Geologic Magnetic Data Processing

ODP logging contractor: LDEO-BRG

Hole: 1022C

Leg: 167

Location: California Margin (tropical NE Pacific)

Latitude: 40° 4.482' N

Longitude: 125° 20.558' W

Logging date: June, 196

Bottom felt: 1937.5 mbrf (used for depth shift to sea floor)

Total penetration: 387.7 mbsf

Total core recovered: 378.8 m (97.7 %)

GHMT Logging Runs

Two passes were recorded. Due to malfunction of the magnetic induction tool (NMRS) only magnetic susceptibility data were recorded. The magnetic susceptibility (MAGS) record is of good quality: data is from pass 2, open-hole section (53.5-378 mbsf).

Wireline heave compensator was used to counter ship heave.

Hole Conditions

Magnetic susceptibility data from pass 2 were corrected for borehole variations and using an average caliper value of 14 inches from the top of the logged interval to 101 mbsf and the FMS caliper from 101 mbsf to the bottom of the hole.

Depth Shift

The original logs have been interactively depth shifted with reference to HNGS from DIT/HLDT/APS/HNGS pass 2, and to the sea floor (- 1937.5 m). The program used is an interactive, graphical depth-match program, which allows to visually correlate logs and to define appropriate shifts. The reference and match channels are displayed on the screen, with vectors connecting old (reference curve) and new (match curve) shift depths. The total gamma ray curve from the NGT and/or HNGS tool run on each logging string is used to correlate the logging runs most often. In general, the reference curve is chosen on the basis of constant, low cable tension and high cable speed (tools run at faster speeds are less likely to stick and are less susceptible to data degradation caused by ship heave). Other factors, however, such as the length of the logged interval, the presence of drill pipe, and the statistical quality of the collected data (better statistics is obtained at lower logging speeds) are also considered in the selection. A list of the amount of differential depth shifts applied at this hole is available upon request.

Lithology

Three major lithologic units (I-II-III) are identified along the logged section, which includes a Quaternary to late Pliocene sequence.

The boundary between unit I and II of the unit is marked by a drastic decrease in nannofossil content. Unit II consists of siliclastic clay with minor amounts of silts, diatoms, and nannofossils.

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 167. For further questions about the logs, please contact:

Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia