Standard Wireline Data Processing
DSDP operator and logging contractor: Scripps Institution of Oceanography
Hole: 511
Leg: 71
Location: Falkland Plateau (SW Atlantic)
Latitude: 51° 00.28' N
Longitude: 46° 58.3' W
Logging date: January 1980
Sea floor depth ("bottom felt"): 2602 mbrf
Sea floor depth (step in GR log): 2602 mbrf
Total penetration: 632 mbsf
Total core recovered: 385.62 m (61 % of cored section)
Oldest sediment cored: black mudstone and nannofossil mudstone (Late Jurassic)
Lithologies: diatomaceous, nannofossil, calcareous, and zeolitic oozes; zeolitic clays, claystones and chalks.
The logging data was recorded by Gearhart-Owen in GO format and subsequently digitized by Centerline data. 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. NL/GR | Main | 0 | 608 | ??? | |
| Repeat | 63 | 206 | ??? |
There is no mention of logging operations in the Initial Reports of the DSDP, Volume 71. It is not clear if logging took place through drill pipe and bottom hole assembly or open hole. The GR and neutron readings, however, do not show the typical attenuation occurring through pipe and pipe collars, thus it is assumed that logging took place open hole. Also, there is no repeatability between runs and GR readings are much higher (200-400 API versus 0-200 API) in the main run. It is possible that the tool did not function properly.
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: The original logs were depth shifted to the sea floor (- 2602 m). No depth matching between runs could be performed due to the ack of good correlation.
The sea floor depth corresponds to the "bottom felt" depth given by the driller. The original blueprint also indicates the sea floor at 2602 mbrf.
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 511, there is no repeatability between runs, which makes it difficult to assess the log reliability. Extreme caution should be used in interpreting the data.
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 71.
For any question about the data or about the LogDB database, please contact LogDB support: logdb@ldeo.columbia.edu.