Schwehr, K., N. Driscoll, Tauxe, L. (2005). "Slumps and sediment
deformation: AMS of the Gaviota and Goleta Slides." AGU Fall Meeting
Abstracts.

During the last year, we have collected six gravity cores from the
northern side of the Santa Barbara Basin for paleomagnetic deformation
tests. The first two cores were collected on the smaller Gaviota Slide
on the western side of the basin. These cores provide the slump end
member, since one core comes from the evacuated zone while the other
comes from the toe or accumulation zone. Two additional cores were
collected on the toes of the much older Goleta Slides and were
designed to provide an undeformed reference fabric; it was our hope
that they would be mostly pelagic drape but also penetrate into the
top of the deformed material. One core appears to be an excellent
reference core with clear laminations, while the other has distorted
laminations that show the sediment has undergone some type of
deformation. In between the two slides, we collected two cores on
either side of the crack that runs between the two slides to
investigate creep and slope stability. All cores have been sampled at
a 3 cm interval with 8cc cubes to measure anisotropy of magnetic
susceptibility (AMS) and AF demagnetiziation. The Gaviota slide
sediments show a dominantly triaxial fabric with some alignment of the
maximum eigen values, while the drape materials from the Goleta Slide
show a typical oblate undeformed fabric. There are hints of
deformation at major clay layers, which we continue to
investigate. Several of these cores appear to show a biogentic
component to the AMS signal that fades with depth. This component has
a tendency to mask the deformation signal in the top sections of the
cores. The NRM inclinations of the deformed core regions tend to be
shallow and erratic showing what look at first glance to be
excursional features.

Conclusion

Through the use of AMS and percent weight water techniques, past
slides and unconformities can be identified that were not necessarily
visible in the core materials. It appears that sediment morphology is
controlling the ability of sediments to dewater as they accumulate
overburden.  The laminated zones hinder fluid flow and create zones of
overpressure. We believe these zones are weak and present likely
failure points for future deformation.  Our model predicts that in the
area between the Gaviota and Goleta slides, the failure will likely
occur at a depth of 85-100cm and fail in a manner much like the
smaller Gaviota slide.

Acknowledgments

We would like to thank NSF and BP for funding this research. The
multibeam data comes from the MBARI EM300 survey. Seismic processing
was done by D. Brothers and J. Dingler.  Core processing was done at
the SIO Geologic Collections and the SIO Paleomagnetic Laboratory.