Standard Wireline Data Processing


DSDP operator and logging contractor: Scripps Institution of Oceanography

Hole: 73

Leg: 8

Location: Clipperton Fracture Zone (tropical central S Pacific)

Latitude: 1° 54.58' N

Longitude: 137° 28.12' W

Logging date: November 1969

Sea floor depth: 4387 mbrf

Sea floor depth (step in electrical log): unclear.

Total penetration: 302 mbsf

Total core recovered:  169.8 m (97.5 % of cored section)

Oldest sediment cored: Middle Eocene

Lithologies: calcareous and siliceous oozes, chalk, limestone, and chert.




The logging data was recorded  by Welex in analog format only. The data was digitized by Centerline Data in 2004 and processed at the Borehole Research Group at the Lamont-Doherty Earth Observatory in July 2004. The electrical log could not be digitized down to the bottom of the hole because, due the lack of a backup scale on the original log, the data ended at 202 mbsf.


Logging Runs


Tool string Pass Top depth (mbsf) Bottom depth (mbsf) Bit depth (mbsf) Notes
1. EL/SP
Recorded open hole


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 shift to sea floor: Because of the lack of a clear step in electrical log, the original logs were depth shifted to the sea floor by 4387 m. This amount corresponds to the value used to depth-shift the cores, and gives a total logging depth that is consistent with the total penetration in the hole.


Quality Control


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).


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 8. For further questions about the logs, please contact:


Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia