SCIENTIFIC MEASUREMENTS STRATEGY

Because the central theme of Leg 184 was the Neogene coevolution of tectonics and climate, the shipboard focus was on recovering continuous sediment sections capable of recording millennial- to orbital-scale variations. This focus is reflected in the Leg 184 shipboard measurements program as well as its sampling plan and shore-based analysis.

The shipboard measurement strategy was to acquire high-resolution (2-5 cm) core-logging records from all holes, including MS, gamma-ray attenuation (GRA) bulk density, NGR, and CR. These data were used to construct the meters composite depth (mcd) scale, which was used to evaluate the completeness of the stratigraphic section and to splice a complete, representative record for each site. Routine measurements, taken at frequencies of one per section to one per core (intervals of ~1.5-10 m), included biostratigraphy (calcareous nannofossils and foraminifers), paleomagnetism, hydrocarbon gas analysis, interstitial water chemistry, moisture and density, carbonate, X-ray diffraction, and P-wave velocities.

The Leg 184 downhole logging plan was designed to provide (1) complete stratigraphic coverage, especially in the incomplete XCB intervals; (2) proxy data not available from core measurements, such as resistivity and yields of K, U, and Th; and (3) in situ sonic velocity for the construction of synthetic seismograms. Sites 1143, 1144, 1146, and 1148 were logged using the following three downhole tool strings:

1. The triple combination tool string, which includes the dual induction tool to measure resistivity, the accelerator porosity sonde to measure porosity, and the hostile environment lithodensity sonde to measure bulk density and general lithology. Also included on this tool string were the hostile environment natural gamma-ray sonde (HNGS) to measure total NGR and to calculate K, U, and Th yields and the Lamont-Doherty Earth Observatory temperature logging tool to measure borehole fluid temperature.
2. The FMS-sonic tool string, which includes the Formation MicroScanner (FMS) with the general-purpose inclinometry tool to measure microresistivity at centimeter resolution and the dipole sonic imager to measure compressional and shear-wave velocity.
3. The geological high-resolution magnetic tool (GHMT), which includes the nuclear magnetic remanence sonde to measure the total magnetic field and the susceptibility measurement sonde to measure the MS from induction.