DSDP operator and logging contractor: Scripps Institution of Oceanography
Hole: 482C
Leg: 65
Location: Tamayo Fracture Zone (tropical NE Pacific)
Latitude: 22° 47.34' N
Longitude: 107° 59.57' W
Logging date: February 1979
Sea floor depth ("bottom felt"): 3015 mbrf
Sea floor depth (step in GR log): 3008.5 mbrf
Total penetration: 184 mbsf
Total core recovered: 84.56 m (70 % of cored section)
Oldest sediment cored: Silty clay and dolomite (Quaternary)
Lithologies: Silty clay and dolomite (sediments), basalt interlayered with dolomite (basement)
The logging data was recorded by Gearhart-Owen in GO format, which was subsequently translated into in LIS format. Data were processed at the Borehole Research Group of the Lamont-Doherty Earth Observatory.
| Tool string | Pass | Top depth (mbsf) | Bottom depth (mbsf) | Bit depth (mbsf) | Notes |
| 1. CDL/GR/TEMP |
Downlog
|
0
|
180
|
160.4
|
CDL/GR failed Temp in degF |
| 2. NL/GR |
Main
|
0
|
181
|
160.4
|
|
|
Repeat
|
113.3
|
181
|
160.4
|
|
The CDL/GR/Temperature log was run first but unfortunately the density tool was damaged and the run uphole was aborted when the pad caught under an overhang after only 5 m of basement had been logged. Only a temperature log could be recorded logging down.
The depths in the table are for the processed logs (after depth shift to the sea floor). Generally, discrepancies may exist between the sea floor depths determined from the downhole logs and those determined by the drillers from the pipe length. Typical reasons for depth discrepancies are ship heave, wireline and pipe stretch, tides, and the difficulty of getting an accurate sea floor from the "bottom felt" depth in soft sediment.
Depth match and depth shift to sea floor: No depth match between runs was necessary. The original logs were depth shifted to the sea floor (- 3008.5 m). The sea floor depth was determined by the step in gamma ray values at 3008.5 mbrf. This differs by 6.5 m from the sea floor depth given by the drillers ("bottom felt" at 3015 mbsf).
The quality of the data is assessed by checking against reasonable values for the logged lithologies, by repeatability between different passes of the same tool, and by correspondence between logs affected by the same formation property (e.g. the resistivity log should show similar features to the sonic velocity log). In Hole 482C, the qualitative porosity measurement and gamma ray logs from main and repeat pass show excellent correlation. Only the bottom 20 m of logs were recorded open hole. No hole size measurement was recorded, therefore it is not possible to assess the actual hole conditions.
A null value of -999.25 may replace invalid log values.
Additional information about the drilling and logging operation can be found in the Operations section of the Site Chapter in DSDP Initial Reports volume 65. For further questions about the logs, please contact:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia