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doi:10.2204/iodp.proc.308.209.2009

Summary and outlook

The results of the SEM analyses are consistent with the NRM measurements, showing a complex signal carried by an alternating succession of primary input of iron oxides and presumably secondary precipitated iron sulfides. Detrital magnetite, titanomagnetite, and hemoilmenite grains were detected adjacent to finer clusters of greigite and pyrite. Therefore it has to be kept in mind that the NRM intensity mainly reflects the rock magnetic variations for the investigated four drill sites from Expedition 308. This suggests that standard paleomagnetic interpretations of secular variation and relative paleointensity may not apply straightforwardly in this case.

Nevertheless, the paleomagnetic directional information could be extracted using a careful azimuth correction technique that was used to assist the reorientation of the drill cores required, for example, for further sediment tectonic studies. In general, this reorientation approach seems to work reasonably well (with disorientation of only a few degrees), although in places the inclination and declination records are very noisy because of drilling-induced disturbances.

Additional work has to be performed to obtain a better understanding of the complex depositional and postdepositional processes, such as the distinction of the primary detrital input and its secondary geochemical alteration. The presence of authigenic greigite was shown in more detail for Hole U1319A by Fu et al. (2008) and can be assumed for all four investigated drill sites. This complicates a straightforward interpretation of the recovered remanence signals and requires further rock magnetic measurements and geochemical modeling but also suggests a high potential for paleoenvironmental (magnetic) implications.

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