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LOGGING PLAN

Downhole logging will be used during Leg 197 to address issues concerning possible deviation of holes from vertical, in situ basalt magnetizations, core orientation, volcanic stratigraphy, and eruptive morphology. Whereas core recovery is often biased and incomplete in lithologies such as alternating pillows and massive flows, logging data are continuous and therefore provide useful information over intervals of low core recovery. During Leg 197, we are particularly interested in determining the number of flow units, which has implications for how well geomagnetic secular variation has been sampled, and hence, how well paleomagnetic paleolatitudes can be constrained. If time permits, we also plan to use logging data to create synthetic seismograms, which will then lead to improved correlation between the seismic records and the lithologic units recovered from the boreholes. As shown in the Operations Schedule (Table 1), we tentatively plan to log at each site. Subject to time constraints, this logging plan may be adjusted at the discretion of the co-chiefs within the guidelines of the normal JOIDES logging policy.

To achieve the Leg 197 scientific objectives, the proposed sites will be logged with the standard logging tool strings (triple combination [triple combo] and Formation MicroScanner [FMS]). Specifically the logging plan includes one triple combo and one FMS run along the whole drilled section and a second FMS run in the basalt intervals. A triple combo run and one FMS run may be extended into the sedimentary section depending on time constraints. The characteristics of these logging tool strings can be found at the Borehole Research Group web site at http://www.ldeo.columbia.edu/BRG and are briefly described in the next paragraph.


In addition, we plan to log one site with a magnetic logging tool being developed by the Geophysical Institute of the University of Göttingen, Federal Republic of Germany (referred to as the Göttingen Borehole Magnetometer [GBM]), and with a third-party magnetic susceptibility borehole tool (referred to as the SUSLOG 403-D). The GBM has three fluxgate sensors that measure three orthogonal components of the magnetic field, whereas the SUSLOG 403-D obtains an estimate of bulk magnetic susceptibility useful for modeling the contributions of induced magnetizations to the total magnetic signal recorded by the GBM. The effectiveness of these tools will be evaluated during the leg, and, time allowing, they may be run at additional sites.

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