Data

The logging data was recorded by Schlumberger in DLIS format. Data were processed at the Borehole Research Group of the Lamont-Doherty Earth Observatory.

Logging Runs

Tool string	Pass	Top depth (mbsf)	Bottom depth (mbsf)	Bit depth (mbsf)	Notes
1. DIT/APS/HLDS/HNGS	Uplog	0	292	58
2. FMS/DSI/GPIT/SGT	Pass 1	46	292	57	Reference
	Pass 2	97	292
	Repeat	166	191		Schlumberger WHC test
3. WST		105	285		30 stations, every 5 m

Prior to logging the hole was displaced with 10.5 ppg (barite) mud. The tool strings reached to 6 m of the bottom of the hole. The APS tool had a Minitron malfunction at 103 mbsf. The TAP was run, but no data could be acquired, possibly due to faulty batteries. The WST run went smoothly with stations every 5 m; only 4 stations had bad coupling. The heave was around 3 m, but the LDEO WHC worked well and did not stoke out during logging. The Schlumberger WHC was successfully tested on the short FMS/DSI/GPIT/SGT repeat pass.

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: FMS/DSI/GPIT/SGT Pass 1 was used as the depth reference, and the other passes were matched to it using the gamma ray and caliper logs. All passes were then shifted to the sea floor (-1280 m), based on the step in gamma radiation at the sea floor in the DIT/APS/HLDS/HNGS pass. The FMS/DSI/GPIT/SGT Pass 1 was chosen as the reference run because it covered the whole open hole interval and because the HLDS calipers and hence the HNGS logs (which are corrected from the caliper measurement) are suspiciously large.

Depth matching is typically done in the following way. One log is chosen as reference (base) log (usually the total gamma ray log from the run with the greatest vertical extent and no sudden changes in cable speed), and then the features in the equivalent logs from the other runs are matched to it in turn. This matching is performed manually. The depth adjustments that were required to bring the match log in line with the base log are then applied to all the other logs from the same tool string.

The sea floor depth was determined by the step in gamma ray values in the DIT/APS/HLDS/HNGS pass at 1280 mbrf (after depth matching). This differs by 1 m from the sea floor depth given by the drillers (see above).

Environmental corrections: The HNGS and SGT data were corrected for hole size during the recording (note that . The APS and HLDS have been corrected for standoff and hole diameter respectively during the recording.

High-resolution data: Bulk density and neutron porosity data were recorded at a sampling rate of 2.54 and 5.08 cm, respectively. The enhanced bulk density curve is the result of Schlumberger enhanced processing technique performed on the MAXIS system onboard. While in normal processing short-spacing data is smoothed to match the long-spacing one, in enhanced processing this is reversed. In a situation where there is good contact between the HLDS pad and the borehole wall (low-density correction) the results are improved, because the short spacing has better vertical resolution. SGT gamma ray was recorded at 15.24 and 5.08 cm sampling rates.

Acoustic data: The dipole shear sonic imager (DSI) was run in P&S monopole, upper and lower dipole, and Stoneley modes on all three passes. Because of the slow formation, the automatic picking of wave arrivals in the sonic waveforms did not provide reliable results. Reprocessing of the original waveforms was required to extract meaningful compressional and shear velocities. The most reliable shear velocity is the one derived from the upper dipole (VS2), where the lower source frequency used generated more coherent waveforms.

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 acoustic log). The log data of Hole U1328C is of good quality. The hole is oval in cross section, with the minor axis typically around 12 inches, and the major axis > 15 inches. There is a bridge at 116-118 mbsf.

Gamma ray logs recorded through bottom hole assembly (BHA) and drill pipe should be used only qualitatively, because of the attenuation on the incoming signal. The thick-walled BHA attenuates the signal more than the thinner-walled drill pipe. The base of the BHA is shown on the logs at 58 mbsf on the DIT/APS/HLDS/HNGS and 57 mbsf on the first pass of the FMS/DSI/GPIT/SGT.

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 IODP Expedition Reports volume 311. For further questions about the logs, please contact:

Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia

Gilles Guerin

Phone: 845-365-8671

Fax: 845-365-3182

E-mail: Gilles Guerin