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Leg 162 Logging Summary

Shipboard Scientific Party

During ODP Leg 162, the second of two Arctic Gateways expeditions, wireline logging operations were undertaken at four of the eight new sites drilled. Two of these sites (982 and 984) were south of Iceland and were located in eastern N. Atlantic sediment drift sites along the Rockall Plateau and Reykjanes Ridge, respectively. The other two sites (986 and 987) were located along the Svalbard and East Greenland margins, respectively. Logging at Site 985 in the Norwegian Basin, east of the Icelandic Plateau and NE of Iceland was attempted but unsuccessful due to poor hole conditions following coring operation. The location of all sites occupied during ODP Leg 162 is provided in Figure 1.

Figure 1

The standard suite of logging tools were used on this leg, the Quad combination which includes the sonic, electrical, and nuclear tool strings, the Formation MicroScanner (FMS), and the Geochemical toolstring. In addition, the Geologicical High-resolution Magnetic Tool (GHMT), which is made up of a total field measuring tool and a magnetic susceptibility tool, was also deployed. The natural gamma tool (NGT) was also run on every toolstring to provide a means for intercalibration.

The quality of logging data during Leg 162 was generally very good for most of the toolstrings. The logs provided important data both for core-log integration, stratigraphy, and potentially geochronologic control with the GHMT data. The following table and individual site summaries provide information on the type and quality of data available. Any additional questions you may have regarding wireline logging tools or data collected during Leg 162 should be directed to the Borehole Research Group at the Lamont-Doherty Earth Observatory.

LEG 162: HIGHLIGHTS SUMMARY

LOGGING CONTRIBUTIONS TO SITE OBJECTIVES


Site 982 (NAMD-1)
The objective of drilling at this relatively shallow site on the Rockall Plateau was to provide information on the longterm evolution of North Atlantic Intermediate Water (NAIW) and circulation patterns over the last ~18 Myr. Wireline logging data from Hole 982B provided stratigraphic control by filling in gaps in core data through use of natural gamma ray (NGR) and shallow focused resisitivity (SFLU) logs (Figure 2).

Figure 2


These logs also helped identify exact depths of important reflectors seen in seismic records. Interpretation of FMS logs provided additional information on the type of sediments and internal structure of the reflectors.

Site 982

Site 984

Site 986

Site 987

Water Depth (m)

Hole B: ~1,144

Hole B: ~1,660

Hole C: ~2,063
Hole D: ~2,062

Hole E: ~1,682

Depth Coreed (mbsf)

~615

~503

Hole C: ~408
Hole D: ~965

~860

Interval Logged (m)

~80-615

~80-500

"C": ~80-408
"D" ~325-490

~77-495

Toolstrings
Deployed

Quad*, FMS,
NGT

Quad, GLT, NGT
FMS, GHMT

Quad, FMS
GHMT, NGT

Quad, FMS
GHMT, NGT


Site 984 (Bjorn Drift)
The high sedimention rate (120-170m/Myr) Bjorn Drift on the east flank of Reykjanes Ridge SW of Iceland was targeted for high resolution Plio-Pleistocene climate evolution studies. The entire suite of logging tools were run in Hole 984B and the overall log data quality is probably the best of all the sites. Wireline logging provide improved stratigraphic control and sedimentation rates through integration of core and log natural gamma and magnetic susceptibility data (Figure 3).

Figure 3



Possible in situ geochronologic control for the interval between 2-5 Myr may come from analyses of GHMT data through the very strong in situ paleomagnetic measurements in these sediments. The GHMT measures both the earth's total field and the magnetic susceptibility within the sediments. The estimated age of sediments at bottom of borehole is approximately 4-5.5 Myr. However, good chronologic control from onboard biostratigraphic markers and paleomagnetic measurements on the cores were limited to the upper 2 Myr.

Site 986 (Svalbard Margin)
The glacial history of the Barents Sea region was the primary interest in drilling along the Svalbard margin. Previous coastal drilling and seismic work had identified seven main seismic reflectors. In Holes 986C and 986D, several logs including the density, natural gamma, and resistivity logs helped identify location of 6 of the 7 main seismic reflectors which turned out to be large mass flow deposits (Figure 4).

Figure 4



FMS logs provided a closer look at structure of these dense mass flows. GHMT data may help tighten up age control as onboard measurements were not possible below ~100m due to poor core recovery and fractured condition of cores that were recovered in the lower 850m. Unfortunately, the logging data covers only the upper ~500 m as poor hole conditions below that level in Hole 986D prevented logging below that level.

Site 987 (East Greenland Margin)
The history and development of the Greenland Icesheet was the primary interest in drilling thick sediment sequence of ~850m. This sedimentary sequence was located near the base of the slope off of Scoresby Sound fjord which is a major drainage pathway for interior Greenland icesheet. Wireline logging in the upper 500 m of this 860 m borehole showed a long sequence of primarily glacial sediments and dropstones interrupted by a massive 60m mass flow deposit at . Resistivity, density, and gamma logs (Figure 5) should provide good stratigraphic control and means for core-log depth integration. GHMT data may help fill in gaps in the already well developed onboard paleomagnetic stratigraphy and provide a good testing ground for this tool.

Figure 5

Logging Scientist:

Sean Higgins (Lamont-Doherty Earth Observatory)



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