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Detecting compaction disequilibrium with anisotropy of magnetic susceptibility

November 3, 2006

In clay-rich sediment, microstructures and macrostructures influence how sediments deform when under stress. When lithology is fairly constant, anisotropy of magnetic susceptibility (AMS) can be a simple technique for measuring the relative consolidation state of sediment, which reflects the sediment burial history. AMS can reveal areas of high water content and apparent overconsolidation associated with unconformities where sediment overburden has been removed. Many other methods for testing consolidation and water content are destructive and invasive, whereas AMS provides a nondestructive means to focus on areas for additional geotechnical study. In zones where the magnetic minerals are undergoing diagenesis, AMS should not be used for detecting compaction state. By utilizing AMS in the Santa Barbara Basin, we were able to identify one clear unconformity and eight zones of high water content in three cores. With the addition of susceptibility, anhysteretic remanent magnetization, and isothermal remanent magnetization rock magnetic techniques, we excluded 3 out of 11 zones from being compaction disequilibria. The AMS signals for these three zones are the result of diagenesis, coring deformation, and burrows. In addition, using AMS eigenvectors, we are able to accurately show the direction of maximum compression for the accumulation zone of the Gaviota Slide.

Publication Year 2006
Title Detecting compaction disequilibrium with anisotropy of magnetic susceptibility
DOI 10.1029/2006GC001378
Authors Kurt Schwehr, Lisa Tauxe, Neal Driscoll, Homa J. Lee
Publication Type Article
Publication Subtype Journal Article
Series Title Geochemistry Geophysics Geosystems
Index ID 70242026
Record Source USGS Publications Warehouse
USGS Organization Western Ecological Research Center