gravity flows. We adapted the standard paleomagnetic tool of Anisotropy of Magnetic Susceptibility \(AMS\) in order to detect minor post-depositional deformation \(i.e., "crypto-slumps"\) in sedimentary successions and applied it to the Humboldt Slide controversy. Crypto-slumps are slumps that are not easily observed in outcrop or core samples. Undeformed sediments show a typical oblate fabric while even slightly deformed sediments develop a triaxial fabric. Based on examining cores from the center and top of the Humboldt Slide structure, we find no evidence for deformation. The cores from the top are in an area that is clearly free from drape and thus we can be sure that we are sampling the structure seen in chirp seismics. We recently sampled a known slide for comparison to the Humboldt Slide. We used 5 gravity cores from the USGS V1-81-SC cruise which sampled the Gaviota Slide. The Gaviota Slide in on the northern slope of the Santa Barbara Basin and is just to the west of the much larger Golita Slide. The AMS measurements from the Gaviota Slide show a clearly deformed fabric that we expect from a slide. From these analyses we found that the fabric is dominantly oblate for the Humboldt Slide while the Gaviota Slide is predominantly triaxial. Based on these results, we re-emphasize our conclusion that the Humboldt Slide is not a slide. We now know that the ridges and swales of the Humboldt Slide appear to have grown as sediment waves on an old slide scar and our chirp seismics show thickening on the upslope side of these structures and continuous reflectors across regions where others have mapped normal faults.
UR: http://schwehr.org/agufall2003
DE: 1518 Magnetic fabrics and anisotropy
DE: 1594 Instruments and techniques
DE: 3005 Geomagnetism (1550)
DE: 3094 Instruments and techniques
DE: 4219 Continental shelf processes
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting