167 Prospectus


A total of seven sites will be logged during Leg 167 (Sites CAM-2, BA-1, CA-1, CA-2, CA-8, CA-11, and CA-15); an additional four sites (Sites CA-4, CA-5, CA-9, and CA-14) will be logged if time permits. Variations in biogenic carbonate, opal, and terrigenous deposition associated with regional paleoclimate and paleoceanographic changes will be reflected in terms of corresponding changes in physical and geochemical properties. Coring may be discontinuous over deeper intervals because of gas expansion or coring disturbance, thus downhole log data present an excellent resource for developing continuous, quantitative paleoclimatic and paleoceanographic time series. Special software for core-core and core-log data integration is being developed and will be used during Leg 167 for this purpose.

Logging at most sites will be comprised of standard Quad (natural gamma ray activity, resistivity, sonic velocity, density/porosity) and Formation Microscanner (FMS) runs, with inclusion of the Geological High-sensitivity Magnetic Tool (GHMT) if appropriate and available. Geochemical logging is only planned for Sites CA-8 and CA-15, with an additional plan for geochemical logging at proposed Site CA-2 if drilling exceeds 400 mbsf.

A primary logging objective of Leg 167 drilling is to obtain high-quality log data for all sites with sufficiently deep penetration depths or for those sites that are particularly central to the scientific objectives of the leg. A special emphasis during Leg 167 will be the collection of highest resolution log data by reducing the logging speed for the Quad runs to enhance the statistics of the nuclear measurements (particularly density and natural gamma). Post-collection processing of density and resistivity log data will significantly increase vertical resolution of these measurements (from ~80 cm to ~15 cm resolution) and increase log sample intervals from 15 cm to 2.5 cm. Many sites will be logged with several passes of the Quad tool to quantify tool vertical resolution and log repeatability. Because high sedimentation rates are expected at a number of sites, this enhanced log resolution opens up the possibility that log data may be useful for detecting and reconstructing continuous records of millennial-scale paleoclimate variability.

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