Standard Wireline Data Processing
DSDP operator
and logging contractor:
Scripps Institution of Oceanography
Hole: 543A
Leg: 78A
Location: Barbados Ridge (tropical NW Atlantic)
Latitude: 15° 2.74' N
Longitude: 58° 39.22' W
Logging date: March 1981
Sea floor
depth ("bottom felt"):
5637 mbrf
Sea floor
depth (step in
temnperature log): 5645 mbrf
Total
penetration: 455 mbsf
Total core
recovered: 69.4 m (48.7
% of cored section)
Oldest
sediment cored:
Ferrugineous, calcareous claystone (Campanian-Maestrichtian)
Lithologies: Mud and nannofossil mud, radiolarian
clay with ash layers, zeolitic clay/claystone, (sediments); basalt (basement,
not logged)
The logging data
was recorded by Gearhart-Owen in GO format and digitized by Centerline Data.
Data were processed at the Borehole Research Group of the Lamont-Doherty Earth
Observatory in December 2004.
Logging Runs
| Tool string | Pass |
Top depth (mbsf) |
Bottom depth (mbsf) |
Bit depth (mbsf) |
Notes |
| 1. TEMP |
Downlog, Upper |
0 |
282 |
282 |
|
Downlog, Middle |
290 |
336 |
|||
Downlog, Lower |
326 |
377 |
|||
| CDL/GR |
Uplog |
255 |
377 |
CDL failed |
The CDL/GR/TEMP
tool string was run first; after logging 20 m down and before reaching the sea
floor a downhole electrical problem developed that caused the loss of
temperature logging capabilities. Even after switching to density-caliper-gamma
ray mode the problem remained and the tool string was recovered. The string was fixed and temperature was
recorded downhole; this run extended past the end of the bottom hole assembly,
but stopped short of basement due to bridging in the hole. When switching again
to density-caliper-gamma ray mode, however, it was found that the detectors had
probably been damaged from trying to pass a bridge and only GR and caliper data
were recorded uphole.
The depths in
the table are for the processed logs (after depth matching between passes and
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.
Processing
Depth match
and depth shift to sea floor:
No depth match was necessary. The original logs were depth shifted to the sea
floor (-5645 mbrf).
The sea floor depth
was determined by the step in temperature log values at 5645 mbrf. This differs
by 8 m from the sea floor depth given by the drillers ("bottom felt" at 5637
mbrf).
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). This process could not be carried out
at Hole 543A. However, the temperature measurements seem to be of good quality.
The log shows a rapid temperature increase from the bottom of the pipe (282
mbsf) downward, to 11 degC.
In Hole 543A the
hole diameter was recorded by the hydraulic caliper on the CDL tool (CALI):
this indicated that the borehole was badly eroded.
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. For further questions about the logs,
please contact:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia