ODP logging contractor: LDEO-BRG

Hole: 888C

Leg: 146

Location: Cascadia Margin (NE Pacific)

Latitude: 48° 9.985' N

Longitude: 126° 39.802' W

Logging date: October, 1992

Bottom felt: 2527 mbrf (used for depth shift to sea floor)

Total penetration: 600 mbsf

Total core recovered: none

Logging Runs

Logging string 1: DIT/SDT/HLDT/CNTG/NGT

No information available about use of wireline heave compensator.

Bottom-hole Assembly

The following bottom-hole assembly depths are as they appear on the logs after differential depth shift (see "Depth shift" section) and depth shift to the sea floor. As such, there might be a discrepancy with the original depths given by the drillers onboard. Possible reasons for depth discrepancies are ship heave, use of wireline heave compensator, and drill string and/or wireline stretch.

        

DIT/SDT/HLDT/CNTG/NGT: Bottom-hole assembly at ~100.5 mbsf.

Processing

Depth shift: Because only one logging tool string was used at this hole, no differential depth shift was necessary. All logs have been depth shifted to the sea floor (-2527 m).

Gamma-ray processing: NGT data have been processed to correct for borehole size and type of drilling fluid.

Acoustic data processing: The array sonic tool was operated in standard depth-derived borehole compensated mode, including long-spacing (8-10-10-12') logs. Because of the extremely noisy character of the sonic logs, no processing has been performed at this stage.

 

Quality Control

Null value=-999.25. This value generally appears in discrete core measurement files and also it may replace recorded log values or results which are considered invalid (ex. processed sonic data).

        

During the processing, quality control of the data is mainly performed by cross-correlation of all logging data. Large (>12") and/or irregular borehole affects most recordings, particularly those that require eccentralization (CNTG, HLDT) and a good contact with the borehole wall. Because of the extremely large hole, the density data are suspicious in the 100-116 mbsf, 175-190 mbsf, 312-320 mbsf, 375-385 mbsf, and 401-440 mbsf intervals.

        

Data recorded through bottom-hole assembly should be used qualitatively only because of the attenuation on the incoming signal. Bad gamma ray (NGT) data have been recorded at 65-72 mbsf, 92-100 mbsf, 360-365 mbsf, and 393-397 mbsf.

        

Hole diameter was recorded by the hydraulic caliper on the HLDT tool (CALI).

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP volume 146.

For any question about the data or about the LogDB database, please contact LogDB support: logdb@ldeo.columbia.edu.