During Ocean Drilling Program Leg 175, cores were taken off the west coast of Africa in the Angola-Namibia upwelling system. The sediments at these sites have a high total organic carbon content and a very low concentration of ferrimagnetic material (Wefer, Berger, Richter, et al., 1998). The weak magnetic susceptibility is dominated by paramagnetic and diamagnetic minerals with a negligible contribution from ferrimagnetic minerals. In addition, Yamazaki et al. (2000) shows that severe postcoring diagenesis caused a loss of up to 90% of the remanent magnetization by the dissolution of fine-grained magnetic minerals during storage.
Environmental rock-magnetic studies of marine sediments often recover paleoenvironmental information through composition, concentration, and grain-size variations of magnetic minerals contained in the sediment (Colin et al., 1998; Hounslow and Maher, 1999). However, in sediments with high organic carbon content, preservation of magnetic minerals is often poor (Richter et al., 1999; Roberts et al., 1999). For Site 1077, the latter is the case, with severe dissolution of fine magnetic grains both in situ and postcoring, preventing the use of magnetic remanence measurements for paleoenvironmental studies.
1Solheid, P.A., and Yamazaki, T., 2001. Data report: Evidence of the dissolution of fine-grained magnetic minerals from measurements of natural and laboratory-induced remanent magnetizations at Site 1077. In Wefer, G., Berger, W.H., and Richter, C. (Eds.), Proc. ODP, Sci. Results, 175, 1-10 [Online]. Available from World Wide Web: <http://www-odp.tamu.edu/publications/175_SR/VOLUME/CHAPTERS/SR175_16.PDF>. [Cited YYYY-MM-DD]
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3Geological Survey of Japan, 1-1-3 Higashi, Tsukuba, Ibaraki 305-8567, Japan.
receipt: 25 February 2000
Acceptance: 9 February 2001
Web publication: 11 July 2001